Morphology and paleobiology of the Late Cretaceous large-sized sharkCretodus crassidens(Dixon, 1850) (Neoselachii; Lamniformes)

Abstract

The definition of the Cretaceous shark genus Cretodus Sokolov, 1965 is primarily based on isolated teeth. This genus includes five species. Among these, Cretodus houghtonorum Shimada and Everhart, 2019 is the only species based on a partially preserved skeleton. Here, the taxonomic attribution of a virtually complete skeleton of Cretodus from the Turonian of northeastern Italy is discussed, together with a few specimens from the Turonian of England. One of the latter is investigated through micropaleontological analysis to determine its stratigraphic position. The material is referred to Cretodus crassidens (Dixon, 1850), the diagnosis of which is emended herein. The dentition is tentatively reconstructed, exhibiting strong similarities with congeneric species, although it differs in having strong vertical folds on the main cusp labial face, a mesiodistally broad tooth aspect, weak and well-spaced ‘costulae’ at crown base, and a different dental formula in the number of parasymphyseal and lateral rows. Some tooth malformations are interpreted as feeding-related or senile characters. The Italian specimen suggests that Cretodus crassidens had a wide and laterally expanded mouth and head, a stout body, and attained a gigantic size. Cretodus crassidens was a moderate-speed swimming shark ecologically like the extant tiger shark Galeocerdo cuvier (Péron and Lesueur in Lesueur, 1822). The age estimate from vertebral-band counting suggests that the Italian individual was at least 23 years old and the growth model indicates a longevity of 64 years and a maximum attainable total length of 9–11 m. Cretodus crassidens occurs both in Boreal and Tethyan domains, implying a broad paleobiogeographic distribution and a preference toward offshore settings.

A new goniopholidid crocodylomorph from the Late Jurassic of Portugal

“…megalodon are short, well mineralized and equipped with densely spaced radial lamellae (Leriche, 1926). This vertebral morphotype, which functionally adds architectural strength, is common within Lamniformes and characterizes both the extant white shark (Newbrey et al, 2015) and many other extinct apex predatory lamniform species (Shimada, 1997;Siverson, 1999;Amalfitano et al, 2022). Yet, the much longer vertebral column length measured by Cooper et al (2022) (11.1 m) than the estimate based on the vertebral diameter sizes of the extant white shark (9.2 m TL) indicates that †O.…”

First evidence of marine turtle gastroliths in a fossil specimen: Paleobiological implications in comparison to modern analogues

“…Paleodepth interpretation of "lastame" in the Sant'Anna d'Alfaedo area is quite controversial and debated (ranging from 50 to 100 m to full bathyal; [44,52,53]). The vertebrate macrofauna so far recovered in the Lessinian "lastame" includes: the sharks Cretoxyrhina mantelli, Cretodus crassidens, Ptychodus spp., the batomorph Onchosaurus pharao, still unidentified teleostean remains, marine turtles (detailed below), and the yaguarasaurinid mosasaurs Romeosaurus fumanensis and R. sorbinii (e.g., [40,42,46,48,[54][55][56]). Vertebrate remains show virtually no current-mediated displacement of bones [40,42,50] and usually represent various degrees of disarticulation of slowly decaying carcasses exposed for extended time intervals on the seabed under low-energy conditions [54].…”

“…“Lastame” dates back to Turonian p.p.-Coniacian p.p. [ 43 , 44 ], but most of the vertebrate skeletons and partial remains so far investigated comes from the middle-upper Turonian interval (e.g., [ 48 ]). A sedimentological peculiarity of “lastame” is represented by the presence of allochthonous stones (pebbles and cobbles) in some beds of the lower half of the lithozone (e.g., [ 43 , 49 ]): these exotic clasts, sometimes associated with teredinid tubes, have been interpreted as dropstones, fragments of rocks carried at sea by floating driftwood that released them on the seafloor after decomposition [ 50 , 51 ].…”