The following information was gained while completing my M.Sc. degree from the University of Iowa, Geoscience Deptartment. I studied bison collected from the Dow's Assemblage. In March 1974, bison remains were discovered in peat-bearing spoil piles left by the construction of I-35 near Dows, in north-central Iowa. All told, the sample included remains at least 23 individuals that lived less than 10,000 years ago. The Dows locality (figure 1) is located under and on both sides of Interstate Highway 35 at the Dows Interchange, near Franklin Co. Road C-47 at Sec. 28 and W1/2, Sec. 27, T91N, R22W (Hudak, 1984). Bison, elk, deer, amphibians, reptiles, birds, mollusks, and plant macrofossils were found in the spoil piles of peat removed and uncovered by the highway construction and grading.
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| Figure 1- Dow's bison mandible 44775AA with the teeth appropriately labelled. | Figure 2- Dow's bison mandible 44775AA with the teeth appropriately labelled. P1 is not shown on this image but would be located before P2. |
Dental elements are the most useful skeletal element for aging bison (Klein
and Cruz-Uribe, 1983). Bison ages are chiefly estimated by dental eruption schedules
and tooth wear. Eruption schedules and tooth wear provides a system of determining
the age, in years, of a specimen based on which molars and premolars have erupted
and/or the degree of tooth wear. Tooth wear is evident by the amount of dentine
on the tooth. As a bison ages it's teeth wear down which results in more dentine
showing. For bison under the age of five it is possible to determine the age
to the month based on the eruption schedule because it is systematic (Frison,
1982). For mature animals, age five or older, it is only possible to estimate
the age to the year based on wear patterns. Another way to determine the age
of mature bison is based on metaconid height of the lower molars. This method
works in almost all bovids due to the relationship between the crown height
and age (Klein et al, 1981), although the statistical relationship between age
and crown height is not always linear because of individual variation in ontogeny
and diet (Lyman, 1987). This method can only be used after the molars are in
full wear (Todd et al., 1996). The measurement is made with a sliding caliper
from the cemento-enamel junction to the crown measured parallel on the mesial
side, figure 3 and can be used on all three permanent
molars, M1, M2, and M3, figures 1 and 2. It has been shown that sample size
will affect the age profiles (Klein et al., 1981). Lyman determined that at
least thirty specimens are desirable for determining correct age profiles (1987).
Steps to Aging Bison Teeth:
1. Arrange the mandibles based on both the eruption sequence and wear patterns. It is best to refer to the actual work from the authors but I have designed a summary chart of their work, see below. See Todd et al, 1996; Frison and Reher, 1970. It might help to draw the occlusal surfaces of the teeth when arranging them, figure 3.
| 0.5 years | M1 erupted and level with other teeth. M2 sometimes seen inside mandible. | |||
| 1.5 years | M1 shows some wear. M2 not level with other teeth and unworn. M3 sometimes seen inside mandible. | |||
| 2.5 years | M1 and M2 show wear. M3 just starting to erpupt. M1 style is worn. (See figure 4 to identify the style.) | |||
| 3.5 years | M1 and M2 show wear. M3 erupted and unworn. | |||
| 4.5 years | M1, M2, and M3 showing wear. Style of M2 is worn. | |||
| 5.5 to 9.5 years | Styles of M1 and M2 look like a loop. M3 style is worn to a circle. M1 worn to half it's original size and roots start to show. | |||
| 10.5 to 14+ | M3 style worn to a loop. All teeth worn to roots. | |||
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| Figure 5- Top view of a mandible showing the styles for M2 and M3. M2's style is past the point of being a loop and M3's style is a loop. |
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# 1 = 4.5 to 5 years old |
| Figure 3- Occlusal surface drawings of the Dow's right mandibles. They are arranged in sequential order. The gray represents the dentine. Mandibles under the age of 4.5 years are not included in these drawings since they can be aged by the eruption sequence. On the left is a list of the associated ages. | |
2. Measure the metaconid height to determine exact ages for mature bison, see pictures below.
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| Figure 4 - Metaconid height measurement (M). Source: Todd et al., 1996. |
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| Figure 6- This image shows how to measure the metaconid height. Notice that the caliper is measuring from the enamal border to the top of the cusp (which is very worn in this specimen). |
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| Figure 7- This specimen's enamel border is located at the gum line. |
3. Compare your metaconid heights with ones from other studies. They should
group together into distinct age groups.
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Age (years)
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M1 metaconid height
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5
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30
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6
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25
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7
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20
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8
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15
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9
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10
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| Example of how the metaconid heights should break into distinct age groups. | |
References
Frison, G. C., The Agate Basin Site: A Record of the Paleoindian Occupation of the Northwestern High Plains. Academic Press, New York, 1982
Frison, G. C. and C. A. Reher, Age Determinations of Buffalo by Teeth Eruption and Wear. In The Glenrock Buffalo Jump, 48CO304, edited by G. C. Frison. Plains Anthropologist Memoir 7:46-50, 1970.
Hudak, C. M., Paleoecology of an Early Holocene Faunal and Floral Assemblage from the Dows Local Biota of North-Central Iowa, Quaternary Research 21, 351-368, 1984.
Klein, R.G. and K. Cruz-Uribe, The Computation of Ungulate Age (Mortality) Profiles from Dental Crown Heights, Paleobiology 9:70-78. 1983.
Klein, R. G., C. Wolf, L.G. Freeman, and K. ALlwarden, The Use of Dental Crown Heights for Constructing Age Profiles of Red Deer and Similar Species in Archaeological Samples. Journal of Archaeological Science 8: 1-31, 1981.
Lyman, R. L., On the Analysis of Vertebrate Mortality Profiles: Sample Size, Mortality Type, and Hunting Pressure, American Antiquity 52(1), pp. 125-142, 1987.
Todd, L. C., D. J. Rapson, and J. L. Hofman, Dentition Studies of the Mill Iron and Other Early Paleoindian Bison Bonebed Sites. In The Mill Iron Site, edited by George C. Frison, pp. 231-237. University of New Mexico Press, Albuquerque. 1996.
Toennies, J. L. Dows Holocene Fossil Bison Assemblage, Franklin County, Iowa: Its Application To Conservation, Interpretation, and Outreach,University of Iowa, Department of Geoscience, M.Sc. thesis, 2003.