Monday, July 5, 2010
This may be old news for those who attended last years SVP meeting, but news of this is (to my knowledge) breaking for the first time online. Matthew Herne has finished a complete osteology of the Australian ornithischian Leaellynasaura, abstract here: http://www.vertpaleo.org/meetings/SVPProgramAbstracts09WEB.pdf.pdf
A few surprising things here. First, Leaellynasaura is traditionally called a hypsilophodontid, or at least basal ornithopod. This study finds that it's even more basal among ornithischians, even sharing some characters with thyreophorans, so it's best placed as a basal genasaurian. Next, the tail lacks the distinctive lattice of ossified, stiffening tendons found in members of many ornithischian clades. Instead, the postzygapophyses of the tail are greatly expanded relative to other members of this order, which may have helped stiffen the back half of the tail.
Most surprisingly, the tail itself is apparently ridonkulously (technical term) long. Leaellynasaurua has over 70 tail vertebrae, more than any other ornithischians save some hadrosaurs, but more astounding is the total length of the tail, which made up 75% the total body length, being three times longer than the torso, head and neck combined. Why such a long tail? One idea floated by Dann Pigdon on the DML today is that if Leaellynasaura had a covering of filamentous feather or fur-like integument (as seen in Psittacosaurus and Tianyulong), it may have been able to use its tail for warmth during cold antarctic nights, wrapping the tail around the body like an arctic fox. It may have also been useful for territorial signaling or mating displays, especially if (as in most animals with filamentous or feathery coats) it could puff the tail up to an apparently larger size by raising its hackles.
I couldn't help taking a break from my Yixian field guide series to try restoring this hypothesis, and the results are above. Can't wait to see this paper officially in print!