WESTERN MINDANAO STATE UNIVERSITY

COLLEGE OF SCIENCE& MATHEMATICS

DEPARTMENT OF BIOLOGY & NATURAL SCIENCES

ZOO-LEC 160 ANIMAL SYSTEMATICS

MARCH 13, 2014

• The Class Chondrichthyes has two subclasses:

– Elasmobranchii, which includes the sharks and rays.

– Holocephali: the chimaeras: ratfish and ghostfish.

16.1

16.2

Figure 24.02

• Modern Chondricthyes include the sharks, rays and Chimeras.

• The Chondrichthyes’ well-developed jaws, highly developed sense organs, powerful swimming ability and streamlined shape have enabled them to thrive as marine predators for more than 350 million years, as other groups have come and gone.

• There are just under 1000 living species, all of which have cartilaginous skeletons, even though they are descended from ancestors that had bone.

• The Chondrichthyes are an ancient group that although not

as diverse as the bony fishes have persisted largely

unchanged for hundreds of millions of years.

• The oldest unambiguous Chondrichthyans are found in the

Early Devonian (Devonian -- 416-360 mya). although there

are older fossils of scales.

• One of the best known extinct genera is Cladoselache a pelagic marine predator from the Devonian.

• It was shark-like in appearance. About 2 meters long with a large gape and three-pronged teeth. As in modern sharks the teeth were arranged on a ligamentous band in a whorl-shaped arrangement.

• Cladoselache had two dorsal fins, each preceded by a large spine.

• It also possessed paired pelvic and pectoral fins as in modern sharks, but the fins were much more broad based than in later sharks.

• The tail was symmetrical externally, but internally asymmetrical with the notochord extending into the upper lobe of the tail.

Cladoselache picture

http://www.dinosoria.com/poissons/cladoselache_03.jpg

Cladoselache

Cladoselache lacked the rostrum (snout) of modern sharks

• By the Jurassic (200-146 mya) sharks of modern appearance had evolved. Several genera from that era are still extant.

• The most distinctive feature of modern sharks is the rostrum or snout that overhangs the mouth.

• Less prominent, but also of major importance was the evolution of solid calcified vertebrae.

• Finally, the teeth are covered with thicker more complex enamel than in earlier sharks.

• Megalodon (Carcharodon megalodon) is another extinct shark species that is the largest predatory shark known.

• Megalodon occurred from 28-1.5 mya and at approximately 16m long (and with a mass estimated at 47 metrics tonnes) it resembled a massive great white shark and was the top ocean predator of its era.

“Megalodon (gray and red) with the whale shark (violet), great white shark(green), and a human (blue) for scale. Note: The maximum size attained by C. megalodon is indicated by the 20 m scale.” From Wikipedia.

http://upload.wikimedia.org/wikipedia/commons/thumb/0/07/Megalodon_scale1.png/220px-Megalodon_scale1.png

http://upload.wikimedia.org/wikipedia/commons/thumb/7/71/Megalodon_tooth_ruler.jpg/220px-Megalodon_tooth_ruler.jpg

http://upload.wikimedia.org/wikipedia/commons/thumb/7/7a/Megalodon_shark_jaws_museum_of_natural_history_068.jpg/300px-Megalodon_shark_jaws_museum_of_natural_history_068.jpg