Miocene

The Miocene is the last and final epoch of the first Neogene period and the fourth of the Cainozoic. It started about 23 million years ago and ended about 5.33 million years ago. The rock beds that mark the start and end are well known, but the exact dates of the start and end of the period are uncertain. The Miocene was named by Charles Lyell. The name comes from the Greek words μείων (meiōn, “less”) and καινός (kainos, “new”) and means "less recent", because it has 18% fewer modern sea invertebrates than the Pliocene.

The animals at the end of the Miocene are quite different from those at the start. What happened was climate change. The initial climate was wet and wooded. Herbivores like elephants and rhinos had teeth suitable for browsing; they ate leaves and small branches, not grass.

The biota becomes 'modern' because the climate has become more like it is today. That much is certain, but what is not certain is the exact cause of the climate change.^[1]

As the Earth cooled, it went from the Oligocene epoch, through the Miocene, and into the Pliocene. The Miocene boundaries are not set at any particular world wide event. They are set at regional boundaries between the warmer Oligocene and the cooler Pliocene epochs.

The plants and animals of the Miocene were not yet modern, and familiar present-day species had not yet evolved. Modern families of mammals and birds existed. Whales, seals, and kelp spread. Modern sharks appeared. Grasslands became more common. Mammalian browsers became less common, and grazer species became more common. About 100 species of ape lived at that time. They lived in Africa, Asia and Europe.^[2] Cetaceans were very common in the seas.^[3] The gigantic shark Carcharodon megalodon may have preyed on them.

The standard reason why the Earth's climate varies is that there are Milankovich cycles. They cause variations in the Earth's orbit. These changes affect the climate. Changes taking place at present have to consider the influence of humans as well. Over long periods the position of continents and the growth and decay of mountain ranges can also have big effects.

1. ↑ Pearson, Paul N. & Palmer, Martin R. 2000. Atmospheric carbon dioxide concentrations over the past 60 million years. Nature. 406 (6797): 695–699. Bibcode:2000Natur.406..695P. doi:10.1038/35021000. PMID 10963587. S2CID 205008176.
2. ↑ Yirka, Bob 2012. "New genetic data shows humans and great apes diverged earlier than thought". phys.org. [1]
3. ↑ Alton C. Dooley Jr., Nicholas C. Fraser & Zhe-Xi Luo 2004. The earliest known member of the rorqual–gray whale clade (Mammalia, Cetacea). Journal of Vertebrate Paleontology 24 #2, p453–463.