Karaurus and the origin of frogs + salamanders

Figure 1. Karaurus in situ. About the size of a living salamander.

Figure 1. Late Jurassic Karaurus in situ. About the size of a living salamander.

Karaurus sharovi (Ivachnenko 1978; Late Jurassic; Figs. 1, 2) nests with Celtedens (Fig. 3) in the large reptile tree (LRT, 1467 taxa; Fig. 4)  and resembled living salamanders (Fig. 5) in size, shape and lifestyle. Here (Fig. 2) certain skull bones are reidentified. The orbit was confluent with an upper + lateral temporal fenestra that appeared by the loss of the posterior circumorbital bones.

Figure 2. Karaurus drawing from Carroll 1988, originally from Ivanchenko 1978, photo of same, DGS of same. Colors standard. Some re-identify bones. Hypothetical eyeball added. It does not have to fill the orbit, but it could.

Figure 2. Karaurus drawing from Carroll 1988, originally from Ivanchenko 1978, photo of same, DGS of same. Colors standard. Some re-identify bones. Hypothetical eyeball added. It does not have to fill the orbit, but it could. The former squamosal is a tabular + supratemporal. The lacrimal and prefrontal are not fused. Postparietals are present.

Post circumorbital bones are also missing,
in Celtedens (Fig. 3). distinct from frogs, like Rana, and salamanders, like Andrias (Fig. 5).

Figure 3. Celetendens is the closest relative to Karaurus in the LRT.

Figure 3. Celetendens is the closest relative to Karaurus in the LRT.

FIgure 2. Subset of the LRT focusing on lepospondyls including salamanders and frogs.

Figure 4. Subset of the LRT focusing on lepospondyls including salamanders and frogs.

The previous illustration of the giant Chinese salamander skull
(genus: Andrias; Fig. 5) is here updated based in new understandings of homologous bumps and sutures.

Figure 3. Revised skull of Andrias japonicas, the giant Chinese salamander. This was informed by recent studies of the mudpuppy, Necturus.

Figure 3. Revised skull of Andrias japonicas, the giant Chinese salamander. This was informed by recent studies of the mudpuppy, Necturus.


References
Ivanchenko KF 1978. Urodelans from the Triassic and Jurassic of Soviet Centra Asia. Paleontological Journal 12(3):362–368.

7 thoughts on “Karaurus and the origin of frogs + salamanders

  1. Dear David,

    here a Link may be a new information for you to check

    https://www.pnas.org/content/early/2020/05/05/2001424117
    A Triassic stem-salamander from Kyrgyzstan and the origin of salamanders
    View ORCID ProfileRainer R. Schoch, Ralf Werneburg, and Sebastian Voigt
    PNAS first published May 11, 2020 https://doi.org/10.1073/pnas.2001424117

    Edited by Neil H. Shubin, University of Chicago, Chicago, IL, and approved April 3, 2020 (received for review January 24, 2020)
    Significance

    The origin of modern amphibians remains controversial, and especially the fossil record of salamanders remains poor. Their tiny, feeble skeletons are rarely preserved in rocks of the early Mesozoic era, the time frame in which they are believed to have originated. Here we report 230 million-year-old fossils from Kyrgyzstan, Inner Asia, providing the most ancient evidence of salamanders. They enable us to reconstruct crucial steps in the evolution of the salamander body plan, sharing numerous features with ancient amphibians, the temnospondyls. These finds push back the rock record of salamanders by 60 to 74 Ma and at the same time bridge the wide anatomic gap among salamanders, frogs, and temnospondyls.
    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.

    https://www.scinexx.de/news/biowissen/aeltester-salamander-der-welt-entdeckt/

    Ältester Salamander der Welt entdeckt
    330 Millionen Jahre altes Fossil wirft neues Licht auf frühe Entwicklung der Amphibien
    Ur-Salamander
    Fossil des 230 Millionen Jahre alten Ur-Salamanders Triassurus sixtelae. © Rainer R. Schoch

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