Reptile Derivatives

Reptile Derivatives

Birds and mammals

Archaeopteryx = “first” bird

Reptilian features

teeth, tail, pelvis – no sternum

skull features

Avian (bird) features

feathers, longer front limbs.

Why feathers ?; insulation

Why fly?: to glide from tree to tree

or to chase insects?

Mammal lung = dead end – incomplete exchange of Oxygen

Bird lung – one way movement = flow through and current counter current = greater efficiency and lighter weight.

Hespirornis = toothed, flightless, loon like diving bird

Rattites = worldwide, ancient flightless birds.

7 is Vega island, off of James Ross Island at tip of Antarctic Peninsula.

Vega Island, Antarctic Peninsula

Pleisiosaur front arm (fin)

Vegavis, from Vega Island in Western Antarctica – Cretaceous in age (pre-meteor)

A ‘duck’

Origin of Modern birds (Neornithes) before end of Cretaceous

Use of DNA

• Gives relationship

• Distance in time (if mutation at constant rate)

• Does not use whole DNA but rather segments that evolve with time

• Different authors use different DNA seqments.

ratites

Ducks and grouse

Unexpected relationships

Hawks, falcons not related

Penguins – albatrosses

Flamingos – grebes !!!

Origin of Mammals

1. synapsids, leading to mammals are the first group of reptiles

2. Based on differences from all reptiles and birds, mostly in features of soft anatomy.

• ventral aorta leaves heart, splits into aortic arches to gills

• in amphibians , single vessel leaves heart, then splits to left and right sides to form dorsal aorta

• in mammals and birds, same system in embryo, but in adults, ventral aorta splits back to the heart so the arches come directly off heart, one to lungs, others to body. In mammals and birds, finally reduced to a single arch

• in reptiles, the split involves a twist. In mammals it does not, so the remaining aortic arch in on different sides in reptiles and birds vs mammals.

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

Hair, tooth regionalization, forward pointed toes of same length, limbs under body,

Reptilian scales with sensory papillae in between.

Papillae become hair – for insulation

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 shelled 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.

Marsupials not primitive, but different

Designed for an unpredictable environment – can dump kid to save mother.

The Path leading to humans: choices along the way.

• bilateral symmetry

• internal skeleton

• active life – carnivore, omnivore? warm blooded, good senses

• daylight living – visual shape perception = brains for memory storage

• tropical climate – k species strategy

• social organization – based on?? Food sources? Defense?

This gets us to monkeys or squid. Now what to lead to humans?

Suggested, upright, tools, social structure, none correlated to big brain

probably speech – (no direct fossil record)

Human origins – arboreal nocturnal monkey

Arboreal diurnal monkey

Terrestrial monkey to terrestrial ape

To human , with what does the change correlate ?