Читать книгу Hadrosaurs - David A. Eberth - Страница 87

New fossil material recovered from the Arlington Archosaur Site (AAS; North Arlington, Tarrant County, Texas) includes the most complete hadrosauroid (Dinosauria: Ornithopoda) recovered from the Woodbine Formation to date, and allows for a detailed study of the postcranial anatomy of a basal hadrosauroid. The depositional setting of the AAS was a delta plain, and the host facies comprise fine-grained mudstones and claystones overlying a dense peat bed. The ornithopod fossil-bearing horizon occurs within a paleosol: a clay-rich, heavily rooted histic gleysol with numerous calcareous concretions. Hadrosauroid fossils recovered include cervical, dorsal, and caudal vertebrae; ribs, a scapula and coracoid; an ilium, ischium, and pubis; and a partial juvenile femur. Most of the remains represent a single adult individual, which experienced a complex biostratinomic and fossil-diagenetic history following death. The predominance of relatively dense bones from the axial column and limbs, and disarticulation are indicative of hydraulic sorting and limited transport of the remains. The new hadrosauroid material from the Woodbine Formation demonstrates a unique mix of plesiomorphic hadrosaurid characters and derived iguanodontian features. Whereas its exact taxonomic affinity cannot be determined presently, it is expected that this specimen will prove informative in understanding hadrosauroid evolution.