A new solution to an old riddle: elongate dinosaur tracks explained as deep penetration of the foot, not plantigrade locomotion

The dinosaur track record features numerous examples of trackways with elongate metatarsal marks. Such “elongate tracks” are often highly variable and characterised by indistinct outlines and abbreviated or missing digit impressions. Elongate dinosaur tracks are well-known from the Paluxy River bed of Texas, where some had been interpreted as “man tracks” by creationists due to their superficially human-like appearance. The horizontal orientation of the metatarsal marks led to the now widely accepted idea of a facultative plantigrade, or “flat-footed”, mode of locomotion in a variety of dinosaurian trackmakers small to large. This hypothesis, however, is at odds with the observation that elongate tracks do not indicate reduced locomotion speeds and increased pace angulation values, but instead are correlated with low anatomical fidelity. We here interpret elongate tracks as deep penetrations of the foot in soft sediment. Sediment may collapse above parts of the descending foot, leaving a shallow surface track that preserves a metatarsal mark. The length of a metatarsal mark is determined by multiple factors and is not necessarily correlated with the length of the metatarsus. Other types of posterior marks in dinosaur footprints, such as drag and slip marks, are reviewed.

Methods
Literature review; first-hand observations; photogrammetry