Chondrichthyans from the Lower Clayton Limestone Unit of the Midway Group (Paleocene) near Malvern, Arkansas, USA, with comments on the K/Pg boundary

Fossil marine vertebrates (Chondrichthyes, Actinopterygii, Reptilia) from the Upper Cretaceous of Akkermanovka (Orenburg Oblast, Southern Urals, Russia)

“…The number of cusplets was also recognized as a useful character to distinguish between the extant lamniform species Odontaspis ferox ( Risso, 1810 ) (2–3 pairs) and O. noronhai ( Maul, 1955 ) (1 pair) ( Humphreys et al, 1989 ; Pollerspöck and Straube, 2020 ). However, certain fossil odontaspidids appear to exhibit a variable number of lateral cusplets, e.g., Odontaspis winkleri Leriche, 1905 ( Maisch IV et al, 2020 ; Kovalchuk et al, 2023 ; Popov and Lopyrev, 2023 ) and even among extant Odontaspis species, there is at least one report of a divergent tooth pattern ( Ng et al, 2022 ). Therefore, we cannot completely rule out the possibility that these two species are conspecific.…”

Two new species of <i>Mennerotodus</i> Zhelezko, 1994 (Chondrichthyes: Lamniformes: Odontaspididae), from the Paleogene of the southeastern United States

“…With regard to Tobolamna, Malyshkina (2006a) considered some species assigned to this genus to be synonymous with Carcharias acutissimus, and Cappetta 2012has synonymized the entire genus Tobolamna with Borealotodus. Although Araloselachus is primarily considered an Oligocene to middle Miocene taxon, at least one species (A. turgaensis Zhelezko and Kozlov, 1999) has been reported from upper Eocene (Priabonian) strata.…”

“…These species were later moved to the genus Borealotodus Zhelezko and Kozlov, 1999, and apparently the subtle differences between Borealotodus and Mennerotodus were not evident when the morphologies were originally described. Malyshkina (2006a) concluded that Borealotodus karpinsky (Menner, 1928) is a junior synonym of Mennerotodus glueckmani, but Cappetta (2012) maintained B. karpinsky to be valid. Cappetta (2012) noted the similarities between Borealotodus and Mennerotodus but concluded that the genera were distinguished by their anterior teeth.…”