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Re: Microraptor also ate fish



Jason Brougham <jaseb@amnh.org> wrote:

> So, using your methods, do you feel comfortable saying that there is 'no
> way' Pteropus could roost on the terminal branches of trees?

Nope, I do not feel comfortable saying that.  In fact, I saw a bunch
of fruit bats (_Pteropus poliocephalus_) yesterday roosting in the
trees at the local park.  Wonderful creatures.


> It lacks the
> reverse hallux of perching birds. It weighs the same as Microraptor (0.7 -
> 1.2 kg). Like Microraptor it has long, curved foot claws and retains a
> claw on its thumb. And, as I cite you below, you say that, since it lacks
> the perching foot of birds, or scales on its metatarsus, or other
> adaptations that clearly make it adapted to roosting in trees. I think
> you've been clear that its not enough to have a gripping mechanism, it
> must have THE SAME gripping mechanism as any animal that you compare it
> to, like a 1kg raven. Is this correct, Mr. Williams?


Pteropodids have suspensory adaptations, don't they?

(BTW, it's Dr Williams.  I know no offense was intended, and none was
taken.  But in these situations, when in doubt it's often best to use
"HP" as an honorific.)


> My point, of course, is that Microraptor does have a gripping mechanism.
> It has a free thumb with a highly curved claw, and a 2nd manual digit as
> well. It also has a 2nd toe that is apparently opposable to the
> metatarsus. Fowler et al. (2011) found that dromaeosaurs have adaptations
> for gripping in the pes. I refer to Pteropus here to show that two animals
> do not need THE SAME gripping adaptations in order to be used as analogs
> to one another, so long as they both have gripping adaptations.


No, if you are going to invoke analogs, I would prefer to stick with
the *same* adaptations (those involved in gripping, in this case).


> Of course this hypothesis could be tested. The pes of Microraptor could be
> modeled and analyzed to see if it could grip a branch, what diameters it
> could grip, and how the tendons and flexor processes compare to roosting
> birds of the same mass.


Sounds like a great idea!  I'd be quite happy if you were to
demonstrate that _Microraptor_ had the capacity to grasp branches with
its pes.

However, since you bring up Fowler et al. (2011), that study made it
clear that the grasping pes of dromaeosaurs is achieved via a
different mechanism to that of birds, which have an anisodactyl
grasping pes.  In _Deinonychus_ the medially directed first toe
opposes the fourth toe in order to execute the grasp.  The study makes
it quite clear that this is inferred to be a predatory adaptation.
Its utility for perching or roosting has yet to be demonstrated.  It
would be interesting to see how these "arboreal" functions would be
reconciled with digits I and IV enclosing the fist anteroposteriorly
across the plantar surface of the metatarsus.


> My point is that ALL correlations are analogs. This is comparative
> morphology, so comparisons must be made. If you are using morphological
> correlates then you are using analogs but you are apparently loathe to
> admit it.


I'm uncomfortable with extrapolating too much based on analogs.  As
Fowler &c put it: "Although combinations of foot morphological
characters are not identical to extant raptors (i.e. we do not see one
taxon as an ‘‘owl mimic’’ another as a ‘‘falcon’’, etc.) likely
predatory behaviours can be elucidated by comparison of individual
characters and their functional morphology in extant birds of prey."
I think too often analogs lead to over-interpretation, along the lines
of 'fossil taxon A has such-and-such features in common with modern
taxon B, so therefore taxon A had an ecology much like taxon B'.  One
of the most egregious examples is the claim that _Archaeopteryx_
climbed trees like a juvenile hoatzin, despite the presence of very
few (and very superficial) similarities.  I'm trying to steer clear of
these kind of howlers.







Cheers

Tim