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Transitional Vertebrate Fossi15

Transitional Vertebrate Fossi15 - broad-based shark-like...

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Transitional Vertebrate Fossils Transition from primitive jawless fish to sharks, skates, and rays Late Silurian -- first little simple shark-like denticles. Early Devonian -- first recognizable shark teeth, clearly derived from scales. GAP: Note that these first, very very old traces of shark-like animals are so fragmentary that we can't get much detailed information. So, we don't know which jawless fish was the actual ancestor of early sharks. Cladoselache (late Devonian) -- Magnificent early shark fossils, found in Cleveland roadcuts during the construction of the U.S. interstate highways. Probably not directly ancestral to sharks, but gives a remarkable picture of general early shark anatomy, down to the muscle fibers! Tristychius & similar hybodonts (early Mississippian) -- Primitive proto-sharks with broad-based but otherwise shark-like fins. Ctenacanthus & similar ctenacanthids (late Devonian) -- Primitive, slow sharks with
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Unformatted text preview: broad-based shark-like fins & fin spines. Probably ancestral to all modern sharks, skates, and rays. Fragmentary fin spines (Triassic) -- from more advanced sharks. • Paleospinax (early Jurassic) -- More advanced features such as detached upper jaw, but retains primitive ctenacanthid features such as two dorsal spines, primitive teeth, etc. • Spathobatis (late Jurassic) -- First proto-ray. • Protospinax (late Jurassic) -- A very early shark/skate. After this, first heterodonts, hexanchids, & nurse sharks appear (late Jurassic). Other shark groups date from the Cretaceous or Eocene. First true skates known from Upper Cretaceous. A separate lineage leads from the ctenacanthids through Echinochimaera (late Mississippian) and Similihari (late Pennsylvanian) to the modern ratfish....
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