重庆晚侏罗世两处兽脚类足迹组合与四川盆地侏罗纪地层(英文)

重庆市已报道了4处侏罗纪的恐龙足迹点,包括下侏罗统珍珠冲组的大足化石点,该地点发现了中国迄今最古老的蜥脚类行迹;另外两处化石点(南岸和金鸡)的层位曾被视为中或上侏罗统,这里首次将其确认为上侏罗统上沙溪庙组;第4处化石点(成渝), 本文全部作者目前都未曾观察,这里不做描述。南岸化石点是南岸重庆足迹(Chongqingpus nananensis)模式标本的所在地,位于重庆市中心,曾发现过大量兽脚类足迹,如今已消逝在城市化进程中。幸运的是,这批标本被保存于重庆自然博物馆,本文作者曾前后两次对其进行研究,并得出文中的结论。南岸重庆足迹为中型足迹(平均长约29 cm), 最可能被卡岩塔足迹(Kayentapus)所囊括,这批标本中有一些保存着边界不清的拇趾迹。该化石点的其他足迹被归于似异样龙足迹(cf. Anomoepus)。其他较小的、来自重庆市周边中侏罗统中部的足迹此前已被归于跷脚龙足迹(Grallator)。金鸡化石点保存了一条孤立的兽脚类行迹,因其粗壮的特征而被暂时归于似窄足龙足迹(cf. Therangospodus)。金鸡点的行迹也保存了非连续出现的拇趾迹。虽然重庆市和四川盆地及其周边更广泛地区之侏罗纪地层发现的兽脚类足迹日渐增多,但要明确其确切地质年龄及有效的足迹分类依然需要进一步工作。这是因为侏罗纪的恐龙足迹尽管丰富,但显示出连续变化的形态学特征,而保存状况的变化更使其难以在时间与空间上做出定义与鉴别。

Two theropod track assemblages from the Jurassic of Chongqing, China, and the Jurassic Stratigraphy of Sichuan Basin

Four Jurassic dinosaur tracksites have been reported from Chongqing Municipality. These include the Lower Jurassic Dazu site in the Zhenzhuchong Formation, which yields the oldest sauropod trackway known from China. Two of the remaining three sites (Nan’an, and Jinji sites), variously regarded as Middle and Upper Jurassic, are here described in detail for the first time and regarded as Upper Jurassic, both from the Shangshaximiao Formation. The fourth site (Chengyu), so far not accessible to the present authors, is not described. The Nan’an site, and type locality of Chongqingpus nananensis, has yielded a large sample of theropod tracks from the heart of Chongqing Municipality, at a site that has been lost in the urban development. Fortunately the sample is preserved at Chongqing Museum of Natural History and has been studied independently on two occasions to produce the results presented here. C. nananensis is a medium-sized track (mean track length ~29 cm) that may best be accommodated in ichngenus Kayentapus, and may in some cases preserve ill-defined hallux traces. Associated tracks are attributed to cf. Anomoepus. Other smaller ichnospecies from other localities outside Chongqing municipality, and from older middle Middle Jurassic formations, were previously assigned to ichnogenus Grallator. The Jinji site has yielded a single long theropod trackway of a robust form tentatively labeled cf. Therangospodus. This Jinji trackway also provides intermittent evidence of a hallux. Although theropod tracks are becoming increasingly well-known in the Jurassic sections of Chongqing Municipality, the Sichuan Basin and the broader region, determining their precise age and assigning them to valid ichnotaxa remain challenging. This is because Jurassic theropod tracks, despite being abundant, show a continuous range of morphological, and preservational variation that is difficult to define and differentiate in space and time.