A Theropod Footprint Assemblage From The Lower Jurassic Fengjiahe Formation,Xivang,Yunnan,China:morphology And Trackmakers

The central Yunnan basin is a well-known Jurassic dinosaur and mammal-like reptile fossil site.Dozens of dinosaur genera have been reported here,and in addition to the body fossil record,over 10 dinosaur track sites have also been discovered in Yunnan.We here report a theropod track site from the Lower Jurassic Fengjiahe Formation in central Yunnan.It is the third description of dinosaur footprints from the Fengjiahe Formation,and this new track site is the largest(120 tracks has been identified)for theropods in Yunnan so far.Over one hundred footprints are preserved on different layers of a mudstone-dominated succession close to the Lower-Middle Jurassic boundary.According to field observations and previous studies,this area is referred to as a shallow water paleoenvironment.Tracks vary in size,morphology,and preservation.All are bipedal,tridactyl,and digitigrade,and some are identified as undertracks.The best-preserved footprints were divided into three morphotypes(A: small tracks,B:medium tracks,C: large track): one set of small to medium-sized tracks close to Grallator;another set,medium in size,identified as belonging to one particular species of Kayentapus :K.xiaohebaensis;and one isolated footprint,the largest of the assemblage,also referred to Kayentapus.Although the footprint shape is influenced by many factors,biological or non-biological,morphological differences among tracks imply that at least three different kinds of theropod were visiting this site frequently.Theropod body fossils found in the surrounding area,such as Sinosaurus,turn out to be close in size to some estimates based on the length of the footprints and are therefore regarded as potential trackmakers.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,or just randomly passing by.The palaeoenvironment of this locality is inferred to be a lacustrine environment in a tropical-subtropical arid climate.