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Re: Dilophosaurus Forelimb Bone Maladies



Mike Habib <biologyinmotion@gmail.com> wrote:

> He may be responding to me on that one, because I *did* mean to imply that 
> the forelimbs of most theropods would not be used even as an aid in prey
> capture.


Oh.  Ah.


> Without really impressive gymnastics or incredibly perfectly positioned large 
> prey, most theropods couldn’t use the forelimbs to engage
> something they were biting. And if we dial back the classic “theropod death 
> match” model of predation (i.e. attacking things larger than themselves, of
> which we should probably be extremely skeptical), then the mouth basically 
> has to miss before the forelimbs could get anywhere useful (at which point
> the predator is ramming prey it can’t see with its chest and flailing at it 
> with forelimbs that probably have limited prehension).


I take your point.  And I certainly enjoyed the visual images.  :-)
But I was ready and willing to accept that theropod forelimbs could
play an accessory role in predation - holding, positioning or tearing
large prey items nabbed by the jaws.


> And I would go further to say that engaging large prey is something that only 
> very few, if any, theropods probably did with any regularity. The classic 
> image
> of a theropod grappling with a dangerous prey animal needs serious 
> overhauling. Predators overwhelmingly eat juveniles, and only specialist 
> cases hunt
>  things even their own size. Given that the Mesozoic must have been basically 
> full of small juveniles, I don’t see any reason to posit that theropods
> regularly hunted adult or large prey. Hone and Rauhut (2009) cover this well: 
> https://urldefense.proofpoint.com/v2/url?u=http-3A__www.davehone.co.uk_wp-2Dcontent_uploads_2014_01_Hone-2DRauhut-2D&d=CwIFaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=x82f3Wlkwtmbr1z8IAt9jA&m=bouSG7B9Qu3adhjMdAMBBOj8Hva6pmVWKoncNMnoaWs&s=HG1A7WJYVMnSJsa574a7pgmiwfk6e6u8Gz7u4lmFRUg&e=
>  
> 2010-theropod-feeding.pdf


We have evidence of _T. rex_ predation against large prey, from the
Hell Creek Fm of SD, with a tooth embedded in the tailbone of a large
hadrosaur (_Edmontosaurus_?), which subsequently healed (DePalma et
al., 2013).  Even though the hadrosaur got away, it is evidence of
tyrannosaurs hunting large prey.  Hone & Rauhut (2009) list examples
of evidence of large theropods consuming large prey: e.g.,
_Allosaurus_ vs _Stegosaurus_ (cervical plate bitten through),
_Tyrannosaurus_ v Triceratops_ (pelvis with tooth punctures).
Admittedly, in these cases there is no direct evidence of hunting,
only consumption.

I would agree that theropods (including _T. rex _) preferred small and
⁄ or juvenile prey, and might have only irregularly targeted large
prey.  But I would aver that in the latter situations, the forelimbs
might have been useful.  As mentioned in a previous post, the
_Velociraptor_ vs _Protoceratops_ encounter can be parsimoniously
explained by the former attacking the latter.  This might have been
'unusual' behavior for _Velociraptor_.  (There is also the
_Deinonychus_ vs _Tenontosaurus_ kill site, proposed as evidence of
pack hunting; but  the evidence here is more ambiguous.)

Overall, I'll maintain that theropod forelimbs were not really all
that useful in predation - whether prey capture or prey manipulation.
Which is why so many lineages turned them to other uses - including
display structures, or wings, or devices that defy easy explanation
(such as the weird forelimbs of alvarezsaurids, or the huge tapering
claws of derived therizinosaurids).