Originally Posted by Darwin's Finch
And, to quote Isaac Newton, "We are to admit no more causes of natural things than such as are both true and sufficient to explain their appearances. Therefore, to the same natural effects we must, so far as possible, assign the same causes." One could simply attribute the rarity of hopping ichnofossils to the absence of hopping in dinosaurs, especially given the lack of otherwise supporting evidence for that mode of locomotion.
The Newton quote is off-point. Obviously, alternating footprints means alternating footfalls and therefore a symmetrical walking gait. No argument there. Newton also said hypotheses non fingo
when it came to the cause of gravity, and especially "action at a distance," an absurd notion, which even Sir Isaac acknowledged, but upon which his theory of universal gravity is based.
As far as the rarity (or even absence) of asymmetrical (hopping) footprints, then you are stating a hypothesis -- dinosaurs did not hop -- from which you deduce an empirical and testable prediction -- therefore, hopping dinosaur footprints will never
be found. That's great! But, following Popper, if we find a single set of hopping footprints, i.e. counter-evidence, then your hypothesis will be falsified. Unfortunately, IMO, footprints can never be used to test my hypothesis that (primitive) dinosaurs hopped because the absence of asymmetrical footprints does not falsify it. Therefore, we must look to other sources of evidence, esp. fossilized bones and skeleton. My hypothesis predicts that in order to become efficient hoppers and for dinosaurs to maintain their stability when hopping (as opposed to running), dinosaurs needed to restrict leg motion to the parasagittal plane with no lateral deviations, and that's exactly what their pelvis and upper leg elements reveal.
Incidentally, there is also a paucity (or absence) of running trackways of large theropods. Here's what mainstream paleontologist Gregory Paul said about that in his book on predatory dinosaurs: "It cannot be proven that large theropods were slow by their trackways because, as Iíve explained, this would be another case of unfair use of negative evidence. Someday the prints of a 5-tonne theropod running at high speed may be found and settle the issue once and for all. Until and unless that happens, we must turn to the design and stressing of the theropod skeleton for evidence of their speed."
Couldn't have said it better myself.