Re: Mesozoic mountains?

[Tim Williams <twilliams_alpha@hotmail.com>]

Amtoine Grant wrote:

> My take on the theory that spinosaurs are derived coelophysids.

Is this the same theory that Gregory S. Paul proposed in 1988, in _Predatory 
Dinosaurs of the World_?

> Also, the gracile build, relatively similiar body proportions, and kinked 
> snouts - unless the latter trait evolved again in these theropods, wouldn't 
> be the first time.

If by "kink" you mean the elevation of the premaxillary tooth row relative 
to the maxillary tooth row, then this is present in _Baryonyx_ and 
_Suchomimus_, but not in _Spinosaurus_ AFAIK.  (Sereno et al. [1998] show a 
nice comparison of baryonychine and spinosaurine snouts.)

In coelophysoids, this "kink" is more of a diastema between the premaxillary 
and maxillary tooth rows, also called a subnarial "gap" or "notch".  I am 
not at all certain the conditions in spinosaurs and coelophysoids are the 
same.  I would argue the "stepped" snout of some spinosaurs and the 
subnarial gap of coelophysoids evolved independently.  Also note the 
position of the narial openings relative to the premaxilla-maxilla 
articulation - it is very different in coelophysoids and spinosaurs.

> If there indeed was a chain of periodic landmasses in the Atlantic Ocean, 
> this affinity with water lends reason to the piscivorous adaptations. It 
> would also explain the recently discussed purpose of the spinosaurs jaws 
> being suited for small(er) prey than more robust-jawed theropods such as 
> allosaurs, megalosaurs & tyrannosaurs.

Hmmm.... I was left with the distinct impression this discussion argued 
AGAINST piscivorous adaptations in spinosaurs.  Sure, they did catch fish 
(as shown by the fish remains inside _Baryonyx_'s torso).  But spinosaurs 
fed on young iguanodonts and pterosaurs as well - these were also 
"small(er)" prey".

> We all [should] know that when animals take up residence on islands, they 
> tend to experience a reduction in body size,

Big animals can certainly get smaller (e.g., island-dwelling ungulates and 
subungulates).  But small animals can get bigger once they establish 
themselves on islands that are free of predators.  Birds tend to fall into 
the latter category: moas (New Zealand), elephant birds (Madagascar), dodo 
(Mauritius).

> And no, I haven't taken into account Irritator from South America, but then 
> again none of know ALL the answers. Also, if I recall, spinosaurid sizes go 
> from smaller to larger starting in Europe with Baryonx, reaching their peak 
> with Spinosaurus in North Africa.

I believe that the type specimen of _Baryonyx_ is subadult, so the 
individual was not fully-grown when it died.


Tim