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

Abstract

Associated and isolated teeth of the extinct elasmobranch Ptychodus latissimus Agassiz, 1835 from the Upper Cretaceous Scaglia Rossa pelagic limestone of northern Italy are described and discussed here in detail for the first time. The dentition of this widely distributed species consists of low-crowned molariform teeth that exhibit marked and strong occlusal ornamentations suitable for crushing hard-shelled prey. The associated tooth sets and isolated teeth analyzed here are heterogeneous in size and crown outline, but unambiguously belong to a single species. Re-examination of this Italian material consisting of ca. 30 specimens mostly coming from historical collections allows for a rigorous assessment of the intraspecific variability of P. latissimus, including the identification of three different tooth “morphotypes” based on their positions within the jaws. The relatively flat crowns and occlusal sharp and thick ridges indicate a high adaptation for crushing hard-shelled prey in P. latissimus indicating that the durophagous adaptations of this species were certainly more pronounced than in all other species of Ptychodus. We hypothesize that P. latissimus was a third-level predator occupying habitats with abundant thick-shelled prey, such as inoceramid bivalves and ammonites.

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

“…As already was reported for other species (e.g. Hamm, 2017 ; Amadori et al, 2020a , b ), lower symphyseal teeth also represent the most diagnostic dental elements in † P. maghrebianus sp. nov.…”

“…Where necessary, results were adjusted using the ‘Bonferroni correction’ (multiplying by the number of pairwise comparisons) and/or ‘Jackknife resampling’ functions (deleting single observations from the original sample) in order to reduce any possible bias or spurious positives ( Smith et al, 2005 ; Sahinler and Topuz, 2007 ; Hammer, 2019 ; Galán et al, 2019 ). The software package Past 3.25 was used for all the statistical analyses performed herein (see Hammer et al, 2001 ; Marramà and Kriwet, 2017 ; Galán et al, 2019 ; Hammer, 2019 ; Amadori et al, 2020b ).…”

“…† Ptychodus was a ubiquitous elasmobranch, as its associated and isolated teeth are widely reported from the Upper Cretaceous of Africa, Asia, Europe and North and South America (e.g. 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 ).…”

“…† Ptychodus most likely was a durophagous predator able to crush hard-shelled prey with its pavement-like dentitions (e.g. Williston, 1900a , b ; Fossa-Mancini, 1921 ; Kauffman, 1972 ; Shimada, 2012 ; Everhart, 2017 ; Hamm, 2017 , 2019 , 2020 ; Amadori et al, 2020a , b ). Opportunistic feeding also was hypothesized for some cuspidate species largely preying on soft-bodied molluscs, crustaceans, and small fishes (e.g.…”

“…Opportunistic feeding also was hypothesized for some cuspidate species largely preying on soft-bodied molluscs, crustaceans, and small fishes (e.g. Shimada et al, 2009 ; Amadori et al, 2019b , 2020b ).…”