Mammals Flashcards
Mammals
Sub-group of synapsids
Typical body plan includes four-legged terrestrial animals, but some mammals are adapted for sea, air, trees, and have two legs
Amniotes that have body hair and produce milk
Mammal Shared Derived Traits
- Mammary glands that produce milk
- Hair or fur for insulation, protection, and sensory perception
- Three middle ear bones from left over jaw bones
- Endothermic
- Unique dentary squamosal jaw point
- Differentiated (Specialized) teeth
- Larger brains and viviparous
Origin of Mammals
Synapsids evolved during Carboniferous period with dominant tetrapods then Permian mass extinction drastically reduce synapsid diversity
Then in Triassic, synapsids evolved mammalian traits and true mammals emerged in Jurassic period
Early Evolution of Mammals
Progressive enlargement of dentary bone then development of secondary palate
By the early Cretaceous, there were three main lineages of mammals and then mammals greatly diversified after Cretaceous mass extinction
Major Clades of Extant Mammals
Based on mode of birth and development
- Monotremata
- Marsupialia
- Eutheria
Monotremes
Includes echidnas and the platypus are a small group of egg-laying mammals
Oviparous but still provide milk to young after hatch
Lack teeth
Shared Derived Traits of Marsupials and Eutherians
- Viviparous
- Placenta bearing
- Postpartum nursing
Marsupials
Include opossums, kangeroos, and koalas
Embryo development within a placenta in the mother’s uterus
Born partially developed embryos and has to craw through mother’s fur to reach the pouch that encloses milk glands
Eutherians
Non-marsupial mammals distinguished by a more complex placenta (chorioallantoic placenta)
Eparate urinary and anal openings with NO cloaca
Undergone adaptive radiation
