Intraspecific dental variations in the deep-sea shark Etmopterus spinax and their significance in the fossil record

An important character on several taxonomic levels for shark identification is the tooth morphology. Sharks show a variety of highly specialized dentitions reflecting adaptations to their feeding habits. Intraspecific variation of tooth morphology such as sexual or ontogenetic dimorphism is poorly known in many species, even though tooth morphology plays a decisive role in the characterization of the fossil record of sharks, which comprises mostly fossil teeth. Here we analyzed the dentition of 40 jaws of the Velvet Belly Lantern Shark Etmopterus spinax and identified ontogenetic and sexual dimorphic characters such as total number of teeth, number of upper teeth, cusplet numbers in upper jaw teeth and width of lower jaw teeth. Dimorphic characters may reduce intraspecific competition for food, as E. spinax segregates by sex and size and may allow for identifying the male sex. The lower jaw tooth height, a sexually non-dimorphic character, was used to re-calculate the total length of specimens, which represents the first such approach for a squaliform shark. Results derived from the extant E. spinax are subsequently applied to fossil Etmopterus sp. teeth (Miocene) to gain individual information such as sex or size, but also characterize the extinct population from the excavation site by a size distribution profile in comparison to data from extant populations. This approach indicates the presence of multiple ontogenetic stages in the extinct population.publishedVersio

New records of fossil deep-sea shark teeth from the Lillebælt Clay (Early–Middle Eocene) of Denmark

This study describes for the first time a number of distinct fossil teeth documenting several deep-sea shark species from the Eocene, which were previously not recorded from the North Sea Basin, including Apristurus sp., Orthechinorhinus cf. pfeili, Deania cf. angoumeensis, Squaliolus sp., Etmopterus cf. cahuzaci and Paraetmopterus nolfi. Our findings significantly increase the deep-sea shark diversity documented from this area so far. Despite the fact that the North Sea Basin had already lost direct connections to the neighbouring marine areas in the Eocene, the fauna shows highest similarities with documented Eocene deep-sea faunas of France, Austria and northern Morocco using cluster analysis.publishedVersio

Parasquatina zitteli nov. sp. (Elasmobranchii: Orectolobiformes) aus dem Maastricht von Oberbayern (Gerhartsreiter Schichten, Siegsdorf) und Bemerkungen zur Verbreitung der Ordnung Orectolobiformes

Pollerspöck J, Beaury B: Parasquatina zitteli nov. sp. (Elasmobranchii: Orectolobiformes) from the Maastrichian of Upper Bavaria (Gerhartsreiter Ditch, Siegsdorf), with remarks on the distribution of the order Orectolobiformes. The genus Parasquatina is documented for the first time from the Gerhartsreiter Ditch near Siegsdorf (Upper Bavaria, Germany). The fossils are interpreted as a new species, for which the name Parasquatina zitteli nov. sp. is proposed, because they differ in morphology from all other species in that genus, especially with regard to the labial apron, which is absent in P. zitteli. Assignment of the genus Parasquatina to the order Squatiniformes is reversed, and the genus now placed in the order Orectolobiformes. In addition, a survey of recent records of Parasquatina is given, together with an up-to-date overview of the stratigraphic distribution of the order Orectolobiformes, and resulting questions are discussed.Aus dem Gerhartsreiter Graben bei Siegsdorf wird der erste Nachweis der Gattung Parasquatina dokumentiert und aufgrund der morphologischen Unterschiede zu den bisher bekannten Arten die Art Parasquatina zitteli nov. sp. beschrieben. Parasquatina zitteli nov. sp. unterscheidet sind von allen beschriebenen Arten dieser Gattung insbesondere durch das Fehlen des labialen Aprons. Die bisher bereits zweifelhafte taxonomische Zuordnung von Parasquatina zur Ordnung der Squatiniformes wird aufgegeben und die Gattung zur Ordnung der Orectolobiformes gestellt. Neben einer Zusammenfassung über die bisher in der Literatur dokumentierten Funde von Parasquatina wird eine aktuelle Übersicht über die stratigraphische Verbreitung der Ordnung Orectolobiformes vorgestellt und die sich daraus ergebenden Fragen diskutiert

Revision of the Cretaceous shark Protoxynotus (Chondrichthyes, Squaliformes) and early evolution of somniosid sharks

Due to the peculiar combination of dental features characteristic for different squaliform families, the position of the Late Cretaceous genera Protoxynotus and Paraphorosoides within Squaliformes has long been controversial. In this study, we revise these genera based on previously known fossil teeth and new dental material. The phylogenetic placement of Protoxynotus and Paraphorosoides among other extant and extinct squaliforms is discussed based on morphological characters combined with DNA sequence data of extant species. Our results suggest that Protoxynotus and Paraphorosoides should be included in the Somniosidae and that Paraphorosoides is a junior synonym of Protoxynotus. New dental material from the Campanian of Germany and the Maastrichtian of Austria enabled the description of a new species Protoxynotus mayrmelnhofi sp. nov. In addition, the evolution and origin of the characteristic squaliform tooth morphology are discussed, indicating that the elongated lower jaw teeth with erected cusp and distinct dignathic heterodonty of Protoxynotus represents a novel functional adaptation in its cutting-clutching type dentition among early squaliform sharks. Furthermore, the depositional environment of the tooth bearing horizons allows for an interpretation of the preferred habitat of this extinct dogfish shark, which exclusively occupied shelf environments of the Boreal- and northern Tethyan realms during the Late Cretaceous.publishedVersio

Trophic position of Otodus megalodon and great white sharks through time revealed by zinc isotopes

Diet is a crucial trait of an animal’s lifestyle and ecology. The trophic level of an organism indicates its functional position within an ecosystem and holds significance for its ecology and evolution. Here, we demonstrate the use of zinc isotopes (δ66Zn) to geochemically assess the trophic level in diverse extant and extinct sharks, including the Neogene megatooth shark (Otodus megalodon) and the great white shark (Carcharodon carcharias). We reveal that dietary δ66Zn signatures are preserved in fossil shark tooth enameloid over deep geologic time and are robust recorders of each species’ trophic level. We observe significant δ66Zn differences among the Otodus and Carcharodon populations implying dietary shifts throughout the Neogene in both genera. Notably, Early Pliocene sympatric C. carcharias and O. megalodon appear to have occupied a similar mean trophic level, a finding that may hold clues to the extinction of the gigantic Neogene megatooth shark.publishedVersio

Shark fossil diversity (Squalomorphii, Squatinomorphii, and Galeomorphii) from the Langhian of Brielas (Lower Tagus Basin, Portugal)

The fossiliferous marine Miocene sediments of the Lower Tagus Basin (Portugal) present a great diversity of Chondrichthyes forms. The current study focuses on the fossil sharks from the Langhian Vc unit of the Brielas section, located in the Setúbal Peninsula. A total of 384 isolated fossil teeth were analysed and ascribed to 17 species from the Orders Hexanchiformes, Squaliformes, Squatiniformes, Lamniformes, and Carcharhiniformes. Centrophorus granulosus and Iago angustidens are described for the first time in Portuguese sediments, whereas Pachyscyllium dachiardii and Rhizoprionodon ficheuri represent only their second reported occurrence. Galeorhinus goncalvesi was already known from the Portuguese uppermost Miocene (Alvalade Basin), but it is now recognized in older sediments. Furthermore, the new material seems to include the first reported occurrence of Hexanchus cf. agassizi in Miocene sediments. As a whole, these new findings support the previous palaeoenvironment characterization of a warm infralittoral setting gradually deepening to a circalittoral one, where seasonal upwelling phenomena could have occurred

Intraspecific dental variations in the deep-sea shark Etmopterus spinax and their significance in the fossil record

An important character on several taxonomic levels for shark identification is the tooth morphology. Sharks show a variety of highly specialized dentitions reflecting adaptations to their feeding habits. Intraspecific variation of tooth morphology such as sexual or ontogenetic dimorphism is poorly known in many species, even though tooth morphology plays a decisive role in the characterization of the fossil record of sharks, which comprises mostly fossil teeth. Here we analyzed the dentition of 40 jaws of the Velvet Belly Lantern Shark Etmopterus spinax and identified ontogenetic and sexual dimorphic characters such as total number of teeth, number of upper teeth, cusplet numbers in upper jaw teeth and width of lower jaw teeth. Dimorphic characters may reduce intraspecific competition for food, as E. spinax segregates by sex and size and may allow for identifying the male sex. The lower jaw tooth height, a sexually non-dimorphic character, was used to re-calculate the total length of specimens, which represents the first such approach for a squaliform shark. Results derived from the extant E. spinax are subsequently applied to fossil Etmopterus sp. teeth (Miocene) to gain individual information such as sex or size, but also characterize the extinct population from the excavation site by a size distribution profile in comparison to data from extant populations. This approach indicates the presence of multiple ontogenetic stages in the extinct population