The dentition of the enigmatic pycnodont fish, Athrodon wittei (Fricke, 1876) (Neopterygii, Pycnodontiformes; Late Jurassic; NW Germany)

The Pycnodontiformes is a monophyletic group of predominantly Mesozoic fishes with mostly deep and laterally compressed bodies (Nursall 1996, 1999; Kriwet 2001a; Poyato-Ariza & Wenz 2002). They are highly specialised with regard to their prey, which is expressed in their durophageous dentition with rounded teeth arranged in more or less defined rows forming dental plates on the unpaired vomer in the upper and paired prearticulars in the lower jaws. The premaxillae and dentaries generally bear a single row of few grasping teeth, which are incisiform in more derived forms (Kriwet 2001b, 2003, 2005). Pycnodonts are considered to represent the sister group of teleosts (e.g., Arratia 1999: fig. 19; Kriwet 2001a). Some 700 nominal species belonging to several dozens of genera have been described to date. About ten genera are based entirely on isolated dentitions and only 78 species are known from skeletal remains. The evolutionary history of pycnodontiforms encompasses a period of approximately 175 million years (Delsate & Kriwet 2004; Kriwet & Schmitz 2005). They first appear in the Late Triassic (Norian) on the northern margins of Tethys (Tintori 1981) and persist into the Palaeogene (Eocene) (e.g., Longbottom 1984). During the Jurassic they rapidly diversified and pycnodont remains are common in marine and brackish sediments of Late Jurassic and Cretaceous age (Kriwet 2001c). They had a nearly world-wide distribution in the Mesozoic and Palaeogene and are considered major components of marine fossil fish assemblages. The distribution and ecology of pycnodont fishes has been described in general terms only to date by Schaeffer (1970), Nursall (1996a), Poyato-Ariza et al. (1999), and Kriwet (2001b, 2001c). Most pycnodonts are small to medium sized fishes with a standard body length of some 25 cm or less. Only few large forms with a standard body length of more than 50 cm are known. Gyrodus circularis is the largest known pycnodont with a standard body length up to 200 cm (Kriwet & Schmitz 2005). Fossil Record 11 (2) 2008, 61–66 / DOI 10.1002/mmng.200800002