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Paleocene epoch(pā`lēəsēn'), first epoch of the Tertiary periodTertiary period
, name for the major portion of the Cenozoic era, the most recent of the geologic eras (see Geologic Timescale, table) from around 26 to 66 million years ago. The name Tertiary was first applied about the middle of the 18th cent.
..... Click the link for more information. in the Cenozoic eraCenozoic era
, last major division of geologic time (see Geologic Timescale, table) lasting from 65 million years ago to the present. The Cenozoic is divided into the Tertiary (from 65 million years ago until 2 million years ago) and Quaternary (2 million years ago to the
..... Click the link for more information. of geologic time (see geologic timescalegeologic timescale,
a chronological scale of earth's history used to measure the relative or absolute age of any part of geologic time. Of the numerous timescales, the most common is based on geologic time units, which divide time into eras, periods, and epochs.
..... Click the link for more information. ) between 60 to 66 million years ago. In W North America, the uplift of the Rocky Mts. that marked the end of the Mesozoic eraMesozoic era
[Gr.,=middle life], major division of geologic time (see Geologic Timescale, table) from 65 to 225 million years ago. Great crustal disturbances that marked the close of the Paleozoic and the beginning of the Mesozoic eras brought about drastic changes in the
..... Click the link for more information. continued throughout the Paleocene, and the Cretaceous inland seas gradually withdrew from the Great Plains area and central and SW California. In Montana and Wyoming the Fort Union shales and sandstones, laid down during this epoch, are noteworthy because they overlie undeformed upper Cretaceous sediments, thus recording the demise of the dinosaurs and the rise of mammals. The Paleocene mammals were mostly small herbivores similar to their Mesozoic ancestors. By mid-Paleocene, the ungulates, or hoofed mammals of mostly five-toed forms, became abundant. Prosimian primates (tree shrews and tarsiers) also increased in number. Except for part of N France, Europe was largely emergent (i.e., above water). During this epoch, the opening of the Norwegian Greenland Sea eventually resulted in a much more significant mixing of waters, creating the cold North Atlantic Deep waters. Greenland began separating from Europe as the northern mid-Atlantic Ridge formed. On the other side of the world, Antarctica and Australia had separated; India had completed its separation with Africa, resulting in an outpouring of basalts; and India, Africa, and Australia were about to collide with Eurasia. By the end of Paleocene time, N America's last large sea retreated to the Gulf of Mexico. Some of the fossil evidence from Paleocene sediments is difficult to explain; Alaska, for example, clearly had broad-leafed evergreen floras that typically grow in tropical forests. As the land has not changed significantly in latitude since the Paleocene, the evidence of these floras is a puzzle.