Presentation on theme: "Chapter 12 Turtles. Introduction from Chapter 11 Early division of amniotes produced 2 evolutionary lineages that include the vast majority of extant."— Presentation transcript:
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 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 3 rd 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 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 (3-4 o 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)