Dental homologies in lamniform sharks (Chondrichthyes: Elasmobranchii)

Abstract

The dentitions of lamniform sharks are said to exhibit a unique heterodonty called the "lamnoid tooth pattern." The presence of an inflated hollow "dental bulla" on each jaw cartilage allows the recognition of homologous teeth across most modern macrophagous lamniforms based on topographic correspondence through the "similarity test." In most macrophagous lamniforms, three tooth rows are supported by the upper dental bulla: two rows of large anterior teeth followed by a row of small intermediate teeth. The lower tooth row occluding between the two rows of upper anterior teeth is the first lower anterior tooth row. Like the first and second lower anterior tooth rows, the third lower tooth row is supported by the dental bulla and may be called the first lower intermediate tooth row. The lower intermediate tooth row occludes between the first and second upper lateral tooth rows situated distal to the upper dental bulla, and the rest of the upper and lower tooth rows, all called lateral tooth rows, occlude alternately. Tooth symmetry cannot be used to identify their dental homology. The presence of dental bullae can be regarded as a synapomorphy of Lamniformes and this character is more definable than the "lamnoid tooth pattern." The formation of the tooth pattern appears to be related to the evolution of dental bullae. This study constitutes the first demonstration of supraspecific tooth-to-tooth dental homologies in nonmammalian vertebrates.

Skeleton of the Fossil SharkIsurus denticulatusfrom the Turonian (Late Cretaceous) of Germany—Ecological Coevolution with Prey of Mackerel Sharks

“…Wellnhofer). Shimada [6,[10][11][12][13][14][15]29] and Shimada et al [14] published very well-preserved, nearly complete and new skeletons of "Cretoxyrhina mantelli" from the Niobrara Formation, Kansas (North America). Other specimens (a complete skeleton plus another partial one)…”

“…Both characteristics are present in other lamnidae and correspond to a plesiomorphic character (cf. [1,6]). Some lateral and symphyseal teeth from the late Cenomanian (C. naviculare and M. geslinianum Zone) of Halle/Hesseltal (Figures 6(f)-6(h), 7(d)-7(f) and 7(k), [23]) fall into the typical variety of the tooth morphology of I. appendiculatus, whose separation must have occurred during the Cenomanian-Turonain boundary.…”

“…Macroneoselachians have in most cases ancestors reaching into the upper early or lower Late Cretaceous (e.g., [1][2][3][4][5][6]). The largest shark of the lower-middle Late Cretaceous (Cenomanian-Campanian) was described as Isurus [7,8] or Cretoxyrhina [9] controversially until today (e.g., [6]), which was globally distributed (Figure 1(a)).…”

“…The largest shark of the lower-middle Late Cretaceous (Cenomanian-Campanian) was described as Isurus [7,8] or Cretoxyrhina [9] controversially until today (e.g., [6]), which was globally distributed (Figure 1(a)). Cretaceous and Tertiary shark researchers did not review the isurid sharks in the past critically, whereas complete skeletons are rare form different stratigraphical units (e.g., [6,10]).…”

“…The largest shark of the lower-middle Late Cretaceous (Cenomanian-Campanian) was described as Isurus [7,8] or Cretoxyrhina [9] controversially until today (e.g., [6]), which was globally distributed (Figure 1(a)). Cretaceous and Tertiary shark researchers did not review the isurid sharks in the past critically, whereas complete skeletons are rare form different stratigraphical units (e.g., [6,10]). The revision of Mesozoic Isurus and its evolutionary trend, especially in the dental morphology change, is highly important to understand its fairly long evolutionary trend, which is the basic to understand the white shark evolution and non-origin of megatooth sharks from isurid ancestors (cf.…”