Letters to Nature

Nature 403, 185-188 (13 January 2000) | doi:10.1038/35003183; Received 8 June 1999; Accepted 22 October 1999

The most primitive osteichthyan braincase?

Alison M. Basden1, Gavin C. Young2, Michael I. Coates3 & Alex Ritchie4

  1. Centre for Ecostratigraphy and Palaeobiology, Department of Earth and Planetary Sciences, Macquarie University, New South Wales 2109, Australia
  2. Department of Geology, Australian National University, Canberra 0200, Australia
  3. Department of Biological Sciences, University College London, Gower Street, London WC1E 6BT, UK
  4. Australian Museum, College St., Sydney South, New South Wales 2000, Australia

Correspondence to: Alison M. Basden1 Correspondence and requests for materials should be addressed to A.B. (e-mail: Email: abasden@laurel.ocs.mq.edu.au).

Most living vertebrates, from teleosts to tetrapods, are osteichthyans (bony fishes)1, but the origin of this major group is poorly understood2. The actinopterygians (ray-finned bony fishes) are the most successful living vertebrates in terms of diversity. They appear in the fossil record in the Late Silurian but are poorly known before the Late Devonian. Here we report the discovery of the oldest and most primitive actinopterygian-like osteichthyan braincase known, from 400–million-year-old limestone in southeastern Australia. This specimen displays previously unknown primitive conditions, in particular, an opening for a cartilaginous eyestalk. It provides an important and unique counterpart to the similarly aged and recently described Psarolepis from China and Vietnam3, 4. The contrasting features of these specimens, and the unusual anatomy of the new specimen in particular, provide new insights into anatomical conditions close to the evolutionary radiation of all modern osteichthyan groups.