Arch Lake Woman: Physical Anthropology and Geoarchaeology

Post-cranial Measurements

Study of the Arch Lake Site 48 Post-cranial Measurements ✦ M etric analysis of post-cranial bones has focused on the femur and tibia, and interpretation emphasizes the biomechanical, behavioral, and adaptive implications of size and shape. Basic post-cranial dimensions could be obtained on the somewhat fragmented remains of the Arch Lake skeleton. Table 17 presents femur and tibia measurements and indices for Arch Lake and three comparative samples: Pecos Pueblo, Coalescent Arikara, and American whites from the Terry anatomical collection. Pecos data were obtained from E. Hooton’s data cards (Weisensee 2001), the Coalescent Arikara from Cole (1994), and the Terry data were provided by S. D. Ousley, Department of Anthropology, national Museum of natural History. Arch Lake variables were tested against the comparative samples using a t-test comparing an individual to a sample, as recommended by Jolicoeur (1999). The platymeric, pilastric, and cnemic indices are computed as the anterior-posterior (a-p) dimension divided by the medial-lateral (m-1), so that a value > 1.0 describes a-p elongation, and values < 1.0 reflect m-1 expansion. Robusticity indices at the level of the femur midshaft, subtrochanter, and nutrient foramen of the tibia are computed as (a-p + m-1)/maximum bone length x 100. The humerus was treated in the manner described by Collier (1989) in order to use his comparative data. Humerus robusticity is computed as circumference/humerus length. Arch Lake’s values and data from Collier (1989) are presented in table 18. The platymeric, pilastric and cnemic indices presented in table 17 describe the shape of the diaphyses at the subtrochanteric and midshaft levels of the femur and at the nutrient foramen of the tibia. The most striking feature of Arch Lake is the absence of platymeria, a feature commonly seen in recent native Americans (Gill 1995). Arch Lake differs significantly from the two native American samples in table 17 but is similar to American whites. Arch Lake is also somewhat more robust in the subtrochanteric region than other groups, but not significantly so. 48 49 TAbLe 17. FeMur ANd TibiA diMeNSiONS (MM) ANd SeLeCTed iNdiCeS FOr ArCh LAKe COMPAred TO TWO FeMALe NATive AMeriCAN SAMPLeS ANd AMeriCAN WhiTeS. variable Arch Lake Pecos Pueblo Coalescent Arikara+ American Whites N Mean s. d. N Mean s.d. N Mean s. d. Fem max length 447 109 394.51** 17.49 192 415.20 17.30 56 426.50 22.63 Subtroch a-p 29 109 21.45** 1.54 193 22.40** 1.80 56 26.23 2.03 Subtroch m-l 31 109 29.26 1.91 193 32.10 1.90 56 27.75 2.06 Midshaft a-p 28 109 25.12 2.08 194 25.90 2.10 56 26.45 2.12 Midshaft m-l 26 109 23.11* 1.41 194 24.40 1.50 56 26.07 1.92 Platymeric index 0.94 109 0.74** 0.66 193 0.72** 0.06 56 0.95 0.09 Pilastric index 1.08 109 1.09 0.10 194 1.06 0.09 56 1.02 0.09 Subtroch robusticity 13.42 109 12.87 0.72 192 12.88 0.68 56 12.66 0.78 Midshaft robusticity 12.08 109 12.24 0.71 192 12.11 0.65 56 12.31 0.79 Tibia max length 359 74 323.46* 15.34 192 348.00 16.10 56 343.86 19.42 Nut foramen a-p 32 74 30.17 1.95 194 31.20 2.50 56 29.13 1.92 Nut foramen m-l 21 74 19.50 1.58 194 22.00 2.20 56 23.00 2.05 Cnemic index 1.52 74 1.56 0.15 194 1.43 0.15 56 1.27* 0.11 Nut for robusticity 14.76 74 15.38 0.93 192 15.30 1.03 56 15.16 0.93 Crural index 80.31 67 82.48 2.21 17483 .882 .0254 80.44 2.64 * P < 0.05 ** P < 0.01 + From Cole 1994, from raw data. Study of the Arch Lake Site 50 Ruff (2000) has argued that femur cross section shape reflects mobility. The argument, briefly, is that mobility imposes anterior-posterior loading on the femur midshaft, which results in remodeling to enable the femur to resist the loading pattern with an a-p elongated femur midshaft. Hence the degree of femur a-p elongation has been taken as an indicator of mobility, even to the point of referring to it as a mobility index (Larsen 1997). Later, Ruff (2000) argued that terrain was the most important variable explaining femur a-p elongation. Wescott (2001) tested and elaborated this hypothesis using north American samples that included a wide range of subsistence types, culture areas , and terrain types. His results provide some support that femur cross sectional morphology reflects activity, as opposed to mobility, and that the effect is greater at the subtrochanteric level than at the midshaft. Shaft robusticity also reflects activity (Collier 1989). Arch Lake’s femur midshaft, expressed by the pilastric index, shows a-p elongation comparable to the two native American comparative samples and greater than in the nineteenth-century whites. Arch Lake’s robusticity exceeds the comparative groups at the subtrochanteric level but is more gracile than the comparative groups at the femur midshaft. The Arch Lake tibia is also gracile and, along with Pecos, has a-p elongation exceeding that of the other groups. The humerus picture is quite different. Its maximum length is short, below average for all comparative groups, and its circumference is large, above average for all comparative groups. neither dimension differs significantly from TAbLe 18. ArCh LAKe huMeruS MeASureMeNTS (MM) COMPAred TO WOrLd POPuLATiON SAMPLeS. Group humerus Length humerus Circumference robusticity Mean s. d. Mean s. d. Mean s. d. Arch Lake 284 - 64 - 22.54 Australian 306.4 17.6 52.3 4.8 17.1* 1.6 Whaling eskimo 284.4 17.4 55.8 4.7 19.6 1.4 riverine eskimo 285.7 14.8 53.4* 2.9 18.7* 1.1 American Whites 304.0 14.9 56.2 4.0 18.5* 1.4 Arikara indians 301.1 13.1 57.1 3.1 19.0* 1.1 romano-britons 298.3 13.8 57.1 3.2 19.1* 1.2 * differs significantly from Arch Lake 51 the comparative groups, except for Riverine Eskimos, but length and circumference taken together present a picture of a very robust humerus that differs from nearly all comparative groups. Given her nitrogen stable isotope value indicating a diet dominated by high quality protein, a strenuous recurrent task that might account for this robusticity was working bison hides. Arch Lake femur and tibia lengths exceed the means of all three comparative groups. In the case of Pecos, the difference is significant. Arch Lake femur and tibia lengths do not differ significantly from Coalescent Arikara or Terry collection whites. The combined length of the femur and tibia also exceeds means for neanderthals, European Upper Paleolithic, Mesolithic, and recent humans. The crural index (tibia length/femur length x 100) of Arch Lake is lower than seen in Coalescent Arikara or Pecos and roughly equal to the white sample. It is not as low as seen in cold-adapted populations, such as Eskimos, but not as high as seen in the European Upper Paleolithic or Mesolithic (Holliday 1999). Estimation of stature, while not necessary in terms of understanding bone dimensions, is useful to provide an indication of how early remains relate to modern people using a widely understood measure. It is difficult to know which formula to use, because we do not know the body proportions of the Arch Lake woman. Many modern native north Americans have relatively long legs (Jantz et al. 2002), and some, such as the Coalescent Arikara, have relatively high crural indices (Hall et al. 2004). However, many Mexican tribes have relatively short legs (Faulhaber 1970). Ruff has argued that stature formulae applied to fossils should be matched as closely as possible to the limb proportions of the fossil. Following that advice would lead to choosing the formulae of whites, the group to which the crural index of Arch Lake is most similar. Classical calibration can also be used, regressing bone length on stature and then solving for stature, which yields unbiased estimates (Konigsberg et al. 1998). Table 19 presents stature estimations using various approaches. Using whites assumes the Arch Lake woman has relatively short legs in relation to stature, while using blacks assumes she has relatively long legs relative to stature . Arch Lake’s crural index suggests her proportions may have been more like those of whites. The femur exhibits lower positive allometry with stature, so it is likely the more reliable. Tibia estimates are lower because of the relatively short tibia of Arch Lake. The humerus yields the lowest estimates, indiPost -cranial Measurements Study of the Arch Lake Site 52 cating that it is relatively short compared to the legs. The estimates in table 19 indicate that the Arch Lake female could have been quite tall. The largest estimate of 166.5 cm (5 feet 5½ inches) places her approximately equal to modern American whites. If one assumes relatively long legs; however, she would be somewhat shorter. TAbLe 19. eSTiMATiON OF STATure OF The ArCh LAKe FeMALe uSiNG iNverSe CALibrATiON (TrOTTer ANd GLeSer 1952) ANd CLASSiCAL CALibrATiON. Source Femur Tibia Humerus Trotter and Gleser Whites 164.51 ± 3.72 (64.8”) 162.74 ± 3.66 (64.1”) 153.36 ± 4.45 (60.4”) Trotter and Gleser Blacks 161.68 ± 3.41 (63.7”) 158.16 ± 3.70 (62.3”) 152.14 ± 4.25 (59.9”) Classical Calibration Whites 166.50 ± 4.76 (65.6”) 163.41 ± 5.33 (64.3”) --Classical Calibration Blacks 162.16 ± 3.79 (63.8”) 156.86 ± 4.53 (61.8”) --- ...