| Abstract from DBPedia | The Paleocene, ( /ˈpæli.əsiːn, -i.oʊ-, ˈpeɪli-/ PAL-ee-ə-seen, -ee-oh-, PAY-lee-) or Palaeocene, is a geological epoch that lasted from about 66 to 56 million years ago (mya). It is the first epoch of the Paleogene Period in the modern Cenozoic Era. The name is a combination of the Ancient Greek παλαιός palaiós meaning "old" and the Eocene Epoch (which succeeds the Paleocene), translating to "the old part of the Eocene". The epoch is bracketed by two major events in Earth's history. The K–Pg extinction event, brought on by an asteroid impact and possibly volcanism, marked the beginning of the Paleocene and killed off 75% of living species, most famously the non-avian dinosaurs. The end of the epoch was marked by the Paleocene–Eocene Thermal Maximum (PETM), which was a major climatic event wherein about 2,500–4,500 gigatons of carbon were released into the atmosphere and ocean systems, causing a spike in global temperatures and ocean acidification. In the Paleocene, the continents of the Northern Hemisphere were still connected via some land bridges; and South America, Antarctica, and Australia had not completely separated yet. The Rocky Mountains were being uplifted, the Americas had not yet joined, the Indian Plate had begun its collision with Asia, and the North Atlantic Igneous Province was forming in the third-largest magmatic event of the last 150 million years. In the oceans, the thermohaline circulation probably was much different from what it is today, with downwellings occurring in the North Pacific rather than the North Atlantic, and water density mainly being controlled by salinity rather than temperature. The K–Pg extinction event caused a floral and faunal turnover of species, with previously abundant species being replaced by previously uncommon ones. In the Paleocene, with a global average temperature of about 24–25 °C (75–77 °F), compared to 14 °C (57 °F) in more recent times, the Earth had a greenhouse climate without permanent ice sheets at the poles, like the preceding Mesozoic. As such, there were forests worldwide—including at the poles—but they had low species richness in regards to plant life, and were populated by mainly small creatures that were rapidly evolving to take advantage of the recently emptied Earth. Though some animals attained great size, most remained rather small. The forests grew quite dense in the general absence of large herbivores. Mammals proliferated in the Paleocene, and the earliest placental and marsupial mammals are recorded from this time, but most Paleocene taxa have ambiguous affinities. In the seas, ray-finned fish rose to dominate open ocean and reef ecosystems.暁新世（ぎょうしんせい、Paleocene）は地質時代の時代区分の一つで、約6,600万年前から約5,600万年前までの期間を指す。新生代最古の世。古第三紀の第一の世。 前時代である中生代白亜紀には主役であった恐竜のグループは、鳥類を唯一の例外として、そのほかはK-Pg境界においてことごとく絶滅している。（ただし、アラモサウルスなどのごく一部の属は境界における絶滅を免れ、この時代のダニアン期まで生き延びていた可能性が化石から示唆されている）。海中におけるアンモナイトや首長竜類、モササウルス類も全て滅びた。 (Source: http://dbpedia.org/resource/Paleocene) |
