Re: The retroverted hallux of birds

["Jaime A. Headden" <qilongia@yahoo.com>]

Henri Rönkkö wrote:

<So the first metatarsal does articulate to the second, huh? It doesn't
do that in other animals than predatory dinosaurs, does it?>

  Of all limbed vertebrates, I beleive no animals bear a metatarsal I
that contacts any other metatarsal without some rather unique
tranformation. Segnosaur dinosaurs have a metatarsal I that is
proximally expanded across the surface of metatarsal two at the tarsus,
or just below it. As Perle (1979, 1908, 1981) states, the metatarsals
are not found in articulation and as preserved and illustrated, did not
articulate as commonly seen, but much closer to each other, probaby
similar to other coelurosaur metatarsi. No published analysis, and I
couldn't demonstrate this for a while.

<You mean that this ball-and-socket joint joins the metatarsal (I) to
the digit (I)?>

  You got it. Its the tendons that limit the mobility of the proximal
phalanx. From personal examination, including a turkey, chicken, and
eagle.

<Not the Dorking Fowl!>

  Like I said, "I beleive" [sic]. :) I haven't done a whole lot of
comparative research on this particular bit (fusion) but so far, this
does not seem to be a very strong phenomenon, and it could be predicted
that a terrestrial bird would not require a fused mtI to mt II or the
rest of the metatarsal cannon, based on the theory of fusion as a
result of stresses to an arboreal bird, as related to landing pressures
in the pes, etc.. Why living ratites lack a hallux? Heh heh.... :)

=====
Jaime "James" A. Headden

  Dinosaurs are horrible, terrible creatures! Even the
  fluffy ones, the snuggle-up-at-night-with ones. You think
  they're fun and sweet, but watch out for that stray tail
  spike! Down, gaston, down, boy! No, not on top of Momma!

__________________________________________________
Do You Yahoo!?
Yahoo! Calendar - Get organized for the holidays!
http://calendar.yahoo.com/