Monday, December 20, 2010
A Christmas Caudipteryx Chapter III
In spite of recent finds, there are still several coelurosaur ghost lineages. Using phylogenetics, it's possible to predict whether a certain clade existed at a certain point in time. If phylogenetic analyses are correct (and they might not be), we know that clade simply must have been around at that time. However, we may not find any actual fossils of that clade from that time period. When this happens, we end up with a ghost lineage.
For a long time, Archaeopteryx was the oldest known maniraptor, dating from the Late Jurassic. But Archaeopteryx was an avialian, one of the most derived maniraptors. If avialians were around in the Jurassic, where were all the other Jurassic maniraptor groups? The BAND jumped on this fact, calling it the "temporal paradox" and using it as "evidence" that birds couldn't have descended from dinosaur ancestors. But the BAND were wrong (and still are). The real answer to the "paradox" was that we simply hadn't found the other Jurassic maniraptors. Throughout the last ten years or so these ghost lineages have slowly been filled up. We now have Jurassic deinonychosaurs (Anchiornis, as well as some teeth and an undescribed troodont nicknamed "Lori"), alvarezsauroids (Haplocheirus), and even a possible therizinosaur from the Early Jurassic (Eshanosaurus). The odd group out is the oviraptorosaurs. What did Jurassic oviraptorosaurs look like? Only time will tell.