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.
Highlights
Ptychodus Agassiz, 1834 is a genus of Cretaceous elasmobranchs ranging from the Albian to the Campanian with worldwide distribution (Woodward, 1912; Cappetta, 2012)
The Italian record of Ptychodus latissimus Agassiz, 1835 is primarily represented by numerous isolated teeth and rare associated finds mostly coming from the Turonian beds of “Lastame” lithofacies of Scaglia Rossa Formation of northeastern Italy
Various specimens come from upper Turonian to upper Campanian “Pietra di Castellavazzo” lithofacies (Scaglia Rossa Fm) indicating that these species might have lived for more than 10 million years, which is in contradiction with the assumption of Hamm (2020), who considers that the last occurrence of this species dates back to lower Coniacian
Summary
Ptychodus Agassiz, 1834 is a genus of Cretaceous elasmobranchs ranging from the Albian to the Campanian with worldwide distribution (Woodward, 1912; Cappetta, 2012). The fossil record of this enigmatic predator mainly includes isolated teeth, very rare associated, and articulated dentitions and mineralized cartilaginous elements (Nicolis, 1889; Woodward, 1889; Tan, 1949; MacLeod, 1982; Everhart & Caggiano, 2004; Shimada et al, 2010; Cappetta, 2012; Shimada, 2012; Diedrich, 2013; Hamm, 2017; Amadori et al, 2019a, 2019b, 2020; Jambura & Kriwet, 2020). Ptychodus exhibits relatively flat or markedly cusped dental crowns, which could suggest opportunistic or more specialized feeding adaptations, respectively (Shimada, 2012; Diedrich, 2013; Amadori et al, 2019b, 2020)
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