MOSASAUR FRILLS & TAILS

[darren.naish@port.ac.uk]

I'm going through my email backlog, and have seen just the one below 
from Ben Creisler. Concerning the presence of a 'nuchal frill' on 
mosasaurs, Ben explained that..

>  However, Williston later realized his error and printed a short           
> retraction in 1902. This correction has forgotten and overlooked, 
> and as far as I can determine, there is NO preserved fossil 
> evidence for a frill along the neck or back of mosasaurs. 
> All fine and good EXCEPT that Lingham-Soliar restored 
> Mosasaurus with some kind of low crocodile-like dermal 
> frill along its back in his recent 1999 article in Science 
> Spectra! Now I'm confused. What's the story? The frill is 
> gone...or not?  

Ben, you are right in thinking that there is no evidence for a frill in 
mosasaurs and, as Williston (1902) explained, the original evidence 
for it was erroneous. Incidentally, this subject was discussed here on 
the list some years ago - Gary Kerr, Tony Thulborn, and Tracy Ford all 
helped me with questions. Apparently most preserved impressions of 
mosasaur skin reveal smooth, diamond-shaped scales, but there are 
some _Clidastes_ scales that are supposed to have a mid-line keel like 
that seen in some living rough-skinned vipers and rattlesnakes. Surely 
this would increase drag in a swimming animal. Perhaps the mosasaur 
experts on the list can help? Anyway, there are no preserved sagittal 
fringes of tall scales/dermal spines in any mosasaur. 

Not only is the original evidence for the mosasaur frill erroneous, 
there is positive evidence against the presence of such a structure: 
namely, their phylogenetic position - nuchal frills in squamates are 
restricted to iguanians (however, some of the smaller varanids do have 
keeled, blade-like caudal scales..). Basically, if a contemporary artist 
depicts a mosasaur with a skin frill, they have not done their 
homework, and I suspect that this would be the case for the artist that 
did the pictures for the Lingham-Soliare 1999 article (errmm.. unless 
the pictures were done by Lingham-Soliare himself - I know he is a 
competent artist. If that is the case I'm not sure what he's playing at).

> Also, I can find no record of fossils showing that 
> Clidastes had an extra soft-tissue sea-snake-like 
> expansion of the enlarged flattened bones at the end of it 
> tail, as commonly depicted.

There are elongated neural spines and a slight tailbend in _Clidastes_ 
and some other forms, suggested a slightly expanded distal tail fin. Dan 
Varner and Bruce Schumacher had a JVP abstract on this some years 
back and they are still working on this idea. Incidentally, Robert 
Bakker has been restoring his mosasaurs with well-developed tail fins 
and dorsal fins (!). I think this is pretty fanciful.


DARREN NAISH 
PALAEOBIOLOGY RESEARCH GROUP
School of Earth, Environmental & Physical Sciences
UNIVERSITY OF PORTSMOUTH
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