Caseasauria

Abstract: This study represents a re-investigation of two historical fossil discoveries, Callibrachion gaudryi (Artinskian of France) and Datheosaurus macrourus (Gzhelian of Poland), that were originally classified as haptodontine-grade sphenacodontians and have been lately treated as nomina dubia. Both taxa are here identified as basal caseasaurs based on their overall proportions as well as dental and osteological characteristics that differentiate them from any other major synapsid subclade. As a result of poor preservation, no distinct autapomorphies can be recognized. However, our detailed investigations of the virtually complete skeletons in the light of recent progress in basal synapsid research allow a novel interpretation of their phylogenetic positions. Datheosaurus might represent an eothyridid or basal caseid. Callibrachion shares some similarities with the more derived North American genus Casea. These new observations on Datheosaurus and Callibrachion provide new insights into the early diversificatio...

Abstract: In this study, the evolution of the long bones in a group of basal synapsids was analysed, belonging to the caseids (Synapsida, Caseasauria, Caseidae), a crucial Palaeozoic group of terrestrial vertebrates. During their evolutionary history, caseids transitioned from small faunivorous tetrapods such as Eocasea martini (reaching ~20 cm total length), to gigantic herbivores such as Cotylorhynchus hancocki (reaching almost 7 m in length). In this analysis, morphometric techniques (i.e. Principal Component Analysis, Reduced Major Axis (regression) slopes) and phylogenetic methods (construction of metric trees) were used in a comparative and integrated way in order to study the major changes in the long bones in the course of caseid evolution, and identify in which nodes and terminal branches more extreme repatterning of structures is concentrated. The analysis showed a decoupling between the long bones of the fore- and hindlimbs, with the hind leg remaining more conservative and congruent to a basal pattern. By contrast, the forelimbs (especially the ulna and radius) show greater restructuring in the course of evolution, with an allometric strengthening not limited to species of very large size. An overbuilt appendicular skeleton was detected as early as taxa small to medium in size, indicating that the strengthening is not related in a simple and linear way to a structural response to gigantic body size. Because this robust structure is already present in small- to medium-sized taxa, it may have been subsequently exapted, allowing to reach the colossal body size of more derived members of Caseidae, which rank among the largest reached throughout the Palaeozoic.

Abstract: The Early Permian amniote Oedaleops is generally considered to be one of the basalmost pelycosaurian-grade synapsids. Thus it occupies a key position for understanding the phylogenetic relationships of basal synapsids specifically and basal amniote interrelationships more generally. This assessment has until now been based almost exclusively on the remains of a single skull from the Lower Permian Cutler Formation of north-central New Mexico. The identification of additional cranial as well as numerous postcranial elements of at least three additional individuals now permits a more complete understanding of its anatomy and allows the first attempt at a partial body reconstruction of this basal pelycosaurian-grade synapsid. Oedaleops is confirmed as an extremely basal synapsid taxon, but the addition of postcranial data from Oedaleops to data matrices of earlier phylogenetic analyses unexpectedly weakens, as opposed to strengthens, support for the hypotheses of a monophyletic Eothyrididae.

Abstract: A new genus and species of a basal synapsid Caseidae, Martensius bromackerensis, is described based on four partial to nearly complete mostly articulated skeletons that provide a comprehensive knowledge of the skeletal morphology. All four specimens were collected from a single site, the Bromacker quarry, in the Lower Permian Artinskian Tambach Formation, Germany. The Bromacker caseid is the first to be reported from Germany and can be easily distinguished from all other caseids based on substantial lists of autapomorphic and plesiomorphic characters. Of the four caseid specimens only the smallest, a juvenile, and the largest, an adult designated as the holotype, are nearly complete, articulated, and possess skull material: in the juvenile a small partially articulated portion of the skull, and in the adult a nearly complete but dorsoventrally crushed skull. The two specimens are distinguished from one another by features attributed to different ontogenetic stages of development, which include skeletal ossification, proportional dimensions of elements, and most interestingly marginal dentitions. The last category includes a feature unique among caseids of an ontogenetic change in the dentition from insectivorous in the juvenile specimen to what is believed to be an omnivorous dentition in the adult.A phylogenetic analysis posits the Late Pennsylvanian Eocasea martiniReisz and Frobisch, 2014, as the basalmost member of the monophyletic Caseidae and the later occurring middle Early Permian Bromacker caseid as the sister taxon of the remaining late Early and Middle Permian members of the clade. This series of relationships parallels a proposed chronology of evolutionary changes in the dentitions and associated diets of caseids.