Jarðsaga 1

- Saga Lífs og Lands –

Ólafur Ingólfsson

- 144 - 65 MY: a period of dramatic changes and a transition towards the modern world -

The Cretaceous World

Late Jurassic-Early Cretaceous: Pangea is ripping apart, creating new landscapes and

habitats and changing evolutionary conditions

Continental drift and Ocean spreading causes transgressions in N America and Europe

Texas

Large scale trans-gression from both north and south connects Arctic to Gulf region, dividing North America into two landmasses. Europeundergoes a seriesof transgression-regression events

Turonian Stage(93.5-88.5 million

years ago)

Climate and landscapes during the early Cretaceous

No major mountain-building episode for 100 MY. Erosion and deposition prevailed.Widespread plains and lowlands, deltas, swamps and warm, shallow seas.

There were no glaciers anywhere on Earth, and global sea level was 60m +

Early Cretaceous: A world steaming under near-tropical conditions...

(cool temperate climates at very high latitudes, >70oN and S)

... with incredible diversity of both fauna and flora, as well as optimal conditions for evolution and occupation of new evolutionary niches...

Oceanic circulation

The fossil story reflecting warm conditions

Finds of Cretaceous fossil tree-trunks

The fossil story reflecting warm conditions

Cretaceous vs modern temperatures

http://www.clas.ufl.edu/users/emartin/GLY3074S01/figures/cretgradient.htm

Laterite and BauxiteLaterite

Thick, red, greatly weathered and altered strata of tropical ground. Laterites are red because silicates have been leached out, and iron and aluminium salts now predominate.Horizons are unclear and the nutrient status of the soil is low. Laterite is soft but hardens rapidly when to the air until it has a brick-like hardness.

BauxiteThe chief ore of aluminium, consisting of hydrous aluminium oxides and aluminous laterite. It is a claylike amorphous material formed by the weathering of silicate rocks under tropical conditions. The chief producers are Australia, Guinea, Jamaica, Russia, Brazil, and Surinam.

Residual deposits formed under tropical climate conditions, where sili-cate-rich rocks are leched during a wet season and subject to strong evaporation during dry season...

Deltas and swamps...

Crocodile-like animals appeared in the Late Triassic, and true croc´s in Jurassic times. Some Cretaceous crocodiles were awesome: the giant Deionsuchus ('terrible crocodile') was 12-14 m long and had a skull 1.8 m long

SarcosuchusThe crocodile is believed to havereached 14 m in length. The animallived about 110 million years ago inwhat is now the windswept TénéréDesert in central Niger. The snoutand > 100 teeth were designed for grabbing prey–fish, turtles anddinosaurs that strayed too close. This enormous reptile would have made Africa’s ancient riverbanks a dangerous place, even for a dinosaur. The fossils belong to an extinct creature named Sarcosuchus imperator ("flesh crocodile emperor")

Fossil remains of one of thelargest crocodilian speciesever to live have beenfound in the Sahara by a team led by Paul Sereno (University of Chicago).

Metriorhynchus –purely aquatic crocodile

Metriorhynchus was ca. 3 m long. It was a highly modi-fied aquatic predator whichhad evolved from its cousins, the land living crocodiles. Apart from its long snout,itbears little resemblance to the conventional crocodile shape. Metriorhynchus was specially adapted to an aquatic way of life with flippers to replace the legs and a vertical fin at the end of its tail to help it swim.

Metriorhyncus probably movedby sideways beatings of its tailand it had evolved to be moreflexible and mobile than its land-living relatives, making it faster in water. Its skin was also less scaly and more flexible than that of the land-crocodiles, reducing its resistance through the water.

Snakes and lizzardsSnakes are uncommon as fossils: Theyhave lightly constructed skeletons andskulls comprised of separate moveable sections and so are generally too fragile to preserve well.

They were the last major group of reptiles to appear in the fossil record. One of the earliest known forms was Dinilysia, meaning 'terrible destroyer', which lived in the Early Cretaceous period. It seems likely that snakes evolved from aquatic lizards, although most have now returned to life on land.

The morespecialisedpoisonous snakesare not thoughtto have evolveduntil the middle of the Tertiary period, perhaps 30 MY ago.

And then there were the dinosaurs...

Cretaceous dinosaurs lived on all Gondwana-Laurentia continents, except Antarctica

Developmenttowards heavier

herbivorae armour and more vicious

predators

The break-up of Pangea affected

dinosaur evolutionDinosaurian paleobiogeography: Temporally calibrated areagramshowing the breakup of Pangaeainto 10 major land areas by theend of the Cretaceous. Checkeredbars indicate high-latitude con-nections that may have persisted into the Late Cretaceous. Five paleogeographic reconstructions divide continental areas into dry land (black) and shallow (epieric) seas (unshaded).

Different lines of evolution among the allosaurs

Dinosaurian paleobiogeography. Acrocanthosaurus, Giganotosaurus, andCarcharodontosaurus, living on N America, S America, and Africa, respectively, approximately 90-110 MY.

Dino´s walked across existing land bridges...

The geographic distribution of ceratops and some other groups duringLate Cretaceous can only be explained by dispersal across Beringia.

The Dino´s... The dinosaurs came in all varieties including carnivores (meat-eaters), herbivores (plant eaters) and omnivores (all-eaters). Some were small as a chicken and others as big as a house, some of them flew like birds. They occupied almost every nisch...

Within the last decaded there has been a transformation in our under-standing of dinosaur paleobiology. They now are regarded as active, agile, and adaptable, as opposed to huge, awkward, lumbering versions of large reptiles.

HERBIVORES: Plant-eating dinosaurs were the most common large animals in the Cretaceous ecosystems

• Biomechanical problems. Some paleobiologists argue that the mechanics of muscle and tendon attachment would not permit these animals to raise their long necks that far above the horizontal.

• Blood pressure. It is difficult to imagine how sufficient blood could have been provided to the head at extreme elevation to avoid unconsciousness when the head was held up for any extended period.

A group of Omeisaurus, medium-sized sauropods, are reconstructed browsing in aconifer forest. Their physology is poorly understood, and some aspects are widely debated:

The huge sauropods, so typical for LateJurassic dinosaurs, continued to live in

Gondwana, but died out in Laurassia

Paralititan stromeri, a new, giant sauropoddinosaur from Upper Cretaceous mangrove deposits in Egypt.

Titanosauria, Madagaskar

Ankylosaurs: They were relatively small, heavily armored Cretaceous herbivores. Their ecology is poorly understood, but their build suggests that they fed primarily on vegetation at ground level.

Laurassic herbivores relatively small and heavily armed

Hadrosaurs: A small group of Telmatosaurus, hadrosaurs from the Upper Cretaceous of central Europe. Hadrosaurs were a very diverse group of bipedal herbivores and were the most important herbivore group during the Cretaceous.

Ceratopsians

The most widely recognized ceratopsian dinosaur is Triceratops, but this was a very diverse group of Creta-ceous herbivores and the only group that may have been adaptively radiating near the end of the period.

No armour, quick and agile: an alternative strategy...

Curiously, the most abundant and diverse of the Cretaceousherbivores were the unarmoured ornithopod dinosaurs, specifically the hypsilophodontids and iguanodontian lines, all of which achieved cosmopolitan distribution.

Dinosaur CarnivoresGiven the relatively large size of most dinosaur carnivores, they would have required significant numbers of large prey animals to sustain their populations. Carnivores would thus be much less numerous than herbivores in any Mesozoic ecosystem.

An Ornithomimus, Cretaceous, USA.These animals were probably very quick and agile and may have preyed largely on the eggs of other dinosaurs.

The Therapods

The theropod (meaning "beast-footed") dinosaurs area diverse group of bipedal saurischian dinosaurs. Theyinclude the largest terrestrial carnivores ever. Birdsare the descendants of small nonflying theropods.

http://www.ucmp.berkeley.edu/diapsids/saurischia/theropoda.html

T-Rex and friends...

Tyrannosaurus rex was a huge (12 m long, about 6 m tall, 5-7 tons) meat-eating dinosaur that lived during the late Cretaceous, 85-65 MY ago. T. rex lived in a humid, semi-tropical environment, in open forests with nearby rivers and in coastal forested swamps. Until recently, Tyrannosaurus rex was the biggest known carnivorous dinosaur; Gigan-otosaurus and Carcharodontosaurus were slightly bigger.

How fast did the dinosaurs move:

There is a general relationship between speed and stridelength in living animals. This can be used to estimate how fast the dinosaurs were:

• Sauropods and ankylosaurs were slowest, ~ 3-5 km/hr

• Most ornithopods were faster, ~ 5-7 km/hr

• Theropod predators were fastest, ~ 10 km/hr, bursts up to 40-50 km/hr

Velociraptor ("Speedy Thief“)Velociraptor was a fast-running, two-legged dinosaur. This meat-eater had about 80 very sharp, curved teeth in a long, flat snout; some of theteeth were over 2.5 cm long. This predator had an s-shapedneck, arms with three-fingered clawed hands, long thin legs, and four-toed clawed feet. Velociraptor's head was about 18 cm long. Velociraptor may have been able to run up to roughly 40 km/hr for short bursts.

Velociraptor’s murder weapon

A 9 cm long, sickle-like, retractible claw was onthe middle toe of eachfoot. This claw was itsmain weapon, and could probably kill most of its prey (plant-eaters like hadrosaurs) easily.

A small but smart killer

Velociraptor was 1.5-2 m long, and 1 m tall. It may haveweighed about 7-15 kg. It had a stiff tail that worked asa counterbalance and let it make very quick turns. Velociraptor's brain was relatively large in comparison to its body size (this is true for all the Dromaeosauriddinosaurs, who were the most intelligent dinosaurs).

How brainy were the dinosaurs?

• Big Sauropods and Stegosaurs: EQ of ~0.1-0.6

• Ceratopsians and Ornithopods: EQ of 0.5-1.5

• Big Theropods: 0.9-1.9

• Some smaller Theropods, likevelociraptor: EQ 5-5.8

EQ is the ratio of the brain weight of the animal to the brain weightof a "typical" animal of the same body weight. We are comparing dinosaurs to reptiles, but even the “dumbest” mammal has twice the brain size of a similar sized reptile

Are the dinosaursstill around (as

birds)?During Late Creta-ceous, there was anextraordinary range of birds and dinosaur-likeprotobirds. It is impos-sible to tell where dinosaurs ended and birds began...

There are numerous striking similarities between

carnivorous dinosaurs and birds.

Oviraptor

Oviraptor (“Egg thief”), Upper Cretaceous (85-75 MY);Length (up to) 1.8 m; omnivorous; Found in Mongolia

Ornithomimidae ("Bird Mimics")

Ornithomimids were a distinctive group of theropoddinosaurs, who are a good example of convergent evolutionwith the birds such as ostriches. Ornithomimids were generally slender, lightly-framed, and reached huge sizes (some attaining lengths of 7 m).

Feathered dinosaursA new range of fossil finds, mostly from China, are revealing that a large number of small dinosaurs were covered by feathers

Sinornithosaurus was a small dinosaur that probably fed on animals such as reptiles and mammals. Like larger raptors the animal may have attacked with a jumping stance, as shown here. Although quite bird-like, this dinosaur could not glide or fly, which raises the issue as to why it evolved feathers.

Why Feathers?• Sexual Display. One possibility is that feathers may have served to enhance sexual display as part of mating behaviour.

• Insulation. One important role for feathers may well have been insulation. If some dinosaurs were warm blooded, small individuals would face a problem of significant heat loss due to an unfavorable(high) surface to volume ratio.

• Large vs. Small Bodies. The hatchling has a covering of feathers to assist in retaining body heat, but the feathers are lost as the animal grows to adult size.

Caudipteryx

Yet another feathered dinosaur/bird from China...

Uenlagia (“half-bird”)

Several features of Unenlagia(originally described fromUpper Cretaceous of Argentina) are more birdlikethan in any other non-aviantheropod so far discovered. The evidence suggests that it could flap its arm, although Unenlagia was much too heavy to fly with such a short wing.

The development of birds...The Jurassic Archaeopteryx was one tran-sitional form between birds and reptiles. Unlike all living birds, Archaeopteryx had a full set of teeth, a flat breastbone, a long, bony tail, and three claws on the wing which could have still been used to grasp prey (or maybe trees). However, its feathers, wings, wishbone and reduced fingers are all characteristics of birds.

Ichthyornis: This ‘fish bird’ was an 30 cm long bird of the Cretaceous period that dived to catch fish. Ichthyorniscould probably fly and had long wings. It had teeth in its jaws, unlike modern birds. Its remains were found in Kansas, USA.

IchthyornisIchthyornis wasfirst described in1872, from sedi-ments in Kansas, and originally thought to be a marine reptile.

Birds of the CretaceousThe evolution of birds is not well known, since they

preserve badly as fossils

Hesperornis or ‘western bird’ was a >1 m long flightless bird of the Late Cretaceous period.Fossil skeletons have been found in Kansas and Alberta, Canada. This fish-eating bird had large, possibly webbed feet and may have been a good swimmer and diver.

Enantiornithes

http://www.sino-collector.com/eng/_private/cjyd/zjlt/hjs-hs/hjs02-3.htm

Action in the skies

A flock of Criorhynchus soars above a long-necked Elasmosaurus, while the ternlike Ichthyornis skims the waves at lower left.

...action in the skies...

The Pterosaur Quetzalcoatlusnorthropi had a wingspan of 12-13 m, making it the largest known flyer of all time...

The giant Quetzalcoatlus has been compared with large modern birds such as condors and eagles and it has been concluded that, like them, it ate carrion. But the anatomical evidence does not support this. Quetzalcoatlus had a long inflexible neck that would not have been desirable for vulture-like feeding. Its long, tweezer-pointed, and toothless jaws were not suited for tearing apart dinosaur cadavers, and are more suggestive of a diet of fish or molluscs and arthropods in shallow flood basins.

The diatoms (kísilþörungar) appear

They are among the most important aquatic micro-organisms today: they are extremely abundant both in the plankton and in sediments in marine and freshwater ecosystems, and because they are photosyn-thetic they are an important food source for marine organisms. SomeCretaceous rocks are formed almost entirely of fossil diatoms, and are known as diatomite or diatomaceous earth. These deposits are mined commercially as abrasives and filtering aids. Analysis of fossil diatom assemblages may also provide important information on past environmental conditions.

Enormous Cretaceous chalk deposisits

The massive chalk deposits (>200 m) of NW-Europe(Denmark, England, N France) are composed of the armour plates of calacareous nannoplankton (kalkþörungar)

Life on the sea floorLife on the sea-floor began totake on a modern appearance during the Cretaceous Period.

Cretaceous Oysters – some grew to very large sizes

Rudists build reefsRudists were the dominating Cretaceous reef-builders, at the

expense of the corals

Rudist: An extinct bivalve mollusk from the Jurassic and Cretaceous thathad two different sized and shaped shells; they usually were attached to the substrate and were either solitary or in reeflike masses.

Reef builderssince the Permian

The shallow seas

Helioceras was a loosely-coiled cephalopod that lived in the shallow seas that bisected North America in the Cretaceous.

A gigantic (0.3 m) ammonite shell of

Placenticeras

The shallow seas...

A very large Cretaceous marine turtle (Archelon)

Plesiosaurs were marine reptiles with a stocky body,

four large flippers, and a long tail.

Mosasaurs were large marine lizards up to 9 m in length. They preyed largely on fish

A mosasaur in action

The mosasaurs are distinctrelatives of modern snakes and perhaps the Komodo Dragon of Indonesia

http://www.oceansofkansas.com/mosasaur.html

http://www.oceansofkansas.com/Greatrep.html

Reconstruction of marine life in upper Cretaceous of USA

The Teleost fishes (beinfiskar)develop

Teleosts are characterized by symmetrical tails, round scales, specialized fins and short jaws

By Late Cretaceous time, a wide variety of tele-osts existed, includingclose relatives of themodern sunfish (“tungl-fiskur”), carp (“vatna-karpi”), swordfish (“sverðfiskur”), eel (“áll”) and salmon (“lax”).

Diplomystus brevissimus

Fish-in-a-fish

Xiphactinus audax, (Bulldog Fish), was a species of verylarge (5 m) predatory fish that lived in the ocean during the Late Cretaceous.

Enter the mammals...The three modern mammal groups: monotremes (nefdýr), marsupials(pungdýr), and placentals (legkökudýr) originate during the Cretaceous.

The earliest mammals, such as Morganucodonstarted to develop during latest Triassic and early Jurassic. Most Mesozoic animals were small and would remain so until the extintion of the dino-saurs opened niches that permitted the adaptive radiation of mammals in the early Cenozoic.

Echydna and Platyphus

Bandycoot, a small marsupial

Koala

Geological rangesfor mammals

Insects develop before the appearance of flowering plants

Insects make up over three-fourths of all known animal species on the planet...

A 95 million year old fossil insect (a wasp) in amber from the

Raritan formation of New Jersey

The oldest true flies are Triassic in age; butterflies appear in the Jurassic; and by the end of the Cretaceous, almost all the familiar true flies groups had appeared. Insects and flies, as far as we can tell, were completely unaffected by the extinction event at the end of the Cretaceous...

Ants, termites, wasps, bees...They all originated during the Cretaceous

The sudden emergence of flowering plantsMore than one-hundred years ago, Darwin called the origin of angiosperms an "abominable mystery".

One of the biggest questions about early angiosperms, besides their origin, is the nature of their growth habit. Were the first angiosperms woody trees and shrubs, or were they small herbs?

First appearing in the tropics during the Lower Cretaceous, around 125 MY ago, the flowering plants first radiated in the middle Creta-ceous, about 100 million years ago. By the end of the Cretaceous, a number of forms had evolved that any modern botanist would recognize. No fossils showing a transition from gymnosperm to angiosperm have been discovered.

The flowering plants little secrets of success...

1. Double fertilization. First fertilization produces egg within the ovary (eggleg); second fertilization produces a storey of food for the seed.

The rapid manufacturing of this food supply allows for the quick release of a well fortified seed.

Most gymnosperms havereproductive cycles of 18-24 months; angiosperms have reproductive cycles of few weeks!

A photomicrograph of lily (lilja) double fertilization.

Pollinating by insects...2. Symbiotic relationships between flowering plants and insects.Isects benefit from the nutritiousnectar that the flowers provide;

The flowers benefit because theinsects (unknowingly) carry pollenfrom one flower to another, fertilizing the plants on which they feed

-Gymnosperms dominated the Mesozoic landscape, but are today mostly confined to cooler temperate climates

- Angiosperms dominate since the Late Mesozoic

Oldest flowering plant in the worldChinese and U.S. scientists have identified what is believed to be the world's oldest flowering plant. The 140-million-year-old fossil was found in northeastern China. Sun Ge, a researcher with the Academia Sinica in Nanjing, China, and David Dilcher with the University of Florida, worked together earlier this year to identify the specimen, which predates the previous oldest-known flower by 25 million years.

Did dinosaur grazingboost flowering

plants?

Angiosperms and the modern world...• Nearly all of our food comes from flowering plants:grains, beans, nuts, fruits, vegetables, herbs and spices; as do tea, coffee, chocolate, wine, beer, tequila...

• Angiosperms are the staple for herbivores that we in turn eat: sheep, cattle, goats, pigs... you name it...

• Much of our clothing comes from them as well: cotton and linen are made from "fibers" of flowering plants, as are rope and many commercial dyes are extracted from other flowering plants.

• We also owe them credit for a large number of our drugs, including aspirin, numerous prescribed drugs and controlled drugs such as opium, cocaine, marijuana, and tobacco.

Late Cretaceous: Active plate boundaries and mountain building start changing the scene...

The Rockies were formedin the Mesozoic and EarlyCenozoic eras during theCordilleran orogeny. Theyare geologically complex, with remnants of anancestral Rocky Mt. system and evidence thatuplift, which involvedalmost all mountain-building processes, occurred as a series of pulses over millions of years. The mountains have since been eroded to expose ancient crystalline cores flanked by thick upturned layers of sedimentary rocks.

The Cordilleranorogeny

• Cordilleran orogeny: A protracted episode of deformation affecting the western margin of NorthAmerica from Jurassic to Early Cenozoic time; typically divided into three separate phases called the Nevadan, Sevier, and Laramide orogenies.

• Cretaceous Interior Seaway: An interior seaway thatexisted during the Late Cretaceous; formed whennorthward-transgressing waters from the Gulf of Mexico joined with southward-transgressing water from the Arctic; effectively divided North America into two large landmasses.

• Laramide orogeny: The Late Cretaceous to EarlyCenozoic phase of the Cordilleran orogeny; responsible for many of the structural features of the present-day Rocky Mountains.

The Laramide orogeny

A series of mountain-building events that affected muchof western North America in Late Cretaceous and Early Tertiary time. Evidence of the Laramide orogeny is present from Mexico to Alaska.

Laramide thrusts

The Keystone thrust. This fault shows the CambrianBonanza King formation (gray) over folded Jurassic Nugget sandstone (red).

Rocky Mts landscapes

Summing up the Cretaceous• Latitudional temperature gradients were gentle –warm even at high latitudes and no glaciers

• The Cretaceous was an extreme greenhouse situation

• Gondwana broke apart during the Cretaceous Period, forming the South Atlantic. The Tethys seaway existed, that carried warm waters through the Mediterranean region

• On land, flowering plants diversified and evolved, together with the insects

• The mammals evolve and diversify

• In the sea, the phytoplankton assumes a modern character, and crabs and teleost fishes evolve and diversify significantly

K/T BoundaryThe Cretaceous-Tertiary boundary is marked by a mass extinction: 50-60% of all living species of animals and plants became extinct. Caused by a large meteorite

impact?

Causes-effects of the 65 MY K/T extinctionDuring the K-T extinction (65 MY ago) 85% of all species disappeared. The dinosaurs perished in the K-T extinction, and several other terrestrial and marine groups were also severely affected or eliminated. Among those that perished were the pterosaurs, belemnids, many species of plants, ammon-ides and marine reptiles. Groupswhich were severly affected included planktonic foramini-fera, diatoms, molluscs and fish. Remarkably, most mammals, birds, turtles, crocodiles, lizards, snakes, and amphibians were primarily unaffected by the K/T extinction...

Evidence for catastrophismat the K/T boundary is found in a layer containing unusually high concentrations of Iridium, originating either from the earth's mantle or from extra-terrestrial meteors. This layer has been found found in both marine and terrestrial sediments, at many sites around the world.

90 million years ago 80 70 65

Cretaceousextinctions

60

?

Figure 15.5

Meteorite Impact or Volcanic Eruptions?

• The widespread distribution of the Iridium layer may have beencaused by a meteorite impact. Recent research suggests that the impact site may have been in the Yucatan Peninsula of Mexico.

• The high concentrations of Iridium in the boundary layer could be result of massive volcanic eruptions at the K/T boundary: either in the Deccan Traps (India and Pakistan) or at the Iceland hot spot. These eruptions produced thousands of km3 of lava and enormous amounts of ash. They could have affected global climate and ocean chemistry.

• Both volcanic and meteorite impact hypotheses are viable mechanisms for causing the K/T mass extinction, although the latter is more popular...

Major events of the Cretaceous Period

References, web resources• Stanley, Earth System History, chapter 17.

• http://www.ucmp.berkeley.edu/mesozoic/cretaceous/cretaceous.html

• http://www.bbc.co.uk/dinosaurs/fact_files/

• http://www.ucmp.berkeley.edu/diapsids/saurischia/theropoda.html

• http://www.sino-collector.com/eng/_private/cjyd/zjlt/hjs-hs/hjs02-3.htm

• http://www.palaeos.com/Mesozoic/Cretaceous/Cretaceous.htm

• http://www.oceansofkansas.com/

• http://www.scotese.com/

• http://jan.ucc.nau.edu/~rcb7/globaltext2.html

• http://www.nytimes.com/library/national/science/122199sci-archaeo-flowers.html

• http://www.napa.ufl.edu/98news/flowerph.htm

• http://www.colby.edu/~ragastal/Paleobotany/angiorigins.htm

• http://www.pbs.org/wgbh/evolution/library/03/4/l_034_01.html