Re: 'SAILBACKS' (was Re: Deinosuchus and Tyrannosaurus)

[Dinogeorge@aol.com]

In a message dated 97-06-24 09:51:41 EDT, Pieter.Depuydt@rug.ac.be writes:

<< Well if my memory does not play tricks on me, also non-dinosaurian 
 archosaurs already developed various sail-backed forms by Middle and 
 Late Triassic times, for example the odd Lotosaurus (a rauisuchian 
 according to some) and the enigmatic Spinosuchus, with laterally 
 flattened elongated neural spines. 
 There is also a record of a creature called Ctenosauriscus, probably 
 archosaurian (or archosauriform?), with very elongated, spiny, rod-like
 neural spines, very reminiscent of those from the early Permian sail-backed
 sphenacodontid 'pelycosaurs'. A similar spine has been found in the Middle 
 Triassic of Devon, UK. >>

You are quite correct. I should note that none of these genera was dorsally
armored; they had lost the primitive archosaurian dorsal armor secondarily.
_Spinosuchus_ is a very interesting case (no pun intended, but if you see the
pun, award yourself ten points), since the vertebral anatomy strongly
resembles that of the much smaller animals _Megalancosaurus_,
_Drepanosaurus_, and _Dolabrosaurus_ and suggests it should be classified in
the same family. The spines of _Spinosuchus_ aren't laterally flattened but
are rather spikelike, with very prominent craniocaudal dorsal expansions,
unlike the spines of _Lotosaurus_ and _Ctenosauriscus_, which are flattened
and lack craniocaudal dorsal expansions. The sail of _Lotosaurus_ is much
lower than that of _Ctenosauriscus_. Perhaps these sails were connected with
thermal aspects of changing metabolic regimes; who knows? But the elongate
spines of _Megalancosaurus_ and its relatives seem to have more to do with
controlling body flexibility and operating a prehensile tail in an arboreal
environment than with thermoregulation.