Research ArticleANTHROPOLOGY

A nearly complete foot from Dikika, Ethiopia and its implications for the ontogeny and function of Australopithecus afarensis

See allHide authors and affiliations

Science Advances  04 Jul 2018:
Vol. 4, no. 7, eaar7723
DOI: 10.1126/sciadv.aar7723
  • Fig. 1 A. afarensis juvenile foot DIK-1-1f.

    DIK-1-1f shown in (clockwise from top left) medial, dorsal, and lateral views. To right, dorsal view of DIK-1-1f and the adult A. afarensis foot A.L. 333-115. Scale bars, 1 cm.

  • Fig. 2 Calcaneal ontogeny in apes, humans, and A. afarensis.

    (A) Standardized cross-sectional area of the calcaneal tuber in juvenile (light gray) and adult (dark gray) apes, A. afarensis, and modern humans. The vertical line represents the taxon median, the box represents the interquartile range, and the whiskers indicate the range of the data. A higher number corresponds with increased robusticity. Notice that, unlike in apes or humans, in A. afarensis, the calcaneus exhibits a significant developmental increase in robusticity; the Dikika juvenile is chimpanzee-like, while the Hadar adult is human-like. All juveniles are significantly different from adults for each taxon (P ≤ 0.05) except for Homo sapiens (P = 0.53). (B) Three-dimensional (3D) surface renderings of DIK-1-1f, chimpanzee (top), and human (bottom) juvenile calcanei shown in lateral view. Notice the ape-like gracility of DIK-1-1f, the proximodistally long and dorsoplantarly shallow distal calcaneal region, and the large peroneal trochlea. As in humans, however, there is a plantarly positioned apophyseal flange (indicated by the asterisk) for the lateral plantar process (epiphyseal surface outlined).

  • Fig. 3 Medial cuneiform ontogeny in apes, humans, and A. afarensis.

    (A) The radius of curvature of the distal medial cuneiform facet and the angulation of the facet relative to the navicular facet are plotted for juvenile humans (green), gorillas (blue), and chimpanzees (purple). Humans have distally directed facets (angle ~90° to 100°), with facet convexity that ranges from ape-like in small juveniles (see fig. S5) to flatter joints in subadults (9). Ape juveniles have convex, medially directed facets. The DIK-1-1f morphology is intermediate between humans and gorillas, with a facet orientation between human and ape, and a more ape-like joint convexity. (B) When standardized by the dorsoplantar height of the medial cuneiform, facet curvature can be assessed independent of size. While facet curvature differs little between juvenile and adult apes, humans experience a developmental flattening of the joint with growth. Both DIK-1-1f and A.L. 333-28 are more convex than similarly sized humans but less so than apes and, when paired, have the ape-like pattern of maintained convexity with growth of the bone (fig. S5). The box-and-whiskers plot shows the mean (dark vertical line), upper and lower quartiles (boxes), and range (whiskers).

  • Table 1 DIK-1-1f comparative anatomy.

    ML, mediolaterally; DP, dorsoplantarly; PD, proximodistally.

    BoneHuman-like featuresApe-like featuresAdult A. afarensis featuresDevelopmental changes in
    A. afarensis morphology
    CalcaneusLateral plantar
    process apophyseal
    flange position
    Secondary ossification
    center for peroneal
    tubercle
    Large depression for
    calcaneofibular ligament
    Gracile in juvenile; becomes
    more robust in adults
    Plantarly wide (ML) tuberDP short and vertical
    cuboid facet
    Small lateral plantar process
    apophyseal surface
    Rugosity for lateral plantar
    ligament not present in DIK;
    present in adults
    Medial tubercle flat
    (not beaked)
    Medially angled distal
    calcaneus at peroneal
    trochlea inflection point
    Low DP height of distal
    calcaneus; enlarges
    in adults
    TalusModerately wedgedML broad talar headWeak angle of declinationHead expands DP
    Equal heights of trochlear rims
    ML flat trochlear body
    Talar axis angle
    CuboidPD elongated laterallyArticulates with navicularUnknownUnknown
    Dorsal surface twisted to
    face laterally
    Beak eccentrically positioned
    Medial cuneiformDistally positioned tibialis
    anterior sub-bursal sulcus
    ML convex Mt1 surfaceML convexity and angulation
    of Mt1 surface greater
    than in humans; less than
    in apes
    Mt1 facet maintains
    convexity developmentally
    Mt1 facet becomes less
    medially oriented
    Lateral cuneiformContact facet with Mt4PD foreshortenedTransverse arch more
    developed than in apes;
    less developed than
    in humans (especially
    medially)
    Juvenile is PD short and
    becomes more elongated
    with age
    Intermediate cuneiformNested into angled lateral
    surface of medial cuneiform
    Unknown
    NavicularFacet for medial cuneiform
    slightly convex DP and ML
    MetatarsalsStrong external torsion Mt4Mt2 proximal base weakly
    angled ML
    Mt2 base enlarges DP
    Mt4 base DP tall

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/7/eaar7723/DC1

    Supplementary Text

    Fig. S1. The discovery of DIK-1-1f by D. Geraads on 21 January 2002 during excavation at DIK-1 locality.

    Fig. S2. DIK-1-1f in various views.

    Fig. S3. Talus ontogeny in apes, humans, and A. afarensis.

    Fig. S4. Calcaneal ontogeny in apes, humans, and A. afarensis.

    Fig. S5. Medial cuneiform ontogeny in apes, humans, and A. afarensis.

    Fig. S6. Cuboid ontogeny in apes, humans, and A. afarensis.

    Fig. S7. A clean section through the metatarsal shafts of the articulated DIK-1-1f shows the transverse arch of this foot.

    Fig. S8. Compared to the apes, humans have proximodistally elongated cuneiforms.

    Fig. S9. The calcaneus, talus, navicular, and medial cuneiform have been rearticulated in a human, chimpanzee, gorilla, DIK-1-1f, and a composite Hadar foot.

    Fig. S10. Metatarsal base ontogeny in apes, humans, and A. afarensis.

    Data file S1. Raw measurements used in this study.

  • Supplementary Materials

  • The PDF file includes:
    • Supplementary Text
    • Fig. S1. The discovery of DIK-1-1f by D. Geraads on 21 January 2002 during excavation at DIK-1 locality.
    • Fig. S2. DIK-1-1f in various views.
    • Fig. S3. Talus ontogeny in apes, humans, and A. afarensis.
    • Fig. S4. Calcaneal ontogeny in apes, humans, and A. afarensis.
    • Fig. S5. Medial cuneiform ontogeny in apes, humans, and A. afarensis.
    • Fig. S6. Cuboid ontogeny in apes, humans, and A. afarensis.
    • Fig. S7. A clean section through the metatarsal shafts of the articulated DIK-1-1f shows the transverse arch of this foot.
    • Fig. S8. Compared to the apes, humans have proximodistally elongated cuneiforms.
    • Fig. S9. The calcaneus, talus, navicular, and medial cuneiform have been rearticulated in a human, chimpanzee, gorilla, DIK-1-1f, and a composite Hadar foot.
    • Fig. S10. Metatarsal base ontogeny in apes, humans, and A. afarensis.

    Download PDF

  • Other Supplementary Material for this manuscript includes the following:
    • Data file S1 (Microsoft Excel format). Raw measurements used in this study.

    Files in this Data Supplement:

Navigate This Article