The Uto-Aztecan Premolar and a Back-Migration of American Indians to the Old World

American Journal of Physical Anthropology 143 (4): 570-578, 2010 DOI: 10.1002/ajpa.21351

The Uto-Aztecan Premolar Among North and South Amerindians: Geographic Variation and Genetics

Miguel E. Delgado-Burbano, G. Richard Scott, and Christy G. Turner II

The Uto-Aztecan premolar (UAP) is a dental polymorphism characterized by an exaggerated distobuccal rotation of the paracone in combination with the presence of a fossa at the intersection of the distal occlusal ridge and distal marginal ridge of upper first premolars. This trait is important because, unlike other dental variants, it has been found exclusively in Native American populations. However, the trait’s temporal and geographic variation has never been fully documented. The discovery of a Uto-Aztecan premolar in a prehistoric skeletal series from northern South America calls into question the presumed linguistic and geographic limits of this trait. We examined published and unpublished data for this rare but highly distinctive trait in samples representing over 5,000 Native Americans from North and South America. Our findings in living Southwest Amerindian populations corroborate the notion that the variable goes beyond the bounds of the Uto-Aztecan language family. It is found in prehistoric Native Americans from South America, eastern North America, Northern and Central Mexico, and in living and prehistoric populations in the American Southwest that are not members of the Uto-Aztecan language stock. The chronology of samples, its geographic distribution, and trait frequencies suggests a North American origin (Southwest) for UAP perhaps between 15,000 BP and 4,000 BP and a rapid and widespread dispersal into South America during the late Holocene. Family data indicate that it may represent an autosomal recessive mutation that occurred after the peopling of the Americas as its geographic range appears to be limited to North and South Amerindian populations.


American Journal of Physical Anthropology 146 (3): 474-480, 2011 DOI: 10.1002/ajpa.21593

Brief Communication: New Evidence on the Spatiotemporal Distribution and Evolution of the Uto-Aztecan Premolar

Kent M. Johnson, Christopher M. Stojanowski, Kathryn O’D. Miyar, Glen H. Doran, and Robert A. Ricklis

American Journal of Physical Anthropology 149 (2): 318-322, 2012 DOI: 10.1002/ajpa.22125

Uto-Aztecan premolar (UAP) is a rare morphological feature of the maxillary first premolar that occurs in Native American populations with frequencies ranging 0–16.7%. A recent summary of UAP by Delgado-Burbano et al. (2010) suggests the trait evolved around 4,000 BP in the American Southwest where the earliest cases occur and where the trait exists at the highest frequencies among contemporary populations. In this article, we present new data on UAP prevalence from an Archaic North American sample from Buckeye Knoll, Texas (circa 7,500–6,200 cal BP). Buckeye Knoll preserves a single case of UAP, and a sample frequency of 3.6%. In addition, we confirm the presence of UAP in other eastern North American Archaic skeletal samples from the Windover and Harris Creek at Tick Island sites in Florida. We also review the dental morphological literature to assess: 1) whether UAP prevalence is limited to New World populations, and 2) whether the trait’s antiquity can be extended further into the Early Holocene Paleoindian period. Additional cases of UAP are presented from the Pacific coast of South America, Europe, Asia, and Australia. Combined, these data greatly expand the spatial and temporal distribution of UAP and suggest the trait evolved considerably earlier than previously thought.


Brief Communication: The Uto-Aztecan Premolar in Early Hunter-Gatherers From South-Central North America

Matthew S. Taylor

The Uto-Aztecan premolar is a discrete dental trait found in low frequency (<2%) among world populations. The highest frequencies of the trait have been found among the indigenous populations of North America and, to a lesser extent, South America. Because of the trait’s relatively higher frequency in the Western Hemisphere, the antiquity and distribution of the feather is important for reconstructing the biocultural interactions of prehistoric populations. While early research concluded that the Uto-Aztecan premolar originated in the American Southwest around 4,000 years Before Present (BP), more recent studies have discovered the trait across the Americas and in parts of Europe and Asia. For this study, over 300 dentitions representing foragers and farmers in south-central North America were examined. The trait was found in relatively high frequency (over 11%) in Archaic hunter-gatherer populations from Central Texas, with high frequencies also found in the adjacent western Gulf Coastal Plain. The presence of this trait in Early Archaic populations suggests that the trait was present by 8,000 BP and persisted at a high frequency into the Late Archaic period.


There seems to be one paper every year devoted to the Uto-Aztecan Premolar (UAP). UAP is an ambilateral (present on either left side, right side or both sides) upper premolar polymorphism first attested by D. H. Morris (“Maxillary Premolar Variation among Papago Indians,” Journal of Dental Research 46: 736-773, 1967) in a sample of Papago Indians. It’s technical name is distosagitttal ridge (Turner C. G., C. R. Nichol, and R. G. Scott. “Scoring Procedures for Key Morphological Traits of the Permanent Dentition: The Arizona State University Dental Anthropology System,” in Advances in Dental Anthropology, edited by M. Kelley and C. Larsen. Pp. 13-31. New York: Wiley-Liss, 1991). On the outside it’s distinguished by a pronounced ridge that extends from the apex of the buccal cusp to the distal occlusal border at or near the sagittal sulcus. Typically, a distal fossa sits between the distosagittal ridge and the distal occlusal border of the buccal cusp (see below, from Johnson et al. 2011; Taylor et al. 2012). The crown identification of UAP in ancient remains is often problematic because of dental wear. In this case one aspect of premolar root structure can be used as a proxy for crown morphology: in premolars with a distosaggital ridge, there is a mesial rotation of the buccal surface as well as buccolingual expansion of the paracone.








There are three kinds of dental traits in terms of their distributional pattern. There are traits that are moderately frequent in some regions, highly frequent in others and very infrequent elsewhere (e.g.., shovel-shaped incisors, Carabelli’s cusp). Then, there are traits that are highly frequent in one region but very rare everywhere else (e.g., the Bushman canine). Finally, there are traits that are rare no matter where they are found. For instance, Europeans have 5-10% frequency of two-rooted lower canines. UAP is a rare polymorphism found mostly in the New World. It’s not counted as a defining feature of such taxonomic categories as Sinodonty, Sundadonty or Afridonty. Up until the recent research reported at the American Journal of Physical Anthropology, UAP was considered to be a regional dental feature with a very shallow time depth. Morris et al. (Morris D. H., S. G. Hughes, and A. A. Dahlberg. 1978. The Uto-Aztecan Premolar: The Anthropology of a Dental Trait,” in Development, Function, and Evolution of Teeth, edited by P. Butler, and K. A. Joysey. Pp. 69-79. London: Academic Press, 1978) hypothesized that the trait dated back to at least 3200 YBP and suggested it arose as a point mutation among desert-adapted hunter-gatherers of the Southwest.

As it is often the case with traits observed among American Indians, the original assumption of UAP recency and limited distribution were proven to be wrong. Taylor (2012) found this trait at moderate frequency in Archaic forager populations from Central Texas and the adjacent western Gulf Coastal Plain. The presence of this trait in Early Archaic populations suggests that the trait was present by 8,000 BP and persisted at a high frequency into the Late Archaic period. Johnson et al. (2011) speculate that the trait may be 15,000 years old. Outside of the American Southwest and Southeast, the variant has been observed in the Ohio Valley, Central Mexico, California as well as in Ecuador, Chile, Columbia, Brazil and Venezuela (see Reyes G., A. Padilla, M. Palacios, J. Bonomie, X. Jordana, and C. Garıa C. 2008. “Posible presencia del rasgo dental ‘premolar Uto-Azteca’ en un cranio de epoca prehispanica (Siglos II a.C. Siglo IV d.C.), cemeterio de ‘las Locas’, Quibor, (Estado Lara, Venezuela),” in Boletın Antropologico 72: 53-85). The attested antiquity and the wide distribution of UAP in both North and South America show the limitations of Sinodonty and the more controversial taxon “Sundadonty” in capturing American Indian dental variation.

The distribution of the UAP straddles across the hypothetical divide between Na-Dene vs. the rest of American Indians. It is present in Southern Athabascans (Navajos) at 2.29% (Delgado-Burbano 2010, 572), which is higher than the frequency of this trait in neighboring Pueblos defying the possibility of gene flow from the latter to the former. The presence in Southern Athabascans of a rare genetic variant Albumin Naskapi (Al*Naskapi), otherwise found in Algonquin-speakers, provides a possible parallel to the distribution of UAP. Both traits being rare is good evidence against the perspective recently revived by Reich et al. (2012) on the basis of autosomal markers that postulates three migrations to the New World, with Na-Dene-speakers coming as a separate wave.

Better sampling has also turned up surprises regarding the presence of UAP in the Old World. UAP was detected in a Bronze Age individual from the Trans-Baikal region of Siberia, a Bronze Age individual from northwestern Mongolia, a single Bronze Age individual from Spain, a prehistoric specimen from Australia, an individual from Bengal that dates to the 19th or early 20th century, and four German clinical specimens that likely date to the 20th century (Johnson et al. 2011, 477-478). The first two locations (Trans-Baikal and Mongolia) are noteworthy because it’s precisely in these two areas (Okunev and Sopka and Chandman/Xiongnu) Bronze Age craniological samples have turned up skulls with specific North American Indian traits. The German specimens are noteworthy as they provide clear examples of UAP in living populations from outside the New World and they are consistent with both the phenomenon of receding shoveling in European dentition and the recently detected Amerindian autosomal component in European populations.

More research will likely support the hypothesis (out-of-America III) whereby there was a Late Pleistocene-Early Holocene back migration of American Indians to East Asia and that this migration affected not just Northeastern Siberia but also regions at least as far south as Trans-Baikal region and Mongolia. The presence of UAP in Europe and Australia may be evidence of an earlier migration out of the New World more consistent with the predictions of out-of-America II.