[N] 2006 Sauropod trackways from the Middle Jurassic of Yunnan, China
Varricchio, D., Yang, C.W., Zhong, S., Huang, T. & Knell, M. (2006) Sauropod trackways from the Middle Jurassic of Yunnan, China JVP 26(3) Abstracts pp. 135
A recently discovered footprint locality occurs in the Chuanjie Formation of the central Chuxiong Prefecture of Yunnan, China. The Chuanjie Formation is equivalent to the basal section of the forenamed Upper Lufeng Formation or Upper Lufeng System and has a potentially early Middle Jurassic age. The trackway horizon sits within a 2 m plus sequence of dull red siltstones and mudstones. These are thinly bedded from < 1 cm to 5 cm and show multiple alternating layers of mud cracks and ripple marks. The track-bearing unit is a thin (~5 cm), dull red muddy siltstone and exhibits both ripples and mud cracks. The horizon covers 105 m2 and contains six distinct trackways as well as an additional band of densely packed and overprinted tracks representing at least two additional trackways.
Each of the narrow-gauge trackways consists of alternating manus/pes couplets. Manus tracks are crescent shaped, but their appearance changes with stride length and overprinting by the pes track. Pes tracks are sub-triangular to oval with a laterally pointing apex. Afew show four small impressions of anteriorly directed unguals. Strides measure from just less than 1 to 1.7 m and roughly correlate to pes size (length). Within single trackways, sameside manus and pes tracks remain distinct and non-overlapping with short stride lengths. But as stride lengthens, pes tracks begin to overprint the posterior margin of the manus track. The quadrupedal posture, semi-digitigrade pes, and digitigrade manus with reduced phalanges indicate a sauropod origin for these tracks.
Only one sauropod taxon, Chuanjiesaurus, of unknown affinities is currently known from the formation; its manus and pes are represented by only a single ungual phalanx. The narrow gauge and forward pointing digits of these tracks suggest a more primitive sauropod with a morphologic grade akin to Shunosaurus or Vulcanodon. This is consistent with recent interpretations on the timing of basal sauropod evolution.