BIOLOGY IN FOCUS
EVOLUTION OF AUSTRALIAN BIOTA
Chapter 1 Australia’s past: part of a supercontinent
i˜`>Ê
,7ÊÊ-Ìi«…>˜ˆiÊ"-
PRELIMINARYCOURSE
Changing ideas in science—the platypus enigma
■
identify data sources, gather, process and analyse
information from secondary sources and use available
evidence to illustrate the changing ideas of scientists in
the last 200 years about individual species such as the
platypus as new information and technologies became
available
")/,/'9
). &/#53
Linked to
page 250
Task 3 Information that you should gather, process and analyse
Table CD1.1 Impact of technology on knowledge and understanding (PFA P3)
KNOWLEDGE AND UNDERSTANDING
THEN
PAST: at the time of the discovery of the
platypus by natural scientists (1798–1800s)
NOW
CURRENT:
IMPROVEMENT in (progressive accumulation of) knowledge and understanding:
TECHNOLOGY
Identify technology and outline its uses and limitations)
(Identify
THEN
PAST: at the time of the discovery of the
platypus by natural scientists (1798–1800s)
NOW
CURRENT: technology (outline
outline three ways in
which technology was used for current research)
IMPROVEMENT (advance) in technology:
1
Copyright © 2008 McGraw-Hill Australia. Permission is granted to reproduce for classroom use.
BIOLOGY IN FOCUS
Suggested resources
Books
Moyal, A. (2002) Platypus: The extraordinary story of how a curious creature baffled the world.
Allen & Unwin, Crows Nest, Australia.
This book makes for entertaining reading. It is written in clear language that is easy to understand
and will be enjoyed by both teenagers and adults. It tells a fascinating story of how the discovery
of the platypus and its classification challenged the problem solving skills of scientists. As the story
unfolds the reader gains a good feel for the nature and practice of science.
Websites
www.science-frontiers.com/sf075/sf075b08.htm
A reader-friendly article outlining Ann Moyal’s findings in her book Platypus. Very informative in
terms of historical developments in the classification of the platypus.
www.chemistrydaily.com/chemistry/Platypus#Scientific_history
www.wisenet-australia.org/issue59/Controversy-the%20platypus.htm
www.medicine.utas.edu.au/research/mono/Taspaper.html
These websites have interesting technological information related to studies of the platypus.
Scientific journals
Bethge, P, Munks, S, Otley, H and Nicol, S (2004), ‘Platypus burrow temperatures as a subalpine
Tasmanian lake’, Proceedings of the Linnean Society of New South Wales, 125, pp 273–6
Grigg, GC and Beard, LA (2001), ‘Radiotelemetry of echidnas and platypus’, 15th International
Conference on Biotelemetry, May 9–14, 1999, Juneau, Alaska, pp 493–500
Grigg, GC, Beard, LA, Grant, TR and Augee, M, ‘Body temperature and diurnal activity patterns
in the platypus (Ornithoryhnchus-Anatinus) during winter’, Australian Journal of Zoology, 40(2),
pp 135–42
Henning, S, Langner, G, Tidemann, C, Coles, RB and Guppy, A (30 January 1996),
‘Electroreception and electrolocation in platypus’, Nature, 319, pp 401–2
2
Copyright © 2008 McGraw-Hill Australia. Permission is granted to reproduce for classroom use.
BIOLOGY IN FOCUS
Answers
Task 3 Information that you should gather, process and analyse
1. Outline ideas held 200 years ago about the platypus and its relationship to other
individual species.
(a) Use the background information above and the information in Tasks 1 and 2
to answer this question relating to the platypus specifically.
1790: Specimens of the platypus sent to Britain were thought to be fake.
1800–1830s: Platypus was alternately placed in different groups (Reptiles, Birds
and Mammals) as taxonomists continued to debate their particular points.
■ Structurally, it appeared to be a ‘transitional form’—an ‘intermediate’ species
somewhere between the three groups:
—reptilian features: poison gland (similar to poison fangs, e.g. snakes)
—bird-like features: bill, webbed feet
—mammalian features: hair on body
■ Reproduction: unknown?
—Most people thought it produced eggs that developed inside the female’s
body, like some reptiles: Was it ovoviviparous? (Scientist Richard Owen
seemed to think so.)
■ Suckled its young? (Mammary gland tissue found, as a result of dissections by
Richard Owen, certainly suggested this.)
(b) Also research the knowledge that the Aboriginal people had about the
platypus at that time.
Aboriginal people at the time had longstanding knowledge of the platypus and
its reproductive habits—they knew and informed scientists that it suckled its
young and that it laid white eggs—scientists at the time were fairly dismissive
of the indigenous people and their evidence was misinterpreted and ignored.
2. State the main difficulty involved in trying to classify the platypus.
Was it a hoax—a mythological beast? Once scientists established that it was not,
they were faced with the problem of placing it into a classification group:
■ Was it, as its brown pelt suggested, a mammal?
■ Or did its webbed feet make it a reptile (amphibians were grouped as reptiles
at the time)?
■ Did its duck-like bill mean it was part of the warm-blooded bird group?
3. Research the work of scientists in trying to solve the problem of platypus
classification and evolution:
(a) hypotheses posed (see hypotheses listed in Task 2)
Hypotheses
■ The platypus gives birth to live young. False
■ The body temperature falls rapidly when a platypus swims and it has to
return to its burrow to warm up. (Radiotelemetry used to measure platypus
temperature and data loggers used to measure burrow and water temperatures.)
False
■ The platypus is a rare species (studies used tagging, monitoring, radio-tracking
and reporting on platypus sightings). True
■ The platypus has more sets of chromosomes than mammals do; its
chromosomes may be more similar to those of birds or reptiles. (Microscopic
examination of chromosomes: research at Monash University.) True
3
Copyright © 2008 McGraw-Hill Australia. Permission is granted to reproduce for classroom use.
BIOLOGY IN FOCUS
■
■
■
■
■
The platypus does not rely on vision, but on specialised sensory perception
to locate food underwater. (Website search hint: type ‘electroreception in
monotremes’ into your search engine.) True
The platypus as we know it is not a ‘primitive’ animal; it has evolved from
an ancestral form. True
Platypus fossil ancestors such as Obduron lived before Gondwana split.
True
Fossilised platypus ancestors may occur in southern continents other than
Australia. True
Studies of evolutionary relatedness show that monotremes (such as the
platypus) are more closely related to marsupials than to placental mammals.
(Research involves analysis of nuclear DNA and mitochondrial DNA.) False?
(Disagreement between mtDNA and nuclear DNA studies.)
The answers to Questions 3 b, c and 4 involve gathering the content material
needed to answer Question 5. Once this information is analysed it should be
recorded in the table provided on the Student Resource CD, to make answering
Question 5 simpler. To avoid repetition, sample answers to these questions
are given very briefly, and a detailed outline of the information that should be
recorded in the table is given instead.
(b) evidence collected and technology used (research each hypothesis and
briefly outline the technology used and the scientific findings for each)
(See Table PFA P3 on next page.)
(c) conclusions drawn
(See Table PFA P3 on next page.)
4. Outline the ‘new idea’ in science—how the platypus is classified today compared
with the confusion of 200 years ago.
The platypus is definitely classed as a Mammal, but belongs to the group
Monotremata—an unusual group of mammals that have one common opening
(a cloaca) from the reproductive, excretory and digestive tracts. The only other
organisms that belong to this group are the echidnas. Monotremes are egg-laying
mammals, as opposed to marsupials and placental mammals which give birth to
live young. The platypus is also thought to be a highly evolved organism, rather
than a remnant of a primitive species.
5. Putting it all together: explain how the ideas of scientists changed and how
technology helped scientists to gather evidence to support their current
conclusion.
The sample answer in the table below is very detailed—beyond what one would
expect at a student level. This level of detail has been included to assist teachers
to understand this complex area of research. A good student answer should
demonstrate an understanding of ‘THEN’:
■ the lack of knowledge about platypus reproduction and behaviour when it was
first discovered
■ one or two difficulties classifying it
■ the lack of technology then.
4
Copyright © 2008 McGraw-Hill Australia. Permission is granted to reproduce for classroom use.
BIOLOGY IN FOCUS
They should demonstrate a knowledge of the technology that developed to allow
progression to what we know ‘NOW’:
■ technology
—improved microscope techniques
—use of radio transmitters and electronic equipment (data loggers)
—biochemical studies (DNA, genes and chromosomes)
■ understanding now:
—The platypus is a mammal.
—The platypus is highly evolved and not a primitive relict.
Sample answer:
PFA P3: Impact of technology on knowledge and understanding
KNOWLEDGE and UNDERSTANDING
THEN
PAST: at the time of the discovery of the
platypus by natural scientists (1798–1800s)
General
■ Late 18th and early 19th century:
—scientists were refining the classification
systems
—evolution was not commonly accepted by
scientists
—Amphibians, Reptiles, Birds and Mammals
were all considered to be unrelated
groups.
Platypus studies
■ 1790: strange mixture of characteristics =
hoax (fake)
■ 1800–1830s, scientists disagreed on its
classification:
—Reptile? Poison glands (similar to ‘fangs’
of reptiles) and ovoviviparous?
—Bird? Bill and webbed feet?
■ Mammal? Mammary glands present and
body covering of fur.
■ 1836: Darwin observed the platypus and
queried ‘two creators’—contributed to his
idea of evolution.
■ 1884: William Caldwell discovered, with
the help of Aboriginal people, an egg-laying
platypus (i.e. oviparous).
■ Thought the platypus was a ‘primitive’ animal
(‘living fossil’) or ‘transitional form’.
NOW
CURRENTLY:
General
■ Scientists recognise that classification
systems are created (products of the
human mind) and therefore can and must
be changed if new organisms are discovered
that do not fit the old systems.
■ The idea of evolution is supported by a large
amount of scientific evidence.
Platypus studies
■ Platypus is a mammal that belongs to a
different order—monotremes—which have
only one opening for both the reproductive
and excretory systems (found in echidnas
and in beavers), different from other
mammals.
■ Mammals lay eggs, suckle their young, and
regulate their body temperature internally.
■ Their bill has a highly advanced
electroreceptor sensory organ, indicating
that the platypus is not a primitive ‘living
fossil’ or a ‘transitional form’, but a highly
evolved modern-day animal much more
advanced than the fossil forms found to
date back to over 100 million years ago.
■ Results of recent DNA studies disagree
about whether the platypus is closer to
eutherian mammals (cows, humans, etc.)
or to marsupials (kangaroos, koalas).
Improvement in knowledge and understanding:
Advances have been made in the understanding of the classification of the platypus and its ancestral
beginnings. It is no longer thought of as a primitive remnant or a transitional form, but rather as
a ‘great survivor’ which left the mainstream of mammalian evolution long ago to evolve into the
advanced, unique animal known today.
continued . . .
5
Copyright © 2008 McGraw-Hill Australia. Permission is granted to reproduce for classroom use.
BIOLOGY IN FOCUS
TECHNOLOGY
(Identify
Identify technology and outline its uses and limitations)
THEN
PAST: at the time of the discovery of the
platypus by natural scientists (1798–1800s)
■ Early 1800s: observation and dissection
■ 1884: William Caldwell—observation; he
communicated with Britain via telegraph
(that the platypus is egg laying)
■ 1927: Burrell suggested a ‘sixth sense’ for
capturing food, based on observation
NOW
CURRENT: technology (outline
outline three ways
altogether, in which technology was used for
current research)
■ 1973: suggested platypus could not regulate
body temperature as precisely as other
mammals—data loggers used—later found
truly mammalian thermoregulation
■ 1980s: fossilised jaw of 110 million year
old platypus found, suggesting it was an
ancestor of the modern day ‘great survivor’.
■ 1988: Studies of chromosomes
—advanced microscope techniques and
genetic fingerprinting showed that their
chromosomes resemble those of reptiles
(they have both large chromosomes and
micro-chromosomes, Griffiths, 1988)
—use of fluorescent markers to stain
chromosomes; discovered platypus has ten
sex chromosomes instead of the normal
two in mammals. This arrangement of sex
chromosomes is characteristic in some
mammals and birds (www.chemistrydaily.
com/Platypus#Scientific_history and
www.wisenet-australia.org/issues59/
Controversy-the%20platypus.htm)
—radiotelemetry, implanted transmitters to
track and record body temperatures year
round (Grigg, Gordon and Beard, 2001)
—use of data loggers to determine
behavioural patterns; genetic fingerprinting
and fluorescent studies of chromosomes
to find genetic distances in relatedness
of existing species of platypus
(www.medicine.utas.edu.au/research/
mono/Taspaper.html)
■ 1990s: discovered electroreception in
platypus bill:
—experiments where platypus would seek
and attack immersed, hidden batteries
—use of cathodal currents to activate
receptors and mimic electric fish
—use of electrical fields in studies.
Studies of mitochondrial DNA to determine its
relatedness to other mammals contrast with
those of nuclear genes. Palaeontology and
nuclear gene studies show that the platypus is
closer to placental (eutherian) mammals than
marsupials, but mtDNA shows the opposite.
continued . . .
6
Copyright © 2008 McGraw-Hill Australia. Permission is granted to reproduce for classroom use.
BIOLOGY IN FOCUS
IMPROVEMENT (advance) in technology:
Scientists 200 years ago were limited by the lack of technology available and had to rely on
observation and their dissection skills to determine the classification of the platypus based on
comparative anatomy of structural features and type of reproduction. Advances in technology have
led to enormous progress in the understanding of the structure, reproduction and behaviour of the
modern day platypus, revealing it as a highly advanced evolved animal with an electrosensory system
that suggests a very different path of evolution. However, modern-day technology has still not reached
the point where it is irrefutable—the problem of relatedness amongst mammals continues.
Additional note to teachers on DNA technology
Mitochondria, the cell’s energy-producing organelles, have their own genes that are
inherited through the maternal line. Scientists use mtDNA fingerprinting because
mtDNA is more accessible, easier to sequence, and all multicellular animals have
mitochondria, whereas all animals do not share the same nuclear genes.
Using large nuclear genes for molecular evolutionary studies has its advantages:
the genes are very large; a gene such as the insulin-like growth factor II receptor
(IGF2R) is shared by all mammals and is even present in fish and molluscs; and
it provides critical information on the evolution of a genetic phenomenon called
imprinting, giving large amounts of statistically meaningful data for determining
the evolutionary relationship between mammals.
7
Copyright © 2008 McGraw-Hill Australia. Permission is granted to reproduce for classroom use.