New insights into the ontogeny of Paranthropus boisei offered by a juvenile maxilla from the Shungura formation (Ethiopia).

Abstract

Early hominin juvenile fossils are key for elucidating the developmental basis of adult phenotypic variation and enhancing our understanding of phylogenetic relationships. Since the discovery of the Taung child a century ago, numerous findings have expanded our knowledge concerning craniodental ontogeny of Australopithecus africanus and A. afarensis, and more recently, Paranthropus robustus. However, less is known about the highly-derived, robust species P. boisei from eastern African. In this study, we present a juvenile specimen of P. boisei recently recovered from the Shungura Formation (Ethiopia), offering insights into the craniodental development of eastern African robust hominins. To give an age at death, the dental developmental stage was studied and compared to those of P. robustus individuals. We then examined the expression of derived morphological features in the studied individual, comparing them to those observed in various published fossils, in order to explore the craniofacial ontogeny of the genus Paranthropus. Our results show that OMO 362-10001 age at death is estimated to have been around 3.8 to 5 years old. The OMO 362-10001 maxillary morphology indicates that some of the derived features shared by species of Paranthropus are already evident by this stage of development while others are not. This present ontogenetic pattern differs in some way from that of P. robustus, suggesting ontogenetic variation within the clade Paranthropus.

Arthur Thiebaut and colleagues report a newly identified immature maxillary specimen from Member K (unit K-1) of the Shungura formation in southern Ethiopia, collected by the Omo Group Research Expedition (Thiebaut et al., 2026).

On the basis of stratigraphic context, radiometric dating and tephrostratigraphic correlation, OMO 362-10001 is dated to ca. 1.485 ± 0.014 Ma. This age places it among the geologically youngest specimens of Paranthropus boisei, in the Omo-Turkana basin, alongside specimens such as KNM-ER 404 and KNM-ER 5877 (Marchal et al., 2025).

OMO 362-10001 consists of a right hemi-maxilla fragment preserving mixed dentition, including erupted dP3, dP⁴, and P3, P4 and M1, indicating that this is an immature individual. The estimated age of death ranges between around 3.8 and 5 years old.

The reviewers agree that the authors’ qualitative and quantitative analyses are robust, and that the figures and tables provide high-quality documentation of the specimen. Furthermore, the discussion effectively places the results within the context of current knowledge regarding the ontogeny, morphology and systematics of Paranthropus boisei.

Linear measurements (mesiodistal, buccolingual (for post-canine teeth) and labiolingual (for canine tooth)), combined with morphological analyses of the dentition and maxilla (for example sub-nasal morphology, the position and morphology of the zygomatic root, the morphology of the maxillary sinus), demonstrate strong affinities between OMO 362-10001 and P. boisei. Furthermore, the relative enamel thickness (RET) of the upper M1 is among the highest thickness value recorded for P. boisei.

This immature maxilla provides rare and valuable insights into craniofacial ontogeny in P. boisei. As the authors point out, juvenile hominin remains are extremely rare, particularly for P. boisei. Previous ontogenetic reconstructions within the genus Paranthropus relied primarily on infant specimens of P. robustus, due to the limited availability of comparable material for P. boisei (e.g., Bromage, 1989 ; McCollum, 2008 ; Braga et al., 2023).

Data from OMO 362-10001 reveal a complex maxillary morphology combining both adult and juvenile-like features, suggesting that this specimen exhibits a relatively mature morphology, with most of the differences observed compared to the adult stage being related to differences in size.

The authors highlight that the growth pattern of OMO 362-10001 differs from that documented in P. robustus, suggesting the existence of potential developmental variation within the genus Paranthropus. Furthermore, this individual appears to have possessed a fully functional masticatory apparatus, likely capable of processing an adult-like diet.

These findings provide the first direct evidence regarding the ontogeny of the maxilla in P. boisei, thereby making a significant contribution to our understanding of the growth dynamics, functional morphology, and evolutionary characteristics of Paranthropus. This specimen and the associated analyses provided by Thiebaut et al. (2026) therefore represent a major contribution to the study of the paleobiology, ontogeny, and systematics of P. boisei.

References

Braga, J., Wood, B. A., Zimmer, V. A., Moreno, B., Miller, C., Thackeray, J. F., Zipfel, B., and Grine, F. E. (2023). Hominin fossils from Kromdraai and Drimolen inform Paranthropus robustus craniofacial ontogeny. Science Advances, 9(18), eade7165. https://doi.org/10.1126/sciadv.ade7165

Bromage, T. G. (1989). Ontogeny of the early hominid face. Journal of Human Evolution, 18(8), 751–773. https://doi.org/10.1016/0047-2484(89)90088-2

Marchal, F., Reed, D., and Prat, S. (2025). The hominin fossil record of the Omo-Turkana Basin. Journal of Human Evolution, 209, 103731. https://doi.org/10.1016/j.jhevol.2025.103731

McCollum, M. A. (2008). Nasomaxillary remodeling and facial form in robust Australopithecus: A reassessment. Journal of Human Evolution, 54(1), 2–14. https://doi.org/10.1016/j.jhevol.2007.05.013

Thiebaut, A., Guy, F., Hlusko, L. J., Surault, J., Towle, I., Redae, B. E., and Boisserie, J.-R. (2026). New insights into the ontogeny of Paranthropus boisei offered by a juvenile maxilla from the Shungura formation (Ethiopia). PaleorXiv, wj7yt, ver. 4 peer-reviewed by PCI Paleo. https://doi.org/10.31233/osf.io/wj7yt_v4

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New insights into the ontogeny of Paranthropus boisei offered by a juvenile maxilla from the Shungura formation (Ethiopia).

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