A newly discovered 324-million-year-old fossil suggests insects did not conquer land in a single dramatic leap, but instead spent millions of years in a semi-aquatic, amphibious phase. The ancient species, named Chosha praecursor, still carried paddle-like abdominal limbs, a relic from its aquatic ancestors. This finding, published in Nature on August 26, fills a critical gap in understanding how insects became the most species-rich animal group on Earth.
A Fossil Bridge Between Water and Land
The fossil was identified by an international team led by Prof. Chenyang Cai of the Nanjing Institute of Geology and Paleontology of the Chinese Academy of Sciences (NIGPAS) and Erik Tihelka, a joint training Ph.D. student at the University of Cambridge. The researchers also reexamined mysterious stem insect fossils from the Early Devonian chert deposits of Britain and the Late Carboniferous Mazon Creek biota in the United States. Together, these specimens provide direct evidence that the transition from aquatic to terrestrial life was gradual, not abrupt.
Closing an 80-Million-Year Gap
Molecular clock studies have long suggested that hexapods split from their marine crustacean relatives and began adapting to land as early as the Cambrian-Ordovician interval. However, the fossil record has been incomplete. Undisputed hexapod body fossils first appear in the Early Devonian Rhynie Chert around 405 million years ago, but clearly recognizable insect fossils do not become abundant until the Late Carboniferous. This leaves an approximately 80-million-year gap in the fossil record, with intermediate steps extremely rare.
Chosha praecursor, dating from the Late Mississippian period, helps bridge that gap. Its paddle-like abdominal limbs are a clear sign that early insects retained and modified features from their aquatic ancestors, rather than discarding them overnight. This challenges long-standing ideas about how the insect body plan developed and how pancrustacean ancestors made the transition onto land.
The researchers worked with colleagues from the United States, Spain, and other countries. The study was published in Nature on August 26, 2026.
Why This Matters for Understanding Life on Land
The rise of complex ecosystems on land was a major turning point in the history of life. As organisms expanded beyond the oceans, terrestrial environments became home to increasingly diverse communities. Insects eventually became central to these ecosystems, but important parts of their early transition from water to land have remained unclear. This fossil provides the first direct evidence that the shift was a long, amphibious process, not a sudden event.
The discovery of Chosha praecursor offers a tangible link in the evolutionary chain, showing how early insects adapted gradually to terrestrial life. It also highlights the importance of fossils in testing molecular clock predictions. The findings not only close a gap in the fossil record but also reshape our understanding of how one of the most successful animal groups on the planet came to dominate land.
