Two-Headed Animals: Dicephalia From Sharks to People

by Lucy Hagger

In 2011, fishermen caught an adult bull shark in the Gulf of Mexico. The adult was pregnant, and they soon realised that one of the foetuses was a lot more interesting than first thought.

The foetus had developed normally in all aspects, except that it had two heads. This bizarre phenomenon is known as dicephalia, and is when a single fertilised egg develops into a foetus with two heads. Dicephalia is something that occurs across nature and we humans generally refer to it as conjoined twins.

So the idea of a two headed animal is not hugely novel, however, the occurrence of this phenomenon in chondrichthyes (cartilaginous fish) like sharks, rays and skates is very rare.

C. Wagner and his team from Michigan State University managed to get hold of this truly unique shark and tried to understand the mechanisms of development that caused this two-headed marine animal. They released a paper this week that discusses the finding of this unusual shark and delves deeper into the interesting science behind the development of dicephalia.

The two-headed foetus was not the alone in the womb, with other normal foetuses having been found. The foetuses had developed enough that they were severed from their umbilical cords and released back into the wild. The two-headed foetus died soon after it was severed from the mother and was preserved in 70% ethanol to enable the research on this unique creature.

Other Examples of Dicephalia

This finding got me delving into other dicephalic creatures that have been found, so I thought I’d share some of the cases with you. I find it all really interesting except some of the science behind it is pretty complex, so if you do end up looking into it I wouldn’t get too bogged down in all the detail.

This is Abigail and Brittany Hensel, these are the most well known human dicephalic twins. Each twin has its own set of main organs (heart, liver, lungs etc.) but can only control one half of their body. So each twin has control over one leg and one arm. This meant that learning movements that required coordination between both halves was very difficult as it requires cooperation. This meant that walking, running clapping etc were highly difficult things to master.

This two-headed albino Honduran milk snake is an example of dicephalia in reptiles. Other two-headed snakes have been known to live up to 20 years in captivity. However, in the wild it is likely that survival is reduced due to the difficulty that comes with two heads controlling one body.

Another two-headed reptile; but this time a baby tortoise. Apparently this individual shows little difficulty in carrying out normal functioning and just goes about its daily business like any other tortoise.

 

An example of dicephalia in felines. This pair are from Massachusetts and are called Frank and Louie. They hold the world record for the longest living two-headed cat. Seems a pretty niche category.. but I swear most world records these days are a bit ridiculous.

 

Hope you enjoyed looking at some of the world’s weird and wonderful creatures, even if they do have more heads than normal.

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