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Dental variation in the molars of Mammuthus columbi var. M. imperator (Proboscidea, Elephantidae) from a Mathis gravel quarry, southern Texas
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Quaternary International 142–143 (2006) 166–177
Dental variation in the molars of Mammuthus columbi var. M. imperator (Proboscidea, Elephantidae) from a Mathis gravel quarry, southern Texas George E. McDaniel Jr., George T. Jefferson California Department of Parks and Recreation, Colorado Desert District Stout Research Center, 200 Palm Canyon Drive, Borrego Springs, CA 92004, USA
Abstract A large sample ðN ¼ 149Þ of Mammuthus columbi molars was excavated from a gravel quarry of Rancholabrean North American Land Mammal Age (NALMA) near Mathis, San Patricio County in southern Texas. This attritional assemblage, which also includes Xenarthra, Equidae, Camelidae, Cervidae, and Bovidae, was recovered from fluvial point-bar deposits. Standard mammoth dental measurements and metrics (enamel thickness, plate width, plate number, and lamellar frequency) from a minimum of 25 individuals vary widely. The number of plates in the tooth (PN) is the most reliable measurement in the identification of the molar to the species level. Enamel thickness and lamellar frequency suggest that the Mathis sample represents a local population of Mammuthus columbi that approaches molar morphologies found in Irvingtonian NALMA populations usually placed in M. imperator. Published by Elsevier Ltd.
1. Introduction A collection of 149 Mammuthus teeth and fragments of teeth was recovered in 1974 from a gravel quarry in southern Texas by E. Lundelius, and housed in the Texas Memorial Museum (TMM), Austin. The site, TMM 41724, is located near Mathis, San Patricio County, TX (Fig. 1). Fossil materials were exposed by a dragline operator, and specimens were collected at various levels within the gravel quarry. The exposed sedimentary section represents fluvial point bar deposits and contains lag gravels. In addition to Mammuthus, the locality yielded the remains of Xenarthra, Equidae, Camelidae, Cervidae, and Bovidae. This attritional assemblage, presumably timeaveraged, is late Rancholabrean in age (Lundelius, pers. comm., 1999). The sample of 149 Mammuthus teeth possibly represents a minimum of 25 individuals, and provides an adequate base for metric and statistical analyses of dental variation. Enamel thickness and plate frequency exhibited by these Corresponding author.
E-mail address: [email protected] (G.T. Jefferson). 1040-6182/$ - see front matter Published by Elsevier Ltd. doi:10.1016/j.quaint.2005.03.014
teeth (Tables 1 and 2) approach that found in Irvingtonian age materials generally assigned to M. imperator (Maglio, 1973; Madden, 1981). M. imperator and M. columbi are considered conspecific by Agenbroad (2003). We concur with Agenbroad, and herein refer to materials that would have been placed in M. imperator as M. columbi var. M. imperator. The dental characteristics of the Mathis sample show that local level variation was present in the dentitions of late Pleistocene, Rancholabrean NALMA Mammuthus columbi from southern Texas, US. 2. Nomenclature, measurements and methods Several systems of nomenclature have been proposed for Elephantidae cheek teeth. These are: Laws (1966), M1, M2, M3, M4, M5, M6; Saunders (1970) (follows Osborn, 1942), Dp2, Dp3, Dp4, M1, M2, M3; Sikes (1971), I, II, III, IV, V, VI; Madden (1981), dP2, dP3, dP4, M1, M2, M3; and Froelich and Kalb (1995), P2, P3, P4, M1, M2, M3. According to Haynes (1991), most modern paleontologists use Saunders’ (1970) nomenclature, while most field biologists, including Haynes, follow Laws’ (1966) system because of its simplicity. The dental nomenclature of
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Fig. 1. Locality map, TMM 41724 (x), Mathis, San Patricio County, TX, USA.
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Madden (1981) is used herein. Upper and lower molars are distinguished by using a slash, with uppers above the slash and lowers below (e.g. M3= ¼ upperthirdmolar; M=3 ¼ lowerthirdmolar). The first three cheek teeth in mammoths are deciduous premolars. In both Elephas maximus and Loxodonta africana, all six cheek teeth are first generation, and develop directly from the dental lamina that originates in the oral epithelium (Kozawa et al., 2001, pp. 639–642). The permanent premolar buds (second generation) are present, but do not develop (Kozawa et al., 2001). Most systematic studies of elephantid dentitions are based on characters present in the third molars, M3 (Maglio, 1973) as this tooth is in wear longer than the preceding teeth and is the tooth most often recovered in paleontological samples. All identifiable cheek teeth in the TMM 41724 sample were grouped by tooth position (M1, M2, M3 upper and lower) based on standard criteria (Saunders, 1970; Maglio, 1973; Madden, 1981; Graham, 1986, pp. 171–190). No premolars were identified in the sample. These smaller, less durable teeth may not have been preserved, may not have been recovered, or may be represented by unidentifiable tooth fragments.
Table 1 Dental measurements of mammoth molars from the Mathis quarry (locality TMM 41724) Tooth position
Parameters
Width (mm)
Lamellar frequency (lamellae/10 cm)
Enamel thickness (mm)
M3/
Number Range Mean Median
34 78.4–115.6 97.4 95.6
34 4.0–8.0 5.7 5.6
28 2.3–3.3 2.6 2.5
M/3
Number Range Mean Median
24 74.1–107.3 91.0 86.4
24 4.1–7.5 5.7 5.6
22 2.3–3.1 2.6 2.6
M2/
Number Range Mean Median
18 68.1–92.3 80.4 83.8
14 4.5–8.2 6.3 6.3
13 2.1–3.2 2.6 2.5
M/2
Number Range Mean Median
16 65.2–86.9 74.2 74.5
14 4.1–7.9 6.2 6.5
11 2.2–2.9 2.5 2.4
M1/
Number Range Mean Median
3 62.8–74.0 66.7 68.1
3 6.7–9.1 7.2 7.4
3 2.1–2.5 2.3 2.2
M/1
Number Range Mean Median
2 63.6–70.6 67.1 67.1
2 6.6–7.4 7.0 7.0
2 2.4–2.9 2.7 2.7
Upper and lower molars are distinguished by using a slash, with uppers above the slash and lowers below the slash (e.g. M3/ ¼ upper third molar; M/3 ¼ lower third molar).
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Table 2 Distribution of mammoth molars from the Mathis quarry (locality TMM 41724) Tooth position
M1 M2 M3 Unknown
Upper
Lower
Total
Right
Left
Unidentified
Right
Left
Unidentified
7 21 5
3 8 11 10
3 2 12
1 10 10 5
1 4 12 7
1 2 2
Total
5 33 58 41 137
2.1. Size and characters Dental characters and dimensions change during tooth wear (Dubrova, 1994, pp. 426–451). Some of these characters can vary from the buccal to lingual side of the same tooth, or from the basal to apical parts (Fig. 2). The occlusal surfaces of mammoth teeth change in length and width through normal wear (Roth, 1992). The length of a tooth decreases as the anterior lamellae are worn down and lost. Interdental pressure between teeth can produce deformation of the posterior lamellae of the anterior tooth (Roth, 1989). Anterior lamellae of a molar may be lost prior to eruption, by contact with the tooth anterior to it, and the last lamella of the molar in wear may be lost before it comes into wear due to pressure between the teeth (Haynes, 1991). Where possible, the number of lamellae in the molar (PN) was recorded (See Appendix A in the online version of this article). However, most specimens are partial molars, for which the PN could not be determined. The process of depositing cementum between the lamellae is unclear. In unerupted lamellae there is little or no cementum between the lamellae. The cementum is not deposited between the lamellae until just prior to the eruption of each lamella (Laws, 1966; Roth and Shoshani, 1988; Roth, 1992). Thus the maximum length will not be reached until all lamellae have been erupted and are in wear. For example, in the African elephant the M3 erupts over a period of 20–21 years (Table 3), with the anterior lamellae coming into wear while the posterior lamellae are still forming and before cementum is deposited between them. Deposition of cementum must occur through this period. It is difficult to compare length, height, and width of two teeth unless they are in the same stage of wear (Table 3). The overall length (L) can be determined by two different methods (Fig. 3). When the tooth is rooted in the maxilla or dentary, only the occlusal surface can be measured (Lo). In an isolated tooth, the length of a line perpendicular to the general orientation of the majority of the lamellae (Ld) can be measured. These two methods yield different values. The first method (Lo) does not measure the unerupted lamellae, and thus does not provide a maximum length for the tooth. Length should be used
Fig. 2. Sources of error in measurements of lamellar frequency for mammoth teeth due to the non-parallel arrangement of the lamellae (after Maglio, 1973). LF ¼ lamellar frequency; A ¼ occlusal view; B ¼ buccal view.
only in comparing complete specimens in the same wear stage, and is useful in differentiating the various cheek teeth one from another. The second metric (Ld) is used in this study (See Appendix A in the online version of this article). Many specimens from the Mathis sample are incomplete, many have numerous unerupted lamellae, and in some, the entire tooth had not erupted. The width and lamellar frequency (LF) (see below) of an upper tooth is greater than the corresponding lower. As a mammoth matures, the width of the lamellae of the cheek teeth increases from dP2 through M3, the LF decreases, and the enamel thickness increases slightly. The lamellae (and molars) are wider in the middle part of the tooth, and
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Table 3 The wear stage and Craig Scale for age estimation (Haynes, 1991) Wear stage (Laws)
Age (Craig Scale, AEY)
Tooth in wear P4
III V VII
2 3 5
VIII IX X XI XII XIII XIV XV XVI XVII XVIII XIX XX XXI XXII XXIII
6 8 10 12 14 15 16 18 20 22 24 28–30 32–33 35 37–38 40–42
XXIV XXV
45–46 46–48
XXVI XXVII XXVIII XXIX XXX dead
50 52–54 56 56–58 60 dead
15–20% wear 75% wear 100% wear, front smoothing 75% left 30% left Smooth Gone
M1
20% wear X50% wear 75% wear 100% wear 100%, front smoothing 85% left 75% left, smoothing 30% left or less Gone, or very smooth
M2
10% wear 30% wear 50% wear 80–90% wear X90% wear 100% wear 75% left 50% left 30–40% left 30% left 20–25% left Very smooth or gone, hole in jaw No hole in jaw
M3
Lamellae unfused Lamellae fused 20–30% wear 40% wear 50% wear 65% wear 80% wear 90% wear 100% wear, front smoothing 65% left X50% left 50% or less left 30% left Nearly smooth
Note: Wear Stage ¼ relative age group of Laws (1966); AEY ¼ African elephant years.
the posterior lamellae are the narrowest. A lamella increases in width from the occlusal aspect, reaches a maximum width, then decreases to the root. In this study, the greatest width (W) of the widest lamella of the molar (including the cementum covering) is measured (Fig. 3), not the width of the occlusal surface. The width of the occlusal surface increases with wear until the maximum width is reached, and then decreases. Lamellar frequency (LF) refers to the number of lamellae per 10 cm of length (Maglio, 1973). The LF can be measured on the occlusal surface or on the lateral side of the tooth (Fig. 4). The root of a lamella is thicker anteroposteriorly than the crown, and as the tooth wears, the width of any lamella at the occlusal surface increases. The long axis of the tooth curves, and the lamellae are not parallel vertically or horizontally (Fig. 2). To obtain consistent and comparable LF measurements, they should be taken either at midline on the occlusal surface or on the lateral side of the tooth (Fig. 4). If taken on the occlusal surface, the measurement points should be from the center of the cementum, and should not include lamellae worn to the root nor lamellae not in full wear. The tooth erupts at an angle to the occlusal surface, and thus LF measured on the occlusal surface can be greater than that measured on
the lateral side of the tooth. If measured on the occlusal surface, only those lamellae that are perpendicular to the occlusal surface should be included. If taken on the lateral side, the measurement should be perpendicular to the orientation of the lamellae (Fig. 4). The measurement must contain an exact number of complete lamellae. The distance between these two points (D) is measured in cm. The number of lamellae (L) included between these two points is noted. The LF is calculated as follows: 10L–D ¼ LF. Larger teeth generally exhibit thicker lamellae. Thus, with the number of lamellae constant, the LF decreases as tooth size increases. Molar height (H) is taken on the tallest lamella in the specimen (Fig. 3). This measurement is dependant on the stage of wear at death, and does not necessarily measure the maximum height of the tooth. The maximum crown height should be measured only when the tallest lamella has just come into wear. Enamel thickness (ET) varies between elephantid species (Maglio, 1973; Madden, 1981). Generally the lamellae are not perpendicular to the occlusal surface. Measuring ET on the occlusal surface will give a value higher than in a crosssection perpendicular to the lamellae. Care must be taken to measure the enamel thickness at right angles to the
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Fig. 4. Left M/2 of Elephas namadicus, showing the measurable parameters and structural characteristics of elephant teeth (after Maglio, 1973). A ¼ occlusal view; B ¼ buccal view, anterior to the right.
estimated value (See Appendix A in the online version of this article). 2.2. Minimum number of animals represented
Fig. 3. Profile view of an upper molar (A), a lower molar (B), and an occlusal view of a lower molar (C) (from Agenbroad and Mead, 1994, modified from Saunders, 1970). Lo ¼ length, occlusal surface; Ld ¼ length of plane perpendicular to the general orientation of the majority of the lamellae; H ¼ height of the tallest lamella; W ¼ width of the widest lamella (including cement).
height of the lamella. The ET remains fairly constant in an antero-posterior longitudinal section. Ten measurements were taken on each specimen and the average reported. If insufficient lamellae are in full wear, as many measurements as practical were taken, averaged, and reported as an
Although several complete teeth were recovered, one or more incomplete tooth parts may be from a single tooth. Each animal has at least four teeth in wear at any time, and one tooth, e.g. the M3, may be erupted at a different time in each quadrant. Thus, it is difficult to estimate the number of individual mammoths represented by the sample. The teeth identified to position represent a minimum number of 25 ðN ¼ 25Þ individuals. The number of specimens representing each of the molars (M1, M2, and M3 upper and lower) is listed by quadrant in Table 2 and the measurements are listed by tooth position and quadrant in Appendix A. We can estimate the minimum number of individuals as follows: 1. There are 21 right M3/s. These include two complete teeth (TMM 41724-66, TMM 41724-69) in full wear. There are 11 posterior sections (TMM 41724-28, TMM 41724-31, TMM 41724-46, TMM 41724-57, TMM 41724-78, TMM 41724-84, TMM 41724-103, TMM 41724-106, TMM 41724-114, TMM 41724-115, TMM 41724-130), indicating 11 minimum individuals. There is one aberrant section (TMM 41724-61) with lamellae at a 451 angle, one central section with 11 unerupted lamellae (TMM 41724-102) that does not match any posterior
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sections, one anterior section (TMM 41724-27) that has a high LF (7.5), and two anterior sections (TMM 41724-37, 41724-58) that match no posterior sections. This yields a total of 18 ðN ¼ 18Þ minimum individuals based on the right M3/s. 2. There are seven specimens identified as right M2/s. One is complete (TM 41724-59). The differences in the LF of three anterior sections (TMM 41724-22, TMM 41724-29, TMM 41724-156) and three posterior sections (TMM 41724-109, TMM 41724-113, TMM 41724-119) of the remaining fragments precludes them from representing less than six teeth. The wear stages of the seven right M2/s indicate that none are from the same individual as any of the right M3/s. Only two have reached wear stage XVII (100% wear), and the youngest of the 18 M3/s listed above is as young as wear stage XIX (20–30% in wear) (see Table 3). The right M2/s indicate a minimum of seven ðN ¼ 7Þ individuals. 3. There are no right M1/ s in the sample.
2.3. Age determination The approximate age of African elephants can be determined from tooth wear (Laws, 1966; Haynes, 1991). The estimation of the age of a mammoth so determined is given in African Elephant Years (AEY). However, tooth wear may vary between individuals. Teeth in any given quadrant may not erupt at exactly the same time, and thus could exhibit different wear stages. The lower teeth are smaller than the uppers, and wear faster (Haynes, 1991). Also, an individual chews more on one side than the other, resulting in different wear stages from side to side. Assigning an estimate of age based on the wear stage of one tooth may not reflect actual age of the individual. It is difficult to estimate age from incomplete teeth (guidelines are provided in Appendix B). However, these estimates provide information on the relative age
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structure within a fossil assemblage, and are more precise than those based on tooth position alone. The Laws scale (1966) (Table 3) classifies the wear stage of a tooth (referred to as ‘‘Relative Age Group’’ by Laws), and provides an estimated age. However, the Laws scale often results in anomalous age distributions (Fatti et al., 1980), and certain age categories may be missing. The Craig scale (Haynes, 1991) (Table 3) is preferred by Haynes as Craig’s sample was much larger than that of previous studies and has more age categories. The late wear stage of one tooth overlaps the early wear stage of the next tooth, so more than one tooth fragment in the Mathis sample may be in occlusion from the same quadrant of one animal. The wear stages of the mammoth teeth from the Mathis sample are plotted in Fig. 5. Individual age at the time of death can be estimated in 60 of the Mathis specimens. These are plotted in an age distribution histogram (Fig. 6). Sexual maturity in mammoths occurs at 18–20 years (Haynes, 1991), although this can vary. In the African elephant, this is reached between 12 and 15 years of age. Sexual dimorphism in size becomes more apparent as mammoths reach maturity. It first appears at age 5, and increases as the animal matures (Haynes, 1991). In African elephants, the teeth of males usually are larger than those of females of the same age, although some older females can have larger teeth than others (Haynes, 1991). The M3s of males are longer, wider, and higher crowned than in females. The PN of males may be the same as in females, but the LF is lower in the male (the individual lamellae are thicker anterioposteriorly and there is more cementum between the lamellae). The ET may be slightly higher in males. The M3s of African elephants erupt and come into wear about the age 27–28 (Haynes, 1991). Male M3s are larger than the female M3s, and it is assumed that most of the largest molars within a particular age group represent males. Figs. 7–12 show the distribution of width, lamellar frequency and enamel thickness of mammoth molars from
Fig. 5. Distribution of the wear stage (Relative Age Group of Laws, 1966) of the mammoth molars from the Mathis Quarry (locality TMM 41724) (after Laws, 1966; from Haynes, 1991).
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the Mathis quarry, and is the source of the criteria used in classifying a tooth or tooth fragment as male. If a specimen meets two of the three criteria (Table 4), it is presumed herein to be from a male, and others are judged to be females or males under 5 years of age. 3. Discussion and conclusions The Mathis sample is not catastrophic, and does not represent a single elephantid herd. The specimens were recovered from different levels within the Mathis gravel quarry and appear to represent an attritional accumulation within the fluvial deposit. However, there is a taphonomic or sampling bias. No premolars were recovered, and the
Fig. 6. Age distribution, in African Elephant years (AEY) of the mammoth molars from the Mathis quarry (Locality TMM 41724). The specimens are grouped in increments of 5 AEY. Age estimated according to the Craig Scale (Haynes, 1991).
younger animals are not represented. The assemblage likely reflects an otherwise unbiased adult population. Of the 149 teeth or fragments of teeth in the Mathis sample, 96 have been assigned a tooth position (Table 2). Thirty-nine of the specimens can be classed as male (see criteria discussed above), and 59 as female (See Appendix A in the online version of this article). Of the specimens used to establish the 25 minimum number of individuals, only eight are males, and of these, five of the eight are mature males (See Appendix A in the online version of this article). Note the marked drop in frequency between the ages of 25 and 35 AEY (Fig. 6), which is the period when the M3s are coming into wear (Table 3). Fig. 13, a scattergram, exhibits two clusters, one representing M1s and M2s, and a second representing M3s. Note the gap between the two clusters. We have no plausible explanation for this. Fig. 13 also shows a wide variation in width in animals of the same age. The width is greater in males and also in uppers as expected. ET and LF vary directly with molar width, reflecting the size of the tooth. Larger molars exhibit a lower LF, higher ET, and greater width as expected (Figs. 14–19). These scattergrams also show a wide variation in values. There is a wide variation in molar width in animals of the same age, and molars of approximately the same width there is great variation in LF and ET. ET varies considerably among molars with approximately the same LF. The correlation between tooth size and enamel thickness also relates to sexual dimorphism. A molar may be in the high end of the range in one parameter and in the low range or midrange in the others. The ET of the M3/s has a range from 2.3 to 3.3 mm (mean 2.6 mm), the M/3s a range of 2.3–3.1 mm (mean 2.6 mm) (Table 1). These values are comparable to those recorded for the imperator variety of Mammuthus columbi (Saunders, 1970; Madden, 1981). The LF of molars in the Mathis sample ranges from 4.0 to 8.0 (mean 5.7). These measurements are comparable to those typically found in
Fig. 7. Comparison of the distribution of widths of mammoth upper molars from the Mathis quarry (locality TMM 41724). The specimens are grouped by 5 mm increments.
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Fig. 8. Comparison of the distribution of widths of mammoth lower molars from the Mathis quarry (locality TMM 41724). The specimens are grouped by 5 mm increments.
Fig. 9. Comparison of the distribution of lamellar frequencies of mammoth upper molars from the Mathis quarry (locality TMM 41724). The specimens are grouped in increments of 0.5 lamellae.
Fig. 10. Comparison of the distribution of lamellar frequencies of the mammoth lower molars from the Mathis quarry (locality TMM 41724). The specimens are grouped in increments of 0.5 lamellae.
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Fig. 11. Comparison of the distribution of enamel thickness of mammoth upper molars from the Mathis quarry (locality TMM 41724).
Fig. 12. Comparison of distribution of enamel thickness of mammoth lower molars from the Mathis quarry (locality TMM 41724).
Table 4 Criteria used to classify a tooth or tooth fragment from the Mathis quarry (locality TMM 4172) as presumed male Tooth position
M3/ M/3 M2/ M/2
Criteria Width (mm)
Lamellar frequency (#/10 cm)
Enamel thickness (mm)
X100 X95 X85 X80
p5 p5.5 p6.0 p6.0
X2.7 X2.6 X2.4 X2.4
Note: A specimen meeting two of the three criteria is assumed to be male.
later M. columbi (Saunders, 1970; Madden, 1981). The PN (See Appendix A in the online version of this article) also falls within the parameters of the imperator variety of M. columbi. The Mathis sample of molars exhibit more primitive dental characteristics than would be expected from
Rancholabrean NALMA mammoths. They compare closely to the imperator variant of Mammuthus columbi that is typically recovered from Irvingtonian NALMA localities. The Mathis assemblage represents a local variant population of Mammuthus columbi present in the southcentral US. The degree of variation in the measurements of the specimens from the Mathis quarry supports the conclusion of Lister (2001, pp. 648–651), and Lister and Sher (2001) for European specimens, that the PN is the most reliable measurement for tracking evolutionary advancement. The LF, while not as reliable as the PN, may be used when the PN cannot be determined. Appendix A See the online version of this article for a table showing the dental measurements of Mammuthus colombi specimens from TMM Locality 4172, Mathis, TX at doi:10.1016/ j.quaint.2005.03.014
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Fig. 13. Correlation of age and molar width of mammoth cheek teeth from the Mathis quarry (locality TMM 41724). Age estimated according to the Craig scale (Haynes, 1991) (Table 3). The line is the mean (M1s and M2s on the left, M3s on the right). Legend: () upper tooth, female; (D) upper tooth, male; (J) lower tooth, female; (D) lower tooth, male. Solid line is the mean.
Fig. 14. Correlation of molar width and lamellar frequency of mammoth M1s and M2s from the Mathis quarry (locality TMM 41724). () Upper tooth, female; (D) upper tooth, male; (J) lower tooth, female; (D) lower tooth, male. Solid line is the mean.
Appendix B. Estimation of age by dental wear stage The following guidelines are followed to estimate the age of a section or fragment of a mammoth tooth (see Table 3): (A) Anterior section of tooth 1. If the anterior lamellae are in wear and the posterior lamellae of the section are not erupted or just coming into wear, a wear stage can be assigned and an age estimated.
Fig. 15. Correlation of molar width and lamellar frequency of mammoth M3s from the Mathis quarry (locality TMM 41724). () Upper tooth, female; (D) upper tooth, male; (J) lower tooth, female; (D) lower tooth, male. Solid line is the mean.
2. If all lamellae of the section are in wear, by counting the lamellae in the fragment, we can determine the minimum portion of the tooth in wear and assign a wear stage and estimate a minimum age for the section. 3. If the anterior lamellae of the section are smoothing (Table 3), a minimum wear stage can be assigned and a minimum age estimated. (B) Central section of tooth 1. From the shape of the fragment, in many cases it may be possible to estimate the number of plates
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Fig. 16. Correlation of molar width and enamel thickness of mammoth M1s and M2s from the Mathis quarry (locality TMM41724). () Upper tooth, female; (D) upper tooth, male; (J) lower tooth, female; (D) lower tooth, male. Solid line is the mean.
Fig. 17. Correlation of molar width and enamel thickness of mammoth M3s from the Mathis quarry (locality TMM 41724). () Upper tooth, female; (D) upper tooth, male; (J) lower tooth, female; (D) lower tooth, male. Solid line is the mean.
missing, and a minimum or maximum wear stage may be assigned and an age estimated. 2. If the posterior plates are barely in wear, a wear stage may be assigned and an age estimated.
Fig. 18. Correlation of lamellar frequency and enamel thickness of mammoth M1s and M2s from the Mathis quarry (locality TMM 41724). () Upper tooth, female; (D) upper tooth, male; (J) lower tooth, female; (D) lower tooth, male. Solid line is the mean.
(C) Posterior section of tooth 1. If all lamellae are in wear, the tooth is at least 100% in wear, but it is not known if the missing anterior lamellae are smoothing (Table 3) or have
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Fig. 19. Correlation of lamellar frequency and enamel thickness of mammoth M3s from the Mathis quarry (locality TMM 41724). () Upper tooth, female; (D) upper tooth, male; (J) lower tooth, female; (D) lower tooth, male. Solid line is the mean.
been shed. However, a minimum age can be estimated. 2. If some posterior lamellae are just coming into wear or are not erupted, the wear stage can be assigned and an age estimated. 3. If no lamellae are erupted, we can estimate the minimum portion of the tooth that is not in wear, and a maximum age can be estimated. References Agenbroad, L.D., 2003. New localities, chronology and comparisons for Mammuthus exilis: 1994–1998. In: Reumer, J.W.F., DeVos, J., Mol, D. (Eds.), Advances in Mammoth Research (Proceedings of the Second International Mammoth Conference, Rotterdam, May 16–20 1999), vol. 9. Deinsea, pp. 1–16.
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Agenbroad, L., Mead, J.I., 1994. The Hot Springs Mammoth Site. The Hot Springs Mammoth Site of South Dakota, Inc., Hot Springs 457pp. Dubrova, I.A., 1994. Fossil elephants of the Commonwealth of Independent States. In: Agenbroad, L., Mead, J.I. (Eds.), The Hot Springs Mammoth Site. The Mammoth Site of South Dakota, Hot Springs, South Dakota 457pp. Fatti, L.P., Smuts, G.L., Starfield, A.M., Spurdle, A.A., 1980. Age determination in African elephants. Journal of Mammology 61, 547–551. Froelich, D.J., Kalb, J.E., 1995. Internal reconstruction of elephantid molars: applications for functional anatomy and systemics. Paleobiology 21 (3), 379–392. Graham, R., 1986. Descriptions of the dentitions and stylohyoids of Mammuthus columbi from the Colby site. In: Frison, G., Todd, C.L. (Eds.), The Colby Mammoth Site. Appendix 2, part 2. University of New Mexico Press, Albuquerque 238pp. Haynes, G., 1991. Mammoths, Mastodons, and Elephants. Cambridge University Press, England 413pp. Kozawa, L.H., Mishima, H., Suzuki, K., Ferguson, M.W.J., 2001. Dental formula of elephant by the development of tooth germ. In: Cavarretta, G., Gioia, P., Mussi, M., Palombo, M.R. (Eds.), The World of Elephants. Proceedings of the First International Congress, Rome, 739pp. Laws, R.M., 1966. Age criteria for the African elephant, Loxodonta africana. East African Wildlife Journal 4, 1–37. Lister, A.M., 2001. A ‘‘Graded’’ evolution and molar scaling in the evolution of the mammoth. In: Cavarretta, G., Gioia, P., Mussi, M., Palombo, M.R. (Eds.), The World of Elephants. Proceedings of the First International Congress, Rome, 739pp. Lister, A.M., Sher, A.V., 2001. The origins and evolution of the wooly mammoth. Science 294, 1094–1097. Madden, C.T., 1981. Mammoths of North America. Doctoral Dissertation, Department of Anthropology, University of Colorado, Boulder, 271pp. Maglio, V.J., 1973. Origin and evolution of the Elephantidae. Transactions of the American Philosophical Society, New Series 63, 199. Osborn, H.F., 1942. Proboscidea, vol. 2. American Museum Press, New York, pp. 805–1676. Roth, V.L., 1989. Fabricational noise in elephant dentitions. Paleobiology 15, 165–179. Roth, V.L., 1992. Quantitative variation in elephant dentitions: implications for the delimitation of fossil species. Paleobiology 18 (2), 184–202. Roth, V.L., Shoshani, J., 1988. Dental identification and age determination in Elephas maximus. Journal of Zoology 61, 547–551. Saunders, J.J., 1970. The distribution and taxonomy of Mammuthus in Arizona. Master of Science Thesis, Department of Geochronology, University of Arizona, 148pp. Sikes, S.K., 1971. The Natural History of the African Elephant. Weidenfeld and Nicholson, London.
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Dental variation in the molars of Mammuthus columbi var. M. imperator (Proboscidea, Elephantidae) from a Mathis gravel quarry, southern Texas George E. McDaniel Jr., George T. Jefferson California Department of Parks and Recreation, Colorado Desert District Stout Research Center, 200 Palm Canyon Drive, Borrego Springs, CA 92004, USA
Abstract A large sample ðN ¼ 149Þ of Mammuthus columbi molars was excavated from a gravel quarry of Rancholabrean North American Land Mammal Age (NALMA) near Mathis, San Patricio County in southern Texas. This attritional assemblage, which also includes Xenarthra, Equidae, Camelidae, Cervidae, and Bovidae, was recovered from fluvial point-bar deposits. Standard mammoth dental measurements and metrics (enamel thickness, plate width, plate number, and lamellar frequency) from a minimum of 25 individuals vary widely. The number of plates in the tooth (PN) is the most reliable measurement in the identification of the molar to the species level. Enamel thickness and lamellar frequency suggest that the Mathis sample represents a local population of Mammuthus columbi that approaches molar morphologies found in Irvingtonian NALMA populations usually placed in M. imperator. Published by Elsevier Ltd.
1. Introduction A collection of 149 Mammuthus teeth and fragments of teeth was recovered in 1974 from a gravel quarry in southern Texas by E. Lundelius, and housed in the Texas Memorial Museum (TMM), Austin. The site, TMM 41724, is located near Mathis, San Patricio County, TX (Fig. 1). Fossil materials were exposed by a dragline operator, and specimens were collected at various levels within the gravel quarry. The exposed sedimentary section represents fluvial point bar deposits and contains lag gravels. In addition to Mammuthus, the locality yielded the remains of Xenarthra, Equidae, Camelidae, Cervidae, and Bovidae. This attritional assemblage, presumably timeaveraged, is late Rancholabrean in age (Lundelius, pers. comm., 1999). The sample of 149 Mammuthus teeth possibly represents a minimum of 25 individuals, and provides an adequate base for metric and statistical analyses of dental variation. Enamel thickness and plate frequency exhibited by these Corresponding author.
E-mail address: [email protected] (G.T. Jefferson). 1040-6182/$ - see front matter Published by Elsevier Ltd. doi:10.1016/j.quaint.2005.03.014
teeth (Tables 1 and 2) approach that found in Irvingtonian age materials generally assigned to M. imperator (Maglio, 1973; Madden, 1981). M. imperator and M. columbi are considered conspecific by Agenbroad (2003). We concur with Agenbroad, and herein refer to materials that would have been placed in M. imperator as M. columbi var. M. imperator. The dental characteristics of the Mathis sample show that local level variation was present in the dentitions of late Pleistocene, Rancholabrean NALMA Mammuthus columbi from southern Texas, US. 2. Nomenclature, measurements and methods Several systems of nomenclature have been proposed for Elephantidae cheek teeth. These are: Laws (1966), M1, M2, M3, M4, M5, M6; Saunders (1970) (follows Osborn, 1942), Dp2, Dp3, Dp4, M1, M2, M3; Sikes (1971), I, II, III, IV, V, VI; Madden (1981), dP2, dP3, dP4, M1, M2, M3; and Froelich and Kalb (1995), P2, P3, P4, M1, M2, M3. According to Haynes (1991), most modern paleontologists use Saunders’ (1970) nomenclature, while most field biologists, including Haynes, follow Laws’ (1966) system because of its simplicity. The dental nomenclature of
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Fig. 1. Locality map, TMM 41724 (x), Mathis, San Patricio County, TX, USA.
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Madden (1981) is used herein. Upper and lower molars are distinguished by using a slash, with uppers above the slash and lowers below (e.g. M3= ¼ upperthirdmolar; M=3 ¼ lowerthirdmolar). The first three cheek teeth in mammoths are deciduous premolars. In both Elephas maximus and Loxodonta africana, all six cheek teeth are first generation, and develop directly from the dental lamina that originates in the oral epithelium (Kozawa et al., 2001, pp. 639–642). The permanent premolar buds (second generation) are present, but do not develop (Kozawa et al., 2001). Most systematic studies of elephantid dentitions are based on characters present in the third molars, M3 (Maglio, 1973) as this tooth is in wear longer than the preceding teeth and is the tooth most often recovered in paleontological samples. All identifiable cheek teeth in the TMM 41724 sample were grouped by tooth position (M1, M2, M3 upper and lower) based on standard criteria (Saunders, 1970; Maglio, 1973; Madden, 1981; Graham, 1986, pp. 171–190). No premolars were identified in the sample. These smaller, less durable teeth may not have been preserved, may not have been recovered, or may be represented by unidentifiable tooth fragments.
Table 1 Dental measurements of mammoth molars from the Mathis quarry (locality TMM 41724) Tooth position
Parameters
Width (mm)
Lamellar frequency (lamellae/10 cm)
Enamel thickness (mm)
M3/
Number Range Mean Median
34 78.4–115.6 97.4 95.6
34 4.0–8.0 5.7 5.6
28 2.3–3.3 2.6 2.5
M/3
Number Range Mean Median
24 74.1–107.3 91.0 86.4
24 4.1–7.5 5.7 5.6
22 2.3–3.1 2.6 2.6
M2/
Number Range Mean Median
18 68.1–92.3 80.4 83.8
14 4.5–8.2 6.3 6.3
13 2.1–3.2 2.6 2.5
M/2
Number Range Mean Median
16 65.2–86.9 74.2 74.5
14 4.1–7.9 6.2 6.5
11 2.2–2.9 2.5 2.4
M1/
Number Range Mean Median
3 62.8–74.0 66.7 68.1
3 6.7–9.1 7.2 7.4
3 2.1–2.5 2.3 2.2
M/1
Number Range Mean Median
2 63.6–70.6 67.1 67.1
2 6.6–7.4 7.0 7.0
2 2.4–2.9 2.7 2.7
Upper and lower molars are distinguished by using a slash, with uppers above the slash and lowers below the slash (e.g. M3/ ¼ upper third molar; M/3 ¼ lower third molar).
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Table 2 Distribution of mammoth molars from the Mathis quarry (locality TMM 41724) Tooth position
M1 M2 M3 Unknown
Upper
Lower
Total
Right
Left
Unidentified
Right
Left
Unidentified
7 21 5
3 8 11 10
3 2 12
1 10 10 5
1 4 12 7
1 2 2
Total
5 33 58 41 137
2.1. Size and characters Dental characters and dimensions change during tooth wear (Dubrova, 1994, pp. 426–451). Some of these characters can vary from the buccal to lingual side of the same tooth, or from the basal to apical parts (Fig. 2). The occlusal surfaces of mammoth teeth change in length and width through normal wear (Roth, 1992). The length of a tooth decreases as the anterior lamellae are worn down and lost. Interdental pressure between teeth can produce deformation of the posterior lamellae of the anterior tooth (Roth, 1989). Anterior lamellae of a molar may be lost prior to eruption, by contact with the tooth anterior to it, and the last lamella of the molar in wear may be lost before it comes into wear due to pressure between the teeth (Haynes, 1991). Where possible, the number of lamellae in the molar (PN) was recorded (See Appendix A in the online version of this article). However, most specimens are partial molars, for which the PN could not be determined. The process of depositing cementum between the lamellae is unclear. In unerupted lamellae there is little or no cementum between the lamellae. The cementum is not deposited between the lamellae until just prior to the eruption of each lamella (Laws, 1966; Roth and Shoshani, 1988; Roth, 1992). Thus the maximum length will not be reached until all lamellae have been erupted and are in wear. For example, in the African elephant the M3 erupts over a period of 20–21 years (Table 3), with the anterior lamellae coming into wear while the posterior lamellae are still forming and before cementum is deposited between them. Deposition of cementum must occur through this period. It is difficult to compare length, height, and width of two teeth unless they are in the same stage of wear (Table 3). The overall length (L) can be determined by two different methods (Fig. 3). When the tooth is rooted in the maxilla or dentary, only the occlusal surface can be measured (Lo). In an isolated tooth, the length of a line perpendicular to the general orientation of the majority of the lamellae (Ld) can be measured. These two methods yield different values. The first method (Lo) does not measure the unerupted lamellae, and thus does not provide a maximum length for the tooth. Length should be used
Fig. 2. Sources of error in measurements of lamellar frequency for mammoth teeth due to the non-parallel arrangement of the lamellae (after Maglio, 1973). LF ¼ lamellar frequency; A ¼ occlusal view; B ¼ buccal view.
only in comparing complete specimens in the same wear stage, and is useful in differentiating the various cheek teeth one from another. The second metric (Ld) is used in this study (See Appendix A in the online version of this article). Many specimens from the Mathis sample are incomplete, many have numerous unerupted lamellae, and in some, the entire tooth had not erupted. The width and lamellar frequency (LF) (see below) of an upper tooth is greater than the corresponding lower. As a mammoth matures, the width of the lamellae of the cheek teeth increases from dP2 through M3, the LF decreases, and the enamel thickness increases slightly. The lamellae (and molars) are wider in the middle part of the tooth, and
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Table 3 The wear stage and Craig Scale for age estimation (Haynes, 1991) Wear stage (Laws)
Age (Craig Scale, AEY)
Tooth in wear P4
III V VII
2 3 5
VIII IX X XI XII XIII XIV XV XVI XVII XVIII XIX XX XXI XXII XXIII
6 8 10 12 14 15 16 18 20 22 24 28–30 32–33 35 37–38 40–42
XXIV XXV
45–46 46–48
XXVI XXVII XXVIII XXIX XXX dead
50 52–54 56 56–58 60 dead
15–20% wear 75% wear 100% wear, front smoothing 75% left 30% left Smooth Gone
M1
20% wear X50% wear 75% wear 100% wear 100%, front smoothing 85% left 75% left, smoothing 30% left or less Gone, or very smooth
M2
10% wear 30% wear 50% wear 80–90% wear X90% wear 100% wear 75% left 50% left 30–40% left 30% left 20–25% left Very smooth or gone, hole in jaw No hole in jaw
M3
Lamellae unfused Lamellae fused 20–30% wear 40% wear 50% wear 65% wear 80% wear 90% wear 100% wear, front smoothing 65% left X50% left 50% or less left 30% left Nearly smooth
Note: Wear Stage ¼ relative age group of Laws (1966); AEY ¼ African elephant years.
the posterior lamellae are the narrowest. A lamella increases in width from the occlusal aspect, reaches a maximum width, then decreases to the root. In this study, the greatest width (W) of the widest lamella of the molar (including the cementum covering) is measured (Fig. 3), not the width of the occlusal surface. The width of the occlusal surface increases with wear until the maximum width is reached, and then decreases. Lamellar frequency (LF) refers to the number of lamellae per 10 cm of length (Maglio, 1973). The LF can be measured on the occlusal surface or on the lateral side of the tooth (Fig. 4). The root of a lamella is thicker anteroposteriorly than the crown, and as the tooth wears, the width of any lamella at the occlusal surface increases. The long axis of the tooth curves, and the lamellae are not parallel vertically or horizontally (Fig. 2). To obtain consistent and comparable LF measurements, they should be taken either at midline on the occlusal surface or on the lateral side of the tooth (Fig. 4). If taken on the occlusal surface, the measurement points should be from the center of the cementum, and should not include lamellae worn to the root nor lamellae not in full wear. The tooth erupts at an angle to the occlusal surface, and thus LF measured on the occlusal surface can be greater than that measured on
the lateral side of the tooth. If measured on the occlusal surface, only those lamellae that are perpendicular to the occlusal surface should be included. If taken on the lateral side, the measurement should be perpendicular to the orientation of the lamellae (Fig. 4). The measurement must contain an exact number of complete lamellae. The distance between these two points (D) is measured in cm. The number of lamellae (L) included between these two points is noted. The LF is calculated as follows: 10L–D ¼ LF. Larger teeth generally exhibit thicker lamellae. Thus, with the number of lamellae constant, the LF decreases as tooth size increases. Molar height (H) is taken on the tallest lamella in the specimen (Fig. 3). This measurement is dependant on the stage of wear at death, and does not necessarily measure the maximum height of the tooth. The maximum crown height should be measured only when the tallest lamella has just come into wear. Enamel thickness (ET) varies between elephantid species (Maglio, 1973; Madden, 1981). Generally the lamellae are not perpendicular to the occlusal surface. Measuring ET on the occlusal surface will give a value higher than in a crosssection perpendicular to the lamellae. Care must be taken to measure the enamel thickness at right angles to the
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Fig. 4. Left M/2 of Elephas namadicus, showing the measurable parameters and structural characteristics of elephant teeth (after Maglio, 1973). A ¼ occlusal view; B ¼ buccal view, anterior to the right.
estimated value (See Appendix A in the online version of this article). 2.2. Minimum number of animals represented
Fig. 3. Profile view of an upper molar (A), a lower molar (B), and an occlusal view of a lower molar (C) (from Agenbroad and Mead, 1994, modified from Saunders, 1970). Lo ¼ length, occlusal surface; Ld ¼ length of plane perpendicular to the general orientation of the majority of the lamellae; H ¼ height of the tallest lamella; W ¼ width of the widest lamella (including cement).
height of the lamella. The ET remains fairly constant in an antero-posterior longitudinal section. Ten measurements were taken on each specimen and the average reported. If insufficient lamellae are in full wear, as many measurements as practical were taken, averaged, and reported as an
Although several complete teeth were recovered, one or more incomplete tooth parts may be from a single tooth. Each animal has at least four teeth in wear at any time, and one tooth, e.g. the M3, may be erupted at a different time in each quadrant. Thus, it is difficult to estimate the number of individual mammoths represented by the sample. The teeth identified to position represent a minimum number of 25 ðN ¼ 25Þ individuals. The number of specimens representing each of the molars (M1, M2, and M3 upper and lower) is listed by quadrant in Table 2 and the measurements are listed by tooth position and quadrant in Appendix A. We can estimate the minimum number of individuals as follows: 1. There are 21 right M3/s. These include two complete teeth (TMM 41724-66, TMM 41724-69) in full wear. There are 11 posterior sections (TMM 41724-28, TMM 41724-31, TMM 41724-46, TMM 41724-57, TMM 41724-78, TMM 41724-84, TMM 41724-103, TMM 41724-106, TMM 41724-114, TMM 41724-115, TMM 41724-130), indicating 11 minimum individuals. There is one aberrant section (TMM 41724-61) with lamellae at a 451 angle, one central section with 11 unerupted lamellae (TMM 41724-102) that does not match any posterior
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sections, one anterior section (TMM 41724-27) that has a high LF (7.5), and two anterior sections (TMM 41724-37, 41724-58) that match no posterior sections. This yields a total of 18 ðN ¼ 18Þ minimum individuals based on the right M3/s. 2. There are seven specimens identified as right M2/s. One is complete (TM 41724-59). The differences in the LF of three anterior sections (TMM 41724-22, TMM 41724-29, TMM 41724-156) and three posterior sections (TMM 41724-109, TMM 41724-113, TMM 41724-119) of the remaining fragments precludes them from representing less than six teeth. The wear stages of the seven right M2/s indicate that none are from the same individual as any of the right M3/s. Only two have reached wear stage XVII (100% wear), and the youngest of the 18 M3/s listed above is as young as wear stage XIX (20–30% in wear) (see Table 3). The right M2/s indicate a minimum of seven ðN ¼ 7Þ individuals. 3. There are no right M1/ s in the sample.
2.3. Age determination The approximate age of African elephants can be determined from tooth wear (Laws, 1966; Haynes, 1991). The estimation of the age of a mammoth so determined is given in African Elephant Years (AEY). However, tooth wear may vary between individuals. Teeth in any given quadrant may not erupt at exactly the same time, and thus could exhibit different wear stages. The lower teeth are smaller than the uppers, and wear faster (Haynes, 1991). Also, an individual chews more on one side than the other, resulting in different wear stages from side to side. Assigning an estimate of age based on the wear stage of one tooth may not reflect actual age of the individual. It is difficult to estimate age from incomplete teeth (guidelines are provided in Appendix B). However, these estimates provide information on the relative age
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structure within a fossil assemblage, and are more precise than those based on tooth position alone. The Laws scale (1966) (Table 3) classifies the wear stage of a tooth (referred to as ‘‘Relative Age Group’’ by Laws), and provides an estimated age. However, the Laws scale often results in anomalous age distributions (Fatti et al., 1980), and certain age categories may be missing. The Craig scale (Haynes, 1991) (Table 3) is preferred by Haynes as Craig’s sample was much larger than that of previous studies and has more age categories. The late wear stage of one tooth overlaps the early wear stage of the next tooth, so more than one tooth fragment in the Mathis sample may be in occlusion from the same quadrant of one animal. The wear stages of the mammoth teeth from the Mathis sample are plotted in Fig. 5. Individual age at the time of death can be estimated in 60 of the Mathis specimens. These are plotted in an age distribution histogram (Fig. 6). Sexual maturity in mammoths occurs at 18–20 years (Haynes, 1991), although this can vary. In the African elephant, this is reached between 12 and 15 years of age. Sexual dimorphism in size becomes more apparent as mammoths reach maturity. It first appears at age 5, and increases as the animal matures (Haynes, 1991). In African elephants, the teeth of males usually are larger than those of females of the same age, although some older females can have larger teeth than others (Haynes, 1991). The M3s of males are longer, wider, and higher crowned than in females. The PN of males may be the same as in females, but the LF is lower in the male (the individual lamellae are thicker anterioposteriorly and there is more cementum between the lamellae). The ET may be slightly higher in males. The M3s of African elephants erupt and come into wear about the age 27–28 (Haynes, 1991). Male M3s are larger than the female M3s, and it is assumed that most of the largest molars within a particular age group represent males. Figs. 7–12 show the distribution of width, lamellar frequency and enamel thickness of mammoth molars from
Fig. 5. Distribution of the wear stage (Relative Age Group of Laws, 1966) of the mammoth molars from the Mathis Quarry (locality TMM 41724) (after Laws, 1966; from Haynes, 1991).
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the Mathis quarry, and is the source of the criteria used in classifying a tooth or tooth fragment as male. If a specimen meets two of the three criteria (Table 4), it is presumed herein to be from a male, and others are judged to be females or males under 5 years of age. 3. Discussion and conclusions The Mathis sample is not catastrophic, and does not represent a single elephantid herd. The specimens were recovered from different levels within the Mathis gravel quarry and appear to represent an attritional accumulation within the fluvial deposit. However, there is a taphonomic or sampling bias. No premolars were recovered, and the
Fig. 6. Age distribution, in African Elephant years (AEY) of the mammoth molars from the Mathis quarry (Locality TMM 41724). The specimens are grouped in increments of 5 AEY. Age estimated according to the Craig Scale (Haynes, 1991).
younger animals are not represented. The assemblage likely reflects an otherwise unbiased adult population. Of the 149 teeth or fragments of teeth in the Mathis sample, 96 have been assigned a tooth position (Table 2). Thirty-nine of the specimens can be classed as male (see criteria discussed above), and 59 as female (See Appendix A in the online version of this article). Of the specimens used to establish the 25 minimum number of individuals, only eight are males, and of these, five of the eight are mature males (See Appendix A in the online version of this article). Note the marked drop in frequency between the ages of 25 and 35 AEY (Fig. 6), which is the period when the M3s are coming into wear (Table 3). Fig. 13, a scattergram, exhibits two clusters, one representing M1s and M2s, and a second representing M3s. Note the gap between the two clusters. We have no plausible explanation for this. Fig. 13 also shows a wide variation in width in animals of the same age. The width is greater in males and also in uppers as expected. ET and LF vary directly with molar width, reflecting the size of the tooth. Larger molars exhibit a lower LF, higher ET, and greater width as expected (Figs. 14–19). These scattergrams also show a wide variation in values. There is a wide variation in molar width in animals of the same age, and molars of approximately the same width there is great variation in LF and ET. ET varies considerably among molars with approximately the same LF. The correlation between tooth size and enamel thickness also relates to sexual dimorphism. A molar may be in the high end of the range in one parameter and in the low range or midrange in the others. The ET of the M3/s has a range from 2.3 to 3.3 mm (mean 2.6 mm), the M/3s a range of 2.3–3.1 mm (mean 2.6 mm) (Table 1). These values are comparable to those recorded for the imperator variety of Mammuthus columbi (Saunders, 1970; Madden, 1981). The LF of molars in the Mathis sample ranges from 4.0 to 8.0 (mean 5.7). These measurements are comparable to those typically found in
Fig. 7. Comparison of the distribution of widths of mammoth upper molars from the Mathis quarry (locality TMM 41724). The specimens are grouped by 5 mm increments.
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Fig. 8. Comparison of the distribution of widths of mammoth lower molars from the Mathis quarry (locality TMM 41724). The specimens are grouped by 5 mm increments.
Fig. 9. Comparison of the distribution of lamellar frequencies of mammoth upper molars from the Mathis quarry (locality TMM 41724). The specimens are grouped in increments of 0.5 lamellae.
Fig. 10. Comparison of the distribution of lamellar frequencies of the mammoth lower molars from the Mathis quarry (locality TMM 41724). The specimens are grouped in increments of 0.5 lamellae.
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Fig. 11. Comparison of the distribution of enamel thickness of mammoth upper molars from the Mathis quarry (locality TMM 41724).
Fig. 12. Comparison of distribution of enamel thickness of mammoth lower molars from the Mathis quarry (locality TMM 41724).
Table 4 Criteria used to classify a tooth or tooth fragment from the Mathis quarry (locality TMM 4172) as presumed male Tooth position
M3/ M/3 M2/ M/2
Criteria Width (mm)
Lamellar frequency (#/10 cm)
Enamel thickness (mm)
X100 X95 X85 X80
p5 p5.5 p6.0 p6.0
X2.7 X2.6 X2.4 X2.4
Note: A specimen meeting two of the three criteria is assumed to be male.
later M. columbi (Saunders, 1970; Madden, 1981). The PN (See Appendix A in the online version of this article) also falls within the parameters of the imperator variety of M. columbi. The Mathis sample of molars exhibit more primitive dental characteristics than would be expected from
Rancholabrean NALMA mammoths. They compare closely to the imperator variant of Mammuthus columbi that is typically recovered from Irvingtonian NALMA localities. The Mathis assemblage represents a local variant population of Mammuthus columbi present in the southcentral US. The degree of variation in the measurements of the specimens from the Mathis quarry supports the conclusion of Lister (2001, pp. 648–651), and Lister and Sher (2001) for European specimens, that the PN is the most reliable measurement for tracking evolutionary advancement. The LF, while not as reliable as the PN, may be used when the PN cannot be determined. Appendix A See the online version of this article for a table showing the dental measurements of Mammuthus colombi specimens from TMM Locality 4172, Mathis, TX at doi:10.1016/ j.quaint.2005.03.014
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Fig. 13. Correlation of age and molar width of mammoth cheek teeth from the Mathis quarry (locality TMM 41724). Age estimated according to the Craig scale (Haynes, 1991) (Table 3). The line is the mean (M1s and M2s on the left, M3s on the right). Legend: () upper tooth, female; (D) upper tooth, male; (J) lower tooth, female; (D) lower tooth, male. Solid line is the mean.
Fig. 14. Correlation of molar width and lamellar frequency of mammoth M1s and M2s from the Mathis quarry (locality TMM 41724). () Upper tooth, female; (D) upper tooth, male; (J) lower tooth, female; (D) lower tooth, male. Solid line is the mean.
Appendix B. Estimation of age by dental wear stage The following guidelines are followed to estimate the age of a section or fragment of a mammoth tooth (see Table 3): (A) Anterior section of tooth 1. If the anterior lamellae are in wear and the posterior lamellae of the section are not erupted or just coming into wear, a wear stage can be assigned and an age estimated.
Fig. 15. Correlation of molar width and lamellar frequency of mammoth M3s from the Mathis quarry (locality TMM 41724). () Upper tooth, female; (D) upper tooth, male; (J) lower tooth, female; (D) lower tooth, male. Solid line is the mean.
2. If all lamellae of the section are in wear, by counting the lamellae in the fragment, we can determine the minimum portion of the tooth in wear and assign a wear stage and estimate a minimum age for the section. 3. If the anterior lamellae of the section are smoothing (Table 3), a minimum wear stage can be assigned and a minimum age estimated. (B) Central section of tooth 1. From the shape of the fragment, in many cases it may be possible to estimate the number of plates
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Fig. 16. Correlation of molar width and enamel thickness of mammoth M1s and M2s from the Mathis quarry (locality TMM41724). () Upper tooth, female; (D) upper tooth, male; (J) lower tooth, female; (D) lower tooth, male. Solid line is the mean.
Fig. 17. Correlation of molar width and enamel thickness of mammoth M3s from the Mathis quarry (locality TMM 41724). () Upper tooth, female; (D) upper tooth, male; (J) lower tooth, female; (D) lower tooth, male. Solid line is the mean.
missing, and a minimum or maximum wear stage may be assigned and an age estimated. 2. If the posterior plates are barely in wear, a wear stage may be assigned and an age estimated.
Fig. 18. Correlation of lamellar frequency and enamel thickness of mammoth M1s and M2s from the Mathis quarry (locality TMM 41724). () Upper tooth, female; (D) upper tooth, male; (J) lower tooth, female; (D) lower tooth, male. Solid line is the mean.
(C) Posterior section of tooth 1. If all lamellae are in wear, the tooth is at least 100% in wear, but it is not known if the missing anterior lamellae are smoothing (Table 3) or have
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Fig. 19. Correlation of lamellar frequency and enamel thickness of mammoth M3s from the Mathis quarry (locality TMM 41724). () Upper tooth, female; (D) upper tooth, male; (J) lower tooth, female; (D) lower tooth, male. Solid line is the mean.
been shed. However, a minimum age can be estimated. 2. If some posterior lamellae are just coming into wear or are not erupted, the wear stage can be assigned and an age estimated. 3. If no lamellae are erupted, we can estimate the minimum portion of the tooth that is not in wear, and a maximum age can be estimated. References Agenbroad, L.D., 2003. New localities, chronology and comparisons for Mammuthus exilis: 1994–1998. In: Reumer, J.W.F., DeVos, J., Mol, D. (Eds.), Advances in Mammoth Research (Proceedings of the Second International Mammoth Conference, Rotterdam, May 16–20 1999), vol. 9. Deinsea, pp. 1–16.
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