This document discusses the classification of mammals. It begins by covering the subclass Prototheria, including the characteristics and two surviving orders - Monotremata which includes the platypus and echidnas. The subclass Theria is then discussed, including the infraclass Metatheria which contains the order Marsupialia. Key details are provided on the characteristics of marsupials, including their short gestation periods and young rearing their young in pouches. Examples like koalas and opossums are provided. Their geographic ranges and habitats are also summarized.

1. Naveed Akhtar
Assistant Professor of Zoology
Punjab Higher Education Department

2. General Characteristics of
Mammals

3. Classification of Mammals

4. Classification of Mammals
 Many earlier ideas have been completely abandoned by
Linnaeus and modern taxonomists, among these are the
idea that bats are related to birds or that humans represent
a group outside of other living things.
 Mammalian classification has been through several
iterations since Carl Linnaeus initially defined the class.
 Most significantly in recent years, cladistic thinking has led
to an effort to ensure that all taxonomic designations
represent monophyletic groups.
 The field has also seen a recent surge in interest and
modification due to the results of molecular phylogenetics.

5. Conti…
 Mammals are actually a class organized into 5420 species;
which are further sub-classified into 135 families, 1,000
genera, 29 orders, and 2 subclasses.
 While studying these subclasses, we come to know several
mammals that were parted some 200-million years ago.
These primitive mammals include egg-laying Prototheria
(platypus and echidnas being the only survivors) along
with live-bearing theria.
 George Gaylord Simpson's[1945] "Principles of
Classification’’ laid out a systematics of mammalian origins
and relationships that was universally taught until the end
of the 20th century.

6.  Though field work gradually made Simpson's classification
outdated, it remained the closest thing to an official
classification of mammals. Various trials have been made
to classify mammals
 Molecular classification
 Standardized classification
 McKenna/Bell classification
 Luo, Kielan-Jaworowska, and Cifelli classification
 Simplified classification
 No classification system is universally accepted; McKenna
& Bell (1997) and Wilson & Reader

7. Standardized classification

8. Cladistics Analysis

9. 1. Subclass Prototheria

10.  Subclass Prototheria (proto-thir ee-a) (Gr. pr|tos, first, thƒr, wild animal).
 Cretaceous and early Cenozoic mammals.
 Extinct
 Some zoologist classify mammals into two majjor groups;
 1. Prototheria: Egg laying mammals that have cloaca throughout life
 2. Theria: Give birth to young
 Infraclass Ornithodelphia
 (orni-tho-delfee-a) (Gr. ornis, bird, delphys, womb). Monotreme mammals
 Order Monotremata
 (monotrema-tah) (Gr. monos, single, trƒma, hole): egg-laying
(oviparous) mammals
 Living prototherians are placed in the monotreams
 Duckbilled platypus, spiny anteater

11.  Three species in this order are from Australia, Tasmania,
and New Guinea.
 The most noted member of the order is the duck-billed
platypus (Ornithorhynchus anatinus).
 The spiny anteater, or echidna (Tachyglossus), has a long,
narrow snout adapted for feeding on ants, its chief food
 Recent fossil evidence showing monotreme dentition that
is characteristic of the subclass Theria has resulted in this
group being reassigned to the latter subclass. The
Prototheria, therefore, contains only extinct forms

12. Characters of Subclass Prototheria
 Shelled Yolky Eggs:
 Mammals that lay eggs with leathery shells and nourish the young ones
with milk from primitive(open) mammary glands.
 Single Cloacal Opening:
 They possess a cloaca like reptiles, have no urinary bladder
 Lack of Teeth:
 Modern monotremes lack teeth as adults; sutures are hard to see; the
rostrum is elongate, beak-like, and covered by a leathery sheath; and
lacrimal bones are absent.
 Testes:
 Testes are confined to the abdominal cavity
 Absence of The Corpus Collosum)
 Brain lacks thre transverse fiber track in brain (The Corpus
Collosum) that connect two cerebral hemispehere in all other
mammals

13.  Monotremes have several important mammalian characters,
however, including fur (but they lack vibrissae), a four
chambered heart, a single dentary bone, three middle ear bones
with larger Incus and Malleus, and the ability to lactate.
 Lack of Nipples:
 They have no nipples, milky fluid exudes from modified sweat glands
onto tufts of hairs in shallow pits of abdomen, from which young lick it
up
 Endothermy:
 Monotreams are endothermic but their body temperature is less stable
than other mammals
 5 species in 2 families in Order Monotremata Earliest
monotreme: 125 mya Teinolophos
 Geographic Range

14.  Duckbills live in pairs in burrows up to 18 m long, in the banks of the creeks
and rivers and spend their most life in water.
 Prototherians are either terrestrial (Tachyglossidae) or primarily aquatic
(Ornithorhynchidae
 Their terrestrial habitats include deserts, sandy plains, rocky areas, and forests
in both lowlands and mountains.
 Platypuses inhabit lakes, ponds and streams; they shelter in burrows along the
banks and spend much of their time foraging in the water.
 They possess web feet to move in water and beaklike muzzle fro detection of
the prey especially mollusks
 During breeding season, female construt nest near water where it lays
eggs of 2 cm diameter and incubate them for 10 to 14 days
 Echidna:
 The spiny anteater, or echidna (Tachyglossus), has a long, narrow snout
adapted for feeding on ants, its chief food

15.  Geographic Range: Monotremes are restricted to
Australia and New Guinea. Their fossil record is very
poor; the earliest fossil attributed to this group is from
the early Cretaceous.
 A fossil from Argentina suggests that the monotremes
were more widely distributed early in their history

16. Classification of Monotreams

17. A duck-billed platypus (Ornithorhychus
anatinus).

18. An echidna or spiny anteater (Tachyglossus
aculeatus)

19. 2. SubClass Theria
 SubClass Theria(Gr. thƒr, wild animal)
 Theria is a subclass of mammals amongst
the Theriiformes.
 Theria includes the eutherians (including
the placental mammals) and
the metatherians (including the marsupials)

20. 2.1 Infraclass Metatheria
 Order Marsupialia
 viviparous pouched mammals: opossums, kangaroos,
koalas, Tasmanian wolves, wombats, bandicoots,
numbats, and others
 These mammals are characterized by an abdominal
pouch, the marsupium, in which they rear their young
 The young are nourished in the uterus for a short time
by way of a yolk-sac placenta.
 Only the opossum is found in the Americas, but
the order is the dominant group of mammals in
Australia; 260 species

21. The koala (Phascolarctos cinereus)
feeds on Eucalyptus leaves in Australia.
An opossum (Didelphis
marsupialis) with young

23. General Characters
 Yolky Placenta:
 Marsupials possess fetal yolk sac (in contact with chorion) which
serve as placenta
 Marsupium
 They are viviparous but have very short gestation periods.
 The young crawl into the marsupium after birth, where they
feed and complete development
 In marsupials, the mammary glands, which vary in number, are
located within the pouch and terminate in a teat.
 The mother may nurse two offspring, differing widely in age,
simultaneously from different mammary glands that secrete milk
of very different composition, designed to meet the different
specific requirements of each offspring

24.  The wall of the marsupium are supported by two
bones(epipubic) that project from the pelvic girdle
 live in the Australian region and the Americas
 Marsupials (and monotremes) also lack a gross
communication (corpus callosum) between the right
and left brain hemispheres

25.  Geographic Range and Habitat:
 The largest and most-varied assortment of marsupials—some
200 species—is found in Australia, New Guinea, and
neighbouring islands, where they make up most of the native
mammals found there.
 In addition to larger species such
as kangaroos, wallabies, wombats, and the koala (Phascolarctos
cinereus), there are numerous smaller forms, many of which are
carnivorous, with the Tasmanian devil (Sarcophilus harrisii)
being the largest of this group (family Dasyuridae).
 About 70 species live in the Americas, mainly in South and
Central America, but one, the Virginia opossum (Didelphis
virginiana), ranges through the United States into Canada.

26.  The niches that marsupials fill are closely associated with
structure. The burrowing species, such as the marsupial
moles (Notoryctes typhlops and N. caurinus) and the wombats,
have powerful foreclaws with which they can tunnel into the
ground for food and shelter.
 Terrestrial forms, such as kangaroos and wallabies, possess well-
developed hind limbs that serve both as formidable weapons and
as catapults by which they can bound over the plains.
 The gliders have a membrane along either flank, attached to the
forelegs and hind legs, that enables these arboreal animals to
glide down from a high perch.
 A few marsupials—such as tree kangaroos, koalas, and
some cuscuses—spend most of their lives in trees. The water
opossum, or yapok (Chironectes minimus), of Central and South
America is semiaquati

27.  Morphology:
 he largest living marsupial is the red
kangaroo (Macropus rufus), males of which can grow
to about 2 metres (6.6 feet) in height, 3 metres (10
feet) from muzzle to tail tip, and a weight of up to 90
kg (about 200 pounds).
 The smallest are the planigales, especially the long-
tailed planigale (Planigale ingrami), measuring barely
12 cm (4.7 inches) in total length. Most marsupials
range from the size of a squirrel to that of a medium-
size dog.

28. Smallest Marsupial (Planigale ingrami)

29.  The diets of marsupials are as varied as the niches they occupy.
Many dasyurids live chiefly on insects and other small
animals. Dunnarts (Sminthopsis) are so hyperactive—
like shrews—that, in order to supply their high energy needs,
they must devour their own weight in food (chiefly insects) each
day.
 The numbat uses its remarkable wormlike tongue to lap up
termites and ants. Many Australian possums, bandicoots, and
American opossums have a mixed diet of plants and insects.
Wombats and many other marsupials are strictly vegetarian.
 The small honey possum (Tarsipes rostratus) is specialized to
feed on the nectar of flowers, and other marsupials also may
serve as important pollinators in that way. Few
large carnivores have ever evolved in Australia, because of the
low productivity of its

30.  Reproduction and Development:
 The life cycle of marsupials exhibits peculiarities that have
long been considered primitive compared with those of
placental mammals but are more likely adaptations to low-
productivity environments.
 The uterine cycle of the female marsupial has no secretory
phase, and the uterine wall is not specialized
for embryo implantation, although a
transitory placenta does exist in the bandicoots.
 The period of intrauterine development in marsupials
ranges from about 12 days in the bilby (Macrotis lagotis)
to 38 days in the swamp wallaby (Wallabia bicolor).

31.  The young, born in a vulnerable embryonic condition,
make their own way to the shelter, warmth, and
nourishment of the pouch; in pouchless marsupials the
young simply cling to the teats.
 Those fortunate enough to survive that hard journey may
succeed in attaching themselves to the mother’s nipples,
which then swell and become firmly fastened—almost
physically fused—to the mouth tissues of the young.
 In that condition the young continue their development for
weeks or months, after which they are weaned and begin to
look after themselves.
 Frequently, the partially developed young outnumber the
available teats, and the excess individuals perish.