RE: tiny-armed theropods

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

Let's keep in mind, too, the sequence of acquisition of the various traits 
associated with forelimb reduction and any other relevant
ecomorphological system we are comparing it to (body size, locomotory 
adaptations, feeding adaptations, etc.).

For example, based on material Sereno presented at SVP last year, forelimb 
reduction in the lineage including Abelisauridae likely
occurred well BEFORE the origin of Abelisauridae and well before the origin of 
the characteristic skull and cervical adaptations of
abelisaurids! In tyrannosauroid history some cranial and locomotory 
specializations had already arisen while forelimbs were still
fairly long, although these continued to be more specialized as body size 
increased and forelimbs decreased. (If only we had good
arms for Alectrosaurus, Appalachiosaurus, Xiongguanlong, and Dryptosaurus!).

Also, a key factor in the success of abelisaurids and tyrannosaurids is the 
loss of larger carcharodontosaurs and spinosaurids. So
the forelimb issues may have nothing to do with the success of the later Late K 
guys: that may be coincidental.

> -----Original Message-----
> From: owner-DINOSAUR@usc.edu [mailto:owner-DINOSAUR@usc.edu] 
> On Behalf Of Ralph Chapman
>
> Let us also remember that there is a great chance that there 
> is not a single explanation for the different lines. What may 
> be, at least in part, a developmental strategy for 
> tyrannosaurids may not work at all for earlier theropods. 
> Bipedalism may simply be preadapted for the generation of 
> various mechanisms for fore-limb reduction or, more probably, 
> fore-limb variation which then leads to the bird oriogin stuffola.
> 
>
> -----Original Message-----
> >From: Augusto Haro <augustoharo@gmail.com>
> >Sent: Oct 5, 2011 10:16 AM
> >To: Dinosaur Mailing List <dinosaur@usc.edu>
> >Subject: Re: tiny-armed theropods
> >
> >Forelimb reduction as a mass-reduction strategy may 
> conceivably be also 
> >useful for small theropods if these need velocity. This may 
> not apply 
> >to those which seem to be the faster dinosaurs, 
> ornithomimids (unless 
> >their slender arms actually decreased their weight by becoming 
> >slender), but can apply to likely similarly fast alvarezsaurids.
> >Although I agree that forelimb mass was relatively small, it is 
> >possible that for the sake of velocity or weight-saving even small 
> >weight saving bears an advantage.
> 


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, 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