Re: CURSORIAL STEGOSAURS?

["Matthew Bonnan" <mbonnan@hotmail.com>]

Sent a message earlier to the list, but it vanished into thin air!  If it 
shows up, you'll note it is very similar to this one. =)  I guess it went to 
George, as he has already responded to most of this on list, so do what you 
will with this less than stellar version.

Matt Bonnan


DinoGeorge writes:
"Metatarsal V was likely present in all known
stegosaurs as the usual dinosaurian splint or vestige, in which form it was
undoubtedly a functional part of the tarsal/metatarsal assembly, likely a
site of muscle or tendon attachment and leverage (otherwise it would
eventually have vanished, as it apparently did in ornithomimids)."

The presence or absence of a digit is not necessarily due to use or disuse.  
Current embryological studies indicate that digit loss or retention can be 
caused by the historical constraints of the genetic program -- digits are 
merely iterations on a digital arch that forms from the ulna posteriorly to 
the radius anteriorly in the embryo.  Their formation or non-formation is 
therefore not directly related to their use or disuse as adults.

"But I was talking about digits, not metatarsals."

Digit refers to both metapodials (metacarpals or metatarsals) and phalanges. 
 All comparative vert and embryology texts use and define digit in this 
fashion.

As for the bipedal origin of stegosaurs, likely yes, but our fossil record 
for stegosaurian ancestors is, as far as I know, relatively poor.  However, 
all quadrupedal dinosaurs probably were descended from a bipedal ancestor, 
including sauropods.  The differences that George notes in the forefoot and 
hindfoot of stegosaurs are not unique and occurs in all quadrupedal 
dinosaurs.  This is part of a body of evidence that suggests sauropods, 
thyreophorans, etc., are secondarily quadrupedal (i.e., this is a hypothesis 
that has strong support).  I know that George does not think that sauropods 
were bipedally descended (as did Charig et al., 1965).

This is not as well written as I had done the first time, but I have no 
saved copy of that draft! =)

Matt Bonnan
Dept. Biological Sciences
Western Illinois University
Macomb, IL 61455*
*as of August 14, 2001.

_________________________________________________________________
Get your FREE download of MSN Explorer at http://explorer.msn.com/intl.asp