Re: Bipedal lizards & pterosaurs, point 4 addendum

[david peters <davidrpeters@earthlink.net>]

>>>Just went to the files over the lunch hour. 
Let's take care of that darn point 4.

Darren wrote: On point (4), as shown
by Russell and Bauer (1992), the most important anatomical
correlate of bipedality in lizards is the presence of a large m.
caudofemoralis longus that inserts relatively distally on the
tail (thus explaining why the lizards that run bipedally are
the same ones that don?t practise caudal autotomy).

>>> Fig. 1 of same ref shows a series of proximal caudal segments in dorsal 
>>> view for five different lizards. A-C are lizards, like the gekko, which are 
>>> known to never even attempt bipedal excursions and they rely greatly on 
>>> lateral undulation during locomotion. They all have meaty tails as 
>>> indicated by the transverse processes which are substantial and continue in 
>>> some cases off the figure distally. D-E are lizards, like the basilisk, 
>>> which have been known to attempt bipedal excursions and during fast 
>>> locomtion rely less on undulation. These lizards, especially the basilisk, 
>>> appear to have a less meaty tail as indicated by a reduction of the 
>>> transverse processes caudally. In fact, the basilisk has lost all trace of 
>>> transverse processes after the first few caudal vertebrae, reminding one of 
>>> a typical prolacertiform tail.

>>> Interesting side fact: Going back to the literature reminded me that some 
>>> lizards run bipedally with the tail held at right angles to the spine -- 
>>> vertically. [ On the web ->  
>>> http://www.biology.uc.edu/faculty/jayne/videos.htm] This is interesting 
>>> because in Longisquama and the most primitive pterosaurs (notably MPUM 6009 
>>> and Austriadactylus) the anterior and posterior processes of the ilium 
>>> diverge at a right angle. The posterior processes were so long that they 
>>> must have 'colonized' a half dozen caudals between them so that the tail 
>>> would have to be held at right angles to the spine all the time.  Kinda 
>>> like a lemur. Yes, this was gleaned from computer scans, but Wellnhofer 
>>> showed us a similar pelvis in Toulouse that is about to be published. 

Thank you Darren for digging into the bipedal lizard literature -- something 
I've been begging the 'pterosaur experts' to do for years. Sorry you missed 
some of the connections that helped me draw the conclusions I've been preaching 
for about a decade now. Hopefully this and the previous email will help you 
understand where pterosaurs are coming from. It's really an unshakeable model.

Best wishes on your studies!

David Peters
St. Louis


Thanks to Darren for the ref:

Russell, A. P. & Bauer, A. M. 1992. The m. caudifemoralis
longus and its relationship to caudal autotomy and
locomotion in lizards (Reptilia: Sauria). _Journal of
Zoology_ 227, 127-143.