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NEW PLIOSAURIDS A-PLENTY



Never thought I'd compare marine reptiles to buses but, well, you wait for ages
and none come along. All of a sudden, loads turn up at once. In a recent post
on the book _Ancient Marine Reptiles_, I noted that South America was revealing
a wealth of marine reptile taxa. How timely that...

GASPARINI, Z. 1997. A new pliosaur from the Bajocian of the Neuquen Basin,
Argentina. _Palaeontology_ 40: 135-147.

.. should appear. Pliosaurids are among the coolest beasts ever without a shadow
of a doubt but one group, the simolestines, are super-cool. They are famous for
a spatulate premaxilla that bears large caniniform teeth. Gasparini's new taxon,
_Maresaurus coccai_ is a simolestine that shares derived characters with
_Simolestes_. These pliosaurids may be related to the rhomaleosaurs - these were
large to huge Liassic forms and have a very complex taxonomic history (reviewed
in works by Taylor and Cruickshank).

_Maresaurus_ is one of only a handful of Bajocian marine reptiles and Gasparini
notes that the only other Bajocian plesiosaur is _Simolestes keileni _
Godefroit, 1994, (a new one on me) from France. _Simolestes_ is also known from
the Callovian of the Moscow Basin and England (type species _S. vorax_) and in
1991 _Thaumatosaurus indicus_ (Tithonian of India) was referred to _Simolestes_.
Another species, _S. nowackianus_ from the Oxfordian of Ethiopia, turns out to
be a teleosaurid croc! As this specimen consists only of a symphasis/premax
(can't remember which), the mistake is forgivable. Evidently the teleosaur was
doing the same thing as the simolestines - but just what is that??

Colin and I have discussed this intensively and I think it's something that
everyone who works on plesiosaurs does at one time or another. Dave Martill
(1991) suggested that _Simolestes_ was adapted for biting chunks out of
ammonites, perhaps while spinning about its long axis (he cited Taylor (1987)
but Taylor (1987) includes no mention of _Simolestes). I was guessing that
simolestines were Mesozoic cookie-cutters - certainly there were lots of big
things to bite (the Oxford Clay pachycormid fish _Leedsichthys problematicus_
was more than 12 m long and perhaps as long as 20 m). Eventually we plumped for
the old macropredatory generalist role - simolestines aren't huge as pliosaurids
go (approx. 6-8 m in life) but were certainly big enough, with robust enough
crania, to catch and dispatch other marine reptiles. Fishes, cephalopods, marine
tetrapods, _Leedsichthys_ tail fins (??): I think a pliosaur, like a gorilla
with a machine gun, can do pretty much whatever it wants.

CRUICKSHANK, A.R.I. 1997. A Lower Cretaceous pliosauroid from South Africa.
_Annals of the South African Museum_ 105: 207-226.

This is a revised account of the Upper Valanginian pliosaurid _Leptocleidus
capensis_. This taxon was first (Andrews 1911) thrown into the _Plesiosaurus_
scrap-basket. Andrews later compared it to _Leptocleidus superstes_, a species
from the English Wealden that he described in 1922 and Stromer (1935) realised
that it was different enough from _Plesiosaurus_ to not belong there: he created
the new genus _Peyerus_. As noted by Persson (1963), _Peyerus_ was actually
enough like Andrews' _Leptocleidus superstes_ to belong within the same genus..
hence it is sunk and the South African pliosaurid is _Leptocleidus capensis_
(Andrews, 1911). Having fun?

Leptocleidines represent another pliosaurid radiation that are evidently rather
more derived relatives of the rhomaleosaurs. They are rather likely to be late
surviving rhomaleosaurs in fact - both share a marked constriction at the
premax-maxillary suture. Eric - the famous opalised pliosaur from Downunder that
Paul Willis calls 'his baby' - is a leptocleidine. 

Interestingly, as Arthur C notes in this paper, southern hemisphere plesiosaurs
have a habit of turning up in lagoonal or near-shore sediments and 'hence a
totally marine association of these predacious aquatic reptiles is not
necessarily to be expected' (p. 208). Plesiosaurs are well known from some
freshwater deposits but how you would go about proving that a plesiosaur was a
strict freshwater denizen seems taxing. Isotope analysis comes to mind - this
has been applied to 'protocetid' whales and the results are encouraging.

"So, let's see - you've just killed two guards during your escape. How long do
you think before they'll have your termination authorised and _implemented_?"

Paul Willis is into _trains_?

DARREN NAISH