Open AccessPectoral fins of rhizodontids and the evolution of pectoral appendages in the tetrapod stem‐group
Author(s) -
JEFFERY JONATHAN E.
Publication year - 2001
Publication title -
biological journal of the linnean society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.906
H-Index - 112
eISSN - 1095-8312
pISSN - 0024-4066
DOI - 10.1111/j.1095-8312.2001.tb01388.x
Subject(s) - biology , tetrapod (structure) , appendage , anatomy , fish fin , pectoral girdle , evolutionary biology , devonian , paleontology , fish <actinopterygii> , fishery
The Rhizodontida are an extinct order of large, predatory, lobe‐finned fishes, found world‐wide in Devonian and Carboniferous freshwater deposits. They are thought to be basal members of the tetrapod lineage. In this paper the pectoral fin skeleton of Rhizodus hibberti , a derived member of the group, is described in detail for the first time. It shows that muscular processes of the humerus (the deltoid and supinator processes) may have appeared later in tetrapod evolution than previously thought. The rhizodontids share an unusual fin‐ray morphology, with highly elongated basal hemisegments, overlapping extensively with the endoskeleton. This morphology raises the possibility that segmentation and endoskeletal overlap share some common upstream genetic control during lepidotrichial development. The relative size of the lepidotrichia and the complexity of the endoskeleton does not fit with a ‘clockface’ model of limb developmental evolution.