Li et al. 2019
bring us “rare evidence of quadrupedal progression in theropod dinosaurs.” They claim, “This is the first example of manus tracks registered while a theropod trackmaker was walking.”
Other Grallator tracks
have been correctly associated with theropods. So the authors of this quadrupedal track description are hanging on to a tradition by labeling the trackmaker a theropod.
“Grallator-type footprints have been found in formations dating from the Early Triassic through to the early Cretaceous periods. Grallator footprints are characteristically three-toed (tridactyl) and range from 10 to 20 centimeters (or 4 to 8 inches) long. Though the tracks show only three toes, the trackmakers likely had between four and five toes on their feet.” Not sure why the Wiki-authors felt they had to write that last sentence. Perhaps some tracks show such traces. Obviously not one genus is responsible for all tracks attributed to the wastebasket ichnotaxon, Grallator.
The thing is…
even quadrupedal theropods, like Spinosaurus, have a large trenchant first digit, but the Grallator trackmaker (Fig. 1) made a small impression. What we’re looking for is a trackmaker with a long-toed theropod-like pes along with a small manus with small unguals. And it’s typically a big taxon.
At present I can’t find a perfect match
from my present list of taxa (Fig. 2). But there are two small South American basal phytodinosaurs, Saturnalia and Pampadromaeus (Fig. 1), that provide some insight. Both were facultatively quadrupdal, based on their proportions. Both have incomplete extremities, but restoration indicates the retention of theropod-like pedes. Phylogenetic bracketing indicates a non-theropod-like manus. There were larger phytodinosaurs in the Late Triassic and Jurassic (Fig. 2), so size is not the issue.
for this issue many possible candidates lack fossil feet and hands. We can only imagine what sort of tracks Middle Triassic trackmakers, Nyasaurus and Turfanosuchus would have made (Fig. 3).
Li D-Q, Xing L-D, Lockley MG, Romilio A, Yang J-T and Li L-F 2019. The first theropod tracks from the Middle Jurassic of Gansu, Northwest China: new and rare evidence of quadrupedal progression in theropod dinosaurs. Journal of Palaeogeography (2019) 8:10. https://doi.org/10.1186/s42501-019-0028-4