Marine Reptiles: Part 2, Sea turtles Marine Vertebrates: Lecture 5

Origins and Evolution Turtles distinct from other reptiles  No “intermediate” fossils between turtles and other reptiles. Why not? “Intermediates” did not fossilize well Evolution occurred in large leaps –Change in 1-2 HOX genes sufficient to create “shell”?

Archelon 200 mya 15 feet 6000 pounds Crushing jaws Perhaps fed on shelled cephalo- pods & clams?

Modern sea turtles Dermochelydae: leatherback turtles Cheloniidae: Six other species  Green  Hawksbill  Kemp’s Ridley  Olive Ridley  Loggerhead  Flatback

Carapace: dorsal shell (Cheloniidae) Photos: Genny Anderson Development: Ribs expand & fuse to vertebral column Bones covered by scutes (keratin)

Plastron: ventral shell (Cheloniidae) Bones form beneath skin  From neural crest cells Unique to turtles  No homologous bones in other vertebrates

Leatherback carapace Photo: seaturtles.org Lattice of thin bony plates (dermal bones) connected by soft cartilage. Covered by a leathery skin  Dolphin-like texture Bony keels  Streamlining

Beak variations (handout)  Green: serrated shredding plants  Hawksbill:pointed Breaking off sponges  Loggerhead, Olive and Kemp’s ridley: large and thick Feed on Molluscs and Arthropods  Leatherback: sharp points Grab/slice jellyfish Skull, beak, bones of limbs

Thermal physiology Ectotherms  But have mechanisms to retain heat generated by swimming Countercurrent exchange Size (low surface/volume) Thick shell Cold stunning  What is this?  Which turtles are most at risk? Basking  Description  Alternate functions (in addition to thermoregulation)

Osmotic regulation Papillae  Location  Function Salt glands  Modified tear glands How saline are excretions?  Enlarged in hatchlings. Why? Kidney Leatherback papillae; Photo: NOAA

Diving Capability  Least adapted?  Best-adapted? Depth record Duration Anatomical and physiological adaptations  Lungs and air passages  Carapace  Heart rate/metabolic rate Senses  Vision  Hearing  Smell  Magnetic sense

Sex determination and sex ratios How is sex determined? Effect of climate change   females Are there too few males?  Leatherback studies Percentage of clutches with >1 father Fertility Male-male competition Resolving the paradox…

Focus: Leatherbacks Diving adaptations  Carapace  Thermoregulation Low S/V ratio Countercurrent heat exchange –Also prevents overheating in tropics Fat layer  Low metabolic rate Photo: Doug Perrin

Focus: Leatherbacks Leatherbacks as record holders in  Size  Speed  Distance  Growth rate (how?) Habitat Feeding Diving Photo: Doug Perrin

Focus: Leatherbacks Status/threats  Critically endangered  Primary causes of decline: Egg harvest Killing of adults Caught in drift nets  Pacific leather- backs most critical Photo: Doug Perrin

Focus: Green sea turtles Found worldwide tropics & subtropics Found as far north as MA Subpopulation, Pacific coast, central S. America, sometimes considered “black sea turtle” Slowest-growing Females return to natal nests Photo: J. Hoover

Focus: Green sea turtles Feeding  Adults: sea grasses and algae  Juveniles: small invertebrates and algae Temperature regulation  Basking  Conserve heat generated by swimming: raise temperature to 14  F above ambient  Hibernation in subtropical lagoons (winter) Burrow into mud Greatly lower metabolic rate Gas exchange primarily through skin and cloaca Cooler water holds more oxygen than warm water Status and major threats  Endangered  Key threats: egg poaching, killing for food

Focus: Hawksbill sea turtles Worldwide distribution in tropical and some subtropical seas. Once a colonial nester, now more often seen nesting alone  Example: In the Seychelles, , 50-75% of nesting females were killed  Faithful to natal breeding grounds Photo: Karen Haberman

Focus: Hawksbill sea turtles Feeding  Primarily on sponges (~95% of diet)  toxic meat  Major impact on the reef community. How? Status: Critically endangered  Less than 10% of the population of a century ago, 0.5% of original population  Main source for tortoiseshell jewelry and other trinkets Photo: Karen Haberman

Focus: Kemp’s Ridley The most endangered Limited to Gulf Coast Mass nesting: arribadas One major site known (Northern MX)  Discovered by Andres Herrera, 1947 Key threats: egg poaching, shrimping Conservation  Beach protection  Reduction of shrimping  TEDs!  Head Start for turtles Photo: Gladys Porter Zoo