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, 2 (3), 443-6

Oldest Coelacanth, From the Early Devonian of Australia

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Oldest Coelacanth, From the Early Devonian of Australia

Zerina Johanson et al. Biol Lett.

Abstract

Coelacanths are well-known sarcopterygian (lobe-finned) fishes, which together with lungfishes are the closest extant relatives of land vertebrates (tetrapods). Coelacanths have both living representatives and a rich fossil record, but lack fossils older than the late Middle Devonian (385-390 Myr ago), conflicting with current phylogenies implying coelacanths diverged from other sarcopterygians in the earliest Devonian (410-415 Myr ago). Here, we report the discovery of a new coelacanth from the Early Devonian of Australia (407-409 Myr ago), which fills in the approximately 20 Myr 'ghost range' between previous coelacanth records and the predicted origin of the group. This taxon is based on a single lower jaw bone, the dentary, which is deep and short in form and possesses a dentary sensory pore, otherwise seen in Carboniferous and younger taxa.

Figures

Figure 1
Figure 1
Stratigraphic position of the Fairy Formation and location of fossil locality in eastern Victoria, Australia.
Figure 2
Figure 2
Eoactinistia foreyi, NMV 218301, dentary in (a, b) lateral, (c, d) dorsal and (e, f) medial or internal views, (g) close up view of dentary pore, internal dentary surface, (h) Gavinia syntrips, representing a phylogenetically basal coelacanth (Middle Devonian, Australia), to illustrate the relationship between the dentary (grey) and other bones of the jaw. Note absence of dentary pore (from Long 1999). Scale, 200 μm; Ang, angular bone; d.pore, dentary pore; Dent, dentary bone; gr, narrow groove; oa.Ang1, 2, overlap surfaces for angular; p.rim, rim surrounding dentary pore; Spl, splenial bone; teeth, teeth associated with dentary in marginal tooth row. Larger arrows indicate anterior. ((h) Courtesy of Western Australian museum.)

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