Re: Deinosuchus and Tyrannosaurus

[Adam Yates <zooamy@zoo.latrobe.edu.au>]

On Sun, 22 Jun 1997 Dinogeorge@aol.com wrote:

> 
> Dorsal scutes are a primitive feature for practically all of Archosauria, and
> crocs retain this feature presumably because it is useful to have the back
> protected. It could well have arisen in early archosaurs for protection from
> above from larger predators, such as therapsids. (Incidentally, therapsids
> did not have dorsal scutes. Although I'm not terribly familiar with the
> group, I can't recall any dorsally armored therapsids. This is probably why
> they were able to evolve finbacks and such.)
> 
Nice speculation, however one group of armoured tetrapods did evolve 
sail backed forms, the dissorophoid temnospondyls. You can see a 
gradation of forms from things like Cacops with just a vetebral row of 
dorsal osteoderms to Aspidosaurus with tall peaked osteoderms fused to 
the neural spines to Platyhistrix with very elongated neural 
spine/osteoderm structures that rival Dimetrodon in proportion. As an 
aside though the tips of these spines probably protuded free, the 
distribution of ornament suggests that a web of skin extended at least 
some of the way up the "sail".