Neogene
[11] Some continental movements took place, the most significant event being the connection of North and South America at the Isthmus of Panama, late in the Pliocene.[12] During the Pliocene, Green Sahara phases of wet conditions in North Africa were frequent and occurred about every 21 kyr, being especially intense when Earth's orbit's eccentricity was high.Neogene also marked the end of the reptilian genera Langstonia and Barinasuchus, terrestrial predators that were the last surviving members of Sebecosuchia, a group related to crocodiles.The oceans were dominated by large carnivores like megalodons and livyatans, and 19 million years ago about 70% of all pelagic shark species disappeared.[11] About 20 million years ago gymnosperms in the form of some conifer and cycad groups started to diversify and produce more species due to the changing conditions.Grasses therefore greatly diversified, and herbivorous mammals evolved alongside it, creating the many grazing animals of today such as horses, antelope, and bison.The International Commission on Stratigraphy (ICS) once proposed that the Quaternary be considered a sub-era (sub-erathem) of the Neogene, with a beginning date of 2.58 Ma, namely the start of the Gelasian Stage.[28] The International Union for Quaternary Research (INQUA) counterproposed that the Neogene and the Pliocene end at 2.58 Ma, that the Gelasian be transferred to the Pleistocene, and the Quaternary be recognized as the third period in the Cenozoic, citing key changes in Earth's climate, oceans, and biota that occurred 2.58 Ma and its correspondence to the Gauss-Matuyama magnetostratigraphic boundary.