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Small quadrupedal ornithopod tracks from Spain + snake origins (free pdfs)



Ben Creisler
bcreisler@gmail.com

Two new papers in open access:

Luis Alcalá, Luis Mampel, Rafael Royo-Torres & Alberto Cobos  (2014) [2015]
On small quadrupedal ornithopod tracks in Jurassic-Cretaceous
transition intertidal deposits (El Castellar, Teruel, Spain).
Spanish Journal of Paleontology 29(2): 183-190
Free pdf:
http://www.sepaleontologia.es/revista/anteriores/REP%20(2013)%20vol.%2029/2/06.%20Alcala%C2%81%20et%20al.pdf


The study of an undescribed part of the El Pozo tracksite in El
Castellar (Teruel, Spain) has revealed two new trackways made by small
ornithopods showing new evidence of basal ornithopod pes and manus
track morphologies in the Jurassic-Cretaceous transition. The site
lies within the Villar del Arzobispo Formation, which was deposited
during the Tithonian-Berriasian in an environment under the influence
of tides. The pes tracks are small tridactyl tracks, the digits are
similar in size, and the heel is open and rounded. The presence of
oval manus tracks in front of the tridactyl tracks in one of the
trackways confirms that the dinosaur was quadrupedal. Probably, the
trackmaker dinosaur is a representative of the dryosaurid or of the
basal Ankylopollexia clades. These tracks are smaller than those
described for the Las Cerradicas site, also located in Teruel and  in
the same formation; consequently, these tracks from El Pozo site
constitute some of the smallest ornithopod trackways with quadrupedal
locomotion ever described in the world. In addition, in the same
tracksite bed, there are some poorly preserved tracks attributed to
big quadrupedal dinosaurs.

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Allison Y Hsiang, Daniel J Field, Timothy H Webster, Adam DB Behlke,
Matthew B Davis, Rachel A Racicot &  Jacques A Gauthier (2015)
The origin of snakes: revealing the ecology, behavior, and
evolutionary history of early snakes using genomics, phenomics, and
the fossil record.
BMC Evolutionary Biology May 2015, 15:87
DOI: 10.1186/s12862-015-0358-5
http://link.springer.com/article/10.1186/s12862-015-0358-5

Background

The highly derived morphology and astounding diversity of snakes has
long inspired debate regarding the ecological and evolutionary origin
of both the snake total-group (Pan-Serpentes) and crown snakes
(Serpentes). Although speculation abounds on the ecology, behavior,
and provenance of the earliest snakes, a rigorous, clade-wide analysis
of snake origins has yet to be attempted, in part due to a dearth of
adequate paleontological data on early stem snakes. Here, we present
the first comprehensive analytical reconstruction of the ancestor of
crown snakes and the ancestor of the snake total-group, as inferred
using multiple methods of ancestral state reconstruction. We use a
combined-data approach that includes new information from the fossil
record on extinct crown snakes, new data on the anatomy of the stem
snakes Najash rionegrina, Dinilysia patagonica, and Coniophis
precedens, and a deeper understanding of the distribution of
phenotypic apomorphies among the major clades of fossil and Recent
snakes. Additionally, we infer time-calibrated phylogenies using both
new ‘tip-dating’ and traditional node-based approaches, providing new
insights on temporal patterns in the early evolutionary history of
snakes.

Results

Comprehensive ancestral state reconstructions reveal that both the
ancestor of crown snakes and the ancestor of total-group snakes were
nocturnal, widely foraging, non-constricting stealth hunters. They
likely consumed soft-bodied vertebrate and invertebrate prey that was
subequal to head size, and occupied terrestrial settings in warm,
well-watered, and well-vegetated environments. The snake total-group –
approximated by the Coniophis node – is inferred to have originated on
land during the middle Early Cretaceous (~128.5 Ma), with the
crown-group following about 20 million years later, during the Albian
stage. Our inferred divergence dates provide strong evidence for a
major radiation of henophidian snake diversity in the wake of the
Cretaceous-Paleogene (K-Pg) mass extinction, clarifying the pattern
and timing of the extant snake radiation. Although the snake
crown-group most likely arose on the supercontinent of Gondwana, our
results suggest the possibility that the snake total-group originated
on Laurasia.

Conclusions

Our study provides new insights into when, where, and how snakes
originated, and presents the most complete picture of the early
evolution of snakes to date. More broadly, we demonstrate the striking
influence of including fossils and phenotypic data in combined
analyses aimed at both phylogenetic topology inference and ancestral
state reconstruction.

**

News release:

http://blogs.biomedcentral.com/bmcseriesblog/2015/05/20/limbless-triumph-origin-diversification-snakes/

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