This Ancient Insect Had 24 Legs—and Could Help Explain How the Ancestors of Modern-Day Bugs Took Over the Land

Insects roam all over Earth, with an estimated 1.4 billion individuals for every human on our planet. Yet despite their ubiquity, scientists have many questions about their evolutionary origins. How did the water-loving, many-legged critters like shrimp and krill that lived millions of years ago become the land-dwelling, six-legged bugs we know today?

A fossilized creature found in Texas is helping to fill a huge gap in the fossil record. It points to a previously undescribed transitional species that lived between land and sea around 324 million years ago, researchers report in a study published August 26 in the journal Nature. Azar peer-reviewed the paper but was not involved with the research.

Five years ago, lead author Erik Tihelka, a paleoentomologist at the University of Cambridge, was flipping through a secondhand Russian paleontology textbook when a drawing caught his eye. It showed a small fossil discovered in 1985, which came from a part of western Texas that was underwater when the creature was buried in sediments 324 million years ago. The specimen was described as a juvenile of the crustacean Tesnusocaris goldichi, but Tihelka couldn’t shake the feeling that it had been identified incorrectly.

So, he traveled to the fossil’s current home, the San Diego Natural History Museum, where the specimen had been tucked away in a drawer and overlooked for decades. At first, it was difficult to make out the finer details of the fossil, which is about the size of a business card. But when Tihelka turned to cross-polarized light imaging, a photography technique that uses polarized light filters to help reduce glare and sharpen contrast, the creature came into clearer view.

It had whip-like antennae, a long tail sandwiched between two shorter ones, an egg-laying tube, an 11-section abdomen and a three-segment thorax—all characteristics of insects. The creature also had three pairs of walking legs, another decidedly insect-like trait. But Tihelka also counted nine additional pairs of short legs on its abdomen, for a total of 24 legs—far more than the six found on modern insects.

The back legs also widened into flat, grooved paddles at the end. Taken together, the evidence suggests the creature was somewhere between a crustacean and an insect—a possible missing link in the 80-million-year evolutionary gap. Additionally, Tihelka and colleagues determined the unusual creature represented a previously unknown genus and species.