Turtles

1
Chapter 12

• Turtles

2
Introduction from Chapter 11

• Early division of amniotes produced 2
  evolutionary lineages that include the vast
  majority of extant terrestrial vertebrates
• Synapsids
• Include mammals
• Suaropsids

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Introduction

• From classification based on temporal
  fenestration two groups of Sauropsida emerge
• Anapsida
• This group include turtles
• Diapsida
• Dinosaurs, tuataras, lizards,snakes, crocodiles
  and birds

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Introduction

• Sauropsids are the bulk of the reptiles plus
  birds while
• Synapsids are the mammal-like reptiles and
  mammals

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Turtles

• Earliest fossil date to late Triassic
• Very little morphological change has taken place
  since that time
• Shell has been their key to success
• Shell has also limited group diversity
• Have Anapsid skulls

6
Turtles

• Systematic relationships with other amniotes
  poorly understood.
• Their combination of ancestral and highly derived
  traits makes determining relationships difficult
• Two hypotheses currently being debated
• Turtles are sister group to reptiles
• Turtles are Diapsids

7
Current Classification

• Kingdom Animalia
• Class Reptilia
• Order Testitudinomorpha
• Extant suborders
• Suborder Cryptodira
• Suborder Pleurodira

8
Distribution

• Worldwide distribution and a variety of habitats
• Turtles and tortoises can be found in all
  continents except Antarctica
• Can also be found in all warm and temperate
  oceans
• Occupy a wide diversity of both terrestrial and
  aquatic habitats

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Turtles

• 13 families
• Two major grps (suborders) of turtles are
• 1. Cryptodires (hidden necked)
• Retract head into shell by bending the neck in a
  vertical s-shape
• can pull their heads, legs, and feet inside their
  shells. In order to make room inside the shell,
  they sometimes have to exhale air out of their
  lungs, which makes a hissing sound.
• Both aquatic terrestrial
• Only type found in Northern Hemisphere
• Marine turtles are cryptodires

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Turtles Pleurodires

• Pleurodires (side necked turtles)
• Other turtles cant pull their legs or heads into
  their shells. Some of these have long necks and
  protect their heads by tucking them sideways up
  against the shell.
• Found only in the southern hemisphere
• Semi-aquatic
• Most terrestrial ones in Africa for example the
  the African Pond turtle. Moves on land from pond
  to pond
• Snake-necked pleurodiran turtles are found in S
  America
• Have long slender necks
• Feed on fishes, mollusks
• Have large palatal surfaces used to crush shells

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Characteristics of turtles

• Horny beaks
• No teeth
• Limb girdles are inside the ribs
• Unique in turtles
• Shell composed of 2 parts
• Carapace- upper shell
• Plastron- lower shell

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Turtle Shell Carapace

• Composed of dermal bone
• Bone grow form 59 centers of ossification
• There about 59-61 bones
• Centers of ossification give rise to several
  series of dermal bones in the carapace
• Peripherals 11 pairs, form margins
• Costals fused to ribs
• Neural formed by 8 plates along the dorsal
  mid-line. Fused to the vertebrae

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Turtle Shell Carapace

• Carapace covered by epidermal scutes (keratin
  scales)
• Epidermal scutes do not correspond in number
  position to the underlying dermal bones of shell
• Row of 5 central scutes
• Four lateral scutes form borders
• 11 marginal scutes on each side turn under edge
  of carapase
• See figure 12.5

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Turtle Shell Plastron

• Formed also from the dermal bone
• Interior of plastron (entoplastron) is formed
  from clavicles and interclavicle
• Covered by a series of 6-paired scutes
• See page 309.

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Turtle shell Hinges

• Some shells have one or two hinges in the
  plastron these are flexible areas
• Front and rear lobes can be pulled upward to
  close openings
• Allows turtles to draw into its shell and then
  close the shell as protection against predation
• Seen on N American Box turtles
• Called kinetic shells
• Exact number position varies
• In others, plastron is reduced in size allowing
  greater mobility. One spp (musk turtle) can even
  climb several feet into trees.

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Variation in shell morphology

• Soft shelled turtles
• Lack peripheral ossification
• No epidermal scales (scutes)
• Carapace and plastron covered with skin
• Soft shelled turtles II
• New Guinea river turtle
• Covered by skin, no scutes
• Peripheral bones present
• In general soft shelled turtles are aquatic, have
  webbed feet for swimming

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Variation in shell morphology

• Leatherback sea turtle
• Carapase formed of cartilage supported by tiny
  bones. Skin is leathery..
• Plastral bones form a very thin edge
• Greatly reduced ossification
• This adaptation allows the turtle to dive up to
  3,000 feet (900 meters) below the ocean surface.
  At this depth, the incredible water pressure
  would crush a turtle with a heavy shell and less
  flexible body.

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Variation in shell morphology

• Terrestrial species tend to have
• High domes
• Broad feet
• E.g. box turtles.

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Turtle Vertebral column

• The Turtle vertebral column has 8 cervical, 10
  trunk, 2 sacral and 16 to 30 caudal vertebrae.
• Cervical vertebra allow the S-shaped bend used to
  retract the head into the shell
• The first caudal as well as all the sacral and
  trunk vertebrae are fused with dermal bone to
  form the carapace.
• The ribs are expanded and fused to the inner
  surface of the costal plates of the carapace.

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Circulatory System

• Double circuit
• Systemic circulation carries blood throughout
  body (head, trunk appendages)
• Pulmonary circuit carries blood to lungs

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Heart

• 3 chambered
• Completely divided atria
• Incompletely divided 3- region ventricles
• Allow complete separation of oxygen rich and
  oxygen poor blood
• High pressure systemic and low pressure pulmonary
• Allows shunting of blood between systemic and
  pulmonary circuit
• Occurs when lungs are not used for respiration
  (during diving or hibernation)

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Heart Structure of ventricles

• Cavum Pulmonale
• Opens into pulmonary artery (RHS)
• Cavum Venosum
• Opens into the right and left aortic arches
• Receives blood from body veins and also from the
  CA.
• Cavum arteriosus
• 3rd region
• Dorsal to the CV and CP.
• Receives blood from left atrium

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Heart ventricle structures

• Muscular ridge partially divides the CV and the
  CP
• Intraventricular canal (IVC)
• Connects the CV with the CA.

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Blood flow

• Right atrium receives poor oxygen blood from the
  systemic circuit via the sinus venosus
• Passes it to the Cavum venosum thru the
  atrioventricular valve (AVV)
• AVV prevent backflow
• Also prevents blood flow into the
  intraventricular canal, hence cannot go the ,
  thus cannot go the Cavum Arteriosus

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Blood flow

• Cavum venosum passes blood to the cavum pulmonale
  which then passes blood to the to the pulmonary
  artery to to the lungs

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Blood Flow

• The left atrium receives oxygen rich blood from
  lungs
• Passes thru the AVV into the Cavum arteriosus
  (CA)
• Ventricle contracts, blood flows from CV to CP.
  As pressure builds up, muscular ridges closes
  passages between the CV and CP, then allows
  blood to flow from the CA to CV and then to
  aortic arches
• Thus the CV handles both Oxygen poor and oxygen
  rich blood, but separately..

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Blood Flow

• O2 Poor blood
• Body RA----av---CV-----CP----Pa---lungs
• Av also closes the IVC.. No blood to CA at this
  point
• O2 rich blood
• LA ----av-----CA-------CV---aortic
  arches---arteries.
• High pressure cause IVC to open to allow blood
  flow into CV from CA

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Blood Flow

• Timing of blood flow thru the heart prevents the
  mixing of Oxygen rich blood coming from the
  pulmonary circulation with deoxygenated blood
  from the systemic circulation

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Respiration

• Ribs fused to carapace are immovable
• Ventilation by moving rib-cage is impossible
• Lungs are large and are also attached to carapace
  dorsally and ventrally
• Thus turtles cannot ventilate by expanding or
  contracting the rib cage/thoracic cavity because
  its rigid.

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Respiration Use of visceral cavity

• Lungs are attached to visceral cavity ventrally
  by a rigid sheet of connective tissue
  Diaphragmatic tissue
• Non-muscle tissue that connects ventral side of
  lungs to the visceral organ
• Wt of viscera keeps diaphragmatic sheet pulled
• Ventilation is by visceral pump
• Viscera push against the pleural cavity to force
  air out of the lungs (exhalation)
• Viscera pull down on diaphragmatic sheet, this
  expands the lungs. Air comes in..

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Respiration Other Muscles

• Exhalation
• Transverse abdominus muscles contract to pull
  viscera upward against lungs
• Pectoralis draws pectoral girdles back into the
  shell. They reduce volume of VC
• Inhalation
• Abdominal oblique
• Pectoral serratus

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Respiration other structures used by aquatic spp

• Pharynx in soft shelled turtles
• Cloaca in diving shells
• In both cases, turtles pump water in and out of
  the pharynx or cloaca and can exchange O2 and CO2
  across membranes of the structures

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Intracardiac Shunts

• Turtles are able to shunt blood from the
  pulmonary circulation to the systemic circulation
  (by pass lungs)
• Occurs during prds of apnea (no breathing)
• When lungs are not being ventilated and there
  would be no oxygen to be taken up into the blood
• Diving is the most common reason for this
• Right to left intracardiac shunt
• Blood shunted directly from the right side to the
  systemic circulation.

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Reproduction

• All Oviparous
• Eggs covered in a leathery membrane to prevent
  sperm from reaching the fertilized egg
• Fertilization is internal before shell is
  produced to coat egg

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Reproduction Courtship

• Courtship signals and other spp recognition
  signals are used
• Employ visual, olfactory, tactile and olfactory
  cues during courtship
• Many pond turtles have distinct series of lines
  on their heads, necks, and forelimbs and on their
  hind limbs and tail
• Used for spp recognition

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Reproduction Courtship

• Several spp have glands in the male that enlarge
  during breeding and produce pheromones that are
  used to mark substrates within a territory
• Tortoises vocalize during courtship. Produce
  grunts, moans, bellows.
• Tactile signals entails that males engage in
  combat that involves biting the head of an
  opponent or ramming him and trying to overturn him

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Reproduction Courtship

• Large tortoise often live in herds and a large
  male is often dominant. Fighting among
  individuals serves to establish the dominancy
  hierarchy- elevating head
• See figure 12-9

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Reproduction Nesting

• Eggs laid in a nest dug by the female
• After this no parental care
• Clutch of eggs laid 4-5 eggs for small spp to
  100 eggs for large spp
• Embryonic development is 40-60 days
• Eggs have a diapause prd during the winter.
  Resume development when temperature rises in
  spring

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Reproduction Nesting

• Nesting Temperature
• Determines sex of offspring
• High temp---- development of larger sex (females)
• Low temp---development of smaller sex (males)
• Range in temp for sex change is very narrow (3-4o
  C)

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Reproduction Nesting

• Wet incubation produces larger hatchlings than
  dry conditions
• In dry conditions turtles hatched are small,
  hatch early, contain more of unmetabolized egg
  yolk
• Cannot run or swim fast as does the wet
  hatchlings- not very successful at escaping
  predation

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Hatching Behavior

• Turtles show self sufficiency at hatching
• Hatchling behavior studied in marine turtles
• Clutch of eggs in a nest hatch simultaneously
• Vocalizations used to get all the nest mates
  synchronized for hatching
• Enmass dig their way to the surface
• At night when temperatures are low, all baby
  turtles emerge from nest at once and then race to
  the ocean

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Hatching Behavior

• Along the stretch of beach, there will be many
  other nests of turtles emerging at same time
• Susceptible to heavy predation simultaneously,
  saturate predators
• Crabs, foxes, raccoons, sharks, bony fishes

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Temperature regulation

• Turtles are ectotherms
• Body temp determined by environment
• Regulation of body temperature is behavioral
• Bask in sun to increase body temperature
• Increases rate of metabolic reactions
• Helps to kill and rid themselves of leeches in
  case of aquatic turtles
• Rate of heating cooling easier with small
  turtles
• Overheating a problem with giant turtles in an
  open sunny habitat

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Temperature regulation

• Some are endothermic
• Marine turtles are very large and endothermic
• Leatherbacks are the largest living turtles ----
  1000 kgs
• Found in Temps of 8, 15 or 20 degrees Celsius but
  with body temps 18 degrees above that of water
• Use countercurrent exchange system of blood
  vessels in the flippers to conserve heat

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Temperature regulation countercurrent exchange

• Venous blood returning from the flipper is cold
• Returns through veins closely associated with the
  arteries that carry blood from the body to the
  flippers
• Cold venous blood is heated by warm arterial
  blood flowing out of the core of body. By the
  time venous blood reaches core of boy it is back
  to body temperature.

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Feeding

• Mostly carnivorous as seen in sea turtles
• Leatherbacks eat jellyfish
• Others are vegetarian
• feed on turtle grass that grows in shallow or
  protected shorelines in the tropics.

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Threats to Survival

• Low reproductive rates
• Lack of parental care
• Habitat loss and degradation
• Overexploitation for food and pet trade
• Asians markets for turtle meat
• Lack of basic natural history information on many
  species
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