Rib Cross-Sectional Mineralized Area in Early Pleistocene Hominins: Insights From the Homo antecessor and H. erectus...

Rib cross-sectional mineralized area provides valuable insights into mechanical loading and bone growth and remodeling. Given the scarcity of Early Pleistocene costal remains in the context of human evolution, we aimed to study the cross-sectional anatomy of fossil ribs from that period and compare them to a modern human ontogenetic series ranging from 8 to over 30 years of age.

We extracted the rib cross section at the midshaft of 6 fossil ribs attributed to several H. antecessor individuals and 10 fossil ribs of the H. erectus s. l. specimen KNM-WT 15000. Then we compared their relative mineralized area with that of the full, unilateral costal series of 27 H. sapiens individuals spanning different ontogenetic stages (pre-pubescent, post-pubescent, adult).

Our findings indicate that rib cross-sectional mineralized area of H. antecessor is close to that of subadult H. sapiens, sharing a similar U-shaped trend along the costal series. Values are considerably lower compared to KNM-WT 15000, which shows a higher mineralized area at the middle thoracic rib levels rather than at the extremes.

Despite possible taphonomic alteration of fossil ribs, these results suggest a different, possibly derived pattern of rib cross-sectional mineralized area in H. antecessor compared to more primitive Early Pleistocene hominins. However, considering the earlier ontogenetic stage of KNM-WT 15000, we cannot discard that ribs of H. antecessor belong to individuals exhibiting a postcranial growth pattern similar to that of H. erectus s. l., but at a more advanced phase in development.