Diagnoza

An euparkeriid similar to Euparkeria capensis, but smaller, having a modal skull length of about 60 mm, modal femur and tibia length about 40 mm and 30 mm, respectively. Osmolskina czatkowicensis differs from Euparkeria in having a slightly overhanging premaxilla (but less so than in proterosuchids) that was weakly attached to the maxilla (with no peg and socket articulation developed), and was probably separated from it by a slit−like additional antorbital space; in having a subquadrangular nasal process of the maxilla, and in having a barely recessed antorbital fenestra. In O. czatkowicensis the preorbital part of the skull is less elongated than in Euparkeria which is best expressed in maxilla proportion, the maximum maxilla length to depth being 5:1 in O. czatkowicensis (7:1 in E. capensis). The estimated tooth count is 13 in both species. The premaxillary body is finer in O. czatkowicensis (maximum length to depth 10:3) than in E. capensis (10:4).The posterolateral process of the premaxilla slopes at an angle of about 50° in O. czatkowicensis while being almost vertical in E. capensis. In O. czatkowicensis the orbit is more rounded while tapering ventrally in E. capensis. The mandible of O. czatkowicensis does not increase in depth posteriorly unlike that of Euparkeria. O. czatkowicensis differs from Euparkeria in the shorter humerus, more twisted femur (distal to proximal end angle in Osmolskina about 55°, in Euparkeria 32°), the extremely anterior position of the coracoid foramen or notch and less compressed teeth. Compared to Dorosuchus (femur about 90 mm, tibia about 70 mm in length, femur twist about 40°), Osmolskina is smaller and has a more twisted femur.

Porównanie

Osmolskina shares with Euparkeria a unique mosaic of character states, some of which are considered plesiomorphic while others are synapomorphic for a more inclusive clade. Both genera differ from Proterosuchus in three apomorphic characters: a subvertical basisphenoid, with ventro−laterally oriented basipterygoid processes, and with the entry foramina for the cerebral branches of the internal carotid arteries lying in a posteroventral position; the absence of teeth on the transverse flange of the pterygoid; and the development of a small anterior process on the ilium. They also differ in having rather short cervicals and well−developed dorsal osteoderms.

As compared to erythrosuchids, Osmolskina and Euparkeria represent a totally different habitus. With the Erythrosuchidae, they share neither the heavy proportions of the skull, nor the extremely short cervical centra. They also differ in a mosaic of braincase character states, and in having a more lightly built locomotory apparatus. Although the polarity of these characters is not clear, the differences suggest that Osmolskina and Euparkeria should both be placed outside Erythrosuchidae.

In contrast to most Archosauria (excluding phytosaurs, but not rauisuchians), Osmolskina and Euparkeria lack an ossified medial wall of the otic capsule, and show poor ossification of the fenestra ovalis. Furthermore, they have a posteroventral, rather than lateral, position of the entry foramina for the cerebral branches of the internal carotid arteries, and retain teeth on the palatine plate of the pterygoid. Osmolskina is thus an archosauriform of a grade above that of Proterosuchus but outside either the erythrosuchids or the crown−group. Its position in the cladogram corresponds to that of Euparkeria.

For stratigraphic reasons, it is important to compare Osmolskina with rauisuchians, the only archosaurian group currently recorded from the Lower Triassic (Late Olenekian of Russia). Apart from the above listed braincase characters, both Osmolskina and Euparkeria differ from rauisuchians in the subvertical life position of the ilium, a weak flexion of its anterior process, and in the absence of a protruding tuber above the anterior part of the acetabulum. They differ from erythrosuchids, rauisuchians, and ornithosuchids in having a flat lateral surface to the maxilla and a straight ventral margin (instead of a convex one).

Autekologia

Terrestrial, carnivorous

Występowanie geograficzne

Only locus typicus

Zasięg czasowy

Only stratum typicum

Materiały muzealne

Institute of Paleobiology PAN, Warsaw (ZPAL)

Literatura

Borsuk−Białynicka, M. and Evans S.E. 2003. A basal archosauriform from the Early Triassic of Poland. Acta Palaeontologica

Polonica 48, 649–652.

Borsuk−Białynicka, M. and Evans, S.E. 2009. Cranial and mandibular osteology of the Early Triassic archosauriform

Osmolskina czatkowicensis from Poland. Palaeontologia Polonica 65, 235–281.

Borsuk−Białynicka, M. and Sennikov, A.G. 2009. Archosauriform postcranial remains from the Early Triassic karst deposits of

southern Poland. Palaeontologica Polonica 65, 283–328.