Era
Cretaceous
29
Eocene
19
Tertiary
12
Carboniferous
9
Permian
7
Precambrian
7
Paleozoic
6
Paleocene
4
Pleistocene
3
Pliocene
3
Proterozoic
3
Triassic
3
Archaean
2
Cenozoic
2
Devonian
2
Mississippian
2
Quaternary
2
19th century
1
Cambrian
1
Dovanian
1
Jurassic
1
Mesozoic
1
Miocene
1
Paleogene
1
Pennsylvanian
1