Glossary of Organisms

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

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

Bryozoans

Colonial marine invertebrates which form coral-like skeletons which can be either branching or irregular in shape
Geologic Range: Early Ordovician to Recent

Corals

Colonial marine invertebrates which were the dominant reef-builders throughout much of earth history
There are three groups:

1. Rugosa: dominant Paleozoic reef-buiders from the Ordovician to the Permian
2. Tabulata: dominant Paleozoic reef-builder which coexisted with the Rugosa from the Ordovician to the Permian
3. Scleractinia: the modern corals dominant in reef ecosystems today
   Geologic Range: Triassic to Recent

Diatoms

Microscopic marine plants which secrete siliceous skeletons
Geologic Range: Jurassic to Recent

Dinoflagellates

Microscopic phytoplankton commonly preserved as organic cysts
Geologic Range:

Echinoderms

A diverse group of organisms(including the crinoids and the blastoids) whose members characteristically exhibit five-fold symmetry (a modern-day example of an echinoderm is the sea urchin)
Geologic Range: Cambrian to Recent

Eurypterids

A group of extinct arthropods which were highly successful Paleozoic predators
Geologic Range:

Fusulinid Foraminifera

Geologic Range:

Mammal-like Reptiles

Members of the group Synapsida who were the predecessors of mammals
Geologic Range: Early Permian to Late Triassic

Marine Reptiles

Successful Paleozoic and Mesozoic marine vertebrate groups including the icthyosaurs, plesiosaurs, and mosasaurs
Geologic Range: Triassic to Late Cretaceous

Molluscs

A highly diversified and abundant group of organisms found in all environments
Geologic Range: Cambrian to Recent
Important molluscan groups include the following:

1. Bivalves: Marine invertebrates with two shells which are mirror images of the other (a modern example is a clam)
   Geologic Range:
2. Cephalopods: A highly efficient group of marine predators which include the modern-day octopus, squid, and chambered nautilus
   Fossil cephalopods include:
   Ammonoids: Coiled marine predators dominant in Mesozoic seas
   Belemnoids: Nektic marine predators similar in appearance to the modern-day squid
   Nautiloids: Extremely successful straight-chambered predators dominant in the lower Paleozoic
   
3. Gastropods: An abundant and diverse group of shelled invertebrated found virtually in all environments (a modern example is the snail)
   Geologic Range:

Ostracodes

Geologic Range:

Pelycosaurs

Geologic Range:

Sauropods

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

Stegosaurs

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

Stromatoporoids

Geologic Range:

Trilobites

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