Strange Sea

At about 5 million years ago, this is the boundary between the Miocene and Pliocene Epochs of the Neogene Period. What in the future will be the coast of the Arequipa Region of Peru is now a coast already, but one of fairly warm waters sporting a very peculiar menagerie, certainly very different from the extant one of the same area. Since the last tale, the climate has continually cooled and the continents have remained comparatively motionless, but they continue on their movements as usual, just not as noticeable due to the decreased timespan. Likely the most important of such motions is the constant approximation of North and South America, which will finally reach its climax in the following millions of years.

The sea we are currently exploring is very rich and this is a result of a conjunction of phenomena, all intersecting to allow for such an exuberant marine biota. First off, coastal waters are, by themselves, more productive than the ones of open oceans. Not only do the shallows allow for light to reach the bottom of the sea, opening space for photosynthesizers on the substrate, but they also increase the speed at which nutrients are recycled: if it were an open ocean, the material would sink all the way to the depths and get effectively locked there for a long period of time. Additionally, coastal waters receive influxes from terrestrial environments and these can be essential in providing organisms with nutrients such as minerals, apart from also constituting adequate spaces for the upwelling of deeper, colder waters containing sunken substances, since the land masses form barriers that facilitate such process. Second off, there is volcanism around here and the ash ejected by volcanoes provides yet another source of nutrients for this already well-loaded sea. Third off, this region, on the western coast of South America, is directly in the path of the Humboldt Current, which, originating way down south and likely appearing somewhen in the midst of the Eocene and Oligocene Epochs, provides significant upwelling, mixing waters and bringing nutrients from the bottom that fertilize the surface.

All of this productivity, however, is still to reach its heyday: in the modern world, these waters are colder and the upwellings produced are more significant. Warm oceans, after all, inhibit nutrient distribution, since warmer water is less dense and forms a cap over colder water (which is denser), leading to stagnation and nutrient-poor conditions. Consequently, even though equatorial seas receive the most sunlight, they are not the most productive. Such a title goes to seasonal seas, which experience a boom, especially in spring. This occurs because, during winter, waters get cold and mix, distributing materials around. Even though this is occurring, there is no sunlight to drive the use of such ample substances. This all changes with spring though (as demonstrated in our previous exploration of a polar habitat), when there is a silver lining of abundant nutrients and sunshine. As the summer progresses, the waters heat up and the nutrients get used up, leading to the end of the boom and stagnation, readying the marine environment to start the cycle anew.

The first organisms to reap benefit of the plenty of nutrients are those constituting the phytoplankton. Due to their unicellular nature, all phytoplankton cells, in contrast to plants, are photosynthetically active, which means that, even though they do not come anywhere near the total weight of their mostly terrestrial counterparts (being around 1% of the plants’ biomass), the amount of carbon they fixate through photosynthesis accounts for roughly half of the total carbon fixated by autotrophs worldwide, a feat helped by their extremely rapid proliferation. One of the most important components of phytoplankton are diatoms, usually microscopic algae especially abundant in this environment (a reality that remains to the present). These lifeforms made initial advances after the great Permian-Triassic extinction event, but remained fairly minor components of phytoplankton until the Cretaceous, when they would progressively expand following the continuous drifting of the continents after the break up of Pangea, a process which released a great deal of nutrients into the oceans. Into the Cenozoic, they continued to expand and diversify like never before, finally reaching their apex, a feat made possible by several factors, one of which was the rearranging of the ocean currents (previously mentioned here) that proved to be highly conducive to their growth.

The photosynthetic ability of diatoms, like in euglenids and dinoflagellates, is associated to ancient endosymbiotic events. Such endosymbiotic events are likely shared with the dinoflagellates proper (as mentioned in the first entry) and occurred through the engulfment of red algae, though there are signs there could be an even older process of endosymbiosis involving green algae (red and green algae form with land plants a probably monophyletic grouping known as Archaeplastida, with green algae being the most closely related to the embryophytes). Diatoms themselves are part of the larger group called the Stramenopiles, similar in rank to the Alveolata clade, which includes ciliates, apicomplexans, and dinoflagellates. The stramenopiles are characterized by the presence of two flagella in some of their cells, a long one of hairy appearance that points anteriorly and a shorter one that points posteriorly. Apart from diatoms, many other organisms constitute this aggregate, including the large kelp algae (still to be better explored), which, though incredibly reminiscent of their very distantly related counterparts on land, evolved similar characteristics in a completely independent manner.

Diatom morphology can be highly variable, but it shares one thing in common: these lifeforms possess cell walls made of silica. The architecture of such cell walls varies greatly and is determined by specific proteins, though there are a few common motifs, such as the fact the silica shells are composed of two halves, which fit perfectly together, being intricately connected. These shells may come in many forms: some are cylindrical, appearing like little barrels, others are star-shaped, a few are like triangle-shaped disks, others are like rods that taper at both ends, some are spherical, while others come in shapes that are indeed quite bizarre. A few diatoms, a subset of those that are bilaterally symmetrical (known as the pennate diatoms), even possess a slit on their underside which allows them to glide on solid surfaces by the secretion of a glue-like substance, which, when left behind, can serve as a primer for the colonization of other organisms, precipitating, for instance, the formation of biofilms. The most commonly encountered diatom in this area is Thalassionema nitzschioides, being shaped like a long rod and forming quite interesting geometrical patterns (such as zig-zags or circles from which the rods stick out like rays) when in colonies, stuck together by the secretion of mucus.

Apart from diatoms, dinoflagellates and coccolithophores are the main other components of phytoplankton. The latter are similar to the diatoms in regards to the fact they also produce mineralized cell walls, but they utilize calcium carbonate instead of silica, though many, however, lack calcification altogether, with these capable of engaging in phagocytosis, as can do some shelled ones with looser coverings. Acquiring their photosynthetic prowess from the same source as its two other phytoplanktonic peers, coccolithophores not only sequester carbon through photosynthesis, but also through their calcium carbonate shells, assembled from many smaller parts and “sculpted” with the help of complex carbohydrates, in a similar way the diatoms also sequester carbon in their silica cell walls. Such cell walls are usually formed by scale-like structures, which join together to yield a bigger, usually roughly spherical shape (some of which may truly be quite spherical and others that more closely resemble pine cones). It is also essential to mention that coccolithophores change significantly through their life cycle, alternating between diploid and haploid forms, with these last ones bearing more delicate or completely absent shells. Also like diatoms, coccolithophores emerged in the new beginning that was the Triassic, after the preceding extinction effectively reset most habitats, allowing for new organisms to take the spotlight. But unlike diatoms, they have not increased in their numbers or diversity following the end of the Mesozoic, staying at similar levels to that of the era before and perhaps even at lower ones as a matter of fact, possibly disadvantaged by the competition brought about by the flourishing diatoms.

Preying on the phytoplankton, there is the zooplankton, also composed by a myriad of unicellular species. Some of these are the radiolarians, which, like the diatoms, may also display silica cell walls. These are most commonly found in the smaller radiolarians, which construct shells of great variety (some being rougly spherical, others conical, and others even of a markedly brutal, spiked design), bearing pores from which pseudopods, similar to the ones of amoeba, peek through to capture and engulf prey. The feeding mechanism can vary quite a bit, however: a few polarize pseudopods in one specific direction to intercept prey, while others are constantly radiating out the cytoplasmatic extensions to all sides. Some even have cell walls not of silica, but of strontium sulfate, a truly unique attribute. Larger radiolarians, in contrast, may lack mineralized shells altogether, possessing a more gelatinous aspect. A few even form colonies consisting of thousands of individual radiolarians, which may grow to several centimeters, up to a few meters! These colonies are held together by a dense mesh of interconnected cytoplasms and by a fluid secreted by them that encloses the whole. Despite their predatory nature, radiolarians, which can even capture and consume small animals, frequently engage in symbiotic relationships with photosynthesizers, be they bacteria or algae.

Close relatives of radiolarians are foraminiferans, both extending all the way back to the Cambrian. Unlike the radiolarians, these are mostly bottom-dwelling, but they also count with some planktonic representatives. These protozoans generally possess an internal calcium carbonate shell of many whorls, which is remarkably similar to that of a few cephalopods, such as ammonoids and nautiluses (though many have different shells and a few are even naked, lacking such internal walls). Food acquisition is similar to that of radiolarians, as many thin and thread-like pseudopods emanate from the organism’s cellular membrane, not only slowly making it crawl along the sea floor (similarly to an amoeba), but also on the search for prey items: mainly diatoms.

Equivalently to the coccolithophores, foraminiferans exhibit differences between haploid and diploid forms. The latter are usually larger, producing tiny haploid individuals that can replicate themselves by mitosis or form gametes also by mitosis. The fusion of gametes will generate the large, diploid form, which will proceed to do the described. One may wonder how a lifeform with a shell like a foraminiferan would even asexually divide and how it does so is by releasing several tiny foraminiferans, which go equipped with everything they need to start a life of their own, budding off from their bigger parent. And also like their close radiolarian relatives, foraminiferans are also frequent harborers of photosymbionts, which may make their bodies a wide array of different colors, such as occurs with corals and their dinoflagellate associates. In the manner of corals, foraminiferans can sustain their own dinoflagellate algae populations, but they also take on several other autotrophs, even the diatoms. The members of Foraminifera that break the norm and adopt a planktonic lifestyle possess several adaptations to prevent sinking: their shells are more globular in shape and may possess long spines to increase friction, while simultaneously they may simply have higher fat contents, making them less dense and more buoyant.

In regards to the sea floor, here can be found true plants, embryophytes that, from land, have returned to the water. These are seagrasses, an informal term encompassing several families of monocot angiosperms of the order Alismatales that have made themselves at home in marine habitats and which are not truly grasses (which are vegetals of the family Poaceae). They grow in shallow and sheltered habitats, like this section of coast. These are specifically of the genus Heterozostera, of the family Zosteraceae, which colonized the sea earlier this era (the other seagrass families arrived in the water already in the Mesozoic). These seagrasses possess long rectangular leaves and, like others of their informal grouping, grow through rhizomes. In order to survive this environment, they have a few set of characteristics in common with other seagrasses. Since in water carbon dioxide is overwhelmingly found in the form of bicarbonate (a product of the reaction between the gas and the water proper), they count with enzymes on their epidermal cells that catalyze the conversion of bicarbonate back into carbon dioxide, allowing it to be used in photosynthesis.

Besides, they lack stomata, which really would not be of much use considering how the vascular system of plants requires evaporation in order to work, as explained in our trip to the Carboniferous. Consequently, the question arises: how then do nutrients get distributed around these monocots? The answer is that seawater does it, as it has free passage in various of the plants’ tissues, filling their interiors and distributing things around. Another problem for these photosynthesizers is the lack of oxygen, since the gas is not very soluble in water. They have circumvented this inconvenience by developing large air-filled spaces, which are replenished with oxygen from photosynthesis, then distributed to the rhizomes and roots, which are without access to light. During nighttime, the oxygen transport gets interrupted and the latter tissues turn to alcoholic fermentation, also undertaken by yeasts (read more about them in another one of our voyages to the sea). The oxygen transported to the roots and rhizomes during daylight does not stay restricted only to those tissues and seeps into the surrounding substrate, also oxygenating it. This is beneficial to these plants, because they trap organic matter between their subterraneous parts, and, as it decomposes, there is the production of hydrogen sulfide, toxic, but ridden of its harmful effects when oxidized.

Apart from this, they also associate symbiotically with another association: bivalves of the family Lucinidae. Lucinids are extremely diverse and widespread clams, burrowing themselves in several different environments and being an ancient lineage, possibly extending further back than the Silurian. A common feature of them all though is the presence of sulfur-metabolizing bacteria in their gills, which are rod-shaped members of Gammaproteobacteria, residing in bacteriocytes. Due to the chemical actions of such bacteria, these bivalves are welcome in the undergrowth of seagrasses: the toxins of one are the nourishment of the other. The similarity of these bivalves to the previously mentioned tubeworms is striking and, indeed, some lucinids also reside in the abyssal hydrothermal vents. Speaking about reproduction, sea grasses, like the terrestrial angiosperms, also flower, though they propagate mostly clonally. The male flowers produce a high amount of pollen and the female flowers have tentacle-like structures, increasing the chances of successful fertilization, with the male gametes being transported by the water. However, in one seagrass species at least (Thalassia testudinum, encountered in the Caribbean and western Atlantic), pollination can be achieved not only through water, but through invertebrates as well, these being small crustaceans and polychaetes that get attracted to the mucus-covered pollen, a rich source of polysaccharides and proteins.

Other invertebrates take to the seagrasses as their homes. Examples of these are caprellids, a family of amphipods (these being generally small and slim crustaceans with seven pairs of legs and many body segments, various times looking quite alike fleas, despite having noticeable antennae) that also reside in algae, coral, etc. Caprellids, though, look nothing like fleas, resembling a cross between a mantis and a stick bug with an almost ghostly complexion, acquiring ranges of just a few centimeters. Their bodies are thin and elongate, with their second pair of legs similar to the raptorial legs of mantises, despite the fact they most often do not serve a predatory role. This is because most members of Caprellidae are detritivores, sometimes even consuming the feces of other creatures. Small bristles in their two pairs of antennae can serve as filter-feeding apparatuses, allowing them to capture tiny food particles. The ones that indeed are predators feed on other crustaceans and also on polychaetes.

Feeding on the meadows of Heterozostera and accidentally on some caprellids are Thalassocnus, marine sloths. They are, in particular, T. natans (around 2.5 meters in length), with this genus possessing several other species that, curiously, likely represent a continuous line of succeeding species, instead of several branching from a single common ancestor, with them following a pattern of increased aquatic adaptation. Like sea cows and hippopotamuses, these xenarthrans possess dense bones, making them apt at walking along the bottom (despite the fact they can also paddle along using all their four limbs), optimal for feasting on the abundant plants that grow here. Even though these waters are already quite warm, they have a relatively thin layer of fat that compensates for the loss of their fur, a loss that has also occurred in other water-going mammals and which can be explained by the increased drag provided by fur in the liquid medium.

And in order to better graze on the embryophytes, these mammals even have downturned snouts and, in order to quickly breath in while partially submerged, they possess high nasal openings, a feature seen in many other aquatic tetrapods, including in non-mammalian ones, such as in plesiosaurians. As extant sea cows, which dig the underground parts of seagrasses using their faces, Thalassocnus instead use their large claws to dig about, unearthing buried treasures. Even their tails show the influence of the underwater environment: they are long and widened, bearing a paddle shape and being used during diving as well to stabilize the animals while they forage on the seafloor. Despite the fact it may seem very strange for sloths to be, of all places, in the sea, even extant sloths, which are much smaller and display an arboreal lifestyle, are surprisingly capable swimmers, sometimes taking to the water.

Close by to the xenarthrans slowly paddling and walking about in the sunlit sea is a mother Odobenocetops, some 3 meters long, with her calf. They are quite bizarre-looking mammals, with cylindrical bodies and a plump, rounded face containing a prominent, exaggerated upper lip, apart from two small tusks emerging from each side of such lip. Such tusks are only small because she is a female, for males possess one large tusk (capable of getting to 1 whole meter in extension) on the right side of their faces, while the left still retains a female-sized tusk. Regardless of the impressive size, these tusks are actually extremely fragile and males especially need to be very careful, swimming with them positioned parallel to their bodies. Consequently, they exert mainly a social function, with males using them to establish dominance in a non-violent manner, just showing off their tusks and occasionally rubbing them, but never engaging in any truly physical confrontation. The winner will have access to the females in his vicinity, while the loser will need to go elsewhere should he desire to mate.

This female has already done all she wished with the dominant male in her area. If not for breeding, they usually stay apart, for Odobenocetops is unusually solitary, only infrequently gathering in groups. The word unusually is used, because this placental is a cetacean and, more specifically, an odontocete (toothed whales, even though Odobenocetops, in particular, lacks teeth besides the tusks), part of the delphinoid superfamily, which, as the name suggests, includes not only dolphins, but the Odobenocetops’ closest relatives: belugas (Delphinapterus leucas) and narwhals (Monodon monoceros), part of the family Monodontidae, both of which are quite social. The narwhals may appear particularly resemblant to these bony fishes because of the whorled, incredibly long forward-facing tusk usually exhibited by males, but these structures are not homologous and evolved independently, though they may function quite similarly as social tools. Curiously, Odobenocetops most closely resembles, not only in the ecological sense, other non-cetacean Artic inhabitants, these being walruses (Odobenus rosmarus). The latter also have quite well-developed upper lips and two large tusks, which likely serve in social matters. Their upper lips share a function as well: they are utilized to prey on bivalves.

This is what the mother Odobenocetops is looking for together with her calf. To aid in such process, they count with long whiskers, just like walruses, which feel about for possible food items, complementing the already very tactile upper lip. Once one of the targets is located, such as a lucinid clam hiding among seagrass undergrowth, they grab the poor mollusk with their lips and, using their powerful tongue as piston, create a sort of vacuum that cleanly sucks out the invertebrate’s soft parts, later ejecting the shell remains. The same strategy is applied by the walruses. As such, it is highly peculiar that two tetrapods, which unrelatedly took up the same lifestyle, both possess such apparently random structures (the tusks in this case), which serve no role in feeding whatsoever. However, that is not quite what happens, for though the tusks serve no direct role in feeding, the bony sheaths from which they emerge serve to keep both the whiskers and the mouth adequately positioned on the seafloor, acting as an important base and thus being important both for the Odobenocetops and the extant walruses.

Another predator of the bivalves is Myliobatis (also an avid consumer of amphipods), an eagle ray. As mentioned before, rays are cartilaginous fishes, being most closely related to sharks, forming with them the clade Neoselachii. Unlike in the Paleozoic, there are no more diverse chimaera relatives, such as the Cladoselache from the Devonian, and these fish are now restricted to the deep sea. Rays, in contrast, have an ample distribution and can be found from the open ocean to shallow waters like these. With a “wingspan” of some 1.3 meters, these rays, gracefully gliding and hovering over the substrate with their wing-like fins, are not only here to feed on invertebrates, which they suck up from the substrate with their ventrally positioned mouths and then crush (releasing an audible crunch that can be heard when near enough), but also to give birth to their young, which are safer in more sheltered areas such as this one. Apart from eagle rays, sting rays are viviparous too and the most viviparous of chondrichthyans so to speak. This is because the embryos, apart from feeding on yolk previously stored in the uteri of their mothers, also receive additional nutrition from uterine secretions. The gestation periods are long and are part of a common theme among eagle rays: their life is slow-paced, with maturity at a later age, low fecundity, and long lifespan. In the present world, this leaves them especially vulnerable to anthropogenic actions, including fishing, which is extremely significant on the Peruvian coast due to its highly productive waters.

For now, at least, many generations of Myliobatis may delicately flap their fins in their underwater flight with no worries about sea-faring primates suddenly ending their lives. They have, however, other worries to contend with. One such nuisance is provided by the flatworm parasite Benedeniella. It is a member of the class Monogenea, which includes many tiny parasites, not only of chondrichthyans, but also of osteichthyans (including tetrapods) and crustaceans. They possess a simple body, usually resembling a tape with a rounded end, with it being at such end where there are hooks for them to hold onto their hosts, adhesive structures that generate tissue irritation and damage. At the start of their body, they have a mouth cavity with which they may feed on epithelium, mucus, or blood of their targets, depending on the location they parasitize, which can be quite varied, from being externally, at the skin or gills, to internally, at mucosal surfaces of digestive organs or the urinary tract. Once the material is ingested, it ends up in blind-ended intestinal ramifications that distribute nutrients.

Benedeniella in particular colonizes the skin, sometimes even infesting the cornea (outer layer of the eye), and is oviparous, depositing a large number of eggs that will give rise to ciliated larvae. Such larvae, as soon they encounter a suitable host, will transition to the ribbon-like shape of the adults. In cases of heavy infestations, small skin damage may give rise to ulcers, which then lead to secondary infections and other complications that may be life-threatening.

Other bivalves that are preyed upon by Odobenocetops and Myliobatis are Anadara, ark clams (family Arcidae). These, like the lucinids, live buried in the sediment, being especially common in shallow waters, despite the fact individuals move into deeper waters as they age, making the shallower ones contain smaller clams, though they all generally do not go over 8 centimeters in length. They possess thick shells with prominent ridges running roughly parallel to each other, shells that protect their inner body, containing two siphons, one through where water enters and one through where it exits. As the liquid passes through these structures, food particles are captured from the surrounding medium. Uniquely, Anadara, as other ark clams, contains hemoglobin (while most bivalves have no respiratory pigment whatsoever, though the most common one for mollusks as whole is hemocyanin), which serves the same function as it does in both annelids and vertebrates, carrying oxygen around its body and allowing it to live even in hypoxic habitats. The oxygen-binding protein, unlike what happens in annelids and like the configuration in vertebrates, is found not only extracellularly, but also bound to analogs of our own red blood cells, with it being heterogenous between different species of ark clam.

Another bivalve that is not as helpless as the lucinids or the Anadara is Chlamys, a genus of scallops (family Pectinidae). This is because they have the incredible ability to swim. These bivalves do so by opening and closing their two shells. This expels jets of water from lateral openings and thus propels them forward, with scallops seeming to bite the water as they take to the liquid medium. Such movements allow them not only to swim but also to jump, dig, and perform other functions. To complement this, pectinids have a very well-developed nervous system and display several eyes as well as tentacles, which are essential for their movement by providing visual as well as mechanical and chemical stimuli respectively. The eyes, of a blue color, and the tentacles emerge from under the shells, going all around the circumference of each.

Despite all this uniqueness, scallops feed much like other bivalves, staying still among the sediment and drawing in water to catch suspended particles. Unlike the just seen Anadara, Chlamys, as other members of its family, lacks siphons and catches its food using gills (like the previously seen Inoceramus too), which pass the mucus-covered particles to its mouth, which itself is protected by a ramified pair of lips (similar to cauliflowers in appearance), important for selecting which particles to ingest or not. Once they are ingested, they are conducted through an esophagus lined by ciliated epithelia, which further move the food into the also ciliated stomach. While larger particles stay to be digested within the stomach and the following intestine, smaller ones are transported into the digestive gland, an organ that surrounds the stomach. There, the particles are absorbed by the cells constituting the tubules of the gland and, in them, such particles are digested, but, amazingly, so are the cells, with the resultant debris being swept back into the stomach. The tubule cells later regenerate, completing a cycle that follows the tides.

Tides themselves are an interesting phenomenon, occurring due to the influence of the Moon and, to a much lesser degree, due to the Sun’s too (our natural satellite exerting a greater influence due to its greater proximity). The reason they occur is the gravitational pull of the Moon and the Sun on Earth, pulls which generate two bulges on opposite sides of the planet. These bulges are much more noticeable with water, which moves more easily than land and it is like this how tides arise: when a certain location of the globe is in a bulge, it has a high tide, when it is out of a bulge, it has a low tide. The areas the bulges affect change because our planet is rotating. Tides also change due to the orbit of the Moon around Earth. Depending on the former’s orientation regarding the Sun, tides may be reinforced (called spring tides) or weakened (called neap tides).

Returning to the bivalves, they, apart from having to contend with many predators, also have to contend, like almost every other living being (such as the Myliobatis), with parasites, some of which can be particularly devastating. Examples of the latter are viruses of the genus Ostreavirus, belonging to the order Herpesvirales, which also contains many vertebrate viruses, some of which will be mentioned in our next journey. Just as other viruses of this order, Ostreavirus is a DNA-based virus, replicating inside the nucleus of its host cells and recruiting icosahedral capsids to its site of replication (keep in mind that, in eukaryotic cells, protein translation does not take place at the same site of DNA replication or RNA transcription and so viral capsids are produced first in the cytoplasm), which will package the DNA and then leave the nuclear region to be further modified in other cellular organelles, only to finally exit the cell, provoking its rupture and acquiring cellular membrane envelopes in the process. This leads to the formation of several macroscopic lesions throughout their bodies, being lethal in many cases. The larvae of most bivalves, which lead a plaktonic lifestyle before descending to the seafloor, are also much affected, having to contend with decreased feeding capacity and compromised swimming. Ostreavirus not only directly causes these health issues, but also opens the path for opportunistic infections by suppressing the mollusks’ immune systems, sometimes causing proliferation of Vibrio bacteria (more explained in this entry) and promoting overall disarray in the microbiota of the targeted invertebrates.

Out of such a grim reality, which fortunately has not affected any of the bivalves of this section of coast, there is certainly a more active mollusk to be discussed, much more so than even the quirky swimming scallops. It is the octopus, in this case one belonging to the genus Octopus, being exceedingly common in the Pacific coast of South America, despite possessing a worldwide distribution. It, like other octopuses, is a voracious predator, feeding on the aforementioned bivalves, crustaceans, fish, and echinoderms too. Just as the ammonoids seen in the Paleozoic and Mesozoic, this cephalopod can quickly swim by propulsion when it squirts jets of water from its siphon, moving backward. But it also has a more unique movement typical of octopuses: it crawls about the marine substrate utilizing its eight sucker-lined tentacles. Very differently from vertebrates, cephalopods display a distributed rather than a central nervous system (but, like vertebrates and unlike other mollusks, their circulatory system is closed, more efficient at pumping blood than the more widespread open circulatory system). In the octopuses, for example, more than half of their neurons are located in their eight tentacles, with each sucker being individually innervated. Despite such decentralization, there is no compromise to coordination or movement, but quite the contrary, as these animals can pry open their bivalve prey and use tools, gathering rocks to form barricades or using discarded shells as shelter, carrying them wherever they go. Apart from this, they are not only quite intelligent, but acutely aware of their surroundings. Information from the external environment is gathered by multiple ways: not only are their tentacles and suckers extremely valuable sources of tactile stimuli, but their eyes are incredibly powerful also, superficially resembling the camera-like eyes of vertebrates, despite both actually being quite different. This great awareness allows them to perfectly blend in, quite literally.

Their soft skin contains chromatophores, which are organs composed of pigment sacs and muscles. After receiving neuronal stimuli, the muscles move the pigments to the periphery, with these returning to a more central location once the electrical signal is gone. This leads to a change in color as well as pattern and can be done in much less than seconds due to the neuronal association. Additionally, skin color can also change through the action of iridophores. In comparison with the chromatophores, iridophores have no muscle, consisting of stacks of thin cells harboring, in their interior, plates that reflect light. The spectrum of the reflected light changes depending on the angle at which it is observed and so this leads to the cephalopod exhibiting different colors based on where it is being seen, giving it an iridescent aspect. Despite not being electrically associated with the nervous system, iridophores can be influenced by the release of neurotransmitters, changing in the span of seconds to minutes, much more slowly than chromatophores, which, since they are located above the iridophores, can change the color of the reflected light depending on the arrangement of their pigment sacs, adding yet another layer of control.

Besides color change, octopuses, as well as other of the so called coleoid cephalods (which do not include nautiluses), such as squid and cuttlefish, can also modify their skin texture through organs known as papillae. They can bulge rapidly thanks to a muscular hydrostatic action and, due to the fact papillae contain both chromatophores and iridophores, this is done with no compromise to the color camouflage. As such, coleoid cephalopods are truly masters of disguise. The octopus we observe is a perfect example: it stands perfectly still among the rocks, matching perfectly not only their colors, but their outlines. Only the most attentive of onlookers can see what hides among them in plain sight. And this is no ordinary octopus as a matter of fact, for this is a female and, for the last couple of days, she has not fed. That is not because she is unable to, as octopuses, counting with their dexterous tentacles and strong, parrot-like beak, deliverer of a venomous bite (curiously, the most venomous octopus, the tiny, but amazingly azure-colored blue-ringed octopus, constituting the genus Hapalochlaena, has the main protein in its venom, a neurotoxin, produced by endosymbiotic Vibrio bacteria, cited before a few paragraphs above) and capable of drilling into bivalves too strong to be opened up, are quite apt hunters.

This is because she is going to spawn. Even though these animals are solitary, female octopuses spend their last days with thousands of their young, which are placed in a secluded space, where they can be nursed until they hatch or just before they do so. Without them, the developing larvae, which, after born, look like very miniature versions of the adults, would fall victim both to microorganism parasitism and to predation by larger lifeforms. They will spend their last days in complete dedication to their offspring, while, on the inside, their muscles and digestive system degenerate, being replaced by fibrous tissue. In their ovaries, no more germinative cells can be found: they truly can only mate once. Most incredibly of all, females who have lost their offspring can take on the role of caretakers of unassisted young, left alone by their dead mothers. Once the larvae emerge from the eggs and find their dead or soon-to-be-dead mother, they will join the zooplankton, until they grow large enough to return to the bottom.

More invertebrates other than protostomes inhabit the substrate. The most noticeable of which must be the echinoderms, fellow deuterostomes like us, chordates. A few are predators just as voracious as the octopuses, constantly on the prowl. In these expanses, an example of such a creature is the Luidia magellanica, a species of starfish with fairly slender arms and a dark, mottled pattern, around 20 centimeters from the tip of one arm to the tip of the opposite one. It is specifically a predator of other echinoderms and, unlike most starfish, it moves quite fast, appearing to glide over the underwater sandy soils. This is because it has a special adaptation in its locomotory apparatus that is, otherwise, shared by the great majority of the representatives of the phylum Echinodermata. Their locomotion is based on the ambulacral system, a complex of fluid-filled canals that runs through their body and arms. It starts out as a ring surrounding the starfish’s mouth and then branches into segments that go into each arm. The contraction of certain muscles leads to the closure of valves inside such segments and this forces water into the so-called tube feet, which are small, tentacle-like appendages that stick out in great numbers from under each arm. Tube feet are thus powered hydrostatically, a mechanism that also occurs in the octopuses' aforementioned papillae. While usual tube feet end in what appear to be suckers (even though they are not, actually adhering to the substrate chemically rather than through the formation of a vacuum), those of a few starfish, including L. magellanica, end in points that allow them to quickly cover distance, while their peers are dramatically slower.

The fluid in the ambulacral system is derived from seawater and, apart from being essential for their locomotion, is also fundamental to the transport of oxygen (the circulation of nutrients takes place through a circulatory system that, like the one of insects and other arthropods, has no respiratory function). Water enters the body of these animals through a sieve structure known as madreporite, located dorsally, close to their anus (even though the starfish we observe, as some of its closer relations, lacks such opening). It is composed of calcium carbonate, just as the rest of the endoskeleton of the starfish (other echinoderms also have calcium carbonate endoskeletons), usually arranged in plate-shaped ossicles that fit together, located below the thin epidermis that forms the outer covering, immersed in a thick dermis of connective tissue. A few of the ossicles exert a way more proactive function and constitute pedicellariae, which resemble small jaws also emanating from the dorsal surface of the deuterostome. They may serve to capture other animals or to defend the starfish against undesired colonizers. However, in the case of L. magellanica, its main weapon is located ventrally, the same side from which emanate the tube feet, as just said. It is, of course, its mouth. Unlike most starfish, which are capable of everting their stomachs and digesting their prey extra-corporally, this one is unable to do that and follows a more orthodox method of first completely engulfing its victim.

Right now, it is trying to do so with an out-of-luck Loxechinus albus, a sea urchin and thus fellow echinoderm. It is quite a small L. albus for that matter, reaching in turn of half the size of larger individuals, about 10 centimeters in diameter. Despite this, it compensates in its defenses, which, hopefully for it, will frustrate the L. magellanica’s attempt at a meal. Nevertheless, the starfish is determined, enclosing its arms around the smaller animal, its various tube feet hungrily expanding and contracting as it shifts to accommodate the sea urchin in its mouth: however, the endeavor, fortunately for the spiky echinoderm, is proving itself harder than the starfish would have expected.

Such spiky covering is also a product of the echinoderm endoskeleton, which, in sea urchins, forms a protective generally almost spherical carapace covering their interior. The spines are components of the endoskeleton as well, being attached to the just cited carapace by joints held in place by muscle, which also confer movement, with them being potentially used as locomotory organs apart from the also present tube feet. Dorsally, the round calcium carbonate armor allows communication with the environment through the anus and the madreporite while ventrally such communication is afforded by the mouth, composed of five hardened parts. These mouthparts are used by L. albus to graze on algae. Smaller individuals feed on bottom-dwelling, glue-secreting diatoms, but also on other algae, while larger ones consume only multicellular forms of these organisms, like kelp.

Apart from these two species of echinoderms, there is more of this phylum to be seen in these shallows. In this case, sea cucumbers of the species Athyonidium chilensis, capable of acquiring lengths greater than 15 centimeters. They live obscured in crevices or buried in sand, leaving out only their tentacles, which capture particles suspended in the medium, a form of feeding very widespread as can already be noticed from all the animals we have previously sighted. Due to their almost secretive mode of life, their body can barely be observed, but it consists basically of a plump cylinder, justifying these animals’ common name. Though this species lives in a somewhat secretive manner, other sea cucumbers are much more visible, such as the species Isostichopus fuscus, an inhabitant of more northern Pacific coasts that, though also located in the sea floor, moves around using rows of tube feet located on its underside. Some abyssal-dwelling sea cucumbers have taken their tube feet to the extreme and possess very enlarged versions which they use to march, immersed in the never-ending darkness of their desolate habitats.

Despite these differences, they all are marked by the tentacles lining their mouth opening, internally sustained by a ring of calcium carbonate, one of the remnants of their endoskeleton, also retained in microscopic ossicles embedded in their skin. Either way, the mouth proceeds to give rise to a long, looping intestine that ends in an anus, opening at the other side of their cylindrical bodies. If they feel threatened, they can even release their intestine, giving a gruesome show to startle predators and go out alive. Eventually, all of it can be regenerated. In regards to the anus, it is there where they conduct their gas exchange, in a ramified organ attached to the end of their gut that also functions in excretion. Curiously, A. chilensis, together with a few other sea cucumbers, possesses hemoglobin-carrying cells, which may be present in the ambulacral or circulatory systems, potentially in both. The reason for this is potentially similar to that of Anadara (and something which also is reflected in certain adaptations of the seagrasses): since both live buried, the availability of oxygen is lower than if they lived completely in contact with water and, thus, they need extra oxygen-binding capacity to ensure they have enough to truly meet their demands.

Finally, one may wonder how can echinoderms look so strange, so unlike other organisms. They are, after all, radially symmetrical bilaterians. Well, many are not so peculiar in their planktonic larval stage, when they exhibit their ancestral bilateral symmetry, only to be lost with maturity (larvae are generated through sexual reproduction, achieved by the release of gametes in water, but, alternatively, echinoderms, such as some starfish and sea cucumbers for example, can reproduce asexually from fragments of their bodies, revealing an astounding regenerative capacity). However, some echinoderms do not go through any bilateral stage at all: some are born already like miniature versions of the adults. That being said, even sea cucumbers show some degree of bilateral symmetry, a curious almost return to their primitive state. It just goes to show how evolution truly has no goal: it is a force that acts on the present, at the moment, it is influenced by the past just in the sense of how bygone presents acted then.

Contrasting with the relative calmness of the scenes we witnessed, there is a frenzy occurring higher up in the water column. Attracted by the coastal upwellings, a shoal of sardines of the species Sardinops sagax has become trapped in the shallows. Many animals are taking advantage of their peril. These ray-finned fish are striking in their metallic coloring, which creates a whole load of reflective hues as they twist and turn coordinatively in their tightly-packed grouping, an incredible feat made possible by the lateral line, discussed in greater detail here. Opening the mouth wide, the sardines feed primarily on zooplankton, but younger ones are more dependent on phytoplankton, exhibiting a greater preference for filter-feeding, while adults may be more selective in what they eat, nibbling on larger particles. Either way, they constitute the basis of this food web for larger carnivores, being the link between the many times microscopic plankton and the macrofauna of this and many other marine environments.

Among the creatures taking advantage of the great sardine concentration are penguins, some jumping into the water from the rocky outcrops right now after sighting the silver colors indicative of the ray-finned fish. Like Thalassocnus and other water-dwelling mammals, these aquatic theropods have dense bones too, which decrease their buoyancy and allow them to dive. Assisting in underwater movement are their flipper-like wings and, giving them extra waterproofness, are their feathers, very densely packed, also helping them retain heat. The waterproof quality of feathers is a result of their intricate structure, which impedes water from penetrating inside them, not being associated with preen oil (produced by the uropygial gland, as is otherwise commonly, but equivocally thought). The oil, however, is important for conserving feather structure and thus serves only indirectly for granting impermeability to birds. Evolving basically at the very start of the Cenozoic, penguins have become quintessential Southern Hemisphere dinosaurs and, in this environment, they can be found as two species of the same genus.

One of these is the extant Spheniscus humboldti, popularly known as the Humboldt penguin, a sporter of striking black and white markings. It is relatively small, varying from 66 to 70 centimeters in length, spending the majority of its time in these waters, seldom exploring farther. Being a pursuit hunter, it is more than apt at plunging into the sardines and quickly swimming after any of the non-tetrapod fish unfortunate enough to separate from the shoal. Some of the Humboldt penguins take their time grabbing as many fish as they can, while others get out of the water just as fast as they got in: these are parents. They are not diving for their own sustenance, but rather just to get sufficient food for their chicks waiting on land. The second one is much larger and more robust, being the now extinct Spheniscus megaramphus. It contrasts with the Humboldt penguin not only due to its size, practically double that of its smaller still living relative, but also due to its beak: it is much longer not only in absolute, but also in relative terms. There are also differences in lifestyle, as S. megaramphus, unlike S. humboldti, frequently forage beyond coastal waters. They spend even more time at sea, consuming a wider array of prey items.

To deal with this increased exposure to seawater, the larger penguin also has more well-developed salt glands, organs which excrete excess salt taken in from the salty water that is characteristic of the marine realm. In birds and sea turtles, the gland is located close to the eyes, secreting tears unusually high in their salt content. Other sea-going reptiles also count with ways to excrete the mineral (even the long gone plesiosaurians and ichthyosaurs, for instance, had salt glands as well), but that can vary, with some having nasal glands and others, like marine snakes, having salivary glands that simply release more salt. Chondrichthyans also count on a salt gland, with it being an unpaired organ that occurs close to the end of their gut, thus called a rectal gland. Many actinopterygians, on the other hand, lack proper glands and excrete sodium and chloride ions through their gills. Marine mammals, in contrast, have no need for salt glands or associated structures, since they can excrete all that is needed conventionally, through their kidneys (the more efficient nature of mammalian kidneys was first brought up here).

Speaking about marine mammals, one of the kind is also taking advantage of the sardines, following a similar strategy to that of some penguins: focusing on the fish that got separated. With this in mind, it is waiting for the more energetic birds to strike and single out the smaller vertebrates, going after the loners, striking them with its long neck and snout, also useful for investigating crevices where some other creatures it eats, like octopuses, may be hiding. This mammal is an Acrophoca, a genus of seal. Seals, like the aforementioned walruses, are pinnipeds, a group of carnivorans that have taken to sea, using all their limbs as flippers (in contrast, for example, with cetaceans, which have no observable hind limbs, using their finned tails as their main method of propulsion). Like their land-dwelling relatives, they have generally remained on a meat-based diet. Unlike their land-dwelling relatives however, they are far from the apex predators of the oceans, for here sharks and artiodactyls, which on land their relatives so many times hunt, are putting they too on their extensive menu. Despite this, they have managed to thrive across the world’s oceans. Not only is Acrophoca a seal, but also a true seal (also called earless seals, due to their absence of external ears, in contrast, for example, with sea lions, which still possess such structures), those of the family Phocidae. Very diverse, phocids range from the long-bodied and gracile Acrophoca, to the extremely large and bulky elephant seals (Mirounga, which receive their names from the trunks their bellicose males display, a dramatic case of sexual dimorphism, also reflected in the much smaller size of their females), and even to the fierce leopard seals (Hydrurga leptonyx), which terrorize penguins in Antarctica. They are, of the pinnipeds, the most adapted to water and, as a consequence, the most cumbersome on land.

A couple of cetaceans that do not take pinnipeds as meals arrive, signaling their entrance with a series of sounds that come in the form of rapid, deep pulses. Opening their mouths wide, they engulf, in one single swoop, tens of sardines. Streams of bubbles emanate as they close their jaws around the desperate little fish, never to see the light of day again. The penguins dart around the two newcomers, targeting with amazing precision the actinopterygians stunned by the attack of the whales, while the Acrophoca continues gorging itself on the poor individuals isolated by the assault of its fellow lobe-finned fishes. These two whales, unlike the previously seen Odobenocetops and the other cetacean yet to be explored, are mysticetes (baleen whales), displaying keratin bristles (baleen) inside their mouths that act as a sieve to filter organisms. After the whales take a huge gulp, they later force the water out from their buccal cavity, leaving only prey items caught between the baleen. As such, they have no teeth to speak of: during their fetal development, tooth buds even begin to form, but they do not last, being reabsorbed and only the baleen bristles remain. Many millions of years ago, mysticetes were, as other cetaceans, toothed, leading quite different lifestyles. However, they eventually lost such attributes, with there likely having even existed transitional forms sporting both teeth and baleen.

These here are Piscobalaena, a genus of small baleen whales that only reach 5 meters from the tip of their snouts to the end of their tails. Despite the great whale diversity of this period, the Neogene, there are still no gigantic mysticetes as can observed, for example, in our present time, such as the blue whale (Balaenoptera musculus), the largest known animal to have ever lived. Even so, these giants have been steadily, albeit gradually evolving here in the Southern Hemisphere, fueled by high productivity in these seas, changed by the rearrangement of ocean currents that occurred earlier in the Cenozoic. They have been so far barred from entering the northern oceans by the Equator, which, with its hot and stagnant waters, is far from favorable to their filter-feeding mode of life.

Other archosaurs besides the penguins are also searching to get their sardine snacks. One of those is the crocodilian Piscogavialis, a gharial to be more exact, characterized by its very long and thin snout adequate for catching fish. This area’s higher temperatures allow ectothermic reptiles such as it to eke out a living and flourish. Swimming by undulating its spiked, broad tail from side to side, the knobby sauropsid, full of bony osteoderms, swims below all other attackers. In an instant, its movement, once rhythmically slow, gets interrupted by a quick thrash of its head, which inserts itself into the shoal and returns with not one, but two fish caught between its conical, elongated teeth. Modern-day gharials are restricted to Asia, but the marine habitat of these ones allows them a much ampler distribution. And, in fact, the marine realm likely was from where the common ancestor of both gharials and crocodiles came from (with alligators and caimans forming another grouping inside Crocodilia), later diversifying into freshwater forms.   

Very large, around 7.7 meters long, Piscogavialis starts out small and defenseless. Even so, as modern gharials, this genus exhibits quite a significant amount of parental care. Females gather to construct colonial nesting sites in the sandy stretches of coast dotted between the predominant rocky outcrops. They watch their nests for the duration of the incubation of the young, with them opening the sandy mounds once the hatched babies start chattering. As soon as they see the light of day for the first time in their lives, the tiny reptiles rapidly make their way to the sea, scurrying over the sand in a similar fashion to baby sea turtles. Unlike those, however, they are far from unattended. The dominant male of the area, which monopolizes breeding rights, is their protector, sticking close to them and rapidly turning up should they call for help. Sometimes, the babies will even gather in their tens at the back of the dominant male, helping navigate his offspring through these tumultuous waters.

In the air, yet other archosaurs are trying to acquire their own fishy meals. The first to have arrived are the magnificent and absolutely titanic Pelagornis, birds with a wingspan of 6.4 meters. Bearing teeth-like projections from their beaks, these are very unique saurischians indeed. Surpassing the theoretical limits for flight in birds, these creatures still manage such a feat due to their extremely long wings, which permit them to glide for very long periods of time. Without the necessity to constantly flap, Pelagornis cross great distances without much effort, making them extremely efficient fliers. However, due to these anatomical perks, they are unable to rest on the water’s surface or dive in search of prey, exhibiting a method of predation very similar to that of previously seen anhanguerid pterosaurs: flying low and catching fish at the sea’s surface. In that regard, they are being aided by the simultaneous attack of the underwater tetrapods, which have concentrated the terrified sardines near the water’s limit. Their pseudo-toothed beaks provide excellent grip and facilitate the retention of the captured osteichthyans. This method of life is so successful, pelagornithids (the family to which Pelagornis belongs) have acquired a global distribution since their origin all the way in the Paleocene Epoch.

Soon, other flying birds will arrive to take part on the banquet. The boobies (Sula) are very different from the Pelagornis and dive quite deep in search of fish, exhibiting long, conical beaks and usually brightly colored feet that match the skin color of their faces. Such feet are important for courtship, being used by females to assess the fitness of a proposing male, which also raise and stomp them in inflated displays. Part of the same order as the boobies (Suliformes) are the cormorants (family Phalacrocoracidae), which, though also divers as the boobies, possess a more elongated, almost serpentine neck, rendering their appearances quite distinct. Monogamous as the boobies, they often choose similar areas to nest in.

Back underwater, even more animals are directing themselves to the sardine shoal. This time, a shortfin mako shark (Isurus oxyrinchus). With a torpedo-shape and acquiring very impressive speeds of more than 50km/h, this cartilaginous fish can dart in and easily catch as many sardines as it wants, passing like a lightning bolt through the many penguins. They are lucky this is a fairly small individual, because larger shortfin makos, capable of getting to some 3.7 meters in length, would very much see them, the nearby Acrophoca and even the Piscobalaena as possible prey. Makos are different from most other sharks not only because of their speed, but also due to one of their physiological attributes that allow them to achieve such speeds in the first place: endothermy, also shared by some other members, such as the great white shark (Carcharodon carcharias), of the order Lamniformes, to which they belong. The main way they maintain higher temperatures inside specific parts of their bodies is through specialized blood vessels that retain metabolic heat in certain organs, such as in their locomotor muscles, intestines (promoting greater digestive efficiency), eyes, and brain. Similar adaptations are convergently evolved in tuna (Thunnus), robust, torpedo-shaped ray-finned fish that, also predatory in nature, display very high swimming speeds. Like the earlier seen chondrichthyan, I. oxyrinchus is another live-bearer, with pups, born already quite large, often having several different fathers, since the shortfin mako practices polyandry, with one female mating with several males.

Faint clicking sounds become ever louder as the once calm tetrapods, a few of them terrorizing much more than unnerved sardines, become unnerved as well. Some of the penguins start a retreat to the shore, while the Odobenocetops mother makes her calf swim along to someplace else and the Piscobalaena interrupt their mouthfuls to escape the scene. The Thalassocnus also get on the move, grabbing their last mouthfuls of Heterozostera before ascending the water column in the direction of the coast. As they do so, the now near clicking sounds decrease in duration, but repeat more and more often, bearing an uncanny resemblance to a squeaky door hinge. One of the xenarthrans gets suddenly surprised when, from its sides, suddenly emerge clouds of debris emanating from the sea floor, blocking its view. It continues forward however, but there too a black shape darts past, lifting up another cloud of marine dust. As the sloth gets progressively confused and disoriented, not only from the wall of suspended substrate that surrounds it but also from the deafening sound of fast, non-ending clicks, it feels terrible, terrible pain. The water soon turns red and its companions can only look back to see a mist of crimson and beige, as the sand mixes with the blood that pours in ever greater quantities from the mammal’s wounds. They also see its killers: roughly 4-meter-long black and white sleek shapes, bearing a hydrodynamic body and beaked faces, revealing big, robust teeth every time their mouths open to deliver another blow.

These are Acrophyseter, predatory sperm whales. Unlike their living relatives, which have reduced teeth and feed by suction feeding, these ungulates are voracious carnivores that bite and tear their meals apart. Despite such fearsome behavior, this genus is the smallest of its group of highly predatory physeteroidans (the sperm whale superfamily) and must take care even when hunting the seemingly harmless Thalassocnus. Around half the length of the whales, the sloths can deliver some serious damage due to their very large claws, usually utilized to dig seagrass roots and rhizomes, and, as such, this pod of cetaceans has developed the strategy cited above to counter the danger: they use their powerful tails to whip up clouds of sand, which compromise their prey’s orientation, leaving them quite more vulnerable and practically defenseless. It works particularly well, because, like other odontocetes (of which the Odobenocetops is an example as previously cited), Acrophyseter is capable of echolocation (even though an older species of Odobenocetops known as O. peruvianus had a vestigial melon or none at all, in contrast to the observed O. leptodon, which has one and thus also echolocates).

They produce their characteristic clicks through the larynx, which emits air into the nasal passages, where it gets pressurized and then passes through structures of the cavity that connects itself to the blowhole. Such passage generates vibrations in fatty bodies, vibrations that get anteriorly reflected by the skull and by nasal air sacs, with them passing through other tissues and the melon, a structure externally formed by a collagen capsule that in its interior contains lots of specialized lipids. This final pathway amplifies the sound, which finally reaches the environment. Outside the artiodactyl, the sound may encounter an obstacle and, if it does, it will be reflected back. Such reflection will provide the whale with its target’s localization, allowing it to navigate even in complete darkness. In the case of sperm whales, they have yet another lipid filled sac called the spermaceti, being less dense than the melon. The functions of such organ are possibly quite a few, aiding in buoyancy control, conduction of produced clicks (similarly to the melon), and even combat. Like the extant giant sperm whale (Physeter macrocephalus), Acrophyseter lives in matriarchal pods containing females and their young, while mature males usually wander alone. Sometimes, there is competition between males and, just like occurs in the modern giant sperm whale, the Acrophyseter can engage in head-butting sessions to settle disputes, though, in their case, the spermaceti is also used to ram into prey to even further disorient them. There is significant variation in hunting strategies between the different pods of these predatory ungulates and males, usually larger than females and solitary, use their sheer bulk to pound into and incapacitate prey, shredding them apart just afterwards.

On land, the attack has provoked quite the commotion. While the coast is normally noisy, it is even more than usual. Not only is it filled by the squeaks of the sloths, but also by the incessant calls of the penguins, which emerged all together from the water. Monogamous (though rarely females will mate with another male and unpaired males will try to usurp the females of paired ones, generating intense conflicts that may end in serious injury or death), they recognize their mates through their singular vocal cues, which range from chirps to loud, almost melancholic calls that can even resemble a crying lament. As they disperse across the rocky outcrops, the Humboldt penguins enter their burrows excavated out of guano (a substrate derived from accumulated bird feces), where they build their nests, with anxious downy, brownish-gray chicks peeping rapidly for food as they see a returning parent. The S. megaramphus, on the other hand, do not burrow and nest superficially, forming mixed colonies with their smaller peers. They throw alarming calls at the passing sloths, trying to avoid they trample on their eggs or chicks. Though the mammals seem unperturbed, they take care while transversing the busy scene, not wanting to take unnecessary pecks from the large bills of their avian neighbors. Thalassocnus, like most other ground sloths, walk rather curiously, with their knuckles on the ground, like an anteater, and also with the soles of their feet facing one another.

Boobies and cormorants also nest on these shores, though the latter will also build such reproductive structures on trees, which, nonetheless, are not so common in this region, since the productivity and richness of the sea is contrasted by the arid and fairly desolate land. They help the Humboldt penguins by contributing to the great amount of guano that accumulates in this locality. More ambiguous visitors also land here, these being the Pelagornis. While they certainly give much in the way of their excrements, their unrivaled size means they bully fellow theropods into submission, not only stealing their food, many times actually reserved for the offspring, but by sometimes going after the chicks themselves. It is not uncommon to see a terrified S. humboldti parent vocalizing desperately from its burrow as it faces off against the intruding fierce beak of a hungry pelagornithid. Even the more aggressively inclined S. megaramphus do not have much in the way of resistance against their much larger cousins. Fortunately for the smaller coelurosaurians, Pelagornis are normally only visitors, since they prefer nesting on small, offshore islands of ancient volcanic origin that offer good cliffs from where they more easily take off.

On the beaches that can be observed from the rocky outcrops where penguins and other birds nest, many Acrophoca, quickly swerving their long necks and waddling around surprisingly nimbly while emitting loud grunts, and gharials can be seen. Apart from the enormous basking Piscogavialis, there also are, intermingled between them, representatives of a smaller genus of marine gharial known as Sacacosuchus, being half the size of their larger relatives, but sporting a more generalized diet that does not consist entirely of small fish. A few sloths transverse close to them, not intimidated in any way by the wide-open jaws of some of the resting crocodilians. Organisms that can menace them in those sandy stretches are much, much smaller, being fleas and, as a matter of fact, the smallest fleas, with body sizes of 1 millimeter. Resembling minuscule, almost invisible darkened jumping specks, these are Tunga penetrans, which have a wide range of possible mammalian hosts, including ourselves, humans. They are most distinctive not because of their diminutive size, but because of the female, which, unlike the male, does not simply suck blood from the targeted mammal, but actively invades its skin, ballooning in size as its abdomen gets distended. From it, several eggs are released, which, in the sandy soils, give rise to worm-like larvae that eventually undergo metamorphosis inside sand-lined cocoons to become the jumping adults. While the burrowing of the female flea does not pose much harm on its own, as it eventually dies and the harmed tissue regenerates, it introduces potentially quite troublesome bacteria. Fortunately for the Thalassocnus, T. penetrans is not such a nuisance due to their aquatic habits, but they certainly are to purely terrestrial mammals.

Among the bird colonies, much smaller organisms thrive in their inherently parasitic ways, these being, of course, viruses and, in this case, influenza viruses. Though these lifeforms are typically associated with avian reservoirs, they have coevolved with vertebrates for many millions of years and thus have a preexistent predisposition for jumping to others of such animals, like those from class Mammalia. Such jumps are facilitated by the fact these viruses are RNA-based and more prone to mutations, since RNA is not as stable as DNA. Not only that, but they frequently exchange genetic material by coinfecting cells, with the RNA of one type of influenzavirus being possibly assembled together with the RNA of another type of influenzavirus. In regards to assembly, capsids are helical and the viral particles may vary in shape: being either rounded, filamentous or aggregating to form string-like structures, but all enveloped either way, counting, apart from the capsid, with an additional layer of proteins between it and the envelope. Such envelope, derived from the cellular membrane, is acquired at the moment they emerge out of the host cell. Even after such emergence, they stay attached, needing an enzyme known as neuraminidase, which cleaves carbohydrates from cellular glycoproteins and thus releases the viral particles. Apart from this action, neuraminidase also aids in the beginning of the infective process by degrading the mucus of the respiratory tract, facilitating virus access to the cells of the respiratory epithelium, in which they will replicate and subsequently promote the typical respiratory symptoms associated with the flu.

Back to the genetic exchanges, they are, just like normal mutations, frequently deleterious, creating new viruses that will shortly go extinct, but some may prove to be pivotal in guaranteeing their continued existence and dissemination. Antigenic variation encounters itself in the pivotal category and ensures a constant process of immune evasion that justifies, for instance, the constant flu vaccines, a remarkable strategy of our kind to try and keep up with these restless viruses. Amazingly, most infections by these parasites start with just a single viral particle and, consequently, the aforementioned genetic exchanges are not very commonplace, occurring mostly in immunocompromised individuals.

Be that as it may, from these rocky shores, a peculiar red shape can be seen, in slightly deeper water than where the seagrass meadows grow. It is very distinct from the red cloud that appeared as the Acrophyseter mangled the body of the Thalassocnus, appearing to have tentacles. But it is large, too large. Indeed, as we approach, we can see it is a squid, a gigantic one at that, reaching a total body length of 12 meters. This is, of course, an Architeuthis dux. It is quite unusual for it to be in such superficial waters, since it is an inhabitant of the deep. But its battered state and lethargic aspect justify its location: it is dying. Normally, in its native habitat, it is an active predator, using its ten tentacles, two of which are extremely elongated, ending in widened tips, to capture fish and fellow squid, coiling around them like a snake, bringing them closer to the beak that, enclosing a radula inside, will tear them up. To keep itself steady while it rapidly swims around through the expulsion of jets of water via its siphon, this squid, like other cephalopods and invertebrates, has statocysts, which are fluid-filled organs in which statoliths, calcium carbonate structures, are immersed, moving around as the squid does so and providing a sense of orientation in a three-dimensional plane as they activate neurons with their movement. Vertebrates have a very similar, convergently evolved organ, known as the semicircular canals, which also count with calcium carbonate structures, called otoliths. Right now, the statocysts are not of much use to this A. dux. It will not be long before it dies on its own or becomes food for nearby opportunists.

These slightly deeper waters the giant squid is in are home to a kelp forest. These very large brown algae are fairly recent in terms of geologic time, probably appearing at the Eocene-Oligocene transition as the world began to cool. Like their diatom relatives, they have seen a dramatic rise associated with such fall in temperatures and only now are beginning to form kelp forests as those seen in the modern day, constituting spaces for a variety of organisms to dwell and live in, for they, like the more familiar terrestrial forests, create a wide gamma of microhabitats, apart from also being a food source by themselves. The sea urchins seen earlier, I. albus, will consume these photosynthesizers should they be big enough for instance. This kelp forest is composed of algae of the genus Lessonia, which has a bushy aspect, but the fellow kelp forests of the South American Pacific coast also count with one more genus: Macrocystis. When occurring together, the latter primarily constitutes the upper canopy due to its great height and sleek profile, while the former is located further down.

Like plants, kelp also count with root-like structures, though these, particularly for them, are called the holdfast and only serve as an anchorage, providing an excellent medium in which echinoderms, polychaetes, crustaceans, bivalves, and gastropods dwell. Higher up, the foliage proper (composed of leaf analogs called blades and stem analogs called stripes) provides shelter for swimming and hanging organisms, like the caprellids cited earlier. They also provide a base on which oviparous chondrichthyans attach their egg capsules. The very elongated Macrocystis count, apart from the holdfast, blades, and stripes, with air-filled bladders (pneumatocysts), which give them buoyancy and help them stand upright. Unlike vascular plants, kelp, despite the great sizes they might achieve, have no system to conduct fluid through their bodies and as such are entirely dependent on the external movement of water to keep them well-nourished, even having serrated blade edges that increase water mixing and thus their access to nutrients. Their reproduction involves the production of spores (containing half the number of chromosomes of their parent kelp), released into the water to eventually germinate into microscopic male or female gametes. If fertilization occurs, a new brown alga arises, from which will come new spores to produce future generations. Very much like plants, they can also reproduce asexually by expansion of their holdfasts or by fragmentation (possible even during the gamete stage).

Even more distant from the coast, one can see a very large dorsal fin, many times larger than that of the shortfin mako already observed. It is, of course, the iconic and famous Otodus megalodon, a shark that can grow and potentially even surpass 15 meters in length. Though fairly resemblant of a great white shark, it belongs to a different and ancient genus called Otodus (as could have already been concluded from its scientific name) that stretches to the early Paleocene. Despite this difference at the generic level, Otodus is still a member of the Lamniformes order. In this aspect, apart from the similarity in appearance, O. megalodon also shares similar features in regard to physiology, being too a regional endotherm. It is hotter than its relatives shortfin mako and great white, a feat facilitated by its very much larger size, which translates into a more significant production of metabolic heat. To accommodate for such great metabolic needs, O. megalodon consumes quite a lot of prey, attacking mainly small cetaceans as well as pinnipeds, being truly the undisputed apex predator of this ecosystem. Its victims are not safe from it even in the shallow waters, as it has no problem following them into those locations. However, immature individuals of this shark are the main ones to inhabit shallows, which constitute a safer environment in which they can feed and grow, a similar strategy also employed by the Myliobatis. This is no coincidence as these two live-bearers have low fecundity and take many years to reach maturity. Consequently, youngsters are not expendable and must have a high survival rate to ensure the continuation of their kind.

The whales killed in the open ocean by the enormous shark slowly drift to the bottom, where they will once again serve as food. The trajectory to the depths is quite an interesting one, as many unusual creatures, normally hidden from sight, make their bizarre appearances. One of the most unusual, but even so quite common (especially in the Atlantic), is the ostracod Gigantocypris, a generally orange-colored spherical crustacean about 3 centimeters in diameter. This is quite remarkable for ostracods, which are usually much smaller, 30 times smaller actually. From inside its two translucent shells, it extends feathery antennae that help it swim, sense its surroundings, and even catch prey (other crustaceans, worms, and young fish), a process aided by its mouthparts that also can slide through. To maintain its neutral buoyancy (in which it neither sinks nor rises), it reduces the sulphate content of its hemolymph.  Inside the shells, it not only houses its young (in the case of gravid females), but two incredibly large silvery eyes that grant it excellent vision. At the depths Gigantocypris lives, those ginormous eyes are not for catching sunlight, but the electromagnetic waves derived from abundant bioluminescent animals that share the same habitat.

The worms consumed by this giant ostracod are known as arrow worms, composing the phylum Chaetognatha, present in the world’s oceans since the Cambrian. They range in size from just 1 millimeter to 12 centimeters long (with most being between 5 millimeters and 4 centimeters), being streamlined creatures with lateral fins and one caudal fin. Their heads are adorned by two compound eyes and end in ventral mouths lined by hooks that serve to catch prey, mainly crustaceans and tiny, young fish, thus possessing a diet similar to that of their Gigantocypris predators. While most are components of the zooplankton, rapidly moving around like darts, others are inhabitants of the substrate, attaching themselves with secretions and acting as ambush hunters, extending their mouths should a prey item make itself known (apart from visual cues provided by their eyes, arrow worms possess, on the junction between their head and main body, a belt of ciliated cells that create a flux of water sufficient to draw in chemical compounds released by prey). The majority of them are actually venomous, paralyzing their prey through neurotoxins administered via their oral hooks. Like in the blue-ringed octopus, such toxin comes from symbiotic Vibrio bacteria.

Returning to the dead artiodactyls, as they finally reach the seafloor, in truly great depths, strange animals emerge to feed on them. A few of these are the eel-like hagfish, jawless vertebrates. These here are whiteface hagfish (Myxine circifrons), similar to other hagfish and sharing much of the same ecology. Relying mostly on fallen gifts from above, they are able to spend many months without feeding, but are truly voracious eaters when the opportunity presents itself, finding carcasses and other food items through olfaction and sensory tentacles lining their mouths. Lacking jaws, they process meat by raking it off using keratinous plates in their tongues and can even tie themselves in knots to tear resistant pieces that do not come off so easily. This is made possible by their cartilaginous skeleton that, curiously, lacks vertebrae altogether, making them extremely malleable and flexible. They become extra-slippery if disturbed, possessing an impressive number of mucus glands that release a great amount of slime, effectively choking any other creature trying to feed on them.

Besides losing vertebrae, hagfish have also lost the complex eyes characteristic of vertebrates, present even in the long-gone conodonts or their close, also jawless, relatives, the lampreys. Instead, they count with simple eyes that only distinguish between light and darkness, resembling the eyes of young lampreys and thus likely being an example of neoteny (when traits of immature individuals are retained even after sexual maturity). Apart from all of these traits, they even display a circulatory system that counts with multiple hearts and is not completely closed, having very large sinuses in which blood pools, leading them to sport the lowest blood pressure of any vertebrate. Another trait that makes them distinct from other vertebrates, but that significantly helps them lower energy expenditure and thus survive for long times without eating, is the solute concentration of their tissues, which is equal to that of surrounding water. While the Neoselachii are alike in this regard, the way they achieve it is through a different mechanism, concentrating high amounts of urea in their tissues instead of simply equalizing ion distribution.

Apart from the unusual hagfish, cetacean carcasses are also explored by other animals. One of the most peculiar of these must be the tubeworm Osedax (read more about tubeworms here). It lives exclusively on vertebrate bones and is incredibly sexually dimorphic: males are microscopic and grow inside the mucous tubes secreted by the females, from which their feather-like, bright red gills emerge.  In the bone itself, the females have their ovarian tissues (from which oocytes are released into the mucous tube where they are fertilized by the males) and a root-like network that houses endosymbiotic bacteria responsible for breaking down bone collagen and lipids, because they, like other tubeworms, have no digestive system. However, unlike other tubeworms, their bacterial endosymbionts are not sulfide-metabolizing (though still members of class Gammaproteobacteria), with it being believed the ancestors of Osedax were more usual in regards to their symbionts, first taking advantage of the abundant production of sulfide in these contexts of decomposition and then making the transition, probably during the Mesozoic, to subsist on the bony skeletons themselves, which they tinge of red with their hemoglobin containing tissues, necessary to transport oxygen not only to the worm but to the aerobic heterotrophic prokaryotes guaranteeing its nourishment as well.

However, Osedax does not have much chance to settle on the ungulate skeletons of this region. The number of diatoms is simply so high that they quickly cover anything resting on the sea floor.  Apart from this, the volcanic material that reaches this sea not only contributes to the diatom bloom, but also to the aggregation of phytoplankton particles, boosting their precipitation. Additionally, cadavers that end up in shallower waters also have another layer of diatom covering, this time from bottom-dwelling diatoms, which grow over the body and further contribute to its preservation. As a result, many fossils will be yielded from here in the future, including parts even more fragile than bone, such as baleen. Not only this, but these waters, being coastal, receive sediments from rivers on land, providing a great flux of sediment that is yet another factor aiding in the concealment of the deceased mammals. The conditions therefore are just right, with rapid burial and inhibition of destructive elements, like the bone-eating tubeworms, that would, in other conditions, destroy the skeletons, for them to be never seen again.

Back to the shallows, these waters are also subject to their own daily periods of darkness as the Sun sets. Accompanying such change in illumination, a whole entourage of animals from the deep rise up to feed. Certainly, one of the most abundant are the lanternfish, a family of small (from 3 to 35 centimeters long) actinopterygians that feed on crustaceans, with big eyes and compressed bodies. In the depths, they are fairly safe from the abundant surface predators such as penguins and pinnipeds that would take them as food, but the lack of plankton means they must move to the surface in order to eat. Like many other deep-sea creatures, they exhibit bioluminescence, possessing luminous spots on their heads and tails as well as photophores distributed around their bodies. The latter not only produce light, but count with more structures that can modulate what is emitted. For instance, photophores on their bellies emit a blue glow that makes them blend in with the blue background above them, a very effective camouflage. Blue is the color of choice since it also is the color of the ocean, because only bluish light effectively penetrates the water column, which filters out other wavelengths. Red light, for instance, has no way to penetrate into deeper waters and, as a result, many dwellers of the depths are red, making them invisible.

A predator of lanternfish uses this to its advantage: the Humboldt squid (Dosidicus gigas), being a crimson color in the darkness, but alternating to a pale whitish palette when on the surface. Though having evolved fairly recently, this feisty cephalopod has already reached very high numbers. It also undergoes the daily migration to the surface, traveling in packs that may number hundreds of individuals. Reasonably large, at 2 meters in length, they differ from the bigger giant squid by their two longer tentacles being not as dramatically elongated and by suckers containing hooks, which they put to great use due to their aggressive nature. Though cannibalistic, they may hunt in packs as well, communicating by changing their colors, with color change possibly occurring in just one part of the body or in just one side, so that there are squids half red and half white. Despite all of their fierceness, they still are prey, being consumed, for example, by the speedy short fin makos, which zoom into their large aggregations and chomp at them using their many pointed teeth. Even so, the makos do not come out unharmed, many sporting scars from their encounters with the hooked-tentacles mollusks. In cases where O. megalodon hunt them, the shark is so big there is not even much space for the invertebrates’ defense and they truly just get eaten right in. However, they have strategies for these encounters: if sensing danger, not only does D. gigas turn red, the color in which it is invisible in the deep, but juveniles can also propel themselves out of the water, throwing themselves into the air in a bid to escape alive. Like other cephalopods, they may also spray ink, which might be just enough to afford them an escape.

The sand tiger shark (Carcharias taurus) hunts in areas like these preferentially at night, patrolling the soft substrate for its main prey items of ray-finned fish and other cartilaginous fishes. Growing to some 3 meters long, it has a bulky body shape, with a cream color interrupted by darker spots on its back and a whitish tone on its underbelly. Swimming slowly, it cruises around the rocky coast during the day, but feeds at night, with fierce-looking ragged teeth that do not seem compatible with its generally calm and placid demeanor. Like the other chondrychtians seen (with C. taurus being of the same family as both the shortfin mako and the great white: Lamnidae), it gives birth to live young and they start life already fierce, consuming their siblings while inside their mother’s womb until only one is left. Though not present in the South American Pacific coast any longer, the sand tiger shark has a widespread distribution in the modern world’s coasts.

At last, we have finally reached the end of this tale. While this environment, as mentioned at the beginning, will continue and achieve even higher levels of productivity, quite a few of the animals seen will not. The continuing drop in temperatures will lead to sea level fall, compromising many coastal habitats, and will make it difficult for O. megalodon to breed for example. At the same time, the abundant mysticetes will suffer with increasingly localized resources and undergo an extinction of their own: a great deal of small species will disappear, even though many larger ones, so characteristic of the oceans of today, will finally attain their fantastic sizes. This baleen whale die-off will further compromise the situation of O. megalodon, which, by occupying the position of apex predator, is inherently at a more fragile position. Marine crocodilians such as Piscogavialis and Sacacosuchus will be unable to survive in the increasingly chillier seas and also die out. Thalassocnus, with its small amount of blubber and lower body temperatures typical of xenarthrans, will not fare much well either.  The highly predatory sperm whales, with the loss of both mysticetes and the sloths, will also die out. The sperm whales of today only managed to carry on due to a specialized feeding niche that was not affected: hunting primarily for cephalopods using suction feeding, with the giant sperm whale in particular being the main predator of the giant squid.

The closure of the Isthmus of Panama, which is to happen in about 2 million years due to the ever falling sea levels, will finally connect the two American continents and lead way to the Great American Biotic Interchange, in which creatures from both continents will spread to one another (from north to south, there will be carnivorans, ungulates such as horses, tapirs, and camelids, proboscideans, among many others, while from south to north there will be terror birds, xenarthrans and even marsupials, though the carnivorous sparassodonts died before the interchange, falling victim to environmental perturbations resulting from the continuing uplift of the Andes, which resulted in ever drier environment along most of South America). However, it will also block ocean currents crossing from the Atlantic to the Pacific, further contributing to the cooldown of the coastal waters of Pacific South America, lending another blow to the animals already struggling to adapt to the global cooler climate. Despite the great loss of predatory species, odontocetes, delphinoids more specifically, will rebound with the evolution of the most formidable aquatic predator to have ever called Earth home: the orcas (Orcinus), which combine not only brute strength, but also very high intelligence. On land, another very formidable predator will also develop and, in the next tale, we will see how much it shall affect the world, even to its most remote corners.

***

1-Octopus

2-Athyonidium chilensis

3-Chlamys

4-Odobenocetops

5-Anadara

6-Heterozostera

7-Loxechinus albus

8-Luidia magellanica

9-Thalassocnus

10-Myliobatis

11-Lessonia

12-Architeuthis dux

13-Acrophyseter

14-Piscogavialis

15-Isurus oxyrinchus

16-Piscobalaena

17-Sardinops sagax

18-Acrophoca

19-Spheniscus humboldti

20-Spheniscus megaramphus

21-Pelagornis