The Cretaceous is usually broken into Lower, Middle, and Upper subdivisions. The Faunal stages from youngest to oldest are: Maastrichtian/Navarro? (Senonian/Eagle? Ford/Austin?/Gulf?/Upper? Cretaceous) Campanian/Taylor? (Senonian/Eagle? Ford/Austin?/Gulf?/Upper? Cretaceous) Santonian (Senonian/Eagle? Ford/Austin?/Gulf?/Upper? Cretaceous) Coniacian (Senonian/Eagle? Ford/Austin?/Gulf?/Upper? Cretaceous) Turonian (Gallic/Nuevo? Leon/Trinity?/Lower? Cretaceous) Cenomanian/Woodbine? (Gallic/Nuevo? Leon/Trinity?/Lower? Cretaceous) Albian/Frederiksberg? (Gallic/Nuevo? Leon/Trinity?/Lower? Cretaceous) Aptian (Gallic/Nuevo? Leon/Trinity?/Lower? Cretaceous) Barremian (Gallic/Nuevo? Leon/Trinity?/Lower? Cretaceous) Hauterivian (Neocomian/Durango?/Lower? Cretaceous) Valanginian (Neocomian/Durango?/Lower? Cretaceous) Berriasian (Neocomian/Durango?/Lower? Cretaceous) |
The end of the Cretaceous is marked by a major, and extensively studied, Cretaceous-Tertiary extinction event.
The Cretaceous is usually broken into Lower, Middle, and Upper subdivisions. The Faunal stages from youngest to oldest are:
Maastrichtian/Navarro? (Senonian/Eagle? Ford/Austin?/Gulf?/Upper? Cretaceous) Campanian/Taylor? (Senonian/Eagle? Ford/Austin?/Gulf?/Upper? Cretaceous) Santonian (Senonian/Eagle? Ford/Austin?/Gulf?/Upper? Cretaceous) Coniacian (Senonian/Eagle? Ford/Austin?/Gulf?/Upper? Cretaceous) Turonian (Gallic/Nuevo? Leon/Trinity?/Lower? Cretaceous) Cenomanian/Woodbine? (Gallic/Nuevo? Leon/Trinity?/Lower? Cretaceous) Albian/Frederiksberg? (Gallic/Nuevo? Leon/Trinity?/Lower? Cretaceous) Aptian (Gallic/Nuevo? Leon/Trinity?/Lower? Cretaceous) Barremian (Gallic/Nuevo? Leon/Trinity?/Lower? Cretaceous) Hauterivian (Neocomian/Durango?/Lower? Cretaceous) Valanginian (Neocomian/Durango?/Lower? Cretaceous) Berriasian (Neocomian/Durango?/Lower? Cretaceous)
During the Cretaceous, the late Paleozoic-early Mesozoic supercontinent of Pangea? completed its breakup into modern continents although their positions were substantially different than the present. The Atlantic Ocean widened, Gondwana? broke up into Antarctica, Australia, Africa and South America. India and Madagascar remained attached to Africa. Within the continents, a broad shallow sea advanced across central North America and then started to recede leaving thick marine deposits sandwiched between economically important coal beds. Other important Cretaceous exposures occur in Europe and China.
On land, plants became quite modern although the now ubiquitous grasses did not evolve until the end of the period. Flowering plants were widespread. Conifers thrived, as they do today. The first representatives of many modern trees--fig?, sycamore?, magnolia? for example--appear in the Cretaceous. On land, mammals were small and a relatively minor component of the fauna. The fauna was dominated by reptile?s and especially by dinosaurs. In the seas, ray?s, modern shark?s and fish became common. Modern birds evolved. Marine reptiles thrived. Although many elements of the marine faunas looked more or less modern, a number of forms including most shelled cephalopod?s (all ammonite?s, most nautilid?s) as well as reef forming rudist clams disappeared at or near the end of the Cretaceous. Among the larger animals, the dinosaurs, and all marine reptiles except turtle?s and crocodile?s disappeared at the end of the Cretaceous.