The upper limb skeleton and behavioral lateralization of modern humans from Zhaoguo Cave, southwestern China.

OBJECTIVES: Aims of the study are to initially describe and comparatively evaluate the morphology of the new Zhaoguo M1 upper limb remains, and contextualize upper limb functional adaptations among those of other worldwide Upper Paleolithic (UP) humans to make inferences about subsistence-related activity patterns in southwestern China at the Pleistocene-Holocene boundary. MATERIALS AND METHODS: The preserved Zhaoguo M1 skeletal remains include paired humeri, ulnae, and radii, among others. These specimens were scanned using micro-computed tomography to evaluate internal structural properties, while external osteometric dimensions of the Zhaoguo M1 upper limb elements also were acquired. Both sets of measurements were compared to published data on Neandertals, and Middle and Upper Paleolithic modern humans. RESULTS: The upper limb elements of Zhaoguo M1 display a suite of characteristics that generally resemble those of other contemporary Late UP (LUP) modern humans, while robusticity indices generally fall within the upper range of LUP variation. The Zhaoguo M1 upper limb elements display fewer traits resembling those of late archaic humans. The Zhaoguo M1 individual exhibits diaphyseal asymmetry in several upper limb elements suggesting left hand dominance. When evaluating the full range of magnitudes of humeral bilateral asymmetry in the comparative sample, Zhaoguo M1 falls at the lower end overall, but yet is relatively higher than contemporary LUP modern humans specifically from East Eurasia. DISCUSSION: The Zhaoguo M1 individual suggests typical LUP modern human upper limb morphology persisted in southwest China until the end of the last glacial period. Upper limb bone asymmetry of Zhaoguo M1 also indicates that behavioral activities attributed to a hunter-gatherer tradition apparently extended through the Pleistocene-Holocene transition in this region.

The diploic venous system in Homo neanderthalensis and fossil Homo sapiens: A study using high-resolution computed tomography.

OBJECTIVES: The diploic venous system has been hypothesized to be related to human brain evolution, though its evolutionary trajectory and physiological functions remain largely unclear. This study examines the characteristics of the diploic venous channels (DCs) in a selection of well-preserved Homo neanderthalensis and Upper Paleolithic Homo sapiens crania, searching for the differences between the two taxa and exploring the associations between brain anatomy and DCs. MATERIALS AND METHODS: Five H. neanderthalensis and four H. sapiens fossil specimens from Western Europe were analyzed. Based on Micro-CT scanning and 3D reconstruction, the distribution pattern and draining orifices of the DCs were inspected qualitatively. The size of the DCs was quantified by volume calculation, and the degree of complexity was quantified by fractal analyses. RESULTS: High-resolution data show the details of the DC structures not documented in previous studies. H. neanderthalensis and H. sapiens specimens share substantial similarities in the DCs. The noticeable differences between the two samples manifest in the connecting points surrounding the frontal sinuses, parietal foramina, and asterional area. DISCUSSION: This study provides a better understanding of the anatomy of the DCs in H. neanderthalensis and H. sapiens. The connection patterns of the DCs have potential utility in distinguishing between the two taxa and in the phylogenetic and taxonomic discussion of the Neandertal-like specimens with controversial taxonomic status.

Investigating the relationship between cranial bone thickness and diploic channels: A first comparison between fossil Homo sapiens and Homo neanderthalensis.

Diploic veins are part of the circulatory system of the head. They transport venous blood and cerebrospinal fluid and are housed in diploic channels (DCs). DCs are highly variable in terms of their position, extension, and size. These parameters were hypothesized to be related to the variations in cranial vault thickness (CVT). For the first time, we analyzed the spatial relationship between CVT and DCs in a sample of eight H. neanderthalensis and H. sapiens cranial fossils. Using micro-CT scanning data, we constructed color maps of the CVT and visually inspected whether the regional thickness variation was associated with the morphology and distribution of the DC branches. The results showed that when regional bone thickness was below a certain threshold, no DCs or scattered small DC branches were present. Larger DC branches appeared only when the thickness exceeded the threshold. However, once the threshold was reached, further increases in thickness no longer resulted in more or larger DCs. This study also found that our sample of H. neanderthalensis and H. sapiens have different distribution patterns in thin areas, which may affect how their DCs connect with different branches of the middle meningeal vessels. This preliminary study provides evidence for the discussion on the interaction between the cranium, brain, and blood vessels. Future research should include more hominin fossils to better document the variation within each species and possible evolutionary trends among hominin lineages.

Frontal sinuses and human evolution.

The frontal sinuses are cavities inside the frontal bone located at the junction between the face and the cranial vault and close to the brain. Despite a long history of study, understanding of their origin and variation through evolution is limited. This work compares most hominin species' holotypes and other key individuals with extant hominids. It provides a unique and valuable perspective of the variation in sinuses position, shape, and dimensions based on a simple and reproducible methodology. We also observed a covariation between the size and shape of the sinuses and the underlying frontal lobes in hominin species from at least the appearance of Homo erectus. Our results additionally undermine hypotheses stating that hominin frontal sinuses were directly affected by biomechanical constraints resulting from either chewing or adaptation to climate. Last, we demonstrate their substantial potential for discussions of the evolutionary relationships between hominin species.