ABSTRACT

Theropod dinosaurs are minor components of Late Triassic ecosystems in North America, comprising coelophysoids and various non-neotheropods from the Chinle Formation of Arizona, Utah, Colorado, and New Mexico and the Dockum Group of western Texas. By the Sinemurian (Early Jurassic), the coelophysoid “Syntarsus” kayentakatae and the large-bodied non-averostran neotheropod Dilophosaurus wetherilli from the Kayenta Formation were the dominant terrestrial predators. Theropods are virtually unknown from the intervening Rhaetian–Hettangian Moenave Formation, with the exception of two partial coelophysoid pelves from somewhere within the Dinosaur Canyon Member, which includes the Triassic–Jurassic boundary and end-Triassic mass extinction. Here we describe an anterior trunk vertebra from a non-coelophysoid, non-averostran neotheropod from the uppermost Whitmore Point Member of the Moenave Formation in southwestern Utah, which is Hettangian in age. The vertebra has prominent vertebral laminae and associated pneumatic fossae, and anterior and posterior ‘shoulders’ on the neural spine that are similar to those found in Dilophosaurus wetherilli. This vertebra belongs to a theropod that may be as many as 15 million years older than Dilophosaurus wetherilli from the middle of the Kayenta Formation in Arizona. This theropod is associated with Grallator, Eubrontes, and Characichnos theropod traces made on the shores of the Early Jurassic Lake Whitmore that are abundant in the Whitmore Point Member in southwestern Utah. Its occurrence in the Hettangian roughly coincides with the appearance of Eubrontes tracks in North America, indicating that not all contemporaneous theropod traces were made by coelophysoids.

摘要

兽脚亚目恐龙是北美晚三叠世生态系统的次要组成部分，包括来自亚利桑那州、犹他州、科罗拉多州和新墨西哥州的 Chinle 组以及德克萨斯州西部的 Dockum 群的腔骨龙类和各种非新兽脚类恐龙。由 Sinemurian（早侏罗纪）、体腔鱼“ Syntarsus ” kayentakatae和大型非阿佛罗斯龙新兽脚亚目双脊龙 wetherilli来自 Kayenta 组的食肉动物是主要的陆地捕食者。除了来自恐龙峡谷成员内某处的两个部分体腔骨外，兽脚类恐龙几乎不知道来自其间的雷蒂安-赫坦阶 Mo​​enave 地层，其中包括三叠纪-侏罗纪边界和三叠纪末大灭绝。在这里，我们描述了来自犹他州西南部 Moenave 地层最上层 Whitmore Point 成员的非体腔骨、非 averostran 新兽脚类动物的前躯干椎骨，该地层年龄为 Hettangian。椎骨具有突出的椎板和相关的气动窝，神经棘上的前后“肩部”与双脊龙中发现的相似. 这块椎骨属于一种兽脚类恐龙，它可能比来自亚利桑那州 Kayenta 组中部的Dilophosaurus wetherilli早多达 1500 万年。这种兽脚类恐龙与在早侏罗世惠特莫尔湖岸边发现的Grallator、Eubrontes和Characichnos兽脚亚目动物的踪迹有关，这些踪迹在犹他州西南部的惠特莫尔角成员中很丰富。它在赫唐阶的出现大致与北美欧布龙特足迹的出现相吻合，这表明并非所有同时期的兽脚亚目动物足迹都是由体腔动物产生的。