HP Marjanovic wrote:
You've conflated the two parts of the Yixian Fm, which have different ages. And you've added the Jiufotang Fm, which is quite a bit younger (source of *Microraptor* including *Cryptovolans* and many if not most of the birds).
I was actually wondering about that when I was writing. Makes sense.
And don't forget the fact that there are lots of mammals, lizards, other
reptiles, etc. in the assemblage. So far, the Yixian carnivorous theropods
are not of a size that prevents them from being feeders on non-dinosaurs (in
contrast to, for example, Allosaurus or Tyrannosaurus, which really didn't
have the option of too many non-dino meals as adults...).
Well, take a look at the rest of the fauna from the Yixian: there was an incredible abundance of birds and several pterosaurs, many of which would have represented prey species to several of the Yixian theropods.
On another perspective, there were also several different distinct layers opf the Yixian with distinct taxa, including the lowermost Lujiatun, the younger Sihetun, and so forth, which affect the actual concentration of species.
See above. :)
Think of it: there must have been countless birds living in other Cretaceous environments, but relatively few have been found. It is probable that small non-avian theropods were likewise much more common elsewhere than the fossil record indicates.
Mike D.