Vertebrate Evolution and Diversity

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Vertebrate Evolution and Diversity
Phylum Chordata Subphylum
Urochordates Subphylum Cephalochordates
Subphylum Vertebrates
Lancet
Tunicate
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Four Anatomical Features Characterize Phylum
Chordata

• Chordates are deuterstomes with 4 unique
  characteristics which appear at some time during
  the animals life.
• 1. Notochord
• 2. Dorsal, hollow nerve cord
• 3. Pharyngeal slits
• 4. Muscular postanal tail

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Notochord
A longitudinal, flexible rod, located between the
gut and nerve cord Persists in some invertebrate
chordates and early vertebrates. In most adult
vertebrates is retained as discs between
vertebrae.
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Dorsal, Hollow Nerve Cord

• Develops in the embryo from a plate of dorsal
  ectoderm that rolls into a tube located dorsal
  to the notochord.
• Unique to chordates (other animal phyla solid)
• The brain and spinal cord (CNS) develop from this
  nerve cord.

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Pharyngeal Slits

• Chordates have a complete digestive system. The
  pharynx is the region posterior to the mouth and
  opens to the outside through several pairs of
  slits.
• permits water to enter without passing through
  entire
• digestive system
• suspension feeding (gills)
• modified for gas exchange (and other functions)
  during the
• evolution of vertebrates

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Muscular Postanal Tail

• A tail extending beyond the anus is found in
  most
• chordates and contains skeletal elements and
  muscle.
• Provides propulsive force in many aquatic
  species

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Chordate Characteristics
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Subphylum Urochordata

• Tunicates
• Entire animal is cloaked in a tunic of
  cellulose-like
• carbohydrate
• Most are sessile marine animals adhere to
  docks etc
• Some planktonic, others colonial
• Filter feeders
• Larval tunicates are free swimmers and possess
  all
• four chordate characteristics
• Adults bear little resemblance to other
  chordates
• lacking notochord, nerve cord and tail

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Subphylum Urochordata
Adult tunicate
Larval tunicate
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Adult Tunicates or Sea Squirts
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Subphylum Cephalochordata

• Animals known as lancets due to their bladelike
  shape
• All four chordate characteristics are prominent
  and
• persistent in the adult.
• They are marine filter feeders
• Feeble swimmers with fishlike motions
• Show muscle segmentation - somites

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Subphylum Cephalochordata
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Introduction to the Vertebrates

• First appeared in the fossil records of the
• Cambrian rocks
• Most zoologists feel the vertebrate ancestors
• possessed all four chordate characteristics and
  were
• suspension feeders.
• May have resembled lancets
• Molecular systematics suggests that
  cephalochordates
• are the closest relatives of vertebrates
• Paedogenesis precocious attainment of sexual
• maturity in a larva
• Cephalochordates resemble urochordate larva

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Chordate Segmentation - Somites
Segmental muscles develop from segmental blocks
of mesoderm called somites.
Segmented units of the mesoderm in an 18-hr old
zebrafish embryo.
Segmentation evident in abdominal muscles.
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Subphylum Vertebrata

• Vertebrates have retained the four
  characteristics while
• adding other specializations.
• Neural Crest cells found within the embryonic
  folds that meet to form the dorsal, hollow nerve
  cord.
• Cephalization high degree of cephalization with
  sensory structures and an enlarged brain.
• Cranium and Vertebral Column protects the brain
  and provides support and movement.
• Closed Circulatory System increased levels of
  activity require a high rate of respiration
  supported by adaptations in respiratory and
  circulatory systems

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The Neural Crest
Cells from the neural crest migrate.
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Overview of Vertebrate Diversity
Subphylum Vertebrata
Superclass Agnatha
Superclass Gnathostomata
Class Chondrichthyes Class Osteichthyes Class
Amphibia Class Reptilia Class Aves Class Mammalia
1. Fish
Jawless Fish
Lampreys Hagfish
2. Tetrapods
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One Hyphothesis for the Evolutionary
Relationships among the Chordates
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Class Agnatha Jawless Fish

• Generally small
• Lacked paired fins
• Filter-feeders
• Lampreys and hagfish are the only extant
  agnathans
• Adult lampreys are blood-sucking parasites
• Marine hagfish are scavengers

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Class Agnatha - Sea Lamprey
Jawless fish Blood sucking parasites
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Class Agnatha - Hagfish
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Evolution of the Vertebrate Jaw
Jaws evolved from the skeletal rods of the
anterior pharyngeal slits. The remaining gill
slits maintained their function in gas exchange.
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Superclass Gnathostomata 1 The Fishes
Class Chondrichthyes Cartilagenous Fish Class
Osteichthyes Bony Fish
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Class Chondrichthyes Cartilaginous Fish

• Well developed jaws
• Paired fins
• Endoskeletons made of cartilage strengthened
  with
• calcium
• The lateral line is a row of microscopic organs
• sensitive to water pressure change

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• Oviparous species lay eggs that hatch outside
  the
• mother
• Oviviparous species retain the fertilized eggs
  until
• they hatch within the uterus
• Viviparous species young are nourished by a
  placenta until born

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Class Chondrichthyes - Cartilaginous Fish
Shark
Ray
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Class Osteichthyes Bony Fish

• Abundant in oceans and fresh water
• Endoskeleton reinforced with a hard matrix of
  CaPO4
• Skin covered with flattened bony scales and
  mucus.
• Water is forced across the gills using muscles
  bony fish can breathe when not swimming.
• Swim bladder controls bouyancy, modified from
  primitive lungs
• Oviparous with external fertilization
• Ray-finned fish familar modern fish
• Lobe-finned fish - coelocanths, muscular fins may
  have enabeled fish to walk
• Lung fish retained lungs

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Class Osteichthyes the Bony Fish
Yellow Perch
Yellow Trumpetfish
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Lobe-Finned Fish
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Anatomy of a Trout
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The Devonian Radiation
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Superclass Gnathostomata IIThe Tetrapods
Class Amphibia Class Reptilia Class Aves Class
Mammalia
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The Origin of the Tetrapod
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Class Amphibia

• Oldest class of tetrapods
• 4000 extant species of frogs, salamanders and
  caecilians
• Thought to have evolved from lobe-finned fishes
• Molecular data suggests closer relationship to
  lungfishes
• Early amphibians aquatic, coming to land to feed
• Order Urodela (salamanders)
• Order Anura (frogs and toads)
• Order Apoda (caecilians)

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Urodeles
Salamanders retain their tails as adults, some
are entirely aquatic, others live on land.

• 400 species, aquatic and terrestrial
• Walk side to side or swim sinusoidally

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Anurans
Poison Arrow Frog
Buggy-Eyed Tree Frog

• 3500 species, adapted to land
• Metamorphosis, air breathing lungs

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Apodans

• Legless, blind,
• burrowing

The caecilians include about 165 limbless
amphibians that inhabit tropical forests of South
America, Africa and Southeast Asia.  Because they
are entirely aquatic or burrowing organisms, they
are seldom seen by humans.  Their food consists
mostly of earthworms and other small
invertebrates. Fertilization in caecilians is
internal, and the male is equipped with a
protrusible copulatory organ.  Viviparity (live
birth) is also seen in some caecilians, with the
embryos obtaining nourishment by eating the wall
of the oviduct of the mother!
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Frog Metamorphosis
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Frog Metamorphosis
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Evolution of the Amniotic Egg

• Specialized adaptations for living on land -
  reptiles could
• evolve from their amphibian ancestors.
• Amniotic egg broke the last ties with the aquatic
• environment
• The shell helps prevent desiccation
• Extraembryonic membranes within the egg develop
  from
• tissue layers that grow out from the embryo
• Specialized membranes function in
• gas exchange - chorion
• transfer of stored nutrients to the embryo
  yolk/vessels
• waste storage (and gas exchange)- allantois
• cushioning/protection - amnion

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The Amniotic Egg
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Phylogeny of the Amonites
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Class Reptilia

• Diverse group, 7000 extant species
• Grouping based on apparent similarities
• Cladistic analysis not including birds in the
  class is
• inconsistant with phylogeny
• Birds appear to be more closely related to
  crocodiles
• than are turtles
• Class Reptilia can only be defined by the absence
  of
• features that distinguish birds (feathers) and
• mammals (hair and mammary glands)

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Reptilian Characteristics

• Adaptations for terrestrial living not found in
  amphibians
• Scales contain keratin to prevent dehydration
• Gas exchange occurs in lungs
• Sexual reproduction and internal fertilization
• Most are oviparous with amniotic egg
• Ectotherms with behavioral adaptations basking
  etc.

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Extant Reptiles - Turtles
Evolved during the Mesozoic and have changed
little in appearance
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Lizards
Relatively small, most numerous and diverse
extant reptiles.
Australian Frillneck Lizard
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Snakes
Descended from lizards that adopted a burrowing
lifestyle. They are limbless carnivores with
adaptations for locating, killing and swallowing
their prey.
Bull Snake
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Crocodiles and Alligators

• Among the largest living reptiles
• Spend most of their time in water.
• Crocodiles are most closely related to dinosaurs.

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Class Aves

• Birds began as flying reptiles
• The amniotic egg and scales on the legs are two
  reptilian
• traits that birds display.
• Bird anatomy has evolved to enhance flight
• Weight is reduced by honeycombed bones, air sacs
  off
• the lungs and lack of teeth.
• Endothermic, feathers and fat help retain
  metabolic
• heat
• Four chambered heart and efficient respiratory
  system
• Excellent eyesight
• Aerodynamic wings

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Form Fits Function
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Origin of Birds

• Cladistic analysis indicates that birds arose
  from
• therapod dinosaurs
• Fossils of Archaeopteryx, an ancient feathered
• creature with clawed forelimbs, teeth and a long
  tail
• have been found from 150 million years ago

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Bald Eagle in Flight
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Archeaopteryx
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Flightless Birds The Emu
Flightless birds include the ostrich, kiwi and
the emu.
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Ducks
Harlequin Duck
Loon
Many duck species exhibit pronounced color
differences between the sexes.
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Albatrosses
Many species have specific courtship and mating
behavior.
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Barn Swallow
This swallow belongs to a group of birds called
perching birds because the toes of their feet
can lock around a tree branch, enabling the bird
to rest in place for ling periods of time.
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Evolution of the Mammalian Jaw and Ear Bones
Jaw Reptilian lower jaw is composed of several
fused bones. Two small jawbones form part of the
jaw joint. The mammalian jaw is reduced to a
single bone and the location of the jaw joint has
shifted. Ear Two reptilian jaw bones become
incorporated into the middle ear of
mammals. These bones enhance hearing by
amplifying sound
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The Evolution of the MammalianJaw and Ear Bones
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Class Mammalia

• Hair made of keratin
• Endotherms with an active metabolism
• Sheet of muscle, the diaphragm, ventilates the
  lungs
• Mammary glands produce milk
• Internal fertilization
• Show differentiation of teeth
• Three major groups
• Monotremes egg-laying mammals
• Marsupials complete embryonic development in
  maternal pouch
• Eutherians placental mammals

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Monotremes
The platypus and echnidas are the only extant
monotremes. The egg is reptilian but they have
hair and produce milk for their young.
Echnida
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Marsupials
Bandicoot
Opossums, kangaroos, bandicoots and koaoas
complete their embryonic development in a pouch
called a marsupium.
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Marsupial and Eutherian Mammals
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Major Orders of Eutherian Mammals
Four main evolutionary lines Order Chiroptera
(bats) Order Insectivora (shrews) Order
Lagomorpha (rabbits) Order Perissodactyla (horses
and rhinos) Order Artiodactyla (deer and
swine) Order Carnivora (cats, dogs, raccoons,
skunks and pinnipeds) Order Rodentia (rats,
squirrels and beavers Order Primates (monkeys,
apes and humans)
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Primates

• Two suborders of modern Primates
• Prosimians lemurs, lorises and tarsiers.
  Probably resemble early arboreal primates.
• Anthropoids monkeys, apes and humans.

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A Crowned Lemur A Prosimian
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A Phylogenic Tree of the Primates
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Old World Monkeys
Pig-tailed Macaques
Lack prehensile tails and nostrils open downward.
A tough seat pad is unique to the Old World
group which includes macaques, mandrills, baboons
and rhesus monkeys.
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New World Monkeys
Squirrel Monkey
New World monkeys such as spider monkeys,
squirrel monkeys and capuchins have prehensile
tails and their nostrils open to the sides
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Apes - Gibbons
Gibbons have long arms and are among the most
acrobatic of all primates. Also the only
monogamous apes
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Orangutans
The orangutan is a shy and solitary ape that
lives in the rain forests of Sumatra and Borneo.
They spend most of their time in trees.
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Gorillas
The gorilla is the largest ape with some males
almost 2m tall and weighing about 200kg. These
herbivores are confined to Africa, where they
usually live in small groups of 10 to 20
individuals.
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Chimpanzees
The Chimpanzee lives in tropical Africa. They
feed and sleep in trees but also spend a lot of
time on the ground. Chimpanzees are intelligent,
communicative and social. Molecular evidence
suggests they are more closely related to humans
than to other apes.
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Hominid Timeline
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Upright Posture
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Two Models for the Origin of Humans