摘要
本文对蜥脚类蜀龙(Shunosaurus)的脑颅分别从其头骨特征、脑垂体、耳区、视觉系统、脑神经等诸方面进行了较为详细的解剖研究,结果表明 Shunosaurus 内颈动脉不分叉;基蝶骨突强烈收缩;外淋巴囊出现在中耳及 IX、X、XI 孔与颈静脉孔内分外合等现象十分独特.因此,Shunosaurus 应视为一种特化的原始蜥脚类.
Since the first description of Shunosaurus lii, more and more skeletons of Shunosaurus have been collected, identified and described in detail (Dong et al., 1984; Zhang et al., 1984; Zhang, 1988). But for its braincase anatomy, little has been known. The present specimen is a nearly complete skull which, judging by the spatulate tooth, morphology of quadrate and the position of squamosal, represents one spieces of Shunosaurus, Some elements of the skull have been freed from the matrix and provide a number of details of the interior of the skull herebefore unrecorded. 1. The foramen of nerve II The brain cavity lies along the anterior side of the occiput and slopes slightly upward to terminate against the frontals just posterior to the midpoint of the orbit. Foramen jugular for vein jugularis internus, foramen lacerun posterius for cranial nerve IX to XI, fenestra ovalis, and openings for nerve V, III, IV are clearly exposed. The upward extension of the braincase is composed of presphenoid, parasphenoid and orbitosphenoid, where the brain nerve I, II, VI located. The exit of nerve II and the anterior cerebral artery lies near the midline, a short distance below the apex of the cleft. This only large fossa is different from those of other sauropods which all have two fossae for exit of nerve II. In Camarasaurus, the fossa is separated by presphenoid itself (Osborn, 1921; White, 1958), while the others such as Diplodocus, Barosaurus, Dicraeosaurus and Brachiosaurus, are separated by parasphenoid (Holland, 1924; Janensch, 1935). 2. Basisphenoid processes The tubera basioccipitalia and the basisphenoid processes project downward and backward. Insofar, as the braincase of the sauropods are known, the length and general form of these processes agree with the taxonomic grouping into families and yet are characteristic for each genus. Brachiosaurus, Apatosaurus and Camarasaurus form one group with strong, robust basisphenoid processes, Diplodocus, Barosaurus and Dicraeosaurus with slender attenuated processes r?present another (White, 1958), while Shunosaurus with small and weak processes uniquely. 3. Perilymphatic sac Below and posterior to the fenestra ovalis is a lateral shallow recess beside the occipital condyle. This is the position of the perilymphatic sac that didn't ever be reported in any other sauropods. Near the dorsal border of this recess is the large oval fissure for the exit of IX, X, XI nerves, together with the vein jugularis internus. There is a deep elongate groove leading to lower recess, and which is mostlikely the passage of the branch of IX, a very primitive phenomena in reptiles (Romer, 1977). 4. Relationship between IX, X, XI and vein jugularis internus In Shunosaurus, the exits of nerves IX, X, XI and vein jugularis internus are separated inside the fossa and merged outside. The exit of three nerves is separated externally from the exit of vein jugularis internus in Plateosaurus (Galton, 1984, 1985). It goes even further in Barosaurus, the exits of three nerves are definitely separated between themselves. Just anterior to the jugular foramen is the large fenestra ovalis, which is 30 mm high and 11 mm wide. Based on the other specimen, the stapes is slender and light and correspondingly slope downward and outward. 5. Internal carotid artery foramen Below the occiput, there is a large round foramen between the basioccipital processes and the basisphenoid processes, the internal carotid artery in the direction of entering. It differs from those of other sauropods and prosauropods. The internal carotid artery of Shunosaurus enters the brain directly from behind, but that of other sauropods branches and enters the brain at two side of basisphenoid processes. From the foregoing descriptions and discussions, it is clear that amongst sauropods, Shunosaurus may represent a unique primitive sauropod. This approach is coincident with that came from the study of postcranial materials.
出处
《古脊椎动物学报》
CSCD
北大核心
1991年第2期108-118,共11页
Vertebrata Palasiatica
