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Re: 11th specimen of Archaeopteryx



Don Ohmes <d_ohmes@yahoo.com> wrote:


> You may wonder why people want to "put Archie into trees", but given that:
> a) no terrestrial animal that is physically able to work it's way into a
> tree, yet does not occasionally do so comes readily to mind -- I have
> observed turtles, alligators, dogs, foxes, goats, leopards, lions, bears,
> rats, coons and 300 lb rednecks in trees at various heights and comfort
> levels


This particular argument comes up quite often: That many modern
terrestrial animals can climb trees in the absence of scansorial or
arboreal adaptations; so terrestrial theropods might have done the
same.  As I see it, there are two problems with this argument.


Firstly, modern mammals appear to be naturally pre-adapted to
arboreality and scansoriality.  Arboreality is likely to have been the
ancestral condition for therian mammals (marsupials + placentals)
(e.g., see Goswami et al., 2011, 108: 16333-16338).  Many modern
mammals still retain fairly mobile wrist and ankle joints, prehensile
hands and feet, and (because they are quadrupeds) fore- and hindlimbs
of comparable lengths.  Goats are a special case; their ability to
climb trees is an extension of their superb rock-climbing
capabilities, including the ability to gain purchase on narrow and
inclined surfaces.  So the "but even goats can climb trees" defense of
possible tree-climbing abilities in terrestrial theropods just doesn't
gel with the lifestyle of goats.


Secondly, if theropods *routinely* spent time in trees we might expect
to see arboreal specializations.  Turtles, alligators and 300 lb
rednecks might indeed be capable of climbing trees.  But they do not
do this routinely (I know this is true of turtles and alligators; I'm
assuming it holds for rednecks).  These are aquatic or terrestrial
animals that can scale trees, but would very much prefer *not* to be
up a tree, out of their comfort zones.  If Archie and other small
theropods did roost in trees, then this would constitute part of its
baseline behavior, and we would therefore expect to see some
branch-grasping abilities.  Unless they roosted in the apex of cycads,
of course.  But AFAIK no modern bird roosts or nests in cycads.


> b) "perching adaptions" are only useful on small limbs -- most
> plants over 3m in height have limbs large enough to sleep on,


Perching adaptations are essential for small limbs, and still useful
for large limbs.  I know there are modern birds that roost on thick
branches without a large, reversed hallux - such as the wood duck and
certain tinamous.  However, the wood duck has very short legs and a
very compact body - not at all like the cursorial proportions of
non-avian theropods (including Archie).  The tinamous have their own
tarsal adaptations for sitting on branches.  But most birds that
forage or hunt in the ground but roost in trees have a hallux capable
of perching - even  cursorial ones such as the secretary bird.  The
advantage that all these birds had over Archie and its kin was that
they can fly up into branches, rather than being forced to climb (or
leap).


> and c)
> Archie-types had claws fore-and-aft plus teeth, and so could indeed climb,
> however laboriously.


I suspect many "Archie-type" theropods did venture up in to trees far
more often than most non-paravian theropods.  There were changes going
on in the feet which point to *something* going on.  The 'advanced'
feathers point to refined aerodynamic behavior, but the pedal
modifications are much harder to make sense of - were they
scansorial/arboreal features, or associated with predation?  However,
it is intriguing that paravians evolved such an elaborate and
aerodynamic plumage long before the appearance of a specialized
perching pes.


> So I wonder why the drive to make poor old Archie sleep on the ground. It
> seems dangerous to me, and run-around-on-the-ground, sleep-in-trees
> lifestyles seem to be popular even today.


Considering how big certain predatory theropods were... how safe was
hiding up a tree for an "Archie-type" theropod?  Say Archie was being
stalked by a large predator... if Archie climbed up a tree, it may
just put itself at eye-level with the predator!


BTW, how dangerous was life for poor old Archie?  If it lived on
islands, its habitat might have been free of large predators.


> As previously stated -- a limited powerstroke really takes the steam out of
> ground-up muscle-powered scenarios.


I certainly agree with you here.  The "limited powerstroke" was not a
good recipe for fighting against the force of gravity (which is the
essence of "gound-up").






Cheers
Tim