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LIST OF THE RICHARDS SPUR (FORT SILL) TETRAPOD PALEOFAUNA Stratigraphic chart of the lower Permian (partial) Content updated March 20, 2006
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OROMYCTER DOLESORUM AND A POSSIBLE NEW FORT SILL CASEASAUR? Synapsida-Caseasauria-Caseidae?
Sullivan and Reisz (1999) reported the presence of an unidentified caseid at Richards Spur, later,this caseid was described, by R.R. Reisz as a new basal member of Caseidae, and the sister taxon to all other caseids. Oromycter differs from all other caseids for the proportions of lacrimal, for the maxilla that lacks the narial emargination, the teeth lack the distal leaf -like serrations, instead, the spatulate apex portion is supported by a midline ridge with the sides roughened. Caseids are basal synapsid, member of Caseasauria, the most plesiomorphic group of Synapsida. They are characterized by an enlarged narial opening, rostrum and bulbous teeth. The teeth are circular at the base, in cross section, the center portion of the tooth is bulbously enlarged, the tips are spatulate and serrated in varying degrees. The centrum of the dorsal vertebrae has the ventral surface broad and flattened and the lateral sides deeply in-pinched. The narrow neural arches have the zygapophyses not extending laterally beyond the vertebral centrum. The caseids phalanges are short with large proximal and distal ends, the interphalangeal surfaces are not perpendicular to the long axis of the phalanx, but are tilted to create large surfaces. The ungual phalanx has a massive retractor process, and a spatulate distal expansion that is separated from the dorsal surface of the bone by two grooves that extend from the level of the retractor process to the tip of the phalanx. Recently it was found at Fort Sill other probable caseasaur material that almost for sure cannot belong to Oromycter. Here there is a short description of this material: 1) premaxilla: it has place for 4 teeth (where Oromycter has only 3), the first is the longer and is slanting forward. The teeth are bulbous with broad round base and blade-like tip recurved on the lingual side, they are similar to the ones described in Oromycter, but are more elongate and lack the extensive bone of attachment around the base of the teeth. As in Oromycter there are large anterior foramina on the external premaxillary surface, the palatal process is modest, and a large foramen open dorsally, at the base of the broken dorsal process of premaxilla. 1) premaxilla: lateral and medial view 2) Premaxilla fragment: the preserved part is identical to the first premaxilla. The fragment is broken in corrispondence of the 2nd t00th, the 4th is perfectly preserved, and show an incipient multicuspid morphology that is typical of the caseids 1) premaxilla fragment: lateral view 2) premaxilla fragment: medial view 3) premaxilla fragment, posterior view 3) Maxilla fragment: is the middle part of the maxilla, the lateral side is not vertical but sligtly tilted as in other caseasaurs, it is delicately sculptured and pierced by supra-alveolar foramina, it has place for 6 teeth, three of them are well preserved and show no differences from the ones present on the premaxilla, or on the dentaries. Medially there is a long surface for the sutural contact with palatine that finished just above the most anterior preserved tooth; anterior to it, it start the maxillary border of the internal naris, above and all along the fragment, is visible the sutural surface for the lacrimal. The height of the maxilla does not increase abruptly in corrispondence of the beginning of the maxillary border of external naris, so, probably the diagnostic large anterodorsal process of the maxilla, is not high as in Oromycter or the other caseids 1) maxilla fragment: lateral view 2) maxilla fragment: medial view 3) maxilla fragment: posterior view 4) Right and left dentaries: two dentaries were found together but not articulated, and, unfortunately, after, were glued together. The left ramus was found exposed, the right ramus was found inside the matrix, perhaps this is the cause of the slight difference of colour. As they are of the same dimensions, probably they belong to a single individual. The right ramus has place for 13 teeth, 5 of them are broken, the left ramus has place for 10 teeth, 2 of them are broken. The anterior teeth are the longer and are slanting forward as the premaxilla ones, the shape of the teeth is the same of the ones described above, but the posterior teeth are more pointed than the anterior ones. Laterally, the dentaries are sculptured in the same way of the maxilla fragment, and are pierced by foramina that are more concentrated anteriorly. The dentaries are quite deep, but reduced their height abruptly at the level of the 8th tooth, where the ventral margin turn medially, so, though the splenial was large and participate to symphysis, probably there is not the typical caseid chin. Medially, there is a well developed splenial sutural surface, and just above it and below the tooth row, on the right ramus, there is groove that start at the level of 9th tooth and extends posteriorly for all the ramus length, a possible sutural surface for a thin anterior coronoid. A fragment of splenial is present below the teeth 4-5-6 of the same right ramus. 1) right and left dentaries: lateral view of the left ramus 2) right and left dentaries: ventral and occlusal views 5) Some caseasaur postcranial material that could belong to Oromycter or to the above described caseasaur 1) caseasaur postcranial: dorsal vertebrae 2) caseasaur postcranial: caudal vertebra 3) caseasaur postcranial: phalanges 4) caseasaur postcranial: ungual phalanx
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