MESOZOIC VICARIANCE, MOSASAURS, ERYTHROSUCHIDS.

["Darren Naish" <dwn194@soton.ac.uk>]

Right, having just done my weekly trawl-through-the-periodicals bit, I
have a few interesting pieces not - ASAIK - previously reported on
this list. I was really looking for the new ankylosaur paper by Walter
Coombs, but the issue of _Palaeontology_ in which it is published is
missing. That's university libraries for you. Having gotten hold of
Sereno et al's _Science_ paper, I now have the questions I asked
answered. I see they're still plugging a Spinosauroidea
(=Torvosauroidea Sereno et al 1992).

First off, non-dinosaurs..

GOWER, D.J. 1996. The tarsus of erythrosuchid archosaurs, and
implications for early diapsid phylogeny. _Zoological Journal of the
Linnean Society_ 116: 347- 375

Gower reassesses the morphology of the erythrosuchid tarsus, showing
that the two _Erythrosuchus africanus_ specimens *are* from this
taxon, and similar to the tarsi of other early archosaurs. This tarsus
is poorly ossified with calc., astrag. and two distal tarsals
(surprises all round then). The tarsi of _Vjushkovia triplicostata_
and _Shansisuchus shansisuchus_ are similar in being dorsoventrally
compressed, with a lateral tubercle and no perforating foramen.
Bottom line is that the erythrosuchid tarsus is more derived than
usually supposed, and though I haven't read it all yet I'm guessing
Gower rearranges some of the taxa in the archosauromorph cladogram -
the abstract says: "The tarsal morphology of several other
archosauromorph taxa is reviewed and many details are found to be at
variance with the literature".

CALDWELL, M.W. 1996. Ontogeny and phylogeny of the mesopodial skeleton
in mosasaurid reptiles. _Zool. Jour. Linn. Soc._ 116: 407-436

This paper really kicks ass. It's incredibly confusing though, mainly
as ontogenic stages of so many taxa are described and figured, and at
least 5 cladograms are to be seen. The patterns of ossification in the
mesopodials are examined and mapped onto phylogeny in order that the
distribution of ontogenetic characters be determined: outcome is that
we get a sequence of elements ossifying in the carpus and tarsus
revealing some very interesting evolutionary trends. What I find
fascinating is that paedomorphosis 'is recognised as a dominant
pattern in the evolution of mosasauroid limbs'.

The phylogeny has Mosasauroidea consisting of _Aigialosaurus buccichi_
+ Mosasauridae (outgroups in one of the cladograms, successively more
distant, are Varanidae, Helodermatidae and
Necrosauridae). Mosasauridae consists of a new taxon (unnamed), the
'Dallas aigialosaur', the Halisauromorpha (includes _A.  dalmaticus_
and the _Halisaurus_ sp.) and the Natantia. Natantia was coined either
by deBraga and Carroll (1993) or Bell (1993) - I don't know - but if
you have Benton's 'Vertebrate Palaeontology' you will recognise it as
the hypothetical clade he invents for fish, marine reptiles and
cetaceans (when explaining monophyletic versus polyphyletic
taxa)... anyway... Natantia consists of Russellosaurinae (is this new
to this paper?) - the tylosaurs and Plioplatecarpini (tylosaurs not
given a tribe name in the cladogram I'm looking at) - and Mosasaurinae
- _Clidastes_ sp, Globidensini and Plotosaurini. Phew!  Don't you just
lurve taxonomy....

I'll have to deal with the Mesozoic vicariance bit of my subject title
in another message. Right now I've gotta get something to eat... Oh
yeah, Tom - Scott Sampson does _not_ have a new paper out in the
Zool. Jour. Linn. Soc.  Guess we'll just have to wait....

"We hear that you're from India"
"By the eight arms of Vishnu I _swear_ that is a lie!"

DARREN NAISH
dwn194@soton.ac.uk