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« on: January 16, 2010, 02:01:02 AM »
I know, I know, it's been slow. But I have good reason! Being unemployed does wonders for one's ability to print out the latest technical papers.
Having said that, there's just not a lot of exciting paleo-news right now. The two biggest stories are:
1) Shaochilong maortuensis just got its own monograph (Brusatte 2010). It's the only known Asian representative of the Gondwana-based Carcharodontosauridae, a subgroup of Allosauroidea. It has a shorter snout compared to its larger cousins like Mapusaurus and Giganatosaurus. The remains are not very complete, but the braincase is incredibly well-preserved, probably the best preserved in all known non-maniraptoran tetanurines. Aside from that, Shaochilong demonstrates that carcharodontids (and thus allosauroids) had a global distribution before the breakup of Pangea (Acrocathosaurus is a North American carcharodontosaur).
2) Crocodilians, despite not having avian lungs or pneumatic bones, have a unidirectional respiratory system. Previously, it was thought that crocs have a basically mammalian gas exchange system. Both are powered by diaphrams, of course. However, a new study by Farmer & Sanders shows that, in fact, crocs have a basically avian ventilation system, though exactly how it works is still a bit mysterious. The importance of this finding is vast, suggesting that unidirectional air flow is basal to Archosauria, and the transition from diaphram-powered lungs to skeletal and soft-tissue pneumaticity is clearer. It's entirely possible that non-crocodilian crurotarsians experimented with pneumaticity to some degree, but living crocodilians are a bit of an exception anyway* so that's not a huge surprise.
*Modern crocs 'n' 'gators have a four-chambered heart, and their ancestors were erect-limbed, fast-moving critters that were probably endothermic. Modern crocs are distinct in that they developed semi-aquatic adaptations. Crurotarsians are generally terrestrial, with some exceptions. However, endothermy would not be advantageous for a water-dwelling ambush predator, so crocs reverse-engineered an ectothermic metabolism and improved their circulation to stay active and functional in cool water.
Many people note that crocs sun themselves just like lizards and snakes, which are truly ectothermic. Well sure, but birds do too, and so do small mammals. There is not such a clear-cut dichotemy between cold and warm-blooded as is usually thought.