Paleogene Period 66 to 23.03 million years ago This period consists of the Paleocene, Eocene, and Oligocene Epochs. The Paleogene is most notable as being the time in which mammals evolved from relatively small, simple forms into a large group of diverse animals. The global climate during the Paleogene began a cooling and drying trend which, although having been periodically disrupted by warm periods such as the Paleocene–Eocene Thermal Maximum, persists today. The trend was partly caused by the formation of the Antarctic Circumpolar Current, which significantly cooled oceanic water temperatures. The beginning of the Paleogene Period was very warm and moist compared to today’s climate. Much of the earth was tropical or sub-tropical. Palm trees grew as far north as Greenland The continents during the Paleogene continued to drift closer to their current positions. India was in the process of colliding with Asia, subsequently forming the Himalayas. The Atlantic Ocean continued to widen by a few centimeters each year. Africa was moving north to meet with Europe and form the Mediterranean, while South America was moving closer to North America. Australia had also separated from Antarctica and was drifting towards Southeast Asia. The plants of the Paleogene Period are very similar to the plants that we have on earth today. The warm climate at the beginning of the period was perfect for the dense forest plants. Mammals became the dominant animals. They filled ecological niches in the sea, on land and in the air. Even the first primates appeared. The Paleogene Period favored the birds. New species evolved. There were many large flightless birds that are now extinct. Fossil remains indicate that whales and other cetaceans (the whales, dolphins, and porpoises) evolved from hoofed land mammals related to sheep, pigs, deer, camels, and cows. These animals returned to the sea about 50 million years ago, during the Eocene Epoch. Going back to the oceans required many adaptations for living in the water, including a backwards and upwards shift of the nostrils, coverings for the nostrils, a streamlined shape, loss of the rear limbs, change of the forelimbs into flippers, addition of flukes for swimming, modification of senses for use in the water, loss of most hair, and addition of a layer of insulating blubber. The Archaeoceti were the first primitive whales to appear. They had tiny heads and pointed snouts with teeth. Penguins, dolphins and dugongs also evolved. In the oceans, fish species branched out. Sharks became more plentiful. The end of the Paleocene (55.5/54.8 Mya) was marked by one of the most significant periods of global change, the Paleocene–Eocene Thermal Maximum (PETM), which upset oceanic and atmospheric circulation and led to the extinction of numerous species. At the PETM CO2 levels were five times today’s concentrations and it was very wet at the tropics. 8 Basking Sharks These fish are second-largest fish in the sea after whale shark. This shark is a filter-feeder and cruises at the surface feeding on zooplankton. To do this it has specialisations, reduced teeth, enlarged gill slits, and bristle-like gill rakers. The Basking Shark (Cetorhinus maximus) is otherwise closely related to the large-toothed mackerel sharks of the family Lamnidae – which includes the Great White. However, these sharks are very gentle and social animals, even with humans and their boats. The average basking shark will reach 6-8 meters long and weigh 7 tons. Basking sharks are slow swimmers and inhabit waters of the Atlantic, Pacific oceans, the southern tips of South America and Africa, Japan, Australia, and the west coast of the U.S. Basking sharks often travel in pairs and can congregate in large schools of 100 individuals. The fossil record of Basking Sharks can be traced back only about 35 to 29 million years (compared with 65 to 60 million years for the earliest lamnid shark, Isurolamna inflata), It has been suggested that there may be as many as four species of Basking Shark with the one from southern Australia (C. maccoyi), but the differences may only be due to different growth rates in each part of the world. There is insufficient evidence at present to separate these species. Plankton is often thinly distributed over large expanses of ocean, varying in abundance both seasonally and regionally. So they travel long distances, but otherwise we know nothing about them. “Perhaps one or more geneticists will eventually obtain tissue samples from each of these purported Cetorhinus species and secure adequate funding to properly investigate the matter”. They are popular with divers and kayakers and there is quite a basking shark watching industry in the UK. It may even have sparked an ancient sea monster story or two.