Around 251 million years ago, the sun rose
on the Triassic period. Although often overlooked, the Triassic marked
the evolution of some of the most unique organisms in our planet’s history — especially under
the waves. Within the waters of the Triassic dwelt reptiles
with hammer-shaped faces, fish with buzz-saw like teeth which confounded scientists for
centuries, and some of the largest — and most often forgotten — marine predators
of all time. So, for this entry into the archive, we’ll
be winding back the clock and looking at the undersea organisms of the Triassic. The Triassic Period began with a global cataclysm. An extinction event known as the Great Dying,
caused by elevated temperatures and oceanic acidification, resulted in over ninety percent
of all life in the oceans, including the long-enduring trilobites, dying out. But in the wake of this great reset, new species
emerged, growing to fill the abundance of unoccupied niches — resulting in some truly
surreal adaptations. This is Henodus, a placodont from the late
Triassic that likely dwelled in the shallows. Henodus, like most members of its order, resembles
a sea turtle — but isn’t actually closely related. Henodus was around 1 meter, or 3.3 feet in
length — and that distinctive, unwieldy shell on their back was almost as wide as
it was long. Exactly why Henodus… or any animal… would
develop such an unusual shell isn’t fully understood. But some have theorized the Henodus’s shell
was such an awkward size, it made it difficult for aquatic predators to fit their jaws around
it. A very straightforward strategy, but a pretty
smart one! Aside from Henodus, the Placodont order during
the Jurassic Period also included Cyamodus. This genus also looks quite similar to sea
turtles, and might actually be more closely related to modern turtles than Henodus. Unlike most species of turtles today, however,
which have just a single shell for protection — Cyamodus had two separate ones. One shell protected its neck to its waist,
while the other one protected its lower-hip region. The dual shells were likely an effective defense
against predators, and gives Cyamodus a one-of-a-kind look. Moving away from the Placodont order, also
living along the Triassic coastline was the noteworthy Mastodonsaurus. A triangular headed amphibian, Mastodonsaurus
had two distinctive long front teeth which likely helped it capture prey. Strangely, however, Mastodonsaurus’s teeth
were so long that — in addition to the animal’s nostrils – there were two extra holes in
their skull which these teeth fit through when their mouths were closed. The Mastodonsaurus’s peculiar upwards facing
eyes also sets them apart from many species. The unexpected eye placement would have been
most suited for looking upwards, suggesting the animal often fed on organisms which dwelled
on land. And with the largest Mastodonsaurus’s reaching
around 6 meters, or twenty feet, there’s quite a lot that would likely be on the menu
for this species. Further out into the ocean, we have an animal
which, for centuries, baffled scientists. Meet the helicoprion, an animal with one of
the most unusual dental records in the history of life on earth. The fish possessed a strange spiral of teeth,
with most geneses possessing more than a hundred teeth in total. When fossils of this tooth-spiral were first
uncovered in the 19th century, paleontologists weren’t sure quite where on the animal it
belonged, with some hypothesizing the tooth-whorl sprouted from the animal’s upper snout…
like a really deadly nose. By the mid 20th century, it became more widely
understood that the fanged-swirl belonged on the bottom jaw of the animal. The exact purpose of the spiral was still
unknown, however, with some speculating that the spiral of teeth could lash out like a
tentacle to grab prey. Today, most scientific reconstructions place
the spiral of teeth further back in the animal’s jaws, or perhaps even in its throat. The most prominent modern theory is that the
tooth-whorl has something to do with replacing old teeth — kind of like the system sharks
have. And yes: despite appearances, the helicoprion
is not a genus of shark, but instead thought to fall within the now primarily extinct classification
of ratfish. A somewhat unfortunate name. Even more unfortunate, helicoprion was already
on its way out when the Triassic kicked off. We think a few species within the Helicoprion
genus made it all the way to early the Triassic period, but sadly, none of these buzz-saw
faced fish endured any further. And while we’re talking about species with
unusual lips, the Atopodentatus is near the top of that particular category. Older reconstructions of this extinct genus
of middle Triassic marine animal are quite the sight to behold. At first, scientists believed that, unlike
almost all other animals, Atopodentatus’s jaw was split down the middle — with teeth
running along the length of this split. As alien and alarming as this might seem,
most scientists thought Atopodentatus used its unusual mouth for filter-feeding — using
the toothed split to filter out unwanted dirt. New, more complete specimens, however, have
demonstrated Atopodentatus’s split mouth was actually a misinterpretation — and the
animal head actually looked like… this. The unusual, wide mouth was possibly an adaptation
to better scrape algae off the sea-floor for consumption, although we can’t say for certain. While the new Atopodentatus model is less
frightening than the old, it’s definitely just as unique-looking. Before we get to the true giants of the sea,
our next group might be a bit more familiar looking. These are the Sauropterygia, a classification
that first appeared at the very start of the Triassic. Orders like the Nothosaur navigated the waters
on paddle like flippers — snatching fish in their fanged jaws with lunges of their
long neck. The Nothosaur likely lived a bit like the
seals of today, as they were rela small — only reaching 3 meters, or ten feet in length. By contrast, the Sauropterygia classification
eventually yielded the much larger Plesiosauria, a group which is much more commonly known,
and the only branch of Sauropterygia to make it out of the Triassic. Most of the biggest and most famous Plesiosauria,
like the Liopleurodon, lived during the Jurassic period, and maxed out at 6.4 meter, or 21
feet in length. Quite the impressive reptile. But even Jurassic-era Plesiosauria were dwarfed
by the true titans of the Triassic waters. Meet the Ichthyosaurs — a diverse group
of reptiles with a long paleontological history. Ichthyosaur fossils were discovered as far
back as the 19th century, which led to some intriguing vintage artistic interpretations
of what these colossal reptiles might have looked like. Mary Anning found various nearly-complete
skeletons during her lifetime. If you’re not familiar with Mary Anning,
she was a pioneering English paleontologist who made vital contributions to the field
9though never got the credit she deserved). One skeleton Anning found was of a Temnodontosaurus,
an Ichthyosaur genus from the early Jurassic. In their overall body-shape and long, toothed
beaks, these unique animals resemble dolphins. While the two animals occupy a similar niche,
they aren’t related, and are just an interesting example of two different animals converging
on a similar body plan due to environmental factors. Unlike the dolphin, however, the Temnodontosaurus
got much bigger, ranging somewhere between 9 to 12 meter in size, or 30 to 40 ft — easily
the largest organism on our list so far. But the very largest of the Ichthyosaurus
were in another class altogether. Meet the Shonisaurus, a Late Triassic genus,
coming in somewhere between 15 and 20 meters, or 49 to 69 ft. What an incredible creature. Like the smaller Temnodontosaurus, the Shonisaurus
was likely also a marine predator who hunted for fish, cephalopods, and other forms of
smaller marine life. After all, there’s not much that could stand
up to an organism of this size. Indeed, the Shonisaurus rivals many of the
largest modern whales with their sheer bulk. Another way in which they’re similar to
whales is that the ancestors of Shonisaurus, and indeed all Ichthyosaurs, once lived on
land before transitioning to fully aquatic animals. Cartorhynchus is a potential distant relative
of the Ichthyosaur beginning the land-to-ocean transition process. While Cartorhynchus likely spent most of their
time in the water, it’s been theorized they could still use their flipper-like forelimbs
to move on land, sort of like juvenile sea turtles. Unlike many of the other groups on this list,
various species of Ichthyosaurs survived beyond the Triassic period. And despite being group’s evolutionary debut,
the Triassic period was the epoch in which the largest Ichthyosaurs reigned. This goes to show you that the Triassic, while
often overlooked, was an incredible era in earth’s history. And that’s the end of our deep dive into
the oceans of the Triassic period. This video was made as part of the Triassic-themed
week E.D.G.E. is currently running, so go check out his channel if you haven’t already. In the meantime, thanks for watching. If you liked this entry, please lend your
support and like, subscribe, and hit the notification icon to stay up to date on all things Curious. See you in the next video.
