Trends in Chordate Evolution

Characteristic Features of the Phylum Chordata - Fig 34.2

Single, hollow dorsal nerve cord

Flexible dorsal notochord

Pharyngeal slits or pouches

Muscular postanal tail

Evolutionary relationships among the chordates - Fig 34.1

Non-Vertebrate Chordates

Tunicates - Fig 34.3

Lancelets - Fig 34.4a - Fig 34.4b

Subphylum Vertebrata- Phylogeny - Fig 34.7

Characteristics of the vertebrates

A vertebral column (Snake skeleton) replaces the notochord - Fig 49.28a

Possess a distinct skull (cranium) enclosing the brain (cephalization)

Endoskeleton with axial and appendicular portions, which grows with organism

Hollow dorsal nerve cord enclosed in a groove in vertebral column

Possess characteristic liver, kidneys, endocrine glands

Circulatory system with a heart and closed blood vessels

Endothermy versus ectothermy - Fig 44.4

- Ectothermy = cold-blooded = poikilothermy - Fig 44.3

- Endothermy = warm-blooded = homeothermy

Trends in circulatory systems - Fig 42.3

Trends in respiratory systems - gills to lungs

Characteristics of All Fishes (3 classes)

Gills - Fig 42.20

Single-loop blood circulation - 2-chambered heart

"Class" Agnatha: Jawless fishes: Hagfishes (Craniata) (Fig 34.8) and Lampreys (Fig 34.9)

Evolution of jaws - (Fig 34.10) occurred 410 million years ago.

Radiation of jawed fishes. - all ectothermic

Class Chondrichthyes: Sharks, skates and rays - Fig 34.11 Manta ray - the movie!

Class Osteichthyes: Bony fishes - Fig 34.13

Most fish are ray-finned fishes.

Lobe-finned fishes (coelocanth - Fig 34.14)

Lungfishes - probable ancestors of land animals

A Devonian tetrapod fish - Fig 34.16

Paired fins consist of fleshy, muscular lobe supported by bone core

The path to land. Hypothetical tree of fishes and amphibians. - Fig 34.15

Class Amphibia - Fig 34.17 - Image

- Legs

- Lungs

- Partially divided heart - 3 chambers

- Ectothermic

- Water-bound reproduction - Fig 34.18

Phylogeny of the amniotes - Fig 34.20

Different views of the taxonomic classes of the amniotes - Fig 34.21

Class Reptilia - Fig 34.24

- Amniotic egg - Fig 34.19

- Hatching reptile - Fig 34.22

- Scales made of keratin

- Most with 3-chambered heart

- Ectothermic

- Septum totally divides ventricle in crocodiles and birds (and likely dinosaurs); makes 4 chambers

Class Aves - Birds - Fig 34.29

- Archaeopteryx - Fig 34.27

- Feathers of keratin - Fig 34.25

- Flight skeleton

- Lungs and air sacs near and in bones of back - Fig 42.25

- Wall dividing ventricle is complete, two circulations do not mix

- Endothermic

- Amniotic egg with calcium carbonate for hardness

Class Mammalia - Mammals

- Hair

- Mammary glands

- Endothermic

- Four-chambered heart

- Keratin is structural material for claws, fingernails, hooves, horns, hair

- Differentiation of teeth and refinement of ear bones - Fig 34.30

The Groups of Mammals - See Table 34.1 and - Fig 34.33

Monotremes: egg-laying mammals

- Includes duck-billed platypus and two species of spiny anteater - Fig 34.31a

- Lay shelled eggs

Marsupials: pouched-mammals (Fig 34.31b)

- Early embryo nourished by abundant yolk within shell-less egg and primitive placenta

- Born at early stage of development and most enter marsupium

- kangaroos, opossum, koalas, wallabies

- Most live in Australia where have evolved to fill niches filled by placentals in rest of world through convergent evolution. - Fig 34.32

Eutherian (placental) mammals

- Produce true placenta that nourishes embryos

- Placenta (Fig 46.17) is first organ to form during course of development

- Held in uterus of mother, contains abundant fetal and maternal blood vessels

- Fetus enclosed in amnion