1. Subdepartment of Evolutionary Organismal Biology, Department of Physiology and Developmental Biology, Uppsala University, Norbyvägen 18A, 752 36 Uppsala, Sweden
2. Western Australian Organic and Isotope Geochemistry Centre, Department of Applied Chemistry, Curtin University, Perth, Western Australia 6102, Australia
3. Earth and Planetary Sciences, Western Australian Museum, Perth, Western Australia 6000, Australia
4. School of Earth and Environment, The University of Western Australia, Perth, Western Australia 6009, Australia
5. Department of Palaeontology, Natural History Museum, Cromwell Road, London SW7 5BD, UK
6. Museum Victoria, PO Box 666, Melbourne, Victoria 3001, Australia
7. Research School of Earth Sciences, The Australian National University, Canberra, Australian Capital Territory 2600,
8. School of Geosciences, Monash University, Clayton, Victoria 3800, Australia

Correspondence to: Kate Trinajstic^2,3,4 Correspondence and requests for materials should be addressed to K.T. (Email: ktrinajs@bigpond.net.au).

Abstract

Recent finds^{1, 2} demonstrate that internal fertilization and viviparity (live birth) were more widespread in the Placodermi, an extinct group of armoured fishes, than was previously realized. Placoderms represent the sister group of the crown group jawed vertebrates (Gnathostomata)^{3, 4}, making their mode(s) of reproduction potentially informative about primitive gnathostome conditions. An ossified pelvic fin basipterygium discovered in the arthrodire Incisoscutum ritchiei was hypothesized to be identical in males and females, with males presumed to have an additional cartilaginous element or series forming a clasper. Here we report the discovery of a completely ossified pelvic clasper in Incisoscutum ritchiei (WAM 03.3.28) which shows that this interpretation was incorrect: the basipterygium described previously¹ is in fact unique to females. The male clasper is a slender rod attached to a square basal plate that articulates directly with the pelvis. It carries a small cap of dermal bone covered in denticles and small hooks that may be homologous with the much larger dermal component of the ptyctodont clasper.

MORE ARTICLES LIKE THIS

These links to content published by NPG are automatically generated.