phylum chordata part three tetrapods: amphibians &...
TRANSCRIPT
Tetrapods are gnathostomes that have limbs
v One of the most significant events in vertebrate history was when the fins of some lobe-fins evolved into the limbs and feet of tetrapods v Derived characters of tetrapods
1. Four limbs, and feet with digits 2. A neck, which allows separate head movement 3. Fusion of the pelvic girdle to the backbone 4. Absence of gills (except some aquatic species) 5. Ears for detecting airborne sounds
The Origin of Tetrapods- Tiktaalik
v Tiktaalik is a genus of extinct sarcopterygian from the late Devonian, with many tetrapod features
v Represents the evolutionary transition from fish to amphibians
v Nicknamed “fishapod,” show both fish and tetrapod characteristics
§ Fins, gills, lungs, and scales § Ribs to breathe air and support body § A neck, and fins have bone pattern of tetrapod limb
v Tiktaalik could most likely prop itself on its fins, but not walk
Figure 34.20
Flat skull
Eyes on top of skull Head
Neck
Shoulder bones Ribs
Scales
Fin Fin skeleton
Elbow Radius
Humerus Ulna “Wrist”
Scales Fins Gills and lungs
Neck Ribs Fin skeleton Flat skull Eyes on top of skull
Tetrapod Characters
Fish Characters
(a) Order Urodela (salamanders)
(b) Order Anura (frogs)
Order Apoda (caecilians)
(c)
Class Amphibia
v Includes ~6,150 species § Orders:
§ Urodela includes salamanders (have tails)
§ Anura includes frogs and toads (lack tails)
§ Apoda includes caecilians (legless, resemble worms)
Amphibian Biology
v Ectotherms § Body temp depends on environment, restricts range
v Tied to water § Thin skin loses water rapidly; restricts terrestrial
forms to moist habitats § Eggs deposited in water or must be kept moist § Larvae depend on gills for respiration
Order Apoda: Caecilians
v ~173 living species v Resemble earthworms or snakes v Mostly live hidden in the ground- least familiar amphibians v Elongate, limbless, burrowing animals v Inhabit tropical forests in (S. America, Africa, India, SE Asia) v Bodies have many vertebrae, long ribs, no limbs v Feed primarily on worms and small underground invertebrates v Fertilization is internal- exception to typical amphibian repro
v ~553 living species found primarily in northern temperate regions
v Most small, under 15 cm long (Japanese giant salamander is 1.5 meters long)
v Burrowing species and some aquatic forms may have lost their limbs
v Carnivorous as both larvae and adults (feed on worms, small arthropods, and molluscs
Order Urodela - Salamanders
v Breeding Behavior § Some aquatic throughout life cycle § Most have aquatic larvae and terrestrial adults § Internal fertilization in most; female recovers in cloaca a
spermatophore deposited on a leaf or stick § Aquatic species lay eggs in clusters or stringy masses § Completely terrestrial species deposit eggs in small, grape-
like clusters under logs or in soft earth
Order Urodela - Salamanders
v Terrestrial species undergo direct development; hatch as miniature adults
v Some North American newts have aquatic larvae that metamorphose into terrestrial juveniles that again metamorphose into secondarily aquatic, breeding adults
Order Urodela - Salamanders
Order Urodela - Salamanders
v Respiration- wide array of respiratory mechanisms! § Vascular nets in skin exchange both O2 and CO2
§ At various stages, may have external gills, lungs, both, or neither
§ Salamanders with aquatic stage hatch with gills which are lost at metamorphosis
§ Some lineages retain gills and a fin-like tail § In species with lungs, lungs are present from birth and
become functional following metamorphosis
Order Anura – Frogs and Toads
v ~5,300 species v Dates from Triassic period, 250 million years ago v Must live near water source
§ Reproduction mode requires water § Skin is water-permeable
v Ectothermy prevents anurans from inhabiting polar and subarctic habitats
v All have a tailed larval stage and tailless, jumping adults (except for 1 species)
Order Anura – Frogs and Toads
v Life Cycle § Most larger frogs are solitary until breeding season § During breeding season, males are especially noisy § Hold forelimbs near body when swimming with hindlimbs § Surface to breathe with only head exposed § During winter in temperate climates,
§ Hibernate in soft mud in bottom of pools § Frost-tolerant frogs prepare for freezing by
accumulating glucose and glycerol in body fluids § During hibernation, the little energy used is provided by
stored glycogen and fat
Order Anura – Frogs and Toads
v Frogs can be easy prey for carnivores § Defend themselves by aggression,
concealment, and poison glands v Climatic change is a threat
§ Reduced water depth at oviposition sites increases ultraviolet exposure of embryos
§ More susceptible to fungus v Invasive amphibian species such as
Bufo marinus can outcompete and/or prey on other frogs
25-15
Order Anura – Frogs and Toads
v Skeletal and Muscular Systems § Well-developed endoskeleton of bone and cartilage
provides for body support and muscular movements § Landing posed new mechanical stress problems § Musculoskeletal changes allowed jumping, swimming § Vertebral column lost much flexibility to transmit
force from limbs to body § Extremely shortened body; only nine trunk vertebrae § Caecilians have not moved toward tetrapod
locomotion and have as many as 285 vertebrae
Order Anura – Frogs and Toads
v Respiration and Vocalization § Amphibians use 3 respiratory surfaces for gas
exchange in air: 1. Skin provides cutaneous breathing 2. Mouth provides buccal breathing 3. Lungs are usually present in adults
§ Frogs and toads depend on lung breathing more than salamanders
§ Skin is critical during winter hibernation § Carbon dioxide is mostly lost across skin while oxygen
is absorbed across the lungs
Order Anura – Frogs and Toads
v Lungs supplied by pulmonary arteries, return blood to left atrium § Frog lungs are ovoid, elastic sacs; inner surfaces divide into
a network of smaller chambers § Absorptive surface is 20 cm2/cc of air compared to 300 cm2
for humans v Positive Pressure Breathing
§ Air moved into lungs by force § Rhythmic throat movements gulp air and force it backward § Rib cage does not expand to draw air into the lung
Order Anura – Frogs and Toads
v Vocal cords are located in the larynx; much more developed in males
v Air is passed back and forth over vocal cords between the lungs to a large pair of vocal sacs
v Most species have unique sound patterns
Order Anura – Frogs and Toads
v Circulation § Circulation is closed with a single pressure pump
moving blood through the peripheral network § Main difference in circuitry is the shift from gill to lung
breathing § Elimination of gills reduced one obstacle to blood flow § Evolution of pulmonary artery provided circuit to lungs § BUT, separation of oxygenated blood from
deoxygenated blood circuit is only partial
Order Anura – Frogs and Toads
v Feeding and Digestion § Most adults are carnivorous (feed on insects, spiders,
worms, slugs, etc) § Free end of tongue is glandular (sticky secretion adheres to
prey) § Any teeth that are present function to hold prey (do not
chew) § Short digestive tract § Tadpoles are usually herbivorous (longer digestive)
Order Anura – Frogs and Toads
v Nervous System and Special Senses § Brain is gradually assuming more information
processing, independent of spinal cord § Frogs are sensitive to low-frequency sound energy
under 4000 Hz (cycles per second) § Except for blind caecilians, vision is dominant sense in
many amphibians
Order Anura – Frogs and Toads
v Reproduction and Development § Ectothermic; breed, feed, and grow during warm seasons § In spring, males call to attract females § When eggs are mature, females enter water and males
clasp them in amplexus § After fertilization, jelly layers of egg absorb water
§ Eggs usually laid in large masses, and development begins immediately (tadpole may hatch in 6–9 days)
§ Tadpole head has horny jaws for feeding and a ventral adhesive disc for clinging to objects
Order Anura – Frogs and Toads
v Typical Metamorphosis § Hindlegs appear first § Forelegs temporarily hidden in folds
of operculum § Tail is resorbed § Intestine becomes shorter § Mouth transforms to the adult
condition § Lungs develop and gills are
resorbed v Exception: Eleutherodactylus mate on
land and eggs hatch directly into froglets
Amniotes have a terrestrially adapted egg
v Amniotes are a group of tetrapods whose living members are reptiles, including birds and mammals
1. Thicker, more waterproof skin § Amniote skin tends to be more keratinized § Structures composed of keratin include scales, hair,
feathers, and claws that project from the skin § Keratin protects skin from physical trauma, and lipids
prevent water loss 2. Lungs are the primary organ for gas exchange
§ Keratin and lipids limit exchange of gases across skin 3. Amniotes lack gilled larvae– no need for aquatic habitats 4. Internal fertilization
§ Penis is the most common copulatory organ, and appears to be an amniote innovation
Characteristics of Amniotes à Terrestrial Life
5. Rib ventilation of the lungs – negative ventilation § Amniotes draw air into lungs by expanding the thoracic
cavity 6. High-Pressure Cardiovascular system
§ Limits mixing of oxygen-rich and oxygen-poor blood § Mammals, birds, and crocodilians have two completely
separated ventricles – 4 chambered heart 7. Water-conserving nitrogen excretion
§ Birds and non-avian reptiles excrete nitrogenous wastes as uric acid- relatively non-toxic, and can be concentrated to reduce water loss
8. Expanded brain and sensory organs
Characteristics of Amniotes à Terrestrial Life
Major Derived Character – the Amniotic Egg
v External shell with internal membranes that protect the embryo § The extraembryonic membranes are the amnion, chorion,
yolk sac, and allantois v Permitted development of a larger, faster-growing embryo v Replacement of the amphibian jelly layer with a shell
§ Better support and movement of oxygen § Provides calcium for growing skeletal structures
Figure 34.26
Extraembryonic membranes
Shell
Amniotic cavity with amniotic fluid
Embryo
Amnion Allantois Chorion
Yolk sac
Yolk (nutrients)
Albumen
33
Early Amniotes
v Living amphibians and amniotes split from a common ancestor ~350 million years ago
v Early amniotes were more tolerant of dry conditions v The earliest amniotes were small predators with sharp
teeth and long jaws
Reptiles - Sauropsids
v The reptile clade includes the tuataras, lizards, snakes, turtles, crocodilians, birds, and extinct dinosaurs
v Most reptiles are ectothermic, absorbing external heat as the main source of body heat
v Birds are endothermic, capable of keeping the body warm through metabolism
v Reptiles have scales that create a waterproof barrier v Most reptiles lay shelled eggs on land
Circulation in Reptiles (Except Birds)
v Turtles, snakes, and lizards have a three-chambered heart (two atria, one ventricle)
v In alligators, caimans, and other crocodilians a septum divides the ventricle
v Reptiles have both a pulmonary circuit (lungs) and a systemic circuit (body)
Reptile Origins
v Diapsids were early terrestrial amniotes, and consisted of two main lineages: the lepidosaurs and the archosaurs § Lepidosaurs- tuataras, lizards,
snakes § Archosaurs- crocodilians, pterosaurs,
dinosaurs (and birds!) v Turtles (Testudines) classification
unclear § Some place them within the
archosaur lineage, some within the lepidosaurs, and some outside the diapsids altogether
Lepidosaurs - Tuataras
v One surviving lineage of lepidosaurs is represented by two species of lizard-like reptiles called tuataras
v Endemic to New Zealand
Lepidosaurs: Squamates – lizards and snakes
v Lizards are the most numerous and diverse reptiles, apart from birds
Testudines: Turtles
v All turtles have a boxlike shell made of upper and lower shields fused to vertebrae, clavicles, and ribs
v Some turtles have adapted to deserts and others live entirely in ponds and rivers
v Marine turtles return to land to lay their eggs
Archosaurs: Crocodilians
v Crocodilians (alligators and crocidiles) coexisted with dinosaurs, avoided extinction at the end of Cretaceous
v Largest extant reptiles
Archosaurs: Birds (Clade Neornithes)
v Birds are archosaurs, but almost every feature of their reptilian anatomy has evolved in adaptation to flight
v Derived characters of birds: § Wings with keratin feathers § Hollow bones § Loss of teeth § Lack of a urinary bladder § Females have only one ovary, small gonads § Hard-shelled eggs
v Flight requires a great expenditure of energy, acute vision, and fine muscle control
Figure 34.30
(a) Wing
Vane
Shaft
Forearm Wrist
Shaft Barb Barbule Hook (c) Feather structure
(b) Bone structure
Finger 1
Finger 2
Finger 3
Palm
Double Circulation in Mammals and Birds
v Mammals and birds have a four-chambered heart with two atria and two ventricles
v Left side of the heart pumps and receives only oxygen-rich blood; right side receives and pumps only oxygen-poor blood
v Mammals and birds are endotherms and require more O2 than ectotherms
Birds’ lungs facilitate rapid gas exchange
v Birds have 8-9 air sacs that function as bellows to keep air flowing through lungs
v Air passes through lungs in one direction only
v Every exhalation completely renews the air in the lungs
The Origin of Birds
v Early feathers might have evolved for insulation, camouflage, or courtship display
v Early feathers might have helped dinosaurs – Gain lift when they jumped – Gain traction running up hills – Glide from trees
v By 150 MYA, feathered theropods had evolved into birds
v Archaeopteryx remains the oldest bird known
Airfoil wing with contour feathers Long tail with
many vertebrae
Toothed beak Wing claw
v Birds probably descended from small theropods, a group of carnivorous dinosaurs
Mammals – last of the synapsids
v Class Mammalia § Amniotes that have hair and produce milk § Represented by >5,300 species
v Mammals evolved from synapsids ca 200 MYA § Two bones that formerly made up the jaw joint
were incorporated into the mammalian middle ear
Derived Characters of Mammals
v Mammals have § Mammary glands, which produce milk § Hair § A high metabolic rate, due to endothermy § A larger brain than other vertebrates of similar size § Differentiated teeth
Modern Mammal Groups
v Differentiated primarily on the basis of how they gestate their young § Monotremes, marsupials, and eutherians
Monotremes
v Monotremes are a small group of egg-laying mammals consisting of echidnas and the platypus
Marsupials
v Marsupials include opossums, kangaroos, and koalas
v Embryo develops within a placenta in the mother’s uterus
v A marsupial is born very early in its development
v It completes its embryonic development while nursing in a maternal pouch called a marsupium
Plantigale
Marsupial mammals
Eutherian mammals
Marsupial mole
Sugar glider
Wombat
Tasmanian devil
Kangaroo
Deer mouse
Mole
Flying squirrel
Woodchuck
Wolverine
Patagonian cavy
Eutherians (Placental Mammals)
v Compared with marsupials, eutherians have a more complex placenta
v Young eutherians complete their embryonic development within a uterus, joined to the mother by the placenta
ANCESTRAL MAMMAL
Monotrem
es (5 species)
Marsupials
(324 species) Eutherians (5,010 species)
Monotremata
Marsupialia
Proboscidea Sirenia Tubulidentata Hyracoidea Afrosoricida Macroscelidea
Xenarthra
Rodentia Lagomorpha Primates Dermoptera Scandentia
Carnivora Cetartiodactyla Perissodactyla Chiroptera Eulipotyphia Pholidota
Figure 34.41a
Figure 34.41ba
Monotremata
Orders and Examples Main Characteristics
Platypuses, echidnas
Echidna
Proboscidea Elephants
African elephant
Sirenia Manatees, dugongs
Manatee
Lay eggs; no nipples; young suck milk from fur of mother
Long, muscular trunk; thick, loose skin; upper incisors elongated as tusks
Aquatic; finlike fore- limbs and no hind limbs; herbivorous
Marsupialia Kangaroos, opossums, koalas
Koala
Completes embryonic development in pouch on mother’s body
Tubulidentata Aardvarks
Aardvark
Teeth consisting of many thin tubes cemented together; eats ants and termites
Hyracoidea Hyraxes
Rock hyrax
Short legs; stumpy tail; herbivorous; complex, multi- chambered stomach
Orders and Examples Main Characteristics
Xenarthra Sloths, anteaters, armadillos
Tamandua
Lagomorpha Rabbits, hares, picas
Jackrabbit
Reduced teeth or no teeth; herbivorous (sloths) or carnivorous (anteaters, armadillos)
Chisel-like incisors; hind legs longer than forelegs and adapted for running and jumping; herbivorous
Rodentia Squirrels, beavers, rats, porcupines, mice Red squirrel
Chisel-like, continuously growing incisors worn down by gnawing; herbivorous
Primates Lemurs, monkeys, chimpanzees, gorillas, humans Golden lion
tamarin
Opposable thumbs; forward-facing eyes; well-developed cerebral cortex; omnivorous
Figure 34.41bb
Figure 34.41bc Orders and Examples Main Characteristics
Sharp, pointed canine teeth and molars for shearing; carnivorous
Hooves with an even number of toes on each foot; herbivorous
Aquatic; streamlined body; paddle-like forelimbs and no hind limbs; thick layer of insulating blubber; carnivorous
Carnivora Dogs, wolves, bears, cats, weasels, otters, seals, walruses Coyote
Cetartiodactyla Artiodactyls Sheep, pigs, cattle, deer, giraffes
Cetaceans Whales, dolphins, porpoises
Perissodactyla Horses, zebras, tapirs, rhinoceroses Indian rhinoceros
Hooves with an odd number of toes on each foot; herbivorous
Chiroptera Bats
Frog-eating bat
Eulipotyphla “Core insectivores”: some moles, some shrews
Star-nosed mole
Eat mainly insects and other small invertebrates
Adapted for flight; broad skinfold that extends from elongated fingers to body and legs; carnivorous or herbivorous
Bighorn sheep
Pacific white- sided porpoise