蜥臀目霸王龙及有鳞目沧龙牙齿组织的微细结构

本文是利用扫描电子显微镜对陆栖恐龙tvrannosaurid与海栖渐增mosasaurid”牙齿结构进行的比较解剖学研究。化石采自加拿大RedDeerhiverValley上白里统Horse－shoeCanyon组。通过研究地层中出现的生物化石,特别是动物牙齿的组织结构,可以了解动物为了适应生活环境而发生的进化过程,也可以推测它们的系统发育关系。tyrannosaund与mosas。id都拥有锥状的同形齿,牙齿侧向扁平,且略向后弯曲。研究结果确认了tyrannosaurid的牙齿由于薄层的无柱釉质bPrismaticenamel）向齿质的侵人而造成许多的凹凸构造,此锯齿状构造沿着牙齿的前后缘,由牙齿的顶端分布至基部。因此tyrannosaurid的牙齿呈现着锐利的切缘;在这些凹凸状切缘的沟与小窝的深部可观察到有机物的沉积。但是类似的锯齿状构造只能在齿冠呈钝圆状的mosasaurid牙齿的基部附近观察到。我们以扫描电子显微镜（SEM）检索,确认两爬行类的齿质皆是属于中间型的真性齿质（intermediatetypeorthodentine）;所谓orthodentine即是细管齿质（tubulardentine）。tyrannosaurid的真性齿质的齿质小管只在齿质一釉质相接处Uentino—enamaljunction）附近放散出规则性的分歧与末枝。但mosasaurid的真性齿质的齿质J。管,在齿质的中间层与表层中,呈现着由复杂     

A fishy mosasaur: the axial skeleton of Plotosaurus (Reptilia, Squamata) reassessed

The concept of convergence, that is, how unrelated animals independently evolve similar morphological traits, is a fundamental aspect of evolution. Hitherto, the Mesozoic ichthyosaurs were regarded as the sole obligate marine reptiles that achieved a fully streamlined body and a semilunate tail fluke. However, analyses of vertebral centrum morphometrics and process orientation have revealed that a subsequent clade of secondarily aquatic reptiles, the mosasaurs (here exemplified by the advanced, mid-Maastrichtian mosasaurine Plotosaurus ), had developed a deep, fusiform body and a probable pursuit-predatory behaviour by the time of their sudden extinction at the Cretaceous–Paleogene boundary. Stringent physical constraints and selection pressures, imposed by the surrounding water, probably were responsible for this spectacular example of large-scale evolutionary convergence.     

A mosasaur from the Cenomanian of Russia

The premaxilla of a mosasauroid lizard from the Lysaya Gora 3 locality in Saratov (Upper Cretaceous, Cenomanian) is described. To date, the oldest known mosasaur remains have been dated Turonian. The premaxilla is most similar in morphology to that of Russellosaurus from the Turonian of the United States; however, the absence of sufficient diagnostic characters only allows its attribution to Mosasauridae indet.     

Mosasaurus beaugei Arambourg, 1952 (Squamata, Mosasauridae) from the Late Cretaceous phosphates of Morocco

Mosasaurus beaugei Arambourg, 1952 was based on isolated teeth from the Maastrichtian phosphatic deposits of Morocco. The recent discovery of new material, including skull and mandibular remains, improves our knowledge of this species. M. beaugei shares the following synapomorphies with the genus Mosasaurus: large teeth bearing two prominent carinae and with asymmetrical labial and lingual surfaces, the labial one being flattened and strongly facetted and the lingual one being convex; premaxillae with a small pointed rostrum and dentary without rostrum; palatal elements closely united; coronoid with very large ventromedial process overlying the prearticular. M. beaugei is characterised by the following autapomorphies: 12-13 maxillary teeth; marginal teeth bearing 3-5 prisms on the labial surface and 8-9 on the lingual one; palatine with posterior border concave and perpendicular to the long axis of the skull; splenial visible laterally on half of the dentary ventral surface; coronoid with anterior wing well developed and bearing two notches. M. beaugei is only known to date in the Maastrichtian phosphates of Morocco.     

Yaguarasaurus columbianus (Reptilia,Mosasauridae), a primitive mosasaur from the Turonian (upper cretaceous) of Colombia

New remains of Yaguarasaurus columbianus found in the Turonian beds of the upper valley of the Magdalena River, in Colombia, are described. Three aspects of the cranial morphology of Y. columbianus are of particular interest. First, its morphology is one of the most primitive among mosasaurs; second, it exhibits most similarities to the cranial morphology of the aigialosaurs; and finally, it exhibits some traits that are unknown in other mosasaurs, including certain cranial features that resemble those of the terrestrial varanoids.