LABORATORY PRACTICAL 3:
Comparison between a fossil and living species of the same group.
OBJECTIVE 2(c): PERFORM A FIRST-HAND INVESTIGATION, GATHER INFORMATION OF NAMED AUSTRALIAN
FOSSIL SAMPLES AND USE AVAILABLE EVIDENCE TO IDENTIFY SIMILARITIES AND DIFFERENCES BETWEEN
CURRENT AND EXTINCT AUSTRALIAN LIFE FORMS.
The two photographs show the upper skull of a 15 million year old fossil platypus (Obdurodon dicksoni) and
the modem platypus (Ornithorhynchus anatinus) taken from the top (dorsal view) and the bottom (ventral
view).
Reconstructions of the whole skulls of the fossil and modem platypuses showing the whole tooth arrangement
are shown.
In the modem platypus the teeth are lost in the adult and replaced by horny grinding pads made up of material
a bit like fingernail. These pads are worn away as the food is ground up but they are continuously replaced.
The fossil species has teeth, although some are missing in the specimen in the photograph.
A: VENTRAL VIEW
B: DORSAL VIEW
Skulls of the extinct fossil Miocene (15 million years old) platypus, Obdurodon dicksoni (top skull), and the modern platypus, Ornithorhynchus
anatinus (bottom skull). (from 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 in the fossil skull. One homy grinding pad is
in place (upper side; dark in colour) in the modem skull. The other is missing but shows the empty socket where the
juvenile teeth have been lost.
B
View from the top (dorsal). In both views the long bones extending forward of the brain case support(ed) the bill.
Drawings made of the fossil (left side) and modern (right side) platypus skulls to include all of the features of the skulls
and to show the complete set of teeth in the 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. (from Musser, A
M. and Archer, M. 1998. New information about the skull and dentary of the Miocene platypus Obdurodon dicksoni, a discussion of
ornithorhynchid relationships. Philosophical Transactions of the Royal Society of London B 353)
ACTIVITY: Answer the following questions in full sentence form. The following sites may be helpful, as well as other sources.
http://www.amonline.net.au/search.cfm?searchstring=platypus put “platypus” into the Search Box.
Digimorph - Obdurodon dicksoni (fossil platypus)
Obdurodon - Wikipedia, the free encyclopedia
Think about the best and most efficient method of answering the following questions.
Should take no more than one page.
a) Describe the similarities between the two skulls.
b) Describe the differences between the two skulls.
Changes from the ancestor of Obdurodon dicksoni and Ornithorhynchus anatinus have come about as a result of natural selection
acting on variations during the evolution of the two species.
c) Suggest possible reasons for both having the similarities you described in the skulls of the two species.
d) Suggest possible changes to the species' enviromnents which could have resulted in the evolution of the differences in the skulls
which you described.
e) What other information about the species' environments would you wish to research in an attempt to support your suggestions?