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Description of Rats as a mammal
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0% found this document useful (0 votes)
99 views14 pagesRat As A Mammal
Description of Rats as a mammal
Uploaded by
faborodeharyomideCopyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF or read online on Scribd
/ 14
ZOO 102: ORGANIZATION OF MAMMALIAN BODY
LECTURE 1
RAT AS AMAMMAL
ORIGIN OF MAMMALS
INTRODUCTION
Animals belonging to the Class Mammalia are referred to as mammals. They are
chordates, possessing a notochord manifested by the vertebral column in adults.
Characteristically, they are animals with well developed milk producing mammary
glands and they exhibit elaborate care of their young ones which are born alive, except
in the extremely primitive ones which are egg layers. Although there are other features
possessed by marhmals, the ones mentioned here distinguish them from other animals.
Other features would be discussed later.
PHYLOGENY
Mammals evolved from reptiles. Their phylogenetic relationship with the existing
reptiles are however hardly traceable, This is because the reptilian subclass which gave
rise to mammals — The Synapsida ~ diverged early on the evolutionary tree. The
relationship of mammals to the synapsids can therefore only be traced using fossil
records.
‘The catastrophe which befell the dinosaurs some 65 million years ago and led to their
extinction gave a chance for the rapid evolution and success of mammals. While the
ysaurs existed they dominated the surface of the earth such that the mammals
existing at that time were mainly insectivorous, unnoticeable shrew-like animals that
foraged for food at night while the dinosaur had become inactive since they were
iurnal. The large mammals were therefore non-existent.
That was the status quo until the extinction of the dinosaurs following which the
surviving mammals suddenly became grazers, browsers and predators, and they
evolved along different ines.
The first mammals appeared some 230 million years ago. This coincided with the time
the dinosaur started dominating the earth. These mammals were distinct from their
reptilian ancestors and co-inhabitants of the earth in that their body was covered with
a coat of hairs called fur. The fur, being an insulator, provided warmth for the mammal,
‘an essential condition for its warn-blooded nature (Woodward, 1988).
‘Among the reptiles, the direct antecedent to mammals were the Pelicosaurs, a group
which lived in the carboniferous and early Permian periods (that is 340 ~ 260 million
years ago).
‘These were extremely primitive reptiles, Notable among them, however, is ophiacodon
which shows striking features that indicates its ancestry with mammals. Such
characters are in the skull structure, including the presence of a single opening in the
temple region of the skull. These pelicosaus were succeeded in the late Permian and
the early Triassic (that is some 225 milion years ago) by the therapsids.
The therapsids were carnivores and active foursfooted runners. They had their elbow
and knee swung in towards the body as in their contemporary descendants. The
advantage of this arrangement is that it makes for better support and speed. In the
advanced Triassic species features such 2s skull, jaw, dentition and limbs closely
resemble the mammalian pattern, one of these mammal like reptiles called Lycaenops
was discovered in the later Permian of South Africa
‘Scanned with CamScanner Intelligent activity alertness and the aforementioned characteristics of mammals were
developed during the period of domicile under the dinosaurs.
EVOLUTION AMONG MAMMALS
From the ancestral therapsids, evolution of mammals have taken place gi
animals of different forms and habits. in this regard there are three m:
evolution. They are presented here in order of evolution and advancement.
The Prototheria: these are the first to evolve from the therapsids. They are also called
monotremes. They appeared in the Jurassic period, some 180 million years ago. TheY
are the most primitive among mammals. These animals are restricted to Australia and
have only two surviving members namely the Duck-bill platypus and the Spiny ant—
eaters. .
ing rise to
n limes of
The monotremes bear many characters which are diagnostic of mammals. They
however retain certain features of their primitive reptilian stock, notably oviposition
(egg-laying).
The duck-bill is somewhat “amphibious” being semi-aquatic. Its feet are webbed, its
body covered with for and it frequent strews where it hunts for snails and mussels. The
ant-eater on the other hand is has its body covered with protective spiny hairs. It is
endowed with powerful clawed feet which endears its remarkable digging ability and
making it effective hunter of subterranean termites. One attribute common to the
monotremes is that thy both make nests in borrows where the shelled eggs are
hatched and the hatchlings are nursed. Also they are toothless as adults. In the duck-bill,
the teeth are replaced by flat and duck-like horny bills while slender horny bills take
place of teeth in the adult ant-eater.
The Metatheria: These are also called the marsupials or pouched mammals. They are
more advanced than the monetremes. They evolved in the early cretaceous (that is
about 130 million years ago) coinciding with the extinction of the dinosaurs. The
marsupials give birth to live offspring, the young are born tiny and immature. Typically
therefore, the females posses a pouch on their bellies where the newborn are nursed
for some time after birth. The marsupials lack placentas needed to nourish the foetus
during gestation (pregnancy). They are therefore primitive mammals. Examples of
marsupial include the Opossum the Tasmanian wolf, the Kangaroos and so on. The
marsupials are found in Australia, although the opossum is also found in the Americas.
Some marsupials such as the kangaroos aré herbivores while others like the Tasmanian
wolf are carnivorous.
‘The Eutheria: these are the placental mammals simply called the placentals. They are
regarded as the true mammals. They contrast sharply with marsupials in that they
possess the placenta — an nutritive connection between the mother and the foetus
during gestation. This enables the foetus to develop to a much more advanced stage
before parturition (birth). The placentals are the most advanced and they include all
higher mammals. They evolved in the Paleocene epoch during the tertiary period (some
65 million years ago) after the extinction of the dinosaurs. Therefore has been rapid
evolution of diverse forms of these mammals. For this and their wide distribution and
abundance reference to mammals are usually made to the placentals.
(Fig 1)-
‘Abundance ant
\d Diversity: There are about 4,000 species of mammals and they occupy
jimost every environment that supports life on earth. Consequently, mammals are
regarded as the most biologically successful group in the Animal Kingdom. They are
highly diverse in size, shape, form and function. The pigmy shrew, for instance
terrestrial mammal measuring less than 4em in length and just a few grams in weig!
‘Scanned with CamScanner 'n contes ‘
Also, Kite, 1, blve whale i an aquatic mammal whose weight is about 190 t00",
mammals alse e252 bat (2.5 6) is only a tittle bigger than the bumble DE
lke the bate gene "om the ardent tunneters lke the moles tothe sPecialve® te
fig tn aga ae Peculiar in that they are the only mammal erouP capable Of
drawn tout renee £0 the wings of pterosaurs and birds, the wing of Bats 1s © To
ut by four of the five “fingers”. Ranges of mammals also include the mom
hangin
'8I9B On tress to dolphins that live entirely in the sea
DIVERSITY AND CLASSIFICATION OF MAMMALS.
Mammals are broadly classified into two subclasses as follows:
(a) Subclass Prototheria
(b) Subclass Tiieria
My ont Edentata ~ Primitime, toothless, anteatess, armadillos & slots.
ler Pholidota ~ characterized by horny scale covering their bod!
are derived from fused bundles of hair. Only one genus - Manis
|. Order Macroscelidea. Although these are not called anteaters, they are adapted for
‘entomophagous life. They possess long legs, large eyes and snout-like nose adapted
for foraging on insects. They are commonly called elephant shrews.
2. Order Largomorpha. The rabbits & hares. They are all herbivores of wide distribution
3. Order Rodentia are the gnawing mammals. They include the squirrels and rats. They
make up to about 40% of all mammals. They are characterized by two sharp incisor
teeth used for gnawing. They have a superb reproductive performance. There are
about 1,591 species of rodents. The important families including:
i. Family Sciuridae e.g. squirvels
Family Muridae e.g, rats & mice
iii, Family Castoridae e.g. beavers
iv, Family Erethizontidae e.g, porcupines
Family Geomyidae (pocket gophers)
vi, Family Crecetidae e.g. voles, lemmings etc.
4. Order Insectivora: there leave namely; they are the most primitive of placental mammals.
They are small with sharp snouts and live mostly underground (e.g. Sorex Cincereus).
They*include shrews, hedgehogs & moles. They are believed in evolutionary term to Be
close to the monotremes.
5. Order Carnivora: These include the dogs, wolves, cats, and bears as well as weasels.
They are regarded as highly intelligent. They are mostly flesh-cating mammals. They
have predatory habits. For instance their teeth are particularly adapted for tearing flesh.
‘The common families include
i. Family Canidae: The dogs consisting of dogs, wolves, foxes, ete
ii, Family Felidae: The cats e.g. the domestic cats, tigers, lion ete
ii. Family Uridae: The bears
Family Mustelidae: The fur-bearing mammals e.g. marlein, weasels, badgers minks
The horny scales
others etc. |
6. Order Pinnipedia: These are aquatic carnivores. Characteristically, their limbs are
modified into flippers used for swimming. All are marine and feed on fish. They include
the sea lions, walruses and seals.
7. Order Scandentia: these are tree shrews. They are small mammals resembling squirrels,
8. Order Dermoptera: This is a very small order consisting of only one genus
(Galeopithecus) which in turn has just two species. They are called the flying lemur,
This nomenclature is however a misnormer. This is because they do not fly in the true
sense of the word but rather glide. They are also not to be confused with the Lemurs
‘Scanned with CamScanner 9,
16,
17.
elated to the true bats which have
relat
which are primates. They are however rather closely
to fly.
Order Chiroptera: these are the only trul
limbs are modified into wings. They are highly
The largest of the bats are found in the tropics wh -
fruit bats belong to the genus Preropu ed for life in
Order Cetacea: These cor fish ike mammals and they are vel ae fetior limbs.
water. They include the whales, the dolphins and porpoises Oh ted) on top of tHe
Their fore-limbs are modified into flippers. They have nostrils si sennme
head, They have no hair covering on their body except for restricted local) Mt
inuzzle, Except for the mammary gland, there are no sland ie the skin. They
jnnae. The blue whale is the largest animals that has ever-live ammals.
Order Siena: these are the sea cows and manatees, These are also aquatic ae
They have large head but lack hind limbs, The fore limbs are modified into flippers ‘They
Order Proboscidea: this order contains mammals with proboscis ~ the elephants. 0y
are the largest land animals. Characteristically, the upper incisors are prolonged to
tusks while the molars are well developed. Only two species of elephants exists viz:
i. Elephas maximus ~ the Indian elephant having relatively small ears.
ii. Loxodonta africana ~ the African elephant having relatively large ears.
Order Hyracoidea: this is the group of the hyraxes (coneys). They are herbivorous and
widely distributed in Syria and Africa, They resemble rabbits. They live in colonies.
Order Tubulidentata: this is the aardvark order. It consists of only one species and is is
found only in Africa. It is a peculiar animal in that it has body like a pig. [ts teeth are
hollow.
THE UNGULATES: These are animals with hooves and teeth adapted for chew’
‘They are into two orders namely Perrisodactyla and Artiodactyla.
Order Perrisodactyla: These are the odd-toed mammals with hooves. The toes are either
one or three, but each has a cornified hoof. They are all herbivorous. They include the
Zebras, Asses, Tapirs and Rhinoceros
Order Artiodactyla: these are the even-tocd hoofed mammals. Most of them have two
toes e.g, the hippopotamus while often have four toes. Each toe is however wrapped in a
comified hoof. Animals in this order are grouped into three sub-orders
1. Suborder Suina — pigs, hippopotamus, ete
2. Suborder tylopoda— carmels
3. Suborder Ruminantia — deers, giraffes, sheep, cattle etc.
Order Primates: These are regarded as the most highly developed manamals, their brain
possessing peculiarly large cerebral hemispheres. They include the lemurs, monkeys,
apes, humans and others. Members of this group have five digits leaving flat nail on the
forelimbs and hand limbs. Except humans, they all have their body covered with hair.
‘Their forelimbs are mainly adapted for grasping. Characteristically, members of the
order lack claws, scales, hors and hoofs. Two sub-orders are known:
i. Sub-order Prosimii: This include the shrews
ii, Sub-order Anthropoidea: These are the Monkeys, Gibbons, Apes.
(a)Super family Ceboidea ~ new world monkeys. They have broad flat nasal septum,
non opposable thumb prehensile tail but not ischial calluses and check pouches
e.g. spider monkey.
(b)Super family Cercopithecoidea - They are the old world monkeys. They lack
prehensile tails, their buttocks bear callused ischial tuberosites and their thumbs
are opposable examples include the savage drill monkey (Cynocephalus sp) and
Rhesus monkey (Macao sp).
(c)Super family Hominoidea — This is where the higher apes and humans belong. The
main characteristic they share is the lack of (1) a tail (2) check pouches. Two
families are known namely the Pongidae and the Hominidae. The Pongidae
include higher apes, gibbons (Halobates) Orangutans (Simia) Chimpanzee (Pan)
and the Gorilla (Gorilla),
s bats. Their fore-
They are bats.
fying mama pout 950 spenies global
ihere they live mainly on fruits. Thes
‘Scanned with CamScanner between maa® M5 Only one species,
Homo sapie he difference
Mand the ‘opens i.e. modern humans.
larger thor em 24 the Pongidae ist
that they are more erect, possess shorter arms with
and they have higher jaws with as
Fe ith smaller front teeth.
its eek ats Semon
Possession of ck atures that are shared with other animals. These include
with vertebrates and pea oer column) and being warm blooded which they Rave
‘0 them, These are presenee ne we THEY however have features which are pect
me aie MeN This isthe external covering of the animal and from it hairs ro
others. Tha per tie whole body of mammals, but it is sparsely distributed in the
thus help ty nts also serve as insulators warening the animal up against cold and
is ong maintaining the body temperature of the mammal, Possession of hairs
Mamveget the characteristic of Mammals. Hairs aré projections out of the
eaalan integument. Hairs are important in Mammals lecture of theit
intulness in the maintenance of a constant internal body temperature. The
internal ‘body temperature of mammals lies between 35 and 40°C. The
maintenance of a constant internal body temperature termed homoithecmy is
achieved partly by the functioning of hairs. The hair covering on the body surface of
mammalsis referred to as fur. The mammalian fur is made up of two kinds of hairs
Mamm:
1
% Under hairs ~ These sense and soft hairs they ray a layer of air which conserves
heat on the surface of the skin and thus insulate the body
b. Guard hairs— These are course and honour relative to the underhairs. They are for
Protection against wear and for giving colour to the animal body.
The coloration
itself is caused by pigmentation in the guard hairs.
MODIFICATION OF HAIRS
1. Sensory vibrissae — ‘These are found under the eyes and on the snout of most
mammals.
2. Bristles - Found in hedgehogs
3. Spines - Found in spiny anteaters, porcupines and some other mammals.
Eurther to hairs:
= Hairs are exclusively found in Mammals
= Hairs are not found in some parts of the body each the palms of the hand and soles of
the feat. Also not found in the parts on the buttocks of some mammals e.g. baboons,
Also from the integument are three different kinds of glands namely the sweat, sebaceous
and mammary glands the mammary gland is usually well developed in females where it
produces milk and function .in suckling the young. This is where mammals derived their
name. Memmals possess mammary glands. In the males, these glands are rudimentary or
absent while they are fully developed and secret milk in the adult female. Mammals derive
their name from this feature. Only Mammals possess mammary glands. The number of
mammary glands possessed by the mammels and their position on the body defers
depending on the species concerned. The number varies from two to twelve or more in
terms of position, these glands may be
(i) Pectoral when they are found in the upper part of the body.
‘Scanned with CamScanner (i) ausiiary
ral and along the long aig
(i) Pectoral- abdominal when they are found on the ventral a
of the bod) two hind legs.
(») Inn ten sey arin the ven ston an between the
1¢ mammary glands are
Eramples of mammals with various numbers and position of the mammary
Presented in Table ..below:
Table 2 Postion and number of mammary gland in some mammals
POSITION OF
NUMBER OF
jee MAMMARY GLAND _| MAMMA GLAND |
1._| Homo sapiens (Humans) 2 (One pair) Pectoral- =
2.__| Multimammate rat Rattus natalensis 4 a =e
3.__[ Pangotins Salone ana | ee ESSERE |Axary!
4. | Cats and dogs =o 5 a
5. [Cows and Horses 2 Or Inguinal
is
2 Sexes and Reproduction: in all mammals the sexes ore separate and reproduction
Prsenaney oF gestation, the exception being the primitive mammals - monotremes,
which lay eggs just like birds. The monatremes are therefore oviparous. Since
Beslation period is the time el takes the embryo to Sevelop up to the birth of the
wrome, monotremes have no gestation period, however the \cubate their eggs. In
‘monotreme eggs, extraembryonic membranes namely amnion, chorion and allautois
are present during development.
In placentals,
le Marsupial Phalanger, Dacrylopsits sp. in
Trae mammals, there are definite mating seasons when the animal is one the males,
Tis happens when the animal is on heat and it coincides with the oestroes cycle,
Man is an exception to this. in man and some develops, the oestrus cycle is the
menstral cycle because it terminates in the shedding off of the uterine linning
endometrium) with some blood which is termed menstruation,
‘Scanned with CamScanner of 0 5 In comparison, reptiles possess
nition, that is several successive sets of teeth. Typically in
Funct’ the teeth are differentiated into different types according to their
Mia Bt the food habits of the animal. This Is referred to ne tatarodene
Gentition. Mammals normally possess four types of teeth namely incisors, canines,
Fammpllts and molars. The description of the dentition of mammals folowe
a aatd Patter. As a rule, the teeth are describe from front to basi in cach halt
Teeth O'S, canines, premolars and molars. The arrangement of each type of
{eth on one side ofthe lower and upper jaw is referred to as dental formula, tach
species of mammal that
has its own dental formula by which it is identified. For
example, the dental formula of Humans is:
12/2 ca Pm 2/2 M22
In this formula
1 = Incisors
c Canines
Pm Premolars
M Molars
The figures above the line are for teeth on the upper jaw which the ones below are thdse on.
the lower jaw. In the formula only one half of the Jaw arrangement of teeth is represented
hence the numbers have to be doubled to obtain the full complement of teeth possessed by
‘the animal. For instance it can be deduced from the above formula that man has 32 teeth.
The maximum number of teeth in mammals is 44 as seen in ‘sections of the dental formula of
mammal are shown. A tongue is attached to the floor of the mouth. The tongue has
numerous sensory reception corpuscles referred to as taste buds. The tongue is therefore
responsible for taste. Salivary glands discharge their secretions — saliva into the buceal
Cavity to ald and commence the process of digestion. There three salivary glands namely (i)
Parotid (i) Submaxillary and (ii) Sublingual. The food chopped and beaten by the teeth
during mastication are rolled with the aid of the tongue into bolus and swallowed ‘through
the oesophagus into the stomach. In most mammals, the stomach is simple but itis divided
into chambers in some. For example in rumninants (e.g. cattle, deer etc) and whales where
itis divided to four chambers.
4. Pinnae: The auditory system is composed of three parts namely the Inner ear Middle
and an Outer ear. There are three bones in the middle ear namely Maleus (hanner),
‘Scanned with CamScanner ws
t cian canal which leads
by the Eustacia he
1 oat external fleshly pina (plural pinnae),
and stapes. The ner ears
wc ee number and funetionsin
etna ear ae connected to the out
susie ofthe animal body and connects with
The pinnae are found exclusively in mammals.
wel
5. Neri system’ this i cerposed of a wel develoned a OO rates,
s ars i
nerves. This is one characteristic that mar
heres are pained, very
The most anterior portions of the brain, the cerebral hemispH NE aft Be
large and expended in most other invertebrates, these hemispheres Man |
cerebral hemispheres provides for a high level of coordination a ese
ving and retentive memory. These in turn are mat eee
See if of several malgns of nerve cells called the srey atte!
}ervous tissue consisting of several mull So
‘mammals also, the senses of sight, smelliig and hearing are well develop:
Joped brain and 12 pairs of cranial
0
6. Circulatory/Transport System: this is composed of a heart of four chambers (two
aurides and two ventricles), left aorta and non-nucleated biconcave red blood cells. TH
heart of mammals is found in a pericardial cavity and it is fully divided into
chambers with two upper atria and two lower ventricles. There is complete separation
of the veinous and arterial blood. Mammals share this feature and arrangement of the
birds.
7. Respiration and the diaphragm: Respiration is effected through a pair of lungs and voice
box. The Diaphragm: this is a sheet of membrane separating the thoracic from the
abdominal region of the mammal. It is found only in mammals. It founds in gaseous
exchange. This is a muscular sheath which separates the thoracic from the abdominal
cavity of the animal. The heart and lungs are in the thoracic cavity which run stomach,
intestine in the urinary system. Functionally, the diaphragm is very important in the
breathing mechanism of the animal. When the diaphragm contracts it becomes cured
him a inverted letter and flattens out in the relaxed state. The contracted diaphragm
forces a reduction in the volume of the lungs, hence an increase in lung pressure which
forces out air (exhalation). When the reverse happens, that is the diaphragm relaxes,
Pressure is reduced in the lungs and so volume increase and draws in air (inhalation),
thus complete the cycle of gaseous exchange or breathing. *
8. Skeletal System of mammals is characterized by two occi
vertebrae and an elongated tail made of caudal vertebrae.
I condyles, seven cervical
9. The excretory system is composed of the kidneys (usually one pair) and ureters that
leads into a bladder. Mammals presses a pair bear-shaped metanephric kidneys
located in the dossal part of the abdominal cavity. When dissected a mammalian
kidney shows the following parts
3. Cortex - This is outer and contain the renal corpuscles, convoluted tubes and blood
vessels.
b. Medulla ~ This is divided into triangular wedges called renal pyramids. The broad
tissues of these pyramids are divided towards the cortex and narrow apices referred
to as renal papillae are oriented towards the centre of the kidney and opens into the
calyx and pelvis.
© Ureter= Each kidney has a ureter, a duct leading into the pelvis empties fluid into
the Urinary bladder,
Urinary bladder - This is an organ where urine is stored before existing to the outside
‘Scanned with CamScanner
bes called the semicircular cana, “!, un
Rephrons consisting gf goach i
Bowman’
BP's Capsile aloy
ney is the ne
ey, Pephron. Each kidney has about 1,500,000
apsule or glomerular capsule. Each
nephrons empty to collecting ducts
the ureter. Within the capsule a
ie begins to ascend after he descent. This shops is called loop
therefore” takes place be od, 2Pilaries tangle with the tubule. Exchange of substances
capilaries ane ad ‘means of active transport and osmosis between the blood
Functions of the kidney
There are three main functions of the kidney
21. Glomerular filtration
2. Tubular reabs:
absorption
3. Tubular secretion
In Mammals living in arid (desert) environments, there is need to concentrate thei urine in
order to retain water which functions is performed by the kidney. The urine concentrating,
ability of the kidney makes it possible for mammals to produce urine that is hyperosmotic to
that of blood plasma ~ in fact up to 25 ties more concentrated than blood plasma. The
highest urine concentration is found in blood plasma of desert living mammals such as the
elephant shrew (Macroscellides sp), insectivorous mammal, Gerbil (Gerbillus pyramidum)
and Jerboa Vaculus jaculus) both of which are rodents. The highest urine concentration is
found in the aquatic species such as the aquatic mole (Desmana moschela), the beaver
(Castor filer) and Water rat (Hydronies chrysogaster). Midway between the arid and aquatic
mammals, in terms of urine concentration are the mesic mammals (i.e. those living in high
moisture environments) like the European hedgehog — Erinaceus europeanus, squirrel
(Scuirus vulgaris) and black- billed hamster Cricetus cricetus
10. All mammals are endothermic and homoeothermic.
II, All mammals have movable eyelids.
MORPHOLOGICAL ADAPTATION TO ENVIRONMENT
1. Body structure: the age and shape of the body of any mammalian species is largely
dependent upon the habitat and habits of the animal. Swift runners such as dogs and deer,
for instance are slender and posses long limbs. Aquatic species such as the whale, and
seals have streamlined bodies like those of the fishes and birds while the burrowers like
the mole have their bodies elongated and posses sharp and strong chaws.
2. The limbs: Typically, mammals possess four limbs. Depending on the medium or the
type of locomotion the mammals need to suit their environment, these limbs are
variously modified. Consequently the mammalian limb may be reduced in number,
‘Scanned with CamScanner cose limbs are adapted for the differen,
y absent or be variously shaped: These
sively fe. Mammals that earry out locom:
vaepalatory while the runners are curs
8s Sulatory and cursorial mammals can be
rogressively slim and are progress
mammals ke lpn the Fibs ere
cexeusively by walking are referred to 9s ambu'
On the basis of limb modification ambula
classified into three categories as follows:
i. Digitigrades, :
Plantigrades and
anagraeToa and most other mammals excluding
clude cats, dogs, bears 0
aaa ase jes a genealyqujker and move more quietly than other mammals
tigrade animal stands or walks on its digits or toes while the heels and wrist are
grade animal stands or
no
aint
sch a humans, too0ns, opposins kangaroos, as mice
Tyre ste feduiogs and squirt seal cary ent lomoton by waking wit
the soles of thei feet (that is the podinls and metatarsals) on the ground. The plantigrade
limb bears the weight of the mammal and confers stability. It has the highest surface area
relative to other limb arrangements. The plantigrade limb however slows down its
‘possessor. In contrast digitigrade animals walk on their distal and intermediate phalanges.
Digitigrade locomotion is responsible for the distinctive hook shape of dog legs. There
are anatomical differences between # plantigrade and digitigrade limb. Digitigrade
animals have relatively long carpels and tarsals, and the bones which would correspond
fo the human ankle are thus set much higher in the limb than in a human, This
effectively lengthens the foot, so much so that a digitigrade animal's "hands" and "feet"
are often thought to correspond only to what would be the bones of the human finger or
ioe
Unguligrade mammals, such as horses and cattle, walk only on the distal-most tips of
their digits, while in digitigrade animals, more than one Segment of the digit makes
‘contact with the ground, either directly (as in birds) or via paw-pads (as in dogs).
Dog A
ha
mee, Off
Unguligrade
Figure : Plantigrade, diratigrade and unguligrade limb of terestial mammals
b Himping and Ricocheting. These are together refered to a8 saltatoral locomotion.
jumping involves the use ofall the four feet asin the antelopes while reechcting
involves propulsion of the body by the use of the hind legs for exanle ie the
Kangaroos. In ricocheting mammals the forelimbs are shorter than the hind limbs
and they are often employed by the animal to manipulate things in the environment
rather than for locomotion. One or more ‘segments of the hind limbs are lengthened.
10
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fective t® mod
he mode of tc,
Mimiming te geet ig
=
ra aes ese ea
5 a or Pais B ati
amy ee em
ee ips ere mid
il the
its ae exten
‘The hing img Se eteniey ane
ou ra el sl adinery Noes at
he embedded in the venal muse
‘ental muscle in
mt gc of eee
ound or ei 'y a claw on the edge of the wing and
aol orig sath cath ee the
) extends from of skin wi is the flight membrane (¢ te
fumb i
the gr
Used to crawl on
{0 cling to surta
called Patagiuay
hind tim and
includes the t
Plate: Bats clingi
Coast, Ghana.
e. Gliding.
3, The Byes and Ears: mammals which serve as prey for others need to be constantly onthe
alert. This necessitates the possession of eyes which are positioned atthe ‘sides of the head.
This is advantages for herbivores and grazers such as rodents, cattle, pig and so on.
Contrary to this, the carnivores such as cats ‘and dogs have eyes which are placed
“Towards to provide binocular vision. Ths is also the case in primates such os monkeys,
and man. In all cases the eyes are protected by movable eyelids. To complement the eyes
jn alertness mammals also possess 0 @ pair of fleshy external ears (pimae). In the grazers
such as deers and horses, each pinna is large and readily movable, It is rather small in
burrowing animals. The pinnae are used in Soolection of sound (from near and far) which
in
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