Subclass Holocephali

The second major group of cartilaginous fishes are the holocephalians, or chimaeras — commonly known as rabbit- or ratfishes. They appeared in the Early Carboniferous, and looked essentially like modern chimaeras, the males complete with penislike claspers. Today, 25 species live in the oceans of the world, usually swimming in deep water and feeding on the seabed.

name: Deltoptychius time: Early to Late Carboniferous locality: Europe (Ireland and

Scotland) size: 18 in/45 cm long This early ratfish had practically all the features of its modern descendants. It swam by flexing the long body and whiplash tail from side to side, and gliding on its outstretched, winglike pectoral fins. Its large eyes enabled it to see better in the ocean depths, while large dental plates (rather than individual teeth) crushed shellfish.

name: Ischyodus time: Middle Jurassic to Paleocene locality: Europe (England, France and Germany) and New Zealand size: 5 ft/1.5 m long

Ischyodus, more than 150 million years old, was practically identical in size and shape to Chimaera monstrosa, the modern ratfish found in the depths of the Atlantic and Mediterranean. It had the same large eyes, pursed lips, tall dorsal fin, fanlike pectorals and whiplash tail of its living relative. It even had a similar spine in front of the dorsal fin, which in the living species is connected to a venom gland, and used for defense.

Spiny sharks and armored fishes

HolocephaliStethacanthus

Spiny sharks and armored fishes

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