Re: The Continuing Story of Gliders to Dinosaurs

[NJPharris@aol.com]

In a message dated 9/29/99 2:12:14 PM Pacific Daylight Time, 
granth@cyberus.ca writes:

> Now, could a jerboa-analogous, cursorial, leaping _Marasuchus_ have had
>  descendants adapted for arboreality, which then *retained* the leaping
>  ability and evolved into indri-analogous vertical tree-leapers?  This would
>  make sense.  Any problems with the idea?

Well, just that it would be difficult to get a theropod into an indri-like 
position.  Indris, and their relatives the sifakas, have shallow bellies, 
divergent legs, and gripping feet so that they can hug tree trunks.  
Incidentally, their widely diverging legs are what cause the odd-looking 
jumping style of indris, as discussed earlier.  It is also what causes the 
sifakas to adopt their bizarre, half-sideways loping motion while on the 
ground.

Theropods, OTOH, have deep bellies (a consequence of the position of their 
pubic bones), narrow hips with non-diverging legs, and feet poorly adapted to 
gripping (at least in the species we have fossil remains from).  Thus, when a 
theropod climbed a tree, its body would be out away from the trunk and its 
feet tucked in beneath the body--not very much like a tree-hugging indri.

Perhaps a better analogue would be a cat climbing a telephone pole.  They 
wrap their arms around the log and dig in their hind claws like loggers' 
spikes.  I can see some very advanced maniraptorans, with their long arms and 
hands, large claws, and retroverted pubes, climbing vertical trunks like 
this.  I have trouble, however, imagining behavior like this in the 
short-armed, small-handed, propubic ceratosaurs and herrerasaurs.  They just 
don't fit right.

--Nick P.