Question

Humans are referred to as the “ideal mammal”.

a) What features of mammals have made them adaptable as a class?

b) Which adaptations have humans created to the mammal plan to be called “ideal”?

c) Compare development observed in the mammals to the Orthinodelphia and Metatheria.

d) What does development of these groups tell one about their evolutionary relationships with one another & the other tetrapod groups?

Answer 1

a. Humans are ideal mammals because they possess Bipedal Locomotion, power of speech and communication, highly developed nervous system, can lead terresttrial life, tail absent. They give birth to young ones, fertilisation is internal. 2 cerebral hemispheres connected by corpus callosum, 12 pairs of cranial nerves present. Lower jaw or mandible is made of sinble bone. Dentition is heterodont, diphyodont and thecodont. Placenta present.

b. Bipedal locomotion, opposable thumb and highly complex brain are the adaptations of a human to be called ideal.

c. Ornithodelphia comes under sub-class Prototheria. The centra of the vertebra are devoid of epiphyses.( Monotremes)

The coracoid articulates with the sternum directly. There is a T shaped inter-clavicle that supports clavicle. Cerebellum is left completely uncovered by cerebral hemispheres. Cochlea in the inner ear is only slightly bent and not coiled into a spiral. Malleus is very large. Long urogenital canal opens into the front part of the cloaca. Testes remain in abdomen throughout life.The mouths of Fallopian tubes are not fimbricated. Mammary glands are situated one upon each. Teat absent.

Ornithodelphia are found in Australia.

Metatheria:

Mammary glands are with teat or nipples. Cochlea is much coiled, Pinna present. Testes extra abdominal. Yolk sac placenta is present. Young ones are born with extremely premature condition and undergo further development in marsupium or abdominal pouch. Brief intra uterine development.

d.Monotremes are primitive mammals . One examle is eg laying mammal. The subsequent developments have risen due to adaptations needed to become highly developed mammals. Egg laying character goes off in higher mammals. Mammary glands are placed horizontally and are with teats. Brain becomes highly developed.Development are the results of evolution.