Beyond scientific thinking about dinosaurs, there are any number of amateur enthusiasts who think outside-the-box about issues scientists are quite circumspect about.
One such issue is the question of how extremely large creatures such as many dinosaurs could have existed at all, let alone in great numbers for great spans of time.
One popular so-called tin foil conclusion is that many millions of years ago the surface gravity of the Earth was significantly reduced. Now, the physics of this and the astronomical implications of this seemingly make it unthinkable. However, lots of people have thought about it and it is, at least, entertaining to read their thoughts. Here is a typical example:
On the Origin of Dinosaurs and Mammals
The coincidence in time of incipient rifting of Pangea and the origin of dinosaurs during the Carnian age (230-225 Ma) of the Late Triassic suggests a fundamental link between the two. That link may have been the onset of Earth expansion, triggered by the Pangean thermal anomaly and resulting in a 20% reduction in surface gravity. In reduced gravity, animals will have less skeletal mass and thinner bones than equally massive animals adapted to normal gravity; a significant increase in maximum body size will also ensue. These predictions, inferred from allometric scaling principles and supported by biomedical space research and gravity tolerance experiments, are borne out in the fossil record: the Late Triassic witnessed the transition from Paleozoic faunas dominated by relatively small and robust synapsid reptiles (therapsids) to Mesozoic faunas dominated by large and gracile diapsid reptiles (archosaurs), including many families of gigantic dinosaurs.
Dynamical principles of locomotion indicate that a gravity reduction will lower the speed at which animals change gait. In adapting to reduced gravity, the advanced thecodonts may have shifted from a bipedal symmetrical running gait to a bipedal asymmetrical hopping gait, much as the Apollo astronauts did on the Moon. This behavioral shift by the thecodonts engendered fundamental structural changes, including the fully erect gait and obligatory bipedal pose that characterized primitive and many advanced dinosaurs. Like kangaroos, the ectothermic archosaurs may have relied on elastic storage and rebound to hop at high speeds over long distances at a low metabolic cost, which gave them a competitive edge over the proto-endothermic therapsids. The latter became restricted to small-scale niches left vacant by the dinosaurs. In the primitive shrew-like mammals, a high surface-area-to-volume ratio increased metabolic requirements and thus hastened the development of the high-grade mammalian physiology.
Triassic archosaurs were the first vertebrates capable of sustained powered flight. In reduced gravity, the capacity for sustained powered flight may have evolved directly from the archosaur's bipedal hopping gait.
Reduced gravity during the Jurassic implies a subsequent increase in gravity to its modern value. A post-Jurassic gravity increase (associated with terrestrial contraction?) may have fostered the transition from faunas dominated by large, high-browsing sauropods in the Jurassic to faunas dominated by smaller, low-browsing ornithischian dinosaurs in the Cretaceous. Finally, a gravity increase in the latest Cretaceous may have played a role in the wholesale extinction of the remaining dinosaurs at the K-T boundary.
Increasingly precise geological data indicate that the Pangean singularity – final supercontinent coalescence and initial rifting – occurred during the Carnian age (230-225 Ma) of the Late Triassic.1 Coincidentally, dinosaurs originated during the Carnian age2 at almost precisely the same time and were dominant by the end of the Triassic (208 Ma). (See Figures 1 and 2. ) Despite an increasing wealth of fossil evidence, many important dinosaur adaptations – including giantism, bipedality, and powered flight – have never been adequately explained. The dinosaurs’ remarkable success at the expense of the once-dominant mammal-like reptiles also remains an open question. In an attempt to solve these problems, it is hypothesized here that the thermal anomaly associated with the Pangean singularity3 actually signals the onset of a brief episode of global swelling during the Early Mesozoic which caused, as a direct consequence, a slight reduction in surface gravity. Such a change in the geophysical environment would have had a profound affect on vertebrate evolution; it will be argued that many of the dinosaurs’ unique adaptations, and their evolutionary success at the expense of the mammal-like reptiles, were made possible by a decrease in surface gravity during the Triassic and Jurassic.