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Re: TRICERATOPS AND PSITTACOSAURUS ARE NOT OVERSPLIT



On Tue, 6 Mar 2001 23:46:27   
 Tetanurae wrote:
>Steve Brusatte wrote:
>
><<I find it hard to believe, in a strict biological sense, that four 
>different species of the same genera would inhabit the same area.  I do know 
>that some of the Psittacosaurus species are from different times, but this 
>notion is still hard to believe.  Dodson, in his book, repeats the fact that 
>there is only one species of giraffe, one species of hippo, and one species 
>of rhino in Africa today.  If there were 8 or 10, then all of the species 
>would be competing for the same general foods and something would go extinct.>
>>
>
>This is not entirely correct....  If you mean Asia, by "same area" then 
>you're correct, but psittacosaurs are known from all over the place.

All over the place in Asia, yes.  Mostly northern China and Mongolia, as Peter 
said, but there is also P. sattayaraki from Thailand (which is so 
fragmentary...has this one been debunked yet?).  However, northern China and 
Mongolia, although very, very large, is still the same general area.  Now, we 
only need more stratigraphy and temporal data, which is always hard to come by. 
 

>Psittacosaurus mongoliensis is known from Mongolia; Nei Monggol Zizhiqu 
>(Inner Mongolia) and Liaoning, in northeastern China. 
>
>P. neimongoliensis is known from Nei Monggol Zizhiqu in northern China. 
>
>P. xinjiangensis is known from Xinjiang Uygur in China's extreme northwest.  
>
>P. meileyingensis is from Liaoning in the northeast of China.
>
>P. sinensis is from Shandong in China's east, as well as Nei Monggol Zizhiqu 
>in the north.
>
>P. youngi (which Sereno regards as a synonym of P. sinensis) is also from 
>Shandong.
>
>P. ordosensis is from Nei Monggol Zizhiqu.

And these are only the accepted ones.  There are 2-4 more (such as P. osborni ) 
which were proved incorrect years ago.  P. osborni is now classified under P. 
mongoliensis now, right?

>Although all psittacosaurs lived in the Early Cretaceous, it's been difficult 
>to find actual ages in the literature.  The only two species that actually 
>lived in the same formation were Psittacosaurus sinensis and P youngi, which 
>actually differed quite a bit.  

Well, you wrote above that Sereno considers the two synonymous.  What is 
different between his analysis and yours?  Sereno, in my opinion, is the world 
expert on these guys, so if he said that P. sinesis and P. youngi were one and 
the same, then I would tend to support him.  However, I would need to be able 
to study the specimens myself...

>Psittacosaurus mongoliensis and P. meileyingensis both had an odd dentary 
>ridge, but differed in almost every other feature of the skull, such as the 
>external anteorbital fenestra, and the rostral length and shape.  P. 
>mongoliensis had a much longer skull profile than any other species, and P. 
>meileyingensis had the tallest skull profile of any species.
>
>Psittacosaurus sinensis, P. ordosensis and P. xinjiangensis had very 
>pronounced jugal horns.  P. sinensis and P. xinjiangensis horns were even 
>more pronounced, so that the rostral edge was nearly perpendicular to the 
>sagital plane of the skull.
>
>Psittacosaurus youngi and P. neimongoliensis both had shorter, squarer 
>skulls, as well as exceptionally deep rostral mandibles.  The predentary did 
>not come to a pointy tip like other ceratopians, but instead looked more like 
>the end of a robust pair of pliers.
>
>All other species of Psittacosaurus are based on fragments and are of 
>negligible use at this time.

All of this is very interesting.  As I wrote earlier, I believe that Sereno 
brought down the 7-8 acceptable species to four species.  I don't have the ref, 
though. Maybe it was in his doctoral thesis.  Four may be a bit too high, but 
if they were separated in time or were further enough apart to compete for 
different food sources, then that is a possibility.  As HP Brian Choo wrote, 
there is something like 5 or 6 (I don't remember exactly) different species of 
the same marsupial genus somewhere in Australia.  This is an exception, but it 
certainly does occur.  Like Peter said, the only way to know for sure is for 
somebody to invent a time machine.  I think Homer Simpson did this, but he went 
back to Cretaceous North America, not Asia :-((

Steve

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