Dental morphology of the pycnodontid fish †Stemmatodus rhombus (Agassiz 1844) (Neopterygii, †Pycnodontiformes) from the Early Cretaceous, with comments on its systematic position

Abstract

The dental morphology of the pycnodontid fish †Stemmatodus rhombus (Agassiz, 1844) from the Lower Cretaceous (lower Barremian) of southern Italy is described in detail. SEM pictures of vomerine and prearticular teeth are provided for the first time allowing the comparison with other Early Cretaceous pycnodonts, which are only known from isolated dental remains. The dentition of †Stemmatodus rhombus consists of incisiform grasping teeth on the paired premaxillae and dentaries and crushing teeth on the unpaired vomer and paired prearticulars. The vomerine teeth are arranged in five longitudinal rows, which display symmetry with a distinct median principal and two lateral rows. The prearticular bears three longitudinal rows. Teeth of the main row are much wider than those of the lateral ones. The tooth crowns are rather flat and expose a shallow apical depression, which is surrounded by a ring of widely-spaced small tubercles. The ornamentation and arrangement of teeth distinguishes dentitions of †Stemmatodus from all other pycnodonts. The wear pattern of the teeth is evaluated and the significance of the dental morphology in pycnodont taxonomy is discussed. In addition, the systematic position of †Stemmatodus is discussed.

The fish fauna of the Late Jurassic Solothurn Turtle Limestone (NW Switzerland)

“…Contrary to earlier suggestions mentioned by Kriwet (2004) pycnodont fishes probably had more than a single generation of teeth. As stated by Longbottom in 1984, both Woodward (1895 and Thurmond (1974) suggested that pycnodont dentitions grew by addition of larger teeth at the posterior end of the vomer or prearticular, a view Longbottom revised and extended.…”

“…Furthermore, the overhanging bulge of each enamel cap created, in combination with its neighbour, a lateral batter along the flank of the tooth row. The outer lateral batter thus formed, in conjunction with the outer lateral tooth rows and the teeth of the other hemi-mandible, a U-shaped through jointly counteracting the upper jaw in the manner of a 'nutcracker' similar to that described of Stemmatodus rhombus by Kriwet (2004). In some specimens the teeth are extremely tightly packed and the bulging enameloid caps in close contact.…”

“…This is an important aspect considering that the crushing dentition of pycnodonts is very durable and often the sole remnant of the fish. Diagnostic character sets may include vomerine and prearticular tooth arrangement (particularly when combined), number and relation of individual teeth and tooth rows to each other and morphological characteristics of individual teeth (Kriwet 2004;Poyato-Ariza and Wenz 2005).…”

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

“…The combination of vomerine and prearticular tooth arrangements and the number of tooth rows is considered to show a taxonomic signal and is therefore indicative for pycnodonts at least on generic level (Kriwet 2001(Kriwet , 2003 in spite of the fact that Poyato-Ariza (2003) strongly argued against using dental characters for assessing the systematic position of taxa within Pycnodontiformes. Consequently, the genus Athrodon, which is only known by isolated dentitions is left as Family incertae sedis here.…”

“…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(Kriwet , 2003(Kriwet , 2005. Pycnodonts are considered to represent the sister group of teleosts (e.g., Arratia 1999: fig.…”