Fossil Field Guide

Fossils and Dinosaurs Glossary

Adaptation
Physical structures, characteristics or behaviors that allow an organism to survive and reproduce in its particular environment.

Ammonoid
Any cephalopod mollusk of the extinct order Ammonoidea, having a coiled, chambered shell.

Articulated
Describing fossilized bones that remain joined as they would have been in life.

Artiodactyl
The group of mammals that includes even-toed hoofed animals, such as camels, cattle, pigs, deer, giraffes, and hippopotamuses.

Asteroid
Any relatively small solar system object, composed mostly of rock, that orbits around the sun. Many of these objects orbit the sun between Mars and Jupiter. Their size can range anywhere from a few meters to almost 1000 kilometers in diameter.

Baleen
Plates of dense, hair-like fibrous material (see keratin) that hang in rows from the roof of the mouth of certain whales for filter feeding purposes.

Belemnites
An extinct group of marine cephalopod, with a bullet-shaped internal shell, similar to the modern squid and cuttlefish.

Bipedal
Describing the ability to walk on the two hind legs rather than all four.

Canids
Members of the family Canidae, including living and extinct species of dogs, wolves, foxes, coyotes, etc.

Carnivore
An animal that eats only meat.

Carrion
The remains of recently dead animals providing food for scavengers.

Cephalopod
A group of marine invertebrate animals that includes the octopus, squid and chambered nautilus.

Conifer
Plants that bear cones and have needle or scale-like leaves, mostly evergreen, such as pines, spruces, firs, etc.

Coralloid
Masses of branched roots that form near or above the surface of the soil in cycads.

Cornified
Formed of a horny layer of skin or skin structures such as nails, hair or scales.

Crinoid
A marine invertebrate, usually possessing a cup-shaped body and five or more feathery tentacles. A few hundred species presently exist, but thousands of extinct species have been found in fossil form, particularly in Paleozoic Era limestones. The crinoids' distinctive skeletons make them important Paleozoic index fossils.

Cyanobacteria
Normally unicellular, aquatic bacteria that manufacture their own food through photosynthesis. They are also known to be the oldest fossils ever found.

Dental battery
Tooth pattern featuring a very large number of small, slender teeth packed very closely together along the jaw, which make up efficient grinding surfaces.

Desmostylians
Group of extinct hippo-like marine mammals characterized by cheek teeth consisting of groups of dentine/enamel pillars or columns.

Diatomite
Very light weight sedimentary rock composed of the remains of diatoms, or microscopic single-celled algae, which are very abundant in marine and fresh water.

Digitigrade
Referring to walking on the front part of the toes or digits, with the hind part of the foot lifted off the ground; for example, as in modern cats and dogs.

Dioecious
A botanical term that refers to having male and female organs on different plants of the same species.

Echinoderm
Any member of the phylum Echinodermata, a group of exclusively marine invertebrate animals including sea urchins, star fish, brittle stars, sea cucumbers, sand dollars, crinoids, etc.

Ectoparasite
Type of parasite that resides on external surface of the host organism.

Extinction
The complete disappearance of a type of organism.

Faunal assemblage
A large group of fossil animals found in the same location and regarded as from the same time period.

Foraminiferan
Very small, unicellular animals, mostly marine, that secrete shells of calcium carbonate or of cemented sand grains.

Fossil
Remain, impression, or trace of an ancient animal or plant that has been preserved in Earth's crust and is older than about 10,000 years.

Genus (singular), Genera (plural)
A rank in classification in taxonomy above the species level; may include several related species.

Geologic time
A very long period of time encompassing from the formation of the Earth to the beginning of recorded history, extending over millions of years.
See Geologic Timeline.

Gymnosperm
Plants that produce seeds that are not enclosed within plant tissue; literally, a “naked seed”. Examples include pines and spruce.

Hadrosaur
Large, bipedal dinosaur with duck-like bills.

Herbivore
An animal that eats plants.

Herbivorous
Feeding on plants.

Heteromorph
Those ammonites whose shell was not spirally coiled.

Hyoid
A U-shaped bone in the throat located at the root of the tongue.

Igneous
Produced under conditions involving intense heat, as rocks of volcanic origin or rocks crystallized from molten magma.

Index Fossil
Describing a species which is abundant and widespread in fossil form, but confined to a specific period of geologic time, such that its presence can be used to geologically date the rocks in which it is found.

Insectivore
Feeding on insects.

Keratin
The protein that makes up nails, hair, hooves, and horns and other such vertebrate structures.

Krill
Small, shrimp-like crustaceans, which form an important food source for filter-feeding marine mammals.

Macroconch
Referring to the female form of an ammonite, in which the female of the species had a larger shell than the male, or microconch.

Magma
Naturally occurring molten rock that forms in the Earth's crust; when it erupts it is known as lava.

Miacid
Extinct family of early carnivores living in North America that gave rise to the dogs, bears, cats, hyenas, etc.

Microconch
Referring to the male form of an ammonite, in which the male of the species had a smaller shell than the female, or macroconch.

Middens
Very old refuse heaps that contain discarded materials, food remains, bones, etc.

Mollusk
Soft-bodied invertebrates including clams, snails, octopi, and squid.

Mosasaur

Mosasaur
Extinct group of carnivorous marine reptiles.

Mya
Abbreviation for million years ago.

Mysticete
Refers to the group of toothless, baleen whales, including gray whales, right whales and rorquals.

Nautiloid
A group of marine mollusks which possess an external shell, the most well known example being the modern chambered nautilus. Also includes many fossil forms.

Niche
The role or functional position of a species within the community of an ecosystem.

Nodosaur
Armored herbivorous dinosaur that lacks a clubbed tail, has leaf-shaped teeth and walks on all fours.

Odontocete
Refers to the toothed whales, such as belugas, narwhals, dolphins, sperm and killer whales

Omnivore
Referring to the habit of consuming a broad variety of plant and animal foods

Oreodont
Diverse group of extinct North American hoofed mammals distantly related to modern camels and pigs.

Ornithischian
Meaning bird-hipped, it is one of two main groups of Dinosauria and refers to the structure of the pelvis or hip-bone. Ornithischian dinosaurs had pelvises with the pubic bone pointing backward and down from the hip sockets.
See also Saurischian.

Ossicles
Small bones such as those embedded as armor in the skin

Osteoderm
A bony plate or scale found in the dermal layers of the skin.

Ostracods
Very diverse group of small crustaceans, mostly only a few millimeters long, occurring in salt and fresh water. Enclosed by a bivalve carapace, they include thousands of living as well as extinct species.

Oxbow lake
Crescent-shaped lake formed when a meander from a stream is cut off to form a lake.

Pinniped
A group of carnivorous, mostly marine mammals including seals, sea lions, and walruses, with fin-like limbs.

Plankton
Aquatic organisms, floating and suspended in open water, with little or no locomotion, that drift with the current.

Plantigrade
Referring to walking so that the flat sole of the foot comes in contact with the ground; for example, as in modern bears and humans

Plate tectonics
The theory that the Earth's crust is structured of large, rigid plates that move independently of one another, which can cause deformation at the plate margins.

Proboscidea
Member of a formerly very successful order of mammals comprising the living elephants and their extinct relatives.

Psilophyte
Any of an order of extinct, alternately branched plants from the Paleozoic Era. This order includes the earliest known terrestrial plants with a vascular structure.

Pterosaur
Extinct bird-like, flying reptiles with hollow bones and long beaks that had a flight membrane stretched between the body and an elongated 4th finger.

Radiometric dating
A method of dating that uses the measurement of decay in naturally occurring isotopes that decay at a constant rate.

Relict species
The remnants of a once widespread species, which typically are now found in very restricted or isolated areas.

Rostrum
The beak, projection, or extension of the snout of an animal.

Saurischian
Meaning lizard-hipped, it is one of two main groups of Dinosauria and refers to the structure of the pelvis or hip-bone. Saurischian dinosaurs had pelvises with the pubic bone pointing forward and down from the hip sockets.
See also Ornithischian.

Scutes
Bony plates under the skin

Sexual dimorphism
The existence of two visibly different forms for the male and female of the same species.

Siltstone
A rock composed of hardened silt, a fine sedimentary material.

Sirenian
Marine, herbivorous mammals that forage near the surface, such as manatees.

Stegosaur
Large dinosaur with a small skull that walked on all fours displaying a double row of alternating upright bony plates and spines down the center of the back.

Therapsid
Any member of a major order, Therapsida. Therapsids were four-legged terrestrial reptiles of the Permian and Triassic Periods. Some were vegetarian; others, carnivorous. They ranged in size from that of a small rodent to a large modern hippopotamus. Most therapsids had died out by the end of the Triassic Period.

Theropod
Carnivorous dinosaurs that had short fore-limbs and ran or walked on their back legs

Trace fossil
Any markings left in sediment by an organism, such as skin prints, foot tracks, borings, burrows, etc. Also called ichnite or ichnofossil.

Trackways
Fossil footprints that reveal a pattern of movement along a particular area.

Tyrannosaurids
Large-headed carnivorous dinosaurs with short, two-fingered hands, that most likely functioned as top predators in the Late Cretaceous ecosystem.

Ungulates
Mammals having hoofs, such as pigs, horses, etc.

Vestigial
Describing an object or organ that has partially or totally lost its original function, such as the appendix in humans.

Vibrissae
Large sensitive hairs found on the upper lip of some mammals that aid in tactile sensing.

Text: Margaret Dykens and Lynett Gillette
Illustrations (ammonite, lambeosaurus and albertosaurus): Tim Gunther
Illustration (mosasaur): William Stout