Marine Reptile Refs and Comments

[bh480@scn.org]

From: Ben Creisler bh480@scn.org

Here are a number of new articles on Mesozoic marine 
reptiles:

Maisch, M.W. &  A.T. Matzke, 2002. Observations on 
Triassic ichthyosaurs. Part IX. The first associated 
skeletal remains of Merriamosaurus n.g. (Ichthyosauria, 
Lower Triassic) and their bearing on the systematic 
position of the Omphalosauria.
NEUES JAHRBUCH FUER GEOLOGIE UND PALAONTOLOGIE: 
ABHANDLUNGEN 226(1) : 59-94.(OCT 2002) 
AB: The first association of skeletal remains of the Lower 
Triassic (Spathian) ichthyosaur Merriamosaurus n. g. 
previously known from isolated bones only, from the Sticky 
Keep Formation of Spitzbergen is described. For the first 
time cranial, vertebral and shoulder girdle material of 
this taxon can be confidently identified so that many new 
data of its osteology become available and an emended 
diagnosis of this little known genus and species can be 
provided. It is demonstrated that Merriamiosaurus is 
unrelated to the contemporaneous omphalosaurid 
Omphalosaurus nisseri, as claimed by previous authors, but 
that it is instead a typical basal longipinnate 
ichthyosaur. The material pertaining to Merriamosaurus 
does therefore not provide any evidence for the 
ichthyosaurian nature of the Omphalosauria. Comparison 
shows Merriamosaurus to be the most derived of the Lower 
Triassic ichthyosaurs currently known.

Comments: Merriamosaurus is replacement name for 
preoccupied Rotundopteryx Maisch & Matzke, 2000. It's 
interesting to see that Maisch and Matzke now accept that 
ichthosaurs are diapsids and are not closely related to 
omphalosaurs.
***
Maisch, 2002. A braincase of Temnodontosaurus cf. 
trigonodon (von Theodori, 1843)(Ichthyosauria) from the 
Lower Jurassic of Germany. Geologica et Palaeontologica 
36: 115-122. (Sept. 2002)

AB: A juvenile braincase of a medium-sized ichthyosaur 
from Banz, Franconia, south-western Germany can be 
identified as Temnodontosaurus cf. trigonodon because of 
the morphology of the parabasisphenoid, supraocciptal, 
opisthotic and stapes. It shows plesiomorphic features, 
such as rentention of a subdivided foramen for entrance of 
the cerebral ramus of the interal carotid artery, wiht a 
narrow spur of the parasphenoid in between, a ventral 
process of the opisthotic which bears part of the 
basiocciptal facet, and a moderately expanded proximal 
head of the stapes. This underlines the plesiomorphic 
morphology of Temnodontosaurus within the Neoichthyosauria 
and supports the phylogenetic position assigned to that 
genus in the analysis of Maisch & Matzke (2000), who 
placed Temnodontosaurus at the base of the 
Neoichthyosauria.
***
Nicholls, E. & D. Meckert, 2002. Marine reptiles from the 
Nanaimo Group (Upper Cretaceous) of Vancouver Island. 
Canadian Journal of Earth Sciences 39(11): 1591-1603. 
(Nov. 2002) 
Abstract: A new fauna of fossil marine reptiles is 
described from the Late Cretaceous Nanaimo Group of 
Vancouver Island. The fossils are from the Haslam and 
Pender formations (upper Santonian) near Courtenay, 
British Columbia, and include elasmosaurid plesiosaurs, 
turtles, and mosasaurs. This is only the second fauna of 
Late Cretaceous marine reptiles known from the Pacific 
Coast, the other being from the Moreno Formation of 
California (Maastrichtian). The new Nanaimo Group fossils 
are some 15 million years older than those from the Moreno 
Formation. However, like the California fauna, there are 
no polycotylid plesiosaurs, and one of the mosasaurs is a 
new genus. This reinforces the provinciality of the 
Pacific faunas and their isolation from contemporaneous 
faunas in the Western Interior Seaway. 
***
Lindgren, J. & M. Siverson, 2002. Tylosaurus ivoensis: a 
giant mosasaur from the early Campanian of Sweden.  
Transactions: Earth Sciences. Royal Society of Edinburgh: 
93(1): 73-93. 
Abstract: The nominal species Mosasaurus ivoensis from the 
latest early Campanian of the Kristianstad Basin in 
southern Sweden, is redescribed and assigned to the 
tylosaurine genus Tylosaurus on the basis of its dental 
and vertebral morphology. A partial skeleton (KUVP 1024) 
from the late Coniacian to earliest Campanian Smoky Hill 
Chalk Member of the Niobrara Formation in western Kansas, 
USA, was previously referred to 'M'. ivoensis. 
Nevertheless, its marginal teeth are markedly different, 
both in size and morphology, from those of topotypic T. 
ivoensis. 
Examination of type specimens and topotypic material of 
the nominal tylosaurines Hainosaurus pembinensis from the 
late early Campanian of Manitoba, Canada, H. gaudryi from 
the late Santonian or early Campanian of northwestern 
France, and H. lonzeensis from the Coniacian or Santonian 
of Belgium, indicates that all three may be Tylosaurus. 
The utility of isolated tooth-crowns in mosasaur taxonomy 
has been hampered by the often poor quality of the 
published illustrations of these fossils in combination 
with poor stratigraphic control. All Swedish remains of T. 
ivoensis, including 172 marginal teeth, 6 pterygoid teeth, 
several jawbone fragments and 12 vertebrae, were collected 
from a narrow stratigraphic interval corresponding to the 
highest biozone in the German eight-fold division of the 
early Campanian, providing the first good insight into the 
intraspecific dental variation in a tylosaurine mosasaur. 

Comments: This paper also straightens out the usage of 
Leiodon  Owen (preoccupied by a fish). Liodon Agassiz is 
the correct name. I discussed this problem on my online 
guide to mosasaurs, and it's good to see the info in print 
at last.

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I'll also pass along some comments from T. Lingham-Soliar 
about the supposed "nuchal fringe" on mosasaurs. He had a 
semi-popular article (Lingham-Soliar, T. (1999) What 
Happened 65 Million Years Ago: The Study of Giant Marine 
Reptiles Throws New Light on the last Major Mass 
Extinction, Science Spectra, No. 17:20-29) a few years ago 
that seemed to show some kind of fringe along the neck of 
a mosasaur:

Don't be confused re. nuchal fringe. If I'm not mistaken 
this structure is found only in agamid lizards. So it is 
therefore worth avoiding them in mosasaur reconstructions. 
However, what you see in my reconstruction is simply flaps 
of connective tissue (sorry if it was confusing), found in 
diverse groups of animals including crocodiles (note they 
are undulating and not compact needle like projections as 
in the nuchal fringe). Since connective tissue flaps are 
found so widely they do not jar scientific senses the way 
a nuchal fringe does because of the uniqueness of the 
latter to a particular systematic group of reptiles. One 
may think about connective tissue flaps the same way one 
may think of complex colour restorations in extinct 
animals - and I think reasonable especially in a semi-
popular article.