Back in the 1980s, a fossil of a partial reptile skull was discovered in British Columbia, Canada, dating to the Early Triassic about 250 million years ago. Its triangular skull shape, large eye sockets, and what seemed to be distinctive spiky frills on the back of its head initially caused it to be identified as a relative of the gliding weigeltisaurids.
But the aptly-named Wapitisaurus problematicus would have had to be a very unusual member of this group. With an estimated length of up to 2m (6'6") it was much larger than any other known weigeltisaurid, it was the only one known from the Triassic side of the "Great Dying" mass extinction event, it was found in a completely different part of the world, and its teeth seemed more like those of marine reptiles like thalattosaurs.
In recent years new discoveries and re-analysis of weigeltisaurid fossil material have resulted in much better modern understanding of their skull structure – and with that came the realization that Wapitisaurus really didn't seem to match with them after all.
So a new study has finally identified what this problematic reptile really was… and it turns out the teeth didn't lie! It was a marine thalattosaur all along!
Wapitisaurus had rather large eyes compared to most other North American thalattosaurs, and although the front parts of its jaws are missing it probably had a long slightly hooked snout similar to its close relative Thalattosaurus. It's also now one of the oldest known members of the thalattosaur lineage, showing that some of their specialized skull features like retracted nostrils had actually appeared very quickly during their evolutionary history.
…Oh, and those "spiky frills" on the back of Wapitisaurus' skull? They were actually all teeth from both the upper jaw and the palate, on broken shards of bone that had been displaced to just the right spot to muddle up its identity for over three decades.
Referred Species: T. alexandrae, T. borealis, T.? shastaensis
Status: Extinct
Time and Place: 237 to 221 million years ago, from the Carnian to the Norian of the Late Triassic
Thalattosaurus is known from California and British Columbia.
Physical Description: Thalattosaurus was a member of the thalattosaurs, a clade of marine reptiles endemic to the Triassic. It had a long and slender body, about 2 meters (7 feet) long with a powerful, paddle-like tail. Like Askeptosaurus, which we have talked about before, Thalattosaurus’s limbs were likely webbed, but not heavily modified into paddles - they still had distinct fingers and claws.
Thalattosaurus’s skull is where things get weird. The front of the upper snout is distinctly downturned and narrower than the corresponding part of the lower jaw. The premaxilla lacked teeth, but had blunt “pseudodont” projections that resembled teeth. Actual teeth were present on the lower jaw and in the back of the jaws, which were robust. The lower jaw had pointy teeth anteriorly and both jaws had broad, bumpy teeth posteriorly. The eye sockets were large and the nares were directed somewhat dorsally.
Diet: The broad, chunky teeth in the back of the jaws suggest Thalattosaurus ate shellfish of various sorts, although I doubt it was particularly picky and wouldn’t turn down a fish or two.
Behavior: Although Thalattosaurus was a good swimmer, it likely spent a good amount of its time on the shore resting and sunning, going out to sea to feed. Its claws would have been useful for clinging onto rocks in heavy surf. It may have caught cephalopods such as ammonites in the open water, using the anterior teeth and pseudodonts to pry out the fleshy bits from the shell (or, failing that, just crush the shell with the back teeth). If I may speculate, it may have also rooted through the sandy seafloor for buried shellfish.
Ecosystem: Thalattosaurus alexandrae and T.? shastaensis are known from the Hosselkus Limestone of California. This was a coastal marine environment, and was also home to the thalattosaur Nectosaurus, the giant ichthyosaur Shastasaurus, and the sharks Hybodus and Acrodus. T. borealis is known from the slightly earlier Sulphur Mountain Formation of British Columbia, which was also home to conodonts, the thalattosaur Paralonectes, and the relatively small ichthyosaur Pharalodon.
Other: The T. alexandrae fossils were collected in the early 1900’s by a team from the University of California. The expedition was very fruitful, recovering many marine reptile remains representing at least three genera, although the area was filled with mountain lions. The recovered material is probably stored in the same building where I wrote this post (although I know at least some of the UCMP’s marine reptile material is stored in a clock tower on campus).
~ By Henry Thomas
Sources under the cut
Hilton, R.P. 2003. Dinosaurs and Other Mesozoic Reptiles of California. University of California Press.
Nicholls, E.L., Brinkman, D. 1993. New thalattosaurs (Reptilia: Diapsida) from the Triassic Sulphur Mountain Formation of Wapiti Lake, British Columbia. Journal of Paleontology 67(2): 263-278.
Nicholls, E.L. 1999. A reexamination of Thalattosaurus and Nectosaurus and the relationships of the Thalattosauria (Reptilia: Diapsida). PaleoBios 19(1): 1-29.
Time and Place: Between 247 and 235 million years ago, from the Anisian to the Ladinian of the Middle Triassic
Askeptosaurus is known from the Besano Formation of Switzerland, as well as the Gejiu Formation of China
Physical Description: Askeptosaurus was a Thalattosaur, a group of strange ancient offshoots, not even proper reptiles - stem-reptiles, not more closely related to any living reptile group than any other - and a fascinating experiment in marine life for land vertebrates completely unique to the Triassic. Like other Thalattosaurs, Askeptosaurus had a long and slender body for streamlined movement through the water. Its tail was built into a paddle, to help with propulsion forward. While their feet were shaped into decent sized paddles, they weren’t adapted into flippers like more thoroughly marine species of reptile. Askeptosaurus also had a long tail and long neck, and an extremely long snout. In fact, this long snout is characteristic of the group of Thalattosaurs Askeptosaurus was a part of. This long, narrow, and pointed skull pushed the nostrils back so they were actually close to the eyes, which themselves were extremely large with a large bony ring around the eye socket. It had very small teeth, though of note - one of its close relatives was toothless, and other Thalattosaurs had distinctively downturned snouts instead. Askeptosaurus had dozens and dozens of teeth all across its mouth, and it also had a lowly-spined back, different from its relatives. It had very slender limbs as well, compared to its relatives. It was probably somewhere between two and three meters long from tail to snout, though that is an extremely rough estimate on my end and no official measurement of its body length has been made.
Diet: Given its many pointed teeth, Askeptosaurus was decidedly a fish eater.
Behavior: Askeptosaurus would have used its paddle-esque feet and hands to steer itself through the water, using the angle and extension of its limbs to turn this way and that. The undulating, long body would have swimped from side to side in order to propel it forward and increase or decrease speed. That extremely long snout was extremely useful for reaching out and grabbing food hiding in rock crevices and other hiding places, as well as for grabbing wriggly and slippery fish and preventing their escape. Askeptosaurus also shows extensive adaptations for deep diving - large eyes suited for low light conditions, as well as a protective ring and strong bones to help in preventing bodily collapse at deep depths. That said, it is at least somewhat a mystery still - did it give birth to live young? Did it live in groups? Given its fairly pad-like limbs, did it spend any time on land? More research on this beautiful group of Triassic creatures is needed to understand their place in the ocean ecosystems.
Ecosystem: Askeptosaurus tended to live near the coasts, still in deep and marine and open habitats but close enough that if it did crawl onto the shore, it would have been able to without going too far out of its way. It seems, based on its distribution, that Askeptosaurus lived throughout the burgeoning Tethys sea, though of course more fossils of this animal in other locations would be helpful to confirm that. It didn’t live near reefs, and preferred open ocean habitats. There was a wide variety of ammonites, brachiopods, snails, and fish - the last of which were, of course, the main prey of Askeptosaurus. As far as reptilian neighbors, there were other Thalattosaurs like Hescheleria and Clarazia; Tanystropheids like Tribelesodon, Tanystropheus, and Macrocnemus; Helveticosaurids like Helveticosaurus and Eusaurosphargis; Placodonts like Paraplacodus and Cyamodus; Ichthyosaurs such as Cymbospondylus and Mixosaurus; Pachypleurosaurus like Keichosaurus, Serpianosaurus and Pachypleurosaurus; Suchians such as Ticinosuchus; and Nothosaurs like Nothosaurus and Lariosaurus. So, an extremely diverse ecosystem - where different marine reptiles had to carve out their own roles for survival - was the cacophony that Askeptosaurus called home.
Other: Thalattosaurs seem to be completely separate from all other reptiles, not even in the crown group - in the Neodiapsids, a group that diverged in the Permian and eventually lead to proper reptiles and their relatives, but Askeptosaurus and other Thalattosaurs broke off from in that time. That means that there should be fossil Thalattosaurs in the Permian, or at least their precursors. Sadly, we do not have them. More research is needed to understand their origins, though their diversity and evolution in the Triassic is fairly clear. Sadly, the end-Triassic extinction killed this beautiful group, and their role in the ecosystem would be replaced by other ,more familiar marine reptiles.
~ By Meig Dickson
Sources Under the Cut
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Carroll, R. L. 1988. Vertebrate Paleontology and Evolution 1-698.
Cheng, Y., X. Wu, C. Li, S. Tamaki. 2007. A new thalattosaurian (Reptilia: Diapsida) from the Upper Triassic of Guizhou, China. Vertebrata PalAsiatica 45 (3): 246 - 260.
Cheng, L. 2011. New Study of Anshunsaurus huangnihensis Cheng, 2007 (Reptilia: Thalattosauria): Revealing its Transitional Position in Askeptosauridae. Journal of the Geological Society of China 85 (6): 1231 - 1237.
Chun, L., D.-Y. Jiang, L. Cheng, X.-C. Wu, O. Rieppel. 2014. A new species of Largocephalosaurus (Diapsida: Saurosphargidae), with implications for the morphological diversity and phylogeny of the group. Geological Magazine 151 (1): 100 - 120.
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PHOTO ABOVE: A depiction of what the Hosselkus Limestone environment looked like during the Triassic. There is a thalattosaur and an ichthyosaur in the picture. Illustration by artist Ken Kirkland from the book Dinosaurs and Other Mesozoic Reptiles of California.
A RETURN TO HOSSELKUS -- University of Alaska Fairbanks graduate student Eric Metz studies ancient marine reptiles. As he was looking around for a project to complete his Master’s Degree, he discovered a unique story that captured both his scientific interest and his imagination, a fossil site that hasn’t been explored in more than a hundred years. Now he is raising money on a scientific crowdfunding site called Experiment to fund an expedition this summer. We asked him about his project, Rediscovering the Lost Triassic Marine Reptile Fossils of Northern California.
How did you find out about this story? I'm studying thalattosaurs for my graduate degree and I went to the University of California Museum of Paleontology last May to look at the material from the Hosselkus Limestone, an outcrop formed during the Triassic between 237 million years and 201 million years ago. I learned the story of how the material was collected and I saw how well preserved it is. When I asked the curators of the museum if anyone had gone back, they said no.
That made me determined to find the location again. The fossils have been eroding out of the mountain for the last hundred years. No one has gone back because at the time they were discovered in 1898, the Shasta Mountain area was difficult to access. There were still grizzly bears in California. Since then other more easily accessible sites from the Triassic have been found. However, the quality of the fossils, their high abundance, and new access means now is a great time to go.
Why are ichthyosaurs and thalattosaurs interesting animals? Why study them? Ichthyosaurs are secondarily aquatic reptiles [which means they were land-based and adapted to live partly in the water]. They superficially look like dolphins and probably filled the same habitat that dolphins now occupy. They gave birth to live young, which is weird for a reptile, and grew to near blue whale sizes. Thalattosaurs are interesting because they are secondarily aquatic reptiles as well but are more semi-aquatic. You can think of them as reptile seals. Thalattosaurs are interesting because they have this down-turned snout (see photo above) that we still don't understand. Studying them allows us to have a better idea of the diversity of the planet and how groups of organisms go extinct and how they diversify.
PHOTO ABOVE: Hosselkus Limestone material fossils from the University of California Museum of Paleontology collection.
What are your plans? The research plans are to find more specimens of the ichthyosaurs and thalattosaurs from the Hosselkus limestone and to prepare the specimens and describe them. The plan is to find more complete specimens than there are currently. I would be able to do some of the acid preparation at the lab here at the University of Alaska Museum of the North.
My immediately career plans are to do a PhD in paleontology and to become a curator of a vertebrate paleontology collection. In academia it is a publish or perish mentality, and also a who you know game. Being able to do collaborative work broadens my knowledge set and my contacts, and gives me the ability to publish the work.
FOR MORE INFORMATION: Visit Eric’s fundraising website to learn more. https://experiment.com/projects/rediscovering-the-lost-triassic-marine-reptile-fossils-of-northern-california
#ThalattosaurThursday! Help fund our fossil hunting expedition campaign on Experiment.com so we can find more of these guys. This awesome model is on display at the Sierra College Museum of Natural History in Rocklin, CA. (at Sierra College Natural History Museum)
FAIRBANKS, AK -- When the rock slabs containing a thalattosaur specimen were shipped to Fairbanks in 2011, Earth Sciences Curator Pat Druckenmiller hoped there would be a skull somewhere in those 500 pounds of rock. Since the tail was well-preserved in the exposed fossil found in a rocky underwater outcrop in Southeast Alaska, Druckenmiller expected to uncover the rest of the skeleton.
Now, thanks to the fossil preparation skills of J.P. Cavigelli, the prep lab manager at the Tate Geological Museum in Casper, Wyoming, that is closer to coming true. When Druckenmiller invited Cavigelli to come north (his first visit to Alaska) this week, he quickly exposed one of the hind paddle-like limbs of the thalattosaur. Today he revealed the skull.
Cavigelli is only here for a few days, but thanks to Tongass National Forest geologist Jim Baichtal and the US Forest Service, who are supporting this project, the work will continue. The earth sciences team expects to have one of the best-preserved thalattosaur fossils in the world and maybe even a new species.
The animal died in the ocean and then settled into mud at the bottom of the sea floor. The mud eventually turned to rock, entombing the skeleton for nearly 220 million years. Because this preservation of a complete fossil is a rare event, the specimen is a major find.
