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.
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See you in the next video.