Re: Size of *Neoceratodus africanus* and/or *N. tuberculatus*

[Tim Williams <tijawi@yahoo.com>]

Re-posting in correct format... apologies for the double-post... 

Graydon <oak@uniserve.com> wrote:


> There's a big difference between "dedicated piscivore" and "has
> adaptations for piscivory".
>
> Spinosaurids do seem to have some adaptations for piscivory. (At least,
> the big thumb claws and the jaw morphology would seem to argue for
> this.)


Yes, but I think that the piscivorous adaptations of spinosaurids have been 
over-emphasized.  The comparative biomechanical analysis by Rayfield et al. 
(2007) found the gharial (gavial) to be the closest modern analog for 
_Baryonyx_, but they held off from arguing that spinosaurids were 
dedicated/specialized piscivores.  Sues et al. (2002) argue that, while fish 
probably formed part of the diet in _Baryonyx_, "there is nothing to suggest 
that spinosaurids were exclusively or even predominantly piscivorous".


I'm not trying to dispute the hypothesis that spinosaurids fed on fish.  (After 
all, the gut contents of _B. walkeri_ is prima facie evidence that they did.)  
I'm only arguing against the hypothesis that spinosaurids were specialized 
piscivores, or even that fish (including giant lungfish) were even a major part 
of their diet.


As for the "big thumb claws" being an adaptation for catching ('gaffing') 
fish...

http://dml.cmnh.org/1998Apr/msg00254.html


Besides, an enlarged ungual of the first finger (pollex, or thumb) is also seen 
in torvosaurids.  Torvosaurids show no piscivorous adaptations in the skull.  
Also, in spinosaurids (as in torvsoaurids) the forearm is quite short, which I 
would interpret as poorly adapted for catching fish - especially if the animal 
was not submerged.  Speaking of which... 


> Does it _need_ wading adaptations?  Multi-ton animals
> have a lot of trouble walking on top of the mud no matter what their
> feet look like.


I take your point; but I was talking more about aquatic (or semi-aquatic) 
adaptations in general.  If fish were a major part of their diet, and 
spinosaurids entered the water to catch them, wouldn't we expect to see at 
least some aquatic adaptations in the postcranium?  Maybe some extra ballast in 
the skeleton, like we see in many (semi-)aquatic reptiles and mammals?  For 
example, hippopotamids and indohyids (both suggested as possible sister taxa to 
whales) show thicker limb elements as a result of osteosclerosis, to improve 
bottom walking. 


Cheers

Tim