List of index fossils

Index fossils (also known as guide fossils or indicator fossils) are fossils used to define and identify geologic periods (or faunal stages). Index fossils must have a short vertical range, wide geographic distribution and rapid evolutionary trends. Another term, "zone fossil", is used when the fossil has all the characters stated above except wide geographical distribution; thus, they correlate the surrounding rock to a biozone rather than a specific time period.

Fossil	Scientific Name	Geological time interval	Million Years Ago
Calico scallop	Argopecten gibbus	Quaternary	1.8 million years ago
	Neptunea tabulata	Quaternary	1.8 million years ago
	Viviparus glacialis	Tiglian (Early Pleistocene)	0.5 million years ago
	Calyptraphorus velatus	Tertiary
	Venericardia planicosta	Eocene
Scaphites	Scaphites hippocrepis	Cretaceous	145 to 66 million years ago
Inoceramus	Inoceramus labiatus	Cretaceous
Perisphinctes	Perisphinctes tiziani	Jurassic	201.3 to 145 million years ago
	Nerinea trinodosa	Jurassic
	Tropites subbullatus	Triassic
	Monotis subcircularis	Triassic
Leptodus	Leptodus americanus	Permian
Parafusulina	Parafusulina bosei	Permian
	Dictyoclostus americanus	Pennsylvanian
	Lophophyllidium proliferum	Pennsylvanian
	Cactocrinus multibrachiatus	Mississippian
	Prolecanites gurleyi	Mississippian
Mucrospirifer	Mucrospirifer mucronatus	Devonian	416 to 359 million years ago
	Palmatolepis unicornis	Devonian
	Tetragraptus fructicosus	Ordovician
	Paradoxides	Cambrian	509 to 500 million years ago
	Billingsella corrugata	Cambrian
	Archaocyathids	Cambrian	529 to 509 million years ago