Research Article

Paleobiological Implications of the Ardipithecus ramidus Dentition

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Science  02 Oct 2009:
Vol. 326, Issue 5949, pp. 69-99
DOI: 10.1126/science.1175824

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  1. Fig. 1

    Representative examples of the Aramis Ardipithecus ramidus dentition. (A) Occlusal view micro-CT–based alignment of ARA-VP-1/300: top, maxillary dentition; bottom, mandibular dentition. The better-preserved side was scanned and mirror-imaged to form these composites. (B) ARA-VP-1/300 in buccal view: top, right maxillary dentition (mirrored); bottom, left mandibular dentition. (C) Comparison of canine morphology (micro-CT–based renderings). Top row, lingual view of upper canines, from left to right: male P. troglodytes (cast), female P. troglodytes (cast), Ar. kadabba ASK-VP-3/400, Ar. ramidus ARA-VP-6/1, Au. afarensis L.H. 6 (cast), Au. afarensis A.L. 333x-3 (cast, mirrored). Lower rows, distolingual view of lower canines, main row from left to right: male P. troglodytes (cast), female P. troglodytes (cast), Ar. kadabba (STD-VP-2/61), Ar. ramidus ARA-VP-1/300, Au. africanus Sts 50 (mirrored), Au. africanus Sts 51. Lowest two specimens are ape lower canines with hominid-like features: left, P. paniscus (cast); right, Ouranopithecus macedoniensis RLP-55 (cast). The Ar. ramidus upper canine is highly derived, with a diamond-shaped crown with elevated crown shoulders. The lower canine tends to retain aspects of primitive ape features. Further details are given in the SOM figures and SOM text S1. (D) M1 morphology (micro-CT–based renderings) showing relatively little morphological variation among the Aramis individuals. Top row left, ARA-VP-1/300 (mirrored); right, ARA-VP-1/1818. Middle row left, ARA-VP-1/3288; right, ARA-VP-6/500. Bottom row left, ARA-VP-6/502 (mirrored); right, KUS-VP-2/154. (E and F) Box plot of upper canine maximum diameter and labial height (in mm). Ar. ramidus includes Aramis and published Gona materials (2). The ~6-million-year-old hominids are represented by Ar. kadabba (ASK-VP-3/400) and O. tugenensis (BAR 1425'00) (7). Symbols give central 50% range (box), range (vertical line) and outliers. See SOM figures and text S1 for additional plots and details.

  2. Fig. 2

    Size and scaling of the Ardipithecus ramidus dentition. Natural log-log scatter diagram of relative upper canine height (y axis) against relative postcanine length (x axis): left, females; right, males. Both axes represent size free variables (residuals) derived from scaling tooth size against body size across a wide range of anthropoids (2). A value of zero represents the average female catarrhine condition. Positive and negative residuals represent relatively large and small tooth sizes, respectively. The diagonal line indicates the direction of equivalent canine and postcanine proportions independent of size. The five great ape taxa plotted are from left to right: P. paniscus, P. t. troglodytes, P. t. schweinfurthi, Gorilla gorilla, and Pongo pygmaeus. Ar. ramidus is plotted by using mean postcanine size and canine crown heights of probable female (ARA-VP-6/500) and male (ARA-VP-1/300) individuals. A hypothetical female body weight of 45 kg or 50 kg was used (right and left stars, respectively). Ar. ramidus is shown to have small postcanine tooth sizes, similar to those of Ateles, Presbytis sensu stricto, and Pan. Relative canine height of Ar. ramidus is lower than that of the smallest-canined nonhuman anthropoids, P. paniscus and Brachyteles arachnoides. See SOM text S2 for further details.

  3. Fig. 3

    Relative postcanine dental size in Ar. ramidus. Postcanine size is compared directly in reference to associated postcranial elements; x axis is natural log of the size variable (body size proxy) of Lovejoy et al. (23), derived from four metrics of the talus and five metrics of the capitate; y axis is natural log of the square root of the sum of calculated areas (mesiodistal length multiplied by buccolingual breadth) of lower M1 (left) and lower P4 to M3 (right). A, Ar. ramidus ARA-VP-6/500; L, Au. afarensis A.L. 288-1; c, Pan troglodytes troglodytes; g, Gorilla gorilla gorilla; o, Pongo pygmaeus (males blue, females red).

  4. Fig. 4

    Enamel thickness and distribution patterns in Ar. ramidus. Left panels: micro-CT–based visualizations of maxillary first molars in arbitrary size. (A) Outer enamel surface; (B) enamel thickness in absolute thickness scale superimposed on topographic contours; (C) enamel thickness in relative scale to facilitate comparison of pattern. The molars [labeled in (A)] are as follows: 1 and 5, Au. africanus Sts 24 (mirrored) and Sts 57; 2, Dryopithecus brancoi; 6, Ar. ramidus ARA-VP-1/3288; 3, Pan troglodytes; 4, Pan paniscus; 7, Gorilla gorilla; 8, Pongo pygmaeus. The Pan species share a broad occlusal basin and thin occlusal enamel. Both Ar. ramidus and D. brancoi are thinner-enameled than Australopithecus but share with Australopithecus a generalized distribution pattern. (D) Maximum lateral enamel thickness, showing that Ar. ramidus enamel is thicker than those of Pan and D. brancoi and thinner than that of Australopithecus species. Horizontal line is median; box margins are central 50% range. (E) Ratio of occlusal (volume/surface area) to lateral (average linear) enamel thicknesses, showing that Pan is unique in its distinctly thin occlusal enamel. (F) Molar durability (enamel volume per unit occlusal view crown area) plotted against projected occlusal view crown area. An isometric line (slope of 0.5) is fitted through the centroid of the three measured Ar. ramidus molars. The least squares regression (y = 0.418x− 1.806) of the combined modern ape sample is also shown. This slope does not differ significantly from isometry. Ar. ramidus and D. brancoi are close to, and Australopithecus species considerably above, the regression line, indicating greater enamel volume available for wear in Australopithecus molars. See (2) for further details.

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