Bit Wear, Horseback Riding and the Botai Site in Kazakstan

17 Pages·1.883 MB·English

by  Brown D., Anthony D.

Journal of Archaeological Science (1998) 25, 331-347
Bit Wear, Horseback Riding and the Botai Site in Kazakstan
Dorcas Brown and David Anthony
Anthropology Department, Hartwick College, Oneonta, NY 13820, U.S.A.
(.Received 18 February 1997, revised manuscript accepted 22 May 1997)
Bit wear is the damage that occurs on the occlusal surfaces of the second premolar teeth when a horse chews the
bit. Bit wear can provide evidence of horseback riding and/or horse draught from teeth found in archaeological
sites. This article revises our earlier definition of bit wear and describes wear on an expanded study collection of
modern bitted and feral horses (72 individuals). An experiment is described in which previously unbitted horses were
ridden with organic bits to simulate the wear made by pre-metallic bits. Because the evaluation of bit wear depends
partially on the age of the horse, a crown-height/age curve for horse lower second premolars is presented. Finally, horse
premolars from the archaeological site of Botai in Kazakstan are evaluated using the new definition of bit wear and are
found to provide evidence for horseback riding in northern Kazakstan between 3400 and 2700 вс.
© 1998 Academic Press Limited
Keywords: TRANSPORT, MICRO-WEAR, HORSEBACK RIDING, DENTAL CROWN HEIGHTS,
ARCHAEOZOOLOGY, KAZAKSTAN.
Introduction bit unobtrusively. Their bad habits, however well
concealed from their riders and owners, are clearly
The study of bit wear on horse teeth is important
revealed by a microscopic examination of their teeth.
principally because it can provide a clear
In 1989 and 1991 Anthony & Brown presented a
answer to a crucial question: were the horses
definition of bit wear and described its occurrence on
whose teeth are recovered from archaeological sites
equid P2s recovered from two archaeological sites:
used as transport animals? Bit wear is the damage that
Malyan in Iran, dated to 2000-1900 вс (Anthony &
occurs on the occlusal (chewing) surfaces of the second
Brown, 1989); and Dereivka in Ukraine, dated to
premolar teeth (P2s), particularly the lower second
4200-3700 вс (Anthony & Brown, 1991; Anthony,
premolars (P2s), when a horse chews the bit. Use of a
Telegin & Brown, 1991; Anthony, 1994). The bit wear
bit indicates control from behind the horse; therefore, a
at Malyan is the earliest unambiguous evidence for
bitted horse must have been either ridden or driven.
the use of the bit in the Near East, although copper
Bokonyi (1972) was the first to suggest bit wear as
stains on donkey teeth from Akkadian Tell Brak
a likely cause for the anomalous bevelling that he
(Clutton-Brock & Davies, 1993) might suggest earlier
recognized on the mesial corner of some Iron Age
bitting. The bit wear at Dereivka is the earliest evidence
horse P2s. Clutton-Brock (1974) observed similar wear
for the use of the horse as a transport animal anywhere
on the P2s of a horse mandible excavated from the
in the world.
Egyptian fortress of Buhen, dated c. 1675 вс. Azzaroli
Our definition of bit wear was based on a study of
(1980: 287) noted the same type of wear on the teeth of
natural (occlusal and dietary) wear on the lower
Iron Age Venetic and Etruscan horses. However, none
premolar teeth of 20 modern feral horses, and of wear
of these authorities could be certain that a bit had
from metal bits on the teeth of 10 modern domestic
caused the wear that they noted. Moreover, like most
horses. Recently we have gathered information from
writers on horsemanship then and now, they thought
42 additional modern domestic horses, bringing the
that bit wear could occur only if a horse was bridled
domestic sample size up to 52 individuals. In addition,
with a badly fitted bit; otherwise the bit should not
we have conducted riding experiments on previously
come into contact with the teeth. Bit wear was
unbitted horses with bits made of rope, leather, and
therefore seen as a symptom of poor management
bone in an effort to define the wear made by organic
that should occur rarely among bitted horses. As we
bits. The data from this larger and more diverse
demonstrate below, bit wear is, on the contrary,
collection of horse teeth has persuaded us to revise the
quite common: over 90% of the frequently bitted
definition of bit wear. In this paper we describe
modern horses that we have examined exhibited bit
how bit wear has been redefined; we then apply
wear. Even well-bridled horses apparently chew the
the revised definition to horse teeth recovered from the
Correspondence to: D. Anthony. E-mail: [email protected]. archaeological site of Botai in Kazakstan.
331
0305^403/98/040331 + 17 $25.00/0/as970242 © 1998 Academic Press Limited
332 D. Brown and D. Anthony
Figure 1. A properly placed bit.
The Modern Comparative Sample with polyvinyl siloxane, a high-resolution moulding
compound. Casts were made from the moulds with
We have examined 97 permanent and deciduous
Tapox. an epoxy resin. Moulds were easily made on
mandibular P2s from 52 modern domestic horses of 10
dry teeth from autopsy laboratories and museums. For
breeds. We were able to obtain detailed riding and
the live horses at the Cobleskill campus of the State
bitting histories (riding frequency, date of last riding
University of New York, the making of moulds
episode, type of bit) for 17 of these horses. We assume
required a protocol that overcame the problems raised
that most of the other 35 domestic horses were bitted
by head motion, tongue action, and saliva. We worked
at least occasionally, because most of them were
with lightly sedated horses that were still able to stand.
identified in autopsy or institutional reports as having
Upper premolars were not studied partly because it
been used in ways that require a bit (racing, harness
proved impossible to make casts of upper teeth on
racing, draught, hunting, dressage, jumping, etc.).
live animals unless they were fully sedated and lying
Our collection of modern feral horse teeth consists of
down, which would have been dangerous to their
37 permanent and deciduous P2s from 20 modern feral
health.
horses. Two populations are represented: four indi­
viduals were Assateague Island ponies from the
Atlantic barrier islands of the Virginia and Maryland
The Definition of Bit Wear
coast, and 16 were mustangs from the Nevada Plains.
These horses were never ridden or bitted. In addition, A bit normally rests on a horse’s tongue and gums in
we examined the P2s of four live domesticated horses the diastema between the molars and the incisors, a
that had never been bitted; these animals were used location called the “bars” of the mouth (Figure 1).
in a riding experiment with organic bits, described When the reins are pulled the bit presses into this
below. When first examined, their teeth did not differ sensitive soft tissue on the mandible, causing the
significantly from those of the feral horses. horse to turn its head or tuck its chin to alleviate
Most of the P2s examined in this project were casts, pressure. Horses can use their tongues to lift the bit off
or replicas. Moulds of the original P2s were made their gums and push it back into the grip of their
Bit Wear Damage 333
step-fracture”. Second, fracture features often cluster
in the centre of the enamel ridges and propagate
longitudinally, creating microscopic linear trenches up
to 1 mm deep that run down the centre of the occlusal
enamel in a worn area. We have called these features
“centre-origin spalls”. Centre-origin spalls can weaken
the enamel sufficiently so that a large chip may break
off laterally. Together, these types of microscopic wear
(abraded step fractures and, centre-origin spalls) are
referred to as “a” wear in this paper.
The “a” wear caused by a horse chewing the bit
generally will not be confused with taphonomic, or
post-mortem fractures and abrasions on the tooth
surface caused either by nature or by clumsy curators.
Taphonomic features are distinctive in three ways: they
are not focused exclusively on the paraconid cusp of
the P2, the step-fractures are not abraded and there
Figure 2. Plan of occlusal surface of right side P2. are no centre-origin spalls. “A” wear does occur
sporadically on feral horse teeth, which is potentially a
second premolars (P2s), where it can no longer cause more serious problem. In the wild it is probably caused
discomfort. The position of the bit between the pre­ by irregular occlusal contact or by biting on stones.
molar teeth'was documented by Clayton & Lee (1984; The “a” wear that we observed on domesticated horse
Clayton, 1985) in fluoroscopic X-ray photographs that teeth, however, was much more extensive than that
showed the action of a bit in living horses’ mouths. observed on the teeth of feral horses.
They established that both bar bits and jointed or Quantitative evidence supporting this conclusion
“broken” bits can be gripped in the P2 teeth. came from scanning electron micrographs of the
It is difficult for a horse to push a bit back into its occlusal surface of the paraconid cusps of six feral P2s
teeth because the corners of the lips are positioned and 10 domestic P2s. These micrographs were enlarged
forward of the premolars. The bit must be gripped very and placed on a digitizing pad. The occlusal enamel
firmly to prevent the cheek corners from pulling it was outlined and its area measured. “A” wear features
forward onto the bars of the mouth, and the bit can be were outlined and their total area was measured in
held only between the tips of the teeth. Very powerful the same manner. Among the feral horses, “a” wear
pressures are loaded onto a small occlusal space on the covered an average of 6-7% of the occlusal enamel on
P2s. Bit wear occurs on the occlusal surfaces of the P2s the paraconid cusp, while for the domestic horses, “a”
because the bit slips across these surfaces as the horse wear covered an average of 66-7% of the occlusal
grasps and releases the bit. In most cases, bit wear is enamel on the paraconid cusp—it was 10 times more
confined to the first or paraconid cusp of the P2. extensive (Table 1). For feral horses, the maximum
Occasionally it extends as far back as the second extent of “a” wear observed on the paraconid cusp was
(metaconid) or even third (metastylid) cusps (Figure 2). 30%, and this was observed on only one of the six teeth
Bit wear is indicated by both microscopic and examined. In contrast, eight of the 10 domestic teeth
macroscopic traits. exhibited “a” wear over more than 58% of the occlusal
enamel of the first cusp. Finally, most of the “a” wear
in feral horses occurred on the buccal or cheek side of
Microscopic bit wear—“a” wear the paraconid cusp. This trait was observed on many of
The occlusal surface of a horse premolar consists of the other feral P2s in our collection. The cheek side
enamel ridges that rise above a softer core of dentine. of the lower tooth row naturally bears most of the
The enamel ridges, which bear the brunt of all wear, damage associated with occlusion, and this buccal-side
form a series of cusps. The microscopic aspect of bit contact probably accounts for much of the “a” wear
wear consists of abraded fractures on the occlusal on mandibular feral horse teeth. Only one feral horse
enamel of the paraconid cusp. Under magnification P2 displayed “a” wear on the lingual side. Among
(12-15 x is sufficient) microscopic wear has two bitted horses, “a” wear occurred on both the lingual
characteristics (Figure 3(a) & (b)). First, bit wear and buccal sides.
causes step-like fractures that reflect the underlying It is the location and intensity of “a” wear that is
linear alignment of the crystal rods composing the diagnostic of bit wear. If “a” wear is observed on 50%
enamel. The tops of the rods, normally worn to an even or more of the occlusal enamel of the paraconid cusp,
plane by occlusion with-the opposing tooth, are broken including the lingual side of the cusp, and similar
unevenly by the bit. The sharp edges of the broken rods abrasion does not occur, or occurs only sporadically,
are then abraded by the action of the bit and by dietary on other parts of the tooth, bit wear is indicated. This
wear, producing a pattern we have called an “abraded pattern of wear is called “significant ‘a’ wear”.
334 D. Brown and D. Anthony
Figure 3. (a) Bit worn P2 of 10-year-old race horse, (b) Unworn P2 of mature feral horse.
Macroscopic bit wear—bevelling bit slipping back and forth over the mesial edge, or
The macroscopic aspect of bit wear is a bevelled wear prow, of the P2. The worn area can take the shape of a
facet on the mesial (anterior) corner of the occlusal real facet, with a well-defined, angular bevel, or it can
surface of the P2. The facet appears to be caused by the have a gradual slope, without a sharp change in angle.
Bit Wear Damage 335
Table 1. Digitized analysis of “a" wear on P2 teeth Table 2. Bevel measurement statistics for feral and domestic horses
Specimen number “A”’ wear (%) Sample size of
horses over
3 years old Average bevel Range Median bevel SD
Feral horses
4R 0
7R 2 Feral horses
17L 3 25 teeth
18L 0 13 horses
28L 5 2 populations 0-78 0-2 0-5 0-66
28R 30
Average “a” wear on feral horse teeth = 6-67% Domestic horses
Median “a” wear is between 2% and 3%. (includes known frequently bitted horses)
73 teeth
Domestic horses
47 horses
12R 80
13R 86 10 breeds 3-11 0-10 2-5 1-93
14R 69
45R 85 Ail measurements are in mm.
45L 58
50R 95
57R 8 are then used to measure the distance between the
61R 4
63R 100 bottom of the ruler and the point on the tooth at which
66L 82 the occlusal surface meets the mesial edge. This
Average “a” wear on domestic horse teeth = 66-70% measurement is rounded to the nearest 0-5jnm.
Median “a” wear is between 80% and 82%.
In our study collection, bevel measurements for
mature domestic horses (mean 3-11 mm) were consist­
ently and significantly larger than those for mature
The depth of the wear facet is measured by placing a feral horses (mean 0-78 mm), and bevel measurements
ruler across the top of the 2nd and 3rd lingual cusps so for mature horses that were known to have been bitted
that the ruler forms a right angle with the lingual side almost daily (mean 3-6 mm) were larger than those for
of the tooth (Figure 4). The ruler serves as a plane, other domestic horses (Table 2 and Figures 5 & 6). The
oriented in one dimension by the crests of the 2nd and mean bevel measurement for mature domesticated
3rd lingual cusps and in the other by a perpendicular horses (З-11 mm) exceeded the maximum measurement
angle with the lingual surface of the tooth. Calipers observed for mature feral horses (2 mm). (Immature
Figure 4. Method of measuring bevel.
336 D. Brown and D. Anthony
suggests that either significant ‘a” wear or a significant
bevel measurement on a horse older than 3 years is
diagnostic of bit wear.
Bit Wear on Frequently Ridden Horses
We were able to collect detailed histories about bitting
practices and frequency of usage for 17 horses. Of
these, 13 animals were bitted and ridden or driven
regularly, two to five times per week, up to the time of
death or the day the tooth mould was made. We
examined 24 P2s from these 13 horses. All 24 teeth
were expected to exhibit bit wear—a significant bevel,
significant “a” wear, or both.
Table 3 shows the incidence of bit wear on these 13
animals. Only one horse had no wear on either the
right or left side P2. This 13-year-old quarterhorse
mare was bitted and ridden several times a week at a
riding school. She simply did not chew the bit. Three
horses exhibited bit wear on only one side. Altogether,
five teeth (21%) derived from four horses exhibited no
bit wear. Bit wear did occur on 79% of all the P2s, and
on at least one side in 92% (12 of 13) of the frequently
bitted horses. Archaeologists should note that an
Figure 5. Box plots of bevel measurements—note that modern
domestic horses are broken into two groups, those of unknown analysis based on individual teeth will undercount the
bitting history and those known to have been bitted frequently. Only number of horses that have been bitted, because wear
horses over 3 years are included. occurs on only one side in some horses. Nevertheless,
bit wear is common and expected on horses that are
ridden or driven almost every day.
horses, 3 years or younger in age, are discussed
separately below.) We have established the threshold
for a bit-induced bevel at 3 mm, which is more than
The Longevity of Bit Wear
three standard deviations greater than the mean bevel
measurement for mature feral horses. We refer to this Horses have high-crowned teeth that erupt continu­
as a “significant bevel”. ously as they are worn away by occlusal and dietary
wear. Depending on diet and environmental factors, it
may take 20-40 years for horses’ cheek teeth to wear
down to the roots. Feral horses in the wild rarely live
The new definition
longer than 20-25 years; domestic horses can survive
Previously we defined bit wear as the combination of more than 40 years. Newly erupted permanent P2s in
a significant bevel measurement and significant “a” our sample (P2s of 3-year-old horses) had a maximum
wear. However, after observing more domestic horse crown height (a measurement of length) of 63 mm.
teeth, and gathering more detailed information about Assuming a P2 life-span of 20 years (which means a
many of them, we have found this definition to be horse life-span of 23 years), the average rate of occlusal
excessively conservative. Analysis of our new collection wear should be 3T5 mm per year. Other published
Table 3. Bit wear on 13 horses known to have been bitted frequently
No. of teeth % of 24 No. of horses % of 13
No wear 5 21 1 8
Significant “a” wear 12 50 7 54
Significant bevel 17 71 11 85
Significant bevel but not significant “a” wear 7 29 5 38
Significant “a” and bevel 10 42 6 46 (old definition)
Significant “a” or bevel 19 79 12* 92 (new definition)
‘Only nine horses (69%) had some kind of bit wear on both P2 teeth.
Bit Wear Damage 337
Figure 6. Bevel measurements of domestic, feral and frequently bitted horse teeth plotted against age. □, Domestic horse teeth (excluding
known frequently bitted teeth) (D), 65 teeth, 34 horses. A, feral horse teeth (F), 33 teeth, 20 horses. O, known frequently bitted teeth (KJ, 24
teeth, 13 horses. 2D, F or K, multiple teeth on this point. Area inside arrows excludes feral horse teeth.
estimates of mean annual cheektooth wear rates for Bevelled wear facets are larger features, so they last
grazing equids are slightly higher, between 3-3 and longer than “a” wear. We have recorded bevel
4-2 mm per year (Hulbert, 1982). Estimates of maxi­ measurements of up to 10 mm on bitted horses. A
mum crown height also vary (Klein & Cruz-Uribe, bevel facet 10 mm deep might be preserved for more
1984: 54). If occlusal and dietary wear remove 3-15 mm than 3 years after the horse was last bitted. In addition,
of occlusal surface per year, most “a” wear features by our definition, “a” wear must be observed on more
should disappear within 4 months. If the rate of wear is than 50% of the occlusal enamel of the first cusp if it is
higher, “a” wear will disappear more rapidly. to be categorized as “significant”. If portions of the
“A” wear does not survive very long. Occlusal and paraconid cusp are destroyed by taphonomic processes
dietary wear probably remove 3-4 mm of occlusal the tooth might fall short of the minimum surface
surface per year on horse P2s, although the rate of required to confirm significant “a” wear. A bevel
wear varies with age and diet. Most “a” wear abrasions measurement, on the other hand, can be taken as long
are less than 1 mm deep, so should disappear within as the critical part of the paraconid cusp is not chipped
1-4 months if the horse is not bitted during that off. A significant bevel can survive the effects of
period. occlusal wear longer, and can be Observed even
338 D. Brown and D. Anthony
when the tooth is partially damaged by taphonomic
processes.
Bevel Measurements and Crown Heights
Are bevel measurements alone a reliable indicator of
bit wear? The answer to this question depends on the
age of the horse. For horses with permanent teeth that
have come fully into wear, our studies suggest that the
answer is yes. To support this statement, we should
first look at our statistics on bevel measurements, and
then consider methods for eliminating young horses,
3 years of age or younger, from bit wear studies.
Among the 13 frequently bitted horses, significant
bevels were observed without significant “a” wear on
seven of 24 teeth (29%) and in five of 13 horses (39%).
These horses were bitted two to five times per week and
clearly chewed their metal bits, yet did not show
Figure 7. Photograph showing deciduous teeth on top of developing
significant “a” wear. Bit wear apparently is not pro­
permanent P2 teeth as they grew in the jaw of a 21-month-old horse.
duced by a continuous process of bit-chewing that White arrows point to the mesial ends..of right and left deciduous
occurs each time the horse is bitted; rather it can be teeth. This view shows the lingual sides. The natural bevel at the
caused by episodic bit-chewing events. The “a” wear mesial end of the developing permanent teeth can be clearly seen.
Photo by Kim Ilowit.
from these events is worn away relatively quickly, but
the bevelled wear facets survive longer. For these
reasons, significant bevel measurements will be seen rounded, conforming to the underside of the deciduous
without significant “a” wear even among horses that tooth that caps it (Figure 7). After the deciduous P2 is
are bitted frequently. shed the occlusal surface of the new permanent tooth is
Bevel measurements alone clearly separate mature gradually worn flat by contact with the opposing tooth.
bitted horses from mature feral horses. Among the 13 The low, rounded prow is one of the last parts of the
frequently bitted horses, the average bevel measure­ new P2 to come into wear. Before it is completely
ment was 3-6 mm, the median was 4-0 mm, and the flattened, the mesial corner often exhibits a bevel of
range was 1-7 mm (Table 2 and Figures 5 & 6). Among more than 2 mm. We have observed this temporary
feral (e.g. unbitted) horses older than 3 years there phenomenon on two live domesticated horses, never
were no bevels greater than 2 mm. ridden, whose P2 bevels were 3-0 mm at age 2-5 years,
but declined to 1-5 mm or less 4 and 5 months later. A
“significant bevel” was present at age 2-5 years, but
Problems with bevel measurements on young horses
disappeared naturally within months. Clearly, the teeth
One feral horse in our study collection had bevels on of horses 3 years old and younger should be eliminated
both P2s of 3 mm. This animal was less than 3 years from analyses of bevel measurements.
old. Unusually high bevel measurements occasionally
occur among never-bitted horses aged 3 years or
younger. The causes of the anomalous bevels lie in the Identifying the teeth of З-year-olds: crown heights and
process of P2 eruption and early wear. Permanent P2s age
erupt at approximately 2-5 years in horses. Both In order to eliminate З-year-olds from bit wear studies,
deciduous teeth and newly erupted permanent teeth one must be able to identify their teeth in archaeo­
can exhibit irregular occlusal surfaces. logical contexts, where teeth are often found isolated
Deciduous teeth are shaped differently from from the jaw. Specialists disagree about the best
permanent teeth and frequently are worn irregularly method for determining the ages of horses based only
because they are not shed simultaneously. An upper on isolated horse teeth (Spinage, 1972; Hulbert, 1982;
might fall out while a deciduous lower tooth is still Klein, 1982; Levine, 1982; Burke, 1993; O’Brien, 1995).
in use. The wear in this case becomes uneven until We chose to analyse cheektooth lengths, or crown
the new upper tooth descends to occlude evenly heights (which decrease as the horse gets older). Levine
with the lower deciduous tooth. If the deciduous has previously published mathematical curves which
tooth is loose, malocclusion might cause further she used to determine horses’ ages from crown heights
irregularities. in archaeological assemblages (Levine, 1982, 1990).
Newly erupted permanent P2s also are irregular and These curves were based largely on indirect measure­
can exhibit anomalously large bevel measurements. ments (from X-rays) taken from a relatively small
This occurs because, prior to eruption, the unworn sample of modern horses of estimated age. We
occlusal surface of the permanent tooth is somewhat re-analysed the correlation between crown height and
Bit Wear Damage 339
Figure 8. P2 crown heights plotted against age. O, Known age (55); A, feral (24); DK, deciduous known age (11); DF, deciduous feral (9);
RF, roots feral (7) (i.e. permanent teeth with roots incompletely formed).
age based on our collection (Figure 8). For the The range of crown heights at each age is very broad.
crown height measurement we used 62 permanent and In addition, we found that there can be as much as
deciduous P2s from 40 domestic horses of known age, 5 mm difference between the crown heights on the right
and 33 permanent and deciduous P2s from 18 feral and left P2s from one horse; i.e. crown heights for two
horses. Feral horse ages were estimated on the basis of teeth that have identical histories—age, diet, genetic
incisor wear and eruption sequences in articulated traits, and riding histories—can differ by as much as
mandibles. All of the teeth were removed from the 5 mm. This greatly complicates attempts to distinguish
mandibles and measured directly. Measurements of the teeth of З-year-olds from those of 4, 5, and
crown height were taken on the buccal side, from the 6-year-olds on the basis of small differences in crown
apex of the junction between the roots, to the midpoint heights.
of the occlusal surface. Earlier in the project we found that deciduous
Figure 8 demonstrates that it is somewhat problem­ teeth and very old teeth (which have similar crown
atic to determine the age of a horse solely on the basis heights) can be differentiated on the basis of occlusal
of a crown height measurement on an individual P2. lengthfwidth ratios (Figure 9). We used the same
340 EL- Brown and D. Anthony
horse younger than 4 years, and should be excluded
from bit wear studies.
This criterion should be sufficient to determine if a
loose P2 recovered from archaeological sediments was
from an animal sufficiently mature to evaluate for bit
wear. The method also will be generally useful for
archaeozoologists attempting to analyse the age struc­
tures of slaughtered horse populations in prehistoric
sites.
Metal Bit Wear Summary
By examining four traits on the P2, we can determine if
a horse was bitted, and therefore if it was used for
riding and/or draught. These traits are: (1) significant
“a” wear, and/or (2) a significant bevel measurement,
Figure 9. Occlusal length/width ratios of permanent P2s with
crown heights of less than 3 cm. Results of /-test of deciduous vs. to identify bit wear; and (3) a crown height of less than
permanent: means of the samples are significantly different. 5 cm, with (4) an occlusal length/width ratio less than
2T2, to identify and eliminate horses of 3 years old and
younger. The absence of bit wear on any individual
horse does not mean that the horse was not bitted.
Twenty-one per cent of the P2s from frequently bitted
horses exhibited no bit wear. The absence of bit wear in
a very large sample of teeth might suggest that bits
were not used on that population. However, the pres­
ence of a significant bevel or significant “a” wear on
the P2 of a mature horse identifies it as a bitted horse.
Organic Bit Wear: The Riding Experiment
Prior to 1992 our descriptions of bit wear were based
entirely on observations of the wear made by modern
metal bits. Prehistoric bits made of organic
materials—bone, rope, or leather—might have caused
different wear signatures. Some archaeozoologists
have speculated in conversation that significant bit
wear might be produced only by a metal bit. The
experiments described below have established that
significant bit wear can be caused by organic bits.
In 1992 we conducted an experiment to define the
wear caused by organic bits. We acquired four horses
Figure 10. Occlusal length/width ratios of permanent P2s of horses
ages 5/6, 4, and 2/3 years. Results of /-tests comparing means of that had never been bitted or trained. The horses were
samples at the 0-05 level: 2/3 vs. 5/6 years, significantly different; 2/3 trained without a bit so that their teeth would remain
vs. 4 years, significantly different: 4 vs. 5/6 years, not significantly “clean” until the experiment started. We used a train­
different.
ing technique called “free lunging” in which the rider
establishes dominance prior to mounting the animal
by controlling its space in a series of one-on-one
method to separate З-year-olds from 4—6-year-olds encounters inside a closed pen. After dominance is
(Figure 10). The results were less clear, but Student’s established, riding is relatively easy. Similar training
/-tests indicate that the mean length-width ratio for techniques, which mimic the behaviours used in nature
З-year-olds is significantly different from that of 4, by dominant horses in horse bands, might well have
5, and 6-year-olds. The P2s of З-year-olds can be been attempted by the earliest riders. Once trained, the
identified by correlating crown height with a specific experimental horses were bitted and ridden in a ring by
length-width ratio. The precise threshold measure­ two students. When the horses were not being ridden
ments might change if we examine larger samples, but they were kept together in an outdoor paddock and
for the moment, we propose the following rule: if the were pastured or fed hay rather than prepared feeds to
length-width ratio is 2T2 or more, and the crown simulate “primitive” dietary wear on their teeth. The
height is 5 cm or more, the tooth is probably from a experiment lasted 8-10 months, depending on the