Lungfishes and Ancestral Tetrapods

1. Lungfishes and Ancestral Tetrapods Lecture 8a Take your time, I can do this all day.

2. SuperclassGnathostomata Class Placodermi Class Chondrichthyes Class Sarcopterygii Subclass Elasmobranchii Subclass Holocephali SublassDipnoi Lungfish Placoderms Coelacanth Rays Sharks Chimaeras Tetrapods

3. Subclass Dipnoi: Lungfishes • Originated ~400 mya • Common until ~225 mya • Most were marine • Six extant species

4. Subclass Dipnoi: Lungfishes • Originally classified as amphibians • “The lungfishes have singularly embarrassed taxonomists!” – Duvernoy 1846 • Have paired lungs—obligate air breathers • Extend ventrally off pharynx • Extend most of body length • Composed of many air sacs • Gills are reduced structures • Naso-pharyngeal connection Why would a fish need to evolve air breathing?

5. Subclass Dipnoi: Lungfishes • Estivation—up to 4 years (usually ~7 months) • Fills chamber with mucus  forms cocoon • Metabolism slows • Convert ammonia  urea

6. Subclass Dipnoi: Lungfishes

7. The Transition to Land • Tiktaalik—biggest fossil discovery in decades • Findings published in 2006 • Fossils from 380 mya, 12 million years before first tetrapod (amphibian) fossils • Found in alluvial deposits

8. The Transition to Land • Shared common ancestor with lungfishes • Lobed fins with rays • Loss of dorsal/anal fins • Transition pectoral skeleton • Up to 9 feet long • No bony operculum • Mobile neck • Functioning wrist joint • Primitive digits

9. Lecture 8b Marine Reptiles

10. Sea Turtle—life cycle

11. Sea turtle anatomy • Carapace—fused to backbone • Fused-bony scutes • Keratin coating • Ventral plastron • Limbs modified  flippers • No true teeth—keratin beak

12. Evolutionary history Originated 120 mya • Evolved from more terrestrial form Five major lineages existed—three went extinct 65 mya Seven living species Leatherbacks diverged >100 mya

13. Diversity & Diet • Carapace covered by leathery skin • Thousands of tiny bones beneath • Jellyfish diet—dive up to 4,000 ft. • Weigh up to 2,000 lbs. Leatherback • Average adult weight—300 lbs. • 2nd largest • Adults nearshore—herbivorous • Mostly south of Carolinas Green • Average adult weight—250 lbs. • Adults nearshore—carnivorous • Bigger head/jaws • Migrate up east coast Loggerhead

14. Osmoregulation • Keratin in skin (scales)—water tight • Salt gained when feeding • Papillae— • Muscular esophagus— • Kidneys have no water re-absorption ability • Tear gland modified into salt gland • Urine consists of NH3 and urea

15. What are some issues a deep diving sea turtle faces? What adaptations might sea turtles possess to equip them for deep diving?

16. Diving & Breathing • Only spend 5% of time at surface • Dive duration—20 to 50 minutes • Basking— • Surface interval < 5 sec. • High tidal volume of lungs— • Up to 10x other reptiles • Large airways—networked • Breathing is active • Body muscles ventilate lungs http://www.youtube.com/watch?v=8nmmYAtmag0

17. Diving & Breathing—leatherbacks • Dive > 5x the depth of other species • Flexible plastron • > 50% of O2 is stored in blood & tissue • Much higher concentration of blood cells • Other species store most O2 in lungs • Dive duration shorter

18. Evolution of the heart

19. Can sea turtles get the bends? • The bends—N2 under pressure dissolves into blood • Comes out of solution during rapid ascent • Sea turtle lungs collapse at depth • Compressed air restricted to fortified airways • non-respiratory surfaces • Pulmonary artery constricts • Blood flow to lungs restricted Reptiles have 3-chambered heart with incomplete partition

20. Reproduction Age at maturity varies by species • 15 to 40 years • Max lifespan 50 to 80 years • Females do not reproduce annually • 2-3 year intervals • Replenish fat • Males more often Aging sea turtles

21. Reproduction—Mating behavior • Males are aggressive with females • Also bite each other • May remain coupled > 1 hour • Males well endowed—bifurcated penis • Females mate with multiple males • Sperm stored

22. Reproduction—Nesting • Foraging & mating/nesting typically in different locations • Most species nest in Florida or Caribbean • Loggerheads more widespread • Nesting occurs during warmer half of year • 1 to 2 hours • Females nest innatal region • Advantage? Arribadas!

23. Reproduction—Nesting Females produce multiple clutches in a breeding year • Leatherbacks—6 times; Kemp’s Ridley—2 times • Resting interval 10 to 30 days • Number and size of eggs varies by species • Leatherback—80 eggs, 75 g each • Hawksbill—130 eggs, 25 g each • Eggs hatch after 45 to 75 days • Depends on species and temperature

24. Reproduction—Hatching • Clutch hatches together • Early evening—cooler & tougher for predators • “Hatchling Frenzy”— • Hatchlings orient towards brightness • In coastal water orient into waves • Offshore use magnetic orientation

25. Migration • Populations have common nesting grounds • Foraging areas differ • Population mixing on foraging grounds Loggerheads

26. Migration • International cooperation important for sea turtle recovery Leatherbacks

27. Threats to sea turtles Low reproductive output & low offspring survival Natural mortality Fisheries bycatch

28. Threats to sea turtles Legal harvesting Poor nesting areas Poaching Boat strikes Tortoiseshell