Cladoselache sp. - fossil shark from the Devonian of Ohio, USA. (Cleveland Museum of Natural History, Cleveland, Ohio, USA)

From museum signage: Cladoselache shark A fossil shark found in the Rocky River valley

This group of fishes is similar to the bony fishes, in constrast to the Agnatha and Placodermi in possessing jaws, paired nostrils, true teeth, scales, paired pectoral fins and girdles. They are distinctive, however, in having a cartilaginous internal skeleton, which if mineralized, is characteristically calcified into only a thin layer of prismatic granules.

Sharks were long ranked next to jawless fishes in primitiveness. Their appearance in the Middle Devonian is late in the fossil record of fishes. Their drastically reduced ossification, progressively through time in many other groups of vertebrates, may in fact be an advanced specialization.

Sharks are the second most numerous group of animals in the Ohio Shale fauna. They represent our only good view of the early forms, because of unusual conditions (which are not yet understood) which preserved the specimens of Cladoselache and Ctenacanthus. Not only are teeth, scales, and cartilage present in the fossils, but also soft parts, including musculature! Variety is shown in the different modifications of the spine of enlarged scales which occurs on the leading edges of the fins.

Classification: Animalia, Chordata, Vertebrata, Chondrichthyes, Cladoselachiformes, Cladoselachidae

Stratigraphy: Cleveland Shale Member, upper Ohio Shale, Famennian Stage, upper Upper Devonian

Locality: Rocky River Valley, Cleveland urban area, western Cuyahoga County, northeastern Ohio, USA

See info. at: