The document discusses the characteristics and phylogenetic relationships of prototheria, the subclass of primitive egg-laying mammals. It notes that prototheria include monotremes like the platypus and echidna, which lay eggs but nourish their young with milk. While prototheria share some traits with reptiles like claws and an interclavicle bone, they also share traits with mammals like fur, mammary glands, and a four-chambered heart. The document outlines the anatomical features and development of prototheria in detail.

1. Structural peculiarities and
phylogenetic relations of
Prototheria

2. Mammals
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.
 Hairy skin.
 Skin richly glandular.
 Differentiated dentition.
 Double occipital condyle.
 Double headed ribs.
 Constant body temperature.
 Three ear ossicles.
 Respiration always by lungs.
 Increase intelligence.

3. Subclass – Prototheria
This include primitive egg laying mammal. They nourish
their young with milk from mammary gland. It comprises
only one living order.
 Order- Monotremata
 Mammary glands without nipples.
 No external pinna.
 Females oviparous.
 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
neighbouring Island.
 Habit and habitat-
Aquatic or terrestrial
Burrowing
Mainly insectivorous
Nocturnal

5. External features
 Body small covered by hair
and spines.
 Muzzel or snout produced
into beak.
 External ear absent.
 Mammary glands without
teats.
 Male carries a hollow,
horny, tarsal spur on each
hindleg connected
internally to a poison gland.
Ref. – A Textbook of Zoology by Parker & Haswell

6. Body cavity - Divided by a typical mammalian
diaphragm.
 Endoskeleton
 Skull dicondylic.
 Malleus and incus relatively
large.
 Lower jaw consist of single
bone dentary.
 Cervical vertebrae 7
 Ribs unicephalous.
 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
embryo.
 Respiratory system-respiration pulmonary by
lungs.
 Circulatory system- heart four chambered,
right valve incomplete, R.B.C small circular and
non-nucleated.
 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
abdominal, penis
retractile for passing
out sperms not urine.
 In female right ovary is
reduced and oviduct
lead separately into
cloaca.
Ref. – www.edu.com

9. Development
 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
fully grown.
Ref. – Man & Vertebrates by Romer

10. Phylogenetic relationship
 Subclass- Prototheria shows its affinity to
reptiles and birds with little advance over
them.
 Affinities with class - Reptilia
 Claws are present.
 A median T shaped interclavicle present.
 They can survive during starvation for a
longer period.
 Eggs calcareous, uterine gestation is
absent.
 Testes abdominal.

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
cavity.
 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
Prototheria :
 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
rostrum.

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