Chosha praecursor fossil discovery

Researchers have identified a 324-million-year-old fossil, named Chosha praecursor, which provides new insights into the evolutionary transition of insects from water to land. Discovered in the Tesnus Formation of western Texas, the specimen was previously misidentified as a crustacean larva and had been held at the San Diego Natural History Museum since 1985.

Unlike modern hexapods that possess six walking legs, this Carboniferous-period species featured 24 appendages, including three pairs of thoracic legs and nine additional pairs along the abdomen. Some of these abdominal limbs possessed paddle-like structures, suggesting the species maintained a semi-aquatic lifestyle in shallow coastal or delta environments.

The discovery, led by researchers from the University of Cambridge and the Nanjing Institute of Geology and Paleontology, utilized polarized light microscopy to reveal these anatomical details. The findings help illustrate the evolutionary shift from multi-limbed ancestors to the six-legged body plan characteristic of modern insects.

New analysis suggests the discovery fills a critical research gap between the divergence of hexapods from crustaceans approximately 450 million years ago and the appearance of definitive insect fossils in the Carboniferous period. While the specimen exhibits a typical insect body plan with six legs and two antennae, its long abdomen and paddle-like tail—features characteristic of crustaceans—indicate a hybrid anatomy. Researchers suggest this supports the theory that early ancestral insects likely led an amphibious lifestyle in moist microhabitats at the transition between aquatic and terrestrial environments.