Micro-CT Based Description of Dorsetichthys bechei (Actinopterygii: Teleostei): Cranial Anatomy of an Iconic Early Teleost

Teleost fishes comprise more than 36,000 living vertebrate species and occupy a wide range of aquatic ecosystems. Despite their overwhelming success, extinct taxa outside of the living radiation--stem teleosts--remain poorly understood. Dorsetichthys bechei is an Early Jurassic stem teleost of historic importance. Although D. bechei is well described, its proximity to the teleost crown and relationships with other stem teleosts is challenging due to previous associations with the wastebasket assemblage known as "pholidophorids". Here we present a new, three-dimensionally preserved specimen of Dorsetichthys bechei from the Blue Lias Formation (Sinemurian) Lyme Regis, UK. High-resolution CT scanning of this specimen plus additional material reveals previously unknown internal morphological information, including of the jaw and palate, hyoid arch, and gill skeleton. Importantly, this previously undescribed articulated specimen permits description of the external dermal skeleton and internal endoskeleton for the same individual, clarifying past accounts drawing on composite descriptions of two- and three-dimensionally preserved specimens. We confirm the presence of important teleost synapomorphies such as a mobile premaxilla and quadratojugal process. However, contrasting previous accounts, we find no evidence for dorsal and ventral hypohyals or a postarticular process of the lower jaw. We also confirm the presence of a prearticular. The presence of a mobile upper jaw, elaborate gill rakers and reduced dentition also support a possible facultative filter feeding ecology. These new anatomical data support removal of D. bechei from Pholidophoridae and Pholidophoriformes as currently defined but indicate that finer-scale patterns of relationships among more crownward members of the teleost stem are some way from being resolved.