Level 1 - Absolute Beginner
Scientists found a very old fossil. It is about 324 million years old.
The fossil is a small animal called Chosha praecursor. It is one of the oldest insects ever found.
This animal had legs for walking, like insects today. But it also had paddle shaped legs for swimming.
This shows that early insects lived both on land and in water for a long time before they became land animals.
- fossil
- the remains of a very old plant or animal turned to stone
- insect
- a small animal with six legs, like an ant or a fly
- million
- the number 1,000,000
- paddle
- a flat shape used for pushing through water
- swim
- to move through water using the body
- ancestor
- a relative who lived a long time ago
- amphibious
- able to live both on land and in water
- discover
- to find something for the first time
Level 2 - Elementary
Scientists have identified a newly described fossil insect called Chosha praecursor, dated to about 324 million years ago. This makes it one of the oldest insect relatives ever found.
The fossil was actually dug up in West Texas back in 1985, in a shale bed called the Tesnus Formation. For decades, people thought it was a crustacean, an animal group that includes crabs and shrimp. Only in 2026 did researchers correctly identify it as an early insect relative.
Chosha praecursor had a very unusual body. Like modern insects, it had three pairs of walking legs. But unlike modern insects, it also had extra segmented limbs along its abdomen, and the rear limbs were shaped like flat paddles for swimming.
This mix of features shows the animal was amphibious. It could walk on land using its legs, but it also kept swimming paddles from its water living ancestors. Scientists say this proves insects did not move from water to land all at once. Instead, they went through a long in between stage.
- shale
- a type of rock formed from layers of mud and clay
- crustacean
- a group of animals with hard shells, such as crabs and shrimp
- abdomen
- the back section of an insect's body
- segmented
- divided into separate connected parts
- limb
- an arm, leg, or other body part used for movement
- transitional
- describing a stage of change between two forms
- identify
- to correctly recognize what something is
- formation
- a layer of rock formed over a long period of time
Level 3 - Intermediate
An international team of researchers has described a newly identified fossil species, Chosha praecursor, dated to roughly 324 million years ago in the Late Mississippian period. The find, published in the journal Nature on August 26, 2026, ranks among the oldest known insect relatives and offers a rare window into how six legged insects evolved from their aquatic arthropod ancestors.
The specimen was originally excavated in 1985 from a shale bed in the Tesnus Formation in West Texas, but it sat misidentified as a crustacean for decades. It was only correctly recognized as an early insect relative in 2026, when researchers led by Prof. Chenyang Cai of the Nanjing Institute of Geology and Palaeontology, working with Erik Tihelka and an international team including scientists from the United States and Spain, re-examined the specimen closely.
What makes Chosha praecursor remarkable is its body plan, unlike anything alive today. It already possessed the three pairs of thoracic walking legs characteristic of modern insects, yet it also retained segmented limbs along abdominal segments one through nine, with the rearmost pair flattened into paddle like structures suited to swimming.
The researchers interpret this combination as evidence of a semi-aquatic, or amphibious, lifestyle: an animal capable of moving on land with its walking legs while still relying on ancestral swimming paddles and likely spending considerable time in water. The finding supports the view that insects did not make an abrupt transition from water to land, but instead passed through a long transitional phase, gradually losing and simplifying their aquatic abdominal limbs as they adapted more fully to terrestrial life.
- arthropod
- an invertebrate animal group with jointed limbs, including insects and crustaceans
- specimen
- an individual example used for scientific study
- excavate
- to dig up and carefully remove from the ground
- thoracic
- relating to the middle body section of an insect, where walking legs attach
- semi-aquatic
- living partly in water and partly on land
- terrestrial
- relating to life on land
- hexapod
- an animal with six legs, the group that includes all insects
- gradually
- happening slowly over a long period rather than suddenly
Level 4 - Advanced
Paleontologists have described a newly identified fossil species, Chosha praecursor, dated to approximately 324 million years ago in the Late Mississippian period, placing it among the oldest known insect relatives yet recovered. The findings, published in Nature on August 26, 2026, address a long standing gap in the fossil record concerning how hexapods, the six legged lineage encompassing all living insects, emerged from their aquatic arthropod ancestors.
The specimen's history is itself notable. It was originally excavated in 1985 from a shale bed within the Tesnus Formation in West Texas, but was misclassified as a crustacean for four decades. Only in 2026 did a re-examination by a team led by Prof. Chenyang Cai of the Nanjing Institute of Geology and Palaeontology, part of the Chinese Academy of Sciences, together with Erik Tihelka, a doctoral candidate jointly trained with the University of Cambridge, and international collaborators from the United States and Spain, correctly recognize it as an early insect relative.
The fossil's significance lies in a body plan with no direct modern analogue. Chosha praecursor already possessed the three pairs of thoracic walking legs diagnostic of crown group insects, yet it simultaneously retained segmented appendages along abdominal segments one through nine, with the posterior-most pair modified into flattened, paddle shaped structures evidently adapted for propulsion through water.
The researchers interpret this juxtaposition as decisive evidence of a semi-aquatic ecology, an organism equipped to traverse terrestrial substrates on its thoracic legs while retaining, and presumably still relying upon, ancestral swimming appendages inherited from an aquatic lineage. Rather than supporting a scenario of abrupt terrestrialization, the fossil corroborates a protracted transitional interval during which early hexapod ancestors incrementally reduced and simplified their abdominal limbs, a process that in extant insects has left only the three pairs of thoracic walking legs, the abdominal appendages having been all but eliminated over the course of subsequent evolution.
- crown group
- the group made up of all living descendants of a common ancestor plus that ancestor
- analogue
- something comparable or similar to another thing
- appendage
- a body part that extends from the main structure, such as a limb
- propulsion
- the force that drives something forward, such as through water
- juxtaposition
- the placing of two contrasting things close together for comparison
- terrestrialization
- the evolutionary process by which aquatic organisms adapt to life on land
- protracted
- lasting for a long time, drawn out
- extant
- still existing, currently living, as opposed to extinct
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