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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- Spring '10
- Geology, Devonian, Jurassic, Upper Cretaceous, simple shark-like denticles