Crocodile Virgin Birth Discovery Suggests Dinosaurs Could Do the Same

Scientists have documented the first “virgin birth” in a crocodilian—and the discovery suggests that dinosaurs may have also had this unusual ability.

In a study published in the Royal Society journal Biology Letters, researchers describe a case of “facultative parthenogenesis” in an American crocodile.

This is the ability of sexually reproducing species to sometimes produce offspring asexually.

“Facultative parthenogenesis is the production of offspring without the genetic contribution of a mate—sometimes referred to as virgin birth,” Warren Booth, an author of the study with Virginia Polytechnic Institute and State University, told Newsweek.

“The offspring produced are not clones of the mother, but essentially half clones.”

An American crocodile in Costa Rica
Stock image: An American crocodile with its mouth open in Costa Rica. Scientists have documented the first crocodilian “virgin birth” in an American crocodile.

The unusual mode of reproduction has been documented in multiple species of birds, lizards, snakes, and fishes in the elasmobranch group, which includes sharks, skates and rays.

But questions have long persisted regarding the occurrence of “virgin birth” outside of these animals—particularly the crocodilian group, which includes crocodiles, alligators and gharials.

In the study, Booth and colleagues provide the first evidence of facultative parthenogenesis in crocodilians.

The researchers describe a case that occurred at a reptile park in Costa Rica called Parque Reptilandia, which at that time was owned by a co-author on the paper—Quetzal Dwyer.

Dwyer found a female crocodile that had been isolated from a male for 18 years aggressively guarding a nest in her enclosure.

He excavated the nest, assuming the crocodile would be infertile, but found a dozen eggs. The eggs were incubated and after they failed to hatch, researchers opened them and in one found a fully-formed but dead fetus.

Subsequently, scientists sequenced the entire genome of the mother and the fetus, finding that they were genotypically identical. They also determined that paternal genes were absent, which the researchers had predicted due to the 18 years of separation from a possible mate.

The findings of the study have “significant” implications for our understanding of reproduction in crocodilians and related animals, Booth said.

Crocodiles are part of an evolutionary lineage known as the archosaurs. These start with crocodiles and end with the most recent ancestors, birds. In between these, but now extinct, are the dinosaurs and pterosaurs. Just prior to this group are the reptiles—snakes and lizards.

“The mechanism across snakes, many lizards, and birds, is the exact same mechanism that we have found here in crocodiles,” Booth said. “As such, this is not likely to be a trait that has evolved independently in each lineage but is instead a trait ancestral to these lineages.

“What this also tells us, is that as crocodiles and birds use the same mechanism, their extinct relatives—dinosaurs and pterosaurs—are also likely to have been capable of parthenogenetic production. The idea that life finds a way—as in Jurassic Park—is not science fiction at all.”

While the crocodile, in this case, was stillborn, this does not mean it would be in all cases, according to Booth.

“We have numerous records in birds, snakes, and lizards, that record parthenogens being born, and surviving. As such, with this new record, we are just starting to scratch the surface in understanding the long-term ecological and evolutionary significance of this trait,” Booth said.

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