324-Million-Year-Old Fossil Revealed as New Insect Species

A fossil reclassified after four decades

Few cases of scientific misidentification are as remarkable as this one.

A fossil approximately 324 million years old, long believed to be a juvenile crustacean, has now been recognised as an entirely new insect species.

The account began in 1985, when fossils of an ancient animal were first uncovered in a rock formation in western Texas.

Within several years, specialists had identified the specimen as a young Tesnusocaris goldichi - a segmented aquatic animal related to crabs and shrimps.

Now, in 2026, a study in Nature has reached a very different conclusion.

An international research team has determined that the fossil belongs to a previously unknown insect species: an unusual 24-legged creature named Chosha praecursor.

Correcting the classification places this ancient animal within the hexapod clade. It may also help address a longstanding question in biology: how insect evolution took these creatures from the sea onto land hundreds of millions of years ago.

Chosha praecursor and the insect transition to land

The researchers say that C. praecursor, alongside other related fossils they examined, indicates that this move may have been more gradual than previously assumed. Its unconventional anatomy provides evidence for that possibility.

"Our phylogenetic reconstruction recovers C. praecursor as a hexapod, strongly favoring its placement as an early-diverging insect," write the researchers in their published paper.

"A revision of three other enigmatic hexapod fossils, the Devonian period Leverhulmia and two undescribed Carboniferous fossils from the Mazon Creek Lagerstätte, demonstrates diverse body organization in Palaeozoic wingless insects."

The initial confusion over C. praecursor is understandable. Its fossil was discovered in a layer containing other Tesnusocaris species, and appears as a dark impression against dark rock, making its features exceptionally hard to distinguish.

However, doubts emerged over whether it was truly a crustacean. The authors of the new study therefore re-examined it with cross-polarised light imaging, which cut down glare and revealed finer details of the fossil.

Using this evidence alongside evolutionary models, they classified it as a new species.

Unusual anatomy points to a semi-aquatic life

Although C. praecursor displays some typical insect traits, it is notable for several unusual features. Rather than the usual six legs, it has dozens of paddle-shaped limbs, attached to an abdomen resembling that of a crustacean.

"The unusual abdominal gill-like appendages of Chosha suggest a semiaquatic mode of life in at least some stem-insects and revise our understanding of the assembly of insect morphological organization," write the researchers.

The other specimens assessed by the team came from separate locations but are related hexapods that have also puzzled palaeontologists. Together, they suggest that certain early insects may have been amphibious, capable of living both on land and in the sea.

Establishing this has proved difficult because of the ‘hexapod gap’: an 80-million-year absence in the hexapod fossil record, including insects. This gap has created discrepancies with genetic family trees, which are partly calculated using molecular clocks.

"Together, these stem-group fossils represent the earliest uncontested insects and partly reconcile the incongruence between molecular clock estimates and the fossil record," write the researchers.

The finding also pushes the known history of the earliest insects further back in time. At the same time, it offers evidence of the physical adaptations linking crustaceans with the insects that split from them over millions of years.

The study raises the prospect that some of the first insects prospered along shorelines and in wetlands, feeding on dead vegetation and helping to establish some of the conditions for animal life on land.

"Recognized as stem-group Ectognatha, these fossils represent the oldest insects," write the researchers.

"They thus help to close the gap in the early fossil record of insects and provide a valuable calibration point for studies of arthropod terrestrialization."

The research was published in Nature.

This article was fact-checked by Rachel Garner and edited by Peter Dockrill. Although we take pride in our process, we are only human. If you notice an error, please let us know.