Sea Turtle Bicephaly

Blog Post By: Ashlyn, Sea Turtle Intern
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Before you ask—no, I wasn’t scheduled for dawn patrol that morning. And by that morning, I think you know that I am talking about the morning that a hatchling loggerhead sea turtle with two heads was discovered here at Edisto Beach State Park. Ask the rest of the turtle team—Leah, Chase, or Karoline—who were all on patrol that morning, about their firsthand account. All I know is that my alarm clock that early morning was a stream of text messages of pictures of this turtle marvel, rather than my typical ringing sound.

At first glance of those pictures that flooded my message inbox that morning, my mind sparked with curiosity at this turtle anomaly. How often does the presence of two heads in a single individual occur? Is this common among reptile hatchlings?

The head is one of the most complex structures of the body, derived from three primary dermal layers and specialized neural crest cells. The development of the head region of the body during embryogenesis is quite complex, involving hundreds of genes interacting to regulation the proliferation, migration, and differentiation of cells. Within all of these regulatory processes, there is susceptibility to dysregulation, as is to be suspected.

In fact, the highest reported mutations in green, loggerhead and, olive ridley sea turtles are craniofacial malformations. The development of brain, cranium, and facial region are interconnected and complex, as the signaling pathways during development have extremely complex regulators and growth factors.

Among marine reptiles, sea turtles in particular have a history of reported bicephaly, or the presence of two heads in a single individual. Bicephaly is an umbrella term, describing developmental alterations such as the duplication of head structures, incomplete splitting of zygotes (conjoined twins), or terminal bifucation of the notochord while neurulation is taking place. Research suggests that sea turtles with this condition have an extremely short life expectancy, only hours or days. The rarity of observing this phenomenon has limited our scientific understanding of potential causes of the presence of two heads. It is believed, however, that a combination of genetic, environmental, and developmental causes may all play a role.

More research regarding bicephaly in reptiles has been focused on snakes, as the most reported malformation in wild and captive snakes is indeed the presence of two heads. While still a relatively new direction in the field, preliminary research suggests incubation temperatures, inbreeding depression, hybridization, chemical toxins, and environmental pollution all are associated with snake bicephaly.

​In short, no—no I did not witness the two headed turtle that has been circulating the news this week firsthand. But yes—yes I did marvel and research and marvel yet again at the wonderful anomaly that crawled on our beach.