On a new stereospondylomorph temnospondyl from the Middle/Late Permian of Southern Brazil
Authors:
Strapasson et al
Abstract:
A new temnospondyl is described from the Middle/Upper Permian sequence of the Paraná Basin (Rio do Rasto Formation) in southern Brazil. The material consists of disarticulated cranial and postcranial elements, preserved in association. The cranial elements include part of the orbital region of the skull roof, the basicranium, a number of endocranial elements, stapes and a right hemimandible. The postcranial elements include vertebrae, ribs, pectoral girdle elements, a right femur and a cluster of scales. The new species displays a rhinesuchid pattern, which is similar to the South African rhinesuchids from the Upper Permian Beaufort Group of the Karoo Basin, but differs from them by the presence of a robust and elongated epipterygoid with a blade-like anterior process in addition to elongated and deeper muscular pockets on the parasphenoid, which allow the assignment of this specimen to a new species. However, the phylogenetic analysis grouped the material described herein and Australerpeton cosgriffi (Barberena, 1998) inside Stereospondylomorpha, in a transitional position between the Laurasian assemblages and South African temnospondyls. This result supports a connection between the Brazilian and Eastern European Permian fauna and provides important data for future biostratigraphic studies.
An Eryops-like interclavicle from the Early Permian of the Saar-Nahe Basin, and a discussion of temnospondyl interclavicle characters
Authors:
Witzmann et al
Abstract:
A large, isolated temnospondyl interclavicle from Rockenhausen, Rhineland-Palatinate, is described that is derived from the Early Permian Meisenheim Formation of the Saar-Nahe Basin, south-western Germany. The element resembles closely the interclavicle of the North American genus Eryops in the following characters that justify its assignment to an eryopid temnospondyl: (1) The broad-ovate shape with a narrow, convex anterior margin and slightly convex or straight anterolateral margins, and the length-to-width ratio of approximately 0.7; (2) the ventral surface with a raised triangular field and the irregular dermal sculpture consisting of transversely oriented ridges, furrows and pits; (3) the anteroposteriorly shortened clavicular facets. The interclavicle from Rockenhausen represents the first unambiguous remain of an eryopid in the Saar-Nahe Basin. In contrast to dissorophoid and stereospondylomorph temnospondyls that constitute autochthonous faunal elements in the lakes of the Saar-Nahe Basin, eryopids seem to be allochthonous and might have been washed in from more distant habitats. Comparison of the morphologies and proportions of temnospondyl interclavicles suggests that the plesiomorphic state for temnospondyls is a proportionally small interclavicle equal in length and width or slightly longer than wide. Interclavicles that are broader than long are a derived character of zatracheids, certain dissorophoids (branchiosaurids) and Eryops and the specimen from the Saar-Nahe Basin, but evolved convergently in these groups. The much enlarged, elongate interclavicles appear to be a synapomorphy of stereospondylomorphs.
A new specimen of the temnospondyl Australerpeton cosgriffi from the late Permian of Brazil (Rio do Rasto Formation, Paraná Basin): comparative anatomy and phylogenetic relationships
Authors:
Eltink et al
Abstract:
A new temnospondyl specimen from the Rio do Rasto Formation (late Permian, Paraná Basin) of south Brazil is composed of a left mandible, right pelvis, femur, tibia, and fibula. Preserved lower jaws are rare for Australerpeton cosgriffi, and the weak ossification of the temnospondyl postcranium renders their preservation generally uncommon. A detailed comparative description of the material allowed its assignment to Australerpeton cosgriffi, and yielded new information about the morphology of mandible, pelvis, and hind limb of that taxon. This long-snouted temnospondyl has uncertain affinities and has been assigned either to stereospondyl Rhinesuchidae or to archegosaurid Platyoposaurinae. Reassessment of the phylogenetic placement of Australerpeton cosgriffi, with information drawn from the new specimen, confirms a basal stereospondyl position, between Peltobatrachus pustulatus and Rhinesuchidae. The synapomorphies shared with other stereospondyls include tabular and exoccipital contacting in the paroccipital process; parasphenoid articulates with corpus of the pterygoid forming a broad contact along the lateral margins of the parasphenoid plate; internal carotid passes through the dorsal surface of the parasphenoid plate; and parasphenoid denticles field enlarged to a transverse ‘belt’ extending between the pterygoid-parasphenoid articulations. Accordingly, Australerpeton cosgriffi represents one of the first stereospondyls, and the oldest long-snouted member of the group. The Paraná Basin can be included within the stereospondyl ancestral range, and dispersion and diversification of this clade appears to have happened before the Permo-Triassic boundary.
Paleohistology and histovariability of the Permian stereospondyl Rhinesuchus
Authors:
Julie McHugh
Abstract:
Rhinesuchids are a basal group of stereospondyls, one of the most successful groups of early amphibians. They are also the only group of stereospondyl amphibians present prior to the Permian–Triassic boundary. Here, Rhinesuchus postcranial material is sampled for paleohistological analysis for the first time and gives us a model for growth in basal stereospondyls. Bone microstructure confirms an aquatic lifestyle for Rhinesuchus, and indicates that it was a long-lived taxon (greater than 30 years), growing seasonally like other amphibians. The shaft of the iliac dorsal process preserves the largest number of rest lines, suggesting it as a preferred element to estimate minimum age in basal stereospondyls. Femoral diaphyseal sections are readily comparable to distal rib sections for skeletochronological purposes, but preserve fewer rest lines than the ilium. Narrowly banded annuli and rest lines in the inner cortex of Late Permian elements indicate a taxon that was able to weather successive seasons of harsh conditions, and perhaps indicates a reason for the success of Stereopsondyli through the Permo-Triassic mass extinction.
