A Cretaceous Time Scale

Copyright 2001-2009 by Mike Everhart

Last revised: 07/11/2009

The Cretaceous Period was the the last of three periods (Triassic, Jurassic and Cretaceous) that made up the Age of Dinosaurs.  It encompasses a segment of time from about 142 million years ago to about 65 million years ago and saw the evolution of most of the dinosaurs that we are familiar with today.   In addition, it includes the last 30 million years when mosasaurs evolved and came to dominate the Earth's oceans.

Table 1 gives the approximate duration of ages that comprise the Upper Cretaceous, with remarks regarding mosasaurs.

Maastrichtian 65.4 - 71.3 MYA (5.9 MY) Greatest diversity and distribution; invasion of freshwater habitats
Campanian 71.3 - 83.5 MYA (12.2 MY) "Second Wave" mosasaurs; Mosasaurus, Plioplatecarpus, Prognathodon, Globidens
Santonian 85.5 - 86.3 MYA (0.8 MY) Mosasaurs get much larger; world-wide distribution
Coniacian 86.3 - 88.7 MYA (2.4 MY) "First Wave" mosasaurs; Tylosaurus, Platecarpus and Clidastes
Turonian 88.7 - 93.3 MYA (4.6 MY) Early mosasaurs; Clidastes and Tylosaurus / Platecarpus precursors
Cenomanian 93.3   98.5 MYA (5.2 MY) Ancestral mosasaurs (Aigialosaurs) return to the ocean

Table 2 provides approximate dates for the beginning and end of the various ages that make up the Cretaceous Period.

Age Boundary Millions of Years Ago Remarks
Maastrichtian - Paleocene 65.4 +/- 0.1 MY End of the Cretaceous  - The "K/T Boundary" - Beginning of Tertiary
Campanian - Maastrichtian 71.3 +/- 0.5 MY Record in Kansas ends in the Campanian Pierre Shale
83 MYA Deposition of the Smoky Hill Chalk ends; Pierre Shale begins
Santonian - Campanian 83.5 +/- 0.5 MY
Coniacian - Santonian 86.3 +/- 0.5 MY
88 MYA Deposition of the Fort Hays Limestone ends; Smoky Hill Chalk begins
Turonian -Coniacian 88.7 +/- 0.5 MY Deposition of the Fort Hays Limestone begins
Cenomanian -Turonian 93.3 +/- 0.2 MY Dakota Sandstone / Carlile Shale / Graneros shale / Greenhorn Limestone (approx)
Upper Cretaceous above this line - Lower Cretaceous below
Albian - Cenomanian 98.5 +/- 0.5 MY Comanche Sandstone / Kiowa Shale
Aptian - Albian 112 +/- 1.0 MY No record in Kansas
Berremian -Aptian 121 MYA No record in Kansas
Hauterivian - Berremian 127 MYA No record in Kansas
Valanginian - Hauterivian 130 MYA No record in Kansas
Berriasian - Valanginian 135 MYA No record in Kansas
Tithonian - Berriasian 142 MYA Morrison Fm. / End of the Jurassic - Beginning of the Cretaceous

Adapted from:  Obradovich, J. D., 1993. A Cretaceous time scale. pp. 379-396 In Caldwell, W. G. E., and E. G. Kauffman, eds., Evolution of the Western Interior Basin, Geologic Association of Canada, Special Paper 39.