Lesson 11 of 12 · 7 min
Birds and mammals
NCERT §4.2.11.6, §4.2.11.7, Table 4.2
Crows and pigeons fight over rice on Ammu's terrace. At dusk fruit bats flap out of the tamarind tree. On the last day, her teacher asks her to tell the bat and the pigeon apart using only features, not the fact that one has fur.
The lesson in notes
In short
Birds (Aves) are marked by feathers, and most can fly; flightless ones such as the ostrich are the exception. They have a beak, and the forelimbs are modified into wings.
The hind limbs usually bear scales and are adapted for walking, swimming or clasping branches. Bird skin is dry, and its only gland is the oil gland at the tail base.
The bird endoskeleton is fully ossified, and the long bones are pneumatic: hollow, with air cavities inside. The gut has two extra chambers, the crop and the gizzard.
Birds have a completely four-chambered heart and are warm-blooded (homoiothermous), keeping a constant body temperature. They breathe with lungs, helped by air sacs connected to the lungs. Sexes are separate, fertilisation internal, eggs are laid and development is direct. Examples: the crow Corvus, the pigeon Columba, the parrot Psittacula, the peacock Pavo, the vulture Neophron, the penguin Aptenodytes and the flightless ostrich Struthio.
Mammals live in every kind of habitat, from polar ice caps and deserts to mountains, forests, grasslands and dark caves, and some fly or live in water. Their most distinctive feature is mammary glands, which make milk to feed the young.
Mammals have two pairs of limbs, which may be built for walking, running, climbing, burrowing, swimming or flying. The skin has hair, external ears (pinnae) are present, and the jaw carries different types of teeth.
Mammals have a four-chambered heart, are homoiothermous and breathe by lungs. Sexes are separate and fertilisation is internal. Nearly all give birth to live young, and development is direct.
Mammal examples. Egg-laying: the platypus Ornithorhynchus. Viviparous: the kangaroo Macropus, the flying fox Pteropus, the blue whale Balaenoptera, the common dolphin Delphinus, the camel Camelus, the monkey Macaca, the rat Rattus, the dog Canis, the cat Felis, the elephant Elephas, the horse Equus, the tiger Panthera tigris and the lion Panthera leo.
Table 4.2 ties the phyla together: segmentation is present only in Annelida, Arthropoda and Chordata; the gut is absent in Porifera and incomplete in Coelenterata, Ctenophora and Platyhelminthes; circulatory and respiratory systems appear in the table from Annelida and Arthropoda onwards respectively.