Developmental Constraints Conserve Evolutionary Pattern in an Osteichthyan Dentition

Spatial and temporal pattern for the dentition in the Australian lungfish revealed with sonic hedgehog expression profile

“…The direction of growth of the dentition for the dentary of the trout (Berkovitz 1977;Fraser et al 2004;2006a,b) is also in a posterior direction. This unique dipnoan pattern of tooth addition without replacement has been a strongly conserved developmental process for at least 350 Myr (Reisz & Smith 2001;Smith & Krupina 2001;Smith et al 2002) as discussed by comparison of Neoceratodus with a superbly preserved growth series of a Late Devonian lungfish.…”

“…Each one forms as an independent module in development supported only by the individual bone of attachment (Smith & Hall 1993). The dental bone of the tooth module in Neoceratodus links them all together and is located on the dorsal antero-lateral edge of Meckel's cartilage as the functional support of these transitory lower jaw teeth (Smith et al 2002). Any dermal ossification centre for the dentary bone is absent in the extant forms of the group (Bartsch 1993).…”

“…Apart from the marginal teeth (dentary), the specialized inner tooth plates of upper (pterygoid) and lower (prearticular) jaws in dipnoans are dentitions radically different from all other osteichthyans. However, even these fused tooth plates also begin their development from individual and separate teeth and have one pioneer tooth for each tooth plate (Kemp 1977(Kemp , 1979(Kemp , 2002Smith 1985;Smith & Krupina 2001;Smith et al 2002). A pioneer tooth for each of the dentate bones, with sequential initiation of teeth on the jaw, is a pattern recognized for many teleosts (Huysseune 2006).…”

“…Also, lungfish do not form replacement teeth for those in the primary tooth rows. We have previously shown (Smith & Krupina 2001;Smith et al 2002) that ongoing successive tooth addition is a one-directional pattern in all tooth plates even in the dentary equivalent, where this is posterior (proximal). The direction of growth of the dentition for the dentary of the trout (Berkovitz 1977;Fraser et al 2004;2006a,b) is also in a posterior direction.…”

The cranial morphology of a new genus of lungfish (Osteichthyes: Dipnoi) from the Upper Jurassic Morrison Formation of North America

“…The partial skull of Ceratodus sturii from the Late Triassic (Carnian) of Austria has alternately been attributed to the genus Ceratodus (Kemp, 1998;Cavin et al, 2007) and placed in the genus Tellerodus (Lehman, 1975;Schultze, 1981), but has since been returned to the genus Ceratodus based on dental similarities with the holotypic material of the genotype, C. latissimus Agassiz (Kemp, 1998;Schultze, 2004). Similarities exist between the dental plates associated with this skull and with other dental plates attributed to the genus Ceratodus, but diversity within the genus Ceratodus and conservatism in dental morphology throughout Mesozoic lungfishes (Smith and Krupina, 2001;Smith et al, 2002;Ahlberg et al, 2006;Pardo, 2007) hinder further inference concerning constancy of skeletal morphology and monophyly of the genus. This is particularly perplexing because fossils attributed to the genus Ceratodus span the entire Mesozoic and are found on every continent.…”