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Re: tyrannosaurs and phorusracids



> Date:          Wed, 21 May 1997 17:47:37 -0400 (EDT)
> To:            dinosaur@usc.edu, Pieter.Depuydt@rug.ac.be
> From:          "Thomas R. Holtz, Jr." <th81@umail.umd.edu>
> Subject:       Re: tyrannosaurs and phorusracids (was reply to:Large theropod
>                body.

> At 12:20 PM 5/21/97 +0000, Pieter Depuydt wrote:
> >I would like to add my thought of two pennies worth.

> Since we do not have living phorusrhacids to examine while hunting, the
> above scenario is speculation.  We do NOT know that phorusrhacids hunted
> that way: it might be quite likely, but we do not have any more direct
> evidence (less, even) of their predatory techniques than of those of
> tyrannosaurs.
> 
> >Phorusracids preyed upon mammals 
> >smaller than themselves which they swallowed whole (all according to 
> >Marshall's publication);
> 
> Again, whoa!  Based on what?  Are there specimens on which this hypothesis
> is based?  I would not be surprised if phorusrhacids could attack mammals of
> around their own size, given those tremendous skulls they had.  However, we
> do not have (to my knowledge) direct evidence of this.

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). 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... 

And this applies also the topic of hadrosaur defense I think:
all we know about them is they lived in really giant herds, 
had a lot of intraspecific display, brooded in large rookeries, 
and had apparently no anatomical features useful for defense against
predators except of their large body mass. And all the rest is 
speculation, more or less plausible and reasonable, but still 
speculation...

> >perhaps tyrannosaurids also preferred smaller prey, such as hadrosaur 
> >juveniles...
 
withdrawn 

> Just to remind people, there IS documented evidence that tyrannosaurs did
> attack living adult hadrosaurids: the Denver Museum of Natural History
> Edmontosaurus has a bite mark of the proper size, shape, and position to
> have come from a T. rex (the only known predator of the appropriate size and
> shape in the vicinity).  As the wound healed (somewhat), the attack was
> unsuccessful, but it does indicate that at least one Tyrannosaurus attacked
> a living, adult Edmontosaurus at least once in the history of these two 
> genera.

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).

Pieter Depuydt