Elephant's sixth toe

Researcher Re-Discover Elephant’s Long-Lost Sixth Toe

London’s Royal Veterinary College has recently re-corrected a long-standing error in elephant anatomy. According to a study recently published in the science journal RVC elephants have a sixth toe, a previously unknown and underrated digit that is critical in helping the enormous mammals ambulate.


Ironically, when the first detailed study of an elephant cadaver was carried out over 300 years ago by the Scottish physician Patrick Blair, he wrote in his notes that the massive pachyderm had six toes. But subsequent studies ‘corrected’ Dr. Blair’s observations, noting that the supposed ‘sixth toe’ was actually a prepollex, or a cartilaginous rod, not a bone.

However, some three centuries later the Royal Veterinary College has vindicated Blair’s original assessment, stating that the dubious prepollex is, in fact, an elongated bone just like those used to secure tendons in other mammals.

In massive mammals like elephants, these typically small structures known as ‘predigits’ take on elephantine proportions and are almost as large as their true toes.

In the case of the elephant’s sixth toe, what has so long thrown experts in animal anatomy for loop is the bizarre development of the structure.

Professor John R. Hutchinson who led the research team at Royal Veterinary College explained that these curious sixth digits first begin developing as cartilaginous rods–just like those described by most previous studies–but that they eventually transform into bone later in the elephant’s adult life.

Other mammals are known to have analogous anatomical structures which usually serve significant evolutionary functions. The giant panda, for instance, is known to have an extra thumb which helps it grab bamboo branches, and moles also have small finger-like appendages that have been adapted to help them dig.

Professor Hutchinson’s team was initially perplexed as to the function of the extra elephant digit–than is until they did a scan of the pachyderm’s huge feet and realized that the sixth toe is critical in helping the enormous mammals to balance their weight, which can be up to 20,000 lbs. in some species.

The researchers explained that the toe helps to redistribute some of the weight from the animal’s foot into its leg bone and ankle joints. The team examined the fossil record as well and believes that the toe evolved around 40 million years ago, when the elephant’s ancestors began growing larger and spending less time in the water.

“As far as we know, elephants are the only animals to use enlarged sesamoid bones in this new supportive role,” a spokesperson from the RVC told the Daily Mail Online.

“Other large land mammals have lost them and correspondingly never developed a large fatty foot pad or other features unique to elephant feet.”

http://www.redorbit.com/news/science/1112445753/researcher-re-discover-elephant%e2%80%99s-long-lost-sixth-toe/