Storytellersunplugged

FORENSICS 112: OUCHES, LARGE AND SMALL

(Part 2)

There were no words to describe the dry heat. The sky was cloudless, and air above the parched earth shimmered under a merciless Sun. The remains of a river lay in but a few shallow pools. Local animals were forced to share what little was left, and many did not take kindly to such foreign behavior. As water gradually disappeared, dead bodies began to litter the area. Still-living animals fed on the dead and smaller live animals. Eventually, the large animals were forced to eat each other, even others of their own species. The last one finally died, and its bones joined others scattered about the dried pool.

When I mentioned that there were no words to describe the dry heat, I meant it literally. The scene took place on the island of Madagascar some 65 million years ago, and there weren’t many humans around back then to voice any words. The last animal to die was a majungasaurus. It would have been at least 26 feet long, weighed 2400 pounds, and been the apex predator on the island. Fossilized bones of it and others like it bore tooth marks that had been engraved as flesh was torn from the bones and devoured. Some tooth marks on majungasaurus bones were identified as being made by teeth belonging to other animals of the same species, which indicated that they had cannibalized each other. That is an interesting fact, but many other creatures - including lions, tigers, bears, chimpanzees, hamsters, squirrels, birds, spiders, rats and bats - eat members of their own species, even members of their own families. The relevance of the dinosaur business to forensics has to do with the fact that bite marks - even those found on fossilized bones - can be matched to those of animals that did the biting.

The field of studying bite marks possibly connected to a crime is known as forensic odontology. Human teeth are usually not thought of as being weapons, but their marks have been found on a surprising number of physical assault victims. As a matter of fact, they appear, as defense wounds, on a fair number of attackers as well. Bite marks have been found on nearly every location on a human body. Females are most often bitten on breasts and legs during sexual attacks, and men suffer bites most often on arms and shoulders. Defensive wounds most often appear on arms and hands.

Beginning from the front center and proceeding rearward along one side, adult human teeth include a central incisor, a lateral incisor, a cuspid (commonly referred to as a canine), two bicuspids (premolars), two molars and sometimes a third molar (commonly referred to as a wisdom tooth). Upper teeth form what is known as a maxillary arch, or arcade; and lower teeth form what is known as a mandibular arch, or arcade. Bites can result in a wide range of wounds including bruises, scrapes, cuts, lacerations and avulsives. An avulsive bite is one that tears away flesh. A previously mentioned majungasaurus could easily inflict many such bites on a large scale, and a person can also, but on a somewhat smaller scale. Bite marks can be ring shaped or be formed like a pair of spaced-apart, U-shaped arches. Bite mark characteristics fall into two basic categories, namely, class characteristics and individual characteristics. Class characteristics identify the group sharing them, such as humans, animals, fish, etc. For example, a bite mark having four relatively linear or rectangular contusions (bruises) is a class characteristic of human incisors.

Individual characteristics identify individual variations; and there are two types, namely, arch characteristics and dental characteristics. Arch characteristics refer to the arrangement of teeth within a bite mark. These might include a combination of misaligned or rotated teeth or of separated teeth that could distinguish one individual from another. Dental characteristics refer to features, such as uncommon wear, chips or fractures, of individual teeth.

Even when teeth are not used to bite another person, bite marks can provide important forensic information. Chewing gum or food such as cheese, apples, melons and, of course, Janet’s favorite, chocolate, left at a crime scene can preserve dental impressions from which casts can be made. The casts can then duplicate at least portions of the teeth that made the impressions and can be compared to casts made of a suspect’s teeth. Depending on the condition of a bite mark on flesh, an impression might be taken of it also. A cast could then be made that would capture not only the bite mark but also a victim’s body contours.

Teeth can be long, short, narrow, wide, thick, thin, buck, spaced and crooked. Incisors tend to create rectangular wounds, and cuspids (often referred to as canines), triangular wounds. Individual arrangements of teeth owe much to their eruption sequence (teeth do not erupt

simultaneously) of anterior (front) and posterior (back) teeth. Cuspids (canines) have to wedge themselves into a dental arch between teeth that erupted before them, and this often causes displacement and rotation of adjoining teeth. Incisors are the teeth that are most affected by crowding.

During their existence, teeth can be subject to what are referred to as accidental or individual traits including congenital malformations, rotations, fractures and, of course, wear. All the foregoing factors contribute to creating bite marks that are relatively unique. Just how unique is still being debated. Some progress has been made in standardizing comparison procedures, but determinations often depend on an expert’s experience and judgment.

There are pitfalls in depending exclusively on bite-mark evidence for convictions. In 1991, a Phoenix cocktail waitress was found dead, the victim of eleven stab wounds, a bite on her breast made through a tank top and another bite on her neck. There was very little evidence, but an Arizona State dental expert testified that bite marks on the victim’s breast matched the teeth of one Ray Krone, who soon became known as the “snaggletooth killer.” Krone was sentenced to death and spent several years on death row. In a subsequent retrial, he was sentenced to life imprisonment. After spending a decade in jail, Krone was released when a DNA test proved that saliva from the victim’s tank top did not match his. DNA not only cleared Krone but implicated another man already serving a term in prison for attempted child abuse.

Especially with surviving victims, but also with dead victims, the sharpness of bite mark evidence, and its forensic value, gradually decreases over time. It is thus important to record the evidence as soon as possible. Photographing a bite mark preserves a visual image that, if done properly, can be later compared to other dental evidence. A reference scale, such as a ruler, is placed next to, and in the same plane as, the mark so that accurate measurements of mark details can be made. A camera is positioned with its lens pointed at right angles to the plane of the mark to avoid perspective distortion. Even when great care is taken, a comparative analysis is not an easy task due to the fact that skin is curved, is easily distorted and is often undergoing edema (swelling). Illuminating a wound site with different colored lights often brings out details not evident when exposed to normal light. In fact, finding a faint bite mark can be greatly facilitated by using an ultraviolet light. A bite wound is accompanied by saliva, and human saliva glows brightly in ultraviolet light. A variety of photographic filters are also sometimes used to enhance photographs.

It sounds obvious, but an investigator must make certain a wound being analyzed is actually a bite mark. Forceful contacts with certain circular or elliptical objects, or even some burns, can appear to be bite marks. A lack of class characteristics such as the rectangular and triangular wounds made by individual teeth as mentioned previously will, however, disqualify them. An investigator must also be careful to check an individual’s teeth if there exists a possibility that a bite might have been self-inflicted.

Since biting and sucking deposit saliva on skin, DNA is often retrievable from a bite or suction wound. A simple procedure involves using a first cotton swab to wash the area contacted by tongue and lips with sterile distilled water. A second, dry swab is then used to collect moisture left by the first swab. Both swabs are air dried at room temperature for at least 45 minutes and are then placed in a sterile paper evidence envelope or box that will allow some air circulation. They are not to be sealed in plastic bags or containers. (I seem to recall seeing TV crime scene investigators plunking swabs into what appeared to be small plastic bottles.) The swabs should be kept at room temperature if they are to be submitted for analysis within six hours or refrigerated if they are to be stored for a longer period. A sample of a victim’s blood or tissue is also usually taken for DNA comparison with that from the swabs.

Extra facts:

Male teeth are usually somewhat larger than female teeth, but the difference is usually insufficient to guarantee accurate sex identification from them or their bite marks.

Human bites are more likely to become infected than are animal bites. Errol Flynn wrote that a neglected wound he had received when he punched someone in the mouth almost resulted in a loss of his hand.

Cannibalizing animals are not only common, they can also be impatient. Some can’t even wait until they’re born. Sand tiger sharks have two uteruses, and their embryos develop teeth. Only the largest embryo in each will survive to be born. Guess what happens to the smaller ones.