Fish Fossil Shows Why Humans Have Two Arms, Legs

An unusual prehistoric fish with fins near its butt has helped to solve the mystery over why most animals, including humans, have paired limbs.

Fish FossilThe fish, Euphanerops, is possibly the first creature on the planet to have evolved paired appendages, which in this case were fins. The 370-million-year-old species is described in the latest issue of Biology Letters.

“Fins are the world’s first limb-like appendages,” lead author Robert Sansom told Discovery News. “Paired limbs would subsequently develop from paired fins in the transition from sea to land, but the first evolution of paired appendages was a big, important step in the evolution and development of vertebrates,” which are animals with a backbone or spinal column.

Sansom, a researcher at both the University of Leicester and the University of Manchester, and colleagues Sarah Gabbott and M.A. Purnell analyzed 36 Euphanerops specimens unearthed in Quebec, Canada. This was a jawless fish that lived long before dinosaurs first emerged.

Many living fish have a single anal fin, located at the center back of the fish’s underside near its rear end. The fin is thought to help maintain control of body position.

Euphanerops, however, evolved two such fins. Some subsequent fish did not evolve the paired appendages, so fish with all sorts of fin combinations existed for a while.

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