Karaurus and the origin of frogs + salamanders

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. 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 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.

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