Ruiz Pérez, Javier2026-01-142026-01-142026-01-05https://hdl.handle.net/20.500.14352/130258A recent paper by Prescott et al. (2015, Biology Letters 21, 20250191) presented a strong criticism of the works calculating speeds for dinosaurs from fossil trackways. These authors based their conclusions on experimental data from two helmeted guineafowl individuals walking on compliant substrate, which moved more slowly than the theoretical predictions from the classical methodology proposed by McNeal Alexander (or from subsequent modifications and refinements of it). Here I demonstrate that the experimental results presented by Prescott et al. (2025) are unreliable for obtaining any valid conclusion on the stride length-speed relationship, because the experiment set-up or execution most probably affected the gait and speed of the walking birds. In any case, we must be aware that speeds calculated from fossil trackways following Alexander’s method or related ones are modeled speeds, which have associated uncertainties. If this is taken into account along with the assumptions made for the calculations, “model-speeds” derived from fossil trackways can be considered informative.engAttribution-NonCommercial-NoDerivatives 4.0 Internationalhttp://creativecommons.org/licenses/by-nc-nd/4.0/otheropen access56.012.3Paleontología2416.05 Paleontología de Los Vertebrados