Mammals evolved from reptiles during triassic period. It is
most highly evolved group of animals.
Characters of Mammal:
Mammary glands on females for suckling the young ones.
Skin richly glandular.
Double occipital condyle.
Double headed ribs.
Constant body temperature.
Three ear ossicles.
Respiration always by lungs.
3. Subclass – Prototheria
This include primitive egg laying mammal. They nourish
their young with milk from mammary gland. It comprises
only one living order.
Mammary glands without nipples.
No external pinna.
Testis are abdominal.
Teeth only in the young ones.
Heart is four chambered.
Example- Ornithorhynchus , Echidna
4. Distinctive characters of Prototheria
Distribution-these are distributed in the
entire Australian region, including
Australia, Tasmania, Newguinea and
Habit and habitat-
Aquatic or terrestrial
5. External features
Body small covered by hair
Muzzel or snout produced
External ear absent.
Mammary glands without
Male carries a hollow,
horny, tarsal spur on each
internally to a poison gland.
Ref. – A Textbook of Zoology by Parker & Haswell
6. Body cavity - Divided by a typical mammalian
Malleus and incus relatively
Lower jaw consist of single
Cervical vertebrae 7
Presence of epipubic bone.
A large T-shaped
interclavicle is present.
Limbs and girdles reptilian
like held laterally. Ref.-The life of Vertebrate – J.Z Young
7. Digestive system- teeth develop only in
Respiratory system-respiration pulmonary by
Circulatory system- heart four chambered,
right valve incomplete, R.B.C small circular and
Excretory system- Kidney metanephric, ureter
open into urinogenital sinus which terminate
into common cloaca.
Nervous system-brain small without carpus
8. Reproductive system
In male testes is
retractile for passing
out sperms not urine.
In female right ovary is
reduced and oviduct
lead separately into
Ref. – www.edu.com
Eggs large with much yolk and plastic shell.
Cleavage is meroblastic.
No uterine gestation
Newly hatched young are very immature.
These are fed on milk in abdominal pouch till
Ref. – Man & Vertebrates by Romer
10. Phylogenetic relationship
Subclass- Prototheria shows its affinity to
reptiles and birds with little advance over
Affinities with class - Reptilia
Claws are present.
A median T shaped interclavicle present.
They can survive during starvation for a
Eggs calcareous, uterine gestation is
11. Affinities with birds
They have following resemblances-
Teeth are absent.
Feet are webbed.
Tarsal region contain spur.
Oil gland is present.
12. Affinities with mammals
Body covered by hair.
Skin richly glandular containing sweat
and sebaceous gland.
Mammalian diaphragm divides body
Skull dicondylic, presence of four optic
lobes, cervical vertebrae seven.
Liver is lobed like mammals.
Heart is four chambered, only left aortic
13. Peculiar characters of Prototheria
The following characters are peculiar to
Presence of tarsal spur in male.
Milk gland derived from sweat glands
and without teats.
Temporary abdominal mammary pouch
in female during breeding season.
Jaws elongated forming a beak or