Mammalia Reproduction By Rachel Nico Brandon Lauren Mammalia

Mammalia & Reproduction By: Rachel, Nico, Brandon, Lauren

Mammalia • Evolved from reptiles during the Mesozoic era • This is around the time when dinosaurs evolved from different reptiles • Underwent adaptive radiation to fill major land niches during the Cenozoic era

Major Characteristics of Mammalia • Fur or hair • Subcutaneous fat-fat under the skin used for insulation • Most give birth to LIVE young • Mammary glands ▫ ▫ glands that produce milk to feed young after birth Sweat glands Oil glands Saliva glands

Groups of mammals 1. Monotremes 2. Marsupials 3. Placentals

Monotremes • Oviparous-lay eggs ▫ Offspring have reptilian-like amniotic eggs �Amniotic egg: waterproof egg that provides nourishment for the embryo �When hatched, baby looks like miniature adult • Found only in Australia and New Guinea • Examples: ▫ duckbill platypus ▫ Spiny anteater (echidna)

Marsupials • Viviparous-give birth to live young ▫ Young are born very early, and so must finish development in the mother’s pouch • Found mostly in Australia and South America • Examples: ▫ Koalas ▫ Kangaroos ▫ Opossums

Placentals • Viviparous-give birth to live young ▫ Capable of longer period of development in mother’s uterus because of placenta Placenta: made of tissues; allows for oxygen, nutrients, and waste to be transferred from mother to baby or baby to mother • Examples: ▫ Humans ▫ Mice ▫ Whales ▫ Manatees

Mammalia & Reproduction

Reproduction of Fish and Amphibians Fish Amphibians • External fertilization 1. Lay lots of little eggs: ▫ Each egg has lower chance of surviving ▫ Requires less energy ▫ Mostly Osteichthyes 2. Lay few big eggs: ▫ Requires lots of energy ▫ Egg has greater chance of surviving ▫ Mostly Agnathans • External fertilization • Oviparous-egg laying • Eggs must be kept moist, so most Amphibians lay their eggs in water

Reproduction of Reptiles and Birds Reptiles (Reptilia) Birds (Aves) • Internal fertilization • Most oviparous, some are ovoviviparous ▫ Ovoviviparous-keep eggs internally and bear live young • Development in amniotic egg • Most do NOT care for young • Internal fertilization • Oviparous-lay eggs • Most of development is in an amniotic egg • Egg shell is made of calcium, and so is harder than a reptilian shell • Sometimes birds taken turns having babies and caring for babies

Amniotic Egg • Shell: prevents water loss • Albumen: extra food • Chorion: allows for gas exchange • Yolk: provides food for the embryo • Amnion: cushions embryo in fluid • Allantois: collects waste and helps in gas exchange