The Curious Case of a Coastal Croc
Benggwigwishingasuchus eremicarminis takes a stroll along a Triassic coastline. Credit: Jorge Gonzalez.
“Our first reaction was: What the hell is this?”
The question is traditional in paleontology. Whether in the sun-beaten desert or under the bright lights of the preparation lab, the true nature of fossil creatures often takes a great deal of work to clarify. Sometimes the puzzling remains turn out to be something mundane or expected. But when University of Bonn paleontologist Nicole Klein asked the aforementioned question, it was of bones that seemed wrong for where they had been found. Klein and colleagues were looking at the remains of a terrestrial creature that had somehow become buried out at sea among ammonite shells and ichthyosaur bones.
It was like finding a deer skeleton scattered over a coral reef.
The curious fossils came from the Favret Formation near Nevada’s Augusta Mountains. Season after season, paleontologists return to the area in search of marine reptiles - like the giant, predatory ichthyosaur Cymbospondylus youngorum - and other organisms that lived in what was then the Panthalassan Ocean along Pangaea’s western coast, around 245 million years ago. A partially-articulated skeleton found in these rocks, dubbed LACM-DI 158616, didn’t look like any ichthyosaur or other marine reptile. The creature’s anatomy seemed best suited to moving on shore, not paddling through the sea.
What Klein and colleagues found wasn’t just out of place. The bones also represented a species of Triassic reptile no one had seen before. Described earlier this month, and named with input from Yvonne Mori of the Fallon Paiute Shoshone, the bones have been dubbed Benggwigwishingasuchus eremicarminis - a crocodile relative that once padded along the sandy beaches of a Triassic seashore.
Among the wildly branching tree of Triassic reptiles, Benggwigwishingasuchus is a popsauroid. The group is part of the broader family that includes today’s crocodiles and their close prehistoric relatives, and the poposauroids were a croc subgroup that flourished in the Triassic. In fact, poposauroids have made a splash among paleontologists for their rough resemblance to early dinosaurs - just like the “terrible lizards,” poposauroids evolved upright limb postures and were sometimes bipedal. Benggwigwishingasuchus didn’t belly crawl and slide along the seashore, but strode across the sand on powerful hind legs.
Benggwigwishingasuchus is the first croc of its kind found on Pangaea’s west coast during the middle of the Triassic. The yellow dots represent similar, previous finds made along the supercontinent’s eastern coastline. Credit: NHMLA
Paleontologists have found similar Triassic crocs from other parts of the world. Coastal reptiles like Benggwigwishingasuchus have been uncovered from rocks of similar age that represent coasts on the other side of Pangaea, alongside the Tethys Ocean. Part of what makes Benggwigwishingasuchus special is that it is the first such reptile found from the opposite side of the supercontinent, indicating that poposauroids and their relatives had flourished from the interior of Pangaea to its coasts during a time when crocs ruled and dinos drooled.
So far as Klein and colleagues have been able to determine, Benggwigwishingasuchus came to rest on the seabed tens of miles away from the closest shore. It was far enough out that waves passing overhead would not have disturbed the reptile’s body as it was buried in sediment. How the reptile wound up in such a place, there may be no way to tell. Perhaps it was a storm, a swim that went awry, a riptide current, or the croc died somewhere inland only to have their body washed downstream and out to sea. No matter what happened, the reptile’s preservation was a one in a million chance, something strange that took even its discoverers by surprise.
And yet, the sunken bones have outlined a great flourishing of crocs millions of years before dinosaurs stepped into the ecological foreground. Without the unusual path to fossilization, we wouldn’t have known crocs spread to the continent’s western coasts as well as the eastern shores and interior. More than that, the fossil is a reminder that the fossil record is brimming with surprises that we can never anticipate.
It’s a joy to find what we’re looking for, but it’s even luckier to stumble across something that makes us shout “What the hell is that?”
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