Chapter 12

Turtles

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

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

Introduction Sauropsids are the bulk of the reptiles

plus birds while Synapsids are the mammal-like reptiles

and mammals

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

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

Current Classification Kingdom: Animalia Class: Reptilia Order : Testitudinomorpha Extant suborders

Suborder: Cryptodira Suborder: Pleurodira

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

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

Turtles; Pleurodires Pleurodires (side necked turtles)

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 Have long slender necks Feed on fishes, mollusks Have large palatal surfaces used to crush shells

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

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

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

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.

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.

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

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.

Variation in shell morphology Terrestrial species tend to have

High domes Broad feet E.g. box turtles.

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.

Circulatory System Double circuit Systemic circulation carries blood

throughout body (head, trunk & appendages)

Pulmonary circuit: carries blood to lungs

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)

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

Heart: ventricle structures Muscular ridge partially divides the

CV and the CP Intraventricular canal (IVC)

Connects the CV with the CA.

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

Blood flow Cavum venosum passes blood to

the cavum pulmonale which then passes blood to the to the pulmonary artery to to the lungs

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..

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

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

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.

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..

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

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

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.

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

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

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

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

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

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)

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

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

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

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

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

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.

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.

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

(Read text for more details)