Vertebrates 2

Vertebrates 2 - Vertebrates 2: Mammals and human evolution...

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Unformatted text preview: Vertebrates 2: Mammals and human evolution Mammalian Radiation in Wake of Cretaceous Extinctions (65 mya) With extinction of dinosaurs & fragmentation of continents at close of Mesozoic, mammals undergo extensive adaptive radiation ~ 5,300 extant species of mammals Derived characters of mammals Mammalia defined by presence of mammary glands Milk, a balanced diet of fats, sugars, proteins, minerals, & vitamins Mammals also have hair, made of the keratin Hair & subcutaneous fat retain metabolic heat Mammals are warm blooded ( Endotherms) supports active metabolism, made possible by efficient respiration & circulation Muscular diaphragm & four-chambered heart 4 3 2 1 37&C 5& C Relaxed homeotherms Derived characters of mammals Born, not hatched Fertilization internal, embryo develops in uterus In eutherian (placental) mammals & marsupials lining of uterus & extraembryonic membranes form placenta , which nourishes embryo Generally, with larger brains than vertebrates of equivalent size Many species capable of learning Relatively long parental care extends time for learning important skills from parents Feeding adaptations of jaws & teeth (differentiation) Unlike uniform conical teeth of most reptiles, mammalian teeth have various shapes & sizes ANCESTRAL MAMMAL Monotremata Marsupialia M o n o t r e m e s ( 5 s p e c i e s ) M a r s u p i a l s ( 3 2 4 s p e c i e s ) E u t h e r i a n s ( 5 , 1 s p e c i e s ) Xenarthra Rodentia Lagomorpha Primates Dermoptera (flying lemurs) Scandentia (tree shrews) Carnivora Cetartiodactyla Perissodactyla Chiroptera Eulipotyphla Pholidota (pangolins) Proboscidea Sirenia Tubulidentata Hyracoidea Afrosoricida (golden moles and tenrecs) Macroscelidea (elephant shrews) Mammal phylogenetic tree Fig. 34-35a By the early Cretaceous, the three living lineages of mammals emerged: monotremes, marsupials, and eutherians Mammals did not undergo a significant adaptive radiation until after the Cretaceous Monotremes (meaning single opening) Monotremes are a small group of egg-laying mammals consisting of echidnas and the platypus Platypus No nipples! Low body temp No teeth in adults Cloaca Reptile-like egg Short-beaked echidna Marsupials Marsupials include opossums, kangaroos, and koalas Higher metabolic rates, give birth to live young, have nipples The embryo develops within a placenta in the mothers uterus A marsupial is born very early in its development It completes its embryonic development while nursing in a maternal pouch called a marsupium Australian Marsupials Australian marsupials fill niches occupied by eutherian mammals elsewhere Convergent evolution of marsupials & eutherian mammals that occupy similar ecological roles Convergent evolution: The evolution of species from different taxonomic groups toward a similar form Eutherians (Placental Mammals) Compared with marsupials, eutherians have a longer period of pregnancy Young eutherians complete their embryonic development within a...
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Vertebrates 2 - Vertebrates 2: Mammals and human evolution...

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