四川盆地上三叠统最古老的兽脚类恐龙和似哺乳四足类动物足迹

摘要

Eubrontes-and Grallator-sized theropod footprints are known from two localities in the Upper Triassic Xujiahe Formation of the Sichuan Basin,southwest China.The larger footprints include a partial trackway with two successive pes imprints that were named as Pengxianpus cifengensis.Compared with robust Eubrontes,they have slender digits,less welldefined pad impressions and display a wider digit divarication similar to the theropod ichnotaxon Kayentapus from the Late Triassic-Early Jurassic.Presently,a synonymy of the latter cannot be proved conclusively and the ichnotaxon is retained here.For both footprints,some small areas preserve skin texture with polygonal scales,the clearest preservation is in a small area on the metatarsal-phalangeal pad Ⅳ of the second imprint.The smaller theropod footprints are also part of an incomplete trackway.They show a wide digit divarication similar to Kayentapus and Pengxianpus but they are here tentatively referred to theropod footprints indet.A peculiarity on the surface with Pengxianpus is the presence of small pes or manus imprints that can be assigned to mammal-like tetrapods somewhat similar to those known from Triassic-Jurassic strata of North America and southern Africa.This is the first report of mammal-like footprints in the Triassic of southeastern Asia.%四川盆地须家河组地层已发现了两处兽脚类恐龙足迹化石点,其大小分别与实雷龙足迹(Eubrontes)和跷脚龙足迹(Grallator)相仿.其中与实雷龙足迹大小相近的足迹包括了两个连续的后足迹,并构成行迹的一部分,已被命名为磁峰彭县足迹(Pengxianpus cifengensis).与粗壮的实雷龙足迹相比,彭县足迹有着较细长的脚趾、保存尚清晰的趾垫、较宽的趾间角,这些特征都与晚三叠世-早侏罗世的卡岩塔足迹(Kayentapus)相似.目前尚不能证明彭县足迹和卡岩塔足迹属于同物异名,彭县足迹仍然被保留.两个足迹的部分区域都保存有皮肤纹理和多边形的鳞片印痕,其中最清晰的是第二个彭县足迹第四趾的跖趾垫处.与跷脚龙足迹大小相近的、较小的兽脚类恐龙足迹也组成不甚完整的行迹.它们表现出的较宽趾间角与卡岩塔足迹和彭县足迹相似,这里暂将其归入兽脚类足迹属种未定.彭县足迹的另一特别之处在于,岩板表面还有着小的前/后足迹,可归入似哺乳四足类动物足迹,其形态类似于北美和南非三叠系-侏罗系地层产出的同类足迹.这是亚洲东南部似哺乳类足迹的首次报道.