Re: Pterosaurs and birds, was Re: birds and pterosaurs

[Michael Habib <mhabib5@jhmi.edu>]

> > Actually, pseudodontorns were pretty common.  Granted, there were 
> > more large pterosaurs for a longer period of time.  However, I 
> > suspect the reason for the abundance of large pterosaurs was that 
> > most Cretaceous forms were marine soaring birds,
>
> I'm not aware of any large soaring birds that overlapped the 
> pterosaurs.  I thought the big pseudodontorns developed after the 
> demise of the pterosaurs. In fact, I don't know of any soaring birds 
> of any size that overlapped the pterosaurs (there probably were some, 
> a few -- but I suspect that the more efficient pterosaurs kept their 
> numbers down).

I'm sorry for the confusion; I never meant to imply an overlap in time. 
 Pseudodontorns were mid to late Cenozoic animals (I believe the 
largest-bodied taxon is Miocene in age).  I only meant that 
pseudodontorns were reasonably common during the time they existed, as 
a response to the argument that large soaring birds were rare when they 
existed.

> > but this is not the same as being 'more efficient' or 'less 
> > restricted' (I suspect it was partially to do with the relatively 
> > lower wing loadings of pterosaurs per unit mass.)
>
> In the bigger sizes, pterosaurs didn't have lower wingloadings per 
> unit mass.  Pterosaurs had relatively more muscle in the inner arms, 
> and they tended to have larger necks and heads than birds.  For 
> example, a 5 meter span Anhanguera piscator could be expected to mass 
> about 18-19 Kg, with only a minimal fat load.  A 4.8 meter span 
> Quetzalcoatlus species could be expected to mass well over 20 Kg.

Ah, gotcha.  Thanks for the clarification.  I admit my data there were 
a bit out of date; Crawford Greenwalt compiled a massive dataset of 
wing parameters for birds, bats, and pterosaurs (the latter 
reconstructed, of course) in 1962.  According to that dataset, the 
large pterosaurs had slightly lower loadings than expected for birds of 
that size (using the scaling relationships found in the monograph).  
Frigatebirds were the most similar.  Actually 20 kg doesn't seem that 
large to me; wandering albatrosses have been caught and weighed at 
16kg.  But in general, I suspect that the data I have are slightly out 
of date (for the reconstructions; presumably the extant species were 
correctly measured).


Thanks for the comments, always appreciated.
--Mike