Scientists document first virgin birth in crocodile, revealing ancient reproductive ability

In 2018, a crocodile named Coquita laid a clutch of eggs at Parque Reptilandia, a zoo in Costa Rica where she had lived alone for sixteen years. When researchers shone a flashlight through the eggs to assess their viability—a routine practice with captive reptiles—they found something unexpected: one egg contained a fully formed crocodile fetus. Coquita had never been housed with a male. There was virtually no possibility of conventional mating. What the team had discovered, confirmed through DNA analysis and published in the journal Biology Letters in June 2023, was the first documented case of parthenogenesis in a crocodile—reproduction from an unfertilized egg, sometimes called a virgin birth.

Dr. Warren Booth, a researcher at Virginia Polytechnic Institute and State University, received a scale from the stillborn fetus and sequenced its DNA. The results showed a genetic match of 99.9 percent to Coquita's own genome, confirming that the offspring had developed without any male contribution. The fetus never hatched, but its existence proved something scientists had long suspected but never before documented in crocodiles: the species possessed an ancient reproductive capacity that required no partner.

Parthenogenesis is not new to science. Researchers have known for over a century that certain animals can produce offspring without fertilization. Pigeons were the first recorded case, though viable fetuses were not immediately identified. Since then, the phenomenon has turned up in snakes, birds, lizards, turtles, and sharks. What makes the crocodile case significant is not that parthenogenesis exists—it is that crocodiles, which diverged evolutionarily from birds millions of years ago, use the same cellular mechanism. Booth emphasized that such a complex biological process is unlikely to have evolved independently in separate lineages. The implication is striking: crocodiles and birds probably inherited this ability from a common ancestor far deeper in time. That ancestor, Booth suggested, was likely the dinosaurs.

The mechanics of parthenogenesis reveal why it remains impossible in humans and other mammals. Mammals rely on genomic imprinting, a system in which specific genes must be activated by the father and others by the mother for an embryo to form. Crocodiles have no sex chromosomes at all. In Coquita's case, the female offspring developed partly because of the temperature at which the egg was incubated. Scientists have created mice through parthenogenesis in laboratories, but only through extreme genetic manipulation—switching genes on and off with precision that nature does not perform on its own.

Animals born through parthenogenesis typically face biological disadvantages. They are, in Booth's phrase, "highly inbred individuals," carrying only the mother's genetic material and thus lacking the genetic diversity that sexual reproduction provides. Many are weak or ill. Yet not all fail to survive. Some reach adulthood and can themselves reproduce, either sexually or through additional rounds of parthenogenesis, though Booth noted that much of this research remains unpublished.

The discovery raises practical questions about how zoos and researchers should handle eggs from solitary females. The study recommends that eggs be assessed for viability even when males are absent, a departure from standard practice. Researchers had previously assumed such eggs were non-viable and discarded them. Of the fourteen eggs in Coquita's clutch, seven were deemed potentially viable through candling. Only one produced a fully formed fetus, but the principle holds: viable offspring can emerge from isolation.

Parthenogenesis likely occurs far more widely than current records suggest. Booth estimated that thousands of bird and reptile species probably possess the capability. The reason it remains largely undocumented in wild populations is simple: no one has been systematically looking for it. The technology to detect it—DNA sequencing—is relatively recent. Researchers are now beginning to mine the genes of wild animals to search for evidence of parthenogenetic reproduction in nature, a project that could reshape understanding of how these species maintain themselves in the absence of mates. Without access to dinosaur DNA, scientists will never definitively prove that the ancient reptiles possessed this ability, but the cellular machinery shared by crocodiles and birds suggests a lineage stretching back to the age of dinosaurs—a reproductive strategy that survived extinction and persists in the living world today.