Asian Saurolophus and other new papers

[bh480@scn.org]

From: Ben Creisler
bh480@scn.org

Here are a few new papers:

Philip J. Currie, Demchig Badamgarav, Eva B. Koppelhus, 
Robin Sissons, and Matthew K. Vickaryous (2011)
Hands, feet and behaviour in Pinacosaurus (Dinosauria: 
Ankylosauridae).
Acta Palaeontologica Polonica in press
available online 04 Jan 2011 doi:10.4202/app.2010.0055
http://www.app.pan.pl/article/item/app20100055.html

Structure of the manus and pes has long been a source of 
confusion in ankylosaurs, owing to the imperfect 
preservation or complete lack of these parts of the 
skeletons in most specimens, and the fact that many 
species appear to have undergone a reduction in numbers 
of digits and phalanges. New specimens of Pinacosaurus 
Gilmore, 1933 from Alag Teeg in Mongolia confirm that the 
phalangeal formula of the manus is 2-3-3-3-2. However, 
there are only three toes in the pes, which has a 
phalangeal formula of X-3-3/4-3/4-X. Importantly, the 
number of phalanges in the third and fourth pedal digits 
can vary between either three or four per digit, even 
within the same specimen. The Alag Teeg site has yielded 
as many as a hundred skeletons of the ankylosaur 
Pinacosaurus, most of which were immature when they died. 
Each skeleton is preserved in an upright standing 
position, with the bones of the lower limbs often in 
articulation. The remainder of the skeleton, including 
the upper parts of the limbs, is generally disarticulated 
and somewhat scattered. Based on the presence of large 
numbers of juvenile Pinacosaurus specimens at Alag Teeg, 
as well as other Djadokhta-age sites (Ukhaa Tolgod in 
Mongolia, Bayan Mandahu in China), it seems juvenile 
Pinacosaurus were probably gregarious.


Phil R. Bell (2011)
Cranial osteology and ontogeny of Saurolophus 
angustirostris from the Late Cretaceous of Mongolia with 
comments on Saurolophus osborni from Canada 
Acta Palaeontologica Polonica in press
available online 04 Jan 2011 doi:10.4202/app.2010.0061
http://www.app.pan.pl/article/item/app20100061.html

Reanalysis of the skull of the crested Asian hadrosaurine 
Saurolophus angustirostris confirms its status as a 
distinct species from its North American relative, S. 
osborni. In addition to its greater absolute size, S. 
angustirostris is differentiated from S. osborni by an 
upturned premaxillary body, a more strongly reflected 
oral margin of the premaxilla, the absence of an anterior 
notch in the prenarial fossa, a sigmoidal contour of the 
ventral half of the anterior process of the jugal, a 
shallow quadratojugal notch on the quadrate, and by a 
strongly bowed quadrate in lateral view. Phylogenetic 
analysis corroborates a sister taxon relationship between 
S. angustirostris and S. osborni. Saurolophus itself is 
characterised by a solid, rod-like crest composed of the 
nasals, frontals, and prefrontals; secondary elongation 
of the frontal and prefrontal resulting in the backwards 
extension of the frontal platform; a frontal platform 
that extends dorsal to the anterior portion of the 
supratemporal fenestra; a parietal that is excluded by 
the squamosals from the posterodorsal margin of the 
occiput; and the presence of two supraorbital elements. 
Although the palaeobiogeographic history of Saurolophus 
remains unresolved, at least two possible dispersal 
events took place across Beringia during the late 
Campanian leading to the evolution of the clade composed 
of Kerberosaurus, Prosaurolophus, and Saurolophus.


David Steinsaltz and Steven Hecht Orzack (2011)
Statistical methods for paleodemography on fossil 
assemblages having small numbers of specimens: an 
investigation of dinosaur survival rates. 
Paleobiology 37(1):113-125. 2011 
doi: 10.1666/08056.1
http://www.bioone.org/doi/abs/10.1666/08056.1

We describe statistical methods to formulate and validate 
statements about survival rates given a small number of 
individuals. These methods allow one to estimate the age-
specific survival rate and assess its uncertainty, to 
assess whether the survival rates during some age range 
differ from the survival rates during another age range, 
and to assess whether the survivorship curve has a 
particular shape. We illustrate these methods by applying 
them to a sample of 22 Albertosaurus sarcophagus 
individuals. We show that this sample is too small to 
provide any confidence in the claim that this species had 
a ?convex? survivorship curve arising from age-specific 
survival rates that decreased monotonically with age. 
However, we show that a sample of 50 to 100 individuals 
has reasonable statistical power to support such a claim. 
There is evidence for the much weaker claim that average 
survival rates for ages 2 to 15 were higher than survival 
rates for later ages. Finally, we describe one way to 
account for size-dependent fossilization rates and show 
that a plausible positively-size-dependent fossilization 
rate results in a substantially non-convex survivorship 
curve for A. sarcophagus.



Jun Liu, Jonathan C. Aitchison, Yuan-Yuan Sun, Qi-Yue 
Zhang, Chang-Yong Zhou, and Tao Lv (2011)
New Mixosaurid Ichthyosaur Specimen from the Middle 
Triassic of SW China: Further Evidence for the Diapsid 
Origin of Ichthyosaurs.
Journal of Paleontology 85(1):32-36. 2011 
doi: 10.1666/09-131.1
http://www.bioone.org/doi/abs/10.1666/09-131.1

Recent cladistic analyses have all suggested a diapsid 
origin of ichthyosaurs. However, an intermediate 
evolutionary stage of the lower temporal region of 
ichthyosaurian skull between basal diapsids and derived 
ichthyosaurs has been absent from the fossil record. Here 
we describe the cranial skeleton of a new mixosaurid 
ichthyosaur specimen with a well-preserved lower temporal 
region from the Anisian Guanling Formation of eastern 
Yunnan. It is characterized by the most primitive lower 
temporal region within known ichthyosaurs. The primitive 
characters of the lower temporal region include both 
external and internal separation between the jugal and 
the quadratojugal, an anterior process of the 
quadratojugal, an apparent posteroventral process of the 
jugal, and a large lower temporal opening surrounded by 
the jugal, the postorbital, the squamosal, and the 
quadratojugal. The lower temporal region of this specimen 
provides the most direct evidence to the diapsid origin 
of ichthyosaurs. It also suggests that the disappearance 
of the lower temporal fenestra is caused initially by the 
reduction of the lower temporal arcade rather than the 
enlargement of the surrounding bones.