No. It is a myth.
As reported by blog.sfgate.com, No type of dog has been found to have a mechanism that enables them to “lock” their top and bottom jaws together. When addressing pit bulls specifically, researcher I. Lehr Brisbin, Ph.D. from the University of Georgia says,
“The few studies that have been conducted of the structure of the skulls, mandibles and teeth of pit bulls show that, in proportion to their size, their jaw structure and thus its inferred functional morphology, is no different than that of any breed of dog. There is absolutely no evidence for the existence of any kind of ‘locking mechanism’ unique to the structure of the jaw or teeth of the American Pit Bull Terrier.”
On the question of measuring the overall “biting power” of different breeds, Dr. Brisbin says,
“To the best of our knowledge, there are no published scientific studies that would allow any meaningful comparison to be made of the biting power of various breeds of dogs. There are, moreover, compelling technical reasons why such data describing biting power in terms of ‘pounds per square inch’ can never be collected in a meaningful way. All figures describing biting power in such terms can be traced to either unfounded rumor or, in some cases, to newspaper articles with no foundation in factual data.”
So, in the absence of measurable evidence, where did the locking-jaw rumor originate? One theory suggests that it came from a specific behavior encouraged by humans. Bulldogs and American Staffordshire Terriers were often bred to compete in the now-banned blood sport of “bull baiting.”
It was considered a prized skill for a dog to possess the tenacity and stubbornness to bite down and hold on to the opponent’s face and head at all costs.
Tip! The English Bulldog was originally bred to work with bulls but is now a popular and well-loved pet. Learn more with English Bulldog facts & images on petMD.