A juvenile early hominin skeleton from Dikika, Ethiopia

Abstract

Understanding changes in ontogenetic development is central to the study of human evolution. With the exception of Neanderthals, the growth patterns of fossil hominins have not been studied comprehensively because the fossil record currently lacks specimens that document both cranial and postcranial development at young ontogenetic stages. Here we describe a well-preserved 3.3-million-year-old juvenile partial skeleton of Australopithecus afarensis discovered in the Dikika research area of Ethiopia. The skull of the approximately three-year-old presumed female shows that most features diagnostic of the species are evident even at this early stage of development. The find includes many previously unknown skeletal elements from the Pliocene hominin record, including a hyoid bone that has a typical African ape morphology. The foot and other evidence from the lower limb provide clear evidence for bipedal locomotion, but the gorilla-like scapula and long and curved manual phalanges raise new questions about the importance of arboreal behaviour in the A. afarensis locomotor repertoire.

Locomotor anatomy and biomechanics of the Dmanisi hominins

“…Nonetheless, two broad grades of locomotor anatomy can be distinguished within the last 4 million years of hominin evolution (Klein, 1999;Bramble and Lieberman, 2004;Conroy, 2005). Members of the older group, the australopithecines, were habitual terrestrial bipeds that retained several primitive features related to arboreal locomotion, including relatively long arms and short hind limbs, long, curved phalanges, and a funnel-shaped torso with narrow shoulders and superiorly oriented glenoid fossa (Aiello and Dean, 1990;Ward, 2002;Bramble and Lieberman, 2004;Alemseged et al, 2006). In contrast, members of the genus Homo possess a suite of derived post-cranial traits associated with greater cursoriality, including longer hind limbs, shorter pedal phalanges, and a rigid longitudinal plantar arch (Shipman and Walker, 1989;Aiello and Dean, 1990;Bramble and Lieberman, 2004).…”

Bringing Up Baby: Developmental Simulation of the Adult Cranial Morphology of Rungwecebus Kipunji

“…The dilemma posed by the kipunji juvenile is analogous to that encountered by paleontologists, who must infer the adult morphology of juvenile fossils to determine their taxonomic affinities (e.g., Tobias, 1978;Alemseged et al, 2006;McNulty et al, 2006). In such cases, developmental simulation of adult cranial shape has proved useful for exploring ontogenetic differences among species and for testing taxonomic hypotheses Richtsmeier and Walker, 1993;Ackermann and Krovitz, 2002;McNulty et al, 2006).…”

Air sacs and vocal fold vibration: Implications for evolution of speech

“…The connection between the ventricles and the air sac passes underneath this bulla. Hyoid bones sometimes fossilize, and it has been DOI: 10.2478/v10235-011-0002-5 found that Neanderthals (Arensburg et al 1989, Arensburg et al 1990 and Homo heidelbergenis (Martínez et al 2008) have a hyoid bone without a bulla, while Australopithecus afarensis (Alemseged et al 2006) appears to have a bulla. This indicates that air sacs disappeared somewhere between 3.3 million years ago and 500 000 years ago in human evolution.…”

“…The hyoid bone (Figure 1) is the only bony part of the vocal tract and the muscles of the larynx and the tongue connect to it. The hyoid bone has a cup shaped extension (called the hyoid bulla) in gorillas, chimpanzees and bonobos, but lacks this cup shaped extension in humans (Kohlbrugge 1896, Brown & Ward 1988, Aiello & Dean 2002, Alemseged et al 2006, Fitch 2009). The connection between the ventricles and the air sac passes underneath this bulla.…”