ASYMMETRICAL SPINES

[darren.naish@port.ac.uk]

On the neural spines of _Amargasaurus_ and other sauropods, Brian 
Franczak wrote...
 
> I would expect near-perfect bilateral symmetry in the living animal, 
> no? If the spines are not straight or parallel, that would indeed 
> seem to indicate to me distortion after death and fossilization. Can 
> anyone supply a reason to think otherwise?

Can't really answer Brian's question but...

Hiccups in  bilateral symmetry are of course not uncommon and 
fusions, morphologies of processes, and such things as pleurocoels 
and foraminae are not infrequently asymmetrical. I have seen strings 
of vertebrae where the bones are fully fused up on one side, but not 
on the other (in some birds, this may be due to viral infection - 
P. Davis pers. comm.). And there is a very interesting little 
dinosaur specimen, currently in press, that has some bearing on this 
issue... 

Given the incidence of pathology and breakage in the spines of living 
animals that have tall neural spines (obviously I have no statistics 
on this, but am going from what I have seen in diagrams, photos and 
specimens), we might predict high-spined dinosaurs with bifurcating 
spines to often be asymmetrical. Also, some high-spined dinosaurs are 
famous for having damaged spines. _Becklespinax_ exhibits what 
appears to be severe vertebral trauma and Stromer's figures of 
_Spinosaurus_ have neural spines that are not straight in cranial 
view, but wiggle from side to side. Though this has been generally 
assumed to represent post-burial deformation, is this really 
definitely the case? Don't know.

"Crocodiles are in no way a relictual or degenerate group"
Carve this into your desks and foreheads

DARREN NAISH
darren.naish@port.ac.uk