Insect fossil find shows water-to-land transition

NANJING — An international team led by Chinese researchers has uncovered an early insect species dating back roughly 324 million years that displays both aquatic and terrestrial features, providing direct evidence of how insects gradually made the transition from water to land.

The fossil specimen, named Chosha praecursor, was recovered from Carboniferous strata in Texas, United States. The work was carried out by scientists from the Nanjing Institute of Geology and Palaeontology of the Chinese Academy of Sciences, in collaboration with colleagues from the United Kingdom, the US and Spain.

Although the insect already possessed the three pairs of walking legs typical of modern insects, its abdomen retained paddle-shaped lobes suited for swimming. The findings were published online on Wednesday in the journal Nature.

Cai Chenyang, a researcher at the institute who led the study, said that abdominal appendages in extant insects are largely reduced, with only the three thoracic pairs remaining. Chosha praecursor, he noted, offers a snapshot of the transition: the ancestral aquatic appendages had not yet disappeared entirely but were being gradually modified and simplified as the insect adapted to life on land.

"This discovery serves as an evolutionary bridge between aquatic and terrestrial life forms," Cai said. "Around 320 million years ago, ancient insects at the water-land interface were progressively evolving new body structures suited to breathing and moving on land."

The fossil, identified as an adult female, measures about 3.2 centimeters in body length, extending to nearly 5 cm with its elongated tail structure, and has a fusiform shape.

Its thorax bore three pairs of walking legs, and its ovipositor and tail already showed typical insect features. However, segments one through nine of the abdomen still carried segmented appendages, with the rear pairs flattened into paddle-like forms.

Given that the fossil was found in nearshore, shallow-water deltaic deposits, the researchers conclude that Chosha praecursor inhabited humid transitional zones between land and water, retaining clear semi-aquatic characteristics.

XINHUA