"Dive" into deep water at night to explore the splendor of ancient marine life

Produced by: Science Popularization China

Produced by: Komeichiren

Producer: Computer Network Information Center, Chinese Academy of Sciences

Editor's note: The author of this issue is a paleontologist who is fascinated by marine paleontology and often imagines seeing these wonderful creatures. Today, let's follow the author to open up our imagination: travel back to the ancient ocean...

The world's largest biological migration occurs after nightfall.

It is late at night, and in order to obtain more abundant oxygen and food, about 100 million tons of organisms will rise from below the ocean's photic zone to the upper layer near the surface; when the sun rises, they return to the depths of the ocean, day after day, promoting the material cycle between the shallow sea and the deep sea.

This magnificent spectacle has been occurring every night in the ocean since the Ordovician plankton explosion.

Blackwater Photography: The Beauty of Plankton

At night, lights are hung about 12 meters underwater by boats or buoys. The photographer then dives down to find the deepest possible sea water and uses a camera to capture images of the small creatures in the water - this is black water photography.

The Mesozoic planktonic crab Callichimaera perplexa is similar to the megalopa of modern crabs, which may be a phenomenon of juvenile persistence. Photo taken in the Early Cretaceous (Image source: drawn by the author)

Tiny zooplankton rise from the depths toward the light, and a host of amazing creatures follow. In every era, gelatinous pelagic invertebrates such as jellyfish and comb jellies are the majority of the animal population in the sea. But in different eras, there are some species with the mark of the era.

In the Ordovician, the larvae of planktonic trilobites, conodonts, and armored fish were the most unique and interesting sea elves;

In the Devonian, it was the ammonites and jawed fish larvae that were newly born in the Devonian nematode revolution and had planktonic larvae;

In the Mesozoic Era, drifting crinoids and arthropod larvae were also a beautiful landscape.

Now, the time and space have come to the year 2200.

At this time, time travel technology emerged, and it became possible to travel through various geological eras to photograph ancient creatures. Next, we will invite photographer Cheng Wen to tell us about her interesting experience in "Black Water Paleontology Photography".

Belemnella Lanceolata, a member of the last swimming animal group of the Mesozoic Era, photographed by the photographer in the Maastrichtian Stage (Image credit: drawn by the author)

Alien Stranger: Planktonic Life in the Paleozoic Era

Most popular science books about paleontology introduce the adult parts of organisms to readers - highlighting their huge bodies that are several meters long and showing off their armor that is as strong and hard as rock.

However, were those giant ancient creatures always so huge when they were young? Obviously, no.

Like modern organisms, ancient marine organisms also go through three major stages of development—juvenile, reproductive, and terminal. In fact, many ancient organisms have different appearances and even different behaviors than adults, telling unique stories about ancient times.

Some of these larvae will spend their entire lives in the seawater, while others will further develop and settle in the sand or grow into species that swim in the pelagic layers. These larvae are the real gems of paleontological blackwater diving.

The blackwater fossil that impressed me the most was a juvenile large-eyed horseshoe crab (Pterygotus macrophthalmus) from the late Silurian period.

When I found it, it was only a few centimeters long and was preying on a conodont larva that was much smaller than itself - its body of a few centimeters conveyed the unchanging truth that the law of the jungle is the law of the jungle.

A juvenile Pterygotus macrophthalmus feeding on conodonts, taken in the Late Silurian (Image source: drawn by the author)

Compared to the adult pterodactyls that are more than 2 meters long, the larvae are more beautiful. The translucent body reflects the sky blue light, and the orange-yellow internal organs are clearly visible through the thin carapace.

Most of the characteristics of pterygoid horseshoe crab larvae - eyes and appendages that are larger than their bodies - are also evident in euryptopsid horseshoe crab larvae, as are some other features.

The larval Eurypede horseshoe crab has a simple eye that is larger than that of the adult. In the early stages of life before the appearance of compound eyes, the simple eye helps the horseshoe crab to look at the world curiously; and the compound eyes that they grow later are also proportionally larger than those of adults and closer to the sides.

In addition, they have a relatively large cephalothorax. The center of the carapace is protruding, and the spines on the back of the carapace may be developed, making the whole body close to a trilobate shape, which is similar to the "trilobate larvae" of horseshoe crabs. This also suggests the relationship between chelicerae and trilobites.

But unlike their modern relatives, horseshoe crabs, larval Eurypedal horseshoe crabs have only nine abdominal segments, with one segment added each time they molt. During growth, larval Eurypedal horseshoe crabs first develop six abdominal segments, then complete the anterior abdominal segments, while horseshoe crabs are born with complete segments.

They were also similar to shrimps and crabs in modern oceans: small claws (chelicerae), and more petals and larger tail fans to balance their agile swimming posture.

Its prey, conodonts, were important components of marine plankton in the Ordovician, Silurian, and Triassic periods when they became extinct. They are the most abundant and widely distributed marine animal fossils known to date, and are also one of the most highly resolved biological phyla in the global marine biostratigraphy from the Late Cambrian to the end of the Triassic (520 million to 205 million years ago).

The conodont Ozarkodina with its mouth closed, taken in the Ordovician-Early Triassic (Image source: drawn by the author)

The Ordovician-Early Triassic conodont I photographed, Ozarkodina, is what are known as living "conodont-bearers" (the most accurate name for these animals whose taxonomy is not yet fully determined), and they are elongated, worm-like creatures with conodonts on their heads.

They have V-shaped myometrium arranged alternately on both sides of their bodies, similar to lancelets. The myometrium of other vertebrates, including lampreys, hagfish, and even the earliest fossil fish, is "W" shaped. Among living animals, only lancelets have this shape of myometrium, but the muscle fibers of conodonts are similar to those of extinct jawless fish.

It looks like a fish but not like a fish: it has a tail fin at the end; there is a rod-shaped notochord on its back, and a pair of large spherical eyes covered by cartilage on both sides of its head. These evidences prove that it has an inseparable relationship with jawless fish.

When the photo was taken, the conodont was staring with its big eyes reflecting orange-red light, waving its tail fin as it swam forward; suddenly, it opened its mouth wide, revealing a mouthful of amber-colored fangs...

In life, the phosphate teeth of conodont carriers are usually light amber, translucent and slightly whitish. In addition, conodonts may belong to "gastrostomes", as opposed to "gnathostomes" of jawed animals. Like modern lampreys and hagfish, they should also be able to close their mouths. In this photography, I was also fortunate to capture the strange images of them opening and closing their mouths, seamlessly switching between cuteness and horror.

Ozarkodina opens its mouth, revealing the light amber conodonts in its mouth - "teeth" made of phosphate. Photographed in the Ordovician-Early Triassic (Image source: drawn by the author)

Another elf is an outlier among the trilobites, a member of the Telephinidae family of the order Proetida.

They are rare planktonic trilobites with huge eyes that occupy most of the space on both sides of the head (free cheeks), allowing them to see front and back, left and right, and even up and down. They also have a streamlined body and a small tail, making them active, visually dominant plankton. Because the weight of the body is mainly in the head, these little guys may swim upside down with their abdomens facing up.

When I found it, it was flying upside down in the water. The long cheek spines on both sides of its body extended to the back of both sides, and its transparent and white tentacles swayed backwards with the water flow; its huge eyes flashed, and its long tail extended behind it. The internal organs in the middle of its body reflected orange-yellow light through the thin shell made of calcium carbonate...

As marine planktonic arthropods, the family of Teleosteiidae shines brightly in the dark ocean like krill. And they are the krill of the Ordovician period.

Beautiful floating trilobites of the Telephinidae family, photographed in the Ordovician period (Image source: drawn by the author)

The Golden Age of the Past: Blackwater Creatures of the Mesozoic Era

Although blackwater photography is done in very deep water, it only means that the water is very deep, and it does not mean that the photographer needs to go deep to find the subject. Because many times, the shooting is done close to the water surface, and the subject will also project ripples on the water, adding another sense of beauty.

The most typical organisms near the water surface are the planktonic crinoids that flourished in the Mesozoic Era. They are the most active chapter in the history of crinoids. All modern crinoids are benthic filter feeders, but some fossil crinoids, such as Seirocrinus, Traumatocrinus and Melocrinus, are pelagic "pseudoplankton".

Why are they called "false plankton"?

Because they cling to driftwood, have long, rope-like stems and enlarged, permanently open tentacles, they lead a passive filter-feeding lifestyle and are very "Buddhist" about eating and drinking.

However, other sea lilies living on driftwood have short and strong arms and tendrils, indicating that they are active filter feeders; some sea lilies have buoyancy sacs and use the velocity gradient of the boundary layer to float independently in the water.

The larvae of Pentacrinites briareus, an "active" filter feeder that lives on driftwood in the ocean (Image source: drawn by the author)

This red crinoid (Pentacrinites briareus) larva clings to a piece of driftwood.

It was about 30 cm in diameter and had a 20 cm long stem; the stem and calyx were densely covered with cylindrical curls that covered the entire stem and could cause water to flush out food, indicating that they had evolved into an active filter feeder (like bivalves and barnacles) rather than a passive filter feeder like modern crinoids.

Uintacrinus was even more different from modern crinoids—it had a very large, spherical calyx that acted as a buoyancy bladder. Uintacrinus could turn itself into a balloon and float above the sea floor while its long arms searched for food on the surface of the muddy bottom.

Their surfaces are made up of many small pentagonal or hexagonal plates, the same as the famous "footballene" - this is a good way to enhance structural strength.

The Uintacrinus crinoids, which float like ghosts near the seabed, transform their calyx into buoyancy sacs to make them semi-floating in the water, photographed in the Cretaceous period (Image source: drawn by the author)

The amazing journey of fish larvae and cephalopods in the Cretaceous oceans

During my trip to the end of the Cretaceous, I was lucky enough to capture a juvenile Bananoggmius, a member of the order Tselfatiformes, whose Latin name means "banana dorsal fin," referring to its unusually high dorsal fin.

They are large fish, with an adult body length of about 1.2 to 1.8 meters, and a height of about one-third to one-half of their body length, with a flat jaw and disc-shaped jaws, and probably fed on mollusks. They lived in the Western Interior Seaway in the Late Cretaceous and lived until the beginning of the Cenozoic.

The juvenile Bannermanus fish is not as majestic as the adult, but its species can be identified at a glance. Like modern lionfish, the fins of the juvenile Bannermanus fish are not brightly colored, but the relative proportion is much larger than that of the adult. It was attracted by the light, with its towering dorsal and anal fins standing upright, showing me its beauty.

A juvenile Bananoggmius with large dorsal and anal fins, from the Late Cretaceous (Image credit: Author's illustration)

Ammonites were very common in the Cretaceous, but the scene of ammonite spawning was very rare - so far, not many fossils of ammonite eggs have been found. Throughout the Mesozoic, the flourishing ammonites had a variety of reproductive strategies, there may be squid-like species that lay eggs in seaweed and on the seabed, and there may also be planktonic eggs like modern oceanic squids. However, most of the ammonite egg fossils found so far are clumped squid-like, and this late Cretaceous Kossmaticeras densicostatus should be no exception.

Contrary to popular belief, the large brown algae that form the underwater forests today are actually quite young in geological terms - they did not appear until the Late Cretaceous and flourished in large numbers during the Cenozoic.

On this Cretaceous brown algae (Julescraneia) that looks a bit like Sargassum, I saw the figure of an ammonite mother, who was guarding her eggs. However, these eggs might be difficult to hatch - after all, it was the end of the Cretaceous period, and the asteroid that had just hit the earth would soon cause ocean acidification, killing these small ammonites that needed calcium to develop.

Female Kossmaticeras densicostatus lays eggs on the Late Cretaceous brown algae Julescraneia. Photographed in the Late Cretaceous (Image source: drawn by the author)

Of course, in today's oceans, the hatched ammonite larvae can survive for some time. This helmet ammonite larvae looks like it has just hatched, with a thin shell that is translucent under the light, revealing the intricate sutures inside.

And in the soft part of its shell, the flickering pigment cells are dotted with the light of fireflies, mysterious and elegant, but this splendor will not last long - all ammonites will disappear in the mass extinction caused by the asteroid impact.

The juvenile ammonite has a very thin shell (less than 0.1 mm) that may appear translucent under the light, revealing fine sutures, taken in the Late Cretaceous (Image source: drawn by the author)

Well, that's all for now, and my blackwater paleontological photography journey is coming to an end. But I still have something to say - the modern ocean is just a tiny cross-section of it in geological time, and in the past, the vast and hidden ocean was a huge and important part of our planet.

So many beautiful creatures once lived here. Even if I had a camera that could travel through time and space, I could only capture a small boat in the vast ocean.

The modern ocean world is colorful and gorgeous. How could the ancient marine life, when it was swimming vigorously, look like the gray and rough fossils discovered today?

They are also living creatures with flesh and blood. If we could see them in the ocean at that time, these ancient creatures would be as beautiful, lively, smart and exquisite as modern marine creatures.

Therefore, I chose this profession - to travel through time and space to photograph these ancient creatures, to capture the beauty of their lives, and to depict their most lifelike appearance with the most elegant forms and the most transparent translucent colors.

When I took these photos, I showed people a world they had never touched before, and made them realize that ancient life was also so gorgeous.

References:

[1]Tappan H, Loeblich Jr A R. Evolution of the oceanic plankton[J]. Earth-Science Reviews, 1973, 9(3): 207-240.

[2]Luque J, Feldmann RM, Vernygora O, et al. Exceptional preservation of mid-Cretaceous marine arthropods and the evolution of novel forms via heterochrony[J]. Science advances, 2019, 5(4): eaav3875.

[3]Kulicki C. Remarks on the embryogeny and postembryonal development of ammonites[J]. Acta Palaeontologica Polonica, 1974, 19(2).

[4]Landman NH, Rye DM, Shelton K L. Early ontogeny of Eutrephoceras compared to Recent Nautilus and Mesozoic ammonites: evidence from shell morphology and light stable isotopes[J]. Paleobiology, 1983, 9(3): 269-279.

[5]Gorzelak P, Głuchowski E, Brachaniec T, et al. Skeletal microstructure of uintacrinoid crinoids and inferences about their mode of life[J]. Palaeogeography, Palaeoclimatology, Palaeoecology, 2017, 468: 200-207.

[6]REHÁKOVÁ D. Plankton evolution and biostratigraphy during Late Jurassic and Early Cretaceous[J]. CARPATHICA 70, 2019: 137.

Ahlberg P. Telephinid trilobites from the Ordovician of the East Baltic[J]. 1995.

[7] TAVERNE L. Revision of genre Bananogmius (Teleostei, Tselfatiiformes), creation of Crétacé supérieur d'Amérique du Nord et d'Europe[J]. Geodiversitas, 2001, 23(1): 17-40.