What 425 Million Years of Evolution Has Done to the Penis

The oldest penis on record goes back 425 million years. It belonged to a crustacean found preserved under ancient volcanic ash at the bottom of a sea that used to cover Herefordshire, in England. The paleontologists who found the shrimp-like creature named it Colymbosathon ecplecticos, from the Greek for “astounding swimmer with a large penis.” Before it was found, the oldest known phallus was 400 million years old. It belonged to a fossilized daddy longlegs from Scotland.

When dinosaurs roamed the ur-continent of Pangaea about 200 million years later, their penises roamed with them. Paleontologists have speculated about dinosaurs’ mating apparatuses and behaviors, using what they know of crocodilians and birds, today’s relatives of those prehistoric creatures. The erect penis of a male titanosaur, for example, may have been 12 feet in length. Experts speculate that the male sauropod, with a body the length of a school bus, approached the massive, receptive female from behind. Like his crocodilian and avian descendants, he likely inserted his penis from this dorsal position and, at climax, ejaculated sperm through a vessel running along the outside of his organ.

Nowadays, Earth’s penises exist in multivaried splendor. Spiny anteaters sport four-headed varieties that rotate between copulations. Although most birds don’t have penises, the phalluses of Argentine lake ducks are nearly eight inches long (almost as long as an ostrich’s), corkscrew-shaped, and festooned with dense, brushy spines that sharpen to hard spikes at the base. Despite a 33-inch member and a penis-to-body ratio of seven to one, Limax redii, a Swiss slug, doesn’t have the most impressive proportions in nature. That title goes to Balanus glandula, which wows the tide pool with its prodigious barnacle penis. Permanently cemented to a tidal rock, the barnacle sports a penis 40 times the size of its body. Barnacle penises, as long as they are, vary in their girth. Barnacles living in rougher waters sport thicker, stronger and sturdier members. But those in calmer surroundings extend their longer filamentous penises in search of distant barnacle “vaginas.”

Fleas and some worms also have hugely proportioned penises. And some animals have more than one. Several species of marine flatworms have dozens of penises. Some snakes and lizards are doubly endowed; switching between their two hemipenes during multiple copulations increases their sperm count by a factor of five. As for insects, so exuberantly inventive are their male genitalia that entomologists scrutinize them to classify entire species.