FIGURE 1. 1, The sand skink Chalcides ocellatus. 2, Sand skink engaged in sand swimming near the sediment surface.


FIGURE 2. 1, Initial stratification of a terrarium filled with ten, 1-cm-thick layers of fine-grained sand. 2, Vertical cut through a core of undisturbed 1-cm-thick layers of coarse-grained sand.

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FIGURE 3. Videos of the burrowing techniques of Chalcides ocellatus. 1, Burrowing by sand swimming or intrusion. 2, Burrowing by excavation. Click on image to activate animation.


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FIGURE 4. 1, A sequence of surficial mounds and depressions in an experiment with alternating sand grain sizes. 2, A terrarium showing the homogenization of the upper 2 cm of fine-grained sand.

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FIGURE 5. 1, Surficial sinuous bilobate trail (SSBT) in medium-grained sand with an enlarged view (insertion). 2, SSBT in coarse-grained sand. 3, A subsurficial sinuous trail from the lower portion of a core from fine-grained sand. 4, SST from the upper portion of a core from fine-grained sand.

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FIGURE 6. 1, Truncation of the upper 2 cm of medium-grained sand (at arrow) and an infilled surficial depression. 2, An isolated U-shaped divot with a sharp boundary in fine-grained sand. 3, An isolated U-shaped divot with a gradational boundary in medium-grained sand. 4, Connected U- to V-shaped divots with gradational boundaries in medium-grained sand. 5, A sharply defined flame structure (arrow) and an accompanying U-shaped divot in fine-grained sand. 6, A small flame structure (arrow) in coarse-grained sand.

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FIGURE 7. 1, Open burrow produced by Chalcides ocellatus in a terrarium with 20% sediment moisture. 2, The open burrow at day 12 of the trial. 3, The resulting biogenic structure from the collapse of the open burrow on day 14 of the trial.

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