evolution of australian biota -...

Gill Sans Bold

BiologyPreliminary CourseStage 6

Evolution of Australian biota

Part 3: Changing environments and biota in Australia

Incorporating October 2002

AMENDMENTS

Part 3: Changing environments and biota in Australia 1

Contents

Introduction ............................................................................... 2

Geological time scale and biota ................................................ 4

Evidence of changing environments ...................................................5

The last 100 million years.......................................................... 9

Environmental change .........................................................................9

Adaptive radiation of marsupials ............................................. 13

Origin of marsupials ...........................................................................15

Origin and radiation of monotremes ........................................ 16

The megafauna ....................................................................... 18

Additional resources................................................................ 21

Suggested answers................................................................. 25

Exercises – Part 3 ................................................................... 27

2 Evolution of Australian biota

Introduction

In Part 2 of this module you became familiar with the theory of platetectonics and saw how it is related to the biota found on the separatecontinents which made up Gondwanaland (Gondwana), especially theAustralian continent. In this part of the module the nature of changingenvironments during the northerly drift of Australia and the resultanteffects on the evolution of ancient and modern flora and faunaare discussed.

Most emphasis is given to the marsupial and monotreme mammals, asthey are typically Australian biota. Although a large number ofmarsupial species also occurs in South America, the species are mainlyvery different from the Australian marsupials. Monotreme fossils havealso been found in South America, but living monotremes are restrictedin their distribution to Australia and New Guinea and most fossilmonotremes have been found here.

In this part of the module you will need to read and work carefullythrough the material provided, to practice important skills especiallygathering, processing and analysing information from secondary sources.This means that you need to be able to research reference material,understand it and present conclusions based on your research.If you have access to a library, CD ROM or the Internet, you can readfurther than the material provided here. However, there is sufficientresearch information in the material provided for you to carry out theexercises and assignments and to achieve the competencies required.

In Part 3 you will be given opportunities to learn to:

• discuss current research into the evolutionary relationships betweenextinct species, including megafauna and extant Australian species

• identify and describe evidence of changing environments inAustralia over millions of years

• identify changes in the distribution of Australian species, asrainforests contracted and sclerophyll communities and grasslandsspread, as indicated by fossil evidence


• discuss current theories that provide a model for these changes.

In Part 3 you will be given opportunities to:

• gather information from secondary sources to describe someAustralian fossils, where these fossils were found and use availableevidence to explain how they contribute to the development ofunderstanding about the evolution of species in Australia.

• perform a first-hand investigation, gather information of namedAustralian fossil samples and use available evidence to identifysimilarities and differences between current and extinct Australianlife forms.

Extract from Biology Stage 6 Syllabus © Board of Studies NSW, originallyissued 1999. Revised November 2002. The most up-to-date version can befound on the Board's website athttp://www.boardofstudies.nsw.edu.au/syllabus_hsc/syllabus2000_lista.html


Geological time scale and biota

As you saw in Part 2, Australia was once part of the huge landmass ofPangaea and then of the southern supercontinent, Gondwanaland(Gondwana). Even before Gondwana split from Pangaea most of themajor groups of plants and animals known today existed on the Earth.Although the fossil record shows that mammals, birds and probably theflowering plants had not yet risen to any prominence by the timeGondwana separated from the rest of the Pangaean landmass.

The table in the Additional resources shows the categories of geologicaltime for the Earth but these are not drawn to scale. All periods are shownas fairly similar sized boxes, but the time span of each period is given,along with the major plant and animal groups from each. The table alsoindicates when it is thought each group evolved, reached prominence inthe fossil or living record and when some became extinct.

You should not be concerned if other sources do not match exactly theone given in the table which has actually been constructed from severalsources of information.

The generally accepted progression of evolution, as deduced by varioustypes of information (especially fossil evidence), will be the same or verysimilar in most of these sources. However, you may find smalldiscrepancies. These may be due to differences in opinion orinterpretation by authors or even to how recently the source has beenwritten or updated.

In Part 2 you saw that Australia’s association, firstly with the other landareas making up Pangaea, and then those bound up into Gondwana,resulted in the biota of the modern Australian continent showing somesimilarities to those of other areas of the world.

However, after its rifting from Antarctica and its movement north withthe drifting of the Indo-Australian Plate, Australia experiencedconsiderable changes in both climate, geography and geology so thatspecies of organisms which were present on the continent were isolated


and exposed to different natural selection pressures, so that they changedand evolved into the groups of organisms present today.

The mechanisms of this speciation and adaptive radiation werediscussed in detail in Part 1. If you need to, return briefly to your notesand assignments from Part 1 just to make yourself familiar again withthese mechanisms and how they are thought to work.

Evidence of changing environments

No one was around to witness the changes occurring in worldenvironments, but a good deal of information on palaeogeography(pre-human geography) and palaeoclimatology (pre-human climate) canbe obtained by a variety of methods including:

• fossils

• tree rings

• dating methods and

• glaciers.

Fossils

The remains of organisms can be preserved in a number of ways,including:

• the preservation of bodies or body parts in amber (gum), peat or tarwhere bacteria are prevented from breaking down the organicmaterial

• replacement of body tissues by minerals (eg. opal)

• impressions in mud which subsequently turns to rock

• the preservation of whole organisms in ice (eg. woolly mammoth).

These fossils often give clues about the environment or climate.For example, finding the fossil remains of marsupials which hadskeletons adapted for climbing and teeth adapted for feeding on leavesand fruits suggest that the area in which they lived at the time wasprobably a forest, not a shrubland or grassland.


A fossilised trilobite indicates a past marine environment.(Photo: © LMP Tim Reid).

If fossilised leaves of rainforest species were also found it might indicatethat the region was part of a rainforest rather than a sclerophyll forest.Similarly, the finding of fossils of fish, turtles and frogs would indicatean aquatic rather than a terrestrial environment. Pollen and spores fromplants can be quite distinctive and are frequently used to deduce thenature of the past vegetation in an area.

Tree rings

Tree rings represent seasonal growth cycles. This means that the ages oftrees can often be calculated. The rates of growth each season can alsobe estimated from tree rings.

Various environmental factors, including rainfall, aspect (sunshine) andaltitude can affect tree growth. In this way the study of tree rings canindicate climate and geography of the place where a tree grows, or whereits fossil remains are found.


Petrified wood from the Permian showing large annual growth rings.This indicates that there were warm conditions at the time that this tree grew.(Fossil Andrew West). (Photo: © LMP Thomas Brown)

Dating methods

The age of rocks which contain radioactive minerals can be determinedby calculating backwards from the amount of the radioactive elementremaining in the rock and the amount of the element into which it decays(changes). For example uranium-235 decays into lead-207.

The rate at which radioactive decay occurs is fixed and is known as thehalf-life of the element. That is, the time taken for half of the originalelement present (parent element) to decay into the other element(daughter element). In the case of uranium-235 changing into lead-207,the half-life is 713 million years. This method is calledradiometric dating.

If fossils, or the rocks in which they are found, can be given a date offormation, then other fossils and rocks can be dated relative to them.If they are found higher in layers (strata) of the Earth, then they musthave been formed later and so are younger, while lower ones are older.Once a fossil type has been dated, then it can be used to establish thedates of other fossils found with it. This is called relative dating.

There can be problems with the method of relative dating, as it is knownthat the positions of rock strata can move in various ways, so that theyounger fossils or rocks may be found under rather than above older


ones. However, other geological evidence can often identify thisdisruption to the layering.

Glaciers

As the ice sheets of glaciers move over the surface of the Earth theyerode rocks and deposit material in a characteristic way. During ice agesglaciers advance and then retreat during warmer periods.

Studying the occurrence of features of glacial erosion can enablescientists to map glaciers and determine a good deal about the climate ofthe time.

Ice cores

Cores of ice taken from glaciers and from polar ice caps can also be usedto determine climate. The higher levels of carbon dioxide in air bubblestrapped in ice can indicate greenhouse global warming. Ash trapped inice can show the presence of volcanic activity at the time the ice wasformed. In an ice core the most recently formed ice is at the top and theolder at the bottom.

Complete Exercise 3.1 now.


The last 100 million years

Environmental change

In this section you will become more familiar with the sequence ofchanges in geography, climate and vegetation of Australia prior to itsseparation from Gondwana and during its drift northward towardssouth- east Asia. It was these environmental changes which almostcertainly gave rise to the evolution of the diverse flora and fauna ofthis continent.

The information that follows outlines the changes in climate and vegetationduring different periods in Australia. You will be using this information tocomplete a table to summarise these changes.

Cretaceous period

The beginning of this period in Australia was cold. The sea level washigh and much of the land mass consisted of islands in a shallow inlandsea. The vegetation was dominated by non-flowering vascular seedplants (conifers, cycads, horse tails and seed ferns) but the first floweringplant fossils also appeared during this period.

The climate warmed later in the Cretaceous, the land of Australia wasuplifted and the angiosperms began to dominate the vegetation.

By the end of the period mass extinctions, which included the Australiandinosaurs, occurred. This was possibly due to a cooling effect broughtabout by the collision of an asteroid with the Earth. This is thought tohave caused dust in the atmosphere and a resulting reduction in theheating of the Earth’s surface by heat from the Sun.


Paleocene-Eocene periods

Australia had broken away from Antarctica by about the end of theEocene period and began drifting north. Australia’s climate went frombeing wet and warm to being cool. Large inland lakes were part of thelandscape and rainforests covered much of the continent. Ferns andconifers were still found, but flowering plants were certainly thedominant land plants, including species belonging to the genusNothofagus or southern beech trees (see Part 2).

Oligocene period

This period was also cold and wet in Australia. Rainforests, includingNothofagus trees, dominated and swamps were common. The firstEucalyptus trees appeared during this period.

Miocene period

In the early Miocene period sea levels varied and the climate fluctuatedbetween being hot and cold. But, it was always wet and rainforests werestill dominant. However, by the late Miocene sea levels fell and theclimate was cold and was becoming drier. Rainforests were beginning togive way to forests of trees with hard dry leaves (sclerophyll), especiallyEucalyptus species, which could tolerate the drier conditions.Casuarina or she oak species of trees and shrubs were also commonangiosperms of this later period.

Pliocene period

This was a time of raised sea levels with rainforests present in the wetconditions at the beginning of the period, but giving rise to sclerophyllforest, woodland and even grasslands later, especially in inland Australia.

Pleistocene period

Both temperatures and sea levels fluctuated during the Pleistocene, asAustralia experienced alternating icehouse and greenhouse conditions.However, in general the climate became more arid and plants andanimals able to cope with such conditions evolved. The giant forms,often called the megafauna evolved early in this period but becameextinct by the end of it.


The table below uses a format similar to the table in the Additionalresources showing the Earth’s geological time periods. Some of theinformation in the table has been filled in but you will need to carefully readthe descriptions given for each period. Complete the worksheet.

Period Time span(million years)

Geography Climate Vegetation

Early Cretaceous

Late Cretaceous

146-97

97-65

islands in shallowinland seas

cold, moist cycads and conifers,horsetails and seedferns

Paleocene-Eocene

rifting fromAntarctica began;large inland lakes;northern drift ofAustralia

rainforests containingferns and conifers butmainly angiosperms,especially Nothofagus(southern beechtrees)

Oligocene first Eucalyptus trees

Early Miocene

Late Miocene 10.5-5

Pliocene

Pleistocene

Recent (holocene) arid inland,north dominatedby summerrainfall andsouth by winterrainfall.;temperaturesincrease fromsouth to north

Check your answers.


The environmental conditions of Australia varied considerably as thecontinent moved north, but the most notable trend in the last 15 millionyears was one of increasing arid conditions. The overall change in theclimate and vegetation from being cool, wet and forested to being warmand with dry mainly woodland, shrubland and grassland ecosystems.

Time (millions of years from present)

15 10 5 today

cool and wet warm and dryClimate

Climate change in Australia over the past 15 million years. The dark shadingshows the increase in warmer and drier conditions.

You will draw on this information in the next part when you willexamine vegetation patterns and the impact on Australian biotaover time.

Complete Exercise 3.2.


Adaptive radiation of marsupials

The changes in environments and vegetation in parts of Australia led tothe evolution of very different animals under the influence of differentselection pressures. The first marsupial mammals are thought to havecome from South America. The likely ancestor of Australian marsupialswas probably a small species like the small South American marsupialcalled Dromiciops australis, which is found in the beech forests ofsouthern Chile. This animal has many features like the small possumsof Australia.

Dromiciops australis a South American marsupial which is thought to belong tothe group (Microbiotherids) from which Australian marsupials evolved.(Photo: © LMP T R Grant)

This species is quite similar in appearance to the Australian easternpygmy possum (Cercartetus nanus). All other American marsupialshave sperm which are attached together in pairs, while Dromiciopsaustralis and the Australian species have single sperm. There is alsoconsiderable similarity in the DNA between this little creature and


Australian marsupials. Dromiciops itself is not the actual ancestor butmay belong to the same ancestral group as the original Australianmarsupials. Once such a marsupial ancestor (or ancestors) reachedAustralia via Antarctica, the group radiated by adaptation to the differentenvironments of the continent to produce the range of unique marsupialsfound in Australia today.

Despite what some books say, there are still lots of species of marsupialsin South and Central America today (around 75 species).American marsupials are called opossums, which are completelydifferent from the Australian group of marsupials which are calledpossums. One species is found in North America, but it almost certainlymoved there quite recently in geological terms. There are no kangaroos,wombats, koalas or bandicoots on the American continent, and mostAmerican marsupials are fairly small creatures, the largest of which isabout the size of the Australian brushtail possum.

During the adaptive radiation of marsupials in Australia a number ofspecies became extinct as conditions changed. There were presumablyno variations within their populations which allowed these marsupials tosurvive the changes.

The major groups of modern Australian marsupials are summarised inthe table below. Adaptation to different habitats has occurred duringtheir evolution and the varied diets of some are shown in the table.

Order Common names Example Diet

Dasyuromorphia dasyurids marsupial ‘mice’Tasmanian devil native‘cats’

carnivores

Peramelemorphia bandicoots bandicootsbilby

insectivores

Diprotodontia • koala

• wombats

• macropods (kangaroos,wallabies, potoroos,bettongs, rat-kangaroos)

• possums

• pygmy possums

• gliders

• koala

• common wombat

• grey kangaroo

• swamp wallaby

• brush-tailed bettong

• tree kangaroo

• ringtail possum,brushtail possum

• eastern pygmypossum

• sugar glider

• leaf eater

• grazer

• grazer

• browser

• fungus, seed, tuberand insect eater

• leaf and fruit eater

• leaves, flowers, fruiteaters

• nectar, pollen eater

• nectar, pollen, insect,sap eater


Optional

You could try to use either the Internet, CD ROMs or go to your locallibrary and have a look at pictures of the members of these groups ofmarsupials. Find out what they look like, what they eat and where theyare found.

Origin of marsupials

As was mentioned earlier, the currently most accepted theory of theorigin of the Australian marsupials is that their ancestors came fromSouth America, probably around 65-55 mya in the late Cretaceous orearly Paleocene period. If this was a reasonable theory, then thefollowing might be reasonable expectations (hypotheses) fromthe theory.

∑ There should be older marsupial fossils in south America than inAustralia.

∑ Marsupial fossils should be found in Antarctica

∑ At least some South American marsupials should show affinities(similar characteristics) with Australian species.

Most modern South American marsupials appear to be more closelyrelated to the earliest marsupial fossils which were found in theCretaceous period in North America (around 100 mya) than to modernAustralian marsupials. The ancestors of the modern South Americanforms quickly disappeared from the north of their range, but theirdescendants persisted in South and Central America during theCretaceous period. It should be noted that the one species of marsupialnow found in North America, the Virginian opossum, has more recentlyinvaded from Central America.

A marsupial fossil has been found on an island off the AntarcticPeninsula, adjacent to the tip of South America. The living speciesDromiciops australis has DNA similarities to Australian marsupials.Dromiciops australis has unpaired sperm, while the sperm of all otherAmerican forms swim together in pairs. These pieces of evidencesuggest that the theory has at least some support.

An alternative theory that the marsupial ancestors entered Australia fromthe north has little support, as no marsupial fossils have yet been found inAsia. It was not until around 15 mya that Australia was close enough tosouth-east Asia for mammals to have reached the mainland fromthe north.


Origin and radiation of monotremes

Monotremes are mammals which lay eggs but, like all other mammals,feed their young on milk. There are currently only three living species ofthe Monotremata group, two species of echidnas (or spiny anteaters) andone species of platypus. The short-beaked echidna occurs both inAustralia and Papua New Guinea; the long-beaked echidna occurs onlyin Papua New Guinea; the platypus occurs only in Australia.

There was once a greater abundance and distribution of monotremespecies in Australia than currently occurs. Fossils of this group showthat it has been here for longer than the marsupials. The oldestmonotreme fossils are from the Lightning Ridge area in westernNew South Wales. These appeared to have been from platypus-likespecies which had teeth possibly adapted for eating crustaceans(eg. shrimps, crayfish). It would seem then that they were probablyaquatic, so that during the Cretaceous period in which they occurred(around 110-115 mya) the environment of the Lightning Ridge areawould have been much wetter than it is today.

Until recently monotreme fossils had only been found in Australia, but in1991 and 1992 several fossil monotreme teeth (which are quitedistinctive) were found in Patagonia in the south of Argentina.These were about 62 million years old. Can you remember in whichgeological period that date falls? No doubt you would have decided thePaleocene period.

Fossils of three ancient species of platypuses have been found that arefrom 15-23 million years old. A number of fossil echidnas have alsobeen found on mainland Australia, indicating greater species abundanceand distribution of the group.

The early age of monotreme fossils, the greater abundance of fossilforms, and the occurrence of living forms in Australia has led somepalaeontologists to hypothesise that the group may have evolved inAustralia, before it broke away from Antarctica, and that the SouthAmerican forms descended from an Australian ancestor. At present thereare insufficient data to support or reject this hypothesis.


Answer the following questions, then check your answers at the end ofthis part.

1 The most accepted theory is that Australian marsupials evolved fromancestors which originally dispersed here from south America.Discuss the evidence which supports this theory.

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2 On the other hand it has been suggested that the fossil monotremespecies found in South America may have evolved from anAustralian ancestor. Briefly describe evidence for such a suggestionand comment on its acceptance by palaeontologists.

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Check your answers.

Complete Exercise 3.3 where you will be comparing a fossil form of aplatypus to a current form.


The megafauna

Gigantism occurred in mammal groups in many parts of the world duringthe Pleistocene period and those in Australia were no exception.The term megafauna refers primarily to large marsupials, such as giantkangaroos (eg. Procoptodon goliah, Macropus giganteus titan) and hugefour legged herbivores (eg. Diprotodon optatum, Zygomaturus trilobus).There were also very large echidnas (eg. Zaglossus hacketti) and a fewlarge carnivores, like the marsupial lion (Thylacoleo carnifex).As well, there were also known to be at least four giant reptiles,including a goanna and constrictor snake, several carnivorous birds and ahorned land tortoise.

During this period such large forms co-existed with smaller species ofthe same groups and all the giant forms had died out before the end of theperiod (about 10 000 years ago.)

Several suggestions have been made to explain the selection pressureacting on ancestral populations to favour large size. The most commonsuggestions are outlined below.

The climate during the Pleistocene period was often very cold and so thesmall surface area to volume ratio of large animals which regulated theirbody temperature would reduce body heat loss and increase survival.

In Australia, soils were often poor in nutrients and so plant growth mayhave been low and food of poor quality (more indigestible).Large digestive systems, especially those with fermentation chambersfull of micro–organisms, could be carried by large animals, allowingthem to make use of the poor quality of vegetation available. Along withthis, the large animals would also lose less body heat and therefore,require less food anyway.

However, there were also large reptiles (which probably did not regulatetheir body temperature) at the time. The climate during the Pleistocenewas not always cold and similar, small species also successfully survivedand reproduced during the period. These things all highlight the


difficulties of research into the environments, flora and fauna ofAustralia in the past.

Australian megafauna. Drawings of hypothetical reconstructions of someAustralian megafauna species. A species of giant kangaroo is shown alongwith a species of giant herbivorous diprotodont. The human is included for asize reference.

There is also controversy over the reason for the demise of themegafauna. Some scientists maintain that they were hunted and killedby Aboriginal peoples, who were in Australia by between40-60 000 years ago, or that Aboriginal use of fire eventually changedthe vegetation and brought about their extinction. Another theory is thathumans killed off the megafauna and this resulted in a change in thevegetation. As large herbivores were no longer eating the vegetation,very intense bushfires occurred due to the accumulation of fuel.

The Aboriginal peoples were thought to have subsequently adjusted thesituation by regular burning, maintaining grasslands and woodlands,where forests had occurred previously.

Again, because history was not recorded at the time, the theories arebased on indirect evidence, some of which is highly speculative.Many botanists believe that the vegetation changed as a result of climatechange and it seems that no one really knows why the megafauna diedout in Australia.

As part of your syllabus requirements you are asked to gather informationfrom secondary sources to describe some Australian fossils, where thesefossils were found and use available evidence to explain how theycontribute to the development of understanding about the evolution ofspecies in Australia.


If you visit the LMP Science online website there are some good startingpoints for your investigation.

http://www.lmpc.edu.au/science

Below are some famous Australian fossil locations that you could use asa basis for your research.

Riversleigh

Bluff Downs

Murgon

Lightning Ridge

Naracoote

Canowindra

Choose two of these sites, describe two fossils found at the site and givethe age of the fossils. If possible say how each fossil contributes to thedevelopment of understanding. Some examples are given in theAdditional resources section.

Write your answers to the above in Exercise 3.4.


Additional resources

Geological time

Era Period Epoch Time spans(millionyears)

Plant life Animal life

Cenozoic Quaternary Recent(Holocene)Pleistocene

10 000-today2 mill-10 000

first Homosapiens,megafauna

Tertiary PlioceneMioceneOligocene

EocenePaleocene

5-225-5

40-25Australia

drifts north(35-45 mya)

55-4065-55

dominance offlowering plants(Angiosperms)

land dominatedby mammals andbird

Cretaceous 140-65Gondwana

begins to rift(approx. 150

mya)

majorextinctionsflowering plantsexpand non-flowering seedplants (eg.conifers,cycads, seedferns) decline

major extinctionslast dinosaursadaptive radiationof insects

Mesozoic Jurassic 210-140Pangaea rift(approx. 170

mya)

angiospermsevolve non-flowering seedplantsdominant

age of dinosaurs,first birds


Triassic 250-210 non-floweringseed plantsdominant

first mammalsfirst dinosaurs

Paleozoic Permian 300-250 majorextinctions,especiallyprimitive plants

expansion ofreptiles majorextinctions,especiallyamphibians andtrilobites

Carboniferous 360-300 primitive landplants thennon-floweringseed plantsand fernsdominant

age ofamphibians firstreptiles first insectradiation

Paleozoic Devonian 410-360 dominance ofprimitivevascular plantsfirst seedplants

age of fishes firstamphibians firstinsects

Silurian 440-410 first vascularland plants

adaptive radiationof fishes

Ordovician 500-440 marine algaeabundant

first landarthropods

Cambrian 550-500 marine algaecyanobacteria

first fishmost invertebratephyla knowntoday

Neoproterozoic 1,000-550 cyanobacteria early cnidaria,annelids,arthropods andechinoderms

Proterozoic

Mesoproterozoic

1 600-1 000 cyanobacteria first animals

Paleoproterozoic

2 500-1 600atmosphere

rich in oxygen

cyanobacteria

Archaean 4 500-2 500


Australian fossils

Riversleigh

Thylacine

The Thylacine or Tasmanian tiger became extinct in the 1930’s.The fossils at Riversleigh show that the animal was not restricted toTasmania but used to live on the mainland of Australia. The fossils alsoshow that there was more than one type of thylacine. This informationcame too late to save this organism from extinction but it does show thatthe remnant species in Tasmania should have been preserved.

Thingodonta

This fossil marsupial is from the Miocene period. It is unlike anyliving marsupial. It lived in the rainforest and may have eatencaterpillars or eggs.

Canowindra

Fish fossils

A chance discovery during road works exposed the rich Canowindra fishfossils. The first find contained the complete fossils of 100 fish from thelate Devonian. There were four types of fish present. Three of thesewere armoured fish and the fourth was an air-breathing lungfish.

Naracoote cave

Marsupial lion

The marsupial lion was part of the Australian megafauna. It was thelargest marsupial carnivore to live in Australia. It would havehunted other members of the megafauna such as Diprotodon duringthe Pleistocene.

Giant short faced kangaroo

This animal lived during the Pleistocene. It was up to 3 metres in height.It was double the size of the largest kangaroos living today. It had frontpaws that were like hooks. Its back legs had one toe.


The Naracoote fossil site included the period when humans first arrivedin Australia. The climate was changing becoming increasing cooler anddrier. There were however, periods of warmer wetter climatecorresponding to the glacial and interglacial periods.

If you are interested in reading more about the changing environmentsand palaeontology of Australia the following books are a good place tostart. Be warned that some are extremely detailed making the textdifficult to read, but all have great pictures and are interesting to skimthrough to see pictures of fossils and reconstructions of fossil species.Long, Vickers-Rich and Rich and White also present information onplate tectonics with good coloured illustrations.

• Archer, M, Hand, S and Godthelp, H. 1986. Uncovering Australia’sDreamtime. Surrey Beatty and Son, Sydney.

• Archer, M, Hand, S and Godthelp, H. 1996. Riversleigh. The Story ofAnimals in Ancient Rainforests of Inland Australia. Reed, Sydney.

• Augee, M and Fox, M. 1999. The Biology of Australia and NewZealand. Pearson Education, Sydney.

• Gould, E and McKay, G. 1998. Encyclopedia of Mammals 2ndEdition. Weldon Owen, Sydney.

• Long, J A. 1998. Dinosaurs of Australia and New Zealand andOther Animals of the Mesozoic Era. NSW University Press, Sydney.

• MacDonald, D. 1984. The Encyclopaedia of Mammals. Volume 2.George Allen and Unwin, London.

• Strahan, R. 1995. The Mammals of Australia. Reed Books, Sydney.

• Vickers-Rich, P. and Rich, H T. 1993. Wildlife of Gondwana. Reed,Sydney.

• White, M. 1994. The Greening of Gondwana. Reed, Sydney.

• White, M. 1994. After the Greening. The Browning of Australia.Kangaroo Press,


Suggested answers

Environmental change

Period Time span(million years)

Geography Climate Vegetation

Early Cretaceous

Late Cretaceous

140-97

97-65

islands in shallowinland seas

cold, moist cycads andconifers, horsetailsand seed ferns; firstflowering plants

Paleocene-Eocene 65-40 rifting fromAntarctica began;large inland lakes;northern drift ofAustralia

cool rainforestscontaining ferns andconifers but mainlyangiosperms,especiallyNothofagus(southern beechtrees)

Oligocene 40-25 swamp cold, wet first Eucalyptustrees rainforestswith Nothofagus

Early Miocene 25-10.5 sea levels varied hot and coldfluctuations

rainforests dominant

Late Miocene 10.5-5 sea levels fell cold, dry reduction ofrainforests.Sclerophyll forestsincreasingcasuarina species

Pliocene 5-2 raised sea levels wet rainforests thensclerophyll forestswoodlands andgrasslands


Pleistocene 2 million-10000 temperature andsea levelsfluctuated

alternatingicehouse andgreenhouseconditions, morearid

Recent (holocene) 10 000-today arid inland, northdominated bysummer rainfalland south bywinter rainfall.

temperaturesincrease fromsouth to north

Woodland,grassland andshrubland

Origin and radiation of the monotremes1 South American marsupial fossils are older than those in Australia.

There has been a marsupial fossil found in Antarctica and the livingspecies Dromiciops australis has DNA and sperm similarities toAustralian marsupials. These pieces of evidence all give support tothe theory.

2 A greater diversity and older monotreme fossils have been found inAustralia than in south America. However, the numbers of fossilsfound so far are quite low and so there are not really enough data yetto support this theory.


Exercises - Part 3

Exercises 3.1 to 3.4 Name: _________________________________

Exercise 3.1: Evidence of changing environments

Identify and describe three sources of evidence for the changingenvironment in Australia over time.

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Exercise 3.2: The last 100 million years

Describe the general trend in the vegetation of Australia form the non-flowering seed plants in the Cretaceous through to today.

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Exercise 3.3: Comparison between a fossil and livingspecies of the same group.

The two photographs following show the upper skull of a 15 million yearold fossil platypus (Obdurodon dicksoni) and the modern platypus(Ornithorhynchus anatinus) taken from the top (dorsal view) and thebottom (ventral view).

In the modern platypus the teeth are lost in the adult and replaced byhorny grinding pads made up of material a bit like fingernail (one ofthese is seen in the ventral view picture). These pads are worn awayas the food is ground up but they are continuously replaced. The fossilspecies has teeth, although some are missing in the specimen inthe photograph.

Reconstructions of the whole skulls of the fossil and modern platypusesshowing the whole tooth arrangement are shown on the next page.


A: Ventral view

B: Dorsal view

Skulls of the extinct fossil Miocene (15 million years old) platypus, Obdurodondicksoni (top skull), and the modern platypus, Ornithorhynchus anatinus(bottom skull). (Source: Grant, T. 1995. The Platypus. A unique mammal.NSW University Press, Sydney. Plates 14 and 15)

A View from below (ventral) - the sockets for the back teeth are seen inthe fossil skull. One horny grinding pad is in place (upper side; darkin colour) in the modern skull. The other is missing but shows theempty socket where the juvenile teeth have been lost.

B View from the top (dorsal). In both views the long bones extendingforward of the brain case support(ed) the bill.


Drawings made of the fossil (left side) and modern (right side) platypus skulls toinclude all of the features of the skulls and to show the complete set of teeth inthe fossil form (X) and grinding plates in the modern skull (Y).

In each drawing the views in a clockwise order are dorsal (upper), ventral(lower) and lateral (side) views.

(Source: Musser, A M. and Archer, M. 1998. New information about the skulland dentary of the Miocene platypus Obdurodon dicksoni, a discussion ofornithorhynchid relationships. Philosophical Transactions of the Royal Societyof London B 353)

a) Describe the similarities between the two skulls.

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b) Describe the differences between the two skulls.

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c) Changes from the ancestor of Obdurodon dicksoni andOrnithorhynchus anatinus have come about as a result of naturalselection acting on variations during the evolution of the two species.

i) Suggest possible reasons for both having the similarities youdescribed in the skulls of the two species.

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ii) Suggest possible changes to the species’ environments whichcould have resulted in the evolution of the differences in theskulls which you described.

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Exercise 3.4: Named Australian fossils

Name of fossil site 1: _______________________________________

Description and age of fossil 1 ________________________________

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Description and age of fossil 2_________________________________

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Name of fossil site 2:________________________________________


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evolution of australian biota -...

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