Growth marks in tibiae of <i>Hipparion concudense</i>.

<p>The figure shows (on the left) the cross sections of tibiae 30686 (top) and 30685 (down) with the lines of arrested growth identified in the cortical bone and (on the right) a detail of the cortical bone with these growth marks. Red lines are LAGs; green lines indicate the LAGs in the bone remodelled areas; gray lines show the inferred position of the LAGs in regions of the section lacking the cortical bone; red arrows indicate the growth marks within the cortical bone; and vertical red lines show the EFS. Scalebar: 5000 µm.</p

Bone histology of <i>Hipparion concudense</i> from Los Valles de Fuentidueña.

<p>Detail of the bone microsctructure observed in the transverse thin sections of mid-shaft from (a) humerus 30779a, (b) femur 30694, (c) tibia 30682, and (d) metapodial 30657-355x. Scale bar: 5000 µm.</p

Growth marks in femora of <i>Hipparion concudense</i>.

<p>The figure shows (on the left) the cross sections of femora 30698 (top) and 30694 (down) with the lines of arrested growth identified in the cortical bone and (on the right) a detail of the cortical bone with these growth marks. Red lines are LAGs; green lines indicate the LAGs in the bone remodelled areas; grey lines show the inferred position of the LAGs in regions of the section lacking the cortical bone; black lines show the partial marks observed in the section; red arrows indicate the growth marks within the cortical bone; and vertical red lines show the EFS. Scalebar: 5000 µm.</p

Growth marks in humeri of <i>Hipparion concudense</i>.

<p>The figure shows (on the left) the cross sections of humeri 30702 (top) and 30779a (down) with the lines of arrested growth identified in the cortical bone and (on the right) a detail of the cortical bone with these growth marks. Red lines are LAGs; green lines indicate the LAGs in the bone remodelled areas; gray lines show the inferred position of the LAGs in regions of the section lacking the cortical bone; black lines show the partial marks observed in the section; red arrows indicate the growth marks within the cortical bone; and vertical red lines show the EFS. Scalebar: 5000 µm.</p

Sample of the limb bones of <i>Hipparion concudense</i> from Los Valles de Fuentidueña.

<p>The table shows data for the specimens analyzed for the comparative histological study. LAG: line of arrested growth; EFS: external fundamental system; max NGM: maximun number of growth marks within the EFS.</p

Bone histology of the metapodials of <i>Hipparion concudense</i> from Los Valles de Fuentidueña and Concud.

<p>The figure shows the histological features characterizing the three ontogenetical groups established in the <i>Hipparion concudense</i> sample from skeletechronological data (a–c) and different growth patterns (d–f). (a) 31186: immature specimens with vascular canals open to the periosteal surface (white arrows); (b) 17083: subadult specimen with fibrolamellar bone tissue, two LAGs and no periosteal canals; (c) 67917: adult specimen showing intracortical fibrolamellar bone with two LAGs and periosteal lamellar with EFS. Red arrows indicate growth marks; (d) 30599: one LAG, one inner EFS (4 LAGs) and one outer EFS (2 LAGs); (e) 17242: one LAG and one EFS (4 LAGs); 17184: (f) two EFSs (6 LAGs in the inner EFS and 3 LAGs in the outer EFS). Growth marks are indicated with red arrows. Scale bar: 500 µm.</p

Detail of high bone remodeling.

<p>Tibia 28826 shows secondary osteons throughout the cortical bone that obscure histological features. Scalebar: 5000 µm.</p

Different degrees of bone remodeling in <i>Hipparion concudense</i>.

<p>The figure shows different degrees of bone remodeling (a) specimen 30657-355x (Mc, LVF) shows a primary cortical bone with no secondary osteons; (b) specimen 67917 (Mt, LVF) shows an increase in bone remodeling; secondary osteons appear in the layer of woven bone tissue among rows of primary osteons (black arrows indicate a row of secondary osteons); (c) the cortical bone in specimen 30613-599x (Mt, LVF) is highly remodelled. Mt: metatarsal; Mc: metacarpal. Scale bar: 500 µm. (d) The graph shows the general increase in secondary osteon density in the ontogeny and differences between populations. The metatarsals from Concud are more remodelled than the metacarpals, whereas the metatarsals from LVF show a peculiar bimodal distribution.</p

Geographic locations of the Miocene sites studied.

<p>The map shows the location of the two fossil sites studied in the present paper. LVF: Los Valles de Fuentidueña (Segovia, Duero Basin) and CD: Concud (Teruel, Calatayud-Teruel Basin).</p

The age structure of the Los Valles de Fuentidueña and Concud samples.

<p>The high number of adults and the scarcity of two–year-old subadult individuals point to an attritional model, in which the specimens are acumulated in the assemblage due to a combination of factors mainly affecting the vulnerable age groups.</p