Miocene Development of Life

Transcription

1 Miocene Development of Life Jarðsaga 2 - Saga Lífs og Lands - Ólafur Ingólfsson

2 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

3 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.

4 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.

5 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.

6 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...

7 The Kelp Forest Ecosystem The Kelp Forest Ecosystem 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.

8 The giant kelp is not a plant, it is a brown algae

9 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.

10 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.

11 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.

12 A landmark study on land bridges Mammals and Land Bridges by George Gaylord Simpson (1940). Journal of the Washington Academy of Sciences 30 (1940): ( P940B.htm)

13 Some aspects of land bridges

14 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...

15 Low Miocene global sea levels helped bridging continents...

16 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.

17 Mammals and the Miocene World North America South America ADAPTIVE RADIATIONS OF MORE EVOLVED PLACENTAL MAMMALS Africa Eurasia Continued isolation of early monotremes and marsupials Extinctions of mammals Antarctica About 20 million years ago, during the Miocene

18 Mammals in the Miocene Maps showing distribution of important fossil sites for Miocene mammals 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. The new grassy plains had a dramatic effect on mammals. Those that adapted to eating grass did well. Many spread across the continents when Africa, Eurasia and North America joined. Only Australia and South America were isolated continents and unique grazers evolved there.

19 Hypothetical cladogram for mammals

20 North American mammals 1 North America was a centre of diversity for hoofed mammals. They were followed by carnivorous cats and dogs, hunting on the open plains. 1. Moropus (a relative of horses and camels); 2. Promerycochoerus ( dogpig ) 3. Menoceras (pig-sized rhino) 4. Oxydactylus (early camel) 5. Daphaenodon ( beardog ) 6. Stenomylus (early camel) 7. Dinohyus ( terrible pig, an omnivore) 8. Merychyus (early ungulate, herbivore) 9. Palaeocastor ( ancient beaver ) 10. Parahippus (early horse) 11. Syndyoceras (ungulate)

21 North American mammals 2 20 MY 10 MY Merychippus represents a milestone in the evolution of horses. It hada longface, andits long legs allowed it to escape from predators 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 million years ago. Frábær heimasíða um Miocen fánu N Ameríku=

22 North American mammals 3 Beavers do more to shape their landscape 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.

23 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 Afrotherian sea cows and almost all the modern groups of whales were present, as well as the early seals and walruses.

24 North American mammals 5 The skeleton is from a fossil sea cow (Dusisiren jordani) that lived in the Pacific Ocean 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.

25 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 1936 Giraffe-like camel Deer, antelope, camel (even toed), and horses (odd toed) covered the continent in huge numbers and specialised in grazing.

26 North American mammals 7 Pseudaelurus is a prehistoric cat that lived in Europe and North America approximately 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.

27 North American mammals 8 By Miocene times, about 20 MY ago, the two superfamilies of carnivores (canines and felines) were distinct. Tomarctus was an early-mid Miocene relative of the dogs (Canis) and foxes (Vulpes) Tomarctus (lower) and Pseudocynodictis (upper). P wasanancestorof T and an early member of the Canidae family, 25 MY ago.

28 Dog evolution in North America The Dog linage began in late Eocene, 37 MY ago in North America in predators that had distinctive 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. It began in the southwest United States, the birthplace of modern dogs.

29 More about N American dogs 8 MY ago a powerful canid called Epicyon attacks a horned herbivore. Epicyon were the size of large wolves The Eucyon, a fox-size canid, developed about 9 MY ago. It spread to Eurasia 7-6 MY ago and gave rise to most modern canids, including wolves, coyotes, and jackals.

30 From wolf to woof All family dogs are senso strictu domesticated wolfs

31 Seals first occurred during the Miocene Kingdom (ríki): Animalia - dýraríki Phylum (fylking): Chordata - seildýr Class (flokkur): Mammalia - spendýr Order (ættbálkur): Carnivora - rándýr Family (ætt): Pinnipedia - seldýr Most scientists believe seals and sea lions may have evolved from the same ancestor because their genes are fairly similar. Using fossils and comparative morphology, scientists believe that both seals and sea lions, under the family name Pinnipeds, originated from an otterlike carnivore found in the North Atlantic during the Miocene.

32 ...and bears first appeared in Miocene time Theoriginsof thebearscanbetracedbacktotheraccoonsized, dog-like Cephalogale from the middle Oligocene and early Miocene (20-30 MY ago) of Europe. Cephalogale gave rise to a lineage of early bears, the genus Ursavus. This genus radiated in Asia and ultimately gave rise to the first true bears (genus Ursus) in Europe, 5 MY ago. Extinct bear genera includes Arctodus, Agriarctos, Agriotherium, Plionarctos and Indarctos.

33 Bears and seals share an ancestor Bears are members of the Order Carnivora, Sub-Order Caniformia, and Family Ursidae. Other members of the Caniformia include wolves and other dog-like mammals (Family Canidae), weasels, skunks, and badgers (Family Mustelidae), raccoons (Family Procyonidae), and walruses (Family Odobenidae), seals (Family Phocidae), and sea lions (Family Otariidae). Although bears are often described as having evolved from a dog-like ancestor, their closest living relatives are the pinnipeds (walruses, seals, and sea lions).

34 South American Miocene mammal development Adrift on its own, South America s strange mixture of marsupials, hoofed animals and native xenarthra (armadillos, sloths and anteaters) were adapting in their own way to the spreading grasslands. South America was the only continent on the planet with representatives from all major mammalian groups.

35 Marsupial carnivores decline killer birds hold their position Thylacinus sp. This group of marsupial carnivores was represented in the Miocene South American fauna Giant carnivorous ground bird (Phorusrhacus), 1.5 m tall. These creatures were wholly indigenous to South America The marsupial carnivores began to decline and only the smaller animals remained by the end of the Miocene.

36 Rodents and primates were both successful Cow-sized guinea pigs ( marsvín ), weighing up to 700 kg, grazed the riverbanks of South America about five million years ago, confirms a newly found skeleton. This biggest-ever rodent, Phoberomys patersoni, shared its home with two-metre turtles, tenmetre crocodiles (sebecosuchids) and three-metre carnivorous birds. Charles Darwin wrote extensively on South American mammals in his book The Voyage of the Beagle. The book is available on the net:

37 The isolated hoofed animals (litopterns and notoungulates) formed herds living on the plains Archaeohyrax Left: Reconstruction of the head of Mesotherium. Right: lateral view of the skull of Eutypotherium superans. Toxodon sp

38 Native xenarthrans adapted The two-tonne, South American glyptodont relative of armadillos became extinct 10,000 years ago. About the size of a Volkswagen beetle, glyptodonts had protective armour that weighed up to 400 kg. The native xenarthrans adapted to the plains and huge grazing glyptodonts roamed alongside giant ground sloths and smaller armadillos. Anteaters lived in the trees.

39 Miocene Australia Big flightless birds develop in the absence of numerous mammalian carnivores. Dromornis stirtoni was one of the biggest bird that ever lived. It weighed over 500 kilos, and stood nearly 3 metres tall. It had a huge beak and jaw capable of great force. Although they looked like giant emus, the Dromornis stirtoni are more closely related to geese. They are part of a family of giant birds called Dromornithidae that lived from 15 million years ago until less than 30,000 years ago. Isolated from other continents, Australia developed its own unique marsupial fauna during the Tertiary. The drying out of Australia in Miocene sped the evolution of animals that live in open and dry habitats...

40 Huge marsupial herbivores Alkwertatherium webbi was a large marsupial almost the size of a rhinoceros. It weighed about 400 kg and was about 1 m tall and 2.5 m long. The Alkwertatherium webbi had a long snout with a mouth like a scoop. This was probably used for finding food under the ground such as tubers, or semi aquatic plants along a river's edge. Alkwertatherium survived through almost all the Miocene period, or from 24-5 million years ago.

41 Kolopsis a large Miocene herbivore Kolopsis torus was a bull-like marsupial that stood nearly 1 m high and was about 2 m long. It is related to our modern day koalas. Kolopsis was a herbivore and ate leaves, stems and small plants. Kolopsis probably lived in large herds. Kolopsis lived during the Miocene period, in a habitat of forests and grasslands and a small permanent water supply.

42 Another large herbivore The Plaisiodon centralis was a very big marsupial with a long narrow head. Its closest living relatives are wombats and koalas. Plaisodons weighed between kg and were about 1.5 m tall and 3 m long. The Plaisiodon was very similar to the Kolopsis torus. Both of these animals ate leaves and coarse foliage and probably lived in herds. The female Plaisiodons were much smaller than the males.

43 Enter the kangaroos... Hadronomas puckridgei was a big marsupial that looked like a kangaroo. It is probably an ancestor of the short-faced kangaroo, and stood about 2 m tall. Hadronomas weighed about 60 kg and had very big feet. It also had small eyes facing outward that gave it a wide field of vision. Hadronomas was a browser and ate leaves and grasses that it chewed with its little nibbling teeth. Hadronomas lived together with herds of large marsupials and large birds but with very few predators.

44 And there were predators... Baru darrowi was a large crocodile. It reached 4-5 m in length and had powerful jaws andlongcurvedteeththatit used to catch marsupials and other mammals or birds. Baru was the largest crocodile to live during late Miocene times around 8 MY ago Thesecrocodileswereamong the few Australian predators. It was adapted to periodic draughts, and spent a lot of time out of the water. Web page on Miocene Australia:

45 Other predators included... Powerful Thylacine (Thylacinus potens) lived 8 MY ago (late Miocene). It was 1.5 m long. Several kinds of thylacine have lived in Australia during the past 25 million years; the Powerful Thylacine was the largest of them all. It was also the largest meateating marsupial of its time. The death of the last known Thylacine in Hobart Zoo, in 1936, marked the end of thylacines for all time. Huge Pythons (>8 m long) and giant lizzards also prayed on animals at waterholes. Both evolved to become top predators in Pliocene and Pleistocene times.

46 Brief summary of Miocene 24 MY ago: Short-term warming and drying. 20 MY ago: Great mountain building. TheCascades, theandesand the Himalayas. These massive Mts disrupt weather patterns and alter rainfall distribution. 20 MY ago: Kelp forests. Support evolving marine life, such as sea otters, as well as established groups of fishes and invertebrates. 20 MY ago: Inland seas dry out. The shifting continents, changing climate patterns, and formation of a polar ice cap cause sea levels to drop and inland seas to shrink. Land routes open between continents. 18 MY ago: Grazing horses. Grazing horses quickly spread from North America to Europe and Asia, and from there to Africa, where some species become today's zebras. 16 MY ago: Orangutan line separates from African ape/hominid line Antarctica's deep freeze, the spread of grasslands, and perhaps even the effects of mountain building probably contribute to the extinction of several browsing mammal species. Animals adapted for cooler conditions and coarse, grassy vegetation fare well.

47 References used when preparing this lecture Stanley: Earth System History. Arnold, London Fortey: Life. A Natural History of the First Four Billion Years on Earth. Vintage, New York. Sánchez-Villagra, M. R., Aguilera, O. & Horovitz, I. The anatomy of the world's largest extinct rodent. Science, 301, , (2003)