The hatchling weighed 5.2 grams, about as much as a nickel, when staff from Mass Audubon’s Wellfleet Bay Wildlife Sanctuary found it at a protected nesting site in Wellfleet, Massachusetts. It was a diamondback terrapin, Malaclemys terrapin, with one shell and two heads. On September 17 it was delivered to the Cape Wildlife Center in Barnstable.
Zak Mertz, CEO of New England Wildlife Centers, which runs the clinic, put the odds in local terms: the animal is the third two-headed terrapin the team has treated in the past five years.
An embryo that split and did not finish
The condition is called bicephaly. Mertz described its origin to Smithsonian Magazine as an embryo that begins to split, as it would for twins, “but doesn’t separate fully.” The result is conjoined twins sharing a single body, each head able to bite, look and decide on its own.
Live Science reports that Mertz also pointed to a mix of genetic and epigenetic factors, and listed features of the species that might contribute: a long lifespan, strong fidelity to a nesting beach, small gene pools and the conditions an egg experiences during incubation. None of these has been tested in this clutch, and the clinic has not said which, if any, applies.
A left head with opinions
The team at the Cape Wildlife Center says the hatchling swam and ate normally on arrival. Lead veterinary technician Robyn Rohm saw the left head biting the day the turtle came in, and Mertz noted that the left head seems to have more personality than the right.
The prognosis for such animals is guarded, and the clinic has described no outcome yet beyond close monitoring. Research cited by Live Science says two-headed turtles can struggle with coordinated movement, feeding and other functions essential for survival, and a hatchling this small has little margin for error. Veterinarians plan CT scans and X-rays once it has grown enough to image clearly, which should show how much of the anatomy is shared and how much is duplicated. If the turtle gains strength, release to the wild is on the table; if not, it will remain in captivity, and in the meantime the clinic is tracking its appetite and behavior day by day.
Two earlier cases and a protected beach
This is not the first such hatchling in the Cape’s terrapin work. In 2021, a conjoined terrapin with two heads, six legs and two spines hatched at a head-start nesting site in Barnstable. Reptiles Magazine reported that the Cape Wildlife Center saw the pair eating, swimming and gaining weight daily after more than two weeks of care, and that the animal seemed to coordinate its two halves to move and surface for air. The clinic’s own words at the time were measured: animals with this condition do not always survive long or live well, it said, though that pair had given the staff reason for optimism. That earlier pair was reported to have separate digestive systems and two spines, a degree of duplication that the 2026 hatchling’s planned scans are meant to map. IFLScience quotes the clinic as saying it has now seen only two other bicephalic cases in the last five years, which keeps this one an especially rare case for the team.
Mass Audubon’s record of its 2024 season describes an earlier two-headed hatchling as “one of only a few ever discovered” in the sanctuary’s nearly five-decade history. Wellfleet Bay has run the terrapin nest protection program since 2005, and its 2024 season set a record: more than 200 nests on sanctuary property alone, 82% egg survival in protected nests, and 4,810 hatchlings released with the help of over 125 volunteers working twice-daily shifts at nine locations.
Diamondback terrapins are listed as threatened under Massachusetts law, and Live Science notes that a federal review is pending. Mass Audubon lists predation, habitat loss, vehicle strikes and sea level rise as pressures on the nesting beaches, which is why volunteers check protected nests twice a day. Adult terrapins are small turtles, five to eleven inches across the shell by IFLScience’s description, and they can live up to 40 years in the wild, so a single clutch that survives to hatch is the start of a very long investment for a threatened population. The Wellfleet sanctuary’s 2024 tally of 4,810 released hatchlings shows the scale of that investment, and it frames how unusual it is for any one of them to carry a developmental error visible to the naked eye.
Against 4,810 ordinary hatchlings in a single record season, one with two heads and a 5.2-gram body is statistically a rounding error. In Barnstable, it is a patient whose scans have yet to be taken.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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