A fish species dated to about 383 million years ago is the earliest known member of the group that includes sharks.

A strange-looking ancient fish that was closely related to modern sharks had an eel-like body and might have gulped small marine creatures whole.

Sharks belong to a group of fishes called elasmobranchs, which have skeletons of cartilage rather than bone. Because cartilage rarely fossilizes, scientists know little about this group’s early members.

Christian Klug at the University of Zurich in Switzerland and his colleagues found the nearly complete skeleton — including preserved cartilage and muscle — of a new species of fish (Phoebodus saidselachus) that lived around 383 million years ago. It is the oldest known cartilage-based fish with an eel-shaped body, and its discovery pushes back the emergence of elasmobranchs 10 million years earlier than previously thought.

The creature’s jaw shape suggests that it had a weak bite compared with other early sharks. The skeleton closely resembles that of the modern-day frilled shark (Chlamydoselachus anguineus). The authors suggest that Phoebodus, like the frilled shark, might have swallowed marine invertebrates and small fishes whole.