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RE: a little background



Jaime Headden wrote: 

> In
> passeriforms and falconiforms especially, the second digit claw is
> _very_ large, as long or longer than the length of the non-ungual digit 
> itself, and an interesting feature for birds that spend most of their 
> life up on branches.

This feature may be limited to anisodactyl perchers (such as passeriforms,
falconiforms, and galloanserine birds, to name a few).  I'll have to check.

>  I drew an example of how I conceived a small, Early Cretaceous
> tree-climbing non-avian theropod would have managed the job, 

The thing is, some modern avians climb trees with no more (and sometimes
considerably less) equipment than dromaeosaurids had.  The climbing ability
of young hoatzins is well-attested.  Japanese shearwaters also climb tree
trunks in an essentially quadrupedal fashion, though they use their elbows
(they have no hand claws) in combination with their feet.  With a strong
grasping manus, sharp claws (irrespective of their exact shape), and small
body size, I can easily imagine a small dromaeosaurid clambering up a tree.

> and it's online, but the link is not functioning for me (grr...) but if 
> anyone does get this (my site infor says it's there, file size and 
> everything) here it is:
> http://qilong.gq.nu/Sinornithosaurus in a tree.jpg

Try: http://qilong.gq.nu/Sinornithosaurus%20in%20a%20tree.jpg 

(where are the legs?)  Nice picture though. 


>All small eumaniraptorans have the claws, so this may have
> evolved as a climbing feature, reduced or adapted in later forms (birds
> lost it, then got it back, and developed other strategies to cope with
> climbing; 

Don't forget, birds can fly too, alleviating the need for specialized
tree-climbing equipment in order to reach the tree-tops (unless the bird is
specialized for vertical climbing, such as woodpeckers).  

Luis Chiappe has argued that the flight abilities of _Archaeopteryx_ and
other early birds removed the need for scansoriality (tree-climbing).  I
disagree.  I don't believe that primitive birds were capable of stationary
take-offs at ground-level.  Becoming airborne therefore required either (1)
a running take-off at ground-level or (2) a take-off from an elevated site.
In a heavily-wooded or uneven terrain, (1) would be difficult, but (2) would
be readily available.

>  I have this odd little hypothesis, running with it for a few years
> now: dromaeosaurs may have adapted into two predatory strategies, co-
> adapted with other theropods as Holtz has written, into a claws-first 
> or a head-first attacker. 

I have an equally odd hypothesis for the evolution of paravians (dromies,
troodontids, birds), which I think stacks up well against the fossil record
and most current phylogenies:  The enlarged sickle-claw represents a shift
from hands-first to feet-first predation.  The latter aided and abetted the
transformation of the forelimb into a wing, via the forelimb's decreased
engagement in predation.


> It is therefore plausible to posit that dromaeosaurines were
> head-first attackers, and may even have reduced ungual equippage as a
> result. They were tyrannosaur-analogues, as it were. Velociraptorines,
> on the other hand (manus), were claw-first, and use the snout to 
> manipulate prey ... but not take it down. 

Hmmm... this is remarkably similar to my own thought, with a few emendations
with regards to possible velociraptorine predatory behavior.


> This adapts the theory of the association to something that both Barrett
> and Tracy Ford have touched on previously (and which a friend and I were
> looking at publishing but now find redundant): *Protoceratops* was the
> aggressor, *Velociraptor* the jackal a defender. 

There's an old adage that "sometimes things aren't as they seem."  The
corollary of this, however, is that most of the time things *are* indeed as
they same.  I think the _Velociraptor_-_Protoceratops_ association is what
it seems to be: the former is the aggressor and the latter is the victim, as
Carpenter and others have proposed.  I'm not denying the plausibility of
other possibilties.  I just believe that the most common interpretation is
most congruent with current ecomorphological interpretations of dromies.


> Rostral teeth in the
> Mongolian--Chinese taxa are elongated and longest in the jaw in
> *Velociraptor*; in *Deinonychus* and *Dromaeosaurus* it is the opposite,
> and these all suggest much different feeding (and by inference, hunting)
> strategies.

I've associated the craniodental features of dromaeosaurids less with prey
seizure (which I think was the purview of the arms and hands) and more with
prey immobilization.  Here's one theory (rampant speculation, if you will):
long, slender jaws were useful in face-to-face confrontations since they
increased the distance between the tip of the jaws and the eyes when the
predator was endeavoring to nip or slash the victim's neck (admittedly
trying to maneuver one's jaws under the bony frill of a _Protoceratops_ is a
tricky business).  This wasn't a big deal when a dromie (such as
_Deinonychus_) was riding on the back of a bucking _Tenontosaurus_.  

>  Back to *Deinonychus* ... it is all circumstantial to place
> *Deinonychus* on the back of a struggling *Tenontosaurus*. 

The evidence is undeniably circumstantial.  It's also (as you note)
exceedingly risky to the predator - even for pack-hunters.  However, you are
assuming that the tenontosaur was in good health and not compromised in any
way.  Maybe the hapless tenontosaur was old, sick or ridden with parasites.
Moose would be virtually invulnerable to (non-human) predators if it wasn't
for one or more of these factors.



Tim 


------------------------------------------------------------ 

Timothy J. Williams 

USDA-ARS Researcher 
Agronomy Hall 
Iowa State University 
Ames IA 50014 

Phone: 515 294 9233 
Fax:   515 294 3163 

  
Tim