Reptile Derivatives Birds and mammals

Archaeopteryx = “first” bird

Reptilian features teeth, tail, pelvis – no sternum skull features Avian (bird) features feathers, longer front limbs.

Shy feathers; insulation

Why fly?: to glide from tree to tree or to chase insects?

Synapsids = mammal like reptiles

Pelycosaurs = Dimetrodon

Function of “sail” Camoflage? Swimming? Thermoregulation Note: nasty carnivore

Therapsids

How to make a Mammal Develop for carnivory = active Hair – warm bloodedness Limbs; under body, toes of equal length Teeth; regionalization, multi roots, cutting Lower jaw – one bone Not there – change in reproduction

A definition of mammal = three bones in middle ear, one bone in lower jaw

Mammals; monotremes, platypus and echidna Lay eggs.

Echidna – egg in pouch, Hatches in 9 days – young in pouch for 12 weeks. Gets milk.

Marsupials and Placentals – Parallelism And no eggs

Marsupial and placental reproduction; clevage total and equal - blastula forms with inner cell mass

Inner cell mass forms layers of cells inside blastula Embryo implants into uterine wall

On plate inside embryo – primitive streak forms Get chorion, amnion, allantois and yolk sac Placenta = chorion plus yolk sac in marsupials Placenta = chorion plus allantois in placentals

Marsupial pouch with ‘baby’

opossum young on nipple. Marsupiaols not primitive, but different Designed for an unpredictable environment – can dump kid to save mother.