Exceptionally preserved shark fossils from Mexico elucidate the long-standing enigma of the Cretaceous elasmobranch Ptychodus

The fossil fish Ptychodus Agassiz, 1834, characterized by a highly distinctive grinding dentition and an estimated gigantic body size, has remained one of the most enigmatic extinct elasmobranchs (i.e. sharks, skates, and rays) for nearly two centuries. This widespread Cretaceous taxon is common in Albian to Campanian deposits from almost all continents. However, specimens mostly consist of isolated teeth or more or less complete dentitions, whereas cranial and post-cranial skeletal elements are very rare. Here we describe newly discovered material from the early Late Cretaceous of Mexico, including complete articulated specimens with preserved body outline, which reveals crucial information on the anatomy and systematic position of Ptychodus. Our phylogenetic and ecomorphological analyses indicate that ptychodontids were high-speed (tachypelagic) durophagous lamniforms (mackerel sharks), occupying a specialized predatory niche previously unreported among both extant and extinct elasmob..., We explored the phylogenetic relationships of the genus Ptychodus Agassiz, 1834 within the elasmobranchs using a modified version of Jambura et al.’s (2023) data matrix. In order to provide a broader context of these relations, several Palaeozoic, Mesozoic, Cenozoic, and Recent chondrichthyan taxa were additionally included as outgroups, with Pucapampella and Doliodus serving as the root. To accommodate the inclusion of these groups, several modifications and additional characters from previous works were added to the present data matrix (e.g., Allis 1923; Holmgren 1940, 1941; Patterson 1965; Schaeffer 1981; Maisey 1980, 1984, 1985, 2001; Compagno 1990a; Nishida 1990; Shirai 1996;  Goto 2001). The resulting data matrix was assembled in Mesquite 3.81 (Madisson and Madisson 2023) and includes 221 characters. Analysis was carried out in TNT v.1.6 (Goloboff and Morales 2023), under Goloboff et al.’s (2021) protocol, considering the inclusion of inapplicable characters. A traditional parsimo..., , # Exceptionally preserved shark fossils from Mexico elucidate the long-standing enigma of the Cretaceous elasmobranch *Ptychodus* (Phylogenetic analyses)

[https://doi.org/10.5061/dryad.12jm63z5n](https://doi.org/10.5061/dryad.12jm63z5n)

This dataset contains all the information needed to perform the phylogenetic analysis carried out in our paper \"Exceptionally preserved shark fossils from Mexico elucidate the long-standing enigma of the Cretaceous elasmobranch *Ptychodus*.\" In this study, our objective was to determine the phylogenetic relations of the Cretaceous extinct shark *Ptychodus* based on the newly described holomorphic specimens described in our paper. A Parsimony analysis was carried out to determine these relations, which involved a traditional search under the TBR algorithm for branch swapping and the use of step matrices.

## Description of the data and file structure

This dataset contains an extensive sampling of morphological characters that includes crown elasmobranc...