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A Triassic stem-salamander from Kyrgyzstan and the origin of salamanders - PubMed

  • ️Wed Jan 01 2020

A Triassic stem-salamander from Kyrgyzstan and the origin of salamanders

Rainer R Schoch et al. Proc Natl Acad Sci U S A. 2020.

Abstract

The origin of extant amphibians remains largely obscure, with only a few early Mesozoic stem taxa known, as opposed to a much better fossil record from the mid-Jurassic on. In recent time, anurans have been traced back to Early Triassic forms and caecilians have been traced back to the Late Jurassic Eocaecilia, both of which exemplify the stepwise acquisition of apomorphies. Yet the most ancient stem-salamanders, known from mid-Jurassic rocks, shed little light on the origin of the clade. The gap between salamanders and other lissamphibians, as well as Paleozoic tetrapods, remains considerable. Here we report a new specimen of Triassurus sixtelae, a hitherto enigmatic tetrapod from the Middle/Late Triassic of Kyrgyzstan, which we identify as the geologically oldest stem-group salamander. This sheds light not only on the early evolution of the salamander body plan, but also on the origin of the group as a whole. The new, second specimen is derived from the same beds as the holotype, the Madygen Formation of southwestern Kyrgyzstan. It reveals a range of salamander characters in this taxon, pushing back the rock record of urodeles by at least 60 to 74 Ma (Carnian-Bathonian). In addition, this stem-salamander shares plesiomorphic characters with temnospondyls, especially branchiosaurids and amphibamiforms.

Keywords: amphibians; evolution; phylogeny.

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Conflict of interest statement

The authors declare no competing interest.

Figures

Fig. 1.
Fig. 1.

T. sixtelae type specimen (PIN-2584/10). (A) Close-up of skull (B and C) Complete skeleton. Salamander apomorphies are in black. b.d, branchial denticles; d, dentary; e, ectopterygoid; f, frontal; fe, femur; fi, fibula; hy, hypobranchial; hu, humerus; il, ilium; m, maxilla; na, neural arch; pl, palatine; p, parietal; pm, premaxilla; ps, parasphenoid; pt, pterygoid; r, rib; ra, radius; sc, scapula; sq, squamosal; sr, sacral rib; ti, tibia; ul, ulna. PIN, Paleontological Institute of the Russian Academy of Sciences Moscow.

Fig. 2.
Fig. 2.

T. sixtelae new, larger specimen (FG 596/V/20). (A and B) Entire skeleton, preserved as natural mold. (C and D) Mirror-imaged close-up of skull as derived from casting natural mold. (E) Restoration of skull (dorsal view). Salamander apomorphies are in black. FG, Technische Universität Bergakademie Freiberg.

Fig. 3.
Fig. 3.

Evolutionary history of lissamphibians, with Triassurus at the base of the salamander stem lineage. Squares denote important synapomorphies, with all those shared by Triassurus mapped in black. The positions of Gerobatrachus and Eocaecilia are considered equivocal, due to substantial conflicting evidence.

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References

    1. Anderson J. S., Focal review: The origin(s) of modern amphibians. Evol. Biol. 35, 231–247 (2008).
    1. Marjanovic D., Laurin M., The origin(s) of extant amphibians: A review with emphasis on the “lepospondyl hypothesis”. Geodiversitas 35, 207–272 (2013).
    1. Pardo J. D., Small B. J., Huttenlocker A. K., Stem caecilian from the Triassic of Colorado sheds light on the origins of Lissamphibia. Proc. Natl. Acad. Sci. U.S.A. 114, E5389–E5395 (2017). - PMC - PubMed
    1. Bolt J. R., Lissamphibian origins: Possible protolissamphibian from the lower permian of Oklahoma. Science 166, 888–891 (1969). - PubMed
    1. Anderson J. S., Reisz R. R., Scott D., Fröbisch N. B., Sumida S. S., A stem batrachian from the Early Permian of Texas and the origin of frogs and salamanders. Nature 453, 515–518 (2008). - PubMed

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