A New Specimen Of Hamipterus Tianshanensis From The Early Cretaceous In Xinjiang, China With Depositional Environment And Taphonomy Analysis

Hamipterus tianshanensis were found in the deposits of the Lower Cretaceous Tugulu Group,Hami of Xinjiang Uygur Autonomous Region,northwestern China.A large number of male and female pterosaurs and hundreds of three-dimensionally preserved pterosaur eggs and embryos were found here.However,previous studies about sedimentary environment,burial characteristics and skull restoration are very few.It is of great significance to do these studies for Hamipterus tianshanensis.A preliminary study was carried out on the characteristics of tooth alveolar arrangement,sedimentary environment and taphonomic characteristics by using methods of paleontology,petrology,sedimentology,taphonomy and statistics,such as thin section analysis,grain size distribution analysis,statistical burial feature.This paper obtains the following new results:Almost all skull and mandible specimens that have been discovered are mostly separated so far,because of which the corresponding relation of the upper and lower jaws is difficult to determine.The new specimen of Hamipterus which skull and mandible articulated together is available for observation and data statistics to find relationship between upper and lower jaw.Based on the observation,the teeth in the dentition between the maxilla and mandible are staggered,each upper tooth is placed in the front of the corresponding lower tooth in cross.Nevertheless,the teeth between the right and left side from same jaw(maxilla or mandible)are symmetrical,causing the first pair of teeth from maxilla is inserted in the middle of the first pair of teeth from mandible.Besides,two trend lines and formulas are obtained by measuring the spacing between the first tooth alveolus and other teeth alveolus in the upper and lower jaw.It was found that if the two coefficients of X are almost same,and the two constant values are less different,and the two lines are parallel and close to each other,by the way,the line of variation of the lower jaw is above on the upper jaw,then they might come from a same individual.The petrology characteristics indicate that Eskxiar-Biyishuangfei section in the study area consists of middle to fine-grained lithic sandstones.According to the grain size distribution analysis,with grain size frequency distribution histogram,the particle size of the cumulative curves,grain characteristic parameters and grain size distribution analysis formula of depositional environment,the sedimentary environment of this section was a lake.Occasionally,events of high energy such as storms occurred here.The taphonomic characteristics indicate that Hamipterus is dominant species in the fauna.The fossils are preserved without orientation and the bones are well preserved.A large number of pterosaur individuals of all ages were preserved together,indicating a mass mortality.The fossils and brown mudstone breccias were preserved together in middle-fine-grained sandstone,indicating that the sedimentary environment was a lake.The high-energy events such as large storms rolled up pterosaurs and mudstones at the bottom of the lake,after a short transport and eventually buried rapidly.