Abstract

The hypsilophodont Oryctodromeus cubicularis from the Cretaceous Blackleaf Formation of Montana represents the first dinosaur interpreted to be from a burrow fill. The skeletal remains occurred within an incompletely preserved chamber at the end of an S-shaped tunnel. Unlike many fossil vertebrates associated with burrows, the Oryctodromeus remains were disarticulated and elevated within the graded fill. To test whether this skeletal arrangement reflected in situ burial from within or transport into the burrow, we constructed a half-scale burrow model using PVC pipes and conducted a series of sediment infilling experiments with appropriately scaled, disarticulated rabbit skeletons. Experimental trials varied incoming flow velocities, sediment supply, dry or water-filled chamber conditions, and initial placement and weight of skeletal elements. Twelve of the 13 trials resulted in complete rearrangement of the skeletons, six trials left bones elevated above the base of the chamber floor, and six resulted in graded fills. Only the trial using saturated bones preserved the skeleton largely undisturbed on the chamber floor. A trial using bones mixed with the sediment prior to deposition resulted in numerous broken elements but did not produce a distinctive bone distribution. Several trials produced bone distributions and sediment fills similar to the original Oryctodromeus burrow assemblage. The experiment as designed failed to falsify the hypothesis that the Oryctodromeus bones were in the chamber prior to burial. Experimental results include bone and sediment configurations similar to those known from the vertebrate fossil record and the former may prove useful in the recognition of burrow assemblages lacking a distinctive fill.

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