The oldest articulated chondrichthyan from the Early Devonian period

Abstract

Chondrichthyans (including living sharks, skates, rays and chimaeras) have a fossil record of scales and dermal denticles perhaps dating back to the Late Ordovician period, about 455 million years ago^1,2. Their fossil tooth record extends to the earliest Devonian period, almost 418 million years ago³, whereas the oldest known articulated shark remains date from the Early Devonian period⁴, about 394 million years ago⁵. Here we report the discovery of an articulated shark that is almost 409 million years old⁵ from the Early Devonian (early Emsian) period of New Brunswick, Canada. The specimen, identified as Doliodus problematicus (Woodward)⁶, sheds light on the earliest chondrichthyans and their interrelationships with basal jawed vertebrates. This species has been truly problematic⁷. Previously known only from isolated teeth^2,6,8, it has been identified as an acanthodian and a chondrichthyan. This specimen is the oldest shark showing the tooth families in situ, and preserves one of the oldest chondrichthyan braincases. More notably, it shows the presence of paired pectoral fin-spines, previously unknown in cartilaginous fishes.