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This 6 page Class Notes was uploaded by Bri M on Tuesday October 18, 2016. The Class Notes belongs to 3030 at Clemson University taught by Blob in Fall 2016. Since its upload, it has received 5 views. For similar materials see Vertebrate Biology in Biology at Clemson University.
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Date Created: 10/18/16
Lecture 16 - Reptile Diversity (Part 1) - Mostly Turtles Relationships of turtles to other sauropsids (controversial) ❖ Alternative hypotheses: ➢ A: T urtles are anapsids and sister group to all other reptiles ■ Older (historical) classification, based on lack of temporal fenestrae ➢ B and C: turtles are diapsids ■ Now widely accepted that turtles are part of diapsid clade, just with highly modified skills that lost temporal fenestrae (molecular/developmental evidence) ■ This may be part of lepidosaurs (B) or ■ Sister to archosaurs (C ) ❖ What you see on the outside of turtles can’t tell you where they fall in the cladogram ➢ There has been more recent findings suggesting other ideas Fossil Turtles ❖ Extensive fossil record (back to the Triassic period → about 2million years ago ❖ Basic turtle body design (shell, etc.) very early ➢ Example: Eunotosaurus ❖ Proganochelys (earliest turtle) ➢ Very early turtle ➢ Shell, looked like modern turtle ➢ Sister group to other turtle ➢ Has very long tail...most modern turtles have short tail ➢ There is no way for this animal to retract its head into shell … modern turtles do ❖ Archelon (cretaceous) ➢ Largest turtle that has ever lived ➢ Giant sea turtle ➢ About 3m shell Phylogenetic Relationships: extant turtles ❖ About 310 species ➢ Some species that are...terrestrial, freshwater(most time on land), marine ❖ Earliest fossils lack neck retraction ❖ Two major clades based on mode of neck retraction ➢ Cryptodira: hidden-neck turtles ■ Neck bends in vertical plane ■ Completely retract head into shell ➢ Pleurodires: side-neck turtles (about 80 species) ■ Neck bends in horizontal plane ■ Cannot truly retract head into shell ❖ Some extant cryptodires have lost ability to retract head ➢ Sea turtles and snapping turtles ➢ This is a new trait Geographic Distribution ❖ Cryptodire turtles on every continent except Antarctica ❖ Carettochelys only non-marine cryptodire in Australia ❖ Pleurodires = Gondwanaland distribution ➢ Only found in southern hemisphere continents ➢ South america, africa, india, madagascar ➢ These species must have originated in southern part of world during pangea Turtle Diversity ❖ Snapping turtles ➢ Long turtles ➢ Triangular beaks for forceful biting ❖ Sea turtles ➢ Elongated tails and flippers ➢ More streamlined body ❖ Softshell turtles ➢ Skin over shell ➢ Elongated body Turtle Synapomorphies 1. SHELL (turtles “most recognizable vertebrate”) a. Bony skeleton + covering (more later) b. Two sections/parts c. Major implications - as a result of their shell..they are dramatically slower (can’t bend side to side) i. Breathing is different because ribs are fused to shell d. Carapace (upper shell) i. ribs , dermal bone, vertebrate (body axis NOT flexible) ii. Makes up animals back e. Plastron (lower shell) i. Animals stomach 2. LIMB GIRDLES DEEP IN RIBS a. Ribs deflect laterally as they develop b. Shoulder girdle is INSIDE ribs i. Human shoulder girdles are OUTSIDE ribs … you can reach around and feel them ii. Example of how a slight variation in growth can completely change shape c. Major different turtles vs other vertebrates 3. NO TEETH (keratin beak only) a. Found in snapping turtle Shell covering ❖ Keratinized scutes: ➢ Most species ➢ Overlap bony structures, adds strength (like bricks in a wall) ❖ Skin ➢ Three aquatic clades: ■ Carettochelyidae ■ Trionychidae ■ Dermochelyids (leatherback sea turtles) Shell Shape: Aquatic vs Terrestrial ❖ Carapace ➢ Aquatic species generally have flattened shells ■ Streamlined to reduce drag and cost of swimming ■ Coefficient of drag: = less drag ● River (fast flow) pop is lower drag than lake (slow flow) pop is ■ The lower number the lower drag ■ Streamline shape is more important than not having a round body making it harder to predators to eat you ➢ Terrestrial species generally have domed shells ■ Adaptation against predators (can’t get mouth around) ■ High domes may protect against predators ❖ Carapace II - reduced ossification ➢ African pancake tortoise ➢ Shell flat, soft, flexible ➢ Inhabits rocky outcrops ➢ Avoids predation by wedging itself into crevices and inflating its body and pushing with its limbs ❖ Plastron : box turtle ➢ Harder for predators to get inside shell ➢ Flap on shell covers opening Turtle locomotion ❖ Tortoises (terrestrial) ➢ Elephantine (club) feet, tiptoes with flat pad ❖ Freshwater turtles ➢ Forefoot paddle caries in degree of webbing ➢ Minimal webbing in foot in slider...more webbing in softshell turtle ❖ Sea turtles and carettochelys ➢ Forelimbs modified into flippers Aquatic locomotion ❖ Rowing swimmers ➢ All non-marine turtles ➢ alternating , anterior posterior L and R fore and hindlimb movements ➢ Propulsion via drag-based thrust ➢ Intermittent thrust : power stroke and recovery stroke ➢ Good for ACCELERATING and low speed maneuvering ➢ Carettochelys unique synchronous rowing ❖ Flapping swimmers ➢ Aquatic flight used by sea turtles ➢ Synchronous left and right forelimb movements ➢ Propulsion via LIFT BASED THRUST ➢ Continuous thrust: generate thrust on up and down stroke ➢ Good for long distance swimming, not good for maneuvering at low speeds or accelerating Feeding ❖ No teeth, keratin beak only ❖ Turtles can be carnivorous, herbivorous, or omnivorous ➢ Tortoises are herbivores ➢ Sea turtles and mostly carnivorous ❖ Most aquatic turtles can only feed in water ❖ Several specialized modes of feeding have evolved ❖ Soft shell - sit and wait predators ❖ Matamata - inflate its throat and increase suction - sucks in fish ❖ Alligator snapping turtle - wiggles worm looking tongue to try and draw fish into its mouth Circulation ❖ Heart structurally complex ➢ Completely divided atria ➢ Incompletely divided into hree-chamber ventricle ■ NOT SEPARATED THEY ARE ALL ONE VENTRICLE ■ Structure similar to lizards ❖ Amniote circulatory system with lungs ➢ Two circuits of blood flow ■ Systemic (to body) and pulmonary (to lungs) ■ Mammals and birds always have sequential blood flow ■ Turtles and lizards can shift blood between circuits shunt) ➢ Right to left intracardiac shunt eans that blood from pulmonary circuit is redirected into systemic circuit ■ Ie bi-passed lungs ➢ Intracardiac means that this shunt is in the heart ❖ Why divert deoxygenated blood from lungs to the systemic circuit? ➢ When holding breath, no reason to send blood to lungs (no 02 there) ➢ Still a little o2 in deox blood Respiration ❖ In amniotes, rib movement facilitates breathing ➢ Fusion of ribs to shell in turtles does not allow this ❖ How do turtles breathe? ➢ Lungs ■ Large and located at top of the shell ■ Attached to sheet of connective tissue ■ Muscular movements of limbs and girdles change body cavity volume ■ Abdominal muscles very important in breathing!!!!! ● Transverse abdominus (TA) - exhale ● Oblique abdominis (OA) - inhale ❖ Cloacal respiration ➢ Several species ➢ Outpockets from the cloaca lined with villi to increase SA ➢ Turtles rarely surface to breathe and swim with cloaca open ■ Pump water in and out at high rates Reproduction and Nesting ❖ Long lived 10-15 yrs to sexualy maturity ❖ Internal fertilization ❖ Plastron in terrestrial males is often concave ❖ Nesting behavior ➢ All lay eggs ➢ Clutch sizes range from 2-3 to over 100 eggs ❖ No parental care ➢ Females dig nests with hindlimbs and then leave ❖ Most females nest on DRY LAND ➢ Embryos die if they are below water level ❖ Some species shoe embryonic diapause ➢ Pause in devel until environmental trigger (temp, flood) Temp dependent sex determination (TSD) ❖ Sex determined by development temps ❖ Max temp is crucial ❖ Three types of TSD ➢ For turtles most common is 1a ➢ Low temp = males ➢ High temp = no males ❖ Prevalence of TSD ➢ 9 families are exclusively TSD ➢ Common in 2 additional families ❖ Effects of global warming Sea turtles - Hatching ❖ Imprinting ➢ Sea turtles imprint on their natal beach ❖ Simultaneous hatching of sea turtles ➢ Predator saturation ❖ Hatchlings are very small and seldom survive Orientation and navigation ❖ After hatching, sea turtles use three primary cues at different life stages ➢ Light and elevation gradient ❖ Waves ❖ Magnetic field ➢ Homing ability ❖
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