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in Li, Peyre de Fabrègues, ... et Xu, 2021. DOI: 10.7717/peerj.11788 |
Abstract
Yunnan Province is famous for its diversified Lufeng vertebrate faunas containing many saurischian dinosaur remains. In addition to the body fossil record, dinosaur ichnofossils have also been discovered in Yunnan, and the number of published track sites is on the rise. We report a theropod assemblage from the Lower Jurassic Fengjiahe Formation in Xiyang, central Yunnan. It is the third report and description of dinosaur footprints from the Fengjiahe Formation, and this new track site is the largest in number of footprints for theropods in Yunnan. Over one hundred footprints are preserved on different layers of a claystone-dominated succession close to the Lower-Middle Jurassic boundary. The track area is referred to as a lacustrine shallow-water paleoenvironment. Tracks vary in size, morphology, and preservation. All are tridactyl and digitigrade, and some are identified as undertracks. The best preserved footprints were divided into three morphotypes: morphotype A (>8 cm–<21 cm) resembling Grallator; morphotype B (>27 cm–<30 cm) identified as Kayentapus xiaohebaensis; and morphotype C, an isolated footprint (39 cm) referred to the ichnogenus Kayentapus. Although footprint shape is influenced by many factors, biotic or abiotic, morphological differences among tracks such as size, divarication angles and proportions imply that at least three different kinds of theropods were visiting this site frequently. Theropod body fossils found in the surrounding area, such as Sinosaurus, turn out to be similar in body size to the projected size estimated from footprint lengths at the track site. In Yunnan, discoveries of theropod body fossils are rare. In that respect, the track record is a useful diversity indicator which can help to encompass theropod diversity patterns. Broadly speaking, large predators (five meters long or more) were uncommon in Early Jurassic ecosystems. Accordingly, large tracks are scarce on the track site, but not absent. Trackmakers of all sizes presumably coexisted in this tropical Jurassic ecosystem, and were regularly drawn to the track site in search of water or food resources.
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| Overview of the Xiyang track site. (A) Photograph of the whole inclined track-bearing outcrop. (B) Outline drawing showing the distribution of the tracks. Morphotypes A, B and C are painted in blue, green, and red, respectively; unidentified tracks appear in brown. |
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| Photographies of well-preserved tracks for each morphotype identified at the Xiyang track site. (A) XIY-053 from morphotype A. (B) XIY-108 from morphotype B. (C) XIY-048 from morphotype C. |
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| Paleoenvironmental reconstruction of the Xiyang track site by Yu Chen. |
Conclusions:
The Xiyang track site preserves 120 exposed footprints made by solitary coelophysoid and tetanuran theropod dinosaurs within a lacustrine setting under tropical paleoclimatic conditions. The footprints are grouped into three morphotypes and show similarities with two widespread ichnogenera: Grallator and Kayentapus. These ichnogenera were both already reported in the Fengjiahe Formation, but not in its lateral equivalent the Lufeng Formation.
The track site is dated from the Late Early Jurassic, and the locality is close to the Lower-Middle Jurassic boundary. In equivalent levels of the Lufeng Formation, typical components of the Lufengosaurus fauna are abundant. Hence, the Xiyang track site can be regarded as part of this fauna. Tracks preserved on multiple layers suggest that this area underwent periodic droughts and flood events. It also implies that dinosaurs of different generations and sizes kept visiting the site.
In the Fengjiahe Formation, the record is dominated by body fossils while ichnofossils are relatively limited. Curiously, little is known about tracks in the highly fossiliferous Yunnan Province. This might be due to the small number of previous studies and lack of suitable facies for abundant track preservation. The Xiyang track site is the track site with the greatest number of theropod footprints found and reported in Yunnan so far. Thus, it provides valuable insights into the diversity and ecology of Early Jurassic theropods in Yunnan. Because theropods are relatively sparse in Yunnan, and some genera were erected on basis of scattered specimens, tracks can help fill the gap to some extent.
Hongqing Li, Claire Peyre de Fabrègues, Shundong Bi, Yi Wang and Xing Xu. 2021. The Largest Theropod Track Site in Yunnan, China: A Footprint Assemblage from the Lower Jurassic Fengjiahe Formation. PeerJ 9:e11788. DOI: 10.7717/peerj.11788
