Rare two-headed baby turtle has been discovered at a protected nesting site in Wellfleet, Massachusetts, giving wildlife specialists an unusual opportunity to study a developmental condition rarely seen in diamondback terrapins.
The tiny hatchling was found last month by representatives of Mass Audubon’s Wellfleet Bay Wildlife Sanctuary. It has two fully formed heads attached to a single body and weighs just 0.18 ounces, about the weight of a nickel. On September 17, the turtle was transferred to the Cape Wildlife Center in Barnstable, where veterinarians are monitoring its condition.
The animal was born with bicephaly, a rare developmental abnormality that occurs when an embryo that would normally develop into identical twins does not completely separate. The result is an animal with two heads sharing one body.
For the Cape Wildlife Center, the discovery is unusual even though staff have encountered the condition before. The center said it had recorded only two other cases of bicephalic diamondback terrapins during the previous five years.
“While we’ve encountered this unusual condition before, every case gives us another opportunity to learn more about these fascinating animals’ anatomy and physiology,” the center said. Veterinarians are currently watching the hatchling’s appetite, growth and behaviour closely as they try to determine how well it can cope with its unusual anatomy.
The challenges can be considerable. Research has found that two-headed turtles may have abnormalities involving the skull, face and spine and can be smaller than typical hatchlings. Having two heads connected to one body can also affect basic functions such as feeding and movement, potentially making survival more difficult.
A 2021 study of two-headed and partially duplicated sea turtles documented some of the physical difficulties associated with these developmental abnormalities. Such cases are rare, however, which means every surviving animal can provide researchers with additional information about how these conditions develop.
Scientists believe bicephaly can have more than one cause. Zak Mertz, chief executive of New England Wildlife Centers, which includes the Cape Wildlife Center, said existing research points to a combination of genetic and epigenetic factors.
He said the biology of diamondback terrapins could also play a role. The turtles can live for many years and often return to the same nesting areas, while their conservation status can limit genetic diversity within some populations.
Environmental conditions during development may also be involved. Mertz said factors such as temperature and humidity during incubation, the physical characteristics of nesting sites and environmental exposure affecting the parents could potentially influence how an embryo develops.
The discovery is not the first example of bicephaly in wildlife. Two-headed animals have been documented in several species, including a two-headed porpoise found off the coast of the Netherlands and a double-headed dolphin discovered on a beach in Turkey. Such findings are extremely unusual and can offer scientists a closer look at developmental abnormalities that are difficult to study in the wild.
The diamondback terrapin itself is a species adapted to a distinctive coastal environment. It lives in brackish marshes along the Atlantic and Gulf coasts of the United States, where freshwater and seawater mix. In Massachusetts, the species is protected under the state’s Endangered Species Act and is classified as threatened.
That conservation status gives the unusual hatchling added significance. While one two-headed turtle cannot provide a complete picture of the health of a population, studying its development could help researchers better understand the factors that affect terrapin reproduction and development.
For now, the focus remains on the individual animal. Veterinarians at the Cape Wildlife Center are tracking its feeding, growth and behaviour while assessing whether it can survive with its condition. Its extremely small size and unusual anatomy make its development difficult to predict, so careful observation will be important.
Mertz said the case could ultimately contribute to a broader understanding of bicephaly and the factors that cause it. The center’s team will continue caring for the hatchling while recording what it can learn from the animal’s development.
“It is fascinating and an area that certainly merits more study,” Mertz said. “We are excited to care for these two and learn as much as we can to inform future study in the process.”
