Virgin Birth Is a First for This Species

A crocodile has for the first time been found capable of a virgin birth—a finding that suggests the species' dinosaur cousins were capable of the same feat. An 18-year-old female crocodile who'd been isolated from other crocodiles since the age of 2 laid 14 eggs at a Costa Rican zoo in January 2018, the BBC reports. That in itself wasn't so unusual. Isolated crocodiles have been known to lay clutches of eggs, though they're normally assumed to be nonviable and discarded. These eggs were incubated at Parque Reptilandia near Dominical, however, then opened once they failed to hatch within three months, per Live Science. Inside one was a fully formed, though nonviable fetus.

Experts in virgin births, or parthenogenesis, at Virginia Tech found the fetus was more than 99.9% genetically identical to its mother, which confirmed self-reproduction, as described Wednesday in Biology Letters. Parthenogenesis has previously been reported in lizards, snakes, birds, and elasmobranch fish, including sharks. Though this is a first for a crocodilia—an order including crocodiles, alligators, caimans, and gharials—researchers describe "an astounding growth in the documentation of vertebrate facultative parthenogenesis," or the growth of embryos from unfertilized eggs, in recent decades due in part to "awareness of the phenomenon itself and advances in molecular genetics/genomics and bioinformatics."

As parthenogenesis has now been recorded among birds and crocodilians, the only living archosaurs, researchers speculate that other archosaurs, including dinosaurs and pterosaurs, had the same reproductive capabilities, inherited from a common ancestor. Without DNA, however, "we'll never be able to prove they could do it," Virginia Tech entomologist Warren Booth tells the New York Times. The research also indicates crocodile eggs "should be assessed for potential viability when males are absent," the researchers write, adding that examples of facultative parthenogenesis among female crocs who live with males are likely to be "overlooked without genomic testing." (More crocodile stories.)