Sea Turtles 101 | National Geographic

Scientific Concepts, Discoveries, and Nature Phenomena

Ancient Lineage / Evolutionary History

• Sea turtles have existed since the time of the dinosaurs.
• The earliest known marine turtle is Desmatochelys padillai (around 120 million years ago).
  • Approximately 6 feet long
  • Had modern-like features such as:
    • A carapace (top shell)
    • Paddle-like limbs

Diversity of Living Sea Turtles

• There are seven species of sea turtles alive today.
• The leatherback is the largest:
  • Up to ~8 feet long
  • Up to ~2,000 pounds
• It is noted as larger than what is known from fossils of its prehistoric ancestor (padillai, as referenced in the subtitles).

Reproduction and Early Survival

• Females can lay more than 150 eggs per clutch.
• The clutch helps hatchlings survive their earliest stages.
• After nesting, the female returns to the sea, leaving hatchlings to fend for themselves.
• Survival to adulthood is extremely low:
  • Fewer than 0.1% survive
  • (At least partly due to predators on the beach.)
• Emerging in large numbers increases the odds that some hatchlings survive.

Temperature-Dependent Sex Determination

• Sea turtle sex is determined by nest temperature, not sex chromosomes.
• Approximate temperature thresholds mentioned:
  • Warm (~88°F): most hatchlings become female
  • Cooler (<~82°F): most hatchlings become male

Navigation Using Earth’s Magnetic Field (Geomagnetism)

• Sea turtles use Earth’s magnetic fields for navigation—described as an “internal GPS.”
• Proposed mechanism:
  • Magnetite in the brain helps the turtle sense orientation toward Earth’s magnetic poles (compass-like function).
• Magnetic imprinting:
  • Hatchlings imprint on the unique magnetic signature of their natal beaches.
  • This creates a “magnetic map” that can help them return to the same beaches years later to nest again.

Conservation Status and Threats

• All seven sea turtle species are described as threatened with extinction.
• Reported causes of decline over roughly the past two centuries include:
  • Bycatch in fishing nets (accidental capture)
  • Illegal harvesting of turtle eggs
  • Trafficking of turtle products
  • Ocean pollution
• Suggested interventions and policies:
  • Reduce bycatch
  • Protect turtle habitats
  • Prohibit killing turtles and their eggs
• Overall claim: continued human intervention can help reverse declines.

Researchers / Sources Featured

• No specific researchers, institutions, or published sources are named in the provided subtitles.