Evolution of Vertebrates

Chapter 19

Chordate Characteristics

• Dorsal, hollow nerve cords• Notocord between GI tract and nerve cord• Pharyngeal slits • Post-anal tail

Phylum Chordata

Subphylum Urochordata• Tunicates or Sea squirts• Substrate causes metamorphosis

– Larva: all 4 characteristics & motile– Adult: slits only & sessile

• Mucus aids filter feeding

Subphylum Cephalochordata

• Lancets• All 4 characteristics present

– Swollen tip of nerve cord

• Mucus for filter feeding• Shows segmentation

Development of Vertebrates

Emphasizes (in blue) characteristics of vertebrate evolutionShould refer back to with each Class

Class Agnatha (Jawless fish) Craniates, no jaws, and notochord as main support

Hagfishes• Weak vision, developed touch

and smell (habitat)• Enter prey through openings

or create holes• Can knot body or secrete

slime

LampreysBeginnings of vertebraeLarvae are suspension

feeders that live in stream sediment

Fish parasitesProblematic in Great Lakes

from St. Lawrence Seaway

Class Chondricthyes (Cartilaginous fishes)Craniates, jaws, and cartilage vertebrae as main support

Lateral line system to detect changes in water pressure and vibrations

No operculum or swim bladderClades

SharksMost are predators with powerful jaws (largest are filter feeders)Detect prey muscle movement through electrosensors on their

headSharp vision, keen smell, and streamlined bodies

Stingrays and skatesSuspension feedersDorsoventrally flattened with eyes on top of headBarbed tails with venom glands (not skates)

Class Osteichthyes (Bony fishes) Craniates, jaws, and bony skeleton as main support

• Calcium phosphate mineralized cartilage • Flattened scales covered in mucus = reduces drag• Operculum , protective flap covering the gills

– Can breathe without swimming, contrast to most sharks• Swim bladder keeps them afloat• Two dorsal fins, paired pectoral and pelvic fins (one

bone)• Clades

– Ray-finned fishes– Lobe-finned fishes

• Coelacanth, lungfishes, and tetrapods

Evolution of Tetrapods

• Lobe fins seem homologous to limbs– Digits to create ground force

• Early development of lung-like structures

• Sense organs from water to land

• Fossils show fused girdles and head/neck separation– Fish with necks

Class AmphibiaTetrapods with 2 pairs of limbs

Damp habitats so skin stays moistSkin has poison glands and coloration for defenseDistribution limited by vulnerability to dehydrationEctothermic = metabolism doesn’t make heat must absorbClades

Salamanders and newtsWalk side to side

Caecilians legless

FrogsMost adult life on land, but lay eggs in waterMetamorphosis from tadpole (fish characteristics) to adult frog

Class ReptiliaTetrapods with terrestrial egg (amniotes)

• Eggs develop in fluid-filled amniotic sacs protected by a leathery shell• Skin with scales and waterproofed by keratin• Rib cage helps ventilate lungs• Ectothermic

– Small dinosaurs may have been endothermic, using metabolism• Clades

– Turtles and tortoises• Shell and vertebrae are fused

– Lizards and snakes• Snakes likely lost legs due to burrowing nature; can detach jaws• Lizards can detach tail, moveable eyelids, and external ear openings

– Crocodilians• Most time in water with nostrils out• Advanced behavior resembles birds and mammals

Class AvesFeathered reptiles adapted to flight

• Lightened body structure– No teeth, tail with few vertebrae, feather shafts hollow, and

honeycombed bones• Feathers of keratin provide lift and maneuverability

– Wings resemble air foils with large breast muscles• Basis for classification

– Courtship and insulation role too• High metabolism = energy for flight and endothermic • Highly efficient circulatory system, lungs, and vision• Complex behavior, both sexes incubate hard shelled

eggs and feed

Class Mammalia• Hair (keratin) and mammary glands

– Hair to insulate and increase size (goose bumps)– Milk to nurture young

• Efficient respiratory and circulatory systems for high metabolism– Endothermic

• Large brain and long parental care• Differentiation of teeth for variety of foods• One evolution from reptiles (current view)• 3 lineages

– Offspring are hatched or birthed (loss of the egg)

Monotremes

• Egg-laying mammals– No nipples, milk sucked

from glands on belly

• Only in Australia and New Guinea

• 2 existing members– Duck-billed platypus (1)– Spiny anteaters (4)

Marsupials• Higher metabolic rates

and nipples• Birth live young

– Complete development while nursing in external pouch

– No direct yolk sac/amnion connection

• Most live in Australia and New Zealand– Opossums only ones in

North America

Eutherians (Placental Animals)• Longer gestation = fully developed live young

– Nurtured by a placenta• Placenta nurtures by nutrient diffusion between mother’s and embryo’s

blood

• Many resemble marsupials convergent evolution

Order Primate Phylogeny

Order Primates• Limber joints, 5 digits, flexible thumb and big toe

– Aids grasping and manipulation behaviors– Adapted for arboreal (tree-dwelling) life

• Flat nails, not claws• Reduced olfaction, increased vision

– Smaller noses, but larger forward facing eyes• Smaller litter size, longer gestation, increased

maternal care• Fewer specialized teeth

– 2 incisors, 1 canine, 3 premolars, and 3 molars in each quadrant

• 2 taxonomic arrangements (generally)

Prosimians• Lemurs

– Only in Madagascar– Primarily nocturnal– Most social

• Lorises– Africa and southern Asia– All nocturnal

• Tarsiers– Specialized for vertical climbing and leaping– Southeast Asia and Indonesia– Diet is almost completely animal matter

Tarsier

Loris

Anthropoids• Fully opposable thumb• Monkeys

– Active during the day and live in social bands

– Fore- and hindlimbs about equal length

– New world• Central and South America• Nostrils wide open and far apart• Long prehensile tail• E.g spider monkeys and tamarins

– Old world• Africa and Asia• Lack prehensile tail• Nostrils open downward• E.g macaque, baboons, and rhesus

• Hominoids (Apes)

Hominoids (Apes)• Lack tails• Long arms and short legs• Mainly vegetarians

– Humans are omnivorous, eating plants and animals

• More flexible• Larger brain relative to

body size• High degree of social

organization• 5 divisions

Hominoid (Ape) Divisions• Gibbons

– 9 species, all in Southeast Asia– Only entirely arboreal apes– Smallest, lightest and most acrobatic– Monogamous for life

• Orangutan– Solitary species in rain forests of Sumatra and Borneo– Largest arboreal mammal, occasionally move on ground

• Gorillas– Largest ape, found only in African rainforests– Live in groups of up to 20– Stand upright, walk on 4 legs with knuckles on the ground

Hominoid (Ape) Divisions (cont.)• Chimpanzees (and bonoboos)

– Knuckle walkers– Tropical Africa– Behavior closely mirrors humans

• Make simple tools• Respond to mirrors

– Can learn human sign language• Humans

– Bipedal, larger brain, capable of language, thought, and complex tools

Vertebrate Diversity Review

List characteristicsresponsible for each branch point (a-i)