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Fwd: Re: tyrannosaurs and phorusracids



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From: "Thomas R. Holtz, Jr." <th81@umail.umd.edu>
To: dinosaur@usc.edu
Subject: Re:  tyrannosaurs and phorusracids 
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At 10:37 AM 5/22/97 +0000, Pieter Depuydt wrote:

>You're completely right of course; there is one other similarity 
>between tyrannosaurs and phorusracids: there are only some skeletons 
>left of them and no human has observed a living one (except perhaps 
>some Paleoindians a phorusrhacid).

Well said!

>I think Marshall based his 
>predatory scenario of phorusracids on observation of the nearest 
>relatives of them: the seriemas, which are agressive, cursorial 
>("running") birds that dash at their prey and  shake it to death, just 
as
that other 
>living theropod, the secretary bird (doesn't that one kick his prey 
>too?). Of course all these extant ("now-living") dinosaurs are 
>medium-sized or small hunters, and it is difficult extrapolating 
>observations on them to those massive predators of the past, for 
>which we have really no living analogue... 

Precisely (although, as you note, the survival of close relatives to 
the
phorusracids gives us greater insight into their anatomy and behavior 
than
is available for tyrannosaurids).

I find the tyrannosaur/phorusrhacid comparison is very similar to other
pairs of  Asiamerican Late Cretaceous dinosaurs and South American (and
southern North American) late Cenozoic vertebrates: 
ankylosaurid/glyptodont
and therizinosaur/giant ground sloth comparisons, for example.  Except 
for
some paleoindians, no humans have seen phorusrhacids, glyptodonts, or 
giant
ground sloths, all of which might had made better "contemporary" 
analogues
for certain dinosaur than are found among living animals.

>Isn't there also a record of tyrannosaur bite marks on an adult 
>ceratopian pelvis, from which bite forces were estimated? (I think 
>this was published in Science or Nature last year).

True, but (as I recall) there is no evidence that the Triceratops lived
after being bitten.  It could, therefore, have been scavenged.  Our 
best
direct evidence that large theropods were active hunters is going to 
come
from evidence of their failed attempts, documenting that they did 
strike at
living animals.  (Okay, I'd also accept a giant equivalent to the 
"fighting
dinosaurs" pair, with, for example, a Tyrannosaurus and Triceratops 
caught
in mortal combat, but I sincerely doubt we will ever find as 
spectacular a
specimen as that!!).

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:th81@umail.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661