Re: Insane Yixian theropod diversity

[Dino Guy Ralph <ralph.miller@alumni.usc.edu>]

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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