Amniote origins and classification

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Amniote origins and classification

• The possession of a shelled egg unites the
  mammals, birds and reptiles into a monophyletic
  group the amniotes.
• The shelled egg freed the amniotes from the need
  to reproduce in water that hampered the
  amphibians ability to spread into harsh
  environments.

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The Amniotic egg

• The amniotic egg is hard shelled and is called an
  amniotic egg because the embryo develops within a
  sac called the amnion.
• The embryo feeds on yolk from a yolk sac and
  deposits its waste into another sac called the
  allantois.
• The allantois and another membrane the chorion
  together lie against the shell, and being richly
  supplied with blood vessels, exchange gases with
  the outside through the pores in the shell.

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The Amniotic egg

• Unlike amphibians amniotes lack a larval stage
  and after hatching develop directly into the
  adult form.
• The evolutionary origins of the amniotic egg are
  unclear because early amniote fossils are scarce
  and eggs especially so. The oldest known eggs
  are from the Early Permian and were probably laid
  by a Pelycosaur (early primitive synapsids e.g.,
  Dimetrodon. This lineage ultimately gave rise to
  the mammals).

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The Amniotic egg

• It has been suggested that the earliest amniotes
  were probably amphibious of semi-aquatic as were
  their immediate amphibian ancestors.
• They probably inhabited quite humid environments
  and eggs may have been laid out of water
  initially perhaps to reduce their risk of
  predation. Gradually eggs may evolved to have
  become less vulnerable to dessication.

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Amniote origins and classification

• There is considerable disagreement between
  cladistic and traditional classification of the
  amniotes.
• Traditional classification recognizes three
  classes
• Reptilia reptiles
• Aves birds
• Mammalia mammals

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Amniote origins and classification

• Because the class Reptilia does not include all
  the descendents of their most recent common
  ancestor (i.e., the birds) the reptiles are a
  paraphyletic group.
• Birds and crocodilians share a most recent common
  ancestor and thus form a monophyletic group (the
  Archosauria), which includes the extinct
  dinosaurs, but neither is more closely related
  than the other to the members of the Reptilia

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Amniote origins and classification

• Traditional classification considers birds
  because of their endothermy and feathers to be
  members of a different grade to the crocodilians
  and reptiles and so places them in their own
  class the Aves.
• Cladistic classification in contrast groups the
  amniotes on the basis of common ancestry.

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Amniote origins and classification

• One of the major characteristics used to classify
  the amniotes is the structure of the skull.
• The stem group of amniotes diverged into three
  lineages in the Carboniferous period
  (approximately 350 mya). These were the
  synapsids, anapsids and the diapsids.

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Anapsids, synapsids and diapsids

• These three groups are distinguished from each
  other by the number of openings in the temporal
  region of the skull.
• Anapsids (which include the turtles and their
  ancestors) have a solid skull with no openings.

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Anapsids, synapsids and diapsids

• Synapsids (which include the mammals and their
  ancestors) have one pair of openings in the skull
  associated with the attachment of jaw muscles.
• Diapsids (lizards, snakes, crocodilians, birds,
  and ancestors) have two pairs of openings in the
  skull roof.

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Anapsids

• The anapsids are characterized by having no
  temporal opening behind the eye sockets.
• They are represented today by the turtles a group
  that has changed little since it evolved about
  200 mya.

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20.1
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18.2
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Synapsids

• The synapsids diverged from the Sauropsida
  (anapsids and diapsids) and radiated into a
  diverse group of herbivores and carnivores
  collectively named the Pelycosaurs (although
  thats a paraphyletic group).

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Synapsids

• Pelycosaurs looked lizard-like and include
  Dimetrodon (a predatory dinosaur you may be
  familiar with), which possessed a large sail on
  its back a characteristic of many pelycosaurs,
  which probably played a role in thermoregulation.

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Edaphasaurus (left) an herbivorous pelycosaur
Dimetrodon (below and below left) a carnivorous
pelycosaur. About 11 feet long 280-260 mya)
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Synapsids

• The pelycosaurs were the dominant group of the
  Permian period, but disappeared in the Great
  Permian extinction (approx 245 mya).
• During the Permian a synapsid lineage the
  therapsids diverged from the Pelycosaurs. This
  lineage is the one that gave rise to the mammals
  during the Triassic period

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Fig 18.1
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Therapsid to mammal transition

• A series of evolutionary changes occurred in the
  therapsids that were passed on to their surviving
  descendants the mammals.
• These included
• an efficient upright stance with the limbs
  positioned under the body rather than sprawled to
  the side.
• Homeothermy there is fossil evidence that the
  therapsids evolved homeothermy. Cross sections
  of bones show Haversian canals, which are
  characteristic of fast-growing, warm blooded
  animals.

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Therapsid to mammal transition

• Additional evolutionary changes in the therapsids
  include
• Diaphragm there is indirect fossil evidence in
  the rib shape of therapsids that suggests they
  possessed a diaphragm another unique mammalian
  characteristic.
• Heterodont teeth Differentiation of teeth into
  multiple specialized types.
• Secondary bony palate separating nasal from oral
  cavities.
• Turbinate bones in nasal cavity increase
  retention of body heat.

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Therapsid to mammal transition

• Additional evolutionary changes in the therapsids
  include
• Three inner ear bones and a single jaw bone. An
  excellent series of fossils over about 40 million
  years documents the transition from the
  multi-boned jaw of pelycosaurs to the single
  dentary of mammals.
• During this transition therapsids evolved a
  double jointed jaw and eventually two bones from
  the original pelycosaur joint were incorporated
  into the inner ear.

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First mammals

• The earliest mammals first appear in the
  mid-Triassic (about 210 mya) and most were small
  mouse-sized animals.
• For about 150 million years they lived in a world
  dominated by the dinosaurs and underwent large
  scale diversification only late in the reign and
  rapid evolution of large body size only after the
  disappearance of the dinosaurs in the Great
  Cretaceous extinction 65 mya.

Morganucudon http//www3.interscience.wiley.com81
00/ legacy/college/levin/0470000201/chap_tutorial/
ch12/images/le12_60.jpg
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Diapsids

• The third lineage derived from the stem amniotes
  was the diapsids.
• The diapsids split into two major lineages the
  Lepidosauria (which includes the Tuatara, modern
  snakes and lizards) and the Archosauria (which
  includes the extinct dinosaur lineages,
  crocodilians and birds).

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Differences between reptiles and amphibians

• Reptilian skin is dry and scaly, which limits
  water loss.
• The reptiles amniotic egg frees reptiles from
  the need to lay eggs in water. Thus they can
  occupy much drier habitats.

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Differences between reptiles and amphibians
Reptilian jaws

• Reptilian jaws are more powerful and can apply a
  crushing grip.
• The openings in the skull provide additional
  surface area for muscle attachment allowing
  greater pressure to be exerted.
• In snakes, skull and jaw flexibility allows very
  large prey to be swallowed.

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Differences between reptiles and amphibians
Dentition

• With the exception of turtles which have a horny
  beak (sometime serrated) all reptiles possess
  teeth and many have them on both the palate and
  the jaws.

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Python teeth http//whiteafrican.com/wp-content/sn
ake2.jpg
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• Most reptiles have homodont dentition, but
  partial heterodonty occurs in snakes and a number
  of lizards.
• Monitor lizards have incisors, canine-like teeth
  and molars.

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Komodo Dragon http//www.tropicalisland.de/komodo/
images/BMU20Komodo20Island 20Komodo20dragon20
gargantuan20monitor20lizard20209203008x2000.j
pg
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Differences between reptiles and amphibians
Orientation of limbs

• In amphibians, such as salamanders, the
  orientation of the limbs is outward from the main
  axis of the body. As a result salamanders
  sprawl.
• In most reptiles, in contrast, the appendages are
  rotated towards the body and the long axis of the
  limbs lies more parallel to the bodys main axis.

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Differences between reptiles and amphibians
Orientation of limbs

• In addition, the angle between the upper and
  lower limbs is reduced so the limbs are overall
  straighter. In the forelimb the elbow is
  oriented towards the tail.
• In combination, these modifications provide
  better support for the weight of the body and
  raise it higher off the ground. Together these
  changes make greater agility and speed possible.

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Differences between reptiles and amphibians

• Reptiles have internal fertilization and so males
  have a copulatory organ either a penis or
  hemipenes.
• Reptiles also have a more efficient nervous
  system and a more efficient circulatory system.

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Differences between reptiles and amphibians
circulation

• Reptiles are the first truly terrestrial
  vertebrates and the cardiovascular system
  reflects the loss of gills and the need for
  efficient pulmonary circulation to bring blood to
  and from the lungs.
• In contrast to the situation in amphibians, the
  ventricle in reptiles has developed a septum that
  partially divides the ventricle into separate
  left and right chambers. In crocodilians (and
  birds) the separation of the ventricles is
  complete.
• This greatly reduces the mixing of oxygenated and
  deoxygenated blood.

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• Vertebrate circulatory systems

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Differences between reptiles and amphibians
respiration

• Reptiles depend almost entirely on lungs to
  oxygenate their blood and reptilian lungs are
  more developed than those of amphibians.
• In amphibians the lungs are simple sacs, but in
  reptiles they have divided into chambers and
  subchambers (called faveoli), which increases the
  surface area for gas exchange.

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Differences between reptiles and amphibians
respiration

• Most reptiles breathe by expanding and
  compressing the pleurpoperitoneal cavity by
  movements of the ribs produced by contracting the
  intercostal muscles.
• Turtles cannot move their ribs and instead use
  specialized sheets of muscle to expand and
  contract the lungs.

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Differences between reptiles and amphibians
respiration

• Although reptilian respiration primarily depends
  on lungs, some gas exchange takes place across
  the skin, the inside of the mouth and in the
  cloaca particularly in various turtles.
• In soft-shelled turtles up to 70 of gas exchange
  may take place across the leathery skin that
  covers the shell

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Softshell turtle http//www.tortoisetrust.org/arti
cles/3162658.jpg
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Modern reptiles

• The modern reptiles being a paraphyletic group
  include anapsids and diaspids.
• The anapsid representatives are the turtles
  (Order Testudines). Turtles have changed little
  from the oldest known fossil forms 210 mya.
• Turtle fossils from 210 mya are known from across
  the globe so the group clearly originated some
  time before this.

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Turtles

• Turtles have a shell that consists of a dorsal
  carapace and a ventral plastron.
• Ribs and vertebrae are fused to the shell and the
  head and limbs can be withdrawn into it.

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Turtles

• The carapace and plastron are both made of dermal
  bone overlain by horny scutes.
• In the carapace a series of 8 bony plates run
  along the dorsal midline and are attached to the
  neural arches of the vertebrae.
• On either side of the midline are pairs of costal
  bones that are fused to the ribs and 11 pairs of
  peripheral bones lie outside these.

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Bones of the turtle carapace http//reptilis.net/i
ndex4/shell.jpg
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Turtles

• Flexible areas called hinges are found in the
  shells of many turtles.
• In box turtles the anterior and posterior ends of
  the plastron can be raised to close off the front
  and rear openings of the shell.

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Box turtle inside its shell http//www.dogbreedinf
o.com/images21/TurtleBoxTurtle1.jpg
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Turtles

• Soft-shelled turtles lack peripheral
  ossifications and epidermal scutes.
• Instead the plastron and carapace are covered
  with skin.

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Turtles

• Turtles have no teeth and instead have a
  keratinized beak.
• This does not mean they cant have an impressive
  bite as snapping turtles demonstrate.

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Alligator Snapping Turtle http//www.dausettrails.
com /snapturtle.jpg
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Body size

• Turtles are unusual among the reptiles in having
  a large number of species that achieve very large
  body sizes.
• Large size means thermal stability because larger
  animals heat and cool more slowly than smaller
  ones, but large size may make temperature
  regulation difficult in habitats where shade is
  scarce.

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Body size

• The marine turtles are the largest members of the
  group and leatherbacks (the largest species) can
  weigh 1,500 lbs and are more than two meters in
  length (largest ever was just over 3m). Their
  large body size plays a major role in allowing
  them to range into very cold ocean waters yet
  maintain a body temperature that may be as much
  as 18º C higher than the surrounding water.
• The largest land dwelling members are the Giant
  tortoises of the Galapagos.

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Leatherback Turtle http//jcote1271.transworld.net
/files/2008/11/home-turtle.jpg
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Galapagos Giant Tortoises
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Ecology and Behavior of Turtles

• Turtles are very long-lived.
• Even small species such as the painted turtle do
  not mature until aged 7 or 8 and even box turtles
  may live to be 50 years old.
• Large tortoises and turtles can live at least as
  long as humans and perhaps longer, although
  accounts of several hundred year old turtles are
  likely exaggerated.

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Ecology and Behavior of Turtles

• Not surprisingly, being naturally long-lived,
  turtle populations are vulnerable to increased
  adult mortality (as e.g., are sharks).
• Thus, increased adult mortality in sea turtles as
  a result of fishing has severely reduced their
  populations.
• However, the use of turtle excluder devices on
  shrimp nets has reduced mortality.

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Loggerhead turtle escaping through Turtle
excluder device http//users.aber.ac.uk/jrd6/ted_l
oggerhead.jpg
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Turtle Reproduction

• All turtles are oviparous and the eggs are laid
  in a nest in sand or soil that the female
  excavates using her rear limbs.
• As is true of a number of other reptiles
  (including crocodiles, tuataras and some
  lizards), incubation temperature plays a major
  role in determining the sex of individual
  turtles. Higher incubation temperatures produce
  the larger sex, which in turtles is female.

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Loggerhead Turtle laying eggs http//www.fws.gov/a
rchiecarr /photos/LOGGER-2.jpg
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Turtle Reproduction

• Young turtles when they hatch are on their own
  because adults provide no parental care.
• Marine turtles lay their 100 or so eggs on sandy
  beaches. When the young hatch they must escape a
  host of waiting predators to get to the sea and
  mortality is high.

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Green turtle hatchlings http//www.naturephoto-cz.
com/photos/sevcik/green-turtle--chelonia-mydas-2.j
pg
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Turtle Reproduction

• Simultaneous emergence of large numbers of young
  turtles from multiple nests swamps the predators
  and allows some to escape.

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Turtle Reproduction

• Where young marine turtles go once they reach the
  sea is a mystery.
• Most nesting beaches are upcurrent from feeding
  grounds so the young likely drift to suitable
  nursery areas.
• In areas where currents meet, accumulations of
  weed and other flotsam provide refuge from
  predators and a supply of invertebrate food, and
  these are likely nursery areas for young turtles.

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Movement and Navigation

• Although where young sea turtles go remains a
  mystery we know that adults when ready to nest
  return to the beaches where they hatched.
• Given the lack of landmarks in the ocean and the
  often huge distances between nesting and feeding
  grounds the navigational success of these animals
  is remarkable.

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Movement and Navigation

• The movements and navigation of green turtles has
  been extensively studied for more than 50 years.
• Green turtles use four major nesting sites
  including Tortuguero on the Caribbean coast of
  Costa Rica and Ascension Island in the
  mid-Atlantic east of Brazil.
• Mating takes place off the nesting beaches where
  males congregate to wait for the females.

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Adult Green Turtle http//img5.travelblog.org/Phot
os/1/217471/f/1659239-Green-Turtle-1.jpg
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Movement and Navigation

• Studies of tagged green turtles at Tortuguero
  have shown that in a nesting season females
  typically lay three clutches with about 12 days
  between clutches.
• However, they do not lay every year. One third
  lay every second year, the remainder every third
  year.
• Information from tag recoveries shows that after
  breeding the turtle disperse throughout the
  Caribbean.

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Movement and Navigation

• The ability of female turtles nesting at
  Tortuguero to return to the same kilometer of
  nesting beach is impressive, but pales in
  comparison to the challenge of locating Ascension
  Island, which is 2,200 km east of Brazil and only
  20km in diameter.

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Movement and Navigation

• In navigating to Ascension it appears that
  chemosensory cues provide important information.
• The South Atlantic Equatorial current passes
  Ascension and flows west towards Brazil. Young
  turtles that drift on this current as hatchlings
  may learn its odor signature.
• Satellite-tracking studies of nesting females
  have shown that they take a quite direct route to
  Ascension from off the coast of Brazil and travel
  much of the way along the current apparently
  working their way up the odor plume.

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Movement and Navigation

• Other studies of marine turtles have shown other
  cues are also important in navigation.
• For example, when initially trying to get to sea
  young loggerhead hatchlings respond first to
  light and crawl towards the brightest visible
  light, which in a natural situation would lead
  them to the sea.

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Movement and Navigation

• Once in the water the baby loggerheads swim into
  the waves and this moves them offshore and
  ultimately to the Gulf Stream.
• This current carries them up the east coast of
  the U.S. and across the Atlantic. Off the coast
  of Portugal, the Gulf Steam splits into northward
  and southward branches.
• The turtles need to take the southward branch
  which will bring them back across the Atlantic
  and a lot of evidence suggests they use the
  Earths magnetic field to orient themselves
  correctly.

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Turtle Conservation

• Turtles and tortoises because of their delayed
  maturity and slow growth rates are very
  vulnerable to increased adult mortality or
  reduced juvenile recruitment.
• Marine turtles are threatened by coastal
  development that destroys nesting beaches and
  generates light pollution that fatally disorients
  young turtles. In addition, adult mortality
  caused by entanglement in fishing nets and long
  lines has put additional stress on populations.

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Turtle Conservation

• Smaller freshwater turtles are also under severe
  threat in China and southeast Asia in general.
• Turtles have traditionally been used for food and
  medicine in China and millions are consumed each
  year. Chinese populations have been severely
  depleted and as a result China has been importing
  large numbers from neighboring countries.

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Turtle Conservation

• Tortoises are also threatened, but instead of
  being taken for food they are illegally taken for
  the pet trade.
• In addition, in the southwestern U.S. deserts
  degradation of desert habitat and bacterial
  disease (likely introduced from pet tortoises
  released back into the wild) have caused desert
  tortoise populations to fall by 30-70.

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Turtle Conservation

• All of these threats coupled with widespread
  habitat degradation and enormous numbers of road
  deaths mean that turtles and tortoises face as
  severe a global crisis as amphibians do.

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Tuataras Order Sphenodonta

• The order is represented by two living species
  found only on offshore islands in New Zealand.
• They are the last survivors of a group that was
  much more diverse 200 million years ago.

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Tuataras

• Tuataras retain many features of their distant
  ancestors including a diapsid skull with two
  openings and associated complete arches and a
  well developed parietal third eye on the top of
  its skull.

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Tuataras

• The parietal eye has a lens, cornea, and retina,
  but a degenerated nervous connection to the
  brain. It is not used for vision, but may help
  regulate day-night cycles or absorb UV rays to
  manufacture vitamin D.

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Tuataras

• Adult Tuatara are about 2 feet long, nocturnal
  and live in seabird burrows.
• Tuatara have two rows of teeth on the upper jaw
  (one on the maxilla, the other on the palatine
  bones).
• When they bite the single row of teeth on the
  lower jaw fits between those on the upper jaw.

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Tuataras

• The feeding ecology of Tuatara is dictated by
  their association with seabird colonies.
• They eat seabirds, which are most vulnerable to
  attack at night. In addition, the birds guano,
  food scraps and dead bodies attract lots of
  invertebrates that the Tuatara also eat and in
  fact invertebrates make up most of their diet.

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Modern reptiles diapsids Squamata

• Subclass Diapsida Order Squamata.
• The Squamata includes about 95 of all living
  reptiles including three suborders
• Sauria lizards,
• Serpentes snakes
• Amphisbaenia worm lizards.

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Modern reptiles diapsids

• The diapsid skull of squamates has been modified
  from the ancestral condition by the loss of bone
  behind and below the temporal opening.
• Most squamates have a kinetic skull, which has
  movable joints that allow the snout and upper jaw
  to be moved against the skull and raised.

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Kinetic skull

• Mobility of the skull allows squamates to seize
  and manipulate prey and also increases the force
  of the bite.
• Snakes show the most extreme development of the
  kinetic skull and are capable of swallowing prey
  several time their own diameter.

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Order Squamata Suborder Sauria the lizards

• Lizards are a very diverse group that includes
  terrestrial, burrowing, aquatic, arboreal and
  even gliding members.
• There are about 4800 species ranging in size from
  about 3cm to 3m long.
• Most lizards are insectivorous and small (80
  weigh 20 grams or less).

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Lizards

• Lizards have invaded many of the worlds hottest
  areas by evolving a suite of adaptations that
  make survival in deserts possible.
• These include a thick skin that contains lipids,
  which reduce water loss, and the excretion of
  uric acid which minimizes water loss.

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Lizards

• Reptiles are ectothermic and adjust their body
  temperature by moving from one microclimate to
  another to bask or cool down.
• Cold climates do not suit lizards as there are
  too few opportunities to warm up.
• Because they spend relatively little energy
  keeping warm, ectotherms in general do well in
  low productivity ecosystems such as tropical
  deserts and grasslands.

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Lizards

• Lizards are very adaptable and occupy a wide
  range of habitats. In addition to deserts and
  grasslands they occur in swamps, along coasts,
  above timberline on some mountains and many
  species are arboreal.

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Lizards

• Lizards have good vision and an external ear,
  which snakes lack. They also have eyelids, also
  a trait that snakes lack.
• Most lizards have four limbs, although some
  species (the Amphisbaenians) are completely
  legless.

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Lizards

• Well known species of lizards include
  chameleons, geckos, iguanas, and monitor lizards,
  which include the largest species, the Komodo
  dragon.

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Chameleons

• Chameleons are the most arboreal lizards.
• Their zygodactylous feet (the toes are fused
  together) allow them to grip branches firmly and
  they have a prehensile tail.
• The eyes are raised on small cones that can
  rotate independently. This arrangement allows
  chameleons to gauge distance accurately, which is
  very important is prey capture. They catch prey
  by projecting their long tongue

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Chameleon catching an insect with its sticky
extensible tongue.
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Geckos

• Geckos are among the smallest lizards (3cm to
  30cm), but they are very successful with more
  than 1,000 species and they occur on every
  continent but Antarctica.
• They have modified scales on their feet (setae)
  that allow them to cling to vertical surfaces

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Gecko (note the flattened pads on the toes.
Ridges on these pads enable the gecko to cling to
smooth surfaces).
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Iguanas

• Most large lizards are herbivorous and many
  iguanas are arboreal. In areas without mammalian
  predators (e.g. islands in the West Indies)
  larger species have evolved that spend much of
  their time on the ground.
• Iguanas occur throughout South and Central
  America and some species (e.g. the Chuckwalla)
  occur in the western U.S.
• The marine iguanas of the Galapagos Islands are
  behaviorally very specialized and they dive and
  swim to obtain seaweed.

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Green Iguana http//animals.nationalgeographic.com
/staticfiles/NGS /Shared/StaticFiles/animals/image
s/primary/ green-iguana.jpg
Galapagos Marine Iguana http//www.bio.davidson.ed
u/people/midorcas/animalphysiology/websites/ 2008/
Belcher/marine-iguana.jpg
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Monitor Lizards

• Unlike other large lizards monitor lizards are
  active predators and feed on a wide variety of
  prey.
• Monitors have evolved a positive pressure gular
  pump to assist the axial muscles in lung
  ventilation. This enhanced respiration enables
  them to sustain high activity levels.

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Water Monitor Lizard http//www.mongabay.com/image
s/ malaysia/06/malaysia0513.JPG
Komodo Dragon http//blog.turntablelab.com/images/
KomodoDragon.jpg
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Monitor Lizards

• Monitor Lizards are widely distributed throughout
  the Old World with large species found throughout
  the range.
• In Australia and New Guinea a diverse array of
  smaller monitors occur and this appears to be due
  to a lack of small placental mammal carnivores.

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Monitor Lizards

• Monitors display complex hunting behavior and
  will adjust their strategies depending on the
  behavior of their prey.
• For example, Komodo dragons hunting deer wait in
  the morning to ambush deer as they move along
  paths between resting and feeding areas. If they
  are unsuccessful, they then switch to active
  stalking for deer in the thicket habitats where
  they are most likely to occur.

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Monitor Lizards

• Komodo Dragons can dispatch smaller prey easily,
  but do not have to kill larger prey in their
  initial attack.
• Komodo mouths contain a diverse stew of bacteria
  and bites inevitably become infected. A bitten
  animal rapidly develops sepsis and dies. The
  monitor that bit it merely needs to trail the
  victim for a few days until it succumbs to its
  wounds.

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Amphisbaenians

• Leglessness has evolved multiple times among
  lizards and one large group the Amphisbaenians is
  exclusively legless (apart from 4 species in one
  genus that retain forelimbs).
• These are tunneling lizards and have a variety of
  specialized adaptations for digging and moving in
  burrows.

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Amphisbaenians

• Amphisbaenians burrow using by ramming their
  heads against the soil and pushing dislodged
  material to the sides.
• The head is heavily keratinized and there is
  variation in head shape that relates to the
  particular mode of tunneling used.
• For example, those with shovel-shaped snouts ram
  their heads into the end of the tunnel and then
  compress the material into the roof.

109
Gray Amphisbaenian http//4.bp.blogspot.com/_LbccU
VbSRd8/RdteZVPJ4iI/AAAAAAAAAZk/ 3gDlu3kFXlk/s400/p
uertoricangrayamphisbaenian_kingsnake1com.JPG
110
Amphisbaenians

• Amphisbaenians skin is distinctive and rings
  called annuli encircle the body.
• The integument has only a few connections to the
  body so that the trunk is free to move within a
  tube of skin.
• To move, the animal contracts integumentary
  muscles between selected annuli. This bunches the
  skin so it presses against the tunnel and the
  trunk then slides forward within the tube of skin.

111
Order Squamata Suborder Serpentes the snakes

• There are approximately 2900 species of snakes
  and they range is size from 10cm long burrowing
  forms that eat termites to almost 10m long
  anacondas and pythons.

112
Snakes

• Snakes are limbless and usually lack both the
  pectoral and pelvic girdles.
• They have numerous vertebrae, which are shorter
  and wider than those in other vertebrates and
  allow them to make undulatory movements.

113
Snakes

• There are three major lineages of snakes
• Scoleophidia more than 300 species of small
  burrowing (fossorial) snakes.
• Alethinophidia About 160 species that include
  the boas, pythons and a variety of boa-like
  snakes.
• Colubroidea more than 2400 species including the
  Colubridae, Elapidae and Viperidae.

114
Aletinophidia

• Alethinophidia Boidae Includes the 26 species
  of pythons (Pythoninae) and 33 species of boas
  (Boinae).
• The pythons are Old World constrictors that are
  large to enormous (approaching 10m) in size. The
  boas are the New World equivalent of the pythons
  and have a similar range of sizes.

115
Emerald Tree boa http//www.infovisual.info/02/pho
to/emerald20tree20boa.html
116
Anaconda http//www.oregonreptileman.com/sitebuild
ercontent/sitebuilderpictures/anaconda.jpg
117
Snakes

• The large constrictors primarily use rectilinear
  motion to move.
• Alternate sections of the ventral integument are
  raised off the ground and pulled forward by
  muscles that connect the ribs and ventral scales.
• Waves of muscles contraction travel down the
  snake which moves in a straight line.

118
Colubroidea

• Colubroidea includes most of the living species
  of snakes and the Colubridae alone contains 2/3
  of all snakes.
• Many colubroid snakes are venomous and the
  Elapids and Viperids possess hollow fangs at the
  front of the mouth and have highly toxic venom.
• Many colubrids possess venom glands but they do
  not have the hollow teeth specialized to inject
  venom.

119
Colubroid movement

• Several different forms of motion are used by
  colubroids, but horizontal undulations and
  concertina-like movements are the most common.

120
Colubridae

• The group is a bit of a phylogenetic dumping
  ground and includes more than 1800 species that
  occur worldwide (except Antarctica).
• Most are medium sized, all lack a pelvid girdle,
  have no vestigial hindlimbs and in all the left
  lung is absent or very reduced in size.
• North American colubrids include garter snakes,
  kingsnakes, hognose snakes, racers, and corn
  snakes.

121
Corn Snake http//www.pitt.edu/mcs2/herp/snake.pi
cs/corn.gif
122
Prairie Kingsnake http//www.pitt.edu/mcs2/herp/
Lc_calligaster.html
Common Garter snake http//www.pitt.edu/mcs2/herp
/snake.pics/t_sirtalis.jpg
Striped whipsnake http//www.pitt.edu/mcs2/herp/s
nake.pics/Masticophis_taeniatus.jpg
123
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124
Viperidae

• In members of the Viperidae the long fangs rest
  horizontally when the mouth is closed.
• Viperids range in size up to about 2m and include
  both the true vipers, which occur in Eurasia and
  Africa and the pit vipers, which occur in New
  World and Asia.

125
Viperidae

• True vipers include the Gaboon Viper and Puff
  Adder.
• Pit vipers include rattlesnakes.

126
Gaboon Viper http//homepage.mac.com/wildlifeweb/r
eptile/gaboon_viper/gaboon_viper01tfk.jpg
127
Gaboon Viper Skull http//www.kostich.com/gaboon_
viper_skull.jpg
128
Puff Adder http//kolobe.com/photo_gallery/Anml_Ga
l/slides/Puff20Adder.JPG
129
Rattlesnake http//i.pbase.com/v3/29/530429/1/4515
5303.Rattlesnake.jpg
130
Elapidae

• Elapids have functionally hollow fangs (the tooth
  is folded over to form a groove that is almost
  closed down which the venom runs) that are
  shorter than those of the viperids, but they are
  permanently erect.
• Elapids include the mambas, cobras, kraits and
  sea snakes.

131
King Cobra http//www.digitalcamerareviews.org.uk/
wp-content/uploads/ 2009/01/a-full-sized-indian-ki
ng-cobra.jpg
132
Black Mamba http//s3.amazonaws.com/readers/2009/0
3/26/black20mamba_1.jpg
133
Sea snakes

• Sea snakes (members of the Elapidae) are
  morphologically specialized for life in the
  water.
• The tail is laterally flattened so it can act as
  an oar. Nostrils are located dorsally on the
  snout and are equipped with valves to keep water
  out. More primitive sea snakes lay eggs on the
  land, but the more derived species give birth to
  live young.

134
Yellow-bellied sea snake http//elapidcatcher.com/
elapidcatcher.com/images/stories/snakes/ yellow20
bellied20sea20snake.jpg
135
Snakes

• Snakes are an extremely successful group of
  predators. Although most have poor vision (with
  the exception of arboreal species) and limited
  hearing ability they use other sense organs to
  track prey.
• Snakes have pit-like Jacobsons organs in the
  roof of the mouth, which are olfactory organs.
  The forked tongue when extended samples the air
  and picks up molecules that are delivered to the
  Jacobsons organ when the tongue is withdrawn.

136
Snakes

• Crotaline vipers (pit vipers such as
  rattlesnakes) have heat-sensitive pit organs on
  their heads between the nostrils and eyes.
• These are very sensitive to radiant heat and can
  detect temperature differences as slight as
  0.003ºC. The vipers use the organ to track prey
  and to aim their strike when biting.

137
18.22
138
Predation

• Snakes use one of three methods to catch and kill
  prey.
• Most catch prey by grabbing it and swallowing it
  alive. Most such species are quick and
  concentrate on small, easy-to-handle prey.
• The other two group kill their prey either by
  constriction or with venom.

139
Constrictors

• A variety of snakes including pythons and boas
  kill by constriction.
• They coil around their prey and every time the
  prey breathes out they tighten their coils a
  little more until the prey can no longer breathe
  and suffocates.
• Most constrictors are large, slow-moving ambush
  predators and the largest snakes, the anaconda,
  boas and pythons are all constrictors.

140
Venomous snakes

• About 20 of all snakes are venomous (although in
  Australia 80 of snakes are venomous). About
  50,000-60,000 people die annually worldwide from
  snake bite, most of them in the Indian
  subcontinent.
• Snakes with venom lethal to humans include the
• vipers (including the American pit vipers) which
  have large movable tubular fangs at the front of
  the mouth
• elapids (cobras, mambas, coral snakes, kraits,
  sea snakes) which have shorter, but permanently
  erect fangs in the front of the mouth

141
18.20
142
Venomous snakes

• Snake venoms are highly modified salivas and
  complex in constitution including a variety of
  proteins and enzymes.
• Elapid venom is neurotoxic and works by shutting
  down the respiratory system whereas viper venom
  is more painful and attacks the vascular system
  bringing about coagulation of blood and clotting
  of arteries as well as often severe tissue damage.

143
Result of a rattlesnake bite http//images.townnew
s.com/helenair.com/ content/articles/2008/05/25/to
p/80na_080525_rattlesnakes.jpg
144
Crocodiles and Alligators Order Crocodilia

• Modern crocodiles and birds are the only
  survivors of the Archosaurian lineage that
  included the dinosaurs.
• Crocodiles have changed little in almost 200
  million years a testament to the success of their
  design.

145
Crocodiles

• All crocodiles have their teeth set in sockets a
  trait found otherwise only in mammals and fossil
  birds and also like mammals have a complete
  palate which enables them to breathe even if the
  mouth is filled with water or food.
• They alos possess a four chambered heart as do
  the only other extant members of the Archosauria,
  the birds

146
Crocodiles

• Crocodiles are ambush predators that kill by
  grabbing and drowning their prey. The largest
  Nile and Estuarine crocodiles (called salties
  in Australia) can exceed 1000 kgs in weight and
  can attack and kill almost anything.

147
Crocodiles

• The muscles used to open a crocodiles mouth are
  quite weak, but those used to close the jaws are
  massive and powerful.
• Broad nosed crocodiles can for example crush an
  adult turtle.
• A crocodiles snout contains large numbers of
  touch and pressure receptors. These enable the
  animal to lunge at a prey animal in darkness or
  immediately snap the jaws closed on a fish or
  other animal that brushes against the animals
  open mouth.

148
Crocodiles

• Crocodiles do not chew their prey. Smaller prey
  animals are swallowed whole, but larger animals
  are eaten piecemeal.
• Crocodiles often allow the animal to decompose
  for several days to make it easier to tear chunks
  off.

149
Classification

• There are 23 species of crocodile divided into
  three lineages
• Alligatoridae,
• Crocodilidae
• Gavialidae.

150
Alligatoridae

• The Alligatoridae includes the alligators and
  caimans and, with the exception of the Chinese
  alligator, is solely a New World group.
• Alligators and caimans are exclusively found in
  freshwater and, in general, they have broader
  snouts than crocodiles.

151
Alligators

• The American Alligator is found throughout the
  Gulf states and caimans occur in Central America,
  South America and the Caribbean.
• Alligator populations in the U.S. had declined
  enormously as a result of hunting for meat and
  especially skins, but Federal protection has
  caused their numbers to rebound so that they are
  again common.

152
American Alligator http//www.wildanimalfightclub.
com/Portals/41405/images//gex-american-alligator_j
pg.jpg
153
Crocdiles

• In contrast to alligators, crocodiles occur in
  both freshwater and salt water and readily move
  from one to the other.

154
Crocodiles

• The saltwater crocodile is probably the largest
  living crocodile and may be capable of reaching
  7m in length although hunting pressure in recent
  history means there may not be old enough
  individuals around for maximum size to have yet
  been attained.

155
Australian saltwater Crocodile with a hooked
Barramundi http//www.ntnews.com.au/images/uploade
dfiles/editorial/pictures/2008/04/29/ barra_croc.j
pg
156
Gharial

• There is only a single species in the Gavialidae
  the gharial.
• Gharials were once widespread in large rivers in
  India and Burma but are now threatened species.
• It has a very narrow snout and is a specialist
  fish predator.

157
Gharial picture
Gharial http//homepage.mac.com/wildlifeweb/reptil
e/gharial/gharial01tfk.jpg