periodicity with strong 1.2 million year modulations. According to proponents of this hypothesis, radiometric dating indicates that major activity from the Siberian Traps ended very shortly after the end-Permian extinction and did not span the entire Early Triassic epoch, thus not being the primary culprit for the climatic changes throughout this epoch. Early Triassic life Fauna and flora The Triassic Period opened with the Permian-Triassic extinction event. The massive extinctions that ended the Permian Period and Paleozoic Era caused extreme hardships for the surviving species. The Early Triassic Epoch saw the recovery of life after the biggest mass extinction event of the past, which took millions of years due to the severity of the event and the harsh Early Triassic climate. Many types of corals, brachiopods, molluscs, echinoderms, and other invertebrates had disappeared. The Permian vegetation dominated by Glossopteris in the southern hemisphere ceased to exist. Other groups, such as Actinopterygii, appear to have been less affected by this extinction event and body size was not a selective factor during the extinction event. Different patterns of recovery are evident on land and in the sea. Early Triassic faunas lacked biodiversity and were relatively homogeneous due to the effects of the extinction. The ecological recovery on land took 30 million years. Terrestrial biota The most common land vertebrate was the small herbivorous synapsid Lystrosaurus. Often interpreted as a disaster taxon (although this view was questioned), Lystrosaurus had a wide range across Pangea. In the southern part of the supercontinent, it co-occurred with the non-mammalian cynodonts Galesaurus and Thrinaxodon, early relatives of mammals. First archosauriforms appeared, such as Erythrosuchus (Olenekian-Ladinian). This group includes the ancestors of crocodiles and dinosaurs (including birds). Fossilized foot prints of dinosauromorphs are known from the Olenekian. The flora was gymnosperm-dominated at the onset of the Triassic, but changed rapidly and became lycopod-dominated (e.g. Pleuromeia) during the Griesbachian-Dienerian ecological crisis. This change coincided with the extinction of the Permian Glossopteris flora. In the Spathian subage, the flora changed back to gymnosperm and pteridophyte dominated. These shifts reflect global changes in precipitation and temperature. Floral diversity was overall very low during the Early Triassic, as plant life had yet to fully recover from the Permian-Triassic extinction. Microbially induced sedimentary structures (MISS) are common in the fossil record of North China in the immediate aftermath of the Permian-Triassic extinction, indicating that microbial mats dominated local terrestrial ecosystems following the Permian-Triassic