Reptile Derivatives Birds and mammals. Archaeopteryx = “first” bird.

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.