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

Reproduction

Reproduction of Fish and AmphibiansFish Amphibians

• External fertilization1.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