Thursday, June 3, 2010

Yinlong and the Roots of the Ceratopsian Family Tree

In December, I wrote about one of the coolest toy lines I've seen in a long time: Evolvems, plush animals that reveal one of their evolutionary descendants when turned inside out. The Evolvem I posted was the lone dinosaur pair in the line: Yinlong-Styracosaurus. Styracosaurus is one of the most popular ceratopsids, appearing in children's books and toy lines for years because of its handsome, spike-studded frill. Yinlong, however, is pretty obscure.

It's easy to understand why. It's a recently discovered dinosaur, its Chinese name (meaning "hidden dragon") doesn't immediately suggest "dinosaur" to English-attuned ears, and it's not exactly a giant. To most people, it probably seems pretty humble.

Yinlong downsi by Andrey Atuchin, via the Natural History Museum, London

But the Evolvems brain trust picked Styracosaurus' partner-in-plush for a good reason. Discovered in China in Jurassic rock, Yinlong downsi is the oldest ceratopsian yet discovered. It lived alongside Guanlong wucai, an early relative of T. rex. If you were going to give T. rex and Triceratops the "Muppet Babies" treatment, you could set it in Late Jurassic China.

This spells out a likely Asian origin for the ceratopsians. Sinoceratops, the new Chinese ceratopsid, opens the possibility that these more derived members of the group may also have their origin in China, rather than arising in North America after more primitive ceratopsians found their way there via the Asian-Alaskan land bridge formed in the Cretaceous. It's also plausible, to me at least, that Sinoceratops or its recent ancestors wandered back to Asia from North America. Perhaps something about its biology - more generalized, mixing traits of the centrosaurines and chasmosaurines - made it better suited for its Chinese habitat, thus making this hypothetical migration - probably occurring over many generations - a reasonable pursuit. Bear in mind, I haven't read anyone put this forward, so it's just my idle speculation. Hopefully some earlier Cretaceous strata will cough up some ceratopsids of their own.

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