Not only are they beautiful reptiles, sea turtles overcame hardships of the transition from life on land to life in sea. The sea turtle’s oldest ancestor, Archelon, dates from as far back as 100 million years ago and survived until 66 million years ago1, when it fell alongside most of the remaining during the Late Cretaceous-Tertiary extinction event thought to have been caused by a meteor strike. The Archelon top shell, or carapace, is massive, extending to 3.5 meters in length in fossilized samples. In comparison, 3.5 meters equals the height of two stacked refrigerators and or twice the height of Michael Jordan of Chicago Bulls basketball renown. The largest living sea turtle species, the leatherback turtle (Dermochelys coriacea) average 1.5 meters in length2,3, is less than half the size of its 3.5 meter long ancestor. The photo below shows the difference in size of Archelon to a human7.
Just as human generations change with time, sea turtles follow suit. Sea turtles have unique body parts that allow them to be a recondite species of the sea. Get your swim caps on if you want to face a sea turtle in a swimming race. Sea turtle forelimbs, or flippers, have paddle-like shapes to efficiently push water back and swim rapidly4. Green sea turtles (Chelonia mydas) can swim up to 2.3 kilometers per hour and the leatherback clocks in at 9.3 kph. In contrast, the average human swims at a rate of 5.9 kph5. Furthermore, sea turtle flippers have bones that reflect their ancestors, called vestigial structures, which resemble finger bones of humans6. The photo below shows the unique bone structure hidden in the sea turtle flipper.
Not only do sea turtles have specialized flippers with secret hand bones inside, they have a hydrodynamic shell to allow them to better glide in ocean currents. The top, dorsal shell of a sea turtle is called a carapace and the bottom, ventral shell is called a plastron4. The sea turtle is attached to its body and cannot retract its limbs in and out like many terrestrial turtles and tortoises. The shell is covered in scutes, hard bony plates made of keratin, the same protein in hair, nails, and animal hooves. The unique designs of sea turtle scutes, as seen in the photo below in the critically endangered Hawksbill turtle (Eretmochelys imbricate) are caused from distinctive melanin pigments8, 9.
Sea turtles are amazing creatures. We have keratin in our fingernails and hair; sea turtles have it on their shells! They have hand bones just like us! From Archelon to present day sea turtles, these reptiles have overcome extensive anatomical adaptations to survive in the sea. Stay tuned for the next article that delves into more unique adaptations of sea turtles!
- Archelon. (2016). Encyclopedia Britannica. Retrieved from http://www.britannica.com/animal/Archelon
- National Geographic. “Leatherback Sea Turtles.” National Geographic. National Geographic, 2016. Web. 20 June 2016.
- Sea Turtle Conservancy. “Sea Turtle Tracking: Caribbean Leatherback Tracking & Conservation Project.” Sea Turtle Conservancy. Sea Turtle Conservancy, 2016. Web. 20 June 2016.
- Sea World. “Sea Turtles Adaptations for an Aquatic Environment.” Sea World. Sea World, 2016. Web. 20 June 2016.
- Livestrong. “The Speed of Human Swimming.” LIVESTRONG.COM. LIVESTRONG.COM, 18 Dec. 2013. Web. 20 June 2016.
- Wyneken, Jeanette, PhD. “The Anatomy of Sea Turtles.” 2016. 20 June 2016.
- “The Largest Species of Prehistoric Turtle Weighed Two Tons.” 2016. Web. 20 June 2016.
- “Leatherbacks.” SEE Turtles. 2016. 20 June 2016.
- “Anatomy of the Turtle’s Shell.” Anatomy of the Turtle’s Shell. Web. 20 June 2016.