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A restoration of the therizinosaur Nothronychus. Art by Nobu Tamura, altered by ArthurWeasley. Image from Wikipedia.

“Therizinosaur” isn’t a household name. This group of feathery dinosaurs hasn’t been around long enough to have the same cultural cachet as the tyrannosaurs, “raptors“, or other famous dinosaur tribes. But the therizinosaurs really do deserve more popularity. Although they were cousins of the carnivorous, sickle-clawed deinonychosaurs, the therizinosaurs were long-necked, pot-bellied omnivores and herbivores, albeit ones that had insanely long claws on their hands. They are some of the strangest dinosaurs ever found, and a track discovered in Alaska adds a few flourishes to our picture of the therizinosaurs.

Paleontologists Anthony Fiorillo and Thomas Adams describe the trace fossil in the new issue of the journal PALAIOS. Discovered in the roughly 70 million year old rock of Alaska’s Denali National Park, the track is the impression of a dinosaur’s hind foot. Exactly what genus of dinosaur left the footprint is unknown, but, based on the arrangement of toes and other details of foot anatomy preserved in stone, Fiorillo and Adams narrowed the list of candidates to an as-yet-undiscovered therizinosaur that must have once walked in southern Alaska. The four large, slender, and forward-facing toe impressions were the key – no other group of dinosaurs had feet quite like that.

The lone track is the first record of a therizinosaur from Alaska. And even though the Arctic habitat the dinosaur lived in would have been a bit warmer than Alaska today, this wasn’t a steaming jungle or warm swamp. As Fiorillo and Adams point out, Alaska’s Cretaceous dinosaurs would have experienced short summers and long, dark winters. Just think of something like Nothronychus shuffling through the snow during the extended Arctic night. The image is wholly different from the dinosaurs I first met as a kid, and the unconventional setting is perfect for a creature that has pushed the boundaries of what we think a dinosaur is.

Reference:

Fiorillo, A., Adams, T. (2012). A THERIZINOSAUR TRACK FROM THE LOWER CANTWELL FORMATION (UPPER CRETACEOUS)
OF DENALI NATIONAL PARK, ALASKA PALAIOS DOI: 10.2110/palo.2011.p11-083r