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Origin(s) of living amphibians (free pdf)



From: Ben Creisler
bcreisler@gmail.com

A new non-dino paper of interest (pdf is open access):

David Marjanovic & Michel Laurin (2013)
The origin(s) of extant amphibians: a review with emphasis on the
"lepospondyl hypothesis".
Geodiversitas 35(1):  207-272
doi: http://dx.doi.org/10.5252/g2013n1a8
http://www.mnhn.fr/museum/front/medias/publication/49713_g2013n1a8.pdf



The origins of the extant amphibians (frogs, salamanders, caecilians)
remain controversial after over a century of debate. Three groups of
hypotheses persist in the current literature: the “temnospondyl
hypothesis” (TH) which roots Lissamphibia Haeckel, 1866 (the smallest
clade composed of the extant amphibians) within the Paleozoic
temnospondyls, the “lepospondyl hypothesis” (LH) which postulates a
monophyletic Lissamphibia nested within the Paleozoic lepospondyls,
and the “polyphyly hypothesis” (PH), according to which the frogs and
the salamanders are temnospondyls while the caecilians are
lepospondyls. The discovery of the Middle Jurassic to Pliocene
albanerpetontids, which are very similar to the extant amphibians, has
complicated rather than resolved this situation. We present a review
of recent publications and theses in this field, several of which show
more support for the LH than for the TH and considerably more than for
the PH. In addition, we show that there is no particular attraction
between long-bodied lissamphibians (caecilians) and long-bodied
lepospondyls (such as the lysorophians): when they are removed from
two published matrices, reanalyses nonetheless find the LH. In one
case the LH is found even when all salamanders are removed as well. We
furthermore propose that the complex of characters called the
salamander mode of autopodium development is (in its less extreme
forms) plesiomorphic for limbed vertebrates, so the apparent presence
of this mode of development in temnospondyls cannot support the TH or
the PH. Still, a consensus will not be reached soon, despite the
increasingrange of data and types of analysis that are used
(morphological, molecular and combined phylogenetics, development
biology, molecular divergence dating, paleontological supertree
dating, combined dating, and calculation of confidence intervals on
first appearances in the fossil record). We present examples of
pertinent character state distributions and explore a large gap in the
fossil record of small stegocephalians.