Dentition—the [system] or arrangement of teeth peculiar to any given animal.
Devonian—the fourth oldest [period] of the [Paleozoic] era, follows the [Silurian], precedes the [Mississippian].
Dip—the angle of inclination which the bedding plane of rocks makes with a real or imaginary horizontal line.
Distillation—in fossils that process by which volatile organic matter is removed, leaving a carbon residue.
Dolomite—a mineral composed of calcium magnesium carbonate (CaMg(CO₃)₂).
Dorsal—pertaining to the back.
Echinoderm—a marine invertebrate with [calcareous] [exoskeleton] and usually exhibiting a five-fold [radial symmetry]; member of [phylum] Echinodermata; includes cystoids, blastoids, crinoids, starfishes, and sea urchins.
Echinoid—bottom-dwelling, unattached marine invertebrate with [exoskeleton] of [calcareous] plates covered by movable spines; member of class Echinoidea; sea urchins, heart urchins, biscuit urchins.
Endoskeleton—the internal supporting structure of an animal.
Eocene—the next to earliest of the [Tertiary] epochs, follows the [Paleocene] and precedes the [Oligocene].