Instructions for printer-friendly copy.

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    Deuterostomia

    Like protostomes, deuterostomes are

    • bilaterally symmetrical
    • triploblastic
    • coelomate

    Unlike protostomes, in deuterostomes

    • blastopore becomes the anus
    • secondary opening becomes the mouth
    • coelom is (usually) derived via enterocoely.
    • cleavage is radial.
    • cleavage is indeterminate.
    • nervous system is primitively dorsal.
    • circulatory system is primitively ventral.

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(click on pic for larger image)

    Deuterostome Phylogeny

    The major deuterostome clades are
    • Echinodermata (The Spiny-skinned Animals)
    • Hemichordata (The Acorn Worms)
    • Chordata (The Chordates)
      • Urochordata (The Tunicates)
      • Cephalochordata (The Lancelets)
      • Vertebrata (The Vertebrates)

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    Echinodermata
    The Spiny-skinned Animals

    Echinoderms are characterized by...
    • pentaradial symmetry
    • exclusively marine life history
    • slow movement and benthic habit
    • thin epidermis covered with gills and other projections
    • internal calcium carbonate skeleton
    • water vascular system derived from coelom
    • complete digestive tract
    • reduced, decentralized nervous system (no brain)
    • reduced circulatory system
    • vestigial/non-functional excretory system

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    Bilateral to Pentaradial Symmetry

    Although they are pentaradially symmetrical as adults,
    echinoderms develop from a bilaterally symmetrical
    larva known as a brachiolaria.

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required video:

    The Water Vascular System

    The water vascular system is derived from the coelom.

    It is used for locomotion and prey capture.

    Water...

    • enters via the aboral madreporite (sieve plate)
    • is distributed radially into the
      • stone canal
      • ring canal
      • ring canals
      • tube feet

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(click on pic for source)

    Echinoderm Divesity

    There are five extant clades within the Echinodermata.
    • Crinoidea - The Sea Lilies
    • Asteroidea - The Sea Stars
    • Ophiuroidea - The Brittle Stars
    • Echinoidea - The Sea Urchins
    • Holothuroidea - The Sea Cucumbers

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    Echinodermata: Crinoidea
    The Sea Lilies

    There are about 600 described species of sea lilies.
    They are ...
    • benthic (bottom dwelling)
    • usually sessile (attached to the substrate)
    • able to swim to change location
    • suspension feeders (via ambulacral groove)

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(click on pic for source)

    Echinodermata: Asteroidea
    The Sea Stars

    There are about ~1800 described species of sea stars.

    Asteroids are characterized by...

    • distinct pentaradial symmetry
    • (Some species have many more than five arms (some up to 50!))
    • Slow movement
    • benthic life history
    • predatory life history, feeding mostly on bivalves

    Sea stars can regenerate an entire starfish from one ray,
    as long as part of the central disk is attached.

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    Echinodermata: Ophiuroidea
    The Brittle Stars & Basket Stars

    There are about 2000 described species of ophiuroids.
    (Greek ophis, meaning "serpent")

    Brittle stars are characterized by...

    • distinct central disk
    • five long, snakelike arms radiating from disk
    • relatively fast-movement
    • detritivory/scavenging
    • secondarily lost anus (dual purpose mouth)
    • cilia-lined sacs (bursae on the oral side of the disk
      • perform gas exchange
      • excrete nitrogenous waste

    There is no functional excretory system.

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    Echinodermata: Echinoidea
    Sea Urchins and Sand Dollars

    The name derives from Greek echinos, meaning "spine".

    Echinoids are characterized by...

    • hard, calcium carbonate test (skeleton)
    • ambulacral grooves running oral to aboral
    • herbivory or carnivory, depending on species

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(click on pic for source)

    Eating

    The mouth bears a specialized,
    five-part chewing apparatus,
    Aristotle's Lantern.

    Muscles inside the test move the plates,
    enabling the urchin to feed with the
    hard, calcareous external "teeth".


(click on pic for source)

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(Click on pic for source)

    Being Eaten

    Some consider sea urchin gonads full of eggs
    to be a special delicacy.

    If you've eaten uni at a sushi bar,
    you can tell us your opinion.

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    Echinodermata: Holothuroidea
    Sea Cucumbers

    Sea cucumbers are pentaradially symmetrical,
    but lie on one side so that oral and aboral surfaces
    are positioned as anterior and posterior.

    Sea cukes are characterized by...

    • complete gut with a mouth and anus.
    • tube feet that help transfer food to the mouth.
    • unique and somewhat gross defense mechanism. (see video)

    And then there's Our Friend the Sea Pig.

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(click on pic for source)

    Hemichordata: The Acorn Worms (~350 described species)

    About 350 species of fossorial acorn worms inhabit benthic marine communities around the world.

    The body consists of

    • proboscis
    • neck
    • trunk

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(click on pic for source)

    Evolutionary Links

    Acorn worms are of evolutionary interest because they share some characters with echinoderms and some with chordates.
    • Hemichordate tornaria larva is very similar to the echinoderm brachiolaria.
    • Like Chordates, acorn worms have ciliated, pharyngeal gill slits.
    • Like Chordates, acorn worms have a dorsal, sometimes hollow nerve cord (though its homology with the chordate nerve cord is uncertain).

(click on pic for source)

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    Chordata - The Chordates

    Chordates share synapomorphies present at least during ontogeny,
    though they may be lost in the adult.
    • pharyngeal gill slits
    • dorsal, cartilaginous notochord
    • dorsal, hollow nerve cord
    • endostyle or thyroid gland
    • post-anal tail
    • segmentally arranged muscle bundles (myomeres)

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    Chordate Phylogeny

    Chordata includes three subphyla:
    • Urochordata
    • Cephalochordata
    • Vertebrata

    Vertebrata is further subdivided into
    a nested hierarchy.

    • Gnathostomes - animals with a mandible
    • Osteichthyes- "bony fishes"
    • Lobe fins
    • Tetrapods - four-legged animals
    • Amniotes - animals producing an amniotic egg

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(click on pic for source)

    Chordata: Urochordata
    The Tunicates

    More than 3000 species of these soft-bodied,
    sessile creatures inhabit the world's oceans.

    The free-swimming tadpole larva exhibits the chordate synapomorphies.

    The adult looks nothing like the larva.

    Both larva and adult are filter feeders,
    straining water through the porous pharynx.

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(Watch at least up to 2:00 for lancelets.
But the whole video is good.)

    Chordata: Cephalochordata
    The Lancelets

    The marine, eel-like lancelets exhibit all the chordate characteristics.

    There are only 32 extant species of these
    fossorial filter feeders.

    The lancelet burrows into the substrate, tail down,
    and protrudes its head into the water to feed.

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Craniata: Animals with Skulls

The defining synapomorphy uniting all Craniates is the cranium,
a bony skull encasing the brain.

Craniates can be divided into:

  • Myxini (Hyperotriti) (hagfishes)

  • Vertebrata
    • Petromyzontida (Hyperoartia) (lampreys)
    • Gnathostomata (jawed vertebrates)

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    Craniates: A Progression of Complexity

    Extant Craniate taxa exhibit a progression of derived characters
    that reflects the sequence in which these traits evolved.

    Hagfishes

    • evolution of a simple cranium

    Lampreys

    • evolution of a vertebral column

    Bony Fishes

    • evolution of a hinged jaw derived from gill arches
    • evolution of a mineralized (bone) skeleton

    Lobe-finned Fishes

    • evolution of four fleshy, muscular limbs

    Lungfishes

    • evolution of lungs (lung fishes)

    Tetrapods

    • evolution of five digits at the end of each limb

    Amniotes

    • evolution of amniotic egg
    • evolution of leathery skin

    Mammals, Birds

    • convergent evolution of
      • homeothermy
      • insulating skin derivatives

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    Craniata: The Hagfishes

    Hagfishes are benthic (bottom-dwelling), eel-like animals.
    • The skeleton is cartilaginous.
    • Dorsal support provided by notochord.
    • Vertebrae are absent.
    • Cranium is cartilaginous and rudimentary.
    • Small, conical eye spots unchanged for 500 milliion years
    • Diet: carrion (dead animals) and small invertebrates

    Hagfish are famous for a remarkable defense mechanism,
    which gives them their other nickname, "slime eels".

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(click on pic for source)

    Chordata: Vertebrata
    The Vertebrates

    There are about 70,000 species of vertebrates,
    most of them bony fishes.

    All share these synapomorphies:

    • highly developed brain
    • bony cranium housing the brain
    • articulated, dorsal vertebral column
    • nerve cord protected inside vertebral column
    • bony skeleton (primitive condition)
    • well developed epithelia
    • complex camera eye
    • closed circulatory system with multi-chambered heart
    • three types of muscle tissue
    • well developed endocrine system

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(click on pic for source)

    The Vertebrate Body Plan

    Vertebrates have three main body regions:
    • head
    • trunk
    • postanal tail
    • (a neck comes later)

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    Vertebrate Characteristics:
    Big Forebrains

    Brain morphology reflects natural history.

    The mammalian neocortex is highly derived
    with respect to the ancestral vertebrate brain.

    Birds lack a neocortex or anything homologous to it.
    However, the avian dorsal ventricular ridge (DVR), also derived from the telencephalon, contains nuclei (neuron clusters) that appear to function as neocortical neurons do.

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(click for source)

    Vertebrate Characteristics: Epithelia

    Vertebrate internal and external surfaces are lined with well developed epithelia.
    The external integument (skin) functions in
    • protection
      • first line of defense against pathogens and other foreign bodies.
      • two layers: epidermis over dermis
    • thermoregulation - Evaporative cooling and dermal blood supply are regulated by skin..
    • Vitamin D production - Vitamin D precursor (7-dehydrocholesterol) is converted to Vitamin D upon exposure to UV light..
    • absorption and secretion - Skin absorbs and secretes water and water-soluble molecules.
    • respiration - The skin is a vital respiratory organ in amphibians and some other vertebrates.

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    The Vertebrate Camera Eye

    The image-forming camera eye was
    a major evolutionary innovation.
    • cornea is the outermost lens
    • aqueous chamber provides nutrition, intraocular pressure
    • lens changes focal distance
    • iris controls pupil aperture
    • vitreous chamber provides most of the intraocular pressure
    • retina is the sensory layer

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(click on pic for source)

    Vertebrate Photoreceptors

    The vertebrate retina may have two types of photoreceptors.
    • rod photoreceptors confer
      • high sensitivity to light (night vision)
      • low image resolution ("grainy" picture)
      • no color information

    • cone photoreceptors confer
      • relatively low sensitivity to light (day vision)
      • high image resolution (clear picture)
      • different classes of cones absorb different λ of light
      • This allows color discrimination.

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    Convergent Eyes

    Recall that cephalopods also have a camera eye.

    The cephalopod and vertebrate camera eyes
    evolved independently.

    They are a product of convergent evolution.

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    Vertebrate Characteristics:
    Closed Circulatory Systems

    Closed Circulatory System:
    • Heart pumps blood through a circuit of blood vessels.
    • Gas exchange and nutrient transfer takes place in the smallest diameter blood vessels.
    • May form one or two blood circuits.
    • Found in all Annelids, Cephalopods and Vertebrates.

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    Vertebrate Characteristics: The Heart

    Modern vertebrate hearts may have
    two, three, or four chambers.

    Two-chambered hearts (fish) pump blood through
    one circuit of blood vessels:

    • heart --> gills --> body --> heart

    Three- and four-chambered hearts pump blood through
    two separate circuits:

      1. systemic circuit (heart --> body --> heart)
      2. pulmonary circuit (heart --> lungs --> heart)
      xxxOR
      xxxpulmocutaneous circuit (heart --> lungs/skin --> heart)

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    Vertebrate Characteristics:
    Muscle Tissue

    Together with the nervous system,
    muscle tissue facilitates movement.

    Vertebrates have three types of muscle tissue,
    each specialized for different functions.

    • skeletal striated muscle (voluntary control)
    • cardiac striated muscle (involuntary control)
    • smooth muscle (involuntary control)

    • tendons attach skeletal muscle to bone
    • ligaments attach bone to bone

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(click on pic for source)

    Vertebrate Characteristics:
    Coelom

    In vertebrates, the coelom forms the
    • pericardium surrounding the heart
    • peritoneum surrounding the viscera

    In tetrapods, it also forms the pleura surrounding the lungs

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    The End: Cloaca

    In many species, both the excretory system and the reproductive tract
    join the intestine near its end.

    In this arrangement, the posterior exit provides egress for

    • nitrogenous/excretory waste
    • reproductive products (eggs or sperm)
    • fecal waste

    This multi-purpose exit is is known as a cloaca.
    (Cloaca (Latin) translates as "sewer".)

    Cloacae are found in

    • many invertebrates
    • most fish
    • most amphibians
    • all reptiles and birds
    • monotreme mammals (platypus, echidna)

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    Vertebrate Characteristics:
    Endocrine System

    A gland is one or more cells that produce and secrete a particular product.

    A gland may be

    • exocrine (product is secreted onto skin or into body cavities)
        • milk
        • oil
        • sweat
        • bile
        • mucus
        • digestive enzymes

    • endocrine (product (hormone) is secreted inside the body)
      • unicellular (gland cell)
      • multicellular (gland)

      • discrete - endocrine cells grouped and adhered together (e.g., thyroid)
      • diffuse - scattered among non-endocrine cells (e.g., intestinal epithelium)
      • intermediate - between discrete and diffuse (e.g., Islets of Langerhans)

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    A Word About Body Temperature

    Forget "cold blooded" and "warm blooded" .
    Replace with precise, physiological terms describing...

      1. Heat Source
        a.ectotherm
        • main heat source is the external environment
        • from the Greek ecto meaning "outside"
        b. endotherm
        • main heat source is internal metabolic reactions
        • (from the Greek endo meaning "inside")

      2. Temperature Regulation
        a. poikilotherm
        • temperature regulated primarily by environment
        • (from the Greek poikilo meaning "variable")
        b. homeotherm
        • temperature regulated primarily metabolically
        • (from the Greek homeo meaning "constant")

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(Click on pic for source. )

    Vertebrate Diversity

    Major taxonomic groups of extant vertebrates:
    • Agnathans - jawless fishes
    • Chondrichthyes - cartilaginous fishes
    • Actinopterygii - ray-finned (bony) fishes
    • Lobe-finned fishes - coelacanths and lungfishes
    • Amphibia - salamanders, frogs, caecilians
    • Mammalia - mammals
    • Testudines - turtles
    • Lepidosauria - tuataras, lizards, snakes
    • Archosauria - crocodilians and birds

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    Vertebrata: The Lampreys

    Lampreys are jawless, eel-like, catadromous predators.
      • live most of their lives in freshwater
      • migrate from freshwater to the sea to spawn

      Lampreys use their sharp-toothed, circular mouthparts
      to latch onto prey much larger than themselves.
      The lamprey slowly eviscerates and ingests its prey.

      Lampreys have been introduced accidentally into freshwater lakes,
      where they wreak havoc on native fish such as salmon and trout.

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    Vertebrata: Gnathostomata
    Hinged Jaws

    Gnathostomata includes
    • Chondrichthyes (sharks, skates and rays)
    • Actinopterygii (ray-finned fishes)
    • Sarcopterygii (lobe-finned fishes and tetrapods)

    In fish, the cartilaginous pharyngeal gill arches bear gills.
    In tetrapods, gill arches became the bones of a hinged jaw.

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    Your Inner Fish

    Mammals took things a step further.

    Several of those jaw bones evolved into
    the bones of the mammalian inner ear.

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(photo by Scott Wilson; click on pic for source)

    Vertebrata: Chondrichthyes
    The Cartilaginous Fishes

    This taxon includes sharks, sawfishes, skates, and rays.

    Cartilaginous fishes...

    • are all carnivorous/predatory
    • have placoid scales derived from dermis
    • these scales also form the replaceable teeth.
    • have a keen sense of smell
    • sense vibrations with a lateral line system

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(click on pic for source)

    Bone Came First

    A 380-million-year-old fossil shark, Gogoselachus lynbeazleyae, found in Western Australia has bone cell remnants in its cartilaginous skeleton.

    This suggests that the cartilaginous skeleton represents
    a derived condition, with bone secondarily lost
    .

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(click on pic for source)

    Keep On Swimming

    A few shark species are obligate ram ventilators:
    they must force water across the gills for oxygen,
    and so must swim constantly.
    • Family Lamnidae (e.g., Great White, Mako)
    • Whale Shark

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    More Ways to Egg

    Oviparous animals lay eggs that hatch outside the mother's body

    Ovoviviparous animals brood eggs that hatch inside the mother's uterus,
    and and are then released.

    Viviparous animals have young that develop inside the mother's uterus,
    where they are nourished prior to birth via a connection with the mother's bloodstream (placenta).

    • Skates are oviparous.
    • Sawfish are ovoviviparous.
    • Rays may be oviparous, ovoviviparous, or viviparous, depending on species.
    • Sharks also may be any of the above, depending on species.

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(photo by Jose Carballada; click for source)

    Actinopterygii - The Ray-finned Fishes

    Ray-finned fish exhibit a vast array of form and natural history.
    At 24,000 species, they are the most diverse vertebrates.

    • Skeleton composed primarily of bone
    • Fin rays are composed of cartilage or bone
    • Dermal scales protrude through epidermis and shed easily.
    • Skin copiously supplied with mucous glands
      • mucous is an adjective
      • mucus is a noun
    • Fins are either
      • medial and unpaired
      • lateral and paired
    • Toothy, terminal (i.e., at the end of the body) mouth
    • Gill arches covered by a bony operculum
    • Swim bladder (derived from gut) provides buoyancy.
    • Two-chambered heart

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    Sarcopterygii
    The Lobe-finned Fishes

    The lobe-finned fish are the closest relatives of tetrapods.
    • well-developed bony skeleton with strong fin bones.
    • Fleshy, lobed fins resemble and move like tetrapod limbs.
    • Lungs are homologous to tetrapod lungs.
    • Gills are also present and used to breathe under water.

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    The Move to Land

    Ancient sarcopterygiians evolved adaptations
    that made terrestrial locomotion possible.

    They probably looked something like Tiktaalik,
    an ancient lobe fin that had all the skeletal and respiratory
    equipment to make that first move onto land.

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(photo by Julian Fennessey; click on pic for source)

    Tetrapoda: We Haz Landed

    A tetrapod has four limbs, or is descended from a four-limbed ancestor.

    Tetrapods exhibit
    • loss of gills (at least as adults)
    • four limbs, each with five digits
    • skeletal and muscle adaptations for terrestrial movement
    • cranial adaptations to keep the head stable during movement
    • a layer of dead epithelial cells to slow evaporation
    • a well-developed, muscular tongue
    • a parathyroid gland to control blood calcium levels
    • Harderian gland to lubricate the eyes
    • a vomeronasal organ for chemoreception

    Tetrapoda includes
    • Amphibia (cecilians, salamanders, frogs)
    • Reptiliomorpha (reptiles, birds, dinosaurs, mammals, etc.)

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    Amphibia

    Amphibians are characterized by...
    • being ectothermal poikilotherms
    • scaleless, moist skin that is
      • respiratory in function
      • equipped with poison glands
    • three-chambered heart
    • large mouth with very small teeth
    • being insectivorous/carnivorous
    • primitively oviparous, but may be ovoviviparous or viviparous
    • aquatic larvae (with gills and lateral line system)

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    Amphibia: Salamanders and Newts

    Modern salamanders and newts most closely resemble the ancestral amphibian,
    which had a tail and five-digits on each limb.

    Gilled, aquatic larvae lose their gills
    when they metamorphose into adults.

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    Amphibia: Caecilians

    If you didn't notice the mouth,
    you might think it was a huge worm.

    Caecilians are tropical amphibians that have
    lost their legs and taken up a semi-fossorial existence.

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Red-eyed Tree Frog (Agalychnis callidryas):

    Amphibia: Frogs and Toads

    All toads are frogs, but not all frogs are toads.

    Frogs
    • smooth, mucous skin
    • capable of fast, powerful leaps

    Toads
    • drier, warty skin
    • poisonous parotid glands behind eyes
    • usually walk to move, and can't leap far
Common Toad (Bufo terrestris)

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(photo by Kevin Schaefer, Getty Images)

    Reptiliomorpha: The Amniotes

    Reptiliomorpha includes all animals that
    encase their young in an amniotic egg.

    • "Anapsida" turtles
    • Diapsida reptiles (including birds)
    • Synapsida - mammals

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    Cranial Synapomorphy

    Cranial morphology can reveal common ancestry:

    • Anapsida - No temporal opening behind the eye orbits
      • turtles and tortoises
    • Synapsida - Single temporal opening behind the eye orbits
      • mammals
    • Diapsida - Two temporal openings behind the eye orbits
      • tuataras, lizards, snakes, crocodilians, birds


      (To which group do we belong?)

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    The Egg:
    Provisioning & Protecting

    An egg consists of
    • an ovum
    • nutritive yolk
    • protective envelope

    In fish and amphibian eggs

    • yolk is stored in the developing embryo's gut
    • the embryo is enclosed in a simple shell or gelatinous capsule

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    An Egg to Beat Them All

    Amniote reptiliomorphs enclose their young in an amniotic egg,
    which allows true independence of a watery environment.

    From inside to outside, the amniotic egg components are

    • gas-permeable, desiccation-resistant shell
    • outer membrane lining the inside of the shell
    • inner membrane enclosing the albumin
    • proteinaceous albumin surrounding fluid-filled membranes:
      • chorion - encases the internal membranes
      • amnion - encloses the growing embryo
      • allantois - collects embryo waste products
      • yolk sac - contains nutritive yolk connected to embryo gut

      The amniotic egg necessitates internal fertilization.
      Ovum and sperm must fuse before the shell is made.

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    Mammalian Amniotic Homology

    The eutherian (placental) mammal amniotic egg
    has undergone evolutionary modification.

    • amnion surrounds the embryo
    • yolk sac and allantois form the umbilical cord.
    • chorion
      • surrounds the other membranes
      • fuses with the uterine wall
      • forms nutrient/waste removal bridge
        between mother and offspring

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    Amniote "Anapsids"
    Turtles and Tortoises

    Turtle and tortoise characteriistics:
      • ectothermic poikilotherms
      • three-chambered heart
      • scaly, keratinous skin
      • absence of teeth
      • sharp cutting edges on maxilla and mandible
      • three-chambered heart
      • external bony shell consisting of
        • dorsal carapace
        • ventral plastron
        • shell is an integral part of the skeleton.

      Turtles may be marine, fresh water, or terrestrial.

      Tortoises are entirely terrestrial.

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(click on pic for source)

    Amniote Diapsids:
    Squamata

    Squamata includes more than
    10,000 species of lizards and snakes.

    Squamate characteristics:

    • ectothermic poikilotherms
    • three-chambered heart
    • scaly, keratinous skin
    • overlapping, epidermal scales (do not shed)
    • molting of skin with growth
    • movable quadrate bones allowing the maxilla to move
      relative to the neurocranium (brain case)
    • tremendous variability in size, morphology, and natural history

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(Deleted Scene from "Peter Pan: The Prequel")
(click on pic for source and the full story)

    Amniote Diapsids: Crocodilians

    Crocodilians and birds split from an Archosaurian dinosaur ancestor.
    Both are the last living descendants of the dinosaurs.

    Crocodilia includes large, predatory, semiaquatic reptiles:
    • crocodiles
    • alligators

    • caiman
    • gharial
    Crocodilian characteristics:
    • ectothermic poikilotherms
    • four-chambered heart
    • respiratory air flow (like birds)
    • large, solidly built
    • long flattened snout
    • laterally compressed tail
    • eyes, ears, and nostrils dorsal on the head
    • non-overlapping epidermal scutes
    • strong swimmers and sprinters

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Photo by Lieselot. Dalle on Unsplash

    Amniote Diapsids: Birds

    Aves characteristics:
    • endothermic homeotherms
    • four-chambered heart
    • grasping feet with digits of different sizes
    • long, flexible neck
    • maxilla and mandible sheathed in a keratinous, toothless bill
    • epidermal scales modified to form feathers
      • uropygial oil gland (base of tail) for feather waterproofing via preening
      • Leg scales are comparable to those of other diapsids.
    • hollow bones
      • decrease body mass
      • are an adaptation for flight

    • Unidirectional respiration via rigid lungs connected to inflatable air sacs
    • breathing via costal (rib) expansion/contraction
    • There is no diaphragm. So don't squeeze them. They die.
    • Voice box at distal end of trachea allows vocalizations.

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    Avian Reproduction

    Sex determination is via the female parent.
    • male = ZZ sex chromosomes
    • female = ZW sex chromosomes
    • (in mammals, male = XY and female = XX sex chromosomes)

    The avian egg
    • contains a huge amount of yolk
    • shell is calcified and brittle

    Young may be either precocial or altricial,
    depending on species.

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    Synapsida: The Mammals

    Mammals were the first vertebrates to
    adaptively radiate into a wide diversity of terrestrial habitats.

    Mammalian synapomorphies:

    • endothermic homeotherms
    • four-chambered heart
    • mammary glands
    • muscular lips for suckling (marsupials and eutherians)
    • hair (grows between epidermal homolog of reptilian scutes/scales)
    • anucleate red blood cells
    • muscular diaphragm separates thorax and abdomen
    • Ancestral jaw bones evolved to form inner ear bones
    • jaw musculature increased in size and complexity
    • bony plate (hard and soft palates) separates
      the mouth and nasal cavities
      • allows animal to breathe with food in its mouth
      • allows young to breathe while suckling

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    Mammalian Innovation:
    The Diaphragm

    The flat, muscular diaphragm separates
    the trunk into thorax and abdomen.

    The diaphragm contraction and relaxation
    inflates and deflates the lungs.

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    Mammalia: Monotremata

      Monotreme mammals...
      • are the only living mammals that lay eggs
      • Eggs are yolky, essentially reptilian in structure and development
      • Cone photoreceptors have oil droplets, as in reptiles/birds.
      • Oil droplets have been lost in all other mammals.
      • Y chromosome is similar to X chromosome.
      • Have a cloaca like that of diapsids

      The echidna and the platypus are the only extant monotremes.

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    Mammalia: Marsupialia

    Marsupial mammals...
    • are born at an extremely altricial stage of development
    • Fetus climbs to the mother's marsupium (pouch) and crawls in.
    • Baby latches onto a teat, and completes development in the marsupium.
    • This can take many weeks.

    Examples: kangaroos, koala, wombat, ~ 250 others

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    Mammalia: Eutheria

    Placental (eutherian) mammals...
    • give birth to live young that develop inside the mother's uterus
    • embryos nourished during development via the placenta
    This is the most derived and diverse mammalian taxon.
    There are more than 4400 species in 1000 genera.

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    The Better to Run After You

    In marsupials and eutherians:
    • spine undulates dorsoventrally during locomotion.
    • (In all other vertebrates, spine undulates laterally.)
    • leg joints are rotated under the body
    • skeleton, not muscles, support the body's weight
      • more energy efficient
      • allows fast locomotion

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    Vertebrates

    We love them because they are us.

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