似卞氏兽(三列齿类爬行动物)新材料

本文记述了四川下沙溪庙组发现的三列齿类新材料,归入似卞氏兽属,建立—新种,自贡种.新材料首次揭示了该类动物的鼻腔构造.

NEW MATERIAL OF BIENOTHEROIDES (TRITYLODONT REPTILE) FROM SHAXIMIAO FORMATION OF SICHUAN

Two records of late tritylodonts from Jurassic Sichuan were known: Bienotheroides wanhsienensis (Young, 1982) from Upper Shaximiao Formation and Polistodon chuannanensis (He and Cai, 1984) from Lower Shaximiao Formation. In the May of 1984, when Z. M. Dong visited Sichuan and was observing the dinosaur collection in the Zigong Museum, a tritylodont skull was recognized and brought to IVPP with the consent of the museum and studied by the present author. It come from the same layer as that of Polistodon chuannanensis and the same locality where numerous skeletons of dinosaur were excavated. According to the dinosaur fauna, the age is considered as Middle Jurassic. Apart from the loss of snout region and the skull roof, the skull is relatively complete. All the characteristic features of the genus Bienotheroides are present here. The extreme retreat of maxillary and the extraordinary extension of the lacrimal and palatine, resulted in the direct connect of premaxillary and palatine on the palatal surface. Moreover, the thin and very high zygomatic arch surrounds broadly the whole lateral surface of the skull (plate I). Basi-parasphenoid and pterygoid region is short, wide and flat, without keel-like structure, exactly alike to that of Bienotheroides wanhsienensis. The postcanine teeth are subquadrangular in shape, with breadth slightly exceeds the length. Nevertheless, the cuspules in front of the main cusps are bigger and the minute one at the outer cusp-row is not observed. This makes the teeth more Bienotheriurn-like consequently, and the main reason for erecting a new species —Bienotreroides zigongensis, sp. nov. In addiction, the prootic foramen on the lateral flange of the prootic is doubled in Bienotheroides zigongensis rather than single as in other species. Polistodon chuannanensis has an expanded zygomatic arch not like that of Bienotheroides. The depth of the arch in Polistodon increases gradually backwards, so as to give a triangular outline in lateral aspect. The nasal cavity of this animal is described. It is large and wide, maximum breadth of the preserved portion is 24 mm, it decreases to 10 mm at the rear end. Dorsally, the median ridge of mid-nasal septum, together with the left turbinal ridge are left. From right side, a very short lacrimal duct is exposed, and below it, an ellipsoid fossa should represent the maxilla sinus.