Paleogene (alternatively Palaeogene) period is a unit of geologic time that began 65 and ended 23 million years ago. Lasting 42 million years, this period is most notable as being the time in which mammals evolved from small, simple forms into diverse animals in the wake of the mass extinction that ended the preceding Cretaceous Period. Some of these mammals would evolve into large forms that would dominate the land, while others would become capable of living in marine, specialized terrestrial and even airborne environments. Birds also evolved considerably during this period changing into roughly-modern forms. Most other branches of life on earth remained relatively unchanged in comparison to birds and mammals during this time period. Some continental motion took place. Climates cooled somewhat over the duration of the Paleogene and inland seas retreated from North America early in the Period. In geology, a period or age is a time span of many millions of years that are assumed to have had similar characteristics. ... The table and timeline of geologic periods presented here is in accordance with the dates and nomenclature proposed by the International Commission on Stratigraphy. ... Orders Multituberculata (extinct) Palaeoryctoides (extinct) Triconodonta (extinct) Subclass Australosphenida Ausktribosphenida Monotremata Subclass Eutheria (excludes extinct ancestors) Afrosoricida Anagaloidea (extinct) Arctostylopida (extinct) Artiodactyla Carnivora Cetacea Chiroptera Cimolesta (extinct) Cingulata Creodonta (extinct) Condylarthra (extinct) Dermoptera Desmostylia (extinct) Dinocerata (extinct) Embrithopoda (extinct) Hyracoidea Insectivora Lagomorpha Leptictida (extinct) Litopterna (extinct) Macroscelidea Mesonychia (extinct) Notoungulata... A phylogenetic tree of all extant organisms, based on 16S rRNA gene sequence data, showing the evolutionary history of the three domains of life, bacteria, archaea and eukaryotes. ... Phyla Subregnum Parazoa Porifera (sponges) Subregnum Agnotozoa Placozoa (trichoplax) Orthonectida (orthonectids) Rhombozoa (dicyemids) Subregnum Eumetazoa Radiata (unranked) (radial symmetry) Ctenophora (comb jellies) Cnidaria (coral, jellyfish, anemones) Bilateria (unranked) (bilateral symmetry) Acoelomorpha (basal) Myxozoa (slime animals) Superphylum Deuterostomia (blastopore becomes anus) Chordata (vertebrates, etc. ... An extinction event (also extinction-level event, ELE) is a period in time when a large number of species die out. ... The Cretaceous Period is one of the major divisions of the geologic timescale, reaching from the end of the Jurassic Period (i. ... The worlds oceans as seen from the South Pacific Ocean Oceans (from Okeanos in Greek, the ancient Greeks noticing the strong current that flowed off Gibraltar and assuming it was a great river) cover almost three quarters (71%) of the surface of the Earth, and nearly half of the... Orders Many - see section below. ... For other uses, see Life (disambiguation), Lives (disambiguation) or Living (disambiguation), Living Things (disambiguation) Look up life, living in Wiktionary, the free dictionary. ... Earth (IPA: , often referred to as the Earth, Terra, or Planet Earth) is the third planet in the solar system in terms of distance from the Sun, and the fifth largest. ... This article or section does not cite its references or sources. ...

This period consists of the Paleocene, Eocene, and Oligocene Epochs. The Paleogene follows the Cretaceous Period and is followed by the Miocene Epoch of the Neogene Period. The terms 'Paleogene System' (formal) and 'lower Tertiary System' (informal) are applied to the rocks deposited during the 'Paleogene Period'. The somewhat confusing terminology seems to be due to attempts to deal with the comparatively fine subdivisions of time possible in the relatively recent geologic past, when more information is preserved. By dividing the Tertiary Era into two 'Periods' instead of 7 'epochs', the periods are more closely comparable to the duration of 'periods' in the Mesozoic and Paleozoic Eras. The Paleocene, early dawn of the recent, is a geologic epoch that lasted from 65 Ma to 56 Ma (million years ago). ... The Eocene epoch (56-34 Ma) is a major division of the geologic timescale and the second epoch of the Palaeogene period in the Cenozoic era. ... The Oligocene epoch is a geologic period of time that extends from about 34 million to 23 million years before the present. ... The Miocene epoch is a period of time that extends from about 23 to 5. ... Neogene Period is a unit of geologic time consisting of the Miocene, Pliocene, Pleistocene, and Holocene epochs. ... Tertiary period was previously one of the major divisions of the geologic timescale, from the end of the Cretaceous period about 65 million years ago to the start of the Quaternary period about 1. ...