BEIPIAOSAURUS AND THE LUFENG JAW

[Tetanurae@aol.com]

David Marjanovic wrote:
<<a.. Beipiaosaurus is preserved as jumbled blocks, each of which contains a 
few bones. The block containing the coracoids and furcula could have come 
from some other animal.
b.. The feet of Beipiaosaurus aren't very well preserved, and it is debatable 
whether the first metatarsals really don't contact the ankle (this would be a 
very unusual reversal as has been discussed onlist with the problem of 
sauropod fifth metatarsals).>>

Although you are correct in pointing out that Beipiaosaurus is not the best 
preserved fossil, there are quite a few features that show it is definately a 
theropod and probably a therizinosaur.  The astragulus has a very tall 
ascending process reminiscent of Alxasaurus and the jaw has teeth reminiscent 
of other therizinosaurs as well as saurornithoidids and ornithomimosaurs.  
Additionally, well preserved therizinosaur hands show well developed semi 
lunate carpals.

<<c.. There is this 11 cm long segnosaur dentary from the Early Jurassic of 
Lufeng. AFAIK, it shows evidence for cheeks (suggested for prosauropods, 
unknown in any theropods): Zhao Xijin & Xu Xing: The oldest coelurosaurian 
[sic], Nature 394, 234f. (16 July 1998)>>

This jaw is almost certainly not from a therizinosaur.  The teeth are almost 
identical to those in plateosaurid prosauropods and is probably a juvenile 
_Lufengosaurus_.  This has been discussed at length previously on the list.  
Additionally, even if the jaw *does* belong to a therizinosaur (which is 
probably does not), it does not mean at all that therizinosaurs are not 
theropods.  Please see:

http://www.cmnh.org/fun/dinosaur-archive/1998Jul/msg01075.html

and:

http://www.cmnh.org/fun/dinosaur-archive/1999Jan/msg00489.html

and:

http://www.cmnh.org/fun/dinosaur-archive/1999Jan/msg00538.html

<<d.. A beak at the front of the jaw has been suggested for e. g. 
Massospondylus.>>

Many theropods had beaks, most notibly birds.  Oviraptors and 
Ornithomimosaurs almost certainly had beaks, and beaks have been suggested 
for dromaeosaurs.  To say that Massospondylus might have had a beak, so 
beaked therizinosaurs could only be prosauropods doesn't really follow....

<<f.. Oviraptorosaurs and segnosaurs *look* very different; this might of 
course change with the discovery of more fossils, but judging from the 
present material...>>

Yes, and chordates and echinoderms *look* very different as well, yet they 
are sister taxa to the exlusion of just about all other animals.  General 
looks don't necisarily mean relatedness... you have to look past that.

Pete Buchholz
Tetanurae@aol.com