Thursday, July 30, 2009

A Therizinosaur's Lesson

Therizinosaurs, which until earlier this decade were not known to have lived in the land of the free and the home of the brave, are a delightfully strange clan of dinosaurs. Their hands sported some of the largest claws in all of dinosauria, but we know from their small, beaked heads and massive guts that they were largely herbivorous. Here's a nice side view of Beipiaosaurus inexpectatus, that illustrates just how odd the therizinosaurs looked:
B. inexpectatus via Dinosaur World

Therizinosaurs, including the recently named species Nothronychus graffami from Utah, were maniraptors, a group of theropods which also includes the dromaeosaurs, or raptors. A study led by The Field Museum's Lindsay Zanno has found that among their maniraptoran kin, the therizinosaurs were the earliest branch, pointing to the possibility that they and the dromaeosaurs may have shared an omnivorous or herbivorous ancestor, and hypercarnivory (or the exclusive eating of meat) was not necessarily the norm. It's always nice to have more detailed shading of the frequently cartoonified dinosaurs, which are usually depicted strictly as belonging to two teams: meat-eaters and veggiesauruses. Dinosaurs dominated terrestrial ecosystems for hundreds of millions of years, so it makes sense that their diverse forms evolved to fill niches in all kinds of neat ways. The therizinosaurs are striking in the way they subvert pop culture's roster of standby dinos.

Nothronychus by Victor Leshyk for the Museum of Northern Arizona

Adding a bit of maritime intrigue to the N. grafammi specimen: it was discovered in sediment that would have been 60 to 100 miles from shore, among the remains of ammonites (which with their spiral shells superficially resemble the nautilus but are closer kin to squids). I love when a fossil gives such vivid fuel to the imagination.

Demerit to the Salt Lake City Tribune for this little gaffe:
The discovery adds to science's understanding of therizinosaur, a dinosaur belonging to the therapod (sic) family, whose members include Tyrannosaurus rex and Velociraptor. The study suggests these famous predators may have evolved from plant-eating ancestors.
T. rex and the other tyrannosauroids are distant cousins to the maniraptors. The study only deals with maniraptors and doesn't suggest that T. rex had a vegetarian ancestor. This seems to be a pretty common mistake: reporters throwing out the names of one of the classic dinosaurs as a sort of shorthand.

A traveling exhibit on recent discoveries of therizinosaurs in the United States, THERIZINOSAUR—Mystery of the Sickle-Claw Dinosaur, will be at the Museum of Northern Arizona until August 30, 2009.

More N. grafammi: Live Science, Dinosaur Tracking, and nice personal observations at Chinleana.

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