Rekonstrukcja szkieletu Pamelina polonica.

Rekonstrukcja czaszki w widoku od góry i z boku.

Diagnoza

Small diapsid reptile resembling Late Triassic kuehneosaurids in having confluent nares framed by specialised premaxillae with posterolateral but not dorsomedial processes; maxilla almost excluded from the narial margin by the posterolateral process of the premaxilla; prefrontal with only a narrow contribution to the preorbital skull wall; loss of the parietal foramen; anterolateral flange on the parietal meeting postorbital to exclude the postfrontal from the margins of the upper temporal fenestra; specialised slender squamosal with a strong posterodorsal process but no anteroventral ramus; no supratemporal bone; mediolaterally compressed amphiplatyan vertebral centra with short slender transverse processes throughout the column; dichocephalous ribs on cervical vertebrae, slender holocephalous ribs on dorsal vertebrae; very lightly built skeleton, bones with internal cavities. Pamelina differs from Kuehneosaurus, Kuehneosuchus, and Icarosaurus in lacking teeth on the parasphenoid, and in having more gracile ribs and vertebrae, with short narrow circular transverse processes (unlike the extended processes of Late Triassic taxa) and only limited buttressing on the vertebral body (as against strong buttressing, especially in Kuehneosaurus). Pamelina also differs from the British kuehneosaurs in lacking three-headed ribs on anterior vertebrae (the condition in Icarosaurus is less certain). Pamelina differs from all other known Permian and Mesozoic diapsids in the combination of confluent nares with a reduced squamosal, an incomplete lower temporal arcade, an expanded quadrate, and laterally compressed amphiplatyan vertebrae with long slender transverse processes and extended ribs. The skull of the Triassic Mecistotrachelos is poorly known, but the postcranial skeleton of Pamelina differs in having relatively short cervical vertebrae.

Porównanie

Pamelina is the earliest representative of the specialised kuehneosaurs, predating known British and American taxa by nearly 40 million years. Although the skull is closely similar to those of the Late Triassic genera, Pamelina is postcranially less specialised. Long expanded transverse processes, deep anterior gliding ribs, and strongly buttressed dorsal vertebrae characterise a Late Triassic kuehneosaur clade of which Pamelina is almost certainly the primitive sister taxon.

Although Pamelina shows only a partial development of the unique postcranial morphology of the Late Triassic kuehneosaurs, its skull already shares most of the derived characters of the groups (e.g., confluent nares, loss of the parietal foramen, reduced squamosal, relatively large quadrate, loss of the supratemporal). This supports the view that kuehneosaurs represent an ancient lineage with roots in the Late Permian. Their skulls were superficially similar to those of squamates, but the groups were not closely related. Pamelina also demonstrates that major features of the distinctive kuehneosaur cranial morphology evolved before the development of the specialised postcranium.

Autekologia

Terrestrial, primitive glider, probably carnivorous (insectivorous).

Występowanie geograficzne

Only locus typicus.

Zasięg czasowy

Only stratum typicum.

Materiały muzealne

Institute of Paleobiology PAN, Warsaw (ZPAL)

Literatura

Evans, S.E. 2009. An early kuehneosaurid reptile (Reptilia: Diapsida) from the Early Triassic of Poland. Palaeontologia Polonica 65, 145–178.