Transitional Vertebrate Fossi14

Transitional Vertebrate Fossi14 - first evolved in fish •...

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Transitional Vertebrate Fossils Transition from from primitive jawless fish to bony fish Upper Silurian -- first little scales found. GAP: Once again, the first traces are so fragmentary that the actual ancestor can't be identified. Acanthodians(?) (Silurian) -- A puzzling group of spiny fish with similarities to early bony fish. Palaeoniscoids (e.g. Cheirolepis , Mimia ; early Devonian) -- Primitive bony ray-finned fishes that gave rise to the vast majority of living fish. Heavy acanthodian-type scales, acanthodian-like skull, and big notochord. Canobius , Aeduella (Carboniferous) -- Later paleoniscoids with smaller, more advanced jaws. Parasemionotus (early Triassic) -- "Holostean" fish with modified cheeks but still many primitive features. Almost exactly intermediate between the late paleoniscoids & first teleosts. Note: most of these fish lived in seasonal rivers and had lungs. Repeat: lungs
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Unformatted text preview: first evolved in fish . • Oreochima & similar pholidophorids (late Triassic) -- The most primitive teleosts, with lighter scales (almost cycloid), partially ossified vertebrae, more advanced cheeks & jaws. • Leptolepis & similar leptolepids (Jurassic) -- More advanced with fully ossified vertebrae & cycloid scales. The Jurassic leptolepids radiated into the modern teleosts (the massive, successful group of fishes that are almost totally dominant today). Lung transformed into swim bladder. Eels & sardines date from the late Jurassic, salmonids from the Paleocene & Eocene, carp from the Cretaceous, and the great group of spiny teleosts from the Eocene. The first members of many of these families are known and are in the leptolepid family (note the inherent classification problem!)....
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