Miocene Development of Life

Miocene Development of Life Jarðsaga 2 - Saga Lífs og Lands - Ólafur Ingólfsson Thehigh-pointof theage of mammals The Miocene or "less recent" is so called because it contains fewer modern animals than the following Pliocene. The Miocene lasted for 18 MY, ~23-5 MY ago. This was a huge time of transition, the end of the old prehistoric world and the birth of the more recent sort of world. It was also the high point of the age of mammals Open vegetation systems expand • The overall pattern of biological change for the Miocene is one of expanding open vegetation systems (such as deserts, tundra, and grasslands) at the expense of diminishing closed vegetation (such as forests). • This led to a rediversification of temperate ecosystems and many morphological changes in animals. Mammals and birds in particular developed new forms, whether as fast-running herbivores, large predatory mammals and birds, or small quick birds and rodents. Two major ecosystems evolve Two major ecosystems first appeared during the Miocene: kelp forests and grasslands. The expansion of grasslands is correlated to a drying of continental interiors and a global cooling. Later in the Miocene a distinct cooling of the climate resulted in the further reduction of both tropical and conifer forests, and the flourishing of grasslands and savanna in their stead. Modern Grasslands Over one quarter of the Earth's surface is covered by grasslands. Grasslands are found on every continent except Antarctica, and they make up most of Africa and Asia. There are several types of grassland and each one has its own name. Prairies, plains and savannas are all grasslands. Where do grasslands form? Grasslands develop where there isn't enough rain for forests but too much rain for deserts. Grasslands are filled with - you guessed it - grass. There are many types of grass, though. Fields of wheat are considered grasslands, even though they are often cultivated by people. Grass is special because it grows underneath the ground. During cold/dry periods the grass can stay dormant until it warms up. Consequently, the development of grasslands also signifies increased seasonality... TheTheKelpKelpForestForest EEcosystem The Kelp Forests are very different from other habitats. It is made of seaweed called giant kelp (Macrocystis pyrifera). Giant kelp grows in cool coastal waters where sunlight can go down to a rocky sea floor. Kelp needs sunlight and a hard surface to grow on. Kelp consists of at least three parts: the holdfast, stipe, and blade. Giant kelp is one of the world's fastest growing organisms. It can grow as much as 100 m in a single year. When the tops reach the surface, they keep on growing to form a floating mat. The kelp forest provides shelter and protection for many animals. The giant kelp is not a plant, it is a brown algae Present distribution In North America, kelp forests range from Alaska to California, where they are confined to cool, upwelling water areas. Macrocystis pyrifera is also found on the west coast of South America, south Africa, and southern Australia. They prefer water temperatures between 5-20°C. Mammals and Land Bridges • The great diversification of land mammals during the Miocene is due in large part to the formation of land bridges. These routes, which emerge as sea levels drop and inland seas dry out, connect continents previously separated by water. They provide access to new habitats and enable migrating animals to greatly extend their geographic ranges. Mammals and Land Bridges • Routes between Africa, Eurasia, and North America are the primary migratory paths. • The once-great Tethys Ocean no longer divides Africa and Eurasia. Elephants and apes are among the mammals that venture out of Africa and settle in parts of Eurasia, while rabbits, pigs, saber-toothed cats, and modern rhinos move in the opposite direction. • To the north, a dry corridor, the Bering land bridge, connects what are now Siberia and Alaska. Eventually, both elephants and rhinos make their way to North America, perhaps crossing paths with horses on their way to Eurasia. A landmark study on land bridges Mammals and Land Bridges by George Gaylord Simpson (1940). Journal of the Washington Academy of Sciences 30 (1940): 137-163. (http://clk.about.com/?zi=1/XJ&sdn=geology&zu=http%3A%2F%2Fwww.wku.edu%2F%7Esmithch%2Fbiogeog%2FSIM P940B.htm) Some aspects of land bridges Beringia Land Bridge – bridging two worlds During Miocene and Pliocene the Beringia Land Bridge was available for mainly tectonic reasons. During Pleistocene the growth of ice sheets periodically opened the route... Low Miocene global sea levels helped bridging continents... Land bridge over “Iceland”... The Tertiary biota of Iceland is closely related to the modern Eastern Deciduous Forests of N America. Flora and fauna used the dynamic land bridge between North America and Europe via Greenland-”Iceland” as a migration route during the Paleogene. This land bridge emerged due to hotspot activity on the Mid Atlantic ridge in connection with the opening of the N Atlantic. Mammals and the Miocene World North ADAPTIVE Eurasia America RADIATIONS OF MORE EVOLVED PLACENTAL MAMMALS South Continued isolation America of early monotremes and marsupials Africa Extinctions of mammals Antarctica About 20 million years ago, during the Miocene Mammals in the Miocene • Mammal forms were essentially modern; almost half of modern placental mammal families were present. • Higher primates, including monkeys and apes were present across southern Europe and Asia. Maps showing • The new grassy plains had a dramatic distribution of effect on mammals. Those that important fossil adapted to eating grass did well. sites for Miocene • Many spread across the continents mammals when Africa, Eurasia and North America joined. • Only Australia and South America were isolated continents and unique grazers evolved there. Hypothetical cladogram for mammals North American mammals 1 1. Moropus (a relative of horses and camels); 2. Promerycochoerus (“dog- pig”) 3. Menoceras (pig-sized rhino) 4. Oxydactylus (early camel) 5. Daphaenodon (“bear- dog”) 6. Stenomylus (early camel) 7. Dinohyus (“terrible pig”, an omnivore) • North America was a centre of 8. Merychyus (early ungulate, herbivore) diversity for hoofed mammals. They 9. Palaeocastor (“ancient were followed by carnivorous cats and beaver”) 10. Parahippus (early horse) dogs, hunting on the open plains. 11. Syndyoceras (ungulate) North American mammals 2 Merychippus represents a milestone in the evolution of horses. It hada longface, andits long legs allowed it to escape from predators 20 MY and migrate long distances to feed. It was the first known grazing horse and the ancestor of all later horse lineages. Lived in North America from 17 - 11 10 MY million years ago. Frábær heimasíða um Miocen fánu N Ameríku= http://www.npwrc.usgs.gov/resource/1998/agate/visit.htm North American mammals 3 Beavers do more to shape their land- scape than any other mammal except for human beings, and their ancestors were building dams 10 MY years ago. The Miocene beavers were >2m long. The beaver is a clever engineer, but its brain is embarrassingly small . and they don't see well. Nevertheless, there is abundant evidence that much of their building technique appears to be learned through their long childhood. • The primates suffered with the demise of the forests. The prosimians (lemur group) that had lived in North America disappeared. Rodents were the only survivors of the rodent and primate group. North American mammals 4 Gomphothers, Miocene (12-8 MY ago). They differ from elephants primarily in the form of the chewing surfaces of their molar teeth. Fossils show that there were many different types of gomphotheres. • The first afrotheres, the mastodons and the gomphotheres first appeared in North America. The Afrother- ian sea cows and almost all the modern groups of whales were present, as well as the early seals and walruses. North American mammals 5 The skeleton is from a fossil sea cow (Dusisiren jordani) that lived in the Pacific Ocean 10-12 MY ago. Sea cows are herbivorous aquatic mammals. Like cetaceans (whales, dolphins) sea cows lack hind limbs and are thus restricted to life in the water. Dusisiren was common in the shallow coastal waters of late Miocene California. The climate was slightly warmer than today, and there were many more bays and inland seas over California. The sea cow fed on algae and sea grasses, pulling up the vegetation with the horny pads in the front of its mouth. It did not have front teeth. North American mammals 6 A giant camel skeleton (Late Miocene in age). Gigantocamelus weighted over a ton, twice as much as today's camels. Skeleton discovered in Giraffe-like 1936 camel Deer, antelope, camel (even toed), and horses (odd toed) covered the continent in huge numbers and specialised in grazing. North American mammals 7 Pseudaelurus is a prehistoric cat that lived in Europe and North America approximately 20-10 million years ago. It is regarded to be an ancestor of today's domestic and big cats Cats from Eurasia joined the carnivorous running bears, bear dogs, dogs and mustelids hunting the herbivores on the plains. North American mammals 8 By Miocene times, about 20 MY ago, the two superfamilies of carnivores (canines and felines) Tomarctus (lower) and were distinct. Tomarctus was an Pseudocynodictis (upper). early-mid Miocene relative of the P wasanancestorof T and an early member of dogs (Canis) and foxes (Vulpes) the Canidae family, 25 MY ago. Dog evolution in North America The Dog linage began in late Eocene, 37 MY ago in North America in predators that had distin- ctive pairs of shearing teeth and ran down prey. The canid radiation begins in late Miocene, with the small fox Leptocyon, ancestor of the Canis and Vulpes.

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