Daily Weird News Report
A fossil discovered in western Texas is offering scientists a detailed look at an unusual stage in the evolution of insects: a time when they had begun adapting to land but still retained features associated with aquatic ancestors.
The fossil belongs to a newly described species, Chosha praecursor, which lived about 324 million years ago during the Late Mississippian period. The specimen was recovered from calcareous claystone concretions in the Tesnus Formation, in the Marathon Uplift region.
According to research published in Nature and reported by Phys.org, the fossils preserve adult females measuring about 32 millimeters in body length. Including a central tail filament and two cerci, the insects reached nearly 50 millimeters overall.
The animals had the basic organization of insects, including six walking legs attached to the thorax, a segmented trunk and an ovipositor. But they also possessed segmented appendages along abdominal segments 1 through 9. The rear abdominal limbs had been reshaped into paddle-like structures—features not found in living crown-group insects.
The researchers used cross-polarized light imaging to examine the fossils and concluded that earlier interpretations identifying the specimens as crustacean larvae were incorrect. Their analysis placed C. praecursor within a primitive stem group of insects.
The fossils came from sediments formed in near-shore, shallow-water delta and coastal environments. Based on that setting and the animals’ anatomy, the researchers reconstructed a semi-aquatic or amphibious way of life at the boundary between water and land. The fossils suggest that early insects retained, modified and gradually reduced ancestral aquatic structures rather than abandoning them all at once.
The team also reassessed two other Paleozoic hexapod fossils: Leverhulmia from Early Devonian Scotland and an unnamed hexapod from the Mazon Creek deposits in Illinois. The researchers classified all three as members of a primitive insect stem clade.
The fossils help address an approximately 80-million-year gap between molecular estimates for the early divergence of hexapods and the more limited body-fossil record. They also suggest that the loss of abdominal limbs was an important part of insects’ eventual adaptation to life on land.
The study’s authors propose that these early insects may have consumed humus, plant debris and fungal spores, functioning as decomposers and consumers in environments where aquatic and terrestrial habitats met.
