Herein we emphasise how environment, palaeoecology and palaeobiogeography play key roles in the evolution of organisms. Nineteenth-century ammonoid biochronology led to the definition of the Mesozoic stages. Their beginning and end are bound by the biggest mass extinctions of Earth history. This study deals with the initial Triassic stages that needed a remarkably short biotic recovery time. The Lower Triassic stages, all named after nineteenth-century researchers of the Himalayas, are the Griesbachian, Dienerian, Smithian and Spathian.