Casea

The genus name and specific epithet honor paleontologists Ermine C. Case and Ferdinand Broili.[1]

All Casea broilii specimens come from a single fossiliferous pocket known as Cacops bone bed, located in Baylor County, Texas.[10][8] This locality, discovered and excavated by Paul Miller in 1909 and 1910, is no longer accessible today because it was submerged in the 1920s after the construction of the Lake Kemp dam.[11] The fossil pocket was about 3 m long, 1.8 m wide, and 60 cm thick.[10][8] It was part of a red clay level interspersed between strata of the upper Arroyo Formation and the coarser sediments of the lower Vale Formation (two formations of the Clear Fork Group).[10][8][7] Ammonoids faunas found in marine strata present at the base and top of the Clear Fork Group indicate that the three formations (Arroyo, Vale, and Choza) that compose it represent a relatively short geological duration corresponding to part of the Kungurian.[12][13] The location and faunal composition of the Cacops bone bed indicate the existence of a distinct fauna that lived in a geographical area far from the floodplains and deltas of coastal regions, where lived the well known fauna from the more classical Lower Permian localities of North America.[14] The Casea specimens were in association with very numerous specimens of the armoured and entirely terrestrial amphibian Cacops (more than 50 individuals are listed including ten skulls, hence the name of the bone bed), a dozen skeletons of the Varanopidae Varanops, and fragments of Seymouria and Captorhinus. Many of the bones were covered with a very thin layer of cemented clay; others were more or less cemented together in nodular masses. Most of the skeletons were lying on their belly, but some were found on their backs. On most of the skeletons the limbs were articulated. In others, the phalanges of the feet were more or less dispersed, and the tail or the entire limbs were disarticulated.[10][8] It appears from the position of the skeletons and the conditions of deposition that the bodies underwent very little disturbance after the death of the animals. For Williston, these animals would have died in a pool of stagnant and perennial water. The corpses piled on top of each other in successive layers would correspond to an accumulation spread over several generations.[10] However, no taphonomic study of the site has been published, and given the inaccessibility of the locality today it is difficult to say more.

Currently, the genus Casea contains only the species Casea broilii. In the past, three other species were assigned to the genus, but these represent today separate genera and/or are considered invalid. In 1954, Everett C. Olson reported two new species found in the Clear Fork Group in Texas, Casea nicholsi and C. halselli.[15] In 1974, Denise Sigoneau-Russell and Donald E. Russell established the species Casea rutena for a specimen from southern France.[16] These three species are known from the following material :

• Casea nicholsi is represented by two specimens from the upper part of the Vale Formation in Knox County. The holotype (FMNH UR 86) consists of a partial basicranium and lower jaw (mainly preserved as a natural cast), a large part of the vertebral column (except the tail), part of the pelvis, elements of the forelimbs, and part of the foot. The only referred specimen (FMNH UR 85) was found in direct association with the holotype and, like it, consists of a partial skull, a large part of the vertebral column without the tail, part of the shoulder bones, the pelvis, a femur, and a fibula end.[15][2]
• Casea halselli comes from more recent strata and was named after a very fragmentary skeleton found in the middle part of the Choza Formation, in Foard County. It consists of a pelvic girdle with damaged ilium, partial left femur and tibia, head of the right femur, four caudal vertebrae, and fragments of lumbar vertebrae.[15][2]
• Casea rutena comes from the Lower Permian Rodez basin in the Aveyron department in Occitanie region, in the south of France. It is known by a partial skeleton consisting of an almost complete skull, the cervical vertebrae, shoulder bones, the complete left forearm with the complete articulated left manus, and part of the right arm.[16][4]

In 2008, the first phylogenetic analysis of Caseidae revealed for the first time the paraphyly of the genus Casea, the French species Casea rutena representing a distinct and more derived genus, still not named in this study.[3] Three years later, Casea rutena was removed from the genus Casea and placed in a new genus, Euromycter, with the new combination Euromycter rutenus.[4] In 2015, another study published by Romano and Nicosia again resolved the genus Casea as paraphyletic. Casea nicholsi is identified as a taxon more closely related to the genera Caseoides and Caseopsis than to Casea broilii. Thus, C. nicholsi certainly belongs to a different genus, which is however not sufficiently well known to receive a name. Romano and Nicosia also consider the fragmentary species Casea halselli as a nomen dubium, although important differences with the type species, in the shape and robustness of the femur and tibia, suggest that they belong to a genus other than Casea.[5] According to Werneburg and colleagues, C. halselli is a problematic taxon of uncertain, possibly sphenacomorph affinity.[17]

Front part of the holotype skeleton

In the first phylogenetic analysis of Caseidae published in 2008, Casea broilii occupies a basal position within the caseidae, but is however more derived than Oromycter.[3]

Below the first cladogram of Caseidae published by Maddin et al. in 2008.[3]

A phylogenetic analysis made by Benson shows a similar position for Casea broilii. This analysis also confirms the paraphyly of the genus Casea.[18]

Below the phylogenetic analysis of Caseasauria published by Benson in 2012.[18]

A study published in 2015 by Romano & Nicosia, and including almost all the Caseidae (with the exception of Alierasaurus ronchii from Sardinia, considered too fragmentary), shows a similar position for Casea broilii. C. nicholsi is recovered as a more derived taxon, closer to the genera Caseoides and Caseopsis than to Casea broilii.[5]

Below the most pasimonious phylogenetic analysis published by Romano & Nicosia in 2015.[5]

In the phylogenetic analysis published in 2022 by Werneburg and colleagues, Casea broilii is positioned between Oromycter and “Casea” nicholsi. The latter occupies a more basal position than in the cladogram of Romano and Nicosia, being recovered as a more basal taxon than the genus Euromycter.[17]

Below is the cladogram published by Werneburg and colleagues in 2022.[17]