Newsletter 6
plesio...@gmail.com
(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 plesio...@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 plesio...@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