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Taxonomy Phylum Chordata. Phylum Chordata Invertebrate chordates & vertebrate chordates share some characteristics. 4 anatomical structures appear at some point during animal's life time: Notochord -longitudinal, flexible rod located between gut and nerve cord.
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Phylum ChordataInvertebrate chordates& vertebrate chordates share some characteristics 4 anatomical structures appear at some point during animal's life time: • Notochord-longitudinal, flexible rod located between gut and nerve cord. • Throughout life in some invertebrate chordates and primitive vertebrates. • In most advanced vertebrates, retained only as remnants. • Dorsal, hollow nerve cord. • Pharyngeal gill slits-region just posterior to mouth which opens to outside of the animal through several pairs of slits. • Suspension-feeding devices-invertebrate chordates. • Modified for gas exchange and other functions during vertebrate evolution. • Post-anal tail-extension of the spinal column past the anus. • Provides propulsive force in many aquatic species.
Other characteristics typical of chordates: Bilateral symmetry Endoskeleton Deuterostomes Triploblastic Ventral heart Separate sexes Thermal regulation strategies highly diverse. Ectothermic(heat derived from outside the body). Poikilothermic (variable body T determined by environment). Endothermic (heat derived from animal's oxidative metabolism). Homeothermic (must maintain a constant body temperature).
Subphylum Urochordatatunicates or sea squirts • Exhibit the four main characteristics of all chordates. • Encased by tough layer of skin-tunic-(cellulose-like carbohydrate). • Larval form looks like chordate-adult form only retains gill slits.
Subphylum Cephalochordatalancelets • All four main characteristics of chordates through adult stage
Subphylum Vertebrata • Anterior head containing main sensory organs and mouth. • Elongated trunk-exhibits bilateral symmetry. • 2 pairs of appendages-can be greatly modified (wings, fins) or undeveloped (lamprey). • Postanal tail (modified or absent in some groups). • in most, notochord is later replaced by spinal column. • Endoskeleton (bony or cartilaginous)does not limit growth • Well developed body cavity (coelom) containing visceral systems: • Digestive system with large glands (liver, and pancreas). • Ventral 2-4 chambered heart (near abdomen/lower surface). • Blood contains RBCs, hemoglobin, and WBCs. • Paired kidneys with ducts to drain waste to exterior. • 2 divisions skin-often modified-hair/scales/feathers/glands/horns. • Muscular, perforated pharynx-site of gills in fishes, much reduced in adult land-dwelling forms. • Most vertebrates with two separate sexes, each with paired gonads.
FishFirst class of 7 vertebrate classes • Ectotherms. • Gills covered by operculum (can breathe without breathing-except Chondrichthyes). • Scales cover and protect body fish. (not Agnatha). • Paired fins help propel, steer and balance fish (not Agnatha). • Single loop circulation-2-chambered heart. • Blood flows into the gills, picks up oxygen goes to the body (capillaries) and then returns to the heart. • Maintain water balance-kidneys. • Lateral Line System-line of sensory organs down side that detect very small changes in water P/vibrations-orientate fish in water. • Swim Bladder-gas filled sac for buoyancy (not Chondrichthyes).
Class Agnatha-jawless fishlamprey, hagfish • No jaws. • Paired fins generally absent. • Most have skeleton cartilaginous-embryonic notochord in adult.
Placodermsfirst jawed cartilaginous fishmaybe related to Chondrichthyes
Class Chondrichthyescartilaginous fishessharks, skates, rays • Flexible skeleton made of cartilage. • Mouths are located underneath-jaws. • Resemble bony fish and terrestrial vertebrates in having: • Hinged jaws support gill slits (5-7 pairs but no operculum). • Paired appendages-fins. • Inner ear with three semicircular canals. • Paired nasal cavities-good sense of smell. • Skin with toothlike scales, mucous glands. • No swim bladder. • Lateral line system-compensates for poor eyesight. • Countershading-upper surface dark colored, lower surface light.
Class Osteichthyesbony fishes • Skeleton reinforced by calcium salts. • Excellent smell (like Chondrichthyes)/acute eyesight (unlike Chondrichthyes). • Mouth located in front-jaws. • Skin with scales (dermal) and mucous glands. • Reproduction: • Most species are oviparous/fertilization is external. • Some internal fertilization/internal development .
Lobe-finned fish • Long, fleshy muscular fins (lobes) supported by bones. • Lobes adapted to crawling. • Only one species-coelacanth-still lives. • Lungfish. • Are the sole survivors of group that also gave rise to tetrapods-four-legged vertebrates. • What made land colonization possible. • Thought to be the ancestors of amphibians
Ray-finned fish • Thin, flexible skeletal rays support fins. • Adapted for swimming, not crawling. • Most bony fish.
Amphibians • “Double life”-must live near water-soft skin provides little protection against dehydration. • Ectotherms-time of day, temperature, humidity influences activity: • Where temperature becomes high/humidity low, or during dry seasons, some become inactive-aestivation. • In cold or temperate regions, some go into hibernation and remain inactivity 2-8 months, until warm enough again
Anatomy of the frog • Circulation • Heart consists of 2 atria and 1 ventricle • RA dips into V-O2-poor blood to bottom of ventricle • O2-rich blood into left atrium, then ventricle. • O2-poor blood holds up O2-rich blood-no mixing. • O2-poor goes to lungs and skin to pick up oxygen. • O2-rich blood goes into arteries to body.
Respiration-though adult frogs have paired, simple, saclike lungs, much of the oxygen they receive is through their moist skin. No ribs or diaphragm, and chest muscles not involved in breathing-unlike humans Highly developed nervous system that consists of a brain, a spinal cord, and nerves. Eye is crude-its fixed lens cannot change its focus. Poorly developed eyelids do not move. To close eye, frog draws it into its socket 3rd eyelid (nictitating membrane) drawn over it. No external ear Both eardrums (tympanic membranes) exposed. Only one bone in the frog's middle ear (humans-3) Semicircular canals-maintain balance (like humans)
Order Anura • True frogs: • Long hind legs. • Moist, smooth skin. • Toads: • Shorter legs than frogs. • Dry, warty skin. • All go through metamorphosis
Order Urodela • Tailed salamanders • Poorly developed legs. • Smooth, moist skin. • Aquatic urodeles • Tiny forelegs, no hind legs or pelvis • Feathery gills • Scaleless skin • Only vertebrates that are able to completely regenerate limbs as adults.
Order Apodagymnophion • Blind • Limbless (long, slender bodies) like worms or snakes with scales buried in skin.
Metamorphosis • Most begin their lives in the water as tadpoles, or larvae stage. • Breathe through external gills. • Lasts from several weeks to one year, depending on species and environmental factors (Temperature and humidity) • Salamanders always remain as larva-neoteny • Most reach maturity at 3-4 years-breed for 1st time ~1 year after metamorphosis.
Class Reptilia • Ectotherms-animal obtains most of its heat from environment and has a body temperature very close to that of its environment. • Scales, plates, or shields covering them. • Dry skin-thicker, provides a greater protection against drying out, is keratinized and impermeable to water. • Most have a nearly four-chambered heart (ventricle is partially separated), (except crocodiles-a completely four-chambered heart). • Lungs-very efficient- expandable rib cage, (not turtles). • Well-developed kidneys excrete uric acid, so less water is lost. • Limbs with usually five clawed fingers or toes
First vertebrates to practice internal fertilization (copulation) and to lay eggs protected by leathery shell, not bound to water to lay eggs: Oviparous-eggs are laid and incubated outside the body. Ovoviviparous-eggs are incubated inside body, born live. Viviparous-live birth, no egg (humans).
Amniote eggs contain extraembryonic membranes that are not part of the embryo and are disposed of after development. • They protect the embryo, remove nitrogenous wastes, and provide food, oxygen and water. • Amnion-it fills with fluid to provide watery environment for embryo, cushioning embryo and preventing dehydration. • Yolk sac-contains food enclosed in sac, attached to embryo. • Allantois-membranous sac associated with the embryo’s gut, stores nitrogenous wastes. • Chorion-membrane that forms around yolk, allantois, amnion and embryo and allows O2 to enter and CO2 to leave. • Albumin-egg white-source of additional food/water.
Tuatara • Arose earlier than the dinosaurs-considered oldest living reptiles. • Only live in New Zealand today. • Two pairs of well-developed limbs and a strong tail. • Scales. • Has a bony arch, low on skull behind eye, not found in lizards. • Teeth are attached to rim of the jaw rather than inserted in sockets.
Turtles and Tortoises • Turtles-generally live in water, have flat streamlined bodies. • Turtlesarose earlier than dinosaurs. • Tortoises-live on land and have rounded bodies. • Owes evolutionary success largely to shell of bone covered by horny shields-strong and completely protected: • Bone plates fused with ribs, vertebrae, shoulder and hip girdles. • Lower shell (plastron) so snugly against upper (carapace) that thin knife blade can’t be inserted between them.
Crocodiles, Alligators, Caiman • Crocodiles which arose along with dinosaurs, alligators and caiman are most closely related to dinosaurs. • Only reptile group to care for young, especially female crocs, though some snakes will protect eggs before they hatch. • Long body with short legs and clawed, webbed toes. • Tail is long and massive and well suited to rapid swimming. • Thick, large horny plates over most of body generally arranged in regular pattern. • Powerful jaws. Crocodiles Alligators Long, pointier snout Long, more rounded snout 4th tooth sticks out 4th tooth fits into socket Usually saltwater Usually freshwater
Snakes • Evidence suggests that snakes evolved from lizards that burrowed-retain small leg bones even though they have no legs. • Able to unhinge jaw, swallow prey much larger than them. • Adapted to be long and skinny. • All of their organs are elongated and compact. • The spine can be made of several hundred vertebrae • Like amphibians and birds, snakes have a cloaca. • Jacobson's Organ-located at the roof of the mouth • Helps snake process odors-tract food by smell • Flick of forked tongue sends chemical signals to it • Pit organ-located on the head of some snakes • It detects heat and is used to track prey in the dark
Lizards • Two pairs of legs. • External ear openings. • Movable eyelids. • Brain not totally enclosed in a bony case. • Kidneys symmetrical and to rear (snakes-far forward). • Ribs are never forked, as are one or two pairs in the snake.
Class AvesBirds • Descended from dinosaurs-probably closest living relative of dinosaurs. • Characteristics of the earliest bird include small size, clawed fingers, a tail, and teeth • Archeopteryx-earliest known bird ~150 mya-feathers but limited flying ability • Ancestry of birds is in dispute; some biologists consider them related to bipedal dinosaurs. • Similarities to reptiles include: • One ossicle unlike 3 in mammals. • 5 fused bones make up jaw unlike 1 in mammals. • RBCs have nuclei-none in mammals. • Egg tooth to break out of shells, same egg structures and membranes.
All birds, and only birds, have feathers. Modified reptilian scales-are keratinized. Lighter than hair and provide more insulation. All birds have horny, toothless beaks. Keratin beaks adapted to kinds of food eaten. Head must be very light-need centralized body mass with light extremities (teeth and jaws are heavy). All birds have 2 legs and 2 wings. Wings-may be modified for swimming (penguin) or greatly reduced (ostrich). Most birds have 4 toes. Nearly all have 3 pointing forward, 1 backward (exception-woodpeckers-2 forward/2 backward) A few living only on ground have only 3 toes (ostrich) Warm-blooded (Endothermic)-maintain a constant body temperature.
Birds are adapted to fly: • Hollow bones-large air pockets connected to respiratory system. • Fused bones or reduced in size-less weight/increase skeleton strength • Body mass highly centralized-reduces mass of extremities. • Greatly enlarged breast bone and breast muscles. • Wing feathers divided into different feathers with different functions. • Greatly enlarged heart and very rapid heartbeat compared to other animals of similar size. • Unique respiratory system-air sacs extend into some larger bones. • One-way air flow maximizes gas exchange and oxygenation of blood, needed for muscles • Lung doesn’t expand so there is no change in the aerodynamics of a bird in flight • Increased ability to withstand metabolic stress. • Highest metabolic rate for their size of any vertebrate (fastest in smallest birds-hummingbirds). • High metabolic rates-can fly at very high altitudes. • Four-chambered heart, double-loop circulatorysystem. • Well-developed sense organs and nervous system-very acute vision and excellent muscle reflexes.
Certain characteristics are shared by almost all mammals: • Possess hair at one point in their life. • Homeothermic-produce heat/maintain constant body temperature. • Sweat to cool. • Lower jawbone is made of one bone and much stronger-can produce teeth. • Reptiles’ jaw is made up of 3 and attached loosely to skulls • Jawbones became mammals’ ear bones. • Have 3 bones (stirrup, anvil and hammer) in ear-reptiles have 1. • Diaphragm separates abdominal and thoracic cavities. • All have lungs, 4-chambered hearts and 2-loop circulatory system. • Produce milk (carbohydrates, fats, proteins) from modified sweat glands-mammary glands.
