J. Anat. (2008) 212, pp501–543 doi: 10.1111/j.1469-7580.2008.00870.x REVIEWBlackwell Publishing Ltd Locomotion and posture from the common hominoid ancestor to fully modern hominins, with special reference to the last common panin/hominin ancestor R. H. Crompton,1 E. E. Vereecke1 and S. K. S. Thorpe2 1School of Biomedical Sciences, The University of Liverpool, Sherrington Buildings, Ashton Street, Liverpool L69 3GE, UK 2School of Biosciences, University of Birmingham, Edgbaston, Birmingham B15 2TT Abstract Based on our knowledge of locomotor biomechanics and ecology we predict the locomotion and posture of the last common ancestors of (a) great and lesser apes and their close fossil relatives (hominoids); (b) chimpanzees, bonobos and modern humans (hominines); and (c) modern humans and their fossil relatives (hominins). We evaluate our propositions against the fossil record in the context of a broader review of evolution of the locomotor system from the earliest hominoids of modern aspect (crown hominoids) to early modern Homo sapiens. While some early East African stem hominoids were pronograde, it appears that the adaptations which best characterize the crown hominoids are orthogrady and an ability to abduct the arm above the shoulder – rather than, as is often thought, manual suspension sensu stricto. At 7–9 Ma (not much earlier than the likely 4–8 Ma divergence date for panins and hominins, see Bradley, 2008) there were crown hominoids in southern Europe which were adapted to moving in an orthograde posture, supported primarily on the hindlimb, in an arboreal, and possibly for Oreo- pithecus, a terrestrial context. By 7 Ma, Sahelanthropus provides evidence of a Central African hominin, panin or possibly gorilline adapted to orthogrady, and both orthogrady and habitually highly extended postures of the hip are evident in the arboreal East African protohominin Orrorin at 6 Ma. If the traditional idea that hominins passed through a terrestrial ‘knuckle-walking’ phase is correct, not only does it have to be explained how a quadrupedal gait typified by flexed postures of the hindlimb could have preadapted the body for the hominin acquisition of straight-legged erect bipedality, but we would have to accept a transition from stem-hominoid pronogrady to crown hominoid orthogrady, back again to pronogrady in the African apes and then back to orthogrady in homi- nins. Hand-assisted arboreal bipedality, which is part of a continuum of orthograde behaviours, is used by modern orangutans to forage among the small branches at the periphery of trees where the core hominoid dietary resource, ripe fruit, is most often to be found. Derivation of habitual terrestrial bipedality from arboreal hand- assisted bipedality requires fewer transitions, and is also kinematically and kinetically more parsimonious. Key words biomechanics; ecology; fossils; hominins; hominoids; locomotion; posture. broad pelvis; a scapula located on the back of the ribcage, Introduction and a shoulder joint adapted to allow extensive abduction It has long been held (e.g. see Keith, 1923) and taught (e.g. (Rose, 1993, 1997; Larson, 1998). Keith (1923) and most see Fleagle, 1998) that the living apes share, and are best following him considered that such characteristics are defined by, a set of functional characteristics related to the linked to ‘brachiation’: forelimb-suspensory under-branch trunk and upper limb. These features (e.g. see Ward, 2007) locomotion. However, as we shall show below, both include a stiff lumbar spine; a broad, flattened ribcage locomotor ecology and recent fossil evidence suggests into which the spine is ventrally ‘embedded’; a matching that suspensory locomotion may have been acquired in- dependently by several hominoid lineages. Rather, it is Correspondence actually upright (orthograde) truncal posture which is R. H. Crompton, School of Biomedical Sciences, The University of their common inheritance from their last common ancestor. Liverpool, Sherrington Buildings, Ashton Street, Liverpool L69 3GE, UK. Upright posture is found not only in suspension, but in the E: [email protected] climbing, clambering [in which the forelimbs support the R.H.C. and S.K.S.T. dedicate this paper to our mentor Neill Alexander. majority of body mass, but the hindlimbs may contribute Accepted for publication 7 February 2008 in either abducted (suspensory) or extended (compressive) © 2008 The Authors Journal compilation © 2008 Anatomical Society of Great Britain and Ireland 502 Locomotion and posture in hominins, R. H. Crompton et al. Fig. 1 Ad hoc and purely heuristic diagram of possible relationships of some hominoid genera included in this review. postures (Hunt et al. 1996)] and occasional bipedal loco- Clyde, 2004; MacLatchy, 2004; Young & MacLatchy, 2004) motion shared by all living apes. have suggested that they should therefore be regarded as All living apes fall into the superfamily Hominoidea. a ‘stem’ or ‘archaic’ hominoid radiation, not closely related Hominoidea may reasonably be held (e.g. see Wood & to the ancestry of living hominoids and their fossil affines, Richmond, 2000) to comprise two families, Hylobatidae the crown hominoids, also called euhominoids. (gibbons and siamangs) and Hominidae, the latter in A methodological difficulty exists in any analysis of the turn comprising the subfamilies Ponginae (orangutans), locomotor and postural evolution of the hominoids. The Gorillinae (gorillas) and Homininae. Within the Homininae number of dentocranial fossils far outweighs that of post- are tribes Panini (chimpanzees and bonobos) and Hominini cranial fossils, so that dentocranial remains are usually (modern humans and their immediate fossil relatives). central to phylogenetic analysis of the fossil record. Yet, it Despite a substantial pronograde component, of arboreal appears not only that living apes are best characterized quadrupedalism (as in orangutans) and terrestrial knuckle- by their postcranial adaptations, but fossil postcranials walking in their locomotor repertoire, panins and gorillines attributed to apes show less homoplasy than dentocranial share (as indicated above) the characteristic features of remains (Finarelli & Clyde, 2004), making them in this one truncal morphology found in all other living apes: pongines, case better suited for phylogenetic analysis. While aware hylobatids and hominins. of the circularity this creates, we shall use a working However, our perception of hominin, as well as hominoid, hypothesis of generic relationships (Fig. 1) adapted ad hoc locomotor evolution has probably been coloured by the from features of the most parsimonous morphologically fact that one of the largest and most diverse groups of based phylogenies obtained by Finarelli & Clyde (2004) ape-like fossils, while dentally and cranially ‘ape-like’ and Young & MacLatchy (2004). Both separate procon- shows little postcranial similarity to living apes. This group sulids and their affines as stem hominoids. generally referred to as the proconsulids, comes from the The aim of this paper* is two-fold, first to provide a ‘cradle of mankind’, East Africa, and dates to 12–19 Ma. A single (and thus necessarily non-exhaustive) source of data certain degree of locomotor diversity has recently been on hominoid and hominin locomotor evolution, aimed at established, including, for example, some evidence sug- Honours/senior year undergraduate and beginning post- gesting terrestrial knuckle-walking in Kenyapithecus, and graduate students, and secondly further to explore our perhaps some degree of forelimb-powered suspensory hypothesis (Thorpe et al. 2007a,b; Crompton & Thorpe, quadrupedalism in Nacholapithecus. Nevertheless, pro- 2007; and see also Crompton et al. 2003) that modern consulid postcranials, if anything, tend to resemble those human obligate terrestrial bipedality is ultimately derived of branch-walking monkeys. Thus, they have a mobile from facultative arboreal bipedality in an orthograde last lumbar spine, suspending below it an anteroposteriorly common ancestor (LCA) of crown hominoids. We are by no deep thorax, in distinction to the case in all living apes. means the first to have proposed an arboreal origin for Over the last decade, an increasing number of workers hominin bipedality: Senut (e.g. 2003, 2006) and Pickford (e.g. Larson, 1998; Begun, 2002; Harrison, 2002; Finarelli & (e.g. 2006) in particular have pointed to an increasing © 2008 The Authors Journal compilation © 2008 Anatomical Society of Great Britain and Ireland Locomotion and posture in hominins, R. H. Crompton et al. 503 Table 1 Predicted features of the last common ancestors (LCAs)* LCA of living crown hominoids Positional behaviour Habitually arboreal and orthograde, with some stabilization of lumbar spine and at least gibbon-like thoracic shape. Scapula dorsally placed with elongated vertebral border. Locomotion primarily orthograde clambering, including hand-assisted bipedality. Some quadrupedalism on large branches, suspensory locomotion questionable. Forelimb Long forelimb, capable of extensive abduction, grasping hand with relatively, but not extremely long fingers. Not necessarily adapted for suspensory posture or locomotion. Hindlimb Hindlimb relatively but not extremely short, capable of deep extension at hip and knee, and also widely abductable at hip. Foot grasping, used in inverted but plantigrade posture. Heel-strike appears in LCA of great apes. LCA of Panini and Hominini Positional behaviour Predominantly arboreal, orthograde, extensive stabilization