AP Biology, Chapter 34
Vertebrate Evolution and Diversity

SUMMARY
INTRODUCTION

INVERTEBRATE CHORDATES AND THE ORIGIN OF VERTEBRATES
	Introduction
		1. Distinguish between the two subgroups of deuterostomes.
			a. Echinoderms: starfish; water vascular system, radially symmetrical adults
			b. Chordates: you all, fish, etc.; see #2
	Four anatomical features characterize Phylum Chordata
		2. Describe the four unique characteristics of chordates.
			a. Notochord
				i. Ventral to dorsal nerve cord, supports
				ii. Persists in Cephalochordata and Agnatha
				iii. Develops into backbone in most
			b. Dorsal nerve cord
				i. Dorsal anterior-posterior ridges of ectoderm rise and fuse medially
				ii. Forms central nervous system
			c. Pharyngeal slits
				i. Slits/folds behind the mouth
				ii. Water through the mouth and out the sides (gills, filter feeding)
				iii. Develops into gas exchange, jaw, and gearing structures
			d. Postanal tail: propulsion in aquatic species
	Invertebrate chordates provide clues to the origin of vertebrates
		3. Distinguish between the three subphyla of the phylum Chordata and give examples of 
		each.
			a. Urochordata (tunicates)
				i. Tadpole-like larvae
				ii. Sessile adult lacking notochord, dorsal nerve cord, tail
			b. Cephalochordata (lancelets)
				i. Retain all chordate characteristics as adults
				ii. Marine filter feeders
			c. Vertebrata (fish  mammals)
				i. Neural crest, cephalization, bone and/or cartilage endoskeleton
				ii. Widespread, active, and diverse
		4. Describe the two-stage hypothesis for the evolution of vertebrates from invertebrates.
			a. Cephalochordates are most closely related
			b. Two steps
				i. Paedomorphosis (mutation to produce reproductive larvae)
				ii. Elimination of metamorphosis

INTRODUCTION TO THE VERTEBRATES
	Introduction
	Neural crest, pronounced cephalization, a vertebral column, and a closed circulatory 
	system characterize Subphylum Vertebrata
		5. Describe the specialized characteristics found in the subphylum Vertebrata and explain 
		how each is beneficial to survival.
			a. Neural crest
				i. Gives rise to cranium, cranial and peripheral nervous tissue, part of the 
				heart
				ii. Furthers cephalization; allows for more complex behavior
			b. Vertebral column
				i. Protects nerve cord
				ii. Supports, allows larger size, supports appendages
				iii. Base for more powerful muscles
			c. Complex respiratory and cardiovascular systems
				i. Gathers and delivers more oxygen
				ii. More oxygen, more energy, more complex behaviors
	Overview of vertebrate diversity
		6. Define and distinguish between agnatha, gnathostomes, tetrapods, and amniotes.
			a. Agnatha: jawless fish; lamprey, hagfish
			b. Gnathostomes: all jawed vertebrates
			c. Tetrapods: jawed vertebrates with legs 
			d. Amniotes: jawed vertebrates with legs and complex membranes protecting the 
			egg

SUPERCLASS AGNATHA: JAWLESS VERTEBRATES
	Introduction
	Lampreys and hagfishes are the only extant agnathans
		7. Define and compare the groups Myxini, Cephalaspidomorphi, ostracoderms, 
		conodonts, and placoderms.
			a. Myxini; hagfishes; no larva, mouth surrounded by short tentacles
			b. Cephalaspidomorphi: lampreys; larvae, mouth surrounded by adhesive sucker
			c. Ostracoderms: extinct, armored, bottom feeders
			d. Placoderms: extinct, toothless gnathostomes with paired fins
		8. Distinguish between agnathans and fishes.	
			a. Agnatha: jawless with no paired fins
			b. Fish: jaws and paired appendages

SUPERCLASS GNATHOSTOMA I: THE FISHES
	Introduction
	Vertebrate jaws evolved from skeletal supports of the pharyngeal slits
		9. Describe the function and evolution of jaws.
			a. Function
				i. Move dorsoventrally
				ii. Allow efficient feeding
			b. Evolution
				i. Derived from skeletal supports of anterior pharyngeal slits
				ii. Progressive enlargement first aided efficient respiration
				iii. Similar supports had previously been adapted into the cranium
	A cartilaginous endoskeleton reinforced by calcified granules is diagnostic of Class 
	Chondrichthyes
		10. Describe and distinguish between the classes Chondrichthyes and Osteichthyes, 
		noting the main traits of each group.
			a. Chondrichthyes
				i. Cartilage fish; sharks, skates, ratfish and rays
				ii. Additional adaptations
					.Powerful jaws and swimming muscles
					.Acute senses: vision, chemical, lateral line for pressure
					.Internal fertilization
					.Multiple gill slits
	A bony endoskeleton, operculum, and swim bladder are hallmarks of Class 
	Osteichthyes
			b. Osteichthyes
				i. Bony fish
				ii. Additional adaptations
					.Single gill opening covered by operculum
					.Swim bladder to control buoyancy
					.Flexible fins for better maneuverability
					.Scale-covered skin with mucus
		11. Identify and describe the main subgroups of the class Osteichthyes.
			a. Actinopterygii: ray-finned fish
			b. Sarcopterygii
				i. Lobe-finned and lungfish
				ii. Probable ancestor of tetrapods

SUPERCLASS GNATHOSTOMA II: THE TETRAPODS
	Amphibians are the oldest class of tetrapods
		12. Describe the early evolution of amphibians.
			a. Oldest fossils, 365 million years old
			b. Lungfish adapted to land to escape predators, eat bugs and worms
		13. Describe the common traits of amphibians and distinguish among the three orders of 
		living amphibians.
			a. Common traits
				i. Fish-like tadpole with fins and gills, tetrapod adult with legs and lungs
				ii. Water and gas permeable skin
				iii. Eggs must be laid in water or aqueous medium
				iv. Many have complex social behavior
			b. Extant orders
				i. Urodeles: salamanders; have a tail
				ii. Anurans: frogs and toads; no tail
				iii. Apodans: legless salamanders
	Evolution of the amniotic egg expanded the success of vertebrates on land
		14. Describe an amniotic egg and explain its significance in the evolution of reptiles, 
		birds, and mammals.
			a. Amniote egg
				i. Surrounded by chorion for gas exchange
				ii. Embryo immediately surrounded by protecting amnion
				iii. Yolk sac stores food
				iv. Allantois stores wastes and helps in gas exchange
			b. Allowed egg-laying out of the water; a primary terrestrial adaptation
	A reptilian heritage is evident in all amniotes
		15. Distinguish between the two systems of classifying amniotes (synapsids, anapsids, 
		and diapsids versus reptiles, birds, and mammals).
			a. Synapsid, anapsid, diapsid
				i. Based on number of muscle holes in the skull
				ii. Groups
					.Synapsid: one hole; extinct therapsid reptiles and all mammals
					.Anapsid: no holes; all extinct (?), testudines now with diapsids
					.Diapsid: two holes; lizards, snales, dinosaurs, birds
			b. Traditional
				i. Reptiles, birds, mammals
				ii. Based on classification of extant groups 
		16. List the distinguishing characteristics of members of the class Reptilia and explain any 
		special adaptations to the terrestrial environment.
			a. Amniote eggs with a water-retaining shell can be laid on land
			b. Scaly, keratinized, waterproof skin is wear-resistant and saves water
			c. Well-developed lungs make up for loss of skin respiration
		17. Compare the interpretations of dinosaurs as ectotherms or endotherms.
			a. Ectotherms 
				i. Age of reptiles (Mesozoic) was consistently warm
				ii. Ectotherms require 10% of the food energy
				iii. Large surface-to-volume ratios resist temperature changes
			b. Endotherms
				i. Very active, agile, fast-moving
				ii. Dinosaur that laid the chicken egg was "certainly" endothermic
		18. Characterize and compare the first and second major reptilian radiations.
			a. First: Permian; synapsids, anapsids, diapsids
			b. Second: late Triassic; dinosaurs and pterosaurs
		19. List and compare the traits of the major groups of modern reptiles.
			a. Chelonia or Testudines
				i. Turtles
				ii. Shell; no muscle holes in skull (but rRNAs say diapsid)
			b. Sphenodontia
				i. Two species of tuatara in New Zealand 
				ii. Dorsal spiny crest, pineal eye, primitive skull
			c. Squamata
				i. Lizards and snakes
				ii. Movable upper jaw; very scaly skin
			d. Crocodilia
				i. Crocodiles and alligators
				ii. Four-chambered heart; upturned nostrils for aquatic habits
	Birds began as flying reptiles
		20. List the distinguishing characteristics of members of the class Aves and explain any 
		special adaptations for flight.
			a. Bones are honeycombed and air-filled to reduce weight
			b. Fewer organs: no bladder, one ovary in females
			c. Toothless with lightweight keratin beak instead of bony jaws
			d. Acute senses, larger brain, more complex behavior
			e. Endothermic: high metabolism to power flight
			f. Wings
			g. Feathers insulate and smooth surfaces
			h. Four-chambered heart keeps oxygenated and deoxygenated blood separate
		21. Summarize the evidence supporting the fact that birds evolved from reptilian 
		ancestors.
			a. Some dinosaur fossils show feathers
			b. Archaeopteryx: feathers; long, bony tail; teeth in beak, wing claws
			c. From theropods
				i. Three-clawed foot, wishbone, air-filled bones
				ii. Familiar theropods: T. rex, Velociraptor, and Deinonychus				22. List and compare the major [non-clade] groups of modern birds.
			a. Ratites: no keel/large flight muscle; ostrich, emu, kiwi
			b. Carinates: have keel; most in Order Passeriformes
	Mammals diversified extensively in the wake of the Cretaceous extinctions
		23. Describe the main features of mammals.
			a. Hair for insulation, communication
			b. Milk for nourishing well-developed young
			c. Diaphragm below lungs makes respiration more efficient
			d. Most have differentiated teeth for efficient feeding
			e. Skull remodeled, ear elaborated
		24. Describe the evolution of mammals.
			a. Triassic: 220 mya, synapsid  therapsid  mammal
			b. Mesozoic, ended 65 mya
				i. Most mammals were small and nocturnal
				ii. All of the modern orders appeared
		25. Distinguish among monotreme, marsupial, and placental mammals.
			a. Monotreme
				i. Three species of egg-layers
				ii. Echidnas are also pouched
			b. Marsupial
				i. Young born very immature, mature in a marsupium or pouch
				ii. Kangaroo, koala, opossum
			c. Eutherial = Placental
				i. Feed young in utero, placenta derived from chorion
				ii. Cavy, wolverine, woodchuck
		26. Describe the adaptive radiation of mammals during the Cretaceous and early Tertiary 
		periods.
			a. Monotremes diverged >200 mya
			b. Marsupials and Eutherians diverged 80-125 mya
		27. Compare and contrast the four main evolutionary clades of eutherian mammals.
			a. Xenarthra
				i. Sloths, anteaters, armadillos
				ii. Based on molecular data
			b. Afrotheria
				i. Elephants, aardvarks, hyraxes, manatees
				ii. Based on molecular data
			c. Laurasiatheria
				i. Bats, moles, ruminants, whales, carnivores
				ii. Based on molecular data
			d. Euarchontoglires
				i. Rodents, rabbits, primates
				ii. Based on molecular data