Identifier: scienceguide7692amer (find matches)
Title: Guide leaflet
Year: 1901 (1900s)
Authors: American Museum of Natural History
Subjects: American Museum of Natural History Natural history
Publisher: New York : The Museum
Contributing Library: American Museum of Natural History Library
Digitizing Sponsor: IMLS / LSTA / METRO

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mianof Europe and North America. Acanthodia. (Case 3): The leading characteristics of this order ofprimitive sharks are shagreen close set and scale-like, each web-like finsupported by a spine, eye protected by a ring of bony plates, backbonecartilaginous (notochordal). They appeared in the Silurian and becameextinct in the Permian. Edestidae. (Case 5): These are extinct sharks whose nearest livingrelative is probably the Port Jackson Shark (Heterodontus). Of Edeshis,the only structures preserved have long been regarded as spirals of teethwhich projected in front of the mouth. They have been found in theCarboniferous and Permian of Europe and North America. In mostsharks the most used teeth come to lie in the front Une and eventuallyget broken off. In Edestus, however, the teeth of the symphyseal regionof the lower jaw had such long stout roots that they could not breakoff but gradually grew outward into a tightly wound spiral in which theolder and smaller teeth are nearer the center.
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Fig. 17. Jaws of Carcharodon megalodon. 59 60 AMERICAN MUSEUM GUIDE LEAFLET Skates and Rays. (Case 5): Skates and rays are characterized by acartilaginous skeleton; the skin is often studded with small tubercle-shaped scales; the teeth are flattened, often fused into pavement-likecrushing plates; the gills open in separate slits on the under side of theneck. They were dominant in the Carboniferous and are greatly reducedat the present time. The early forms show many curious specializationsin fin-spines and teeth, some of the latter pavement or plate-like. ICHTHYODORULITES (Case 5J Ichthyodorulites are spines and spine-like structures of fossil fishes,many of which cannot as yet be associated with any particular kinds offishes. CHIMAEROIDS (Silver Sharks)(Case 6) Chimseroids appeared in early geologic times and were most numer-ous and diversified during the Cretaceous. They form a small group ofshark-like fishes whose existing forms with few exceptions inhabit thedeep sea. Some extinct

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