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

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

> Date: Thu, 10 Nov 2011 16:42:55 +1100
> From: tijawi@gmail.com
> To: dinosaur@usc.edu
> Subject: Re: Perching, climbing, roosting was Re: 11th specimen of 
> Archaeopteryx
> Don Ohmes <d_ohmes@yahoo.com> wrote:
> > From an evolutionary perspective, the idea that merely roosting in a tree
> > would counteract a terrestrial ground-foraging lifestyle and alter
> > foot-design in a clawed animal that can already climb is the special
> > pleading.
> It wouldn't "counteract". The hallux could easily have become better
> adapted for grasping branches, without interfering with a
> ground-foraging lifestyle.
> Modern ground-foraging birds show us how
> it can be done (turkeys, peafowl, secretary bird, etc etc). There is
> no reason to assume that ground-foraging and roosting impose competing
> selective pressures on the foot. Turkeys etc do both quite well.

There was a statement earlier in this thread...something along the lines of 
"yes, and those are all descended from perching birds."
> > Ditto the claim that re-arranging foot design to satisfy somewhat
> > anthropomorphic assumptions about roosting stresses is a trivial matter,
> > design-wise...
> I don't see how these assumptions are anthropomorphic. Some
> "re-designing" of the foot was achieved outside the bird clade - look
> at the foot of therizinosaurids or _Balaur_ to see how the hallux can
> be put to good use.
*tries to imagine the tree a grown therizinosaur could sleep in the branches of*
> > Is the flamingo's foot shaped while it sleeps, or while it is foraging?
> I'm afraid I don't understand the relevance of the flamingo. AFAIK,
> it doesn't perch or roost in trees. It spends its days (and nights)
> on terra firma.
 I think his point was a rebuttal of the claim that a bird's (or protobird's) 
feet are shaped by where it sleeps.
> > The foot is already optimized to standing around.
> >
> > "There is no direct evidence of roosting in (...)" is a correct statement.
> > Claiming that simple roosting would necessarily be evident in the bones once
> > the physical capacity to do so is established, is NOT supportable.
> Again, roosting is not as "simple" as you make it sound. It is not
> simply standing/crouching/huddling/squatting on a bough or branch as
> you would on the ground. Even a small shift in position can be fatal,
> so it helps to be adequately secured to the substrate (bough, branch,
> whatever). Both gravity and an uneven substrate are conspiring
> against you.
 By that logic, there shouldn't be anything (that hops or flies) living in 
deserts - that substrate actually moves.
Heck, there shouldn't be rock wallabies  (gravity + uneven rocks + some rocks 
come loose)  or thorny forest lemurs  (gravity + thorn-covered branches)
> > Foraging is out, because their feet are not adapted to foraging in trees.
> > Daily foraging in trees will indeed quickly change the extremities, being a
> > locomotor activity -- keyword = "activity"...
> Briefly, climbing up trunks and foraging within the crown promotes
> different adaptations.

you have to get to the crown in order to feed in it.