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Re: Insane Yixian theropod diversity



For a more complete list of the dinosaur fauna of the Early Cretaceous Liaoning/Hebei region of China, see http://www.dinodata.net/Dd/Namelist/Form/Liaoning.htm. There are eight herbivorous dinosaurs listed (not counting potential theropod herbivores). See also http://www.sinofossa.org/news.htm, which includes photographs of a number of these specimens.

I have not heard anyone characterize this locale as featuring "swamps," but I would be happy to be corrected if such was the case. The 88 plus species of local plants included cycads, gingkoes, conifers, ferns, and emergent angiosperms. Fossils of freshwater animals are very common, providing evidence for numerous isolated lakes. It may be that -- as in the case of California, where I live -- tectonic and volcanic activity repeatedly shaped and reshaped the land and water features, producing a complex topography which would have provided a variety of habitats, which, in turn, promoted frequent speciation. In sum, the great species diversity and the great number of fossil specimens found in Liaoning and nearby regions presents a picture of thriving ecosystems perhaps punctuated by frequent catastrophic events.

In terms of preservational bias, Liaoning may be contrary to most Mesozoic ecosystems. It has been suggested that the local formations have captured "complete biota." This may be an exaggeration, but perhaps not an extreme exaggeration. By contrast, most other fossil sites are relatively poor. It is no secret that the Jehol Biota includes many animals and plants which were small and delicate, and soft tissues were often preserved. As an obvious example, the number and diversity of birds found in the Jehol deposits puts all other Mesozoic formations to shame. I suggest the possibility that we may be seeing more small theropods in the Yixian and Jiufotang Formations because other depositional environments weren't suitable for preserving these delicate, hollow boned creatures. Of course, environmental factors could explain why the region wasn't populated by giant dinosaurs such as we see in other locales.

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. Regarding the dearth of large herbivorous dinosaurs among the Jehol Biota, I would think that we would have seen more fragments of large bones had such animals been common there. Some of the theropods were likely to have been herbivores or omnivores, and some of them clearly ate small non-archosaurian animals, so the predatory theropods didn't feed exclusively on herbivorous dinosaurs, if at all. The environment was apparently more riparian than the drier Late Cretaceous Gobi, for example, but there, too, in formations that preserve delicate skeletons, theropod diversity is very high indeed, and the herbivores, though common, are not so diverse. Perhaps the presence of so many small Yixian and Jiufotang theropods was not unusual at all, but few depositional environments were suitable for preserving such creatures as fossils.
--------
"Dino Guy" Ralph W. Miller III
Docent at the California Academy of Sciences
proud member of the Society of Vertebrate Paleontology
----- Original Message ----- From: "Michael de Sosa" <stygimoloch81@hotmail.com>
To: <dinosaur@usc.edu>
Sent: Thursday, October 07, 2004 3:14 AM
Subject: Insane Yixian theropod diversity



This may have been addressed before on this list before, but I couldn't find it. I'm wondering how come there are so many freakin theropods (actually, just coelurosaurs!) being described from the Yixian and not much else (when it comes to dinosaurs anyway). It reminds me of certain localities in the Morrison.

I mean, for Team Theropod it's:
Beipiaosaurus, Caudipteryx, Cryptovolans, Dilong, Graciliraptor, Huaxiagnathus, Incisivosaurus, Microraptor, Protarchaeopteryx, Shenzhousaurus, Sinornithosaurus, Sinosauropteryx, Sinovenator, Sinusonasus, and Yixianosaurus ... some of which have multiple species, probably forgetting a few (no doubt starting with Sino-), and not even _counting_ the bazillion or so birds that have been found.


vs.

Some Token Herbivores, represented by:
Hongshanosaurus, Jeholosaurus, Jinzhousaurus, Liaoningosaurus, and maybe sauropod fragments.


So why is that? Is it an artifact of preservation (tiny theropods are smaller and more easily buried whole), of collection (small slabs easier to collect and transport than lots of larger bones), or of publication (feathered theropods look sexier on your CV)? Or some other bias? Was it an ancient hockey game with the theropods on the biggest power play in history? Or is it actually representative of the Yixian fauna? Can we even tell?

Mike de Sosa

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