Rare malformations can cause animals to grow two heads – and it seems that kind of thing has been happening for millions of years. In 2006, paleontologists in China described a two-headed fossil from the age of dinosaurs.
Hyphalosaurus is a small, aquatic reptile that lived more than 120 million years ago, and is known from thousands of fossils. But one special specimen sports two complete heads and necks.
“Starting from the level of the pectoral girdle, the vertebral column divides into two cervical series, forming two long necks that end in two skulls,” the researchers wrote in 2006.
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The fossil show a malformation called axial bifurcation, which can occur during development when an embryo begins to split into twins, but doesn’t complete the process. While rare, two-headed animals aren’t unheard of, with snakes, turtles, salamanders, sharks, and even deer found in recent years.
Sadly, two heads usually aren’t better than one – animals with axial bifurcation rarely survive to adulthood. That seems to be the case with the two-headed Hyphalosaurus, which is a mere 70 millimeters long and appears to be either an embryo or a newborn.
It is, however, the oldest-known example of the condition, dating back to the early Cretaceous.
The researchers describing the remains say that while faked fossils from the same area have been reported, this one seems to be legit: a fine coating of sediment still partially covers the bones, and the slab of stone they rest in is completely intact, with no cracks or signs of gluing.
Instead, this seems to be a remarkably lucky find. The number of fossils we find represent a tiny fraction of the lifeforms that existed in the distant past – so for a rare condition like this to be preserved is a statistical anomaly that would make both of your heads spin.
“This two-headed reptile seems to be unique in the fossil record,” the researchers concluded.
The research was published in 2006 in the journal Biology Letters.