Phylum Chordata Part Three Tetrapods: Amphibians & Amniotesstreaming.missioncollege.org/jtaylor/media/BIOSC... · Order Urodela - Salamanders ! Respiration- wide array of respiratory

Phylum Chordata Part Three

Tetrapods: Amphibians & Amniotes Reference: Chapter 34

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

3

The first tetrapods appeared 365 MYA

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


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



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)


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


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


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

25-17


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


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


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


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

25-23


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)


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


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


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

25-28

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 forelimbs 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

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Phylum Chordata Part Three Tetrapods: Amphibians & Amniotesstreaming.missioncollege.org/jtaylor/media/BIOSC... · Order Urodela - Salamanders ! Respiration- wide array of respiratory