How did insects conquer land? A 324-million-year-old fossil with 24 legs and paddle-like abdominal limbs suggests some of their earliest ancestors may have lived in water before becoming terrestrial

Insects are the most diverse group of animals on Earth, with roughly 900,000 living species already known and millions more thought to remain undescribed. According to the Smithsonian, they account for about 80% of known animal species, while an estimated 10 quintillion individual insects are alive on the planet at any given time.

Their extraordinary diversity is the result of more than 400 million years of evolution across terrestrial, freshwater and other environments. But how the ancestors of this enormously successful group first transitioned from aquatic or water-associated environments to life on land has remained difficult to reconstruct from the fossil record.

Now, a 324-million-year-old fossil from western Texas is offering new clues. Researchers have identified the specimen as an early stem-group insect with an unusual body plan that included 24 legs, including nine pairs of abdominal appendages. Some of those rear abdominal limbs were flattened and paddle-like, suggesting that the animal lived in humid or semi-aquatic environments during an early stage of insect evolution.

The 324-million-year-old fossil from western Texas

The fossil, recovered from the Late Mississippian Tesnus Formation in western Texas, was previously interpreted as the possible juvenile remains of a crustacean. In a 2026 study published in Nature on August 26, paleontologist Erik Tihelka of the University of Cambridge and the Chinese Academy of Sciences, along with an international team of researchers, re-examined the specimen and identified it as a previously unknown stem-group insect, which they named Chosha praecursor.

The researchers used cross-polarised light imaging to reveal anatomical details that were difficult to distinguish in the dark fossil. They identified a three-segmented thorax bearing three pairs of walking legs, along with nine pairs of multisegmented abdominal legs. That gives the animal 24 legs in total, six thoracic walking legs and 18 abdominal appendages. The researchers also identified an 11-segmented abdomen, antennae, an ovipositor and a terminal filament.

A 24-legged insect unlike those alive today

The abdominal appendages are particularly significant. Unlike the walking legs on the thorax, the legs on the abdomen were elongated and multisegmented, with those toward the rear becoming flattened and paddle-like.

The researchers note that these structures resemble the gill-like abdominal appendages found in some modern mayfly nymphs. However, their exact function in Chosha cannot be determined from the fossil. They may have assisted with movement in shallow water, although a respiratory function cannot be ruled out.

The anatomy, therefore, provides evidence that some early stem-group insects may have been adapted to humid or semi-aquatic environments. The Tesnus Formation has previously been interpreted as representing nearshore marine, deltaic or littoral environments, while associated fossil plants indicate a terrestrial influence.

Evidence for a gradual transition onto land

The findings challenge the idea that insect ancestors necessarily made a simple transition from an aquatic environment directly to fully terrestrial habitats. Instead, the researchers propose that an amphibious or semi-aquatic stage may have played a role in the early terrestrialisation of at least some stem-group insects.

The study does not establish that all insects followed this route. Rather, Chosha provides evidence that early insect evolution included ecological and anatomical diversity that is no longer represented among modern insects.

The fossil also helps address a long-standing gap in the early insect fossil record. The researchers compared Chosha with other enigmatic Palaeozoic hexapods and identified several of them as early stem-group insects. Their phylogenetic analysis examined 58 morphological characters across 23 taxa and placed Chosha among the earliest-diverging insects.

The results suggest that the early evolution of insects was more complex than the modern insect body plan might indicate. Abdominal appendages, for example, may have been present in early hexapods and subsequently reduced or lost multiple times as different insect lineages evolved.