The early Mesozoic records an important transition in the history of the Earth’s terrestrial ecosystems. As they recovered from the largest known mass extinction (the end-Permian event), organisms in these ecosystems transitioned to new forms that eventually evolved into the classic Mesozoic biotas, and laid the foundations for many groups still flourishing today (Fraser 2006; Irmis & Whiteside 2010; Sues & Fraser 2010). All of this was set against a backdrop of dynamic climatic and physical events that shaped these biotas. This early Mesozoic terrestrial transition reached its culmination in many ways during the Late Triassic, when ecosystems had largely recovered from the end-Permian extinction, but had not yet been affected by the end-Triassic mass extinction (Fraser & Sues this volume). Thus, we see a combination of taxa, with some groups that would not survive the end of the Triassic living alongside early representatives of lineages that flourished later in the Mesozoic (e.g., Fraser 2006; Irmis et al. 2007; Brusatte et al. 2008; Sues & Fraser 2010, this volume) and in some cases are still diverse today. Just one example of this transition, recorded during the Late Triassic, is the origin and diversification of non-avian dinosaurs, the iconic representatives of Mesozoic terrestrial ecosystems (Brusatte et al. 2010; Langer et al. 2010). Although small and rare components of their respective biotas when they first evolved ∼231 Ma, dinosaurs were abundant and had a near-worldwide distribution by the beginning of the Jurassic Period (∼201·3 Ma).