This document discusses the phylogeny and morphology of vertebrates and amphibians. It covers the five classes of vertebrates which are fishes, amphibians, reptiles, birds, and mammals. For fishes, it describes the two types of modern fishes and discusses characteristics of cartilaginous fishes. It also covers taxonomy of fishes and adaptations of body forms. For amphibians, it discusses characteristics and challenges of terrestrial life, orders of amphibians, and patterns of reproduction. Finally, it covers characteristics of reptiles, taxonomy of reptiles including orders, and families of snakes.

1. BIO 203
PHYLOGENY AND MORPHOLOGY
OF …. AND VERTEBRATES

3. VERTEBRATES
• Chordates are animals that have notochords.
• Vertebrates are animals that have vertebral
column.
• There are five (5) classes of vertebrates.
1. Fishes (Pisces)
• Chondrichthyes (cartilaginous fishes)
• Osteichthyes (bony fishes)
2. Amphibians
• Toads, frogs, salamanders and newts.

4. CONT’D
3. Reptiles
• Lizards, snakes, crocodiles, turtles, tortoises.
4. Birds (Aves)
5. Mammals

5. FISHES ( PISCES)
• There are 2 types of modern fishes.
(i) Chondrichthyes - also called the
elasmobranchs or Cartilaginous fishes.
(ii) Osteichthyes – also called Teleosts or bony
fishes
• Fishes evolved during the Devonian period i.e.
about 400 million years ago.
• They evolved from the Acanthodians and
primitive Gnathostomes ( jawed fishes).

6. ELASMOBRANCHS ( ORIGIN/
DISTINCT CHARACTERISTICS)
1. They have no bones in the skeleton.
2. They have no operculum.
3. They have no air bladder.
4. The tail is heterocercal i.e.; the tail is divided
into 2 unequal parts). Homocercal tails have
two equal parts. This means that the tail is
branched and into equal sizes.
5. The body is covered with placoid scales.

7. CONT’D
6. The blood has large amount of urea.
• Urea is soluble in water but uric acid is
insoluble in water.
• Getting rid of excess nitrogen in the form of
uric acid means you want to conserve water.
E.g. reptiles but getting rid of excess nitrogen
in the form of urea means you want to get rid
of excess water. E.g. fishes.

8. CLASSIFICATION OF FISHES
There are two superclasses.
• Superclass Agnatha (Jawless fishes)
• Superclass Gnathostomata ( jawed fishes)
Superclass Gnathostomata
I. Class Chondrichthyes).
a. Sub-class Selachii
i. Order Protoselachii. E.g. Heterodontus.
ii. Order Euselachii. E.g. pacific dogfish, electric ray.

9. CONT’D
II. Class Osteichthyes or Teleostii
• NB: These two classes Elasmobranchii and Teleostii are
referred to as Pisces (group name).
b. Sub-class Acanthodii (These are spiny fishes).
c. Sub-class Actinopterygii ( These are ray-finned fishes and
most modern fishes).
• There are two major groups of the actinopterygians
including primitive and modern members. E.g. cat fishes.
d. Sub-class. Sarcopterygii (lobe-finned fishes). These
normally have fleshy fins

10. CONT’D
• There are two orders of the sarcopterygians
(i) Order Crossopterygii. These members have
lobe fins.
Two sub-orders
1. Sub-order Rhipidistia
2. Sub-order Coelocanthini
(ii) Order Dipnoi. These are lunged fishes.

11. BODY FORMS AND SWIMMING
HABITS OF FISHES
• Pelagic fishes are streamlined. Departure from
this is associated with reduced efficiency in
swimming.
• But this is often compensated by some protective
mechanism.
For example:
There is lateral flattening carried to the extreme in
some fishes. E.g. angelfish (Pterophylum sp.).
• It is long and filamentous and has a brilliant
colouration to give a protective resemblance to
plants amongst which it moves very slowly.

12. CONT’D
• Also, flat fishes like sole and halibuts are much
flattened.
• They feed on molluscs and other invertebrates on
the sea floor.
• The upper side is dark and the lower side white,
which give them protection.
• In order to use both eyes, the whole head is
twisted during the post larval development, to
enable both eyes see at the same time.
• They are poor swimmers because they are
departed from the streamlined body.

13. CONT’D
• However, they have remarkable colouration that
blends the background for protection.
• Other slow swimmers develop armour for
protection. They are spiny. E.g. trunk fish
(Ostracions) and the globe fish(Chilonyctenus)
which is also spiny.
• Others develop elongated bodies. E.g. eels
(Anguilla sp) which have the habit of moving on
the land.
• They can jump out of water. E.g. Salmon can
jump 8-9ft above water.

14. CONT’D
• Flying fishes e.g. Exocoetus sp has a large
pectoral fin for flying up to 400 meters above
water.
• Flying gurnards e.g. Dactylopterus sp are dorso-
ventrally flattened.
• In others, the pectoral fins are modified for
walking normally at the shore or ocean floor. E.g.
Trigla sp.
• Mud skippers (Periophthalmus sp) for example,
chase crustaceans and insects on the land using
pectoral fins as levers

15. CONT’D
• Fishes in fast moving waters and intertidal
zones develop certain suckers for attachment
in order to prevent dislodgement.
• E.g. Gobbies found in intertidal zones use
pelvic fins as suckers,
• and remoras have sucking plates from the first
dorsal fin which they attach to sharks.

16. CLASS AMPHIBIANS
• These are the amphibians.
• An animal that complete part of its life cycle in
water and part on land.
• The larval stages are mostly found in water
and adult on land.
• The larva of amphibians is called tadpole.
Amphibians can be distinguished from fishes
by:
(i) The presence of pentadactyl limbs.

17. CONT’D
(ii) Presence of middle ear (i.e. they both have
the middle and inner ear but not the outer
ear).
• Amphibians evolved from a group of fishes called
Crosopterygians.
• These fishes had lungs.
• Selective pressure, largely shortage of water ,
drought etc. led to the evolution of mechanism to
live on land.

18. PROBLEMS FACED IN
TERRESTRIAL LIVES
1. Respiration. This is solved by the evolution of lungs.
2. Locomotion. This is solved by the evolution of
walking legs.
3. Desiccation, solved by behavioral means.
4. Detection of air borne substances of much greater
dilution than water. This was solved by the evolution
of organ systems.
5. See and hear from predators and preys solved by
evolution of eyes and ears.
6. Getting rid of the lateral line system.

19. ORDERS OF AMPHIBIANS
1. Order Anura e.g. frogs and toads.
2. Order Apoda e.g. caecilians
3. Order Urodela e.g. salamanders and newts.
4. Order Trachystomata (Neantes) e.g. sirens.
• Neantes have minute fore-limbs but no hind
limbs.

20. DIVERGENCE IN REPRODUCTION
PATTERNS OF AMPHIBIANS
1. Eggs: Eggs are laid away from water. Apodans and tree frogs lay
eggs in holes and burrows.
The South American tree frog Phyllomedusa sp
produces eggs in foam nests on tree leaves and branches
overhanging a pool of water.
The foam nest is to keep the tadpole moist. When the eggs
are hatched the tadpoles wriggle and fall down into the pool.
2. Maternal care: E.g. the midwife toad Alytes sp. Eggs are laid in
strips around the hind limbs and the body of the males.
When they are ready to hatch, the male jumps into water for
the larvae to hatch.

21. CONT’D
• In some spp such as Gastrotheca ovifera and
Gastrotheca marsupial, the eggs are laid in
incubating pouches.
• In the Pipa sp, pouches are vascularized (have
blood supply) and gas exchange take place by
the help of the vascularized tail of the larvae
until they hatch.
• In Rhinoderma sp, the male places eggs in
vocal sacs where larvae hatch and emerge.

22. CONT’D
3. Ovoviviparity: Eggs are retained in the body for
part of its development.
• Fertilization is internal
• E.g. In Anurans, there are no copulating
appendages, except in the Ascaphus sp which has
penis-like extensions of the cloaca.
• In Nectophrynoides, the young emerges as
froglets from the oviducts and the larvae have
vascularized tails for gas exchange in the oviduct.

23. CONT’D
• In Urodela, sperms collect in the cloaca as
spermatophores.
• After courtship, the male deposits
spermatophores in the female’s body and the
spermatophores break to release the sperms to
fertilize the egg.
• Aquatic Urodels have prehensile tails.
• In Apodans, ovoviviparity is common.
• E.g. In Geotrypetes, they produce uterine milk on
which the larvae feed. They also have copulating
appendages on the tail.

24. ADAPTIVE RADIATION IN
AMPHIBIANS
1. In Apodans, there is little radiation . Almost all
are burrowers except Typhlonectes sp which
occurs in humid tropics. E.g. Seychelles.
2. Anurans are widespread. They are the most
familiar and most abundant amphibians.
• They are represented in every major geographical
region and occur in wide spectrum of habitat
including desert, burrows.
• E.g. Cyclorona live on desert.

25. CONT’D
• They store water under the skin and glomeruli.
• Rana cancrivora and Bufo viridis are found in
the marine waters and can tolerate 29-35 /oo
salinity.
• The burrowing frog, Heleioporus sp has
radiated to burrowing on land. Only one
manage to go back to water completely. E.g.
Titicaca sp lives in lake Titicaca entirely at the
bottom and takes oxygen for respiration.

26. CONT’D
• All adult anurans are insectivorous.
• They feed on insects but have no specialization
when they are hungry.
• The size of the anuran dictates the size of the
prey but they are generally smaller except the
forest toad and the goliath frog.

27. CONT’D
3. Urodela: They are widespread but mostly
unknown in the tropics. They show some special
adaptations.
• Proteus sp lives in water-filled caves and
therefore lack eyes.
• The mountain dwelling newts and salamanders
are adapted to fast flowing waters by gluing its
eggs directly to rocks.

28. CONT’D
• The major phenomenon of divergence among Urodels is
paedogenesis.
• This is the evolutionary change involving retention in
sexually matured descendants, characters that occur in
younger stages of ancestors.
• E.g. The Mexican axolotl, Ambystoma mexicanum
frequently breathe in the gill state.
• The largest Urodel and amphibian is known as
Megalobatrachus sp (now called Andrias sp), which can
reach 5 ft. Apart from this species, all Urodels are less than
1 ft.
• In terms of diet, salamanders are carnivorous as compared
to anurans.

29. REPTILIA (REPTILES)
CHARACTERISTICS
1. Presence of scales.
2. They produce amniotic eggs
3. They have simple occipital condyle
4. Have single ear
5. They have three chambered heart
6. They are poikilothermic ( i.e. cold blooded)

30. CONT’D
• Reptiles are believed to have evolved from
amphibians during the carboniferous period, some
300 million years ago (mya).
• The original stocks were cotylosaurs which were
extinct about 150 mya during the Jurassic period.
• Before this, they radiated during the Mesozoic era
before going extinct due to environmental
changes.
• They experienced drastic changes in the
environment at the end of the Mesozoic era.

31. CONT’D
• E.g. Birds and mammals evolved and preyed on
the eggs of the reptiles.
• There were 15 orders before the Mesozoic era but
only 4 orders remain extant (living).
• These are;
(i) Order Rhynchocephalia: This comprises a single
species called Sphenodont punctata (Tuatara).
(ii) Order Crocodilia- 25 species
(iii)Order Chelonia- Tortoises and turtles

32. CONT’D
(iv) Order Squamata.
• About 2,000 spp. These are the most dominant.
• They include the snakes and lizards.
• Extinct orders include dinosaurs, marine reptiles
and therapsids. During the transition from
amphibians to reptiles, there were some changes.
A. Evolution of water proof skin consisting of dry
cornified skin covered with scales for water
conservation.

33. CONT’D
B. Improved lungs. The lungs became harder and
compact.
C. Protection of amniotic egg. This was necessary
against desiccation and also as a shock absorber.
The allantoid cavity was a store for secreting waste.
The allantrochorion was used for respiration. The
eggs are covered with leathery scales.
D. Improved kidneys. The terrestrial forms and all
the squamates produce uric acid through the
biochemical pathways.

34. TAXANOMY OF REPTILES
SUB-CLASS ANAPSIDA
This class has no temporal opening behind the eye and
therefore the skull is compact.
Orders of this sub-class include:
1. Order Chelonia- Tortoises, turtles and terrapins.
In this order:
They have a shell of two elements i.e.; the skeletal
element, which consists of the vertebral column and the
ribs and the horny elements which comprises the scales.

35. CONT’D
(ii) They have a plastron, which forms the
ventral part of the animal.
(iii) The chelonians have no teeth but they have
horny-like beak for cropping vegetation.
• Sub-orders of Chelonia
a. Sub-order Pleurodira is different because
the neck folds sideways when withdrawn.
Also, the pelvis is fused with the plastron.
eg snaked-necked turtle.

36. CONT’D
b. Sub-order Cryptodira
The neck folds in a vertical plane when
withdrawn.
Also the pelvis is not fused but free.
SUB-CLASS LEPIDOSAURIA
• This is either a diapsid or the is temporal opening
is lost.
• They have scales on their body.

37. Order Rhyncocephalia
• Members in this order are diapsid with a pair
of temporal foramen.
• They are found in New Zealand. E.g.
Sphenodont punctata
a. Order Squamata
The skin has horny epidermal scales and they
have a quadrate bone which is movable.

38. CONT’D
Sub-orders
i. Sub-order Lacertilia
• These are lizards and their mandibles are fused
anteriorly.
• They have movable eye-lids
• The tongue is usually entire.

39. CONT’D
ii. Sub-order Ophidia (Serpents)
1. These are the snakes
2. The mandibles are joint anteriorly by a
ligament
3. The tongue of ophidians is forked not entire.
4. They have secondarily lost both forament in
the adult; but the juveniles still possess both.

40. CONT’D
• The lizards, including agamas, geckos,
monitors, stinks are cosmopolitan but not
beyond North of Europe.
• Snakes evolved from burrowing forms of
original stock and secondarily radiated to the
surface above.
• They used to be subterranean/ fossorial.

41. FAMILIES OF THE SUB-ORDER
OPHIDIA
1. Family Hydrophiidae. They are water snakes
They are venomous
2. Family Boridae. These are primitive snakes
3. Family Elapiidae. These are members of
green snakes
4. Family Viperiidae. These are rattle snakes.

42. CONT’D
5. Family Columbriidae. These are cobras and are
venomous.
6. Family Typhlopiidae. They are extinct. They
were non-venomous. They were insectivorous.
They were fossorial i.e.. They lived underground in
holes and burrows
7. Family Leptotyphlopiidae. They are
insectivorous They are non-venomous. They are
fossorial. E.g. worm snakes

43. SUB-CLASS ARCHOSAURIA
• These are diapsids.
• The only surviving member is the order Crocodilia
(but included dinosaurs and flying reptiles).
• There are 25 species and are semi-aquatic.
• They have flattened tail, nose and eyes are raised.
• The internal nerves of crocodiles are supported by
values.
Crocodiles are largest living reptiles. E.g. Crocodilus
porosus and it is 25 ft.

44. CONT’D
• Some reptiles have invaded the sea and have
problem in osmotic balance.
• They therefore take in water and the problem
is to get rid of excess salt in the blood .
• To solve this problem, the salt is quickly
absorbed into the blood.
• This process is called Extra-renal excretion.
(it occurs outside the kidney).

45. CONT’D
• E.g. The marine turtle, the Caretta sp uses
lachrymal glands for the same purpose of
extra-renal excretion.
• In Iguana spp, the nasal gland in the nose are
used for extra-renal excretion.
• In the sea snakes, the natrial glands are used
for extra-renal excretion.
• Some reptiles have specialized in fish eating
and therefore take in less water. E.g. Natrix sp.

46. COMPARISON OF THE EYES OF
SNAKES AND LIZARDS
LIZARDS SNAKE
1. Presence of fovea 1. Absence of fovea
2. Pigments are present in the
retina for lizard.
2. Pigments are present in the
lens
3. The retina is normal 3. Retina is with double cones
4. The sclera is present 4. Sclera is absent
5. During accommodation, they
change the lens by ciliary
muscles.
5. Lens is constant in shape but
moves forward and backwards
by the movement of the iris.

47. CLASS AVES

48. CONT’D
• These are birds and are believed to have
evolved from some reptiles called Archosauria
some 140 million years ago.
• This is evident by some similarities between
birds and reptiles.
• eg:
1. Both have scales at the feet.
2. Both have single ear ossicle
3. Both possess occipital condyle.

49. CONT’D
• However, there are some differences between
them.
(a) Birds are warm blooded but reptiles are cold
blooded.
(b) Birds have right systemic arch.
• The earliest fossil bird is Archaeopteryx sp which is
extinct.
• The Archaeopteryx had teeth but lost them in the
course of evolution.
• Its skeleton was close to that of the reptiles.

50. FLIGHT IN BIRDS
• Some of the modification made for effective flight
were:
(i) Changes in the vertebral column, e.g. Formation
of the synsacrum for rigidity.
(ii) Loss of teeth and some vertebrae/bones to
reduce weight.
(iii)Pneumatization of bones (hollowing of bones)
reduces weight and promotes buoyancy in birds.
(iv)Improved respiratory system to provide
continuous flow of air to obtain enough oxygen
especially at high altitude.

51. CONT’D
5. They have aerofoil wings which are convex
above and concave below. They also have thick
leading edge and thin trailing edge.
6. They have specialized flight muscles attached
to a huge keel/carina.
• Keel is reduced in flightless birds and cause
them not to fly. E.g. ostrich.

52. TYPES OF FLIGHT
• There are 3 types of flight in birds. These are:
(i) Gliding
(ii) Soaring
(iii)Flapping

53. Reasons why some birds cannot fly
(I) Undeveloped wings
(II) Reduced keel
(III) Heavy weight
• The keel is the modification of the sternum.
• A bird that has keel present is said to be called a
carinate/keeled bird. i.e. a flying bird.
• The sternum projects into a huge keel to which the
flight muscles anchor.
• Deeply enlarged pectoral muscles originate from the
sternum and insert on the humerus.

54. CONT’D
• Flight has helped birds to radiate.
• But some birds are flightless, e.g. ostrich
which evolved from flying birds.
• They are mostly found on small oceanic
islands.
• They are large in size and lack predators.

55. CLASSIFICATION OF BIRDS
• These are ancient birds and they include
reptile-like birds.
• Sub-class Neornithes
• Neornithes- modern birds.
• These include all other birds and they have
fused metacarpals.
• They have 13 or less vertebrae.

56. CONT’D
• The archaeopteryx spp which is a pigeon-sized
Jurassic birds.
• They had teeth, long reptilian tail consisting of
about 21 vertebrae.
• They had three free hand digit bearing curved
talons/claws.
• But all these features disappeared in the latter
birds.

57. CONT’D
• The Neornithes has two super orders.
(i) Super-order Neognathae
• They have about 19 orders and all have keeled
sternum. Their wings are well-developed and used
for flying in air. Their bones are hollowed or
pneumatized.
(ii) Super-order Paleognathae.
• They are ratites (running birds).
• They mostly cannot fly because they have
unkeeled sternum, weak wings or solid bones.

58. CONT’D
• Examples;
(i) Rhea, i.e. Rhea americana also known as American
ostrich.
(ii) Struthio camelus i.e. African ostrich.
• Both have unkeeled sternum.
• The cassowaries of Australia and New Guinea and the
emus of New Zealand have unkeeled sternum and weak
wings.
• The kiwis of New Zealand have unkeeled sternum with
wings extremely degenerated and remiges absent.

59. CONT’D
• There are 3 groups of feathers depending on their
attachment.
1. On digit (I) are tertiary feathers called Alula or
bastard wing.
2. Primary feathers on digits (II) and (III) and the
metacarpals.
3. Secondary feathers on the ulna.
• Primary and secondary feathers are called
remiges. And both remiges and tail feathers have
the quill.

60. CONT’D
• In primary feathers, the inner side of the vane
is broader than the outer side.
• In secondary feathers, the two parts (inner and
outer) of the vane are nearly equal.
• The feather of the Alula is oval in shape.

61. CONT’D
• Muscles that move the wing are situated on
special part of the sternum called keel or carina.
• Two types of muscles move the wing.
(i) Pectoralis major (on top).
(ii) Pectoralis minor/ supercoracoideus(beneath).
• These are antagonistic muscles that bring about
movement of the wing; when one contracts, the
other relaxes and vice versa.
• Tendons from pectoralis major contract, the wing
is pulled down.

62. CONT’D
• Tendons for the pectoralis minor passes
through the foramen triosseus (an enclosed
hole between three bones; clavicle, coracoid
and scapula) to insert on the dorsal part of the
humerus.
• When the pectoralis minor contract, the wing
is pulled up.

63. CLASS MAMMALIA

64. Variation in Chambered hearts of
vertebrates
• Fish heart has just two chambers, an atrium and a ventricle
• Amphibians are an interesting group, as their hearts vary greatly.
Living on land and in water, many get oxygen using their lungs,
but also take it up via their skin.
• Most amphibians, including frogs and toads, have three-chambered
hearts, with two atria and one ventricle
• Reptile hearts have three chambers, two atria and one ventricle.
The exception is crocodilians, which have four-chambered hearts,
just like mammals and birds. However, there is a hole in the
crocodile chamber wall, so whether there are three or four heart
chambers is up for debate.
• Bird and mammal hearts have four chambers (two atria and two
ventricles).

65. Variation in the ear of vertebrates
• All tetrapods (amphibians, reptiles, birds, and
mammals) have a middle ear with a tympanic
membrane.
• Reptiles, birds, and mammals also have an external
auditory meatus (or canal) which extends from the
tympanic membrane to the external surface of the
head.
• The "labyrinth" or inner ear occurs in all
vertebrates; a distinct middle ear consisting of
pharyngeal pouch and tympanic membrane is found
only in tetrapods; and the "pinna" or external ear is
peculiar to mammals.

66. contd
• For all non-mammalian amniotes - lizards and
crocodilians, the only ossicle in their middle ears
is the stapes.
• The mammalian middle
ear contains three tiny bones known as
the ossicles: malleus, incus, and stapes.
• Having three ossicles in the middle ear is one of
the defining features of mammals.
• All reptiles, amphibians and birds have only one
middle ear ossicle, the stapes or columella auris.
• The other gnathostomes (fishes) have no
functioning ear ossicles.

67. Aortic arch (Arterial arches) in vertebrates
• There are six pairs of arteries in vertebrate embryos, which
connect the ventral aorta to the dorsal aorta by running
between the gill slits.
• The arches are numbered I to VI from the anterior end.
• In adult tetrapods arches I and II are lost,
• III gives rise to the carotid arteries,
• IV (one side of which is lost in birds and mammals)
becomes the systemic arch supplying the trunk and limbs,
• V is lost, and
• VI gives rise to the pulmonary arch supplying the lungs.
• In adult fish IV to VI arches persist as branchial arteries
supplying the gills.

68. Systemic arch in vertebrates
• The aortic arch IV (a pair) becomes the systemic
arch supplying the trunk and limbs
• Systemic arch is a paired blood vessel in the
embryos of tetrapods that carries blood from the
aorta to the trunk and hind limbs. It is derived from
the fourth aortic arch.
• Adult amphibians and reptiles retain both left and
right arches, while birds and mammals only have
one.
• In birds only the right arch is present in adults.
• In mammals only the left arch is present in adults.

69. CHARACTERISTICS OF
MAMMALS
1. They are warm-blooded animals
2. They have pendactyl limbs
3. Presence of hair or fur on skin
4. They have 3 ear ossicles
5. They have 2 types of glands; sebaceous and
mammary glands.
6. They have muscular diaphragm
7. They have a four-chambered heart

70. THREE(3) SUB-CLASSES
1. Sub-class Protheria (egg laying)
• This consists of only one order.
• Order Monotremata. E.g. Duck-billed platypus
or spiny anteater (Echnida).
Some characteristics
(i)They lay yolky eggs
(ii)They have no true mammary glands.

71. CONT’D
2. Sub-class Metatheria
• These are the marsupials also known as
pouched mammals.
• They are found in Australia and South
America.
• The young are born in a miniature state into a
pouch where mammary glands supply milk.
• Examples include; kangaroo, koala, Tasmanian
wolf.

72. CONT’D
3. Sub-class Eutheria
• These are the placental mammals.
• They are viviparous.
• Eutherians are true mammals because of the
presence of the placenta and they give birth to
their young ones directly.
• There are many orders in the sub-class eutheria
which have adaptively radiated.
• Examples include; terrestrial and flying forms
such as bats (order Chiroptera).

73. CONT’D
• Some eutherians have gone back to water.
• The aquatic orders of eutheria are:
I. Order Cetacea: These are the whales, porpoises, and
dolphins
II. Order Carnivora: Examples are, sea lions, otters and seals.
Though other members are terrestrial such as cats, dogs,
bears etc.
III.Order Sirenia: These are manatees and dugongs.
These aquatic mammals come to the surface of the water time
to time to take a deep breath of air outside water as source of
oxygen for respiration.

74. MAMMALS OF THE OCEANS
• There are two groups of oceanic mammals namely whales and seals.
• Order Cetacea has two suborders
• Sub-order Odontoceti i.e. the toothed whales; oceanic dolphins, river
dolphins, porpoises, pilot whales, beaked whales, and bottlenose
whales, as well as the killer whale, sperm whale, narwhal, and beluga
whale.
• and sub-order Mysticeti i.e. Baleen whales also called large whales;
the blue, bowhead, right, humpback, minke and gray whales. Baleen
whales are generally larger than toothed whales except for
the sperm whale which is very big and has teeth.

75. --Ctd
• Whales: They are widespread, motile and have a great range in size.
• The Blue whale is not only the largest whale species, but the largest mammal
on Earth.
• In summer, whales such as the Balaenoptera sp and the humpback whale i.e.
Megaptera sp occur in areas between 35℃ and 65 ℃.
• In winter however, they migrate to warmer waters. E.g. sperm whales that is
Physeta sp, bottle nose whale, killer whale, pygmy sperm whales (Kogia sp)
are all migratory.
• In contrast, Stenella, Sotalia and Steno spp are restricted to the tropic and sub-
tropic.