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Cranial morphology, systematics and succession of beavers from the middle Miocene Valentine Formation of Nebraska, USA

100%

Korth W. W.

Acta Palaeontologica Polonica

2008

tom 53

nr 2

Previously, it was believed that there was a dramatic turn−over in the fauna of beavers (Rodentia, Castoridae) from the Barstovian to the Clarendonian from Nebraska. Stratigraphically controlled collections of fossil castorids from the Valentine Formation, which cross this boundary, now indicate that a complete change in the castorid fauna did not occur, but instead a more gradual change and replacement of earlier taxa with more advanced taxa occurred. The range of Eucastor tortus and Monosaulax skinneri is extended from late Barstovian into the latest Barstovian Devil’s Gulch Member and the range of the otherwise Clarendonian species of Prodipoides is extended downward into the late Barstovian Crookston Bridge Member. The skulls of Monosaulax skinneri and Eucastor valentinensis are described in detail for the first time. The cranial morphology of M. skinneri is primitive for Castoroidini and that of E. valentinensis is specialized for tooth−digging behavior as in the Nothodipoidini. A new genus, Temperocastor, is proposed for E. valentinensis based on its primitive morphology of the cheek teeth and derived cranial morphology. Temperocastor represents the most primitive nothodipoidine.

Cranial morphology of the Plio-Pleistocene giant madtsoiid snake Wonambi naracoortensis

100%

Scanlon J. D.

Acta Palaeontologica Polonica

2005

tom 50

nr 1

New material and additional morphological details of a rare and phylogenetically significant large fossil snake, Wonambi naracoortensis Smith, 1976, are described from Pleistocene and Pliocene cave deposits in southern South Australia. The new data refute some previous interpretations of the morphology of this species, and have implications for the phylogenetic position of Wonambi relative to extant snakes and other fossils, including other Madtsoiidae. The nature of contacts among palatal, braincase, snout, and mandibular elements imply similar functional attributes to those of extant anilioid snakes: maxillae from multiple individuals show corrugated contact surfaces for the prefrontal, implying a tight suture; structures on the anterior and medial surfaces of the palatine choanal process are interpreted as forming extensive contacts with the vomer and parasphenoid; and the distinctly bounded facets on the basipterygoid processes and pterygoid imply little or no capacity for anteroposterior sliding of the palatopterygoid arch, hence absence of the macrostomatan “pterygoid walk”. On the frontal, interolfactory pillars were either absent or very slender, and a deep, sculptured contact surface for the nasal implies a prokinetic joint was also absent. Margins of the frontal and parietal indicate broad entry of the sphenoid into the ophthalmic fenestra, as in Dinilysia. Similarity of elements and features of the braincase (trigeminal foramen, ear region, and basipterygoid processes) with both lizards and extant snakes show that differences between snakes and other squamates have sometimes been overstated. The case for macrostomatan affinities of Wonambi is not supported by new evidence.

Ograniczanie wyników

2 Acta Palaeontologica Polonica

1 Korth W. W.

1 Scanlon J. D.

1 2008

1 2005

Wyniki wyszukiwania

Cranial morphology, systematics and succession of beavers from the middle Miocene Valentine Formation of Nebraska, USA

Cranial morphology of the Plio-Pleistocene giant madtsoiid snake Wonambi naracoortensis