THE PLESIOSAUR DIRECTORY NEWSLETTER. ISSUE 6
(Sunday 26th August 2007)
Events conspired against me producing a newsletter earlier this month, but I’m
back on track now. If you have any comments or recommendations on how I can
improve this newsletter, if you want to recommend a link, image or PDF to feature
in a future issue of the newsletter, if you have any corrections, or if you
think you are the first to find Paddy, please contact me at plesiosauria@gmail.com.
Thanks! Adam
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NEWS
SVPCA plesiosaur talks: abstracts
The 52nd Symposium of Vertebrate Palaeontology and Comparative Anatomy will
take place in Glasgow. Recent years have seen an increasing number of talks
and posters dedicated to plesiosaurs, and with eight such presentations scheduled
for Glasgow, this year is no exception. The titles and abstracts are as follows:
TALKS (X6)
The virtual and physical preparation of the Collard Plesiosaur
Nigel R. Larkin
The ‘Collard Plesiosaur’, found in 2003 in Bridgwater Bay on the
Somerset coast, has been described as ‘probably the best preserved and
most scientifically valuable fossil plesiosaur to have been found in the UK
for at least 150 years, possibly ever’ (Richard Forrest, SPPC/SVPCA 2005).
The skeleton is almost complete and variably-mineralised.
The skeleton (possibly a juvenile Rhomaleosaur) was preserved in Lower Liassic
Kilve Shales - a fine-grained, thinly laminated rock containing little or no
cement. Held together by compression, this lithology is notoriously susceptible
to fluctuations in humidity, severely compromising the integrity of specimens
once dry.
The priorities for the project were to arrest shale delamination caused by environmental
fluctuations and to prepare the specimen for research. The specimen appeared
to be well fossilised in a homogeneous, un-cemented matrix, offering excellent
potential for X-radiography. Therefore before preparation commenced the specimen
was X-rayed and CT-scanned with stunning results, despite some of the limb bones
not being well mineralised. This virtual preparation helped to inform the subsequent
physical preparation of the material.
Investigations were undertaken to select the most suitable tools, materials
and techniques to conserve and prepare the specimen. Attempts to consolidate
matrix samples with the methacrylate co-polymer Paraloid B72 were generally
unsuccessful – the shale layers distorted and delaminated. However, B72
was successfully applied to the sides of the specimen blocks providing a humidity
seal.
Mechanical preparation commenced with the removal of underburden, greatly reducing
the specimen’s weight. The use of a scalpel proved to be the most appropriate
technique for developing its surface and exposing the skeleton, removing one
paper-thin layer of shale at a time.
Processes and flanges: the evolution of the plesiosaur braincase and posterior
palate
Mark Evans
The aquatic adaptations of plesiosaurs have resulted in two obstacles to unravelling
their evolutionary history: morphological “simplification” and a
high degree of homoplasy. The braincase can be thought of as being “isolated”
from the animal’s constraining aquatic medium to a certain extent, and,
while not immune from these obstacles, it provides an important morphological
dataset of flanges and processes which deserves attention.
Material examined includes a specimen from the Early Jurassic (Pliensbachian)
of Gloucestershire, England, representing a new taxon, and specimens of the
early Jurassic taxa Thalassiodracon hawkinsii, Rhomaleosaurus megacephalus and
Occitanosaurus tournemiensis. The Pliensbachian specimen shows an anterior process
of the basioccipital projecting between the conjoined pterygoids and the posterior
processes of the parasphenoid on the midline. This apparently novel structure
can also be recognised in other early plesiosaurs such as R. megacephalus and
T. hawkinsii, where it was previously thought to be formed by the basisphenoid
(O’Keefe, 2001).
The nature of the variable contact of various pterygoid flanges with one another
and the basicranium has also been investigated. This has been found to differ
from the published accounts in T. hawkinsii and O. tournemirensis. A review
of this area of the plesiosaurian skull shows that the pterygoid flanges underplate
the basicranium in different ways in different taxa. This necessitates a reassessment
of the way that these structures are coded in phylogenetic analyses, and a revised
scheme is proposed.
A nearly complete elasmosaur from the Late Cretaceous Bearpaw Formation of
Alberta, Canada
Donald M. Henderson
In May of 2007 the partial remains of a large marine reptile were uncovered
by excavating equipment at the open pit ammolite mine operated by Korite International
approximately 20km south of Lethbridge in southeastern Alberta. This mine is
situated in sediments that were deposited in the short-lived, epeiric Bearpaw
Sea that covered much of west-central North America in the Late Cretaceous (Tsujita
and Westermann, 1998). For three weeks in June of 2007 a crew of 6 from the
Tyrrell Museum uncovered and removed the nearly complete remains of an 8m long
elasmosaur. The specimen is located in a weakly bedded black shale which yields
abundant ammonites of the genus Placenticeras sp. at particular horizons (Tsujita
and Westermann, 1998). The skeleton lies approximately 2m below a 20cm thick
altered volcanic ash layer that forms a unique marker bed in the mine, and should
provide a minimum radiometric age for the specimen. At present the entire axial
skeleton, pelvic and pectoral girdles, and the proximal halves of all the limbs,
and a large quantity of gastroliths have been recovered. The anterior-most cervicals
have been identified, but there is no indication of a skull yet. A complete,
mid-section cervical vertebrae has an overall height of 30cm and a centrum length
of 14cm. The largest gastrolith seen so far has a diameter of 15cm, but stones
as small as 2cm are also present. Two teeth of the shark genus Squalicorax sp.
have been recovered in association with the bones, but no tooth-marked bone
has been observed so far.
A new global phylogeny of Plesiosauria (Reptilia: Sauropterygia)
Hilary Ketchum
Plesiosauria was a diverse clade of predatory marine reptiles secondarily adapted
to life in water, that played an important role in Mesozoic marine ecosystems.
A new hypothesis of the phylogeny of Plesiosauria is presented that incorporates
64 taxa scored for 175 new and critically re-examined morphological characters,
the majority of which are based on personal examination of relevant specimens,
making it the largest and most comprehensive cladistic analysis of Plesiosauria
to date.
The strict component consensus tree of the 18 most parsimonious trees recovered
by the parsimony analysis is well resolved, and removal of only three ‘wildcard’
taxa by reduced consensus methods results in a fully resolved reduced consensus
tree; however, bootstrap proportions and Bremer support indices for the majority
of ingroup relationships are low. In agreement with some previous analyses (e.g.
O’Keefe, 2001) but in contrast to Druckenmiller and Russell (2006), the
present analysis does not support the traditional hypothesis of a simple dichotomy
between taxa with long necks and small heads (‘plesiosaurs’) and
those with short necks and large heads (‘pliosaurs’), which had
dominated pre-cladistic taxonomy for over 100 years. Instead, the large headed,
short-necked clade, Polycotylidae, is more closely related to Plesiosaurus dolichodeirus
than to Pliosaurus brachydeirus. However, the recovered topology differs in
many important respects from those generated by previous analyses, in particular
in the relationships of the more basal taxa, which necessitates re-definition
of a number of clades to produce a stable phylogenetic taxonomy.
A skeletal reconstruction of Rhomaleosaurus and the systematics of pliosaurs
Adam Stuart Smith
The skull of the holotype of Rhomaleosaurus cramptoni, a giant pliosauroid plesiosaur
from the Toarcian of Yorkshire has been prepared by the Paleontology Conservation
Unit (NHM, London). This allows the first detailed examination of the osteology
of this specimen since the superficial description of this species by Carte
and Bailey (1863). The postcranial skeleton is also intended for preparation
and once completed, the fully prepared specimen is planned to form the centrepiece
of a new earth science museum in Dublin. The interpretation of this newly prepared
skull is presented and compared with the older Hettangian form Rhomaleosaurus
megacephalus, warranting generic separation. The new skull reconstruction is
combined with postcranial data from a referred specimen (R. thorntoni) to provide
the first complete skeletal reconstruction of this genus. Rhomaleosaurids combine
a large skull with a long neck and so represent a morphotype somewhat intermediate
between elasmosaurids (long neck/small head) and pliosaurids (short neck/large
head). To assess the ecological significance of the rhomaleosaurid bauplan,
the proportions of the neck, skull, and limb girdles of Rhomaleosaurus are compared
with those of other plesiosaur taxa for which the ecology is better known. Finally,
a phylogenetic analysis of pliosaurs was conducted to elucidate the systematic
position of Rhomaleosaurus and to test the validity of the Rhomaleosauridae.
The results of the cladistic analysis indicate that Rhomaleosaurus fits within
a monophyletic rhomaleosaurid clade, and supports two other monophyletic clades,
Pliosauridae and Leptocleididae.
steological redescription, taxonomical and phylogenetical position of ‘Plesiosaurus’
macrocephalus, specimen NHM 49202, from the Lias of England
Peggy Vincent
The plesiosaur specimen NHM 49202 from the Lias of Lyme-Regis and kept in the
National History Museum of London, includes the complete skull, palate and mandible
with several associated cervical vertebrae. It is an adult plesiosaur of the
species ‘Plesiosaurus’ macrocephalus. An osteological re-examination
of the skull of this specimen allows the addition of new morphological information
to the original description by Andrews (1896). A preliminary cladistic analysis
was performed in order to understand the phylogenetic affinities of this specimen
within Plesiosauria. The Pliosauroidea affinities of the specimen indicate that
this specimen does not belong to Plesiosaurus and its unique set of characters
compared to other pliosauroids suggests that it should be assigned to a new
genus. The specimen possesses plesiomorphic characters, including the lack of
a median suture between both the anterior and posterior interpterygoid vacuities.
These characters may help in clarifying the evolutionary history of the Pliosauroidea.
POSTERS (X2)
Where are the Early Cretaceous plesiosaurs?: The first sacral vertebra of Plesiosauria
(Reptilia: Sauropterygia) found in the Arcillas de Morella Formation (Aptian,
Early Cretaceous) of Eastern Spain
Andrés Santos-Cubedo, Angel Galobart and Carlos Santisteban
Plesiosaur remains are known from all over the world, but in the Early Cretaceous
of Western Europe, only a few localities have been described (Yagüe et
al., 2003; Bardet et al., 2006). Although plesiosaurs are abundant during the
Upper Jurassic and Upper Cretaceous fossil record, the bones of these animals
are poorly represented in the Early Cretaceous. Such sparse record has been
attributed to extinction events (Haggart et al., 2003) and to the inadequacy
of the fossil record (Bardet, 1994, 1995; Haggart et al., 2003). We agree with
Bardet op. cit., that the poor plesiosaur fossil record of the Early Cretaceous
of Western Europe is biased by the scarcity of studies of plesiosaur material
and outcrops of this age. The Arcillas de Morella Formation is a stratigraphic
unit which covers this age. It is composed by marine and non-marine facies,
and is mainly known for its dinosaur fauna. Most of the studies on the vertebrate
fossils of these sites have dealt with this group, leaving some vertebrate fossils
from other groups (such crocodiles, turtles or plesiosaurs) unpublished (Ruiz-Omeñaca
and Santos-Cubedo, 1998; Weishampel et al., 2004). New discoveries provide essential
clues to understand the distribution of the Cretaceous iberian plesiosaurs.
Herein, we report a sacral vertebra of a plesiosaur from the Mas de Rafael site
(Todolella, Spain). This specimen constitutes the first sacral vertebra of Plesiosauria
(Reptilia: Sauropterygia) described in the Early Cretaceous (Aptian) from Spain
and the first evidence of the group outwith the type locality of the Arcillas
de Morella Formation (Morella, Spain).
The palaeobiogeographic distribution of Liassic plesiosaurs
Franziska Großmann
Although their remains date from the early Hettangian or Rhaetian (Storrs and
Taylor 1996), the plesiosaurs were soon dispersed over the entire world, as
Australian plesiosaurs of Toarcian age indicate (Thulborn and Warren 1980).
However, they are most abundant in Europe, which was covered by a shallow epicontinental
sea during the Lower Jurassic, leaving only some small islands. Three main zones
can be distinguished in this area: an English zone, a Norman-Benelux and a German
zone. The best and most abundant discoveries are from the English zone, followed
by the Toarcian plesiosaurs from Germany. It is remarkable that, although the
distance between these zones is not great, and there are no obvious barriers,
species specification, and to a slightly lesser extent also generic specification,
is high. No species is found in more than one zone, and only the genus Rhomaleosaurus
is found in both the English and the German zones. However, the faunal composition
is very similar at family level. Throughout the Liassic, elasmosauroids are
found in all zones, whereas plesiosauroids are less abundant in the Toarcian
than in the Hettangian and Sinemurian, and cryptoclidids have not yet appeared.
And although the pliosauroid species in the English and German zone are not
the same, they belong to similar morphotypes and/or are closely related, indicating
that they occupied similar ecological niches.
For presentation times and a full schedule of talks, visit http://www.svpca.org/years/2007_glasgow/index.php
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UPDATES
New genus added: Bobosaurus
http://www.plesiosauria.com/bobosaurus.html
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PDF-CORNER
This weeks PDF is on North American elasmosaurids, by Ken Carpenter
http://www.plesiosauria.com/pdf/carpenter_1999_elasmosaurs.pdf
Full reference: Carpenter, K. 1999. Revision of North American elasmosaurs from
the Cretaceous of the western interior. Paludicola, 2, 148-173.
Please note that PDFs featured in ‘PDF-Corner’ will only be available
temporarily.
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FEATURED IMAGE
The ferocious-looking skull of Tuarangisaurus: an elasmosaurid plesiosaur from
New Zealand.
http://nzdinosaurs.info/wp-content/uploads/2007/02/plesi-skull1.jpg
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PICK OF THE WEB
Sea Monsters: A Prehistoric Adventure. “Alive for the first time in 82
million years”
In theatres October 2007
http://www.nationalgeographic.com/seamonsters/
It’s a bit bare at the moment, but there are some nice wallpapers to download.
After looking through the Theatre Listings for this exciting IMAX movie, I am
very disappointed to see that the nearest cinema to me is in a different country
- there is not a single screening in Ireland. Come on Dublin, isn’t it
about time we got an IMAX theatre?
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WHERE’S PADDY?
Congratulations to Marlies Fischer who found Paddy last time, on the Links page.
Paddy the Plesiosaur is a cartoon plesiosaur with a letter ‘P’ on
his back - and he is hiding somewhere on the Plesiosaur Directory Website! Be
the first to find him and get a special mention in next weeks Newsletter! Just
email me at plesiosauria@gmail.com with the subject ‘I found Paddy’
and tell me what page he is hiding on. Find out more at http://www.plesiosauria.com/paddy.html
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ADS
The new book by Michael Everhart: Sea Monsters: Prehistoric Creatures of the
Deep. The book accompanies the soon to be released IMAX movie. Available here:
http://www.amazon.com/dp/1426200854/?tag=theplesdire-20
…also available through the Plesio-Store at http://www.plesiosauria.com/store.html
