1. 20.10 chordates

2. Phylum chordata Diverse group of over 60,000 species
A. four features distinguish chordates
1. notochord- flexible rod that extends dorsally. In vertebrates, the notochord is replaced by the backbone.
2. Dorsal, hollow nerve chord- parallel to the notochord, the brain is located on one end. This is a unique feature to chordates.
3. pharyngeal pouches or slits- in embryos, develops into gills or middle ear cavities.
4. postanal tail- a muscular tail extends past the anus in all chordates. It mostly shrivels in humans, chimpanzees and gorillas.

3. B. features used to classify chordates-
Cranium- surrounds and protects the brain. Divided into two clades which are hagfish and vertebrates.
Vertbrae: vertebrates are chordates that have a vertebral column of cartilage or bone which protects the spine.
Jaws: bones that frame the mouth. Expands feeding methods.
Lungs: fish have gills for gas exchange, but land animals have lungs.
Limbs: tetrapods are animals that have two pairs of limbs. Examples include amphibians, reptiles, and mammals. Some animals that are classified as tetrapods do not have four limbs though…like snakes.

4. Amnion: eggs of fish and amphibians must remain moist, but reptiles and mammals can breed in arid environments because they have an amniotic egg. This means the egg has membranes that support the embryo and keep it from drying out.
Body covering:
Fish have scales derived from bone
Amphibians have nonscaly skin
Nonavian reptiles(scales), birds(feathers) and mammals(fur) all have coverings based on the same substance- keratin

5. Additional characteristics: regulation of body temperature- ectotherms have body temperature that fluctuates with environment
Endotherms- maintain body temperature by internal mechanisms

6. 20.11 tunicates and lancelets have no cranium or backbone
Tunicates- 3,000 species
Name comes from the tunic that is a protective body covering that the epidermis secretes.
Looks like a sponge but internally has complex organs such as a heart and a complete digestive tract.
Larva are free swimming once they settle the tail and notochord disappear. Tunicates have no segments.
Lancelets resemble small eyeless fish with translucent bodies. They have gills and display all four major chordate characteristics. There are 30 species.

7. 20.12 hagfish have a cranium but lack a backbone
Hagfish- long, slender eel-like organism. Cartilage makes up the notochord and supports the tail. Hagfish are not vertebrates. They live in cold ocean waters eating invertebrates.
They are sometimes called slime hags because they secrete sticky white slime when disturbed.

8. 20.13 fishes are aquatic vertebrates with gills and fins
Fish- most diverse and abundant group of vertebrates- 30,000 species
A. Fishes changed the course of vertebrate evolution-
Features that arose in fish: segmented backbone, jaws, lungs and limbs.
B. fishes may or may not have jaws- two groups of jawless. Jawed fish have three main clades.
Jawless fish- lampreys- simplest organisms that have to have cartilage around the nerve cord. Spend most of their life as larvae. Adults feed on small in vertebrates, although some are parasites.
Jawless fish- ostracoderms(extinct)- The earliest vertebrates in the fossil record.

9. Jawed fishes- placoderms(extinct)- had a notochord and armor with jaws.
Cartilaginous fishes- sharks, skates, and rays. All have skeletons made of cartilage. They have a lateral line that is a sense organ extending along both sides of the fish. It detects vibrations in the water. They must move continually to draw water over the gills
Bony fishes- includes 96% of existing fish species- they have bony skeletons and lateral lines. Gill coverings direct water the gills, swim bladder adjusts bouancy. 2 clades of bony fish: ray finned fishes and lobe-finned fishes(lungfishes and coelacanths) these are the closest relatives to tetrapods.

10. 20.14 amphibians lead a double life on land and water
A. amphibians were the first tetrapods-
Life on land offered amphibians many advantages, but they remain tied to the water due to non-amniotic eggs. Also, larvae respire through gills, but most adults have lungs and can also absorb oxygen through the skin.
B. amphibians include three main lineages: 1. frogs and toads- large mouths, neckless, external fertilization, indirect development. Adaptations to avoid predation- camouflage, vibrant warning coloration, toxins secreted from the skin. Jumping, playing dead, inflating their mouths so they cannot be swallowed by snakes.
2. salamanders and newts- have tails and four legs, lack scaly skin, no claws, always live near water. Internal fertilization. Both adults and larvae are carnivores.
3. Caecilians- limbless, resemble giant earthworms. Live burrowed under soil, carnivores, internal fertilization

11. 20.15 Reptiles were the first vertebrates to thrive on dry land
Reptiles now includes birds in its classification.
Adaptations that allow reproduction on dry land: tough scales, efficient kidneys, internal fertilization and amniotic eggs. Well developed lungs and enhanced circulation increased respiratory capacity.
A. Non avian reptiles include turtles and tortoises; lizards and snakes; tuataras; and crocodilians. All are ectotherms.
Turtles and tortoises- main feature is the shell which is fused to the vertebrae and ribs. Threatened by habitat destruction.
Lizards and snakes: 95% of nonavian reptiles are snakes or lizards. Very similar but snakes don’t have legs. Adaptations: detached tail, camouflage, venom, coiling to kill prey, unhinged jaws to swallow much larger prey.

12. Tuataras are reptiles that closely resemble lizards
Tuataras are reptiles that closely resemble lizards. Native only to a few islands near New Zealand. Most species are extinct.
Crocodilians are carnivores that live in or near water. Covered with heavy scales. Four legs and four chambered hearts. Acute senses and complex behaviors. Lay eggs in nests which adults guard. Some care for hatchlings.

13. B. Birds are warm feathered reptiles
Unique features of birds that set them apart from other reptiles: Most fly so they have adaptations for flight; tapered body, light weight, hollow bones, powerful flight muscles.
Birds are the only modern animals with feathers(epidermal structures that provide insulation an allow for flight, they are important for mating behavior) Birds are endothermic unlike other reptiles.

14. 20.16 mammals Mammals are warm, furry, milk drinkers. A
Mammals share a common ancestor with reptiles. Mammals and their immediate ancestors are synapsids: they have a single hole on each side of the skull, behind the eye orbits.
Distinguishing features of mammals: mammary glands, three middle ear bones, lower jaw consists of one bone, teeth that have four distinct shapes(molars, premolars, canines and incisors.) Four chambered heart, well developed outer layer of the brain, dome-shaped muscular diaphragm to draw air into the lungs.

15. B. mammals lay eggs or bear live young. Two subclasses: 1
B. mammals lay eggs or bear live young. Two subclasses: 1. marsupials and placental mammals
Monotremes are mammals that lay eggs. Marsupials give birth to very tiny immature young. The babies crawl to the marsupium or pouch to continue development.
Placental mammals are also called eutherians. Young develop in the uterus and the placenta connects that maternal and fetal circulatory systems. Placental mammals have much longer pregnancies.