[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Crocodile-line archosaurs following end-Triassic extinction + Asian goniopholidids (free pdfs)



From: Ben Creisler
bcreisler@gmail.com


Two new papers of interest about Mesozoic crocodilians:

Thomas L. Stubb, Stephanie E. Pierce, Emily J. Rayfield and Philip S.
L. Anderson (2013)
Morphological and biomechanical disparity of crocodile-line archosaurs
following the end-Triassic extinction.
Proceedings of the Royal Society B 280 no. 1770 20131940
doi: 10.1098/rspb.2013.1940
http://rspb.royalsocietypublishing.org/content/280/1770/20131940.abstract
free pdf
http://rspb.royalsocietypublishing.org/content/280/1770/20131940.full.pdf+html

Mesozoic crurotarsans exhibited diverse morphologies and feeding
modes, representing considerable ecological diversity, yet
macroevolutionary patterns remain unexplored. Here, we use a unique
combination of morphological and biomechanical disparity metrics to
quantify the ecological diversity and trophic radiations of Mesozoic
crurotarsans, using the mandible as a morpho-functional proxy. We
recover three major trends. First, the diverse assemblage of Late
Triassic crurotarsans was morphologically and biomechanically
disparate, implying high levels of ecological variation; but,
following the end-Triassic extinction, disparity declined. Second, the
Jurassic radiation of marine thalattosuchians resulted in very low
morphological disparity but moderate variation in jaw biomechanics,
highlighting a hydrodynamic constraint on mandibular form. Third,
during the Cretaceous terrestrial radiations of neosuchians and
notosuchians, mandibular morphological variation increased
considerably. By the Late Cretaceous, crocodylomorphs evolved a range
of morphologies equalling Late Triassic crurotarsans. By contrast,
biomechanical disparity in the Cretaceous did not increase,
essentially decoupling from morphology. This enigmatic result could be
attributed to biomechanical evolution in other anatomical regions
(e.g. cranium, dentition or postcranium), possibly releasing the
mandible from selective pressures. Overall, our analyses reveal a
complex relationship between morphological and biomechanical disparity
in Mesozoic crurotarsans that culminated in specialized feeding
ecologies and associated lifestyles.

==

Thomas J.D. Halliday, Marco Brandalise De Andrade, Michael J. Benton,
and Mikhail B. Efimov (2013)
A re-evaluation of goniopholidid crocodylomorph material from Central
Asia: Biogeographic and phylogenetic implications.
Acta Palaeontologica Polonica (in press)
doi: http://dx.doi.org/10.4202/app.2013.0018
http://app.pan.pl/article/item/app20130018.html

Central Asia is a key area for crocodylomorph evolution, lying midway
between the highly documented deposits in Europe and North America,
but crocodylomorph fossils from this part of the world are rare.
Included among these are specimens collected in the 1970s and 1980s by
the Soviet-Mongolian Expeditions in the Jurassic and Cretaceous of
Mongolia, Tajikistan, and Kazakhstan. Three species, “Sunosuchus”
shartegensis, Kansajsuchus extensus, and Turanosuchus aralensis are
redescribed and subjected to phylogenetic analysis for the first time.
“Sunosuchus” shartegensis and Kansajsuchus are relatively derived
goniopholidids, and part of a pan-east-Laurasian radiation of
goniopholidids from which the European goniopholidids subsequently
radiated. Turanosuchus aralensis is here considered a nomen dubium.
Cladistic analysis suggests that Sunosuchus is polyphyletic,
indicating a higher degree of diversification than was previously
thought, but also pointing to the need for further systematic
revision.