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 14F 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,1980-1982, 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