Glossary of Organisms

Pelycosaurs

Finback reptiles, such as Dimetrodon, which were the dominant reptile group in the Permian
Geologic Range: Pennsylvanian to Late Permian

Placoderms

A group of heavily armored jawed fish that ranged from the Late Silurian to Late Permian
Geologic Range: Late Silurian to Late Permian

Sauropods

A group of saurischian dinosaurs which includes large, quadrapedal forms such as Apatosaurus(Brontosaurus), Brachiosaurus, and Diplodocus
Geologic Range: Early to Late Jurassic

Stegosaurs

A group of ornithischian dinosaurs characterized by their bony armor and large spikes on the tail

Stromatolites

Structures produced by cyanobacteria by entrapment of sediment grains on the sticky surfaces of the bacteria
Geologic Range: Archean to Recent

Stromatoporoids

Primitive sponges that secreted layered calcareous skeletons and were prominent reef-builders
Geologic Range: Middle Ordovician to Recent

Trilobites

Marine arthropods with a chitinous or calcareous exoskeleton
Geologic Range: Cambrian to Permian

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