Falcarius, by Michael Skrepnick. From the University of Utah via NatGeo.
I've written about the therizinosaurs before, because they're some of my favorite dinosaurs: fiercely clawed feathered theropods who've gone vegetarian, some of whom grew to huge sizes. They're primarily known from Asia; North America joined the club in the early 2000's with the discovery of late Cretaceous Nothronychus in New Mexico. Soon afterwards, Falcarius was discovered in Utah, and was found to be contemporaneous with the then-earliest known therizinosaur, China's early Cretaceous Beipiaosaurus. As Zanno notes in her analysis, Falcarius differs from Beipiaosaurus in lacking many of its more derived features - those that would be further refined and emphasized by their ancestors. It's an evolutionary puzzle: why is Falcarius so primitive compared to its Chinese contemporary? Zanno puts forward three hypotheses that will require new discoveries or research to clear up:
- Better dating of the sediments in which the two therizinosaurs were found could reveal that Falcarius is actually a bit older.
- Environmental factors in Asia may have favored therizinosaurs there to evolve at a faster rate than their North American relatives.
- Falcarius shared North America with other therizinosaurs more similar to Beipiaosaurus, which haven't been found yet.
Of course, maybe an apparently advanced therizinosaur from the Jurassic will be discovered in Australia and turn the world upside down. That could happen, too.