Era
Cretaceous
31
Pliocene
20
Eocene
13
Tertiary
13
Paleozoic
12
Mesozoic
11
Ordovician
9
Cenozoic
8
Miocene
8
Pleistocene
5
Devonian
4
Holocene
4
Jurassic
4
Paleocene
4
Pennsylvanian
4
Permian
4
Quaternary
4
Silurian
4
Carboniferous
3
Mississippian
3
Paleogene
3
Neogene
2
Cambrian
1
Oligocene
1
Precambrian
1
Triassic
1