On the Dentition and Affinities of the Selachian Genus Ptychodus , Agassiz

Abstract

Notwithstanding the abundance of the well-known teeth of Pzychodus in the Chalk of many localities, and the long list of specific forms that have already been recognized, very little information has hitherto been published in regard to the precise affinities of the fish to which they originally appertained. So rarely, indeed, are any of the teeth found associated in natural sequence, that it has been necessary to await the results of many years' patient collecting before being able to pronounce a decided opinion; but materials are now forthcoming for at least one further step in the determination of their relationships, and I therefore venture to offer to the Geological Society some account of the accumulated evidence. Since these interesting fossils first became the subject of scientific study, it has been almost the universal custom, as is well known, to refer the genus to the somewhat comprehensive “family” of Cestraciontidæ. An early determination of Mantell, it is true, resulted in the suggestion that they formed the dental armature of fishes allied to the Teleostean Diodons ; but the elaborate researches of Agassiz † , supported by Owen's simultaneous investigation of their microscopical structure ‡, have always been cited as ample proof of the affinity of their original possessor with the Cestraciont Sharks ; and the deeply rooted tendency among palæontologists to refer every isolated crushing–tooth to the same extraordinary group has also contributed to the adoption of this arrangement without, serious question. But the original observations from which the inferences as to

The Italian record of the Cretaceous shark,Ptychodus latissimusAgassiz, 1835 (Chondrichthyes; Elasmobranchii)

“…Another species that shares several characters with Ptychodus latissimus is P. paucisulcatus Dixon, 1850, as previously remarked by various authors (Woodward, 1912;Herman, 1977;Amadori et al, 2020;Hamm, 2020). Although these two taxa have been considered separate species for a long time, their mutual relationships remain uncertain (Woodward, 1887(Woodward, , 1912Leriche, 1902Leriche, , 1906Leriche, , 1929Herman, 1977;Antunes & Cappetta, 2002;Amadori et al, 2020;Hamm, 2020). Dixon (1850) introduced the species P. paucisulcatus based on a flat, isolated tooth and other still undescribed specimens.…”

Scanning electron microscope examination of the dental enameloid of the Cretaceous durophagous sharkPtychodussupports neoselachian classification

“…Some 180 years later, several species have been described, including some from specimens that have associated or articulated dental sets (e.g., Williston, 1900; Woodward, 1904; MacLeod, 1982; Williamson et al, 1991; Shimada et al, 2009; Cappetta, 2012). Similarities to the pavement dentition of durophagous rays led Woodward (1887) to place Ptychodus within the Myliobatidae, a view that was accepted throughout much of the twentieth century but has since fallen out of favor. The two currently favored hypotheses for classification of this genus are as follows: (1) Ptychodus belongs in the primitive shark order Hybodontiformes, mainly because of tooth structure; (2) Ptychodus is a highly specialized neoselachian, evidenced in features of scattered skeletal material (Cappetta, 2012).…”

A new cuspidate ptychodontid shark (Chondrichthyes; Elasmobranchii), from the Upper Cretaceous of Morocco with comments on tooth functionalities and replacement patterns

“… Woodward (1904) and Shimada et al (2009) documented lower dentitions of both low-crowned and high-crowned † Ptychodus species that still are articulated with the Meckel’s cartilages. According to these articulated findings, the lower dentition of † Ptychodus exhibits a symphyseal row composed of the largest teeth within the dental plate, while teeth decrease in size laterally (see also Woodward, 1887 , 1912 ; Williston, 1900a , b ; Everhart and Caggiano, 2004 ; Shimada, 2012 ; Diedrich, 2013 ; Amadori et al, 2020a , b ; Hamm, 2020 ). The articulated tooth set PIMUZ A/I 5056 ( Fig.…”

“…Antunes and Cappetta, 2002 ; Dutheil and Ackermann, 2004 ; Everhart and Caggiano, 2004 ; Cappetta, 2012 ; Shimada, 2012 ; Diedrich, 2013 ; Vullo and Courville, 2014 ; Hamm, 2017 , 2019 , 2020 ; Amadori et al, 2019b , 2020a , b ). The dentition of † Ptychodus consists of teeth that are arranged in antero-posteriorly directed dental rows to form maxillary and mandibular tooth plates exhibiting different degrees of dignathic heterodonty (see Woodward, 1887 , 1904 , 1912 ; Williston, 1900 a, b ; Shimada, 2012 ; Amadori et al, 2019b , 2020a ). The marked interspecific and intraspecific morphological variabilities displayed by the dentitions of † Ptychodus often complicate its taxonomic identification and systematic position to and within elasmobranchs ( Nicholls, 2010 ).…”