Eocene (55-34 MY ago) “Dawn of Recent Life” Jarðsaga 2 - Saga Lífs og Jarðar - Ólafur Ingólfsson Eocene Continental configuration In Eocene, India is starting to collide with Asia forming the Tibetan plateau and Himalayas. Australia, which was attached to Antarctica, began to move rapidly northward. The North Atlantic is opening up. Eocene Warming During the Early Eocene alligators swam in swamps near the North Pole, and palm trees grew in southern Alaska. Much of central Eurasia was warm and humid. Early Eocene climate: Massive global warming! The Early Eocene is thought to have had the highest temperatures of the entire Cenozoic (up to 30° C) and high precipitation in a world that was essentially ice free. The Paleocene-Eocene Thermal Maximum, starting about 55 million years ago and lasting about 150,000 years, is marked by dramatic changes in the fossil record of life in the ocean and on land. Average global temperatures increased by about 5oC (was 14oC warmer than today). The increase in sea surface temperatures at high latitudes was 8-10oC and a 4-5oC increase in tropical sea surface temperatures. “Global Fever”, see: http://scicom.ucsc.edu/SciNotes/0301/warm/index.html N-Atlantic oxygen-isotope changes through the Cenozoic Variation in the oxygen isotope composition of benthic forams from the Atlantic Ocean. Eocene vegetation zones Decidueous forest Sub-tropical forest Tropical rainforest What caused the sudden warming? “The Methane hypothesis” Deep ocean sediments from around the world show that there was a sudden shift in the relative abundance of carbon-12 at this time. Scientists such as Jerry Dickens of James Cook University in Australia have suggested that the shift in carbon isotopes might be attributable to the sudden release of methane from the ocean floors, where massive quantities of the greenhouse gas are stored in the form of methane hydrate. “The India-Eurasia collision hypothesis” • In Early Tertiary, the Indian tectonic plate ran into Asia. In the crumpling and grinding and folding that followed, the Indian plate was subducted. Great quantities of its crust were wedged under the Asian plate, throwing up in turn a >2500 km long orogenic belt including two massive mountain ranges, the Karakoram and the Himalaya, and the immense Tibetan plateau. • Crustal rock driven to depths of 100 kilometers or more began to heat, and so to change. Limestones and dolomites, plentiful in the Himalayan region, would have released massive amounts of carbon dioxide. And where the gas could reach a fault or fissure to the surface, it would have escaped into the atmosphere. “The volcanic activity hypothesis” There was enormous volcanic activity in the Indian Deccan Traps area and the North Atlantic (Iceland) hotspot during early Tertiary (65-60 MY) The Deccan Traps are one of the largest volcanic provinces in the world. It consists of >2,000 m of flat-lying basalt lava flows and covers an area of nearly 500,000 km3 in west-central India. Estimates of the original area covered by the lava flows are as high as 1.5 million km2. The volume of basalt is estimated to be 512,000 km3 “The comet hypothesis” A comet collision with Earth around 55 million years ago may have kick-started a crucial early phase of mammal evolution. Did a comet strike deliver carbon to heat up the Earth? The impact could have triggered the greenhouse warming thought to have encouraged primitive mammals to disperse across the world and diversify into three important groups still with us today. These groups were the Artiodactyla, the Perissodactyla and the Primates - the mammalian order that includes humans. Modern Artiodactyls include sheep, pigs, camels and giraffes. Today's Perissodactyls include horses, tapirs, rhinos and zebras. This evolutionary branching event coincides with a clear boundary in the Earth's geological record dividing the Palaeocene and Eocene epochs. The warming caused/is linked to an explosion in life... ...First came animals such as uintatheres, giant horned bunnies the size of small elephants that eventually went extinct, but may be a close cousin of today's rabbits.... ...Then there was a very rapid diversification of mammals... The oldest known fossils of most of the modern orders (ættbálkur) of mammals appear in a brief period during the Early Eocene and all were small, under 10 kg. Both groups of modern ungulates (Artiodactyla (sheep, pigs, camels and Propalaeotherium, a horse- giraffes) and Perissodactyla (horses, like early perissodactyl. It tapirs, rhinos and zebras)) became was the size of a siamese cat! prevalent mammals at this time, due to a major radiation between Europe and North America. The evolution of primates and rodents The prosimians are a diverse group of primates, today including the lemurs (“lemúrar”, hálfapar), bushbabies (“blökuapar”) and tarsiers (“vofuapar”). All the earliest primates were prosimians, with many of them resembling modern lemurs. Asia was the cradle of most mammals Because of the very warm Eocene, the mammals could spread from Asia to Europe and across the north pole areas to N America. “Global warming may be behind the most profound biotic re- Lower dentition of Chronolestes organization of the Age of simul, an early primate, from the Mammals,” says Chris Wutu Formation, Shandong Province, Beard, a researcher China. These animals dispersed across the Bering land bridge during specializing in early the early part of the Age of mammals at the Carnegie Mammals. Museum of Natural History. Evolution of the Laurasiatheres Artiodactyla (sheep, pigs, camels and giraffes);Perissodactyla (horses, tapirs, rhinos and zebras) Differences between Paleocene and Eocene mammals Mammals of the Paleocene were considerably more primitive than their modern relatives. Tended to have: - Smaller brains - Shorter, stumpier legs - “Flat-feet” (did not walk on toes) During Eocene and later, mammals tend to develop bigger brains, longer legs, and walk on toes. The Messel shales The Eocene (50 MY) oil shales of Messel near Frankfurt, Germany are known for the unusually complete and detailed picture they present of life of the past. The remains of both animals and plants represent a complete ecosystem in an exceptional state of preservation. Not only are the skeletons and other hard parts preserved, but often the soft tissues and even stomach contents. Messel food chain This simple foodchain has been infered from fish intestine contents, coprolites and comparisons with modern ecosystems. It is thought that, for long periods of time, the upper part of the water column was oxygenated and organisms were able to live and feed here. 5th Level Consumers: Crocodiles, Mammals 4th Level Consumers: Adult Fish 3rd Level Consumers: Small Fish 2nd Level Consumers: Insects eg. Hetroptera 1st Level Consumers: Grazing Insects eg. Trichoptera Primary Producers: Algae eg. Tetraedron Substrate: Messel 'Waterlilies' http://senckenberg.uni-frankfurt.de/sm/messel.htm#bild Site of the Messel shales Located 15km south of Darmstadt, near Frankfurt, Germany, the Messel pit is some 60m deep and measures 1km by 0.7km. The Messel lithology is a dark brown-olive green lacustrine (lake) claystone and contains 5-20% petroleum. Sedimentation rate was only 0.1mm per year and included steady smectite (clay) rich deposition and highly organic laminae from seasonal algal blooms. Thelakeformedinanareaof subsidence, duringa period of high local tectonic activity. The sediments accumulated, and intermitent earth movements released gases into the lake and into the surrounding atmosphere, killing any organisms in the area. The Messel site: A killing lake... Many of the Messel animals seem to have drowned - their bodies are in a relaxed state, but there were some strange features. One is the large number of bats - they seem to have just fallen out of the sky. On 26 August 1986, in the Central African Cameroon highlands, a volcanic lake called Nyos suddenly released a huge volume of CO2 gas from its deep waters. CO2 is heavier than air and a dense cloud of the gas rolled down the mountain onto several local villages, suffocating everything in its path, including over 1,700 people. A study of Lake Nyos showed that there was a layer of oxygen-poor water at the bottom of the lake that was so deep that it did not mix with the normal layers of water above it. Over the years large amounts of CO2 from a volcanic spring had built up in this bottom layer of water, the gas being trapped underneath the normal layer of water above. Something caused the two layers of water to mix and all the built up gas was suddenly released in one go killing everything for a distance of up to 20km away. Plant fossils sugges tropical environment Lake Messel was situated in a dense rainforest, shown by the presence of preserved plant material, including palm leaves, fruits, wood, pollen and some water plants. Which animals have been discovered at Messel? This is a python species descovered at Messel Reptiles and amphibians - Snakes, crocodiles, turtles, frogs, lizards and salamanders have been found. Specimens are often whole and very well preserved. Alligator, of course... Diplocynodon Fast-swimming turtles (caught at an unfortunate moment...) “Es wäre möglich, daß es sich um Tiere während der Paarung handelt...” More turtles... Allaeochelys Crassesculptata Eocene Messel, Germany Approximate size: 34cm x 30cm Messel: a key site for fossil fishes Dieses Prachtexemplar des Schlamm- fisches Cyclurus kehreri ist fast 60 cm lang. Fishes - There have been over 10,000 fossil fishes found at Messel. The specimens are mostly from high in the water column and this indicates that the water column was stratified. More Messel fishes Messel Mammals Messel is one of the finest Eocene fossil sites for mammals. Mammals make up only 2% of the fauna, the rest being mainly insects and fishes. Fossils include hoofed mammals, like the Messel horse, Propalaeotherium (of which over 70 have been found), and rodents and primates.