[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Mesozoic mountains?

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.