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MOSASAUR FRILLS & TAILS
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
Burnaby Building
Burnaby Road email: darren.naish@port.ac.uk
Portsmouth UK tel: 01703 446718
P01 3QL [COMING SOON:
http://www.naish-zoology.com]