Plagiosuchus: confluent orbital-temporal fenestra, like birds and mammals

Just another case of convergence here
reminding us not to define clades on traits, but only on two select taxa, their last common ancestor and all descendants.

Plagiosuchus pustuliferus (von Huene 1922; Middle Triassic, 240mya; SMNS 57921) nests with the smaller, Gerrothorax in the large reptile tree (LRT, 1444 taxa). Plagiosuchus has a narrower skull and upper temporal fenestrae confluent with the orbits. This is partly due to the loss of the prefrontals, postfrontals and postorbitals.

Both taxa belong to the first clade
to split off from the remainder of basal tetrapods at the transition from fins to fingers and toes. Both taxa retained gills and likely never left the water.

Figure 1. Plagiosuchus skull from Damiani et al. 2009, lateral view and colors added here.

Figure 1. Plagiosuchus skull from Damiani et al. 2009, lateral view and colors added here. Lost or fused are the postorbital, postrfrontal and prefrontal bones on this basal tetrapod not far from fish. Note the relatively short dentary and long post-dentary bones.

The wide skull and laterally oriented dorsal ribs
indicate Plagiosuchus was a full-time bottom dweller with little use of its limbs other than to paddle them around like fins, supporting itself like another sit-and-wait predator, the extant frogfish.

Damiani R, Schoch RR, Hellrung H, Wernburg R and Gastou S 2009. The plagiosaurid temnospondyl Plagiosuchus pustuliferus (Amphibia: Temnospondyli) from the
Middle Triassic of Germany: anatomy and functional morphology of the skull. Zoological Journal of the Linnean Society, 2009, 155, 348–373.
von Huene F 1922. Beiträge zur Kenntnis der Organisation einiger Stegocephalen der schwäbischen Trias. Acta Zoologica3: 395–459.


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