Chapter 31: Animals: Part II

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Chapter 31 Animals Part II
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Echinoderms

• Echinoderms and chordates are deuterostomes.
• In deuterostomes, the second embryonic opening
  becomes the mouth and a coelom forms by
  outpocketing of the primitive gut making these
  animals enterocoelomates.
• A dipleurula larva is found among some.

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Characteristics of Echinoderms

• Echinoderms are a diverse group of marine
  animals there are no terrestrial echinoderms.
• They have an endoskeleton consisting of
  spine-bearing, calcium-rich plates.
• Echinoderms are often radially symmetrical,
  although the larva is a free-swimming filter
  feeder with bilateral symmetry.

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• Echinoderm Diversity
• Echinoderms include
• Sea lilies (class Crinoidea)
• Sea cucumbers (class Holothuroidea)
• Brittle stars (class Ophiuroidea)
• Sea urchins and sand dollars (class Echinoidea)
• Sea stars (class Asteroidea)

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Echinoderm diversity
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• Sea Stars
• Sea stars are an example of echinoderms and
  possess tiny skin gills, a central nerve ring
  with branches, and a water vascular system for
  locomotion.
• Water enters this system through the sieve plate,
  passes into a ring canal, then into ampullae, and
  into tube feet expansion and contraction of tube
  feet move the sea star along.
• Each of the five arms contains branches from the
  nervous, digestive, and reproductive systems.

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• When a sea star eats a bivalve, it everts its
  cardiac stomach into the bivalve and secretes
  enzymes partially digested food is taken into
  the sea star.
• Echinoderms do not have a respiratory,
  circulatory, or excretory system.
• The water vascular system carries out these
  functions.
• Sea stars reproduce both sexually, and asexually
  by fragmentation.

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Sea star anatomy and behavior
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Chordates

• Chordates (tunicates, lancelets, and
  vertebrates) have
• a suuporting notochord,
• a dorsal hollow nerve cord,
• pharyngeal pouches, and a
• post-anal tail at one time during their
  development.

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Chordate characteristics
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Evolution of Chordates

• The lancelets and tunicates are invertebrate
  chordates.
• Vertebrates include the fishes, amphibians,
  reptiles, birds, and mammals.
• Cartilaginous fishes were the first to have jaws
  amphibians evolved legs and invaded land.
• Reptiles, birds, and mammals have means of
  reproduction suitable to land.

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Evolutionary tree of chordates
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Invertebrate Chordates

• Lancelets and tunicates are the invertebrate
  chordates.
• Lancelets are small animals found in shallow
  water along the coasts they filter feed on
  microscopic organisms.
• Tunicates (sea squirts) live on the ocean floor
  and filter water entering the animal through an
  incurrent siphon.
• Adult tunicates lack chordate characteristics
  except gill slits, but adult lancelets retain the
  four chordate characteristics.

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Habitat and anatomy of a lancelet, Brachiostoma
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Anatomy of a tunicate, Halocynthia
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Vertebrates

• At some time during their lives, all vertebrates
  have the four chordate characteristics.
• The notochord is replaced by the vertebral
  column this endoskeleton demonstrates
  segmentation.
• The internal organs are well developed and
  cephalization places complex sense organs at the
  head.

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• Vertebrates are distinguished in particular by
  these features
• Living endoskeleton
• Closed circulatory system
• Paired appendages
• Efficient respiration and excretion
• High degree of cephalization
• The evolution of jaws allowed some vertebrates to
  take up the predatory way of life.

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Milestones in vertebrate evolution
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Fishes

• Today there are three living classes of fishes
  jawless fishes, cartilaginous fishes, and bony
  fishes the last two groups have jaws.
• Jawless Fishes
• The first vertebrates were jawless fishes, today
  represented by hagfishes and lampreys with no
  scales or paired fins.
• Water moves in and out through gill openings.

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• Cartilaginous Fishes
• The cartilaginous fishes include the sharks, rays
  and skates which have skeletons made of
  cartilage.
• Skates and rays are flat fishes that live partly
  buried in the sand and feed on mussels and clams.
  
• Sharks and rays have a sense of electric currents
  in water, a lateral line system, and a keen sense
  of smell these attributes help detect prey.

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• Bony Fishes
• Bony fishes have jaws and two pairs of fins and
  are the most diverse and numerous of all
  vertebrates.
• Bony fishes include those that are ray-finned
  (most abundant) and a few that are lobe-finned
  some of the lobed-finned fishes have lungs and
  likely gave rise to amphibians.
• A swim bladder may provide buoyancy in ray-finned
  fishes.

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• Most fishes today are ray-finned and have these
  characteristics
• Bony skeleton and scales
• Swim bladder
• Two-chambered heart (one atrium, one ventricle)
• Paired fins
• Jaws
• Gills

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Jawed fishes
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Amphibians

• Amphibians evolved from the lobe-finned fishes
  and are tetrapods with two pairs of limbs.
• They are represented today by frogs, newts,
  toads, and salamanders.
• Amphibians usually return to the water to
  reproduce and require moist habitats.
• Frog tadpoles metamorphose into terrestrial
  adults with lungs.

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• These features distinguish amphibians
• Usually tetrapods
• Mostly metamorphosis
• Three-chambered heart (2 atria, one ventricle)
• Usually lungs in adults
• Smooth, moist skin

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Frog metamorphosis
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Reptiles

• Reptiles include the extinct dinosaurs and
  todays snakes, lizards, turtles, alligators, and
  crocodiles.
• Reptiles have well-developed lungs within a rib
  cage they are covered with scales that protect
  them from desiccation and predators.
• Reptiles have internal fertilization and also lay
  a shelled egg, which contains extraembryonic
  membranes, including an amnion that allows the
  embryo to develop on land.

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• Features that distinguish reptiles include
• Usually tetrapods
• Lungs with expandable rib cages
• Shelled, leathery egg
• Dry, scaly skin
• Fishes, amphibians, and reptiles are ectothermic.
• Reptiles try to regulate their body temperature
  by moving to a warmer or cooler location as
  needed.

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The tongue as a sense organ
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The reptilian egg allows reproduction on land
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Birds

• Birds are characterized by the presence of
  feathers, which are modified reptilian scales.
• Birds lay hard-shelled eggs rather than the
  leathery eggs of reptiles.
• Birds are likely closely related to bipedal
  dinosaurs, although this is still under study.

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Bird anatomy
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• Anatomy and Physiology of Birds
• Features of birds are related to the ability to
  fly.
• Bird forelimbs are modified as wings.
• Bones are hollow and laced with air cavities the
  sternum has a keel to which flight muscles
  attach.
• A horny beak replaces teeth.
• Respiration is efficient due to air sacs.
• Birds have a four-chambered heart, and birds are
  homeothermic.

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Bird circulatory system
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• Classification of Birds
• The classification of birds is based on beak and
  foot types and to some extent on habitat and
  behavior.
• These features distinguish birds
• Feathers
• Hard-shelled egg
• Four-chambered heart
• Usually wings for flying
• Air sacs
• Homeothermic

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Bird beaks
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Mammals

• Mammals evolved from reptiles and flourished
  after the demise of dinosaurs.
• Mammals have hair that helps them maintain a
  constant body temperature.
• Like birds, mammals have a four-chambered heart.
• Internal development in the uterus shelters the
  young.
• Mammary glands allow mammals to nourish their
  young.

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• Monotremes
• Monotremes have a cloaca that is a common area
  for feces, excretory wastes, and sex cells.
• Monotremes lay hard-shelled amniote eggs.
• Monotremes are represented by the duckbill
  platypus and the spiny anteater.

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• Marsupials
• Marsupials have a pouch in which the very
  immature newborn matures.
• Inside the pouch, the newborns attach to nipples
  of mammary glands.
• Marsupials are represented by the American
  opossum, and various Australian animals such as
  koalas and kangaroos.

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Monotremes and marsupials
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• Placental Mammals
• Most mammals are placental mammals, which retain
  the offspring inside a uterus until birth
  extraembryonic membranes are present, including
  the chorion that contributes to the fetal portion
  of the placenta.
• The classification of these mammals is based on
  methods of obtaining food, and mode of locomotion.

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• Mammals are adapted to life on land and can move
  rapidly.
• The brain is enlarged due to the expansion of the
  cerebral hemispheres.
• Internal body temperature is constant.
• Mammals have differentiated teeth the specific
  size and shape of the teeth may be associated
  with whether the animal is a herbivore, a
  carnivore, or an omnivore.

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• These features distinguish placental mammals
• Body hair
• Differentiated teeth
• Infant dependency
• Constant internal temperature
• Mammary glands
• Well-developed brain
• Internal development

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Placental mammals
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Primates

• Primates are mammals adapted to living in trees
  many have an opposable thumb.
• The snout is shortened, enabling stereoscopic
  vision, and cone cells give greater visual
  acuity.
• During the evolution of primates, various groups
  diverged in a particular sequence.
• Prosimians include lemurs, tarsiers, and lorises
  anthropoids include monkeys, apes, and humans.

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• These traits distinguish primates from other
  mammals
• Opposable thumb (and sometimes great toe)
• Well-developed brain
• Nails (not claws)
• Single birth
• Extended period of parental care
• Emphasis on learned behavior

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Human Evolution

• The primate evolutionary tree shows that all
  primates share one common ancestor and that the
  other lines of descent diverged from the human
  lineage over time.
• Humans and apes shared a common ancestor.
• Molecular data indicate we are most closely
  related to the African apes, whose ancestry split
  from ours about 6 MYA.

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Primate evolutionary tree
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Evolution of Hominids

• To be a hominid, a fossil must have an anatomy
  enabling it to stand erect and walk on two feet
  (bipedalism).
• Ardipithecus ramidus kadabba is a 5.6 to 5.2
  million-years-ago (MYA) hominid found in
  Ethiopia Ardipithecus ramidus ramidus is a 4.4
  MYA hominid and less apelike than the older
  fossil.

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• Australopithecines
• Human evolution continued in eastern Africa
  around 4 MYA with the evolution of the
  australopithecines, a group that is a direct
  ancestor to humans.
• Raymond Dart discovered Australopithecus
  africanus in southern Africa in the 1920s this
  fossil was the gracile type dated at 2.8 MYA.
• A more robust form, (A. robustus), from 2 to 1.5
  MYA, had a brain size of 500cc like A. africanus
  these hominids may have been bipedal but still
  had longer forelimbs.

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• The most famous australopithecine is Lucy or A.
  afarensis (3.18 MYA) unearthed in eastern Africa,
  whose brain was small (400 cc) but who walked
  bipedally.
• Since the australopithecines were apelike above
  the waist but humanlike below the waist, it seems
  that human characteristics did not all evolve at
  once.
• This type of evolution of various body parts at
  different rates is referred to as mosaic
  evolution.

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Australopithecus afarensis
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• Australopithecus afarensis, a gracile type, is
  believed to be ancestral to the robust types
  found in eastern Africas A. aethiopicus and A.
  boisei.
• boisei had a powerful upper body and the largest
  molars of any hominid.
• These robust types died out, and therefore, it is
  possible that A. afarensis is ancestral to both
  A. africanus and Homo.

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Evolution of Early Homo

• Fossils are assigned to Homo if the brain size is
  600 cc or greater, if the jaw and teeth resemble
  those of humans, and if tool use is evident.
• Homo habilis
• Homo habilis, (handy man) present at about 2 MYA,
  is certain to have made crude flake-like stone
  tools.
• Speech areas of the brain enlarged and
  contributed to the beginning of society and
  culture.

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Human evolution
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• Homo erectus
• Between 1.9 and 0.3 MYA Homo erectus, with a
  brain capacity of 1,000 cc, a striding gate, and
  a flatter face, was the first to migrate out of
  Africa into Asia and Europe about 1 MYA.
• Males were about 6 feet tall and females
  approaching 5 feet, much taller than earlier
  hominids.
• H. erectus was the first hominid to use fire and
  tools of this time were advanced axes and
  cleavers.

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Homo erectus
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Evolution of Modern Humans

• Two contradicting hypotheses have been suggested
  about the origin of modern humans, Homo sapiens,
  from H. erectus.
• The multiregional continuity hypothesis suggests
  that modern humans originated from H. erectus
  separately in Asia, Europe, and Africa.
• The out-of-Africa hypothesis states that modern
  humans originated in Africa and, after migrating
  into Europe and Asia, replaced the archaic Homo
  species found there.

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Multiregional continuity hypothesis
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Out-of-Africa hypothesis
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• Neanderthals
• The Neanderthals lacked a high forehead and a
  significant chin and are classified as Homo
  neanderthalensis.
• They had massive brow ridges their pubic bone
  was long compared to that of modern humans.
• Neanderthals had a brain larger than that of
  modern humans, and they lived in Europe and Asia
  during the last Ice Age.
• Neanderthals lived in caves, made stone tools,
  and buried their dead with flowers.

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Neanderthals
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• Cro-Magnons
• Cro-Magnons evolved about 100,000 years ago and
  were the first humans (Homo sapiens) to have a
  thoroughly modern appearance.
• They made stone tools, including stones attached
  to wooden handles they threw spears, enabling
  them to cooperatively hunt larger animals.
• The Cro-Magnon culture included art and beautiful
  paintings on cave walls.

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Cro-Magnons
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Chapter Summary

• Both echinoderms and chordates are deuterostomes.
• In deuterostomes, the second embryonic opening
  becomes the mouth the coelom develops by an
  outpocketing from the primitive gut.
• Echinoderms develop radial symmetry and have a
  unique water vascular system for locomotion.

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• Chordates have a notochord, a dorsal tubular
  nerve cord, and a post-anal tail pharyngeal
  pouches occur sometime during the life of
  chordates, and in vertebrates, the notochord is
  replaced by the vertebral column.
• There are three groups of fishes.
• One group is jawless, but the cartilaginous and
  bony fishes (ray-finned and lobe-finned) have
  jaws.

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• Frogs and salamanders are amphibians that evolved
  from lobe-finned fishes they have limbs as an
  adaptation for locomotion on land.
• The shelled egg of reptiles contains
  extraembryonic membranes as an adaptation for
  reproduction on land.
• Both birds with feathers, and mammals with hair
  and mammary glands, evolved from reptiles and are
  able to maintain a constant body temperature.

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• Primates such as prosimians, monkeys, apes, and
  humans are mammals adapted to living in trees.
• Human evolution diverged from ape evolution in
  Africa about six to seven million years ago.
• The australopithecines were the first hominids
  and were ancestors to humans.

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• Homo habilis could make tools Homo erectus
  migrated out of Africa.
• The Neanderthals (H. neanderthalensis) gave
  evidence of being culturally advanced, lived in
  caves, and hunted large mammals they buried
  their dead with flowers.
• Cro-Magnons are the oldest fossils to be
  designated Homo sapiens they made sophisticated
  tools and were accomplished artists and hunters.