Fetal and neonatal maxillary ontogeny in extant humans and the utility of prenatal maxillary morphology in predicting ancestral affiliation

Abstract

Objectives The midface of extant H. sapiens is known to undergo shape changes through fetal and neo-natal ontogeny; however, little work has been done to quantify these shape changes. Further, while midfacial traits which vary in frequency between populations of extant humans are presumed to develop prenatally, patterns of population-specific variation maxillary shape across ontogeny are not well documented. Only one study of fetal ontogeny which included specific discussion of the midface has taken a 3D geometric morphometric approach, and that study was limited to one population (Japanese). The present research project seeks to augment our understanding of fetal maxillary growth patterns, most especially in terms of intraspecific variation. Materials and Methods Three-dimensional coordinate landmark data were collected on the right maxillae of 102 fetal and neo-natal individuals from three groups (Euro-American, African-American, “Mixed Ancestry”). Results Shape changes were seen mainly in the lateral wall of the piriform aperture, the anterior nasal spine, and the subnasal alveolar region. The greatest difference across age groups (2nd Trimester, 3rd Trimester, Neonates) was between the second and third trimester. Euro-Americans and African-Americans clustered by population and differences in midfacial morphology related to ancestry could be discerned as early as the second trimester (p=0.002), indicating that population variation in maxillary morphology appears very early in ontogeny. Discussion The midface is a critical region of the skull for assessing ancestry and these results indicate that maxillary morphology may be useful for estimating ancestry for prenatal individuals as young as the second trimester.

Intraspecific variability in human maxillary bone modeling patterns during ontogeny

“…Freidline, Gunz, and Hublin (2015) compared the ontogenetic and static allometry (i.e., the covariation between shape and size) of several geographically diverse human populations using geometric morphometric techniques. Their results support previous studies by showing that population differences in facial morphology are already present early in ontogeny, possibly prenatally (e.g., Bastir & Rosas, 2004;Lieberman, McBratney, & Krovitz, 2002;Mooney & Siegel, 1986;Nicholas, 2016;Ponce de Leon & Zollikofer, 2001). They also demonstrated subtle differences between populations in the patterns of absolute and relative growth and development.…”

“…Previous studies have already shown that population differences in facial morphology develop early, possibly prenatally (Bastir, O'Higgins, & Rosas, 2007; Bulygina et al, 2006; Freidline et al, 2015; Sardi & Ramirez‐Rozzi, 2012; Vidarsdóttir et al, 2002; Viðarsdottir & O'Higgins, 2003); however, the morphological variation in prenatal stages has only been investigated in few studies (Mooney & Siegel, 1986; Weinberg, 2005; Morimoto, Ogihara, Katayama, & Shiota, 2008; Nicholas, 2016). Using geometric morphometric techniques, Nicholas (2016) found shape differences in the fetal maxilla between African‐ and European‐Americans as early as the second trimester. The results of our morphological analysis further support these findings, as shape differences between the three populations can be observed already around birth (Figure 2).…”

Ontogeny of the human maxilla: a study of intra‐population variability combining surface bone histology and geometric morphometrics

“…), a comparison of specimens from populations with different ancestries will help clarify this question. Nicholas () found morphological differences between European‐Americans and African‐Americans in the maxilla already present before birth; whether this translates into different bone modeling patterns is still unknown.…”

Anatomical Variation in Maxillary Sinus Ostium Positioning: Implications for Nasal‐Sinus Disease

“…As previous studies (Enlow, ; Rosas and Bastir, ) indicate sex‐based differences in external crania starting at puberty, whereby male growth rates increase and female's slow, it could very well be that the slight sex‐based differences found in the current study would be accentuated in an older sample. However, it is important to note that sex‐based differences in external facial ontogeny depend on the specific traits analyzed, and they can appear at different times depending on population affinity (see Bulygina et al, ; Nicholas, ). It is likely that ontogenetic processes related to sexual dimorphism among internal facial structures are equally complicated and need further study among larger, diverse samples.…”