Researchers report a unique skeletal structure in the fins of a tetrapod-like fossil fish. Living four-limbed vertebrates, or tetrapods, exhibit a common skeletal pattern in the proximal part of their limbs, with a single bone at the base of the limb connecting to two parallel radials at the distal end. The same pattern has been observed in tetrapod-like fossil fishes, but the origins of this pattern are unclear. Jonathan E. Jeffery and colleagues describe a near-complete skeleton of Rhizodus hibberti , a fossil lobe-finned fish and member of the stem tetrapod group. The bones at the base of the pelvic fins, the femurs, from both pelvic fins were well-preserved. The distal end of each femur formed joints with three parallel radial bones, in contrast to the two radials observed in other tetrapods, both living and fossilized. Each of the three radials had a distinct morphology, with the morphologies on the left fin matching those on the right fin. Rhizodus may therefore represent an early stage in the evolution of hind limb development, before development became constrained to the familiar one-to-two pattern. The findings suggest that developmental mechanisms were once flexible enough to allow for more varied skeletal patterns than those currently observed, according to the authors.
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Article #18-10845: "Unique pelvic fin in a tetrapod-like fossil fish, and the evolution of limb patterning," by Jonathan E. Jeffery, Glenn W. Storrs, Timothy Holland, Clifford J. Tabin, and Per E. Ahlberg.
MEDIA CONTACT: Jonathan E. Jeffery, University of Bristol, UNITED KINGDOM; tel: +44-7719-688-292; e-mail: < jj13361@bristol.ac.uk >
Proceedings of the National Academy of Sciences