Chosha praecursor fossil reveals 24-legged insect ancestor

A 324-million-year-old fossil discovered in the Tesnus Formation of western Texas is providing new insights into the evolutionary transition of insects from water to land. The newly described species, named Chosha praecursor, possesses a unique anatomical structure that distinguishes it from modern hexapods.

While modern insects are characterized by six walking legs attached to the thorax, Chosha praecursor featured 24 appendages. Researchers found that while six legs were used for walking, the animal also possessed nine pairs of segmented appendages along its abdomen. Some of these abdominal limbs had developed into paddle-like structures, suggesting a semi-aquatic lifestyle in shallow coastal or delta environments.

The international study, published in the journal Nature and led by researchers from the University of Cambridge and the Nanjing Institute of Geology and Paleontology, utilized polarized light microscopy to reveal these fine details. The specimen, which had previously been misidentified as a crustacean larva, measures approximately 32 to 49 millimeters in length. This discovery helps fill a significant gap in the evolutionary history of insects, illustrating how ancestral species transitioned from having numerous limbs to the six-legged body plan seen today.