Plant morphology or phytomorphology is the study of the physical form and external structure of plants. This is usually considered distinct from plant anatomy, which is the study of the internal structure of plants, especially at the microscopic level. Plant morphology is useful in the visual identification of plants.
Plant morphology "represents a study of the development, form, and structure of plants, and, by implication, an attempt to interpret these on the basis of similarity of plan and origin." There are four major areas of investigation in plant morphology, and each overlaps with another field of the biological sciences.
The mammals of Australia have a rich fossil history, as well as a variety of extant mammalian species, dominated by the marsupials, but also including monotremes and placentals. The marsupials evolved to fill specific ecological niches, and in many cases they are physically similar to the placental mammals in Eurasia and North America that occupy similar niches, a phenomenon known as convergent evolution. For example, the top predator in Australia, the Tasmanian Tiger, bore a striking resemblance to canids such as the Gray Wolf; gliding possums and flying squirrels have similar adaptations enabling their arboreal lifestyle; and the Numbat and anteaters are both digging insectivores.
The fossil record shows that monotremes have been present in Australia since the Early Cretaceous 145–99 MYA.