Like other reptiles and mammals, tuatara embryos start budding male genitalia — but then lose it
A rare reptile is shedding light on the evolution of the penis — even though it doesn’t have one.
The tuatara, a lizardlike species in New Zealand, never grows a real phallus. Yet as an embryo, it starts forming tiny nubbins like those that turn into the great diversity of sperm-delivery organs in other mammals and reptiles, researchers at the University of Florida in Gainesville report October 28 in Biology Letters. Tuatara phallus development then stalls, but that initial burst of development supports the scenario that the phallus evolved just once in mammals and reptiles, says study coauthor Thomas Sanger.