A remarkable fossil discovered in Texas is offering scientists a rare glimpse into one of evolution’s biggest transitions: how the ancestors of modern insects moved from water onto land.
The 324-million-year-old creature had the familiar six walking legs of an insect, but it also carried additional paddle-like limbs along its abdomen.
Researchers say this unusual combination suggests that early insects went through a long semi-aquatic stage rather than making a sudden switch to life on land.
The international study, led by researchers from the Nanjing Institute of Geology and Paleontology of the Chinese Academy of Sciences and the University of Cambridge, was published in Nature.
Scientists named the newly described species Chosha praecursor. Its fossils were found in the Tesnus Formation in western Texas and date to the Late Mississippian period.
The specimens are exceptionally well preserved. The researchers identified them as adult females measuring about 32 millimeters long, or nearly 50 millimeters when their long tail structures are included.
For years, some of these fossils had been incorrectly interpreted as crustacean larvae. New imaging revealed that they actually possessed several important insect features, including six walking legs, an egg-laying structure called an ovipositor and a long central tail filament.
But the biggest surprise was found on the abdomen.
Modern insects have six legs attached to the thorax and generally lack walking or swimming limbs on their abdomen. C. praecursor, however, had segmented appendages on nine abdominal sections. Some of the rear appendages had developed into paddle-like structures that could have helped the animal move through water.
The environment where the fossils were preserved also supports an amphibious lifestyle. Geological evidence suggests the area was once a shallow coastal or delta environment where water and land met.
The discovery may help fill a major gap in the history of insects. Genetic studies suggest that the ancestors of six-legged animals separated from marine crustacean relatives very early in Earth’s history. Yet clear fossil evidence of early insects is scarce, leaving tens of millions of years of their evolution poorly understood.
The researchers also reexamined mysterious fossils from Scotland’s Early Devonian Rhynie Chert and the famous Mazon Creek fossil beds in Illinois. Their analysis suggests these creatures belong to a primitive branch close to the origins of insects.
Together, the fossils paint a new picture of how the insect body evolved.
The ancestors of insects probably inherited numerous appendages from aquatic crustacean-like animals. During the transition onto land, those abdominal limbs were gradually modified, reduced and eventually lost. Meanwhile, the six legs on the thorax became the main structures used for walking.
The presence of an ovipositor also suggests that early insects were already developing specialized ways to lay their eggs, an adaptation that may later have helped them spread into many different environments.
Rather than emerging from water as fully terrestrial animals, early insects may have spent millions of years living along the boundary between water and land. They likely moved through wet environments, feeding on decaying plants, organic material and fungal spores.
This amphibious period may have provided the evolutionary bridge that eventually produced the enormous diversity of insects living on land today.
