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Amargasaurus braincase and neck posture + Camarasaurus growth + Texas titanosaurs



Ben Creisler
bcreisler@gmail.com

Sauropod papers in the new issue of Journal of Vertebrate Paleontology:


Ariana Paulina Carabajal, José L. Carballido & Philip J. Currie (2014)
Braincase, neuroanatomy, and neck posture of Amargasaurus cazaui
(Sauropoda, Dicraeosauridae) and its implications for understanding
head posture in sauropod.s
Journal of Vertebrate Paleontology 34(4): 870-882
DOI:10.1080/02724634.2014.838174
http://www.tandfonline.com/doi/full/10.1080/02724634.2014.838174#.U7y27fldXTo

The braincase of Amargasaurus cazaui from the Lower Cretaceous of
Argentina represents the only dicraeosaurid sauropod neurocranial
material known from South America. It has been computer
tomographically (CT) scanned and three-dimensional digital
reconstructions of the endocranium and inner ear have been made. The
cranial endocast is complete, with a volume of approximately 94–98 ml,
excluding the dorsal sinuses. The labyrinth of the inner ear is
dorsoventrally taller than the lagena, which is conical, and
relatively short. The anterior semicircular canal is longer than the
posterior and lateral semicircular canals, as in most non-titanosaurid
sauropods. When the braincase is oriented with the lateral
semicircular canal positioned horizontally, the occipital condyle is
oriented posteroventrally, suggesting that the head was held with the
muzzle pointing downward. The morphology of the atlas and axis,
together with the reconstruction of the osteological neutral pose of
the neck, supports this neck and head position, and also indicates the
presence of the proatlas in this taxon. The evidence presented here
for the skull and neck position of Amargasaurus fits with a midheight
food-gathering strategy. The presence of titanosauriforms and
rebbachisaurids, together with Amargasaurus, supports the niche
partitioning hypothesis for the La Amarga Formation sauropods.

===


Katja Waskow & P. Martin Sander (2014)
Growth record and histological variation in the dorsal ribs of
Camarasaurus sp. (Sauropoda).
Journal of Vertebrate Paleontology 34(4): 852-869
DOI:10.1080/02724634.2014.840645
http://www.tandfonline.com/doi/full/10.1080/02724634.2014.840645#.U7y2dPldXTo

Several histological studies have attempted to derive life history
parameters of sauropod dinosaurs. However, verification of sexual
maturity and growth rate has been impeded by strong remodeling in
sampled sauropod long bones. Here, for the first time, histological
variation in the rib cage of Camarasaurus sp. is studied based on a
single, relatively small, mature individual. The focus is on the
growth history of this individual and its implications for sauropod
growth, age, and sexual maturity. Different bone tissue types were
observed in different skeletal elements. The long bones show nearly
completely remodeled fibrolamellar bone, whereas the ribs show primary
zonal bone, with fewer secondary osteons. Histology reveals that the
general direction of growth in the rib shaft was from proximal to
distal. Therefore, the proximal end of the rib shaft, where growth
originated, was determined to be the best sampling area in ribs,
providing an almost complete growth record. This study provides the
most complete growth record for a sauropod so far, and indicates that
it took 40 years for Camarasaurus sp. to reach full size and 18–19
years to become sexually mature. These results show that the growth
rate and the point of sexual maturity for a small sauropod are
intermediate between the widely divergent previous estimates. With a
larger database of rib samples from more individuals of different
ontogenetic stages, this approach could yield growth curves for other
sauropod taxa.

===


John A. Fronimos & Thomas M. Lehman (2014)
New specimens of a titanosaur sauropod from the Maastrichtian of Big
Bend National Park, Texas.
Journal of Vertebrate Paleontology 34(4): 883-899
DOI:10.1080/02724634.2014.840308
http://www.tandfonline.com/doi/full/10.1080/02724634.2014.840308#.U7y3LvldXTo



New specimens of a titanosaur sauropod from Maastrichtian strata in
Big Bend National Park, Texas, include well-preserved dorsal vertebrae
in association with pelvic elements. Anterior dorsal vertebrae are
characterized by postspinal and centroprezygapophyseal laminae, with
spinodiapophyseal laminae convergent on the anterior base of the
neural spine. Posterior dorsal vertebrae are characterized by
postzygodiapophyseal laminae and divided spinodiapophyseal laminae,
with spinoprezygapophyseal laminae contributing to the prespinal
lamina. The ilium and pubis differ from specimens previously
collected, indicating a greater morphological disparity among
titanosaurs in the Maastrichtian of West Texas than previously
recognized. This disparity may be attributable to intraspecific
variation or to the presence of multiple taxa. The new material is
compatible with the only presently known North American titanosaur,
Alamosaurus sanjuanensis, but is not formally referred due to lack of
overlap with the hypodigm of that species. Comparison with other
derived titanosaurs finds the closest affinities to Trigonosaurus
pricei, Uberabatitan riberoi, and Baurutitan britoi of the Upper
Cretaceous Brazilian Bauru Group, consistent with a South American
immigration event at the end of the North American sauropod hiatus.