Miocene Developmentof Life

Jarðsaga 2- Saga Lífs og Lands -

Ólafur Ingólfsson

The high-point of the age of mammals

The Miocene or "less recent" is so called because itcontains fewer modern animals than the followingPliocene. 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 theMiocene is one of expanding open vegetationsystems (such as deserts, tundra, and grasslands) at the expense of diminishing closed vegetation (such as forests).

• This led to a rediversification of temperateecosystems and many morphological changes inanimals. Mammals and birds in particulardeveloped 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 theMiocene: kelp forests and grasslands. The expansion of grasslands is correlated to a drying of continentalinteriors 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 bygrasslands. Grasslands are found on every continentexcept 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 arefilled with - you guessed it - grass. There are many typesof grass, though. Fields of wheat are consideredgrasslands, 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...

The Kelp Forest EcosystemThe Kelp Forests are very different from otherhabitats. It is made of seaweed called giant kelp(Macrocystis pyrifera). Giant kelp grows in cool coastalwaters where sunlight can go down to a rocky sea floor. Kelp needs sunlight and a hard surface to grow on. Kelpconsists 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 Kelp Forest Ecosystem

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

Present distributionIn North America, kelp forestsrange from Alaska to California, where they are confined to cool, upwelling water areas. Macrocystispyrifera 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 inlarge part to the formation of land bridges. These routes, which emerge assea 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 apesare 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 Sciences30 (1940): 137-163. (http://clk.about.com/?zi=1/XJ&sdn=geology&zu=http%3A%2F%2Fwww.wku.edu%2F%7Esmithch%2Fbiogeog%2FSIMP940B.htm)

Some aspects of land bridges

Beringia Land Bridge – bridging two worlds

During Miocene andPliocene the BeringiaLand Bridge wasavailable for mainlytectonic 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 themodern Eastern DeciduousForests 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 America

ADAPTIVE RADIATIONS

OF MORE EVOLVED

PLACENTAL MAMMALS

South America

Antarctica

Africa

Eurasia

Continued isolation of early monotremes

and marsupials

Extinctions of mammals

About 20 million years ago, during the Miocene

Mammals in the Miocene• Mammal forms were essentially mod-ern; almost half of modern placental mammal families were present. • Higher primates, including monkeysand apes were present across southern Europe and Asia.• The new grassy plains had a dramaticeffect on mammals. Those that adapted to eating grass did well.• Many spread across the continentswhen Africa, Eurasia and North America joined.• Only Australia and South Americawere isolated continents and unique grazers evolved there.

Maps showingdistribution of important fossil sites for Miocene mammals

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)8. Merychyus (early

ungulate, herbivore)9. Palaeocastor (“ancient

beaver”)10. Parahippus (early horse)11. Syndyoceras (ungulate)

• North America was a centre of diversity for hoofed mammals. Theywere followed by carnivorous cats and dogs, hunting on the open plains.

North American mammals 2

20 MY

Merychippus representsa milestone in theevolution of horses. Ithad a long face, and itslong legs allowed it toescape from predatorsand migrate longdistances to feed. It was the first known grazing horse and the ancestor of all later horse lineages. Lived in North America from 17 - 11 million years ago.10 MY

Frábær heimasíða um Miocen fánu N Ameríku= http://www.npwrc.usgs.gov/resource/1998/agate/visit.htm

North American mammals 3Beavers do more to shape their land-scape than any other mammal exceptfor 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 isembarrassingly small . . . and they don't seewell. 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 4Gomphothers, Miocene (12-8 MY ago). They differ from elephants primarily inthe 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 gompho-theres 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 inthe Pacific Ocean 10-12 MY ago. Sea cows are herbivorous aquaticmammals. Like cetaceans (whales, dolphins) sea cows lack hind limbsand are thus restricted to life in the water. Dusisiren was common inthe 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 weightedover a ton, twice as much as today's camels. Skeleton discovered in 1936

Giraffe-likecamel

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 NorthAmerica 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 Americanmammals 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) andPseudocynodictis (upper). P was an ancestor of T and an early member of the Canidae family, 25 MY ago.

Dog evolution in North AmericaThe Dog linage began in late Eocene, 37 MY agoin 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 Canisand Vulpes. It began in the southwest United States, the birthplace of modern dogs.

More about N American dogs

8 MY ago a powerful canidcalled Epicyon attacks a hornedherbivore. Epicyon were the size of large wolves

The Eucyon, a fox-size canid, de-veloped about 9 MY ago. It spreadto Eurasia 7-6 MY ago and gave rise to most modern canids, including wolves, coyotes, and jackals.

senso

From wolf to woof

All family dogs arestrictu

domesticated wolfs

Seals firstoccurred during

the MioceneKingdom (ríki): Animalia - dýraríkiPhylum (fylking): Chordata - seildýrClass (flokkur): Mammalia - spendýrOrder (ættbálkur): Carnivora - rándýrFamily (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 otterlikecarnivore found in the North Atlantic during the Miocene.

...and bears first appeared in Miocene time

http://www.angellis.net/Web/DFG-mam/Cephalogale.htm

The origins of the bears can be traced back to the raccoon-sized, dog-like Cephalogale from the middle Oligocene and earlyMiocene (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.

Bears and seals share an ancestorBears are members of the OrderCarnivora, Sub-Order Caniformia, and Family Ursidae. Othermembers of the Caniformiainclude wolves and other dog-likemammals (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).

South American Miocene mammal development

Adrift on its own, South America’s strange mix-ture 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.

Marsupial carnivores decline – “killerbirds” hold their position

The marsupial carnivores began to decline and only thesmaller animals remained by the end of the Miocene.

Giantcarnivorousground bird(Phorusrhacus), 1.5 m tall. These creatures were wholly indigenous to South America

Thylacinus sp. This groupof marsupial carnivoreswas represented in the Miocene South American fauna

Rodents and primates were both successful

Cow-sized guinea pigs (“marsvín”), weighing up to 700 kg, grazed theriverbanks of South America about fivemillion years ago, confirms a newlyfound skeleton. This biggest-ever rodent, Phoberomys patersoni, shared its home with two-metre turtles, ten-metre crocodiles (sebecosuchids) and three-metre carnivorous birds.

Charles Darwin wrote extensively on South American mammals in hisbook “The Voyage of the Beagle”. The book is available on the net: http://www.literature.org/authors/darwin-charles/the-voyage-of-the-beagle/

The isolated hoofed animals(litopterns and ‘notoungulates)

formed herds living on the plains

Left: Reconstruction of the head of Mesother-ium. Right: lateral view of the skull of Eutypo-therium superans.

Archaeohyrax

Toxodon sp

Native xenarthrans adapted

The two-tonne, SouthAmerican 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 plainsand huge grazing glyptodonts roamedalongside giant ground sloths and smaller armadillos. Anteaters lived in the trees.

Miocene AustraliaBig flightless birds develop in the absence of numerous mammalian carnivores. Dromornisstirtoni was one of the biggest bird that everlived. It weighed over 500 kilos, and stoodnearly 3 metres tall. It had a huge beak and jawcapable 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 itsown unique marsupial fauna during the Tertiary. Thedrying out of Australia in Miocene sped the evolution of animals that live in open and dry habitats...

Huge marsupial herbivores

Alkwertatherium webbi was a large marsupial almost thesize of a rhinoceros. It weighed about 400 kg and wasabout 1 m tall and 2.5 m long. The Alkwertatherium webbihad 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.

Kolopsis – a largeMiocene herbivoreKolopsis torus was a bull-likemarsupial that stood nearly 1 m high and was about 2 m long. Itis related to our modern daykoalas. Kolopsis was a herbivoreand 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.

Another large herbivoreThe Plaisiodon centralis was a very big marsupial with a longnarrow head. Its closestliving relatives are wombatsand koalas. Plaisodonsweighed between 500 - 700 kg and were about 1.5 m talland 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.

Enter thekangaroos...

Hadronomas puckridgei was a big marsupial that looked like a kangaroo. It is probably anancestor of the short-facedkangaroo, 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 ateleaves and grasses that it chewed withits little nibbling teeth. Hadronomas lived together with herds of large marsupials and large birds but with very few predators.

And there were predators...Baru darrowi was a largecrocodile. It reached 4 - 5 m inlength and had powerful jawsand long curved teeth that itused to catch marsupials and other mammals or birds. Baru was the largest crocodile to live during late Miocene times around 8 MY ago

These crocodiles were amongthe few Australian predators. Itwas adapted to periodic draughts, and spent a lot of time out of the water.

Web page on Miocene Australia: http://amol.org.au/discovernet/alcoota/

Other predators included...

Powerful Thylacine (Thylacinuspotens) lived 8 MY ago (late Miocene). It was 1.5 m long. Several kinds of thylacine have lived in Australiaduring the past 25 million years; thePowerful Thylacine was the largest of them all. It was also the largest meat-eating 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) andgiant lizzards also prayed onanimals at waterholes. Both evolved to become top predators in Pliocene and Pleistocene times.

Brief summary of Miocene 24 MY ago: Short-term warming and drying. 20 MY ago: Great mountain building. The Cascades, the Andes and 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, changingclimate patterns, and formation of a polar ice cap cause sea levels todrop 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 perhapseven the effects of mountain building probably contribute to theextinction of several browsing mammal species. Animals adapted for cooler conditions and coarse, grassy vegetation fare well.

References used when preparing this lectureStanley: Earth System History. Arnold, LondonFortey: Life. A Natural History of the First Four Billion Years on Earth. Vintage, New York.

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Sánchez-Villagra, M. R., Aguilera, O. & Horovitz, I. The anatomy of the world's largest extinct rodent. Science, 301, 1708 - 1710, (2003).

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