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Re: Dilophosaurus Forelimb Bone Maladies



I have to disagree. The authors of the paper pointed out that theropod forelimb 
injuries are remarkably common. The Dilophosaurus specimen that they looked at 
showed multiple injuries to the left forelimb that all showed signs of healing 
prior to death (so it did manage to survive the injuries, although I suspect 
that the wording of the last post might have been a bit muddled, since I think 
that is what Mike was arguing). The right arm showed pathologies that agreed 
well with compensatory focus of the right limb over the left, which we wouldn't 
expect if the forelimbs were doing nothing.


The evidence presented in the paper supports theropods (or at least this one 
Dilophosaurus) using their forelimbs a lot. Although we can't say for certain 
that the forelimbs were engaged in prey capture, that is a major activity for 
most extant predators. I imagine that probably held true for extinct predators 
too. It would seem to be a waste of resources to not use all the tools at one's 
disposal. 


As Darius said, we have evidence today of crocs surviving with chunks of their 
jaws missing, yet no one would argue that the jaws played no role in prey 
capture. Similarly, there are reported cases of wild tortoises found with 
naturally amputated forelimbs, yet no one would argue that the forelimbs 
weren't typically being used for locomotion.


If anything, this Dilophosaurus specimen (along with Big Al, and Sue) stands as 
a testament to just how much of a beating theropod bodies could survive.


Jason

 
https://urldefense.proofpoint.com/v2/url?u=http-3A__reptilis.net&d=CwIFaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=x82f3Wlkwtmbr1z8IAt9jA&m=FSlzWJUSxwiMUIrIzpb0zqOIm-0yNefrOhptH5SdHw8&s=ENe_0pfxs6q7UmNCqgYZbIYVz12WQ5OaT8mTRBMuN4k&e=
  "I am impressed by the fact that we know less about many modern [reptile] 
types than we do of many fossil groups." - Alfred S. Romer


----- Original Message -----
From: Mike Habib <biologyinmotion@gmail.com>
To: dariusnau@gmx.at
Cc: tijawi@gmail.com; dinosaur <dinosaur@usc.edu>
Sent: Friday, February 26, 2016 10:53 AM
Subject: Re: Dilophosaurus Forelimb Bone Maladies

Predation isn't the only (or even most likely) way to accumulate injuries, 
however. Furthermore, this animal did not have a single major injury that it 
managed to survive during healing. It accumulated numerous injuries, each of 
which would have compromised the forelimbs for a period of time. We can at 
least say that the forelimbs were not necessary for predation (otherwise these 
injuries would have been lethal). 

Given the additional anatomical evidence against forelimb use in predation 
among theropods, it seems simplest to conclude that the forelimbs just weren't 
used to catch prey for the most part. This makes sense, after all: something 
like Dilophosaurus could easily just grab a prey item in its jaws and swallow 
it; strange circumstances are needed to get the forelimbs involved.

Cheers,

--Mike H

Sent from my Cybernetic Symbiote


> On Feb 26, 2016, at 3:06 AM, Darius Nau <dariusnau@gmx.at> wrote:
> 
> Why then have forelimbs that are so exceptionately prone to pathology, 
> including such injuries as would result from use of the forelimb in predation 
> (e.g. the probable avulsion on the left thumb), if they weren’t actually of 
> much use for that purpose?
> Generally, one would expect a structure that gets used frequently in activity 
> involving significant stresses to be particularly prone to injury.
> 
> Potential activity-related forelimb pathology in this and other theropods 
> could very well be a direct result of their strenuous activity, the animal’s 
> ability to survive without them notwithstanding (unless the argument was only 
> that they weren’t so useful that they were absolutely essential to the 
> animal’s survival).
> 
> Nobody would claim that a crocodile’s jaws aren’t all that useful for 
> predation after all, and yet there is ample documentation of crocodiles that 
> survived having their snouts bitten off.
> 
>> On 26.02.2016 02:44, Tim Williams wrote:
>> The authors propose that during the long healing period, the use of
>> the forelimbs by this smashed-up_Dilophosaurus_   was severely
>> compromised.  But it wasn't fatal.  This supports the interpretation
>> that theropod forelimbs were not all that useful for predation - even
>> when the forelimbs were healthy and undamaged.
> 
> 
> Yours sincerely,
> 
> Darius Nau
> -- 
> dariusnau@gmx.at
> https://urldefense.proofpoint.com/v2/url?u=http-3A__www.paleo.keepfree.de&d=CwIDaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=x82f3Wlkwtmbr1z8IAt9jA&m=uGsXWLSVi2TLSGOsGKS0eoDL6BpFlT6nbXQ6b7V8Iu8&s=Ka96S_MfRmcuiT6aIWKQEDppTZOjEYKXgkCTPWg9rW8&e=
>