Descriptions

All Rising Star material was described by two or more individuals.

Two-dimensional (2D) measurements

All linear measurements were taken with digital calipers; angular measurements from photographs or with a goniometer. Any measurement discrepancies in linear and angular measurements were rechecked by a third team member for accuracy. Unless otherwise specified, all proximodistal (PD) lengths were taken from the midpoint of the proximal articular surface to the midpoint of the distal articular surface, mediolateral (ML) lengths were taken from the midpoint of the medial surface to the medial point of the lateral surface, and DP lengths were taken from the midpoint of the dorsal surface to the midpoint of the plantar surface. The following are exceptions to this protocol: lateral cuneiform PD (measured by placing the caliper edge along the 3rd metatarsal facet and measuring to the proximolateral corner); lateral cuneiform ML (measured by placing calipers along the lateral edge and measuring to the distomedial corner); talar neck PD (measured parallel to the trochlea).

Talar wedging

Talar wedging was measured as the ratio between the maximum ML width of the distal talar trochlea and the maximum ML width of the proximal talar trochlea. African apes were measured at the Cleveland Museum of Natural History (CMNH), American Museum of Natural History (AMNH) and Harvard Museum of Comparative Zoology (MCZ). Humans were measured at Kent State University (Libben) and the Hamann-Todd collection at the CMNH. Sample sizes are listed below the talar wedging graph. Original fossil tali were studied at the School of Anatomical Sciences and the Institute for Human Evolution (now Evolutionary Studies Institute), Johannesburg, Transvaal (now Ditsong) Museum in Pretoria, South Africa, Kenya National Museum (Nairobi). Casts of Ethiopian fossils were studied at the University of Michigan Anthropology Department.

Talar angles

The horizontal angle of the head/neck, angle of torsion of the head/neck and angle of declination of the head/neck were compared with published measurements from Day and Wood14 (Note: Although Day and Wood14 call the plantar angulation of the talar neck and head an angle of ‘inclination’, we prefer the term ‘declination’ and use it throughout).

Calcaneal robusticity

Calcaneal robusticity was measured as detailed in Latimer and Lovejoy18 and modified slightly in Zipfel et al.5. There is plantar damage to UW 101–1322 and the minimum area of the calcaneal tuber was estimated from a digital cross-section (using DeskArtes) of a surface scan of the original fossil. Tuber volume was then calculated as the product of the mimimum cross-sectional area of the tuber times the length of the tuber (from the midpoint of the proximal talar facet to the most proximal point of the calcaneal tuber). Calcaneal robusticity was calculated as the tuber volume divided by body mass. Body mass for the Foot 1 individual was calculated from regression-based equations of McHenry33 based on the talar trochlea width of the associated talus UW 101–1417. Comparative values were generated from data provided in Latimer and Lovejoy18 on modern apes and humans, with modified body masses in the apes from Smith and Jungers34. Data on calcaneal robusticity in Au. afarensis were from Latimer and Lovejoy18 and modified with a body mass generated from the regression-based equations of McHenry33 for talar trochlea width of A.L. 333-147—a not necessarily associated talus, but from a similarly sized individual as A.L. 333-8 and A.L. 333-55. Data on A.L. 333-147 are taken from Ward et al.35. Data for Au. sediba are taken from Zipfel et al.5.

Tarsal elongation

Tarsal elongation was assessed as the maximum PD length of the bone divided by the maximum ML width of the bone in both the lateral cuneiform and the intermediate cuneiform. Chimpanzee, gorilla and orangutan measurements were obtained at the AMNH, MCZ and CMNH. Humans were from the Merida (Mexico) and Mistihalj (Montenegro) populations housed at the Harvard Peabody Museum of Archaeology and Ethnology (PMAE). Sample sizes are reported in the graphs themselves. Original fossils StW 573 (Australopithecus sp.) and UW 88–139 (Au. sediba) were measured at the School of Anatomical Sciences and the Institute for Human Evolution (now Evolutionary Studies Institute), Johannesburg, respectively. The OH 8 original fossil was studied at the Tanzania National Museum and House of Culture. A cast of the Hadar lateral cuneiform A.L. 333-79 was studied at the PMAE.

Metatarsal proportions

Measures of the maximum PD lengths of G. gorilla (n=20), P. troglodytes (n=32), H. sapiens (n=97; all housed at the National Museum of Natural History, Washington DC), Metatarsal (MT) 1–3 lengths, were taken with digital calipers; measurements from LB1 were taken from the original specimen, and Skhul IV was taken from a cast. MT1/MT2 × 100 was found by dividing the length of MT1 by MT2 and multiplying the quotient by 100. MT1/MT3 × 100 was found by dividing the length of MT1 by MT3 and multiplying the quotient by 100. These data were plotted using PAST 3.0 (ref. 36).

Metatarsal head dimensions

Relative metatarsal head dimensions were measured as described in the study by Latimer and Lovejoy25, in which the plantar cornua of the first metatarsal head did not factor into the PD height measurement. Because of ML erosion to the Dinaledi hominins, only the PD height of the first and second metatarsals were compared. Comparative data were generated from African ape specimens measured at the CMNH and humans measured at the PMAE. A cast of A.L. 333-115 was measured at the PMAE and results were comparable to those reported in the study by Latimer and Lovejoy25.

DP curvature of MT4 base

DP curvature of the fourth metatarsal base was measured as described in the study by DeSilva37. Briefly, the base of the fourth metatarsal was depressed into a carpenter’s contour tool in the coronal plane. Fossils were digitally sectioned using DeskArtes 3Data Expert 9.1 from high-resolution surface scans of the original fossils taken with a Next Engine desktop scanner. The maximum depth of the curvature was divided by the maximum DP height of the base: flatter bases resulted in a lower value; more convex bases a higher value. African apes and humans were both measured at the Cleveland Museum of Natural History (sample sizes reported in the graph itself). Data for A.L. 333-160 are from Ward et al.21, and UW 88-22 from DeSilva et al.23. StW 485 and OH 8 values are from DeSilva37.

Metatarsal torsion

The methods used are described in Drapeau and Harmon23. Surface laser scans were made of the complete metatarsals, using ScanStudio software and a NextEngine laser scanner (NextEngine Inc.). Scans were imported into Geomagic, where four landmarks were placed, two delineating the major axis of the metatarsal head and two delineating the major axis of the base. The angle created by these two lines in the coronal plane represents the lateral torsion of the metatarsal. Torsion and intermetatarsal articular facet orientation were used to align the metatarsals in virtual space and model the shape of the transverse arch. Comparative specimens were measures at the Cleveland Museum of Natural History, National Museum of Natural History, Washington, DC, Anthropological Institute of the University of Zurich and the Canadian Museum of Civilization, Gatineau, QC, Canada. All measurements on fossils were taken from the original specimens, except for the Dinaledi specimens, which were taken from laser surface scans.

Metatarsal robusticity

This has been carried out using the method of Archibald21 in which the metatarsal robusticity index is defined as [(mid-shaft diameter × 100)/length]. The mid-shaft diameter was calculated as mid-shaft circumference/π. The metatarsal dimensions used are defined as follows:

Metatarsal 1. Length is measured from the most distal point on the upper part of the proximal articular surface to the most distal point on the distal articular surface. Circumference of the mid-shaft is measured at a point mid-way between the most distal point on the proximal articular surface to the most distal point on the distal articular surface.

Metatarsals 2–4. Length is measured from the most dorsolateral point on the posterior articular surface to the most distal point on the distal articular surface. Circumference of the mid-shaft is measured at a point mid-way between the most dorsomedial point of the proximal articular surface to the most distal point of the distal articular surface.

Metatarsal 5. Length is measured from the most lateral point on the proximal articular surface to the most distal point of the distal articular surface. Circumference of the mid-shaft is measured at a point mid-way between the most medial point on the proximal articular surface to the most distal point of the distal articular surface.

Phalangeal curvature

All phalangeal curvatures were quantified using high-resolution polynomial curve fitting (HR-PCF) methods38. Unlike traditional curvature quantification techniques (that is, included angle, normalized curvature moment arm) that model curvature as an imaginary circular line passing through the center of a bone, HR-PCF models the surface curvature of the bone and can fit a polynomial function to either the dorsal or ventral surface of a phalanx. In the case of the Dinaledi pedal phalanges, the ventral surfaces of many phalanges were interrupted by flexor sheath ridges that create irregularities in the outline of shaft curvature, so the more regular dorsal margin of the outline was chosen for polynomial fitting. Although it could be argued that the dorsal and ventral curvatures are responses to different loading regimes, they are highly interdependent and associated with the same positional behaviour; the dorsal curvature is also simpler. Elements were photographed in a lateral and standardized orientation. JASC PSP (Corel Corporation, 1600 Carling Avenue, Ottawa, Ontario K1Z 8R7, Canada) image editing software was used to convert the resulting 2D images into simple digitized outlines. These digitized outlines contain thousands of individual pixels, each having its own, paired coordinates. End points were selected for each dorsal contour to represent the limits of a discrete 2nd order curve and the co-ordinates of the individual pixels comprising the selected portion of the dorsal contour were used as data points to generate a best-fit 2nd order polynomial function with three coefficients defined as y=Ax2+Bx+C. The three resulting coefficients (A,B,C) can be used as the raw data in a statistical analysis. The first coefficient (A) expresses the nature and degree of the longitudinal curvature, whereas the second (B) and third (C) reflect aspects of the orientation of that curve with respect to the rest of the element (that is, element rotation, element position in 2D space). Given the limitations of coefficients B and C to represent meaningful information about the magnitude of phalangeal shaft curvature, only the 1st (A) polynomial coefficient was considered in statistical analyses performed in the present study.

Although any order of polynomial can be used with HR-PCF methods, a second-order polynomial was chosen over a higher-order polynomial functions because second-order curves (for example, longitudinal phalangeal shaft curvature) have no structural points of inflection, unlike third-order curves and above, which impose either one or more points of inflection. The coefficients of higher-order polynomials (that is, 3rd–6th order) are very sensitive to whatever irregularities exist in the contours of anatomical curves.

Three-dimensional (3D) measurements

x,y,z homologous landmark configurations for the talus and medial cuneiform were collected according to protocols defined in Harcourt-Smith39. All landmarks were collected with a Microscribe digitizer by W.E.H.H-S. Coordinate date was superimposed using generalized Procrustes alignment, which controls for translational and rotational differences and adjusts for size. Aligned coordinates were subjected to a principal components analysis. All generalized Procrustes alignments and principal components analyses were done in morphologika 2.5 (ref. 40). Angulation between articular facets and other anatomical structures on the talus and calcaneus were collected using laser surface scans of the fossils and the software Geomagic Control 2014 (Geomagic Solutions), which allows a best-fit plane to be fitted to a selected area, or an axis to be determined using two landmark points.

All non-human extant samples for the 3D analyses are wild shot adults housed at AMNH, CMNH, MCZ, National Museum of Natural History (Smithsonian), Natural History Museum (London), Powell-Cotton Museum (Kent, UK) and the Royal African Museum (Tervuren, Belgium). Human samples were collected at the AMNH and the Dart Collection, University of the Witwatersrand. Original fossils were studied at the School of Anatomical Sciences and the Institute for Human Evolution (now Evolutionary Studies Institute), Johannesburg, the Transvaal (now Ditsong) Museum (Pretoria, South Africa) and the Kenya National Museum (Nairobi). Primary casts of Ethiopian fossils were studied at the Institute of Human Origins (Arizona State University) and at the Musée de l’Homme, Paris. Primary casts of Tanzanian fossils were measured at the Natural History Museum, London. Sample sizes for the talus 3D coordinates are: H. sapiens=89; P. troglodytes=44; P. paniscus=15; G. gorilla=42; P. pygmaeus=43. For the medial cuneiform 3D coordinates, they are: H. sapiens=77; P. troglodytes=40; P. paniscus=15; G. gorilla=41; P. pygmaeus=32. For the malleolar facet angle, they are: H. sapiens=26; P. troglodytes=25; G. gorilla=18. For the sustentaculum tali angle, they are: H. sapiens= 26; P. troglodytes=25; G. gorilla=23.