Australerpeton cosgriffi

Eltink, Estevan, Dias, Eliseu V., Dias-Da-Silva, Sérgio, Schultz, Cesar L. & Langer, Max C., 2016, The cranial morphology of the temnospondyl Australerpeton cosgriffi (Tetrapoda: Stereospondyli) from the Middle-Late Permian of Paraná Basin and the phylogenetic relationships of Rhinesuchidae, Zoological Journal of the Linnean Society 176 (4), pp. 835-860 : 853-854

AUSTRALERPETON COSGRIFFI , A LONG- SNOUTED BASAL STEREOSPONDYLI

The long-snouted morphology of Au. cosgriffi diverges from other basal stereospondyls that are shortsnouted, e.g. Lap. nana ( Yates, 1999) , Ara. nigra ( Piñeiro et al., 2012) , Pe. pustulatus ( Panchen, 1959) , and Ly. huxleyi ( Jeannot et al., 2006) . Amongst the characters observed in basal stereospondyls, some are related to the short-snouted morphology (with synapomorphies indicated by asterisks): parabolic preorbital region (character 1-0); prenarial portion shorter than naris (character 5-0); lacrimal shorter than nasal (character 28-1*); premaxilla outline parabolically rounded (character 53-0); vomerine plate short, as wide as long (character 60-0); prefrontal longer than frontal, indicating a retraction in the frontal length (character 173-0*).

However, Au. cosgriffi shares with other stereospondyls the contact between tabular and exoccipital in the paroccipital process (character 46-1*) and the oblique ridge on the posterior face of the quadrate ramus of the pterygoid (character 91-1*), differentiating it from non-Stereospondyli Stereospondylomorpha, such as K. vetusta ( Gubin, 1991) and Pl. stuckenbergi ( Gubin, 1991) . These species have the opisthotic forming part of the paraoccipital bar and the oblique crest absent, or rudimentary as in K. vetusta (PIN 521/1). In the posterior region of the palate ( Fig. 12 ), the parasphenoid denticle field enlarged to a transverse ‘belt’ (or posterior margin arch-shaped) (character 199-1/2*) and the ridges on the borders of the interpterygoid vacuity (character 200-1*) are described as synapomorphies of Stereospondyli . In addition, Au. cosgriffi and stereospondyls share the parasphenoid bearing an extensive suture with the pterygoid (character 84-2); ventral ‘pockets’ on the flat ventral surface of the parasphenoid (character 76-2); and the internal carotid artery passing through the dorsal surface of the parasphenoid plate (character 82-2).

Regarding the status of Au. cosgriffi as a longsnouted basal stereospondyl, the elongation of the snout is convergent with that of the Russian non- Stereospondyli stereospondylomorphs. Both taxa were present at the same time (Middle–Late Permian), in Gondwana and Laurasia, respectively, but represent different groups. The long-snouted morphology of Platyoposaurinae (e.g. Pl. stuckenbergi ), Archegosaurinae (e.g. Collidosuchus tchudinovi ), and Tryphosuchinae (e.g. K. vetusta ) is convergent when the tapering of the preorbital region (character 1-1) and the narrowing of the vomerine plate (character 60-1) are observed; here considered as plastic characters. Au. cosgriffi shows that long-snouted forms seem to have been present early in Stereospondyli evolution (Middle/Late Permian), which later was represented by Triassic Trematosauridae , such as the Lonchorhynchinae Aphanerama rostratum and Cosgriffus campi.

Figures

Figure 12. Parasphenoids of Eryopiformes in ventral view, including Stereospondyli (see characters 27, 76, 82, 199, 209 in Supporting information Appendix S2). A, Eryops megacephalus (AMNH 4673). B, Platyoposaurus watsoni (PIN 161/ 20). C, Australerpeton cosgriffi (UFRGS-PV-0224-P). D, Uranocentrodon senekalensis (TM 185). E, Lydekkerina huxleyi (CAMZM T.238). F, Benthosuchus sushkini (PIN 219/2257). Scale bars: A, D = 5 cm, B, C, F = 3 cm, E = 1 cm.