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Alligator osteoderm histology and nothosaur-placodont bonebed in Spain papers



From: Ben Creisler
bcreisler@gmail.com

A couple of recent non-dino papers that may be of interest:

Michael E. Burns, Matthew K. Vickaryous & Philip J. Currie (2013)
Histological variability in fossil and recent alligatoroid osteoderms:
Systematic and functional implications.
Journal of Morphology (advance online publication)
DOI: 10.1002/jmor.20125
http://onlinelibrary.wiley.com/doi/10.1002/jmor.20125/abstract


Statements about morphological variation in extinct taxa often suffer
from insufficient sampling that can be remedied by taking advantage of
larger sample sizes provided by related, extant taxa. This analysis
quantitatively and qualitatively examines histological and
morphological variation of osteoderms from extant and extinct
alligatoroid specimens. Statistically significant differences were
correlated with changes in osteoderm size and shape. These differences
are independent of position on the body, taxonomy, or evolution.
Histological variation in alligatoroid osteoderms is due to
morphological constraints on the elements themselves, and not
taxonomic differences. This has implications for the recognition of
histological characters in the osteoderms of extinct archosaur groups
that lack extant representatives.

==


Matías Reolid, Fernando Pérez-Valera, Michael J. Benton & Jesús Reolid (2013)
Marine flooding event in continental Triassic facies identified by a
nothosaur and placodont bonebed (South Iberian Paleomargin).
Facies (advance online publication)
DOI 10.1007/s10347-013-0360-6
http://link.springer.com/article/10.1007/s10347-013-0360-6



Sudden marine flooding within otherwise continental successions of the
Triassic is unusual. The Tabular Cover of the SE paleomargin of the
Iberian Massif is characterized by continental Triassic redbed facies
composed of sandstones and siltstones, with gypsum-rich levels in the
transition to Jurassic limestones. These Triassic deposits were
developed in a fluvial-coastal system and they are 300 m thick in the
Puente Génave-Villarrodrigo area, eastern Jaén Province, Spain. An
unexpected sandstone-limestone unit in the lower part of this
formation, recognized over more than 30 km, contains marine reptile
bones in a storm bed or tsunami deposit. The lower part of this unit
is characterized by a sandstone with sedimentary structures indicative
of high-energy conditions as well as by fossil remains of marine
reptiles. This bed ranges from 0 to 90 cm in thickness, and in some
outcrops pinches out rapidly within a few meters. The upper part of
the studied unit is a limestone with common trace fossils and abundant
remains of marine reptiles, comprising isolated and fragmented pieces
of sauropterygians (nothosaurs, pachypleurosaurs, and placodonts).
Most abundant are vertebrae and ribs. In some outcrops, the top of
this bed presents a dense accumulation of well-preserved small
gastropods. The limestone is overlain by red siltstones and
sandstones. The studied unit is interpreted as a marine deposit
representing a high-energy event and records exceptional marine
flooding in a distal fluvial environment, in fact the only open-marine
deposit in the Villarrodrigo section. The sedimentary structures in
the lower part of the unit are typical of high-energy deposits and
indicate deposition in a single episode, probably related to a storm
surge or a tsunami. The fragmentation, disarticulation, and dispersion
of the vertebrate bones and the imbrication of bioclasts are
consistent with a high-energy event that favored the concentration of
bones according to size and density.