Vertebrate Natural History
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Phylum Chordata
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Subphylum Vertebrata- animals with a jointed backbone
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Class Agnatha- “Jawless” fish
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Development of:
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Cranium- encloses larger brain; houses sensory organs (ex: paired eyes)
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Lateral Line- series of organs along each side that are sensitive to pressure changes
(senses movement in water)
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2 semicircular canals- senses direction in 2 dimensions
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Extinct forms- Ostracoderms – had cartilage skeletons and bony armor on head; bottom
filter feeders
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2 examples today- lamprey and hagfish
Class Chondrichthyes- “gnathostomes-Jaws”
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Gill slits (used for filtering water) supported by bony arches. These gill arches become
bones in inner ear of mammals
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Jaws and vertebra made of cartilage
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Palatoquadrate- upper movable jaw
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Meckel’s cartilage- lower jaw
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Spiricle- opening behind skull; used for water pasage (dorsal opening in rays)- becomes
Eustacean tube in ear of mammals
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Skin covered with placoid scales with hard enamel; teeth also covered with enamel –
only fossils of sharks commonly found. Teeth are continually replaced as old ones are lost
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No ribs or swim bladder. Buoyancy maintained by large oil filled liver and by swimming
method. Sharks literally ”fly” thru the water; stiff pectoral fins provide lift and tail fin
provides thrust.
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Have paired pectoral and pelvic fins
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3 semicircular canals- senses direction in three dimensions; better sensing for pelagic
lifestyle
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14 families; 350 species; sharks have lived continuously on earth for 300 million years
(since Devonian)
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Elasmobranchi- sharks
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Holocephali- skates and rays
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Heterocercal fin - primitive type of tail of sharks in which vertebra extends all the way to
tip (same as ostracoderms)
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Ampulla of Lorenzini- small sensory pits located on the snout of sharks and rays; important in
electro-perception in which very small electrical currents in muscle movement can be detected; also
blood and some metals
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bone
Placoderms- extinct group; heavily armored; large toothless jaws with sheering plates; first true
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Class Osteichthyes- “Bony Fish”
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Ossified bone (hardened with calcium)
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Swim bladder develops for buoyancy
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One gill slit instead of several; covered by bony operculum
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Tail becomes symmetrical
Two subclasses:
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Lobe-finned fish (Sarcopterygia)
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Bones in fin allow for support
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Probably gave rise to amphibians (same bone formula 1:2:5 digits
EX: Coelacanth (off coast of Madagascar); thought to have been extinct
Two subclasses:
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Ray-finned fish (Actinopterygia)
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Includes most modern fish
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Have overlapping scales
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3 types
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Chonondrosteans- most primitive; thick bony scales Ex: Sturgeon
Holosteans – gar
Telosteans – bass, perch
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Class Amphibians “Tetrapods”
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Adapted to land
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Had functional limbs and rudimentary swimming tail
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Had flat heads with sprawling stance
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Many were plant eaters; some carnivores; needed to be near water to reproduce
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Ex: Ichthyostega (upper Dev.-Tri.)
Class Reptilia- true terrestrial animals (permian – present)
**Certain problems had to be overcome to conquer land
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Interlocking vertebrae- provided support
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Amniotic egg- allowed for reproduction w/o being close to water; they “carried their
water with them”
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Leathery skin with scales- prevented desiccation
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Internal fertilization- had profound effect: Mating! Introduced competitive
selection pressures
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bloodedness)
Ectothermic poikilotherms- body temperature is derived from environment (cold-
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capacity
Skull changes from flat heavy type to a more domed type; allowed for a larger brain
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Development of temporal fenestra: holes in the side of the skull that allowed for more room for
jaw muscle
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Order Chelonia- Turtles (early tertiary – present)
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Very primitive reptiles
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Have anapsid skull
(no fenestra)
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Dimetrodon
Class Aves- birds (jurassic – present)
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carnivores)
Believed to have evolved from archosaurs (sauropod dinosaurs: large bipedal
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Endothermic homoiotherms- ability to maintain body temperature (warm blooded)
advantages: better enzymes and more efficient metabolism
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Diapsid- skull (like dinosaurs)
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2 fenestra in skull
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Thin, hollow bones (to reduce weight); also found in many sauropod dinosaurs. Scales
become feathers.
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attachment)
Loss of bony tail; development of keel on sternum ( for greater area for flight muscle
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Bones become fused in hand: development of wings
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Reptilian holdovers:
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Egg laying
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Scales on legs
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Class Mammalia
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Believed to have evolved from mammal-like reptiles called Therapsids Ex: Dimetrodon-Permian
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Have synapsid- skull with 1 temporal fenestra
Important developmental characteristics:
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Body hair- helps retain body heat (excellent insulation)
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Mammary glands- modified sweat glands that provide concentrated nourishment for rapid
growth of young and aids in development of immune system
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Live birth- developing fetus is protected from fluctuating environmental factors and provided
with constant temperature and nourishment from mother
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Endothermic homoiotherms- ability to maintain body temperature (warm blooded) advantages:
better enzymes and more efficient metabolism (faster movement, better utilization of nutrients, will
provide basis for development larger and higher brain function)
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Order Carnivora
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Suborder Pinnipedea- the seals
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Name means “fin-footed”; hind limbs reduced for swimming; front limbs modified into flippers
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Vibrissae- whiskers that contain blood vessel, very sensitive tactile organ
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Have thick layer of fat that acts as insulation
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Two Groups:
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Eared Seals- sea lions & fur seals
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True seals- many species; found mostly in Arctic and Antarctic waters
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Order Cetacea- whales and dolphins
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Have streamlined body (more hydrodynamic) and forelimbs become flippers (retains 1:2:5 digits
bone formula)
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Pelvic girdle highly reduced (atrophied)
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Body tapers to muscular flippers called “flukes”
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Family Odonoceti- “toothed whales”
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Include Sperm whale, killer, dolphins and porpoise
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Skull modified: blow hole on top of skull. Melon (oil-filled) in front of cranium believed to help
focus sound waves: echo-location (bio-sonar)
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Echolocation
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Dolphins
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Larger group (72 species)
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Very gregarious; strong herding instinct
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Both salt water and fresh water species
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Have longer snout; teeth more conical
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Porpoises
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No snout
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Commonly encountered along shores
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Generally smaller than dolphins; seldom follow ships
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Family Odontoceti- “toothed whales”
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Include Sperm whale, killer, dolphins and porpoise
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Skull modified: blow hole on top of skull. Melon (oil-filled) in front of cranium believed to help
focus sound waves: echo-location (bio-sonar)
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Mystacoceti- the baleen whales
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Teeth of developing embryo replaced with “baleen”
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Finger-like sieve plates that strains water for plankton, krill, and small fish
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Includes the largest animals that ever lived on Earth
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Many make sounds for communication; some of these sounds are very low frequencies that can
travel hundreds of miles
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Some species are very gregarious; show cooperative behavior in defense and feeding
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Many can dive for extended periods (90 minutes)- Sperm Whales); facilitated by special organ
called the Retia: bunches of long, twisted blood vessels and capillaries that acts as a reservoir of blood,
oxygen, and nutrients
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Many products were derived from whales; this led to great demand and in turn to massive kills;
killing out entire families. Whales are now protected animals!