Finger-like divisions in the fins of ancient fish are the predecessors of our fingers and toes, according to a study published online in the research journal Nature this week. The finding comes from a re-examination of a 385-million-year-old fish fossil, Panderichthys, believed to be evolutionarily related to land vertebrates.
Biologists since the 1800s have speculated that the fingers and toes, or digits, of land vertebrates were derived from bony protrusions inside fish fins called radials. But this idea fell out of favor in the 1990s, largely based on early studies of Panderichthys, which appeared to lack digit-like fin radials. In the Nature paper, Catherine Boisvert of Uppsala University in Sweden and colleagues presented a study of the fossil using computerized tomography, or CT, scanning, a form of X-ray imaging.The old interpretation was in error—Panderichthys did indeed have finger-like divisions in its fins, according to the group. Boisvert and colleagues claim previous research went off-track because a thin sedimentary film covering the fins in the relevant place had concealed the underlying skeleton.The team wrote that the finding, together with new data from other fish species, “makes a strong case for fingers not being a novelty of tetrapods,” or four-limbed, vertebrate animals.Rather, fingers and toes are “derived from pre-existing distal radials,” the fin support structures, in lobe-finned fish, they added. Lobe-finned fish are fish with rounded, fleshy, limb-like fins. One group of lobe-finned fish are thought to be ancestors of amphibians and other land-dwelling vertebrates. Lobe-finned fish first appeared in the Ordovician period, about 500 million to 425 million years ago, and are extinct except for the coelacanth and lungfish.
A computer-aided reconstruction of the fin bones of the fossil fish Panderichthys showing what scientists say are finger precursors, toward the bottom in brown.
source: World Science
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