A crocodile makes history with the first-ever virgin birth of its species, researchers say. But none of the 14 eggs hatched much to scientists' disappointment.

• Researchers said the 18-year-old crocodile who lived alone laid 14 eggs.
• In a paper published Wednesday, researchers said one egg held a stillborn fetus.
• Researchers said the fetus lacked paternal genes.

A crocodile at a zoo in Costa Rica made history with the first-ever virgin birth in the species, researchers say.

In a paper published in the Biology Letters journal on Wednesday, researchers said 14 eggs were found in an 18-year-old crocodile's enclosure in 2018.

The crocodile lived alone at an exhibit at Parque Reptilandia in Costa Rica, so the only possible answer for the eggs is what's called facultative parthenogenesis, aka asexual reproduction where an animal becomes pregnant on its own without ever mating.

Just like more traditional pregnancies, these so-called virgin births can come with complications. Researchers said only seven of the 14 eggs appeared to be fertile. None of them hatched, however, which the scientists said was "disappointing," LiveScience reported.

Instead of welcoming baby crocs, the researchers opened up the eggs to study them more closely.

One egg, in particular, contained "a fully formed non-viable fetus" that was stillborn, the researchers reported.

DNA from the fetus and the 18-year-old crocodile matched, researchers said, adding that the fetus lacked paternal genes. In other words, this solidifies the researcher's virgin birth hypothesis.

"The offspring was found to have identical genotypes to the mother at greater than 99.9% of her homozygous loci, demonstrating a lack of paternal alleles," the researchers said in the paper.

Warren Booth, an entomologist at Virginia Tech University, told The BBC that virgin births are common in animals that descend from dinosaurs.

''We see it in sharks, birds, snakes, and lizards, and it is remarkably common and widespread," he added.

He told The BBC that there likely hadn't been a recorded virgin birth among crocodiles before this because most people weren't specifically looking for it.

"Your average reptile keeper doesn't keep a crocodile," Warren told The BBC.