Journal of Vertebrate Paleontology 24(2)

[Christopher Taylor <ck.taylor@auckland.ac.nz>]

    Some papers from the newest Journal of Vertebrate Paleontology (vol. 24,
no. 2) that people may be interested in:

A NEW HADROSAURINE DINOSAUR FROM THE LATE CRETACEOUS OF FAR EASTERN RUSSIA.
YURI L. BOLOTSKY and PASCAL GODEFROIT, pages 351­365.

    Kerberosaurus manakini, gen. et sp. nov. (Dinosauria, Hadrosauridae) is
described on the basis of disarticulated skull elements from the
Maastrichtian Tsagayan Formation of Blagoveschensk, Far Eastern Russia. This
flat-headed hadrosaur is characterized by a unique morphology of the lateral
wall of the braincase, a particularly narrow frontal, a depressed rostral
margin of the parietal, a strong, wide and flattened crest around the
circumnarial depression, and a very prominent hook-like palatine process on
the maxilla. A phylogenetic analysis, based on 21 cranial characters,
indicates that, among hadrosaurines, Kerberosaurus is the sister taxon of a
monophyletic group formed by Prosaurolophus and Saurolophus. Several
independent hadrosaurid lineages migrated from western North America to
eastern Asia, probably by late Campanian to early Maastrichtian time. At the
end of the Maastrichtian, completely different dinosaur faunas developed in
both regions, indicating some kind of geographical or paleoecological
barrier.

    This one's already getting discussed on the list as to the value or
otherwise of its phylogenetic conclusions.

Other non-dinosaurian papers that may interest some:

ON THE CRANIAL ANATOMY OF THE POLYCOTYLID PLESIOSAURS, INCLUDING NEW
MATERIAL OF POLYCOTYLUS LATIPINNIS, COPE, FROM ALABAMA. F. ROBIN O'KEEFE,
pages 326­340.

The cranial anatomy of plesiosaurs in the family Polycotylidae (Reptilia:
Sauropterygia) has received renewed attention recently because various skull
characters are thought to indicate plesiosauroid, rather than pliosauroid,
affinities for this family. New data on the cranial anatomy of polycotylid
plesiosaurs is presented, and is shown to compare closely to the structure
of cryptocleidoid plesiosaurs. The morphology of known polycotylid taxa is
reported and discussed, and a preliminary phylogenetic analysis is used to
establish ingroup relationships of the Cryptocleidoidea. This study also
presents new material referable to Polycotylus latipinnis from the
Mooreville Chalk Formation of Alabama. This skeleton is largely complete,
and although the skull is fragmentary it does preserve several regions not
previously represented. The preserved portions demonstrate that the palate
of Polycotylus is similar to that of Trinacromerum in the possession of
robust epipterygoids, and similar to that of all other polycotylids in the
possession of a large anterior interpterygoid vacuity. Polycotylus therefore
displays the derived palate morphology common to all polycotylids, but also
displays some plesiomorphic features. This impression is confirmed by the
results of the cladistic analysis.

    And two papers on an animal which is near the top of the list of proving
that anything's possible for biology, the marine sloth _Thalassocnus_ (I
know at least one person once asked on this list if it was some kind of
April Fool's joke :) ):

THE YOUNGEST SPECIES OF THE AQUATIC SLOTH THALASSOCNUS AND A REASSESSMENT OF
THE RELATIONSHIPS OF THE NOTHROTHERE SLOTHS (MAMMALIA: XENARTHRA). CHRISTIAN
DE MUIZON, H. GREGORY MCDONALD, RODOLFO SALAS, and MARIO URBINA, pages
387­397.

Two new specimens of the aquatic sloth Thalassocnus from the Pliocene of
Peru are described, one of T. carolomartini McDonald and Muizon, 2002 and
the other T. yaucensis, sp. nov. Comparisons with the type species of
Thalassocnus, T. natans, demonstrates that T. carolomartini and T. yaucensis
are more similar morphologically to each other than to other species of the
genus and are more derived. For example, both have a more elongated rostrum
(premaxillae and mandibular spout) and more robust, quadrate to circular
molariform teeth. The aquatic sloth Thalassocnus is sufficiently distinct
morphologically that it is placed in a new subfamily, the Thalassocninae,
and the Nothrotheriinae is raised to family rank. The morphological features
shared by T. carolomartini and T. yaucensis indicate these species were
better adapted to grazing on marine vegetation than earlier species of
Thalassocnus.

THE EVOLUTION OF FEEDING ADAPTATIONS OF THE AQUATIC SLOTH THALASSOCNUS.
CHRISTIAN DE MUIZON, H. GREGORY MCDONALD, RODOLFO SALAS, and MARIO URBINA,
pages 398­410.

The aquatic sloth Thalassocnus is represented by five species that lived
along the coast of Peru from the late Miocene through the late Pliocene. A
detailed comparison of the cranial and mandibular anatomy of these species
indicates different feeding adaptations. The three older species of
Thalassocnus (T. antiquus, T. natans, and T. littoralis) were probably
partial grazers (intermediate or mixed feeders) and the transverse component
of mandibular movement was very minor, if any. They were probably feeding
partially on stranded sea weeds or sea grasses, or in very shallow waters
(less than 1 m) as indicated by the abundant dental striae of their
molariform teeth created by ingestion of sand. The two younger species (T.
carolomartini and T. yaucensis) were more specialized grazers than the three
older species and had a distinct transverse component in their mandibular
movement. Their teeth almost totally lack dental striae. These two species
were probably feeding exclusively in the water at a greater depth than the
older species.

    The second paper mainly deals with the skull (_Thalassocnus_ gives us a
nice succession of taxa from about the same place, separated in time, each
showing more adaptations for marine life than its predecessors, perhaps one
of the best and straightforward evolutionary transitions series to be found
in vertebrates). It also includes some interesting comments towards the end
on the feet and claws, which were apparently even bigger than in terrestrial
sloths, which already look rather like Freddy Krueger. I'm not sure why they
assume the claws were primarily used in gathering food, but I was very
interested in their almost offhand suggestion that the claws could have been
used to hold the beast to the sea-bottom. They compare it to the marine
iguana, which also shows oversized claws and a shortage of the usual
adaptations to weigh the animal down and keep it under the water (such as
the heavy, thickened bones of sirenians). On the whole, the paper gives a
very good aid to imagining what this most bizarre of beasties may have
looked like alive.

    Cheers,

        Christopher Taylor