[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Microraptor also ate fish

Thank You for your thoughts Dr. Williams.

I have two points.

1) There is scientific value to stating a hypothesis clearly, even before
that hypothesis is tested. It is not unscientific to state a plausible
hypothesis without testing it first. That is, unless the hypothesis is
absurd or violates physical laws. Thus I defend any researcher who
presents a hypothesis about extinct animals based on observations of
living animals. I feel that using living analogs in this way helps to
avoid a pitfall that often accompanies biomechanical analyses: that theory
can make predictions that are unrealistically constrained, and that are
more limited than what living animals are capable of. Just as a quick
example, if eagles were extinct we might conclude that they could only
scavenge and hunt fish in the shallows because, with those fluffy
integuments, huge, cumbersome, wing feathers and unwebbed feet, if they
fell in deep water they would quickly drown. I, for one, would certainly
never think they could swim ashore clutching a fish, until I saw it with
my own two eyes.

2) I don't agree that the evidence for an arboreal (sensu lato) lifestyle
in Microraptor is non - existent. To be more precise, there is evidence
that Microraptor could have moved in trees, but I have never interpreted
this to mean that it was obligately arboreal (sensu stricto). If you'll
recall, my hypothesis was that it may have foraged on the ground and
roosted in trees, as do the clades of living basal birds that are small
enough to do so. There is morphological evidence for this.

To quote
Birn-Jeffery AV, Miller CE, Naish D, Rayfield EJ, Hone DWE (2012)
Pedal Claw Curvature in Birds, Lizards and Mesozoic Dinosaurs ­ Complicated
Categories and Compensating for Mass-Specific and Phylogenetic Control.
PLoS ONE 7(12): e50555. doi:10.1371/journal.pone.0050555

'While our dataset is limited, and the hulls overlap extensively, it
is still plausible based on our data for digit III claws that some
Mesozoic maniraptorans were tree-climbers. Based on outer
curvature data, both A. bavarica and Changchengornis appear to be
Œclimbers¹, although inner claw curvature places A. lithographica in
the Œground-dweller¹ category. Anchiornis and Microraptor have the
potential to be considered Œperchers,¹ and the latter also has
characteristics consistent with some climbing ability.'

The overlaps in this study's data show that it can be hard to distinguish
small predators from climbers or perchers. The paper is also highly
insightful for demonstrating that body mass and phylogeny both have
correlations with claw curvature, making it hard to distinguish lifestyle.

You have characterized Deinonychus as having the same or better gripping
ability to Microraptor. That is just about right. Birn-Jeffery et al.
found Deinonychus to be on the line between predators and climbers, while
Microraptor had several measurements which clustered closer to the center
of climbers, but this is a fine point. It is perhaps meaningful that
Velociraptor's measurements fall far from the other dromaeosaurs; firmly
in the ground animal category and even outside of the predator envelope.

I am sorry that I did not cite this reference earlier.

I envy you getting to observe Pteropus!


Jason Brougham
Senior Principal Preparator
American Museum of Natural History
(212) 496 3544

On 4/28/13 8:42 PM, "Tim Williams" <tijawi@gmail.com> wrote:

>Jason Brougham <jaseb@amnh.org> wrote:
>> We have three winged animals weighing about a kilogram.
>> 1) Perching - adapted raven, Corvus.
>> 2) Microraptor, with gripping pes.
>> 3) Pteropus, with no gripping adaptations.
>> 1 and 3 roost in trees. I don't think you can say, with any logical
>> validity,  that there is no way 2 did.
>I disagree with the premise of this question.  The feet of _Pteropus_
>(fruit bats) have excellent gripping adaptations.  Their toes are very
>much like the fingers of other suspensory mammals, and are highly
>adapted for suspending the animal from tree branches.*  Thus, the pes
>of _Pteropus_ is definitely arboreally adapted.
>BTW, I'm not saying that there is "no way" that _Microraptor_ could
>roost in trees.  My point is that the pedal morphology of
>_Microraptor_ shows no apparent adaptations for roosting or perching.
>If you can put together a case that _Microraptor_ indeed has
>adaptations for roosting (or perching), then go for it.  This sounds
>like a working hypothesis that deserves to be tested.
>However, if your argument is that there are no such adaptations in
>_Microraptor_, but it was capable of roosting or perching anyway, then
>(scientifically speaking) this is where we part company.  There is
>nothing to test here.
>I don't dispute that _Microraptor_ had a pes capable of gripping.  But
>so did the pes of _Deinonychus_.  I remain unconvinced that the
>gripping pes of _Microraptor_ allowed it to roost.  But I'd be quite
>happy to be refuted on this point, by way of solid biomechanical
>evidence.  Intuitively, I really like the notion of an arboreal
>_Microraptor_.  However, the anatomical evidence in favor of an
>arboreal lifestyle is weak to non-existent.  There is certainly
>evidence that _Microraptor_ was scansorial - but this is a long way
>from being arboreal.
>* Among other sources, the pedal morphology of pteropodid bats  was
>discussed (and figured) by Boyer and Bloch (2008) in their chapter on
>plesiadapiforms in "Mammalian Evolutionary Morphology: A Tribute to
>Frederick S. Szalay.")