Vertebrate%20Evolution:%20Animals%20with%20a%20vertebral%20column%20made%20of%20bone%20or%20cartilage

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Vertebrate Evolution Animals with a vertebral
column made of bone or cartilage
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Vertebrates are part of a larger phylum called
Chordata which includes Urochordata (tunicates),
Cephalochordata (amphioxus), Myxini (hagfish)
and Vertebrata (you)
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Phylum Chordata

• Synapomorphies present at some point in the
  development of all chordates include
• Pharyngeal slits (gill slits in fish and other
  critters)
• Notochord (stiff, fibrous rod running the length
  of the body)
• Dorsal nerve cord (your spinal cord)
• Post-anal tail (we have something of a tail
  while a fetus, but it is pretty stumpy in adult
  humans)

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Invertebrate chordates provide clues to the
origin of vertebrates

• Subphylum Urochordata - commonly called sea
  squirts or tunicates
• only show the chordate traits in their larval
  stage
• notochord is restricted to the tail
• adults filter feed

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Invertebrate chordates provide clues to the
origin of vertebrates

• Subphylum Cephalochordata - headless chordates-
  lancelets, amphioxus
• show all four chordate traits as adults
• All early chordates before the evolution of jaws
  and teeth were suspension feeders

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Introduction to the Vertebrates

• Larger, more active lifestyle than other
  chordates
• Cephalization
• Brain (anterior end of dorsal nerve chord)
• Sensory equipment in head region
• Axial Skeleton
• Cranium
• Vertebral column (except in hagfishes)

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Vertebrate Diversity

• Jawless fishes hagfishes lampreys
• Gnathosomes Jaws
• Cartilogenous fish
• Bony fish
• Tetrapods 2 pairs of appendages
• Amphibians
• Amniotes
• Mammals
• Reptiles (traditional)
• Birds

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Class Myxini Hagfishes

• Most primitive living vertebrate (?)
• No Vertebrae
• Cartilogenous cranium and notochord
• Degenerate anatomy was thought to be secondary
• Its now thought that hagfish are the earliest
  branch of the vertebrates

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Class Cephalaspidomorphi Lampreys

• Used to be classified with hagfishes, but are
  more advanced
• No jaws or vertebrae but has cartilage pipe
  surrounding notochord--gt early stage of a
  vertebral column

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Lampreys are parasites

• Lampreys attach their mouths onto victims such as
  lake trout or whitefish, and literally suck the
  life out of them!
• Since its introduction into the Great Lakes in
  the 1930's, sea lampreys have caused many
  problems for the commercial and recreational
  fishing industries and some 10 million dollars
  are spent each year to control them.

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Gnathostomes Jawed Vertebrates

• Jaws evolved by modification of the skeletal rods
  of the anterior pharyngeal slits
• Jaws opened up new lifestyles and nutrient
  sources
• Early Gnathostomes mostly replaced the agnathans
  during the Devonian Period (360-400MYA)--gt Age
  of the Fishes

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Class Chondrichthyes Sharks and Rays

• Cartilogenous skeleton --gtlost dermal bone
• nostrils used only for smelling, not breathing
• Internal fertilization but may be
• Oviparous lay eggs that hatch outside mothers
  body
• Ovovivparous retain fertilized eggs inside moms
  body
• Viviparous young born aliveafter developing in
  uterus

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Class Osteichthyes Bony fish

• Ossified skeleton
• nostrils used only for smelling, not breathing
• 3 extant classes
• Ray-finned fishes
• Lobe-finned fishes
• lungfishes

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Figure 34.14 A coelocanth (Latimeria), the only
extant lobe-finned genus
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Tetrapods

• The earliest tetrapods most likely arose from
  organisms similar to todays lungfishes
• In the Devonian period, plants and insects had
  already invaded land

• Lungfish living in shallow water were able to
  spend increasingly longer amounts of time on land

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Phylum ChordataClass Amphibia

• Salamanders, frogs, caecilians
• Some are strictly aquatic and others terrestrial
• After the Devonian, the Carboniferous period was
  The age of the amphibians

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Most amphibians are still dependent on water to
some extent

• Gas exchange occurs in the lungs or through the
  surface of the skin
• The surface must be kept continuously moist and
  numerous glands continually secrete fluid onto
  the surface of the skin.

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Reproduction is also many times dependent on water

• Fertilization is often external with females
  releasing eggs into water
• Eggs have no shell and will desiccate quickly
• Many (not all) frogs under go metamorphosis --gt
  two lives amphibian

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Whats happening to our frogs?

• Globally frogs are disappearing at alarming rates
  and those that survive are often deformed or
  infertile.
• It's not clear just what the cause of this
• Depletion of ozone layer has increased UV
  radiation reaching these frogs who have little or
  no protection against UV damage to their skin or
  their eggs.
• Pesticides
• Parasites

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Amniotes

• Reptiles, birds, and mammals
• An extra-embryonic membrane, the amnion,
  encloses the developing embryo
• Some amniotes have an additional outer shell
• The amnion freed us from the necessity of
  returning to water to reproduce, and allowed the
  amniotes to conquer the land.

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The number of taxonomic categories of amniotes is
under debate
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Reptiles (Old-fashioned)

• Dinosaurs, snakes lizards, turtles, crocodiles
• Many terrestrial adaptations
• Shelled Egg
• Lungs
• Scales
• Limb placement
• Use environment to regulate temperature
  exothermic

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Reptiles
Testudines
Squamata
Squamata
Crocodilia
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Birds Class(?) Aves

• Flight!
• Feathers are modified scales
• Probably evolved from small,bipedal dinosaurs
• Closest living relative today crocodiles
• Use internal metabolism to regulate body temp
  Endothermic

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The fossil record provides evidence of the
connection between dinosaurs and birds
Sinoauopteryx and Caudipteryx feathered,
flightless dinosaurs
Archaeopteryx, feathered, poor flyer
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Class Mammalia Mammals

• Mammary Glands
• Hair
• 4-chambered heart
• Three major groups
• Monotremes
• Marsupials
• Eutherians (placentals)

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Class MammaliaOrder Monotremata

• Egg-laying mammals
• Platypus echidnas
• Milk, but no nipples

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Class MammaliaOrder Marsupialia

• Early birth
• Young develops in external pouch of mother
• Only 3 families of marsupials outside Australia

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Class MammaliaEutherian mammals

• Placenta lining of mothers uterus and
  extraembryonic membranes of embryo
• Several orders
• Order Proboscidea
• Order Rodentia
• Order Primates
• Order Carnivora
• Order Insectivora

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Figure 34.32 Evolutionary convergence of
marsupial and eutherian (placental) mammals
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Class MammaliaOrder Primates

• Prosimians- lemurs, tarsiers
• Anthropoids-monkeys, apes, humans
• Hominoids- great apes (gorillas, chimps) and
  humans
• Hominids- humans and human ancestors

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The Arboreal Theory of Primate evolution

• Early primates were insectivores (predatory)
• Selection for binocular vision - 60 MBP
• Manual dexterity (opposable thumb), large
  forehead and cerebral cortex, short snout - 50
  MBP
• Color vision (cone cells in retina) in diurnal
  primates helped with depth of field perception

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Brachiating Apes

• Swinging in trees
• Straightened spine
• Legs parallel to spine
• Preadaptation to erect posture?
• Apes are knuckle-walkers
• Bipedalism is unique to humans and our human-like
  ancestors

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A comparison of ape and hominid skeletons
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Side effects of bipedalism

• Necessitated curvature of the spine
  restructured pelvis
• New pelvis had smaller opening (birth problems)
• Necessitated life history changes
• -birth earlier in development
• -Extensive parental care
• Other problems
• Shorter jaw wisdom teeth (no room)
• Back problems (curvature, pressure on lower
  spine)
• Hemmorhoids (pressure of intestinal system on
  lower parts, cuts off blood flow)