Question

Character not shared by monotremes and reptiles

(a) Body covered by hair and a four-chambered heart

(b) A median T-shaped interclavicle present

(c) Presence of cloaca

(d) Thoracic ribs are single- headed

Answer 1

Hint: Monotremes belong to Kingdom Animalia, Phylum Chordata, and class Mammalia. Reptiles are chordates and they too belong to Kingdom Animalia. Monotremes are considered as the most primitive form of mammals. Reptiles are mostly oviparous. Reptiles are cold-blooded and mammals are warm-blooded.

Complete answer:

Character not shared by monotremes and reptiles is a body covered by hair and a four- chambered heart. Monotremes are mammals and reptiles of a different class. The mammals possess a four- chambered heart but the reptiles have a three-chambered heart except for the crocodile which, being a reptile, has a four- chambered heart.

So, the correct answer is `body covered with hair and four- chambered heart`.

Additional information:

- Monotremes are among the three main groups of living mammals besides placentals and marsupials.

- They lay eggs rather than carrying their young ones inside their bodies. But the female monotremes do feed their young ones with milk. They are prototherians (i.e., they don’t have corpus callosum and placenta).

- Platypus is an example of monotremes.

The character which differentiates reptiles from mammals mainly is that mammals have hairs on their bodies and possess the four- chambered heart and have mammary glands, whereas reptiles possess a three- chambered heart except for crocodiles. They possess incomplete circulation.

A median T- shaped interclavicle present-  Only marsupials and placentals do not possess interclavicles while it is present in monotremes.

Presence of cloaca-  Cloaca is present in many adult animals like birds, reptiles, etc. and not in mammals.

Thoracic ribs are single- headed-  Monotremes have fixed ribs that are not single- headed whereas reptiles possess single-headed ribs.

So, the correct answer is (a) Body covered by hair and a four-chambered heart

Note:  Crocodiles are an exception to reptiles as they possess a four- chambered heart. Monotremes belong to class Mammalia and they lay eggs and are an exception to class Mammalia for example platypus (Ornithorhynchus) . All members of class Mammalia are characterized by the presence of mammary glands and hairs on the body surface.