Natural selection and the development of new taxa are associated with ecological replacement and the increase in number of niches with time. Continental faunal interchange was possible globally because of the existence of the super-continent Pangaea during much of the Upper Palaeozoic and Mesozoic. Figures of tetrapod niches vs. time and discussion of this concept for that period were presented. Habitat divisions [4] were used, namely marine, freshwater, lowland and upland. The marine habitat was colonized rather late by tetrapods and these were possibly the 1st predators on the early bony fish which had diversified in the Permian. The radiation of bony fish in the Jurassic was followed by a further increase in variety of their reptilian predators. Predators may have developed some time after the radiation of a new potential prey group. Most early amphibians occupied freshwater habitats in crocodile or frog niches, but from the Triassic tetrapods moved from freshwaters and lowlands into the uplands also. In terrestrial habitats, the replacement of mammal-like reptiles by dinosaurs was tentatively explained in terms of palaeoclimatology and thermoregulatory physiology. Ornithischians capable of dealing with tough vegetation evolved to occupy the new niches produced by the radiation of conifers in the Jurassic. The extinction of dinosaurs was apparently connected with temperature and habitat changes. Published opinions on the palaeoecological roles of early tetrapods were discussed.
