Phylum Chordata - ChordatesInternal skeleton with muscle attachments on outer surfaceAllows for greater range of movement and development of largebody sizeSegmented body plan
All chordates have(in embryo or adult)
notochorddorsal nerve tubepost-anal tailpharyngeal gill slits
Hollow dorsal nerve tube - just below dorsal surfacedifferentiates into brain and spinal cord in vertebrates
Flexible dorsal notochord - located just below nerve cordreplaced by vertebral column in vertebrate developmentpersists in some primitive chordates - provides support
Pharyngeal gill slits - a clue to the aquatic ancestry of all chordatespharynx connects mouth cavity and esophagus to outsidein terrestrial vertebrate embryos slits often form pharyngeal
pouches, become eustachian tubes in some vertebrates
A Post-anal tailextends beyond theanuspresent in embryo ifnot in adult formOther animals withtails have a terminalanus
Phylum Chordata has three SubphylaSubphylum Urochordata - tunicates or sea squirtsSubphylum Cephalochordata - lanceletsSubphylum Vertebrata - fishes, amphibians, reptiles, birds,
mammals
Subphylum Urochordata - Tunicates or “sea-squirts”Most are sessile as adults, may be colonial
Possess notochord and nerve cord only in larval stageAdults secrete cellulose “tunic” around body
Adults are filter feeders lack a body cavity and segmentation
Create water currents with cilia - water drawninto pharynxfood particles trapped in
mucus produced by endostyle
Many have symbiotic photosynthetic bacteria
Most chordate characteristics are only seen in tunicates in thelarval stage
Larvae are free-swimming --after finding a suitablelocation they settle head-firstand transform into the adultform
Subphylum Cephalochordata - lanceletsScaleless, fish-like marine organisms
No obvious head, eyes, nose or earsNotochord runs entire length of body and persists in adults
Bury in substrate, expose anterior end onlySegmentation of muscles readily visibleHave many more pharyngeal gill slits than fishes
Filter-feed throughthe action of cilia inmouth and pharynx -trap food in pharynx
Swim with fish-likeundulations of thebody
The defining chordate characteristics are preserved in the adultlancelet
Subphylum Vertebrata - VertebratesAll vertebrates have a distinct head, with skull enclosing a brainName derived from bony vertebral segments in spinal columnVertebral column - protects dorsal nerve cord notochord surrounded and replaced by vertebral columnPossess a cranium - brain caseGroup also called craniate chordatesMost have a bony skeleton, some use only cartilageAll have a closed circulatory system
All vertebrates also have a unique set of cells that originateabove the neural tube during development - “neural crest cells”
Neural crest cells migrate throughout vertebrate body andcontribute to the development of many organs
The vertebralcentra replacethe notochord
Neural spinesdevelop tosurround andprotect theneural tubebehind the head
Brief overview of vertebrate evolutionFirst vertebrates were marine, lacking jaws or paired fins (550 mya)Jawed fishes then became dominant creatures in the sea (450 mya)Amphibian ancestors first to invade the land (400 mya)Largely replaced by reptiles more suited to live on land (300 mya)Dinosaurs and other reptiles ruled the earth for 150 million years
their extinction (65 mya) allowed mammals to become dominant
Most livingvertebrate groupshave diversifiedgreatly since theirorigin.
The vertebrates are composed of eight classesFour classes are aquatic fishes
Class Myxini - HagfishClass Cephalaspidomorphi - LampreysClass Chondrichthyes - Sharks, skates and raysClass Osteichthyes - Bony fishes
Four classes are terrestrial tetrapodsClass Amphibia - Salamanders, frogs and toadsClass Reptilia - ReptilesClass Aves - BirdsClass Mammalia - Mammals
Characteristics of FishesGills - extract dissolved oxygen from water around them
water passes over filaments rich in blood vesselsblood moves opposite the flow of water - an efficient system
Vertebral columnInternal skeleton with spine surrounding dorsal nerve cordSkeleton may be made of cartilage or boneBrain fully encased in protective skull
Single-loop blood circulationBlood pumped from heart to gillsOxygenated blood from gills passes to rest of body
Heart is series of fourchambers thatcontract insequence
Nutritional deficienciesAll vertebrates are unable to synthesize aromatic amino acidsAll must consume these amino acids in their diet
Overview of Fish EvolutionFirst fishes known were jawless with heavy bony armor
Internal skeleton was made of cartilageSurvived by lampreys and hagfish (“Agnathans” - no jaws)
First jawed fishes occurred 410 million years ago
Early jawed fisheswere replaced bymore agile sharksand bony fishes
Jaws evolved from modified gill archesthe bony area between gill slits
Evolved as a means to close mouth, and then to capture preyFirst gill arch behind jaw became supporting strutJoined rear of lower jaw to rear of skullAllowed mouth to open very wide, an efficient weapon
Jawless fishes today
Hagfishes are scavengers in coolwaters - especially in deep water
Lampreys have two life-styleslarge parasites of other vertebratessmall filter-feeders in freshwater
streams
Sharks became dominant predators about 300 mya
Class Chondrichthyes - sharks, skates, raysSkeleton is made of cartilageHave bony teeth and scales with enamelHave always been large agile predatorsenlarged pectoral fins allow greater lift andmaneuvering during swimming
Have internal fertilizationyoung are well-developed when born
skates and rays have flattened bodies and are more sedentary
Class Osteichthyes - bony fishesEvolved at same time as sharks, but in freshwaterDeveloped heavy skeleton made completely of bone
Ossification replaces cartilage with boneExternal plates and scales also made of boneAdded swim bladder for respiration/buoyancy
Primitive fishes use swim bladder for respiration - a lung
Modern fishes use swim bladder for buoyancy
Modern bony fishes have highly mobile fins, thin scales and symmetrical tails
They are an extremely successful group and are dominant in freshwater and the sea
Two lineages of bony fishes evolvedRay-finned fishes - most modern fish
Internal skeleton of bony rays supportsand stiffens each fin
No muscles within finsSwim bladder used for buoyancy
Lobe-finned fishes - 6 living species5 lungfishes, and the “coelacanth”have fins with muscular lobesswim bladder used for respirationearly form gave rise to amphibians
Important characteristics of bony fishesLateral line systemSeries of small sensory organs that project into a canal beneath
skin surface - sensitive to water pressure changesallows fish to sense movements in water
Similar structures found in all vertebrate ears - for hearingGill coverHard plate covering gills called the operculumHelps to pump water over gills even when stationary
Class Amphibia - Amphibiansincludes frogs, salamanders, caeciliansAmphibians were the first “tetrapods”
the first terrestrial vertebratesThere are three orders of Amphibians
Order Anura - frogs and toadsOrder Urodela - salamandersOrder Apoda - caecilians
Characteristics of AmphibiansLegs - a key adaptation for terrestrial living
Frog and salamanders have two pairs, lost in caeciliansLungs - a modified swim bladder used for terrestrial respiration
swallow air by moving floor of mouth
Cutaneous respiration - gas exchange at skinsupplement lung respiration with a highly vascularized skinMoist skin provides extensive surface area, limits body size
Pulmonary veinsVeins return blood from lungs to heartAerated blood leaves heart at greater
pressure than it leaves lungs
Partially divided heartpartially separated pulmonary and systemic pathwaysimperfect since there is a single ventricle where oxygenated
and deoxygenated blood can mix
Origin of Amphibiansevolved from lobe-finned fishes - skeletal structure of lobe-finned fishes and early amphibians is very similar
Earliest amphibianfossil, Ichthyostega
built for terrestrial lifewith lungs and a stronglegs and backbone
Most amphibians still must lay their eggs in water to keep themfrom drying outBecause of moist skin, adults are also liable to become dehydrated
Modern AmphibiansOrder Anura - frogs and toads - tailless amphibians
Frogs have smooth, moist skin; long legs; live in or near waterToads have bumpy, dry skin; short legs; are adapted to dry
environmentsAll are carnivores, eat a wide variety of invertebratesMost return to water to reproduce
Eggs lack water-tight membranes and dry out readilyEggs fertilized externallyEggs hatch into algae-eating, swimming larval tadpolesTadpoles metamorphose into adults
Order Urodela - salamanders - amphibians with tailsHave elongated bodies, long tails and smooth moist skinLive in moist places, some live entirely in waterLay eggs in water or moist areasFertilization is external in most speciesJuveniles look like adults, do not undergo major metamorphosis
Order Apoda - caecilians - legless amphibiansHighly specialized group of burrowing amphibiansLack legs, have small eyes, are often blindEat worms and soil invertebratesMale deposits sperm directly into female
young are born alive
Class Reptilia - Reptilesincludes turtles, lizards, snakes, alligatorsReptile improvements on the amphibian plan
Leg design allows better body supportLungs and heart are more efficientDry skin covered with scalesWater-tight eggs
Key Characteristics of ReptilesAmniotic egg - Water-tight eggs contain food source (yolk) andfour membranes: Chorion, amnion, yolk sac and allantoisEach important an embryonic life-support system Chorion allows oxygen to enter, but retains water Amnion encases developing embryo within fluid-filled cavity Yolk sac holds food for embryo - extracted by blood vessels Allantois encloses waste products
Dry skin with scales or armor reduces water lossScales develop as surface cells fill with protein keratinKeratin is also used for mammal hair and bird feathers
Thoracic breathing - increase volume of air inspiredExpand and contract rib cage to suck air in and force it outCapacity limited only by volume of lungs
Improved leg design -legs placed more ventrally under trunkallows better support ofthe body and greater mobilityallows larger body size
Reptile Evolution - Reptiles were the dominant land animals for250 my
Four major lineages evolved in series: Pelycosaurs, Therapsids,Thecodonts, Dinosaurs
Pelycosaurs - improved predatorssynapsid skull with temporal openings allowed better muscle attachment and more powerful bite
Dominant terrestrial vertebratesfor 50 million years
Replaced by Therapsids
Therapsids - Mammal-like reptileshad higher food intake, and probably had higher metabolic ratespeculated that these were the first endothermic (“warm-blooded”) vertebrates - likely evolved in cooler climatedominant terrestrial vertebrates for 20 million yearsTherapsids were the ancestors of mammalsReplaced by Thecodont reptiles - a different lineage
They may havehad hair, liketheir mammaldescendants
Thecodonts - greater energy efficiencyWere “cold-blooded” ectotherms like amphibians and early reptiles
environmental change resulted in warmer temperaturesendothermy requires less energy intake for body maintenance
Had an improved skull - diapsid -Diapsid reptiles, had two pairs of temporal holes in skullFirst land vertebrates to walk on hind limbs only
Dominant for 15 my
Replaced by their directdescendants, Dinosaurs
Dinosaurs - greater agilityLegs positioned directly underneath body - allowed larger bodyEnabled running with speed and agilityDominated land for 150 million yearsWent extinct 65 million years ago - likely due to asteroid impact
Overview of the evolution of “amniotes” - reptiles, birds,mammals, and their ancestors
Modern Reptiles - Four surviving ordersTurtles - ancient survivors
Have changed little since before time of dinosaursHave solid skulls (no temporal openings) like first reptilesHave changed little since before time of dinosaurs
Lizards and snakes - most modern reptiles are in this groupAlso evolved very early - 250 myaDiversified after disappearance of dinosaurs
Tuataras - a remnant of a group that was once common
Only two species survive on islands near New Zealand
Small, sluggish, diapsid reptiles,Common in Jurassic, declined in
CretaceousUnable to compete with lizards,
in most environments
Crocodiles - the most derived “reptiles”Descended from same line that produced dinosaursLittle changed in the last 200 million years but with advanced
characteristics they share with birdsparental care, four-chambered heart,vocalizations for mate attraction
Crocodiles and birds more closely related to dinosaurs and eachother than they are related to lizards and snakes
Crocodiles, Thecodonts, Dinosaurs, and Birds form a monophyletic group - the Archosaurs
Other Important Characteristics of ReptilesInternal fertilization - a requirement with a shelled eggImproved circulatory system - Circulatory system provides moreoxygen to bodySeptum in heart extended fromatrium partway into ventricleDecreases mixing ofoxygenated and deoxygenated
Septum totally divides ventriclein crocodiles and birds (a four-chambered heart)
All living reptiles are ectothermic, obtain heat from externalsources - regulate body temperature through behaviors - baskingor seeking shade
Order Chelonia - Turtles and tortoisesTurtles generally live in water, tortoises live on landBodies are encased in a protective shell
Carapace covers dorsal surfacePlastron covers ventral portionVertebrae and ribs fused with carapace
Lack teeth, but have sharp beak
Order Rhynchocephalia - TuatarasTwo species makes up entire orderfound only on islands of New ZealandHas spiny crest running down backHas inconspicuous parietal or “third eye” on top of head
has lens, retina and is connected to brainMay function as a thermostat, protect it from overheating
Order Squamata - Lizards and snakesMales have paired copulatory organslower jaw not joined directly to skull
allows flexibility in jaw movementsmost are predatory carnivores
Lizards have limbs, snakes do notSnakes lack movable eyelids and
external ears - can’t hearLizards are more ancient groupLizards rely on agility and speed
to catch prey and avoid predators
Most snakes depend on stealthMany lizards can loose tail to
escape predator and regenerate new one
Order Crocodilia - Crocodiles and AlligatorsPrimitive-looking reptiles also includes caimans and gavialsSimilar to 200 million year old fossil formsLive in or near water in tropical or subtropical regionsAre aggressive carnivores, bodies adapted for hunting by stealth
Eyes and nostrils on top of head, lie submerged in waterEnormous mouths with sharp teeth and strong neck
Can feed underwater, valve prevents water from entering air passage
The only living reptiles that care for their young
Class Aves - BirdsMost successful of all terrestrial vertebrates
great diversity, 8800 speciesKey Characteristics of Birds
Produce amniotic eggs - like reptilesHave keratin scales on feet and legs - like reptilesLack teeth - developmental mutants have reptile-like teeth
Have very small tail - unlike reptilesFeathers
Modified reptilian scalesProvide lift for flight and insulateDevelop from folliclesHas shaft, with barbs, with barbules, with interlocking hooksFlexible, light-weight, and strongCan be replaced, like scales
Flight skeletonBird bones are thin, hollow,
and light-weightMany have internal struts to
strengthen the bone with little added weight
Many bones are fused to each other - reduces number
Have fused collarbones (wishbone) for recoil of wings during flight
Have keeled breastbone - for attachment of flightmuscles
The Evolution of BirdsArchaeopteryx, the first bird - fossils date to 150 myaShares features with small therapod dinosaurs
Skull has teethVery few bones are fused to each otherBones are solid (bird bones are hollow)Has long reptilian tailHas no breastbone
Considered a bird because of feathers on wings and tail
Modern BirdsBeak and feet characterize many bird habitsHave unique physiology to cope with high energy demands of flightEfficient respiration - “flow-through lungs”
Gas flows throughlungs in only onedirection and oppositedirection of blood flow- an efficient system
No “dead-air” in birdlungs
Efficient circulationHas four-chambered heart -
like mammals but independently evolved
Wall dividing ventricle is complete, two circulationsdo not mix
Flight muscles get fully oxygenated blood
EndothermyBirds maintain higher body temperatures than most mammalsMetabolism in flight muscles proceeds at faster rateFeathers provide insulation to conserve heat
Class Mammalia - MammalsThe least diverse group of vertebrates -
4100 speciesAlmost all large land vertebrates are mammalsMost mammals are not large
3200 species are rodents, bats, shrews, molesGreatest diversity was reached about 15 mya
numbers are declining due to relativelycool climate
Key Mammalian CharacteristicsHairHelps regulate body temperature, allows life in colder climatesNot derived from reptilian scales or feathersEach hair extends like stiff thread from bulb-like hair follicleComposed of dead cells filled with fibrous keratin proteinInsulates against heat lossProvides camouflageWhiskers function as sensory structuresServe as defensive weapons as in porcupines and hedgehogs
Milk-producing glandsAll mammals have mammary glands that produce milkMammary glands are modified sweat glandsMilk is rich in fat, sugar, protein with 95% waterHigh calorie food needed to support rapid growth of newborn
Evolution of MammalsArose from Therapsids in Triassic, 220 myaFirst mammals were small insectivoresHad large eyes - they may have been nocturnalMammal jaw reduced to massive bone with a single joint
Allows strong biteTwo jaw bones moved to middle ear to make three bone chain
that improved hearing - malleus, incus, stapesWere a minor group until the Cretaceous (65 mya)Two groups - Prototheria and Theria
Prototheria - egg-laying mammalsclose relatives of therapsidsSmall, resembled modern shrews
Theria - live-bearing mammalsSubdivided into marsupials (pouched mammals) and
placental mammals
Characteristics of Modern MammalsEndothermy
Allows activity in cooler weather and times of dayAllows colonization of harsh environments, deserts to arcticHair provides insulation to support endothermyHigher metabolic rate required as well
Efficient circulationprovided by four chambered heart
Improved respirationDiaphragm breathing muscle allows
greater volume of air to be inspired
PlacentaMost mammals are placental and viviparous (live bearing)Blood stream of mother and fetus in close contact at placentaFood, water, oxygen pass from mother to childWastes pass from child to mother, carried away
TeethReptiles have homodont dentition - all teeth are the sameMammal dentition is heterodont - variation in teeth in mouthHighly specialized to match food eatenMammals as a group eat a wide variety of foods but individualspecies often have highly specialized feeding
Digestive systems for eating plantsMost mammals are herbivoreswith help of symbiotic bacteria cellulose is major foodSome mammals have four-chambered stomachs
first chamber is large, holds most cellulose-digesting bacteriaPartially digested plants are regurgitated (cud) and chewedSwallowed again and digested by succeeding stomachs
then passes to intestineOther mammals digest plant material in the large intestineHave relatively small stomachs, do not chew a cudBacteria live in pouch called the caecum, off the large intestineHerbivores must eat great mass to gain sufficient nutrition
Hooves, Horns, and Antlersclaws, fingernails, hair, and hooves are made of keratin
Hooves cushion and protect toes in running mammals
Horns have a core of bone surrounded by keratin sheathnot shed, bony core is attached to skullOuter layer is compacted hair-like layers
Antlers are made only of boneMale deer grow and shed a set of antlers each yearCovered by thin skin layer of velvet while growing Velvet dies and is scraped off when antlers are fully grownAntlers used to combat rival males in fall and winterShed in spring after breeding season
Rhinoceros horn composed of keratinized hair
FlightBats are only mammals capable of powered flightWings are modified forelimbs
leathery membrane of skin stretched over bones of four fingersedges attach to side of body and to hind leg
Bats at rest hang upside down from legs
Have sonar system to navigate in dark and find insects
High frequency pulses emitted through mouthor nose
Sound waves reflect off objects, captured by large ears
Modern Mammalsnineteen orders
Seventeen are placental mammalsTwo are non-placental mammals :
monotremes and marsupials
Monotremes - Egg-laying mammalsIncludes duck-billed platypus and two species of echidnaMonotremes retain some reptilian characteristics
Lay shelled eggs which they incubate in a nestShoulder and pelvic bones similar to early reptilesHave a cloaca - a single opening for feces, urine, and eggs
More closely related to early extinct mammalsHave functioning mammary glands
Marsupials - Pouched-mammalsMarsupial fertilized egg is amniotic but lacks shellMarsupial egg has much yolk to nourish embryoEmbryonic marsupial is born early in development
Crawls to marsupial pouch, attaches to nipple, continues to develop for months
Nearly all modern marsupials live in Australia and New GuineaOnly 20 of 280 total species live
elsewhereMarsupials in Australia and New
Guinea fill niches that placental mammals fill elsewhere
Virginia opossum is the only marsupialin North America
Placental mammalsHave well-developed placenta
that nourishes embryosfor entire development
Eggs have little yolkPlacenta forms early in course
of developmentEmbryos develop in uterus (womb)
of motherFetal placenta formed from
chorion and allantoisMaternal placenta formed from
wall of uterusYoung undergo considerable
development before birth Many have extensive parental care