The Mysterious, Intriguing, Utterly Cool Alvarezsaurs

Yesterday at Archosaur Musings, Dave Hone made a brief post about what he thinks is going to be one of the dinosaur clades to receive some major light this year: the Alvarezsaurs. Today, guest-blogger Jonah Choiniere continues the alvarezsaur love with a history of the study of this strange group. Hone promises a major post tomorrow which will accompany a paper to be published in science, a paper announcing a new Jurassic alvarezsaur from China described by Coiniere.

Personally, I'd be thrilled if 2010 is as good to the alvarezsaurs as 2009 was to the tyrannosaurs. The alvarezsaurs are very birdlike group of small theropods, members of the maniraptors, found in Europe, Asia and the Americas. But, as maniraptors go, they actually aren't very closely related to birds. And the basal (more "primitive") members of the group are actually less birdlike. This means that the birdlike features the alvarezsaurs would evolve, especially the deep, keeled breastbone, were examples of convergent evolution, separately evolved for their own purposes. The reason birds have such a deep breastbone is that it's needed for the attachment of the flight muscles.

The forelimbs of alvarezsaurs, on the other hand, are not exactly winglike. They are short, strong, with a pronounced first claw. This claw was so favored that some of the alvarezsaurs, such as Mononykus, have evolved only one finger. Some, like mongolia's Shuvuuia, have drastically reduced second and third digits, which were likely useless in life. This feature, plus what seems to have been a flexible snout, has led to the widely accepted view that this group of dinosaurs were specially adapted to an insectivorous niche, using their powerful little arms to dig into termite mounds, probing for yummy little morsels with their snouts. More color added to our picture of dinosaur lives.


Mononykus reconstruction at AMNH, photo from wikipedia user Ivan Akira.