Download The Vertebrates The Vertebrates Chordates Notochord Hollow

The Vertebrates
The Vertebrates
Chapter 34
Chordates
• Chordates (phylum
Chordata) are animals that
include the vertebrates and
several closely related
invertebrates
• They are united by having
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a notochord
a hollow dorsal nerve cord
pharyngeal slits or pouches
A post-anal tail
Hollow dorsal nerve cord
• Develops from a plate from ectoderm
– Rolls into a tube, dorsal to notochord
• Unique to chordates, other animal phyla have
solid nerve chords, mostly ventral
• Develops into CNS
– Brain and spinal cord
Notochord
• Skeletal structure present in all
chordate embryos
Ascidian (Tunicate) notochord
– composed of cells derived from the
mesoderm, defines the primitive axis of
the embryo
– in lower organisms, it persists throughout
life as the main axial support of the body,
while in higher vertebrates it is replaced
by the vertebral column
Pharyngeal slits or pouches
• In all chordate embryos, series of pouches separated
by grooves forms along sides of pharynx
• Function as suspension-feeding devices in many
invertebrate chordates
• In aquatic vertebrates, these structures
turn into gills
• In tetrapods, pharyngeal pouches
develop into parts of the ear and other
structures in head and throat
Muscular, Post-Anal Tail
• Tail extends posterior to anus
• In many species, lost during embryonic
development
• Contains skeletal elements and muscles
– Provides propelling force in aquatic species
The Vertebrates
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Chordates with a backbone or spinal columns
Originated ~530 mya (Cambrian explosion)
52,000 species
Vertebrata comprises the largest subphylum of
chordates, and contains many familiar groups
of large land animals
– comprise fish (including lampreys), amphibians,
reptiles, birds, and mammals (including humans)
4 wk human embryo
10-12 wk embryo
Lampreys – oldest living lineage of
vertebrates
Origin of Craniates
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Least derived craniate lineage is the Myxini – the Hagfish
Skull made of cartilage
Lack jaws and vertebrae
Have small brain, eyes, ears
Retain notochord as adults
• Marine and freshwater
environments
• Most are parasites
– Clamp round, jawless
mouth onto plank of fish
– Swim in snake-like fashion by pushing against it with their
muscles
• Use slime to protect themselves
– Slime studied for biotech uses
• Skeleton made of cartilage
– also have cartilaginous
pipe around notochord
• Their relationships to other major living vertebrate groups
— the similarly jawless lampreys, and the jawed
vertebrates — remain contentious
Next step: jaws and teeth
• Jawed vertebrates are called
Gnathostomes (“jaw mouth”)
• Include sharks, rays, chimaeras, rayfinned fishes, lobe-finned fishes and land
vertebrates
• Jaw probably a result of transitions in
feeding mechanisms
– Data suggests mineralization of lower
vertebrates began in the mouth
– In more advanced vertebrates, the exoskeleton
began to mineralize too
Gnathostomes are characterized by:
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An additional duplication in Hox genes
Forebrain enlarged
Enhanced sense of smell and vision
Aquatic gnathostomes have lateral line
systems
Class Chondrichthyes
– Sharks, rays
– “cartilage fish”
– Skeleton composed of
cartilage
– Have some traces of bone
Class Chondrichthyes
– 2 subclasses
– Sharks, rays
– Ratfish
• In scales, base of teeth,
surface of vertebrae
– Among largest and most
successful predators in
ocean
– Sharks have acute senses
Class Chondrichthyes
– Sharks have streamline
bodies
– Fast swimmers
• Poor manueverability
– Gains buoyancy by storing
oil in its liver
• Still denser than water
• Must consistently swim to
stay afloat
Sharks
– Largest members are
suspension feeders
• Consume plankton
– Many sharks are carnivores
• Swallow prey whole
• Tear it apart
– Several rows of sharp teeth
• Constantly being replaced
Rays
Osteichthyes
– Flattened bottom dwellers
• Use jaws to crush mollusks and
crustaceans
– Several defense mechanisms
• Whip-like tail with venomous barbs
• Generation of electric current
– Bony fish clade
– Ray finned
• Class Actinopterygii – ray
finned fishes
– Lobe finned
• Class Actinistia –
coelocanths
• Class Dipnoi - lungfish
Osteichthyes
– Bony endoskeleton
• Calcium phosphate matrix
– Breathe with gills
• Have 5 pairs covered by operculum
Ray finned fishes
– Class Actinopterygii
• Common fish
• Sea horses
• eels
– Protective bony flap
– Many control buoyancy with swim
bladder
• Internal air sac
• Air pressure controlled by blood gas
transfer
Ray finned fishes
– Fins supported by bony, flexible rays
• Modified for different adaptations
– Maneuvering
– Defense
Lobe finned fishes
– Rod shaped bones surrounded by thick layer of muscle in
pelvic and pectoral fins
– Class Actinistia
• coelacanths
– Class Dipnoi
• lungfish
Class Actinistia
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Coelacanths
Primitive bony fish
Once thought to be extinct
“rediscovered” in 1938
Found in Indian Ocean
Class Dipnoi
– Lungfish
– 3 genera
– All found in southern
hemisphere
– Lungs supplement O2 from
gills
– Evolved to be able to breath in
waters with low O2
Derived Characters of Tetrapods
Tetrapods
– Limbs supporting weight on land
– Feet with digits
– Bones of pelvic girdle fused to backbone
– Clade with 4 limbs
• Arms and legs
– Evolved from lobe finned fins
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• Permits walking
Amphibians
Reptiles
Birds
Mammals
Meet Tiktaalik
Derived Characters of Tetrapods
Reproduction
– Pharyngeal gill slits disappear during development
• Three major evolutionary innovations gave
tetrapods the ability to reproduce successfully
in terrestrial environments:
• Slits give rise to parts of ears, glands
• Ears adapted to detect airborne sounds
– eardrum
– Amniotic egg
– Placenta
– Elaboration of parental care
Amniote Egg Membranes
• Amnion – fluid filled layer acts
as shock absorber
• Surrounds embryo
• Allantois – disposal sac for
metabolic wastes
• Chorion – gas exchange
• O2 and CO2 diffuse freely
through shell
• Yolk sac – nourishes embryo
• Albumen also nourishes embryo
Amniotes
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Fertilization must occur internally
Before shell is secreted
Many snakes and lizards viviparous
Eggs of most reptiles, birds, some mammals have shells
• Bird egg shell – hard, CaCO3, inflexible
• Reptile eggs – usually leathery and flexible
• Mammal eggs – leathery
– Most mammalian eggs non shelled
– Develop within mother
Placenta
• Most mammal females produce eggs that
lack yolk
• After fertilization, egg is retained, and
mother produces a placenta within the uterus
• Placenta is a specialized organ rich in blood
vessels
Parental care
• Increases chances of offspring
survival
• Most extensive versions observed
in mammals and birds
– Mother and father feed and care for
young
– In mammals, mothers also lactate
– Allows for gas exchange
– Allows mother to provide nourishment
– After a period called gestation, embryo emerges
Amphibians
– Salamanders, frogs, toads, Caecilians
– Feeding: carnivorous
• Sit and wait predators
• Many have extendible tongues
Survey of Tetrapods
Amphibians
• Movement: have well-developed limbs (4)
– Ceacilians lack legs
• Ectothermic
– Do not use internally generated heat to regulate
body temperature
– Reproduction
• Mostly oviparous
• Frogs have external fertilization
• Salamanders and caecilians have
internal fertilization
• Many caecilians are viviparous
Reptilia
• Feeding:
– Most are carnivorous
– Some fierce predators (snakes, crocodiles)
– Turtles, some lizards are herbivores
• Skin is waterproofed
– Scales
• Keratin built up in outermost layer
– prevent breathing through skin
• Rely on lungs for gas exchange
• Ectothermic
• Reproduction:
– Mostly oviparous
– Most reproduce sexually
– Some have extensive parental care (crocodiles)
The Origin and Evolutionary
Radiation of Reptiles
• The oldest reptilian fossils date to about 310
million years ago
• The first major group to emerge were
parareptiles, which were mostly large,
stocky herbivores
• As parareptiles were dwindling, the diapsids
were diversifying
• The diapsids consisted of two main lineages:
the lepidosaurs and the archosaurs
– The lepidosaurs include tuataras, lizards, and
snakes
– The archosaur lineage produced the
crocodilians, pterosaurs, and dinosaurs
The archosaur lineage produced the
crocodilians, pterosaurs, and
dinosaurs
The lepidosaurs include tuataras,
lizards, and snakes
Reptiles provide stem for vertebrate evolution
Reptilia - Birds
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Fossil record provides conclusive evidence that birds
descended from a lineage of dinosaurs with a unique trait:
feathers
Molecular data beginning to support this idea as well
– An adolescent female T. rex died 68 million years ago, but
its bones still contain intact soft tissue, including the oldest
preserved proteins ever found
– A comparison of the protein's chemical structure to a slew
of other species showed an evolutionary link between T. rex
and chickens
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Feathers – unique adaptation in birds
– Used for display and insulation
– Also furnish lift power, and steering required for flight
Archaeopteryx (Cretaceous)
• Reptile-like traits:
– Teeth
– Tail w/ many vertebrae
– Wing claws
Birds
• Warm-blooded
• Feeding:
– Most are omnivores
– Size and shape of beak
correlates sharply with diet
• Bird-like traits:
– Wings
– Feathers
• Reproduction:
– Oviparous
– Provide extensive parental
care
• Contour
• Down
Mammals
• Have fur or hair
– Insulates body
• Like birds, mammals are warm blooded
– Result of oxidation of large amounts of
food, generating heat
– Endothermy is an adaptation that allows for
high levels of activity
Mammals
• Evolved at a time when dinosaurs and other reptiles dominated
the planet
• Earliest mammalian fossil is 195my old
• Mammals diversified after the dinosaurs became extinct
– Diversified into small and large herbivores, predators, or marine hunters
• Earliest mammals were small, and probably mostly nocturnal
– Many modern species of mammal have good nocturnal vision and
strong sense of smell
• Have mammary glands
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Unique structure that makes lactation possible
Gives ability to provide extensive parental care
Mammals are also only animals with facial muscles and lips
Only vertebrates with lower jaw made from a single bone
Mammals form a monophyletic
group
Monotremata
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Most ancient lineage of mammals
Found only in Australia and New Zealand
Egg-laying mammals
Three species exist: 1 Platypus and 2 echidna
Have leathery beak or bill
Marsupiala
Eutheria – Placental Mammals
• Distributed worldwide
• Most species-rich and diverse group of mammals
• Divided into 18 lineages
• Live in Australian region and in
the Americas
• Females have placenta, but
young are born after a short
embryonic period, poorly
develop
• Complete their development
within attached to mother’s
nipple
– Six most species rich are: rodents, bats, insectivores (shrews, etc),
artiodactyls (pigs, hippos, whales, etc), carnivores (dogs, cats, bears,
etc), and primates
• Reproduction: internal fertilization, viviparous
– Extensive placenta
– At birth, young are well
developed
• Size and structure of teeth
correlate closely with diet
– Typically within a pouch, called a
marsupium
A Key Eutherian Lineage: the
Primates
Homo sapiens
• Two main groups
– Prosimians (lemurs, tarsiers, pottos and lorises)
– Anthropoids (New World Monkeys, Old World Monkeys,
gibbons, and Great Apes – or Hominids)
• Primates distinguished by having eyes on front of face
• Hands and feet efficient at grasping
– Anthropoids have opposable thumbs
• Large brains relative to body size
• Complex social behavior
• Extensive parental care
• Humans diverged from their closest relative (sister
species), chimps, 6-7my ago
• Since then, at least 14 human-like species (hominins)
have existed
• Several of these lived in Africa at the same time
• Most lineages went extinct without leaving
descendant populations
• Humans are the only surviving representative of the
initial “out of Africa” adaptive radiation
You! (modern day)
An evolving world
• Earth is ancient, has undergone extensive
changes
• All forms of life undergo changes
– species evolve at different rates
– >90% of all life forms to live on Earth are extinct
• Humans too, have evolved and continue to do
so!
Dinkenesh (Lucy) – 3.2 mya