Lecture 13 Dueterosomes

Echinoderms

Radially symmetrical adults
Larvae are bilateral
Mesodermal skeleton in the dermis (skeletal structure in skin)

Chordates Shared traits

Notochord: embryonic spinal cord

1. forms in mesodermal

Dorsal hollow nerve chord: Becomes the brain and nervous system

1. In Ectodermal

Pharyngeal slits: Opening in the digestive tube posterior to the mouth

Amphioxus: Lancelet

Divergence occurred 520 MYA
Gene loss has not occurred in amphioxus
Gene loss is common in Craniata and Urochordata

Craniata - Organisms with heads

The Skull/Cranium

Vertebrata

Organisms with a spine

Gnathostomes

Jawed vertebrates

1. homologous structure with gill arches

Challenges of Life on land

• Air breathing: Need for lungs

• Limbs: being able to support the body and move.

• Stable, moveable structure: Interlocking Skeletal structure

• Desiccation: preventing loss of water

Exaptation

A preexisting trait that evolves to better suit a change in the environment

Original functions of lungs

Buoyancy

Exaptation from Air Bladder

Amniote egg

Allowed for the separation of the embryo from the water

Structure:

1. Amnion: fluid filled cavity protects the embryo from mechanical shock

2. Chorion: Exchanges gases between the embryo and the air

3. Allantois: Disposal sac for metabolic wastes, and works with chorion to dispose gas waste

4. Yolk sac: Holds nutrients

Tiktaalik

Transition phase from lobe-fined fishes to terrestrial animals

Adaptive radiation

Speciation from new niches.

Feathers

Scales - Feathers
Exaptation