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Texas giant Cretaceous shark + alligator hearing + mammal bone paleohistology + more



Ben Creisler
bcreisler@gmail.com


Some recent non-dino papers that may be of interest:

Frederickson JA, Schaefer SN, Doucette-Frederickson JA (2015)
A Gigantic Shark from the Lower Cretaceous Duck Creek Formation of Texas.
PLoS ONE 10(6): e0127162.
doi:10.1371/journal.pone.0127162
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0127162


Three large lamniform shark vertebrae are described from the Lower
Cretaceous of Texas. We interpret these fossils as belonging to a
single individual with a calculated total body length of 6.3 m. This
large individual compares favorably to another shark specimen from the
roughly contemporaneous Kiowa Shale of Kansas. Neither specimen was
recovered with associated teeth, making confident identification of
the species impossible. However, both formations share a similar shark
fauna, with Leptostyrax macrorhiza being the largest of the common
lamniform sharks. Regardless of its actual identification, this new
specimen provides further evidence that large-bodied lamniform sharks
had evolved prior to the Late Cretaceous.

News:

http://www.livescience.com/51072-giant-cretaceous-shark-uncovered.html

http://www.cbsnews.com/news/20-foot-monster-shark-fossils-found-in-texas/

===

Hilary S. Bierman & Catherine E. Carr (2015)
Sound Localization in the Alligator.
Hearing Research (advance online publication)
doi:10.1016/j.heares.2015.05.009
http://www.sciencedirect.com/science/article/pii/S0378595515001173

Highlights
Physiological and behavioral data support sound localization in crocodilians.
Directional hearing is affected by skull pneumaticity and coupled eardrums.
Evolutionary changes in middle-ear pneumaticity affect localization cues.
Changes in auditory periphery may be reflected in neuroanatomical circuitry.

Abstract
In early tetrapods, it is assumed that the tympana were acoustically
coupled through the pharynx and therefore inherently directional,
acting as pressure difference receivers. The later closure of the
middle ear cavity in turtles, archosaurs, and mammals is a derived
condition, and would have changed the ear by decoupling the tympana.
Isolation of the middle ears would then have led to selection for
structural and neural strategies to compute sound source localization
in both archosaurs and mammalian ancestors. In the archosaurs (birds
and crocodilians) the presence of air spaces in the skull provided
connections between the ears that have been exploited to improve
directional hearing, while neural circuits mediating sound
localization are well developed. In this review, we will focus
primarily on directional hearing in crocodilians, where vocalization
and sound localization are thought to be ecologically important, and
indicate important issues still awaiting resolution.
==



Matthew R. McCurry, Alistair R. Evans & Colin R. McHenry (2015)
The sensitivity of biological finite element models to the resolution
of surface geometry: a case study of crocodilian crania.
PeerJ 3:e988
doi: https://dx.doi.org/10.7717/peerj.988
https://peerj.com/articles/988/


The reliability of finite element analysis (FEA) in biomechanical
investigations depends upon understanding the influence of model
assumptions. In producing finite element models, surface mesh
resolution is influenced by the resolution of input geometry, and
influences the resolution of the ensuing solid mesh used for numerical
analysis. Despite a large number of studies incorporating sensitivity
studies of the effects of solid mesh resolution there has not yet been
any investigation into the effect of surface mesh resolution upon
results in a comparative context. Here we use a dataset of crocodile
crania to examine the effects of surface resolution on FEA results in
a comparative context. Seven high-resolution surface meshes were each
down-sampled to varying degrees while keeping the resulting number of
solid elements constant. These models were then subjected to bite and
shake load cases using finite element analysis. The results show that
incremental decreases in surface resolution can result in fluctuations
in strain magnitudes, but that it is possible to obtain stable results
using lower resolution surface in a comparative FEA study. As surface
mesh resolution links input geometry with the resulting solid mesh,
the implication of these results is that low resolution input geometry
and solid meshes may provide valid results in a comparative context.



========================

Christian Kolb, Torsten M. Scheyer, Kristof Veitschegger, Analia M.
Forasiepi, Eli Amson, Alexandra A.E. van der Geer, Lars W. van den
Hoek Ostende, Shoji Hayashi & Marcelo R. Sánchez-Villagra (2015)
Mammalian bone palaeohistology: new data and a survey.
PeerJ PrePrints 3:e1405
doi: https://dx.doi.org/10.7287/peerj.preprints.1155v1
https://peerj.com/preprints/1155/

The interest in mammalian palaeohistology has increased dramatically
in the last two decades. Starting in 1849 via descriptive approaches,
it has been demonstrated that bone tissue and vascularisation types
correlate with several biological variables such as ontogenetic stage,
growth rate, and ecology. Mammalian bone displays a large variety of
bone tissues and vascularisation patterns reaching from lamellar or
parallel-fibred to fibrolamellar or woven-fibred bone, depending on
taxon and individual age. Here we systematically review the knowledge
and methods on mammalian bone and palaeohistology and discuss
potential future research fields and techniques. We present new data
on the bone microstructure of two extant marsupial species and of
several extinct continental and island placental mammals. Three
juvenile specimens of the dwarf island hippopotamid Hippopotamus minor
from the Late Pleistocene of Cyprus show reticular to plexiform
fibrolamellar bone. The island murid Mikrotia magna from the Late
Miocene of Gargano, Italy displays parallel-fibred primary bone with
reticular vascularisation being pervaded by irregular secondary
osteons in the central part of the cortex. Leithia sp., the dormouse
from the Pleistocene of Sicily, is characterised by a primary bone
cortex consisting of lamellar bone and low vascularisation. The bone
cortex of the fossil continental lagomorph Prolagus oeningensis and
three fossil species of insular Prolagus displays parallel-fibred
primary bone and reticular, radial as well as longitudinal
vascularisation. Typical for large mammals, secondary bone in the
giant rhinocerotoid Paraceratherium sp. from the Miocene of Turkey is
represented by dense Haversian bone. The skeletochronological features
of Sinomegaceros yabei, a large-sized deer from the Pleistocene of
Japan closely related to Megaloceros, indicate a high growth rate.
These examples and the critical summary of existing data show how bone
microstructure can reveal essential information on life history
evolution. The bone tissue and the skeletochronological data of the
sampled island species show that there is no universal modification of
bone tissue and life history specific to insular species.