Dental patterns of the stem-group hexanchoid shark, Notidanoides muensteri (Elasmobranchii, Hexanchiformes)

Abstract

ABSTRACT—Detailed analyses of the dentition of the single preserved holomorphic specimen and isolated teeth of the extinct Late Jurassic hexanchiform shark, Notidanoides muensteri, support previous interpretations that all Jurassic cow sharks belong to the family Crassonotidae, which represents stem-group hexanchoids. The reconstruction of its dentition has enabled the identification of important congruencies (comb-like lateral teeth, presence of a lower (?) symphyseal tooth row) and differences (very weak dignathic and monognathic heterodonties, with anterior teeth being of the same general morphology as laterals). Although the general tooth morphology does not change significantly, ontogenetic trajectories are identifiable, including development of lateral cusplets in symphyseal teeth, reduction of labial tooth crown ornamentation, and more pronounced dignathic heterodonty pattern in adults. The general root morphology is identical to that of Crassodontidanus and represents the plesiomorphic condition within hexanchoids. The Jurassic hexanchoids Notidanus wagneri, N. huegeliae, N. eximius, and N. nikitiini, which are known from isolated teeth only, are synonymized with Notidanoides muensteri based on the dental analyses presented here. The distribution pattern and scarcity of fossil remains indicate that this crassonotid was a typical Tethyan element of Late Jurassic neoselachian faunas and inhabited open-marine environments, probably on the outer shelves and upper continental slopes. Notidanoides appears later in the fossil record than Crassodontidanus and survives into the early Tithonian. By the end of the Jurassic, both seemingly went extinct and were replaced by other plesiomorphic hexanchoids (e.g., Pachyhexanchus) in the Early Cretaceous.