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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 Tibetanplateau and Himalayas. Australia, which was attached to Antarctica, began to move rapidly northward. The North Atlantic is opening up.

Eocene WarmingDuring the Early Eocene alligators swam in swamps nearthe 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 highesttemperatures of the entire Cenozoic (up to 30° C) and high precipitation in a world that was essentially ice free.

The Paleocene-Eocene Thermal Maximum, startingabout 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 zonesDecidueous forest

Sub-tropicalforest

Tropicalrainforest

What caused the sudden warming? “The Methane hypothesis”

Deep ocean sediments from around the world show thatthere was a sudden shift in the relative abundance of carbon-12 at this time. Scientists such as Jerry Dickensof 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 intoAsia. In the crumpling and grinding and folding thatfollowed, the Indian plate was subducted. Greatquantities 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 ormore began to heat, and so to change. Limestones anddolomites, 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 enormousvolcanic activity in theIndian Deccan Traps areaand the North Atlantic (Iceland) hotspot during early Tertiary (65-60 MY)

The Deccan Traps are one of the largest volcanic provincesin the world. It consists of >2,000 m of flat-lying basalt lava flows and covers an area of nearly 500,000 km3 inwest-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 impactcould have triggered the greenhouse warming thought to haveencouraged 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 thePrimates - the mammalian order that includes humans. ModernArtiodactyls include sheep, pigs, camels and giraffes. Today's Perissodactyls include horses, tapirs, rhinos and zebras.

This evolutionary branching event coincides with a clear boundary inthe 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 hornedbunnies the size of small elephants that eventually went extinct, but may be a close cousin of today's rabbits....

...Then there was a very rapiddiversification of mammals...

The oldest known fossils of mostof the modern orders (ættbálkur) of mammals appear in a briefperiod during the Early Eoceneand all were small, under 10 kg. Both groups of modern ungulates(Artiodactyla (sheep, pigs, camels and giraffes) and Perissodactyla (horses, tapirs, rhinos and zebras)) became prevalent mammals at this time, due to a major radiation between Europe and North America.

Propalaeotherium, a horse-like early perissodactyl. It was the size of a siamese cat!

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 warmEocene, the mammals couldspread from Asia to Europeand across the north poleareas to N America. “Globalwarming may be behind themost profound biotic re-organization of the Age of Mammals,” says Chris Beard, a researcher specializing in early mammals at the Carnegie Museum of Natural History.

Lower dentition of Chronolestessimul, an early primate, from theWutu Formation, Shandong Province, China. These animals dispersed across the Bering land bridge during the early part of the Age of Mammals.

Evolution of the Laurasiatheres

Artiodactyla (sheep, pigs, camels and giraffes);Perissodactyla(horses, tapirs, rhinos and zebras)

Differences between Paleoceneand Eocene mammals

Mammals of the Paleocene were considerablymore 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 developbigger 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 anddetailed picture they present of life of the past. Theremains 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 chainThis simple foodchain has been infered from fish intestinecontents, coprolites and comparisons with modernecosystems. 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, Mammals4th Level Consumers: Adult Fish3rd Level Consumers: Small Fish

2nd Level Consumers: Insects eg. Hetroptera1st Level Consumers: Grazing Insects eg. Trichoptera

Primary Producers: Algae eg. TetraedronSubstrate: Messel 'Waterlilies'

http://senckenberg.uni-frankfurt.de/sm/messel.htm#bild

Site of the Messel shalesLocated 15km south of Darmstadt, near Frankfurt, Germany, the Messel pit is some 60m deep andmeasures 1km by 0.7km. The Messel lithology is a darkbrown-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.

The lake formed in an area of subsidence, during a period of high local tectonic activity. The sedimentsaccumulated, 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 arein 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-poorwater 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 largeamounts 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 thepresence of preserved plant material, including palm leaves, fruits, wood, pollen and some water plants.

Which animals have been discovered at Messel?

This is a pythonspecies 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...

AllaeochelysCrassesculptataEoceneMessel, GermanyApproximate size: 34cm x 30cm

Messel: a key site for fossil fishes

DiesesPrachtexemplardes Schlamm-fisches Cyclurus kehreri ist fast 60 cm lang.

Fishes - There have been over 10,000 fossil fishes foundat Messel. The specimens are mostly from high in the water column and this indicates that the water column was stratified.

More Messel fishes

Messel MammalsMessel is one of the finest Eocene fossil sites for mammals. Mammals make up only 2% of the fauna, therest being mainly insects and fishes. Fossils includehoofed mammals, like the Messel horse, Propalaeotherium(of which over 70 have been found), and rodents andprimates. Leaves and fruits have been found in thePropalaeotherium's gut, indicating that they foraged on the ground for their food. They have aslo been found containing embryos at different stages of development. Most are preserved in a relaxed position, indicating either drowning (this subtropical lake was possibly prone to flooding) or by suffocation by the release of CO2, hydrogen sulphide and ammonia from the lake bottom.

A Messel bat

First finds of bats are from the Eocene, at Messel and in the Green River Formation, Wyoming, USA.

Another Messel bat

The Messel bats are so well preserved, that they have been usedwhen the fine details of the development bat navigation (zonar) organs have been studied.

Insectivorous mammalsBodenlebender Insektenfresser (Leptictidium nasutum)

Leptictidium: Perfectly fossilised in the Messel shales of Germany are threespecies of Leptictidium. The fossils show us a complete outline of the body andthe fur. Some of the fossils also have stomach contents fossilised inside them, so we know these animals ate a mixture of insects, smaller mammals and lizards.

Bodenlebender Verwandter der Igel(Pholidocercus hassiacus)

Baumlebendes Säugetier (Kopidodon macrognathus)

Ganz anders ernährte sich dieses rund ein Meter lange Säugetiermit buschigem Schwanz. Charakteristische Abnutzungsspurender Zähne lassen vermuten, daß Kopidodon macrognathus sich von Früchten ernährte, die es offenbar in Bäumen suchte

HeterohyusHeterohyus, an earlyprimate from Messel.

Wasserlebendes Säugetier(Buxolestes piscator)

Buxolestes piscator hunted fish in the lake

Kleines Urpferdchen (Propalaeotherium parvulum)

“Anders als die heutigen Pferde ernährten sie sich nicht von Gras, sondern von Blättern und Früchten. Dies läßt sich nicht nur indirekt aus dem Bau der Zähne schließen, sondern konnte direkt durch Untersuchungen des Mageninhaltes nachgewiesen werden”.

Propalaeotherium: Kopf-Rumpf-Länge ca. 55 cm, Schulterhöhe ca. 30 cm.

Propalaeotherium

Kopf eines Greifvogels(Messelastur gratulator)

Another bird of prey

Blattkäfer (Chrysomelidae)

Gefunden wurde der nur 5 mm große Käfer in der Fossilienfundstätte Grube Messel.

Giant ants from Messel

The ants were giants - the biggest known yet. Only the huge wingedmales and females have been preserved, probably because the smallerworkers could walk on the surface, so didn't drown. The biggest queens had a wingspan of 13cm. These ants were carnivorous!!!

The Green River FormationOne of the most important fossil sites for understanding the Eocene is found at GreenRiver, located at the junction of Colorado, Utah and Wyoming, USA. During the Eocene, 50-48 MY ago, this region was located at much the same latitude it is today. Thefossils, especially plants, found at this site indicate that the climate was moist tempe-rate or sub-tropical, with temperatures ranging from 15-20oC. In addition to the plants, another piece of evidence suggesting that the climate was sub-tropical was the presence of fossilized crocodiles.

http://www.ucmp.berkeley.edu/tertiary/eoc/greenriver.html

Geological setting

During Eocene, a series of large inland lakes extendedacross the region, and it is in the bottoms of these lakesthat various plants and animals were buried and fossilized. These lakes later dried up as the local climate changed, and many of the plants and animals living here went extinct. The lakes were on a high plateu, ~ 2000 m a.s.l.

The sediments The sedimentary compo-sition of the Green Riverlocality includes manylayers. The major sedimen-tary types are primarilyoolitic grindstones (grainsconsisting of multiplecoatings of carbonate, usually calcite and/or aragonite, that precipitated on a nucleus; they are round and smooth, and form in shallow water environ-ments), packstones (porous sedimentary rocks), oil shale and mudstones.

Lepisosteus, a large predatoryfish, common in the Formation. Complete and articulated fossilsfound in the sediments suggest that the lakes present at that time were fairly deep, to allow the anoxic conditions required for preservation.

Plant remainsMore than any other group of fossils, plants areimportant in reconstructing the past climate of a fossil locality. For the Green River sites, the large number of temperate and sub-tropical taxa suggest that the region received ample rainfall, perhaps seasonally, and that temperatures were relatively mild.

Aspleniumdelicatula – a fern

Equisetum winchesteri -a horsetail (“elfting”)

Lygodium kaulfussi - a climbing fern (“burkni”)

Fossil treesA very large number of different leaves, fruits andseeds from trees have been found at Green River

Pinus balli - a pinecone (“furuköngull”)

Sequoia cf. affinis - a redwood (“risafura”).

Fossil trees and bushes

Platanus wyomingensis- a sycamore (“hlynur”)

Lindera varifolia - a linden tree (“Lind”)

Ptelea cassoidea, winged fruit -(“vængjað aldin humalrunna”)

The fossils: fishesThe fish fossils reflect thesituation in the lakes, whichhave been teeming with life,

indicating large primary production

Fossil birds

This beautiful member of theGallinacea, family of the modernchicken and turkey, was found in the Green River deposits

Gruiformes - a gruiform(bustards, cranes, rails: “doðrur, trönur, rellur”)

Fossil bird tracks from the Green River Formation

A long-leggedEocene duck

The large number of tracksand fossils of the wadingbird Presbyornis discoveredin the Green River Formationsuggest it lived in great colonies around the lakes. It was probably a wader rather than swimmer, but modern ducks have inherited its webbed feet.

Fossil reptiles

Fossil crocodile, water snake andfresh water turtle show subropical temperatures

Fossil batsVery well preserved fossilisedbats have been discovered in the Green River Formation

Eocene bats are known from N America, Europe, Australia, Africaand Asia. Four groups, Icaronyc-teris, Archaeonycteris, Palaeo-chiropteryx and Hassianycterisare represented by virtually complete skeletons. All other Eocene bats are known only from fragmentary dental, cranial, and postcranial remains.

Icaronycteris index

Fossil insectsThough not as famous as the fish and other vertebrates, the insects from the Green River Formation are just asspectacular. The preservation of some fossils is good enough to allow not only identification to family and subfamily, but will sometimes show color patterns, wing venation, and sex-related characters.

Diptera (Flie) -Dolichopodidae -a long-legged fly. Nearly every part of this specimenis well-preserved, including the external geni-talia. We know this fly is a male.

Gryllidae - a cricket(“krybba”). The egg-laying tube shows this is an adult female.

More fossil insects

Hemiptera (true bugs, “skortítur”). Reduviidae - an assassin bug.

Hymenoptera (bees, ants, & wasps)Ichneumonidae - ichneumon wasp.

In conclusion...The data from Messel and Green RiverFormation is consistent with and showsthat the Eocene climate was very warm, tropical-to-warm temperate. This is an ideal situation for the development of life...

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

http://jan.ucc.nau.edu/~rcb7/globehighres.html

http://www.scotese.com/earth.htm

http://www.spacedaily.com/news/climate-03zg.html

http://www.acnatsci.org/museum/leidy/paleo/uintatherium.html

http://www.palaeos.com/Cenozoic/Eocene/Eocene.htm

http://news.bbc.co.uk/2/hi/uk_news/education/2997404.stm

http://scicom.ucsc.edu/SciNotes/0301/warm/index.html

http://en.wikipedia.org/wiki/Paleocene-Eocene_Thermal_Maximum

http://volcano.und.nodak.edu/vwdocs/volc_images/europe_west_asia/india/deccan.html

http://www.msnbc.msn.com/Default.aspx?id=3077464&p1=0

http://www.bbc.co.uk/beasts/changing/eocene

http://palaeo.gly.bris.ac.uk/palaeofiles/lagerstatten/Messel/geology.html

http://www.fossilien.de/artikel/messel/43.htm

http://www.redheart.com.au/galleryRivers.html

http://www.soes.soton.ac.uk/staff/pmrp/EH/Eh4/l4.html

http://www.brookes.ac.uk/geology/8361/2003/anne/geology.htm

http://critters.pixel-shack.com/GalleryP.htm