3.4 continued

Vertebrates – phylum chordata Organized into 5 classes: fish, amphibians, reptiles, birds and animals Aside form fish, the other four classes developed from tetrapods – a vertebrate with 2 pairs of limbs Common characteristics: They have a notochord = rod shape that entends the length of the body They have a dorsal nerve = tube shape “

Class - fish All have gills to obtain dissolved oxygen from water Habitat: fresh water or salt water Size: <1cm (dwarf carp)  12m (whale shark) Evolved traits: Paired fins & jaws  sharks and rays Skeleton  “bony fish” Oldest fish = lamprey – no fins, no jaw, no skeleton!

Class - Amphibians First “terrestrial” tetrapods Their life cycle is only partially on land Able to do this because of the evolution of lungs and using their skin as an organ for gas exchange They mostly reproduce using external fertilization This class is generally split up into 2 orders: frogs &toads and salamanders

Class - Reptiles Divided into 3 orders of reptiles: 1) lizards and snakes 2) turtles 3) corcodilians Evolved to not be dependent on living in aquatic ecosystems Development of body scales = waterproof barrier to prevent dehydration Dependent on lungs (no moist skin!) Shelled eggs = prevent dehydration Internal fertilization, since no longer in aquatic environments!

Class - Birds Evolved after reptiles Have feathers Most birds can fly Weight saving adaptations Bones are lightweight and hollow Toothless skull Compact bodies Internal fertilization and shelled eggs, like reptiles

Reptiles vs Birds Although related, based on common characteristics, there are differences that have evolved: Difference #1 Reptiles = ectothermic – dependent on environment for body temp Birds = endothermic – use own metabolism to determine body temp

Difference #2 Reptiles – circulatory system has a 3 chamber heart Birds – have a four chamber heart

Class - mammals Endothermic, 4 heart chambers, well developed brains… Have mammary glands (females) – production of milk for young Have hair for multiple purposes: Insulation Communication / defence Camouflage Some species have “reduced” hair – like humans, elephants and mole rats

Mammals – into 3 groups Momotremes Egg laying mammals! Only examples: duck billed platypus 2) Marsupials Pouched mammals Ex. Kangaroos and koala bears 3) Placental mammals Have a placenta – organ that develops during pregnancy for nutrient and oxygen exchange between the mother and developing offspring

HW: Pg 124 #11-14 Study for test on Friday