Acanthodians: The earliest group of fish with jaws, ranging from the Silurian to the Permian
Acritarchs: Organic-walled microfossils common throughout the Proterozoic and early Paleozoic
Amphibians: A transitional group of vertebrates between fish and reptiles, capable of living on land, but returning to the water to reproduce
Geologic Range: Devonian to Recent
Archaeocyathids: The first reef-buiders dominant from the Middle to Late Cambrian
Geologic Range: Early to Late Cambrian
Brachiopods: A group of clam-like marine invertebrates separated into the Articulata and the Inarticulata based on shell morphology
Geologic Range: Cambrian to Recent
Conodonts: Microscopic tooth-shaped parts of an eel-like swimming vertebrate distantly related to modern chordates
Geologic Range: Cambrian to Triassic