New theropod remains from the Lower Jurassic Fengjiahe Formation of Yunnan, China

The Lower Jurassic Fengjiahe Formation in the Chuxiong Basin, Yunnan Province, is characterised by abundant dinosaur tracks but a scarcity of skeletal remains compared to the coeval Lufeng Formation. Here, we report on a new fossil site at Anle Township, Mouding County, which preserves both a diverse assemblage of an isolated theropod tooth and theropod tracks. An isolated theropod tooth (LGFM 2501) was recovered from a purple calcareous mudstone layer stratigraphically located approximately 10 cm above the track-bearing horizon. This specimen is identified as a tetanuran tooth with close affinities to Allosauroidea based on a variety of analyses. This specimen is distinct from Sinosaurus, the dominant theropod in the Early Jurassic of the region, suggesting a higher predator diversity in the Fengjiahe Formation than previously recognised. The track assemblage consists of approximately 30 tracks divisible into two morphotypes: Morphotype A, medium-to-large tracks resembling Kayentapus with wide divarication angles, strongly mesaxonic digit III and V-shaped ‘heel’, and Morphotype B, small Grallator isp. tracks with narrow divarication angles and high length/width ratio. Notable extramorphological variations, including parallel digit marks and penetrative tracks preserving digit I impressions, indicate a very soft substrate at the time of track formation.