The Evolution of Order Diprotodontia 1 Cura, Maris Hazel A. dela Cruz, Haiezel L. de la Rosa, Marianne Michelle Q. Mora, Jonah Feliza B. Panerio, Rafael Julian G. Biology 140 (Evolutionary Biology) – F Sept. 14, 2011 _______________________ 1 A term paper submitted in partial fulfillment of the requirements in Biology 140 under Dr. William Sm. Gruezo
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The Evolution of Order Diprotodontia1
Cura, Maris Hazel A.
dela Cruz, Haiezel L.
de la Rosa, Marianne Michelle Q.
Mora, Jonah Feliza B.
Panerio, Rafael Julian G.
Biology 140 (Evolutionary Biology) – F
Sept. 14, 2011
_______________________
1 A term paper submitted in partial fulfillment of the requirements in Biology 140 under Dr.
William Sm. Gruezo
TERM PAPER (Group 1): Order Diprotodontia | 2
The Evolution of Marsupials in Australia
Outline
I. Introduction
II. Discussion
A. Paleontological History
B. Systematics and Phylogeny of Order Diprotodontia
C. Morphology and Diversification of Order Diprotodontia
D. Speciation of Order Diprotodontia
E. Prediction regarding the fate of Order Diprotodontia and Marsupials in
General
III. Summary and Conclusion
IV. Literature Cited
TERM PAPER (Group 1): Order Diprotodontia | 3
I. Introduction
Marsupials belong to Class Mammalia under Subclass Theria. They possess the general
characteristics of mammals such as warm-bloodedness, presence of mammary glands, presence
of insulating hair or fur, viviparity and dentition for mechanical digestion.
The main distinction of marsupials from other mammals is that they bear live, immature
offspring in their marsupium. The young instinctively finds its way into their mother’s nipple
and remain attached there until it becomes fully developed.
During the late Cretaceous period, the first marsupials appeared in North America. They
slowly dispersed southwards towards Antarctica until they reached present-day Australia where
they now thrive.
There are ten extant orders of
marsupials namely Order
Didelphimorphia, the cat-sized
opossums of South America with scaled
and hairy tails that are arboreal in nature
and are insectivorous or omnivorous in
nature; Order Paucituberculata, the
shrew-like rat opossums which live in
the Andes forests of South America
wherein females of the species lack a
pouch – an odd characteristic in
marsupials; Order Microbiotheria, with
only one extant species - Dromiciops
gliroides; Order Notoryctemorphia, the
blind, sand-digging marsupials which
have pouches opening backwards, which
Figure 1. The extant marsupial orders
TERM PAPER (Group 1): Order Diprotodontia | 4
live underground and feed on insects; Order Dasyuromorphia, the most carnivorous marsupials
with hairy tails, ranging in size from the size of a mouse to dog; Order Peramelemorphia, the
terrestrial and insectivorous or omnivorous bandicoots and bilbies which are native to New
Guinea and Australia, having pouches which contain the nipples; Order Caenolestidea, nocturnal
rat-sized creatures which may be insectivorous or carnivorous; Order Polyprotodontia, the
known scavengers or omnivores; Order Peramelina, the herbivorous, root-feeding, hopping rat-
sized creatures that live underground; and Order Diprotodontia, the herbivorous endemics of
Australia, which will be the focus of our report.
II. Discussion
A. Paleontological History
The evolutionary history of marsupials is one of the most interesting topics for
scientists; that continuous researches are still held to shed light into their history until today.
One of the products of these endless excavations for answers about their history was the
fossil found in China, specifically in the rocks of the Yixian Formation in Liaoning Province,
by a team of scientists including Zhe-Xi Luo and John Wible, last 2003; and this fossil is
called the Sinodelphys. The Sinodelphys which is about the size of a chipmunk were believed
to have climbed trees. It dates from 125 million years ago (Early Cretaceous Period) and it is
believed to be an early ancestor of the marsupials, since it share many features with the
modern marsupials. This discovery also suggests that marsupials may have originated in
Asia, dispersed in North America, and later migrated to present-day South America. But this
migration eventually took the marsupials to Antartica and Australia, which were believed to
have been united on the ancient landmass, Gondwanaland (MS Encarta, 2006).
TERM PAPER (Group 1): Order Diprotodontia | 5
Figure 2. Fossils found in China, the Sinodelphys.
In 1982, scientists identified the only fossil of a land-dwelling mammal in Antartica
as a marsupial and it lived for about 40 million years ago. This fossil then confirmed, the
migration of marsupials from South America, where other fossils of marsupials dating 65
million years ago was found, to Antartica and then to Australia, their final destination, where
marsupial fossils dating 25 million years ago were found (MS Encarta, 2006).
But the Alphadon is the earliest marsupial ever recorded. Its remains were found in
North America about 80 million years ago, during the Cretaceous period.
Figure 3. Tooth remains of the earliest marsupial ever recorded, Alphadon.
TERM PAPER (Group 1): Order Diprotodontia | 6
The earliest known fossil of the order is from the Late Oligocene. Hypsiprymnodon
bartholomaii from the Early Miocene is the earliest identified species.
Another fossil of the marsupials, specifically of the Diprotodonts is the Diprotodon. It
is a genus of an extinct, giant marsupial, which is closely related to kangaroos. The fossils of
this marsupial, is found in Australia among Pleistocene deposits. Like the kangaroo, they
were herbivorous, but unlike the kangaroo, they used all four legs for walking. The skull of
the Diprotodon was heavy and less than 1 m (about 3 ft) long; the entire animal was about
the size of a rhinoceros. Diprotodon australis is the only known species of this genus. A
related genus, Nototherium (the bones of which are often found with those of the
Diprotodon), was also a giant marsupial. (MS Encarta, 2006)
Figure 4. Diprotodon Fossil.
B. Systematics and Phylogeny of Order Diprotodontia
The Order Diprotodontia is the largest order of marsupials. This order represents 11
families and over 110 species, which includes kangaroos, wallabies, possums, koalas, gliders
and wombats. Order Diprotodontia is an order which is very diverse in terms of size and
habitat. But this order also contains a family of giant diprotodonts that are now extinct
TERM PAPER (Group 1): Order Diprotodontia | 7
Figure 5. Phylogenetic Tree of Order Diprotodontia
The organisms under the Order Diprotodontia share two basic characteristics. These two
characteristic includes the possession of enlarged lower incisor teeth that project forward and an
integument that binds together the second and third digits of their hind feet.
The diversity of species within Diprotodontia is greatly demonstrated by the size range of its
largest and smallest species. And so, along their sizes, their diet is also diversified. Most of the
order is herbivorous but some species prey on invertebrates and small vertebrates. Another point
of diversity within the order is the methods of locomotion. Since some species glide through the
tree tops while the others leap along the grasslands.
C. Morphology and Diversification of Order Diprotodontia
Diversification
In the southern super-continent Gondwanaland, the first mammals with the distinctive
mode of reproduction exhibited by marsupials arose. After the super-continent broke up into
separate continents, marsupial ancestors were separated from placentals and became isolated