A new approach to the analysis and interpretation of tracks: examples from the dinosauria

Abstract

Tracks can potentially offer unique sources of information, providing insight into the environments, gait and posture, locomotion and behaviour. Track preservation can yield important information on substrate consistency and enable the recognition of transmitted subsurface tracks. The ability to recognize transmitted tracks has broad implications for the understanding of palaeoenvironments and interpretation of ichnological assemblages. In order to gain an understanding of how tracks are formed in three dimensions, and of their variability of expression in different substrates, controlled laboratory simulations were undertaken. Experiments were designed to recover subsurface track layers, yielding for the first time detailed information on subsurface morphology that could be related to ‘true’ surface track features. It was found that subsurface track relief can be correlated with the magnitude and distribution (across a foot) of load acting on the surface sediment. This pressure is transmitted through the sediment, and deforms successive layers at depth, producing an undertrack. The most significant factor controlling track morphology, whether surface or subsurface, was found to be the moisture/density relationship within the substrate at the time of track formation. Variability in the dimensions of simulated tracks, relative to the ‘true’ surface track, indicates that caution should be exercised when using fossil tracks to calculate hip height, speed, age, and population dynamics. In addition, comparison of experimental tracks with dinosaur tracks from the Yorkshire coast suggests that many morphological differences between vertebrate ichnotaxa reflect sediment rheology and taphonomy rather than taxonomy of the track-maker.

Does footprint depth correlate with foot motion and pressure?

“…Specifically, SPMs of deep footprints (more than 20 mm max depth) versus pressure records show much greater differences in the forefoot region, with relative footprint depth exceeding pressure magnitude in all individuals (figure 5 and electronic supplementary material, S3-S22). [4,13,14] have largely focused on sediment failure during track formation, but it is clear from our results that understanding the consolidation and ultimate resistance of the substrate to dynamic loading after initial rsif.royalsocietypublishing.org J R Soc Interface 10: 20130009 failure is also critical to understanding pressure-depth correlations in footprints.…”

“…One of the principal assumptions that underpins biomechanical inferences from footprints is that footprint topology-the three-dimensional surface relief of the deformed substrate-is directly indicative of dynamic foot pressure, which, in turn, is integrally linked with overall limb motion of the trackmaker [1][2][3][4]. The same fundamental assumption is implicit in the study of modern forensic footprints [6,7], where threedimensional footprint geometry (or metrics used to describe it) is considered diagnostic of specific individuals.…”

Dinosaur tracks 2011

“…The broad range of preservation quality suggests a certain time-span and history of the substrate condition (water content, e.g. Manning 2004) for the accumulation of the tracks. However, the interplay of trackmaker size, substrate condition and track preservation is complex and not easy to decipher without tight control of the relevant parameters ('goldilocks' effect', .…”

“…Tridactyle tracks located within the pits/bulges (tracks 9, 16, 18) show various amounts of deformation, increasing towards the middle of the structures. These deformations suggest that the pits were formed after the tridactyle tracks and were deformed largely by vertical compression (local shear failure, Manning 2004). A possible explanation of these structures would be an interpretation as sauropod manus/pes tracks.…”

The birth of a dinosaur footprint: Subsurface 3D motion reconstruction and discrete element simulation reveal track ontogeny

“…Experimental tracks have been created predominantly in horizontal layers of colored material that were later sectioned or split apart (15)(16)(17)(18)(19). Such destructive methods lack a temporal component, precluding direct association of individual track features with specific anatomical structures and explicit events in the step cycle.…”