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Re: [dinosaur] T. rex slashing finger claws? + Matheronodon + Mary Anning film + more



The big paradox of tyrannosaur arms is that while they are so small,
they are also so *robust*. So obviously, if they had a function, it
must have been one that required a lot of strength. But we're putting
the cart before the horse here. What if their anatomy is an effect of
increasing muscle mass in that area of the body, and not as a product
of selection for forelimb functionality? EvoDevo can potentially chime
in on this, such as when increasing muscle mass effects just also
happen to increase things like muscle evulsions on bone or producing
high-relief entheses. I do not believe they have at this time, though.

I can, however, offer an alternative opinion.

Why do tyrannosaurs and abelisaurs both possess tiny arms, giant
scapulaocoracoids, the latter are often fused with large regions for
seeming humeral muscle attachments (assuming proposed muscle
attachment homologies are accurate); yet abelisaurs -- esp.
carnotaurines -- have such diminished forearms and manus without the
huge claws and seeming diversity in forelimb to body mass as
tyrannosaurs?

As Mike suggests, the coracoids typically attach certain humerally
inserting muscles that suggest robust forelimb movement, such as M.
deltoideus. But coracoids (and scapulae) also attach a large number of
additional muscles that connect to the top, sides, and base of the
neurocranium, to the quadrate, to the articular, and to various other
back supporting muscles. Conversely with abelisaurs, the scapular
process of the scapula is long, very thin craniocaudally, but
triangular in section with robust regions for muscle attachment that
have nothing to do with arm mobility. In abelisaurs, the process is
much broader craniocaudally, but shorter overall, and the difference
is likely more phylogenetic than morphofunctional. Despite this, both
taxa have typically oversized heads, mobile necks with robust
musculature, and both have been described more or less as "head-first"
hunters, using robust neck muscles to help deliver attacks. This has
also been described for allosaurids by Bakker, but recently work by
Snively et al has rejected this for a more hawk-like ripping behavior
... for which the large forelimbs, hooked claws, etc. can only be
beneficial.

Tyrannosaurs just lack these additional elements. As such, I feel
applying use of the forelimbs as ripping instruments without any
accessory work on dealing with the problems laid above is not merely
premature, but unlikely to be fruitful in producing a result
consistent with that of the premise.

On Fri, Oct 27, 2017 at 7:40 AM, Mike Habib <biologyinmotion@gmail.com> wrote:
> There also doesn’t seem to be an accompanying analysis of how claws would cut 
> (which would be related to the claw shape issue). Most claws are not 
> particularly good at cutting.
>
> The large coracoids are a solid observation, but probably better explained by 
> neck muscle explanation than forelimb muscle retention. At least, that’s my 
> take on the issue.
>
> —Mike
>
> Sent from my Cybernetic Symbiote
>
> On Oct 27, 2017, at 6:49 AM, David Marjanovic <david.marjanovic@gmx.at> wrote:
>
>>> T. rex’s silly-looking arms were built for slashing
>>>
>>> Robust bones and bearlike claws suggest the dino’s ridiculously small limbs 
>>> were far from useless
>>
>> I agree they don't look useless; but given that there's no mention of the 
>> shape of the claws at all, I have to wonder if the "humoral head" mentioned 
>> in the abstract is deliberate.



-- 
Jaime A. Headden
The Bite Stuff: 
https://urldefense.proofpoint.com/v2/url?u=http-3A__qilong.wordpress.com_&d=DwIFaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=UYAZvvoJUYjVomuHAbUkOL4bbdn_lCt9q4SW8NtBrBM&s=El1mDN_w2Tx8zXCVu5pzcVADdBaODAJz5m55OeK8S4A&e=


"Innocent, unbiased observation is a myth" - P. B. Medawar (1969)