Morphological variation of the early human remains from Quintana Roo, Yucatán Peninsula, Mexico: Contributions to the discussions about the settlement of the Americas

Abstract

The human settlement of the Americas has been a topic of intense debate for centuries, and there is still no consensus on the tempo and mode of early human dispersion across the continent. When trying to explain the biological diversity of early groups across North, Central and South America, studies have defended a wide range of dispersion models that tend to oversimplify the diversity observed across the continent. In this study, we aim to contribute to this debate by exploring the cranial morphological affinities of four late Pleistocene/early Holocene specimens recovered from the caves of Quintana Roo, Mexico. The four specimens are among the earliest human remains known in the continent and permit the contextualization of biological diversity present during the initial millennia of human presence in the Americas. The specimens were compared to worldwide reference series through geometric morphometric analyses of 3D anatomical landmarks. Morphological data were analyzed through exploratory visual multivariate analyses and multivariate classification based on Mahalanobis distances. The results show very different patterns of morphological association for each Quintana Roo specimen, suggesting that the early populations of the region already shared a high degree of morphological diversity. This contrasts with previous studies of South American remains and opens the possibility that the initial populations of North America already had a high level of morphological diversity, which was reduced as populations dispersed into the southern continent. As such, the study of these rare remains illustrates that we are probably still underestimating the biological diversity of early Americans.

Digital restoration of the Wilson‐Leonard 2 Paleoindian skull (~10,000 BP) from central Texas with comparison to other early American and modern crania

“…According to these authors, the Quintana Roo material demonstrates a very high degree of morphological and biological diversity among indigenous North Americans in the late Pleistocene and early Holocene, which far exceeds that typically observed among their counterparts in South America. The results of the current study—including the wide range of variation observed among North American samples, the clear separation of WL‐2 from at least some of her contemporaries in the US and Mexico, and the somewhat different associations she seems to exhibit depending on the analytical procedure and/or morphological aspects considered—align well with the general conclusions of Hubbe et al (2020). Moreover, even the seemingly contradictory finding that, unlike the Quintana Roo crania (and many other early North and South American specimens), WL‐2 appears quite similar to recent American Indians is potentially in line with the idea that early North American morphology varied widely, given that multiple different patterns of affinity might well be expected among the individuals in a highly diverse population.…”

“…That several aspects of cranial size and shape in WL‐2 are quite distinct from many of her North and South American contemporaries further supports the idea of significant morphological variation among Paleoindians as a whole, which has been noted by previous authors (e.g., Hubbe et al, 2020; Jantz & Owsley, 2001). Recent work by Hubbe et al (2020) documents extensive morphological variation among a series of Paleoindian crania from Quintana Roo, Mexico, particularly when compared with South American Paleoindians, and found that these individuals exhibited surprisingly different patterns of affinity to early American and modern reference samples. According to these authors, the Quintana Roo material demonstrates a very high degree of morphological and biological diversity among indigenous North Americans in the late Pleistocene and early Holocene, which far exceeds that typically observed among their counterparts in South America.…”

“…A common way to address issues concerning potential biological affinities of the earliest Americans is through analyses of craniofacial morphology (CFM) (e.g., González‐José et al, 2005, 2008; Hubbe et al, 2014; Jantz & Owsley, 2001; Key, 1982; Neves et al, 1999; Neves & Pucciarelli, 1991; Owsley & Jantz, 1999; Powell & Neves, 1999; Steele & Powell, 1992, 1993). CFM studies typically involve detailed comparisons of craniofacial form, both within samples of late Pleistocene and early Holocene (i.e., ~14,000–8000 BP) individuals from the Americas, and between Paleoindians and more recent populations from around the world (e.g., Hubbe et al, 2011, 2014, 2020; Jantz & Owsley, 1997, 2001; Neves et al, 1999, 2007; Neves & Hubbe, 2005; Owsley & Jantz, 1999; Steele & Powell, 1992, 1993).…”

Population history of Brazilian south and southeast shellmound builders inferred through dental morphology

“…Because distances invariably take the information of all the variables and, in the case of MMD and Euclidean distance, variables are all equally weighted, they are prone to be more affected by outlier values in one or few variables. PCA analyses, on the other hand, explores the most relevant axes of covariance among all variables, which results in the noise caused by outliers in one or few variables to not be present in the most important PCs (see a similar discussion in Hubbe et al, 2020). Therefore, the PCA offers a check for the reliability of distance analyses and complement well the analyses based on pairwise distances.…”

Towards an interdisciplinary perspective for the study of human expansions and biocultural diversity in the Americas

“…One of the main challenges that arose from our interdisciplinary debate is the lack of hypotheses and models that can be tested from multiple disciplinary perspectives. On one hand, many studies about the origin of Native American biological diversity are overly focused on describing patterns of variation, 52 rather than testing specific hypotheses 53 . On the other hand, as pointed out by Dillehay, 54 most recent studies are not discussing new evidence in relation to previous models but rather dismissing them and proposing new ones (e.g., References 19,55 in Reference 54).…”