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High High Horse and the bi-pedal pterosaur challenge

High High Horse and the bi-pedal pterosaur challenge

The 'bi-pedal pterosaur challenge' post by Peters (26.01.03) highlights 
some central problems with the current debate. 

One of these is the constant misrepresentation of some contributors ideas 
that pterosaurs 'could not have walked, run or stood bipedally'. If you 
check the innumerable previous postings on this topic, not to mention the 
literature, it is clear that just about everybody, including me, accepts 
that pterosaurs had some bipedal ability (if only for landing and taking 
off). The extent to which they then continued to walk/run bipedally is 
the real problem. 

It seems to me that pterosaurs have lots of anatomical features 
consistent with plantigrade quadrupedality, but they also have some 
osteological features that are found in typical (extant) bipeds. 
Consequently, while anatomical and functional studies certainly give some 
strong hints they are not absolutely decisive. The same goes for 
homology, it may be, for example, that Sharovipteryx is a near relative 
of pterosaurs, but Sharovipteryx also has many features that are not 
found in pterosaurs, so it would be risky to assume that whatever 
locomotor style was employed by this beast (which is also not at all 
clear - may have been a quadrupedal trunk climber, for example), that 
exactly the same style was also true for basal pterosaurs. The same 
argument currently applies to any other taxon that is argued to be the 
nearest relative to pterosaurs. Analogy works best at the single 
structure or organ level, but even then its only really convincing when 
there is a great deal of anatomical similarity. At the whole organism 
level it is, at best, a dubious technique. Bipedal lizards as pterosaur 
analogs? The osteological/soft tissue anatomy and proportions of 
pterosaurs are not even vaguely similar to those of lizards so this is a 
poor case based on a dubious technique. 

Another problem with the current debate is the reluctance by some workers 
to face up to the strongest and most decisive evidence that we have for 
pterosaurs terrestrial ability: their track record. We now know of more 
than 30 localities ranging from the Middle Jurassic to the end Cretaceous 
and found on almost every major land mass. 1000's of tracks have been 
reported but, so far, not a single one shows pterosaurs proceeding 
bipedally on the hind limbs alone, or in a digitigrade fashion. If we are 
going to tackle the issue of pterosaur terrestrial locomotion then it 
MUST deal with this large and ever growing body of hard evidence. 
Certainly, if individuals wish to invest their time in speculating about 
other possible terrestrial locomotor styles fine, go ahead, but until 
there is some good solid evidence to back them up I don't see the need 
for anyone to take them seriously. 

Nuff said,


PS. High Horse reckons that, on the ground, pterosaurs preferred to lie 
on their backs and push themselves along using their feet, but, as this 
was rather undignified, they only did it when no one was looking. I think 
someones been putting 'stuff' in his feed, again. 

David M. Unwin PhD

Institut fur Palaontologie, MUSEUM FUR NATURKUNDE 
Zentralinstitut der Humboldt-Universitat zu Berlin
Invalidenstrasse 43, D-10115 Berlin, GERMANY

Email: david.unwin@rz.hu-berlin.de

Telephone numbers:
0049 30 2093 8577 (office)
0049 30 2093 8862 (department secretary)
0049 30 2093 8868 (fax)