Chapter 12
Turtles
Introduction from Chapter 11
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Early division of amniotes produced 2
evolutionary lineages that include the
vast majority of extant terrestrial
vertebrates
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Synapsids
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Include mammals
Suaropsids
Introduction
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From classification based on temporal
fenestration two groups of Sauropsida
emerge
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Anapsida
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This group include turtles
Diapsida
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Dinosaurs, tuataras, lizards,snakes, crocodiles
and birds
Introduction
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Sauropsids are the bulk of the reptiles plus
birds while
Synapsids are the mammal-like reptiles and
mammals
Turtles
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Earliest fossil date to late Triassic
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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
Turtles
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Systematic relationships with other amniotes
poorly understood.
Their combination of ancestral and highly
derived traits makes determining
relationships difficult
Two hypotheses currently being debated
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Turtles are sister group to reptiles
Turtles are Diapsids
Current Classification
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Kingdom: Animalia
Class: Reptilia
Order : Testitudinomorpha
Extant suborders
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Suborder: Cryptodira
Suborder: Pleurodira
Distribution
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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
Turtles
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13 families
Two major grps (suborders) of turtles are
1. Cryptodires (hidden necked)
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Retract head into shell by bending the neck in a
vertical s-shape
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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
Turtles; Pleurodires
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Pleurodires (side necked turtles)
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Other turtles can’t 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
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Have long slender necks
Feed on fishes, mollusks
Have large palatal surfaces used to crush shells
Characteristics of turtles
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Horny beaks
No teeth
Limb girdles are inside the ribs
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Unique in turtles
Shell composed of 2 parts
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Carapace- upper shell
Plastron- lower shell
Turtle Shell: Carapace
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Composed of dermal bone
Bone grow form 59 centers of ossification
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There about 59-61 bones
Centers of ossification give rise to several
series of dermal bones in the carapace
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Peripherals: 11 pairs, form margins
Costals: fused to ribs
Neural: formed by 8 plates along the dorsal midline. Fused to the vertebrae
Turtle Shell: Carapace
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Carapace covered by epidermal scutes
(keratin scales)
Epidermal scutes do not correspond in
number & position to the underlying dermal
bones of shell
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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
Turtle Shell: Plastron
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Formed also from the dermal bone
Interior of plastron (entoplastron) is
formed from clavicles and interclavicle
Covered by a series of 6-paired scutes
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See page 309.
Turtle shell: Hinges
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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
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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.
Variation in shell morphology
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Soft shelled turtles
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Soft shelled turtles II
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Lack peripheral ossification
No epidermal scales (scutes)
Carapace and plastron covered with skin
New Guinea river turtle
Covered by skin, no scutes
Peripheral bones present
In general soft shelled turtles are aquatic,
have webbed feet for swimming
Variation in shell morphology
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Leatherback sea turtle
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Carapase formed of cartilage supported by tiny
bones. Skin is leathery..
Plastral bones form a very thin edge
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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.
Variation in shell morphology
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Terrestrial species tend to have
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High domes
Broad feet
E.g. box turtles.
Turtle Vertebral column
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The Turtle vertebral column has 8 cervical, 10
trunk, 2 sacral and 16 to 30 caudal vertebrae.
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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.
Circulatory System
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Double circuit
Systemic circulation carries blood
throughout body (head, trunk &
appendages)
Pulmonary circuit: carries blood to lungs
Heart
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3 chambered
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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)
Heart: Structure of ventricles
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Cavum Pulmonale
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Cavum Venosum
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Opens into pulmonary artery (RHS)
Opens into the right and left aortic arches
Receives blood from body veins and also from the
CA.
Cavum arteriosus
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3rd region
Dorsal to the CV and CP.
Receives blood from left atrium
Heart: ventricle structures
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Muscular ridge partially divides the CV
and the CP
Intraventricular canal (IVC)
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Connects the CV with the CA.
Blood flow
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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)
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AVV prevent backflow
Also prevents blood flow into the
intraventricular canal, hence cannot go the
, thus cannot go the Cavum Arteriosus
Blood flow
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Cavum venosum passes blood to the
cavum pulmonale which then passes
blood to the to the pulmonary artery to
to the lungs
Blood Flow
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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
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Thus the CV handles both Oxygen poor and
oxygen rich blood, but separately..
Blood Flow
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O2 Poor blood
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Body – RA----av---CV-----CP----Pa---lungs
Av also closes the IVC.. No blood to CA at
this point
O2 rich blood
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LA ----av-----CA-------CV---aortic arches--arteries.
High pressure cause IVC to open to allow
blood flow into CV from CA
Blood Flow
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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
Respiration
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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.
Respiration: Use of visceral cavity
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Lungs are attached to visceral cavity ventrally
by a rigid sheet of connective tissue:
Diaphragmatic tissue
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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
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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..
Respiration: Other Muscles
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Exhalation
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Transverse abdominus muscles: contract to
pull viscera upward against lungs
Pectoralis draws pectoral girdles back into
the shell. They reduce volume of VC
Inhalation
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Abdominal oblique
Pectoral serratus
Respiration: other structures
used by aquatic spp
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Pharynx in soft shelled turtles
Cloaca in diving shells
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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
Intracardiac Shunts
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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
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Blood shunted directly from the right side to the systemic
circulation.
Reproduction
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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
Reproduction: Courtship
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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
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Used for spp recognition
Reproduction: Courtship
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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
Reproduction: Courtship
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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
Reproduction: Nesting
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Eggs laid in a nest dug by the female
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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
Reproduction: Nesting
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Nesting Temperature
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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)
Reproduction: Nesting
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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
Hatching Behavior
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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
Hatching Behavior
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Along the stretch of beach, there will be
many other nests of turtles emerging at
same time
Susceptible to heavy predation
simultaneously, saturate predators
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Crabs, foxes, raccoons, sharks, bony fishes
Temperature regulation
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Turtles are ectotherms
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Body temp determined by environment
Regulation of body temperature is behavioral
Bask in sun to increase body temperature
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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
Temperature regulation
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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
Temperature regulation:
countercurrent exchange
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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.
Feeding:
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Mostly carnivorous– as seen in sea
turtles
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Leatherbacks eat jellyfish
Others are vegetarian
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feed on turtle grass that grows in shallow
or protected shorelines in the tropics.
Threats to Survival
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Low reproductive rates
Lack of parental care
Habitat loss and degradation
Overexploitation for food and pet trade
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Asians markets for turtle meat
Lack of basic natural history information
on many species
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