Scientists have documented the first known case of a "virgin birth" of a crocodile, which had been living in isolation in a zoo in Costa Rica for 16 years, according to a study published Wednesday.

The female American crocodile laid 14 eggs in 2018 inside her enclosure, a phenomenon not uncommon among captive reptiles. However, the most puzzling fact came after three months of incubation, when it was discovered that one of the eggs contained a fully formed baby crocodile that had been stillborn.

The scientists analyzed the genetic makeup of the crocodile fetus, according to the study published in the journal Biology Letters. They found DNA sequences that showed it was the result of facultative parthenogenesis (PF), or reproduction without the genetic contribution of males.

The phenomenon of FP, which some scientists have referred to by the abbreviation "virgin birth," has also been documented in other species of fish, birds, lizards and snakes. According to scientists, this is the first known example in a crocodile.

In FP, a female's egg can develop into a baby without being fertilized by a male's sperm.

To make an egg, a precursor cell divides into four cells: one becomes the egg and retains key cellular structures and the gelatinous cytoplasm, while the others contain additional genetic material.

Then, one of those cells essentially acts as a sperm and fuses with the egg to become "fertilized."

The American crocodile is considered vulnerable and endangered in the wild. According to one hypothesis, FP may be more common among species on the brink of extinction, the study notes.

Scientists say Costa Rica's "virgin birth" could bring new information about the ancestors of crocodiles that walked the Earth in the Triassic Period, about 250 million years ago.

"This discovery offers a tantalizing insight into the possible reproductive capabilities of extinct archosaur relatives of crocodiles and birds, particularly members of Pterosauria and Dinosauria," the study notes.

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