I don't know why, but a couple of years ago the urge to collect fossil shark teeth hit me like a ton of matrix. I went out on long, tiring excursions and brought back dozens of the shiny pearls-of-the-sand. Dozens grew to hundreds, and hundreds grew to thousands. I was collecting teeth at a much faster rate than I could identify them, and had many more than could be identified by using pictures in books. I even had known species that didn't look like their depicted counterparts. My feeling was that of a person who collects chess pieces without knowledge of the game.

The problem with trying to identify shark teeth is that their form varies according to position in the jaw. Consider the Carcharhinus egertoni Agassiz, 1843, upper and lower teeth, or the Hemipristis serra Agassiz, 1843, upper lateral and lower anterior teeth (fig. 1). These four teeth have been assigned to four separate species in the past. I recently visited a state survey where a lower anterior H. serra tooth was on display as an Odontaspid because it was slender, pointy and had a pair of distinct cusplets. Some sharks have about a dozen differently shaped teeth in their mouths. Multiply the variety of shapes times the number of species and you have something reminiscent of the number of possible moves in a chess game.

Here's where the game begins. The object is to build rows of teeth with similar characteristics until you can isolate a species and identify the mouth position of each tooth. Sound impossible? It is! But the knowledge you gain while having fun will make your assessments ever more accurate, and in some cases you will be right-on.

The requirements are simple: tweezers, some large foam pads, a few display mounts and all of your best specimens. The foam pads should be large enough to hold lots of teeth, and stiff enough to be carried and stacked like trays; which allows you to put them on a shelf somewhere when you're not in the mood. I use ten 15"x9"x1" soft foam-rubber pads. The teeth you use should be in good condition ( the worn and broken ones will only fool and frustrate you), and reliably associated with the same locality, or matrix. When you isolate a species, arrange the tooth groups in a display mount for future reference.

The rules of the game are a bit more complex but can be learned quickly. There are certain traits that are common in most shark teeth relative to their position. Lower teeth tend to be narrower and often more sigmoidal in profile than their upper counterparts. Anterior teeth are sometimes narrower and more inflated while lateral teeth are blade-like and triangular. The cusps of most teeth appear to lean away from the center of the jaw, thereby establishing left-right orientation. The outside (labial) surface is usually flat in contrast to the more inflated and diagnostic inner (lingual) surface. These and many more rules will guide your placement of teeth in like rows, and groups of rows into complete tooth sets. Of course, as with most rules, there are exceptions; like the dreaded backward tooth.

One of the most interesting teeth in the mouth of many Lamniform sharks is the last upper anterior position, away from the center of the jaw. This is the backward tooth (fig. 2, third from left). Before you discover its true position, it will drive you crazy. No matter where you place it in your tooth rows, rules are broken. Put it with the teeth that lean away from the center and the root is backward (this happens in both upper and lower jaws). Orient the root with all of the other roots and the cusp curves the wrong way. The reason this tooth is so weird is the tip of the cusp actually curves toward the center of the jaw, unlike any other tooth position. When you get to know this backward tooth, you will always know its position as the last upper anterior before the intermediates or laterals.

The very books that fall short of identifying every shark tooth, contain a wealth of clues to the rules of tooth position. Drawings are usually labeled as upper, lower, left, right, anterior, lateral, etc., and often depict subtle characteristics common to a species. Drawings of one or two teeth may be all you need to correctly deduce the placement of others. As you get better at working with tooth rows, you will understand why authors need only certain teeth in their drawings to help identify a whole mouthful of differently shaped teeth.

Cheating in the game of chess with ancient sharks is absolutely legal; it takes the form of studying recent shark jaws. If you study the jaw of a recent Carcharias taurus Rafinesque, 1810 (sand shark) for a while, or an Isurus oxyrinchus Rafinesque, 1809 (mako shark), you will be able to make sense of most of the teeth you have collected. Studying natural dentitions of extracted teeth from recent sharks is the best method.

The game itself is played until you have successfully isolated and arranged all of the good teeth you have collected for a certain species (which gives you the victory), or a specific population of teeth has baffled you into submission (victory going to the shark). As you play, the subtle characteristics which determine species will soon unfold. You may have a large row of similar teeth that exhibit the same form and shape, but the cusplets are consistently different on several. These should be placed in a new row. When you start noticing the same differences on other forms of teeth, and organize them likewise, you are hot on the trail of a separate species.

Variation within a species is one of the shark's best strategies for frustrating your efforts. Even after you have isolated a species and deduced the mouth position of every single tooth with reasonable certainty, you will notice a great deal of cusp variation. Cusps tend to vary more than roots. For any given tooth position you will have teeth that are a bit narrower, or less striated, or a subtly different shape than others. Identifying shark teeth by means of the cusp will have you moving small teeth endlessly from one species to another. Put your trust in the root.

When the roots are in good condition, they exhibit remarkable consistency, regardless of tooth size. They hold most of the clues to species and position. In fig.2, the angle between the root lobes increases as the anterior teeth get further from the center of the jaw. Root characteristics offer the quickest and most consistent way to determine position, especially for anterior teeth. H. serra lower anterior teeth would never have been confused with sand sharks were they identified by the root.

In the final analysis you will want to give your isolated species a name. Do not fall prey to the confusion of taxonomy. Genus assignments have been, and continue to be, volleyed about like beach balls. Use your most recent publications.

The use of tooth characteristics to identify species and dental formulae is certainly not new. It has been suggested for many years. However, the process of building artificial tooth sets seems to be overlooked by a great many who collect for a hobby. Perhaps the shark's best strategies for making the amateur forfeit the game of chess with fossil teeth, are the vast number and variety of teeth to be found. But, thanks to bilateral symmetry, once you understand half of your collection, the other half will fall into place.