B.Sc. Zoology Dept. of Zoology, Part- II RLSY College, Bakhtiyarpur (Patna) Patliputra University, Bihar -------------------------------------------------------------------------------------------------------------------------------------- Paper-III Mammals Characters and distribution of Prototheria and Metatheria Mrs. Arusha Modi Assistant Professor CHARACTERS AND DISTRIBUTION OF PROTOTHERIA AND METATHERIA ❖ Introduction Monotremes or Prototherians are egg laying (oviparous) mammals. They are the most primitive mammals. Currently, only three species of Monotremes are extant (surviving) viz. Duckbilled Platypus and two species of Echidnas. Monotremes are found only in Australia and New Guinea. The word “monotreme” means “one opening” which denotes that Monotremes have only one cloaca that is used as anus, unitary tract as well as for reproduction. Marsupials or Metatherians include kangaroos, wallabies, koala, possums, opossums, wombats, numbat etc. There are around 330 species of Marsupials distributed in three continents viz. Australia South America and North America (only two species are found north of Mexico). The term marsupium means a pouch. Marsupials give birth to a relatively undeveloped young, which often resides in the pouch with the mother for a certain time after birth. • Salient features Prototheria (Egg laying mammals) 1. Ear without pinna. 2. No nipple 3. No corpus callosum 4. Testes abdominal, no scrotum 5. Digestive and urinogenital tracts open out through cloaca and cloacal aperture. 6. No marsupial pouch 7. Oviparous 8. No placenta Example of Prototheria: Duck billed platypus (Ornithorynchus anatinus), Anteater (Tachyglossus) B.Sc. Zoology Dept. of Zoology, Part- II RLSY College, Bakhtiyarpur (Patna) Patliputra University, Bihar -------------------------------------------------------------------------------------------------------------------------------------- Metatheria (Pouched mammals or marsupials) 1. Ear with pinna 2. Nipples abdominal 3. No corpous callosum 4. Scrotum in font of penis 5. Digestive and urinogenital tracts open out by separate apertures that are controlled by a common sphincter muscle. 6. Marsupial pouch often present 7. Viviparous 8. Placenta small, intrauterine development brief, young extremely small and helpless, brought up in marsupial pouch, if present. Example of Metatheria: Kangaroo (Macropus), Opossum (Didelphis) ------------------------------------------------------------------------------------------------------- .