text and illustrations by Rick Martin
White Shark Bite Forensics - a Photo Essay
Photo showing the undersurface of the decoy with the embedded tooth re-inserted in the same puncture from whence we originally believed it came. The white objects bristling from the puncture wounds are tie wraps. I inserted one of these at the deepest point in each puncture to measure its depth and distance from neighboring punctures. It also helped reveal the bite rather dramatically.
Rick Allen came up with the idea of using multiple tie wraps to measure all tooth punctures simultaneously. In his his honor, we jokingly named this technique the Allen Dental Depth Index or ADDI (which, it just so happens, is a documentary film-maker's award - so the acronym has a double significance for its inventor).
Notice that there is an 'extra' puncture, immediately to the left of the embedded tooth. Did the shark re-purchase its upper jaws "to get a better grip", or is this due to the loose embedded tooth 'wiggling' somewhat before it was lost? That the surrounding teeth do not show similar multiple punctures leads me to suspect the latter.
Even if we did not know the exact position of the tooth by its location among the upper jaw tooth puncture marks, it is a fairly straight-forward matter to identify the position of origin of an isolated White Shark tooth. My colleague Ralph Collier of the Shark Research Committee - who has studied White Shark teeth and tooth impressions in intimate detail for several decades - kindly and generously taught me some of the fundamentals.
Consider the White Shark jaws at left. These are the infamous "Port Fairy" jaws at the British Museum of Natural History (formerly thought to be from a 36.5-foot [11.1-metre] specimen, a figure which is now known to be erroneous), digitally altered to replace a missing and a broken upper tooth. Notice that, in White Sharks, the upper jaw teeth are strongly differentiated by size and shape. Starting from the symphasis (center) of the jaw and proceeding toward the jaw corners, there are two almost symmetrical "anteriors" (Curiously, in White Sharks, it is the second - rather than the first - upper anterior that is the largest tooth.), a smaller tooth with a sinusoidal (shaped like a 'stretched-out' S) cross-section and a reversed orientation (pointing toward the mid-line of the jaw rather than the jaw corners) called an "intermediate"*, then four or five larger teeth that are increasingly slanted toward the jaw corners called "laterals", followed by five or six much smaller "posteriors". With the exception of those of the 'backward-mounted' intermediate teeth, the longest cutting edge in White Shark tooth blades occurs on the side facing the jaw corners. Also, as an additional clue, the more gracile ('slender') of the two root lobes is oriented toward the symphasis of the jaw.
Since the flattened surface of the tooth blade is the labial or outer surface of the tooth, one can quickly determine that the embedded tooth came from the right side of the lower jaw (the photo of the rear of the embedded tooth shows us how the tooth would be oriented looking forward from inside the shark's jaws - and it is the shark's left or right side that matters here, not our own left or right as we face the shark). The near-symmetry of the embedded tooth tells us that its position in the jaw must have been close to the symphysis, since the blades of White Shark teeth become increasingly 'slanted' toward the jaw corners the farther they develop from the symphysis. To put this another way, the embedded tooth is far too symmetrical to be a lateral or a posterior and lacks the sinusoidal cross-section that characterizes an intermediate tooth. Since the embedded tooth is not quite symmetrical enough to be a first anterior, it must - by process of elimination - be a second anterior. Thus, the embedded tooth removed from our seal decoy was almost certainly an lower, second anterior tooth from an approximately 11-foot (3.4-metre) -long White Shark.
* = There is currently some controversy about the use of the term "intermediate" to describe the reduced third tooth on either side of the upper jaw of the White Sharks and most other lamnoids. For the details, Click Here. To return to the Port Fairy jaws text, Click Here.
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