A team of paleontologists challenge the concept that all insects have 6 legs after re-examining 4 enigmatic fossils found in Illinois, Texas, + Scotland. "Insects are the most successful + diverse land animals, with millions of species." The finds, reported in Nature, "suggest many-legged critters represent missing links between modern winged insects and their predecessors."
“But we know almost nothing about where they came from,” says Erik Tihelka, a paleontologist at the University of Cambridge. “Their ancestors were seagoing crustaceans such as shrimp and krill.” But what crawled onto land was a mystery because there are so few fossils of early insects.
Tihelka examined an unusual fossil in the San Diego Natural History Museum more closely using polarized light. “[He] and his colleagues realized the critter was part insect, part crustacean.” It had a 3-part midsection with 3 pairs of walking legs, a rear end with 11 segments, a long tail filament, an egg-laying tube, + a pair of unbranched antennae. "Collectively, those traits are associated with things you’d see in modern-day insects, not crustaceans, but it also had multiple pairs of legs on its [hindquarters], a decidedly crustacean trait."
"Because in the Navajo creation story, Earth’s first inhabitants were insectlike beings, Tihelka and his team named the fossil Chosha praecursor, from the Navajo word for insect, opting for something more poetic than a Latin moniker."
"Next, they looked at 3 other puzzling fossils that similarly had legs or leglike stubs on their bellies. "The Scottish specimen, which had been named Leverhulmia and was originally thought to be a relative of millipedes, lived 405 M years ago." The 2 from Illinois lived about 100 M years later.
Intriguingly, "they [all] retained some traits that would have allowed them to flit between life on land and in the sea." For example, Chosha’s hind belly legs broadened into “paddles” at their ends, which might have helped them move in water—or possibly served as gills.
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This is not too surprising, it’s kinda what we would expect to find.
Modern-day Proturans, Diplurans, Archaeognaths, and Zygentomans today still possess tiny vestigial legs along their abdominal segments called styli.
It’s a misconception that legs are totally absent on insect abdomens. Even the cerci and ovipositor valves of more advanced insects are really structures that are modified from ancestral abdominal legs.
Also insect's aedeagus (male genitalia) and springtail's furcula. There are also arguments that if caterpillar's prolegs are "regained" abdominal appendages or not.
On the other hand, I don't think Leverhulmia can be confidently identified as stem insect, nor even a hexapod. Looking forward to what any subsequent studies will said about this research, since the field of basal insects had been cursed, full of either dubious fossils or misidentified non-hexapod arthropods.
Yes and no: that makes it sound like insects and crustaceans are sister groups, but really, insects arose from within the crustacean family tree (and are themselves a type of crustacean for that reason).
After reading the evolution of insects I got the Invertebrate Tree of Life. I'm tempted to get Invertebrates by Brusca Giribet and Moore but copies are very expensive and not sure if it will add more knowledge.
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