New Mexico Geological Society Annual Spring Meeting — Abstracts

Measurements of dinosaur track widths are often underutilized, sometimes appearing in the literature as a component of length/width ratios of no great importance. However, if length/width ratios are confidently known, they have great utility.

Many published studies of dinosaur tracks and trackways have used track length, a surrogate for foot length, to estimate the size and speed of the trackmaker. This is because most size and speed equations are based in part on foot length (e.g., Alexander, 1976). Importantly, foot length is not actually preserved at tracksites, and foot length is very often not the same as track length. Compounding this problem, measurements of track length are often subjective due to a lack of reliable landmarks from which to measure. Overestimating foot length from a track will produce a larger, slower individual. Underestimating foot length will produce a smaller, faster dinosaur (Alexander, 1976; Lucas et al., 2024).

At the Clayton Lake Dinosaur Tracksite, we found width measurements were often more objective and unvarying than length measurements (Lucas et al., 2024). In forward-moving animals, the side of the foot experiences less interaction (insertion, loading, removal of foot) with the substrate than the front and back of the foot. At Clayton Lake, deeply impressed tracks produced steep walls on the sides that minimize differences obtained by different measurement strategies (Falkingham, 2016; Lucas et al, 2024). Track length measurements, on the other hand, suffered from sloping heel regions, toe withdrawal dynamics, metatarsal impressions, and a general lack of reliable landmarks. An average of the best-preserved tracks (undertracks) of ornithopods at Clayton Lake yield a length/width ratio around 1.0. If length/width can be established from elite tracks, width can be substituted for length in dinosaur size and speed equations.

Track width (or length/width) places a useful check on track length measurements. Significant discrepancies may be the result of preservation, measurement error, substrate consistency, gait, improper taxonomic identification, and extramorphological variation. Though providing important information, length measurements out of line with width should not be used for size and speed estimates.

Track widths provide a check on measured track lengths, gaits, and taxonomic identification. In partially-registered or poorly preserved tracks, track widths may provide a better substitute for track length in size and speed equations.

References:

1. Alexander, R.McN., 1976, Estimates of speeds of dinosaurs: Nature, v.261, p. 129-130.
2. Falkingham, P.L., 2016, Applying objective methods to subjective track outlines; in Falkingham, P.L., Marty, D., and Richter A., eds., Dinosaur tracks: the next steps. Indiana University Press, Bloomington, p. 73–80.
3. Lucas, S.G., Rogers, J.B., and Kvasnak, M.A., 2024, Photogrammetric study of the Clayton Lake Dinosaur Tracksite, Lower Cretaceous of northeastern New Mexico, US in Louis H.Taylor, Robert G. Raynolds, and Spencer G. Lucas, eds., 2024, Vertebrate Paleoichnology: A Tribute to Martin Lockley. New Mexico Museum of Natural History and Science Bulletin 95.