Node age estimations and the origin of angel sharks, Squatiniformes (Neoselachii, Squalomorphii)

Abstract

The fossil record of angel sharks is reviewed with special focus on skeletal remains. A new family †Pseudorhinidae is established for two species based on complete specimens from the Late Jurassic and a possible third species based on isolated teeth. This clade is a member of the stem lineage of Squatiniformes. Squatinidae represents the crown with a reliable fossil record extending back into the Aptian based on a partial skeleton displaying characteristic morphological traits of Squatina. We also present revised morphological descriptions of the skeletal remains of †Squatina baumbergensis (Campanian of Germany) and †;Squatina sp. (Miocene of Japan). In this study, we used reliable skeletal remains and a modified approach to establish the origin and divergence of the Squatiniformes and the Squatinidae. Isolated teeth are considered to be unreliable because of the poor knowledge of squatiniform dental character traits and their evolution. We estimate a 'hard' minimum age constraint of 156.2 Ma and a 'soft' maximum age constraint of 181.74 Ma for the origin of the Squatiniformes. For the crown represented by the Squatinidae, we estimate a 'hard' minimum age constraint of 114 Ma and a 'soft' maximum age constraint of 157.59 Ma. These age constraints most likely designate the timing of the origin of identifiable squatiniform and squatinid characters as currently understood rather than the origin of the Squatiniformes or the divergence between the †Pseudorhinidae and the Squatinidae. The lack of pre-Late Jurassic pseudorhinids and pre-Cretaceous squatinids probably represents an artefact because characteristic squatiniform tooth morphologies, which generally provide only a restricted set of diagnosable features, might not have yet been fully developed. Consequently, skeletal remains of neoselachians from the Early and Middle Jurassic are crucial for establishing reliable characters of stem-lineage representatives and to avoid misinterpretations resulting from transferring morphological traits of the crown to fossil groups with unresolved interrelationships, as well as sister-group relations. © 2013 Natural History Museum.