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Re: tiny-armed theropods



I am interested that theropod arm reduction and loss is sometimes also 
concomitant with herbivory. This happened in Limusaurus, the basal 
ceratosaurid, and apparently reached its zenith in the complete loss of the 
pectoral appendage in the moa.

In Limusaurus arm reduction occurred along with reduction of the head size, 
which is to say that the arms and head got proportionately smaller concurrently.


To figure out any sort of principles of arm reduction in theropods we'd have to 
do a survey of the distribution of this feature and look for correlates. Others 
have suggested and I agree that there would be several and perhaps innumerable 
different correlates and settings with and in which it happens.





On Oct 5, 2011, at 12:47 PM, Thomas R. Holtz, Jr. wrote:

> 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 
> 

Jason Brougham
Senior Principal Preparator
American Museum of Natural History
jaseb@amnh.org
(212) 496 3544