For centuries, circuses and sideshows have showcased animal oddities; some of these animals have been displayed while alive, and others have been preserved in some manner. These animals are sometimes described as “freaks of nature” or in other derogatory terms, and no matter what curious traits they display, they seem to attract human attention. Recently, a two-headed bull shark fetus discovered near the Florida Keys has been in the limelight. Let’s take a closer look.
One Shark with Two Heads
Not too long ago, a fisherman caught a pregnant female bull shark off the Florida Keys. When he cut the shark open, he discovered several living bull shark fetuses, including one with two heads. These young sharks were fully developed and were capable of living on their own, so they were released back into the water. The fisherman kept the two-headed bull shark, which was still alive while attached to its mother via the umbilical cord, but which died shortly after the cord was cut. Once onshore, the fisherman handed the two-headed shark over to researchers at Florida Keys Community College.
In many cases where an animal or human is born with extra limbs, shared organs, or even a shared body, the cause is conjoining. Researchers vary in their theories concerning what causes conjoining to occur; some believe incomplete egg division causes the phenomenon, while others believe that the twins simply fuse back together while in the womb. Connections are sometimes simple, with only small amounts of tissue joining two individuals, and they’re sometimes complicated, with individuals sharing vital organs. Conjoining in the human and animal world is extremely rare; even so, it happens more often than axial bifurcation.
In the case of the two-headed bull shark, the cause is believed to be axial bifurcation instead of conjoining. In axial bifurcation, an embryo begins to split into two and does so incompletely. In the end, what would have ended up to be a pair of identical twins (bull sharks, in this instance) ends up to be a single organism with two separate and fully functional heads.
The bull shark had five pairs of gill openings and gills, a single pair of nares, a single pair of eyes, and a well-developed mouth with normal dentition on each of its two heads. It is the second such shark to have been found in the region; the first was found in 2011 in the Gulf of Mexico.
Some are theorizing that contamination from the 2010 BP Deepwater Horizon oil spill has caused the pair of animal oddities to occur, but Dr. Michael Wagner, who is a researcher at Michigan State University, says that there is “no evidence to support this cause or any other,” and goes on to say that any connection between the spill and these two cases of axial bifurcation is “unwarranted.”
This is a very rare type of mutation, and it’s one that does occur all throughout the animal kingdom. There are only six recorded cases of axial bifurcation in sharks, but the phenomenon does occur with some regularity among reptiles and amphibians; for example, it’s fairly common for snakes and turtles to emerge from their egg sacs with more than one head.
No matter what the cause of its deformity, the little bull shark with two heads is being studied along with other specimens. Someday, it may help researchers better understand just how these and other birth defects happen – and that may in turn help humans and animals alike.