Divided zygoma in Holocene human populations from Northern China.

Qun Zhang,Shiyu Yang,Quanchao Zhang,Paul C Dechow,Hui‐Yuan Yeh,Hong Zhu,Qian Wang

doi:10.1002/ajhb.23314

Abstract

ObjectivesDivided zygoma (DZ) occurs in contemporaneous human populations, with the highest incidences in people from East Asia and Southern Africa. The present study examines the prevalence and variation of this condition in the Holocene populations of Northern China for the first time.MethodsIn this study, 1145 skulls from various human populations living in Northern China from the Neolithic Age to recent dynasties (5000‐300 years BP) were examined. Specifically, cranial measurements and a CT scan were conducted to quantify craniofacial morphology.ResultsFifteen skulls were identified with DZ, revealing an overall prevalence of 1.3% in the collection, while it was determined to be higher in North Asian and Northeast Asian regional groups. In skulls with unilateral DZ, the superior division of the zygoma was generally slender, while the inferior division of the zygoma was more robust. In skulls with bilateral DZ, the maxillae were generally more laterally extended. Moreover, unilateral DZ skulls displayed differences in cortical bone thickness between two sides of the facial skeleton.DiscussionIn context, the distribution pattern within these data points toward a greater prevalence of the DZ phenotype in North and Northeast Asian regional groups, suggesting a hypothesis that the DZ trait is more frequent in populations characterized by flat and broad faces. Accordingly, further studies into the DZ condition will deepen our understanding of developments in plasticity, variation, and recent evolution of the human cranium.

Highlights

The zygomatic bones are an important component of the midfacial skeleton, and they play a critical role in the support and integration of the craniofacial skeleton as well as the masticatory apparatus
In most divided zygoma (DZ) phenotypes, the bone is transected by a supernumerary suture that divides the facial aspect of the zygoma into upper and lower divisions, giving the bone a bipartite morphology termed os zygomaticum bipartitum, previously called os japonicum due to its high prevalence in the Japanese population (Hrdlicka, 1902)
Crania from Northern China retrieved in archeological excavations were examined to determine the prevalence of the DZ condition in these Holocene populations for the first time

Summary

Introduction

The zygomatic bones are an important component of the midfacial skeleton, and they play a critical role in the support and integration of the craniofacial skeleton as well as the masticatory apparatus. Each zygoma is normally quadrangular in morphology and articulates with the ipsilateral maxilla, frontal, temporal, and sphenoidal bones. Each zygoma provides an attachment for a masseter muscle, and plays an important functional role in the masticatory system. Important in maintaining normal function of the facial skeleton (Wang & Dechow, 2016). In a natural rare form, the zygoma can be divided by extra sutures into two or more parts (Hanihara, Ishida, & Dodo, 1998; Hrdlicka, 1902; Ossenberg, 2013; Wang & Dechow, 2016). In most divided zygoma (DZ) phenotypes, the bone is transected by a supernumerary suture that divides the facial aspect of the zygoma into upper and lower divisions, giving the bone a bipartite morphology termed os zygomaticum bipartitum, previously called os japonicum due to its high prevalence in the Japanese population (Hrdlicka, 1902)

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