RUNNING STEGOSAURS

[Tetanurae@aol.com]

George Olshevsky wrote:                  
> Ancestral stegosaurs were probably excellent runners, to the point that the
> first digit of the foot and even the first metatarsal were entirely lost.


I need to interject here....  Excellent runners compared to what?  The most
basal stegosaurs I am aware of are Huayangosaurus and Dacentrurus, both of
which were probably quite a bit less spritely than Stegosaurus itself.  
Dacentrurus was positively massive, probably bigger than Stegosaurus itself.  
All non-stegosaurin stegosaurids (Stegosaurini = Stegosaurus, Wuerhosaurus,
and Monkonosaurus [no, the name is not official, just something I made up to
facilitate discussion]) were even further slowed by the presence of sometimes
massive shoulder spines, and thicker plates.

Additionally, Minmi, which is probably something close to a basal ankylosaurs
was not built for speed, nor were ankylosaurians or scelidosaurids, nor any
stegosaurs.  I know you don't believe, for whatever reasons that are still
closely guarded secrets, that Thyreophora is an exclusively monophyletic
taxon, but everyone else treats it as such, as will I, unless presented with
evidence to the contrary.

You should also note that animals that tend to cover themselves in armor tend
to be slow: turtles, glyptodonts, pangolins, ankylosaurs, titanosaurs, and
crocodiles (on land).  Granted, not every armored animal is slow, but
covering yourself in armor tends to a) slow you down because of increases
mass and b) protect you from faster predators.

All known stegosaurians had columner, or nearly columner limbs, as did the
closest known outgroups to stegosaurians (Minmi, ankylosaurs,
scelidosaurids), so it is unlikely that any, as of yet unknown stegosaurians
were moving at anything faster than a trot.

Anyway, back to the original questioner's querry concerning bipedal running
in stegosaurians...  Greg Paul suggested way back in 1996, that stegosaurs as
well as apatosaurine diplodocids and dicraeosaurids walked around bipedally:

http://www.cmnh.org/fun/dinosaur-archive/1996Oct/0113.html

This was later written up in a short article for the now defunct dino-mag
"Dinosaur Discoveries."  I am moving in two weeks and have no access to my
lit at the moment, otherwise I would dig out the full reference.

Anyway, sorry for the disjointed post, but bottom line is this: stegosaurians
were not going anywhere fast because of a) columner, or nearly columner limb
joints and b) massive armor.  Additionally, phylogeny dictates that there
were probably not any mystery ghost stegosaurs that were little and spritely
because all of the closest outgroups are rather large and slow.


Peter Buchholz
Tetanurae@aol.com