Lecture 33/34: Chordates

diagnostic features of Chordates

1. notochord: stiff but flexible rod derived from mesoderm

2. dorsal hollow nerve cord (DHNC): conveys neural signals along the a-p axis, derived from ectoderm via process of neurulation

3. post-anal tail: often used for locomotion

where did chordates originate

in aquatic environments

what group colonized terrestrial land

tetrapods

diagnostic features of vertebrates

1. vertebrae surrounding the DHNC

2. cranium (brain case)

diagnostic features of Gnathostomes

1. jaws (derived from cartilaginous gill-arch supports)

2. teeth

3. bone (derived from the mesoderm) provide a rigid endoskeleton

diagnostic features of Osteichthyes

1. swim bladder: a gas filled sac that helps regulate buoyancy

2. operculum: covering over gill arches that facilitate respiration

diagnostic features of Rhipidista

1. lungs: respiratory organs derived evolutionary from swim bladder

   • initially unpaired, with subsequent evolution of paired lungs

diagnostic features of Sacropterygii

1. fleshy fins articulate with the body via signal bony element

diagnostic feature of Tetrapods

1. 4 jointed limbs (derived evolutionary from lobed fins)

tetrapod diveristy

1. amphibians

2. amniotes

amphibians

• restricted to mesic terrestrial habitats bc they have poorly developed lungs

  • many species partially rely on cutaneous respiration

• and reproduction

  • many species are metamorphic with an aquatic larval stage

• includes frogs/toads, salamanders and (secondarily limbless) caecilians

amniotes

• evolved several features that enabled colonization of more fully terrestrial habitats

• includes reptiles and mammals

diagnostic features of amniotes

1. amniotic egg: allows embryo to develop in a contained aqueous environment, thus severing dependence on water for reproduction

2. impermeable skin: reduces water loss from the body

3. efficient kidneys: allow nitrogenous metabolic byproducts to be excreted as concentrated urine to minimize water loss

diagnostic features of reptiles

1. 3-chambered heart

2. two cranial fenestrae (skull opening)

reptile diversity

1. lepidosaurs

2. chelonia

3. crocodilia

4. pterosaurs

5. dinosaurs

Lepidosaurs

ecologically and morphologically diverse group with many secondarily limbless species

ex: Tuatara, lizards, snakes, amphisbaenians

chelonia

primarily aquatic group with a bony shell (compromised of carapace and plastron)

ex: turtles and tortoises

crocodilia

marine and freshwater predators confined to tropical and warm-temperate regions

4 chambered heart

ex: crocodiles, alligators, and caiman

Pterosaurs

now entirely extinct

first group of vertebrates to evolve powered flight , hollow bones, membranous wings, warm blooded with hair-like filaments known as pycnofibers on the head and torso

dinosaurs

were dominant terrestrial vertebrates throughout Jurassic and Cretaceous, with only one group, Birds, surviving the mass extinction

birds are warm blooded, 4 chambered hearts and power flight

ex: Stegosaurs, brachiosaurus, tyrannosaurus, birds

diagnostic features of Mammals

1. mammary glands: secrete nutrient-rich milk to nourish young

2. endothermy: high metabolic rates and facilitates active lifestyles

3. hair/fur: provides insulation to minimize heat loss from body

4. one cranial fenestra: skull opening

mammal diversity

1. monotremes

2. marsupials

3. eutheria

monotremes

lay shelled eggs and occur in australia and New Guinea

ex: Platypus and echidna

marsupials

have placenta and ventral pouches with teats

after emerging from uterus, juveniles crawl to the pouch where they are nourished until fully developed

eutheria

• placentals

• have a well-developed placenta and give birth to developed young.

• group includes ~4000 species that are morphological and ecologically diverse

• most species belong to Chiroptera (bats) and Rodentia (rodents)

  • anteaters, whales, bats, beavers, lions

human diagnostic features

1. large brain size

2. extensive construction and use of tools