A two-headed bull shark fetus Wagner, et. al, Journal of Fish Biology, 2013

The photo above is of a two-headed bull shark. The first ever found. Creepy right?

Actually, it's pretty cool. The find was just published in the Journal of Fish Biology. A fisherman found the fetus in the Gulf of Mexico, off the coast of Florida in April 2011. It has two well-developed heads, the researchers discovered after putting it through an X-ray.

This anomaly is called dicephalia. These are conjoined twin sharks — it's genetically one shark that has grown two heads. When the shark was discovered, it was still alive in its mother, with several other live fetuses.

From the paper, it seems like the fisherman sacrificed the mother and removed the baby sharks, finding this two-headed one. The report says that it quickly died when the umbilical cord was cut. Its siblings survived and were released into the wild.

This two-headed trait has been found in other shark species, including the dogfish shark, ilk shark, and blue shark, among others. This is the first time they've found it in the Bull Shark though.

The mutation could have been caused by environmental pollution, the authors note in the paper:

This latter explanation is tempting given the increasing number of reports of anatomical and physiological deformities in fishes exposed to pollution emitted from the Deepwater Horizon oil spill that took place from 20 April until 15 July 2010.

Assigning the observation of a single deformed specimen to that cause, especially when considering the presence of additional foetuses in the mother with apparently normal anatomy was noted by the fisherman, however, is not warranted by any information developed here.

Here's what the X-rays look like: