RE: therizinosaurs - how did it happen?

["Thomas R. Holtz, Jr." <tholtz@umd.edu>]

> From: owner-DINOSAUR@usc.edu [mailto:owner-DINOSAUR@usc.edu] 
> On Behalf Of B tH
>
> Or perhaps, "why?" would be better ... what forces were to 
> drive a carnivore to a herbivore state?   All through the 
> evolutionary period this would have happened in there were 
> plenty of meat eaters and plant eaters that surely filled all 
> the 'niches.'
> Any idears?
> 
As Lindsay Zanno showed at SVP last year, there is a fairly good chance that
the shift from a strictly carnivorous diet in coelurosaurs may have been a
single event shared by the common ancestor of ornithomimosaurs,
therizinosaurs, alvarezsaurs, oviraptorosaurs, and eumaniraptorans (with
hypercarnivorous eumaniraptorans being reversals). If so, and given the
presence of the ?Early Jurassic? Eshanosaurus, this origin would have been
in a fairly transitional period of dinosaur history. (Of course, the age of
Eshanosaurus is debatable; however, given the presence of Late Jurassic
eumaniraptorans [and maybe even Middle Jurassic ones], the divergence among
maniraptoriforms was certainly a Jurassic event). So the non-carnivorous
coelurosaur radiation may have occurred with the other major dinosaur
radiations of the Early and Middle Jurassic.

All that being said, it is difficult to ascertain why these shifts occur.
For example, why did pandas become herbivores? Or the herbivorous varanids?
Or the herbivorous crocodyliforms?

Thomas R. Holtz, Jr.
Email: tholtz@umd.edu   Phone: 301-405-4084
Office: Centreville 1216                        
Senior Lecturer, Vertebrate Paleontology
Dept. of Geology, University of Maryland
http://www.geol.umd.edu/~tholtz/
Fax: 301-314-9661               

Faculty Director, Earth, Life & Time Program, College Park Scholars
http://www.geol.umd.edu/~jmerck/eltsite/
Faculty Director, Science & Global Change Program, College Park Scholars
http://www.geol.umd.edu/sgc
Fax: 301-314-9843

Mailing Address:        Thomas R. Holtz, Jr.
                        Department of Geology
                        Building 237, Room 1117
                        University of Maryland
                        College Park, MD 20742 USA