Description and Classification

Yelangichnus footprints are tiny, with the entire foot impression often being only a few centimeters long, suggesting the track-making dinosaurs were about the size of a chicken. The tracks are tridactyl, meaning they show three distinct toe impressions, which is common for many bipedal dinosaurs. Digit III (the middle toe) is typically the longest, and the tracks show a symmetrical arrangement around this central toe (mesaxonic). The toe impressions are slender and often show a gentle curve. Sometimes, very small heel impressions are also preserved.

As an ichnogenus, Yelangichnus is a category within ichnotaxonomy, the science of classifying trace fossils. The specific ichnospecies is Yelangichnus curvidigitus, named for the curved appearance of its side toes. While it’s impossible to know for sure exactly which dinosaur species made these tracks without body fossils found in direct association, scientists can make educated guesses. The features of Yelangichnus suggest they were made by either very small ornithischian dinosaurs (a group of plant-eaters that includes dinosaurs like Triceratops and Stegosaurus later in time) or small neotheropods (a diverse group of carnivorous dinosaurs). These prints are distinct from those of larger dinosaurs from the same period, whose tracks might be classified under names like Kayentapus.

Distinguishing Features

Yelangichnus tracks can be identified by several specific characteristics:

• Extremely small size, indicating a chicken-sized trackmaker.
• Tridactyl (three-toed) impressions.
• Mesaxonic foot structure, with digit III being the longest and acting as the central axis.
• Digits II and IV (the side toes) are of similar length, or digit IV may be slightly longer.
• Slender toe impressions.
• Digits II and IV often exhibit a distinct curved or S-shape (sigmoidal).
• Absence of significant claw marks in many specimens, or very fine claw impressions.
• Consistent trackway patterns showing bipedal locomotion with relatively narrow spacing.

Paleoenvironment and Diet

The Yelangichnus footprints were found in rocks of the Zhenzhuchong Formation. During the Early Jurassic, this area in Guizhou, China, was likely a floodplain environment with rivers and lakes, providing water sources and supporting vegetation. The fine-grained sediments, such as mudstone and siltstone in which the tracks were preserved, suggest areas that were periodically wet and muddy, perfect for capturing footprints.

The diet of the dinosaurs that made Yelangichnus tracks is inferred based on the likely identity of the trackmakers. If they were small ornithischians, they would have been herbivores, feeding on low-growing plants like ferns and cycads. If they were small neotheropods, they would have been carnivores, likely preying on insects, small lizards, or even tiny mammals that lived at the time. The small size of the trackmaker suggests it occupied a niche different from larger predatory or herbivorous dinosaurs in its ecosystem.

Significance and Ongoing Research

The discovery of Yelangichnus is significant because these footprints represent some of the smallest known dinosaur tracks from the Jurassic period in China, and indeed globally. They provide important evidence of the diversity of very small dinosaurs that coexisted with their much larger relatives. Such tiny tracks help paleontologists understand the lower size range of dinosaur communities and how different-sized animals shared an ecosystem. Trace fossils like Yelangichnus are crucial for painting a more complete picture of ancient life, especially when body fossils of small, delicate animals are rare because their bones are less likely to preserve.

Ongoing research on Yelangichnus involves further analysis of the trackways to better understand the locomotion and behavior of the trackmakers. Scientists continue to search for more track sites and compare these prints with other ichnofossils from around the world to refine their classification and gain more insights into the early evolution and distribution of small bipedal dinosaurs. The study of these minute footprints helps to fill gaps in our knowledge of dinosaur ecosystems during the Early Jurassic period.