10.2: New Discovery - Homo naledi
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- 62353
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This newest member of our genus has once again confounded the evolutionary history of the Homo lineage. The most exciting aspect is the nature of the remains suggests that they were intentionally deposited in the deep cavern where they were discovered. H. heidelbergensis was heretofore the earliest species thought to have practiced intentional body disposal. The remains appear to be 250,000 years old.
ISSN 2050-084X. Licensed under CC-BY 4.0
It appears that the majority of researchers agree that the remains reflect a new hominin. Like most hominins, the phylogeny of the species is unknown but it likely descended from an australopith ancestry. What makes things even more difficult is that the species shares characteristics with possible extant or near extant species of Homo (H. habilis, H. rudolfensis, and H. erectus), more derived forms (e.g. neanderthals and humans), as well as various australopiths. The mosaic of traits is interesting and further supports the bushy nature of the hominin tree.
The remains of a minimum of 15 individuals, totaling 1550 fossils (see Figure), were excavated in 2013 and 2014 from the Dinaledi Chamber, located within the Rising Star cave system in the Cradle of Humankind World Heritage Site, Gauteng Province, South Africa (Berger et al. 2015). The fossils are the largest collection of a hominin species in Africa (Dirks et al. 2015). The chamber is 30 m below ground and is only accessible via a 12 m narrow shaft (see Figure – top right). Based on depositional data, the bodies were deposited over time (Dirks et al. 2015).
The remains are especially valuable as all body regions are represented, and some bones are articulated, so that anatomical positions and arrangements are preserved, e.g. an almost complete leg of a child and an adult hand (Dirks et al. 2015). The low cranial capacity, elevated shoulder joints, curved phalanges, and trunk and hip morphology are australopith-like. Crania, jaw and teeth morphology, and leg bones are, for the most part, Homo-like. The wrist is most similar to humans and neandertals. The foot is very human-like. Thus, we see an able terrestrial biped that could climb, forage, and take refuge in trees.
Cranial capacity falls within the range for the australopiths, with males averaging 560 cc and females, 465 cc. The base of skull vault is flexed like members of the erectus grade and subsequent species of Homo. The vault bones are thin like those of H. habilis. H. naledi exhibits less postorbital constriction than the earliest australopiths, yet possesses a larger supraorbital torus than any gracile australopith. Taken together, it is an odd combination.
While the hand of H. naledi (see Figure) shares characteristics with other hominins, the combination of characteristics is unique. They had long fingers and the two more proximal digit phalanges are curved even more than those of australopiths, suggestive of arboreal activities. Yet their wrist morphology is most similar to neanderthals and modern humans and, along with their long, robust thumb, they were thus capable of strong manipulatory activities
While the combination of characteristics seen in the leg bones are distinctive, they are Homo-like, except that the femoral neck is long like that of australopiths. The foot (see Figure) is very human-like, with the primary differences being the curvature of their digits and less of a medial longitudinal arch.
The evidence is compelling that the remains could not have been deposited via natural forces, but rather were carried at least part of the way, through a dark and narrow passage. We thus need to reassess our image of the cognitive capabilities and awareness of earlier members of our genus.