INTRODUCTION of Man’s Place in Animal Kingdom
All living organisms can be placed into one of five kingdoms: plants, animals, fungi, nucleated single celled organisms, and bacteria (Relethforth, 2010). Of all these living organisms, about 5 to 10 million species are animals and plants inhabiting on the surface of this earth today (Standford et al.2012). Texonomically animal kingdom in which man belong to can be broadly classified into 2 groups viz.,
Protozoa – Unicellular and
Metazoa – Multicellular. Multicellular animals though differing in form and structure have some fundamental similarities among them such as the arrangement of cells, body symmetry, nature of coelom, segmentation, presence or absence of notochord etc.
Man belongs to this group. On the basis of presence or absence of notochord – a flexible internal rod that runs along the back of the animal which acts to strengthen and support the body, metazoans are further divided into two Phylum – Non-Chordata or Invertebrates (notocshord absent) and Chordata (notochord present). Owing to the presence of notochord, man is placed in the later. Phylum Chordata which includes animals characterized by the presence of a notochord is further divided into three sub-phylum – Urochordata (Notochord in larva stage), Cephalochordata (Notochord extend from head to tail) and Vertebrata (notochord is replace by vertebral column). One characteristic of vertebrates is that they have bilateral symmetry, which means that the left and right sides of their bodies are approximately mirror images. Imagine a line running down a human being from the top of the head to a spot between the feet. This line divides the body into two mirror images (Relethforth, 2010). The presence of vertebral column in man justify his position in the sub-phylum vertebrata which has been further divided into five classes, viz. Pices, Amphibian, Reptilian, Aves and Mammalia. The nature of living and structure of the reproductive organs of Amphibian stand away from considering man as a member of that class. The Reptile is cold-blooded animals and that is sufficient to excluded warm-blooded man for the class Reptile. The absence of feathers would eliminate the idea of including man with the other members of the class Aves. Therefore, naturally, man belongs to the class Mammalia
CHARACTERISTICS OF MAMMALS
- Mammals are air breathing warm-blooded vertebrates,
- They have epidermal covering in the form of hair.
- Presence of mammae or mammary glands is the most important feature which justifies for giving the term “Mammal”
- Most mammals are viviparous i.e do not lay eggs but give birth to young ones directly. young ones are nourished from the blood system of mother through placenta before the birth and after the birth by breast milk of the mother
- Presence of sweat and sebaceous glands
- Presence of inter vertebral disc in the vertebral column.
- Scapula of pectoral girdle articulates with the sternum by means of a clavicle.
- Four chambered heart and lungs freely suspended within the cavity of thorax
- Heterodont i.e., teeth of different types and are thecodont i.e. embedded in the sockets of jaws.
- The skull is dicondylic i.e., with two occipital condyles on two sides of foramen magnum in the skull
- RBCs are circular in shaped and non-nucleated.
- External fertilization.
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