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Re: Perching, climbing, roosting was Re: 11th specimen of Archaeopteryx



David Marjanovic <david.marjanovic@gmx.at> wrote:

> -- Any species that climbs trees and stands around in them for evolutionary
> significant spans of time -- say, a few decades -- will show adaptations to
> this.


I agree wholeheartedly, as far as roosting is concerned.  The hallux
of archaeopterygids and deinonychosaurs remained stubbornly
un-reversed, and fairly elevated.  The argument that these critters
sought out tree crotches or large boughs or the crowns of cycads for
roosting strikes me as special pleading.


> -- Conversely, grasping feet -- including feet shaped by compromises between
> grasping and walking/running -- may not have grasped any plant matter, but
> prey. Today, the most extreme phalangeal ratios, claw sizes and claw
> curvatures are found in predatory birds. The hands of theropods are
> plesiomorphically in that range; this includes *Archaeopteryx*. Perhaps this
> also explains why carnosaurs had less extreme phalangeal ratios than extant
> cursorial birds.


Based on Hospon's (2001) work, the hands of _Archaeopteryx_ and
deinonychosaurs certainly have phalangeal ratios comparable to the pes
of raptorial birds.  However, similar  'raptorial' proportions are
also evident in the hands of certain ornithomimids (and _Deinocheirus_
too), so the proportions are tied to grasping more so than
specifically raptorial ability.  Also, no theropod had an opposable
manus (with the possible exception of _Bambitraptor_).


Another thing is that the hands of paravians like _Archaeopteryx_ and
_Microraptor_ were not adapted for grasping small objects; they could
only grasp large objects with both hands.  Either these objects were
large prey (as posited for velociraptorines)... or something else.
The fact that the teeth of _Archaeopteryx_ and _Microraptor_ appear to
have been adapted for small prey (such as insects) means that it is
unlikely that they tackled large prey _Velociraptor_-style, IMHO.


The next part of David's stream of consciousness concerned how we
should not extrapolate the range of motion that mammalian (especially
therian) skeletons are capable of to dinosaurs.  No arguments there -
I've been banging on about this, but David expressed this sentiment
far more succinctly and articulately than I did.


> -- So far, I don't see a reason to assume any climbing or roosting in any
> dinosaur that wasn't able to fly into a tree. *Confuciusornis* may be an
> exception, but it had moderately grasping feet, huge curved claws on the 1st
> and 3rd fingers, an enormous deltopectoral crest on each robust humerus, and
> IIRC shorter legs than Archie, especially shorter lower legs; it was clearly
> better at trunk-climbing than Archie, even if not much.


I agree that no dinosaur roosted - at least not until
confuciusornithids and sapeornithids came along.  But it's worth
pointing out that many small non-pygostylian paravians show
modifications to the pes, in terms of the relative length and distal
position of the hallux. Yes, these changes could have been related to
predation.  But I think we're long past the point where *every*
evolutionary novelty in Theropoda is automatically tied to predatory
behavior.


> -- As someone mentioned, goats are fairly highly specialized rock climbers.
> Seeing them in a tree isn't any more surprising than seeing 300-lb rednecks
> in a tree. And apparently the tree kangaroos are the sister-group of the
> rock wallabies (*Petrogale*).


I've seen alternate phylogenies that place tree-kangaroos
(_Dendrolagus_) as the most basal taxon of extant Macropodidae (sensu
stricto; i.e., separate from Potoroidae, Hypsiprymnodontidae,
Balbaridae etc within the greater kangaroo clade, Macropodoidea).


> -- *Zhongornis*? Underrated? Isn't it rather an overrated juvenile
> *Confuciusornis*?


I've not heard this suggested before.  If _Zhongornis_ is a juvenile
_Confuciusornis_, it means that the latter had a 'free' tail as a
juvenile that only fused into a pygostyle with ontogeny.









Cheers

Tim