Re: How Sauropods Got So Big

[Tim Williams <tijawi@yahoo.com>]

David Marjanovic wrote:

 
> Well, I think you should ponder the size of *Neoceratodus
> africanus* a bit more. I'll dig up what I have on that. 


I'm not actually arguing that _Spinosaurus_ specialized in preying on 
sauropods.  What I would say is that _Spinosaurus_ might have included 
sauropods in its diet (especially juveniles) as part of a generalist predation 
strategy.  This is based on work done by Sues et al. (2002) on the related 
theropod _Irritator_:


"The skull of _Irritator_ does not appear to be well-suited for catching and 
processing large, resistant prey.  Its structure differs from that in other 
large theropod dinosaurs such as _Allosaurus_ (Rayfield et al., 2001) and 
_Tyrannosaurus_ (Erickson et al., 1996), presumably reflecting different modes 
of feeding.  Most likely spinosaurid theropods rapidly and forcefully seized 
smaller prey, which was then processed by dorsoventral motion of the head 
facilitated by the powerful neck musculature.  (Extensive side-to-side striking 
movements of the head, as employed by extant crocodylians, appear unlikely in 
view of the narrow occiput as well as the weak development of the basal 
tubera.)  Whereas fish formed part of the diet in at least _B. walkeri_, there 
is nothing to suggest that spinosaurids were exclusively or even predominantly 
piscivorous.  Previous anatomical comparisons between the feeding apparatus of 
crocodylians and spinosaurid theropods were
 based only on superficial resemblances."


_Baryonyx_ was preserved with fish and small ornithopod remains in its 
skeleton; and a pterosaur neck vertebra from Brazil was found with a 
spinosaurid tooth embedded in it.  So spinosaurids evidently had a very varied 
diet.

As for the idea that _Spinosaurus_ preyed on lungfish such as _Neoceratodus 
africanus_ - why not?  (I'm not familiar with this critter - e.g. just how big 
was it?)  But I doubt that _Spinosaurus_ specialized on lungfish as a major 
food source.  At least one modern bird, the shoebill (_Balaeniceps rex_) of 
Africa, targets lungfish (_Protopterus_) as a major part of its diet.  Its 
'shoe-like' beak is very unlike the jaws of any spinosaurid: very big and wide, 
and hooked at the tip.  The shoebill's unusually shaped beak is said to be 
specialized for seizing lungfish.  



Cheers

Tim