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Miocene

first Epoch of the Neogene Period

The Miocene is the first epoch of the Neogene period 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 biota becomes 'modern'.

The Miocene was named by Sir Charles Lyell. Its 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.

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 fairly modern, but familiar present-day species had not yet evolve. Modern families of mammals and birds existed. Whales, seals, and kelp spread. Modern sharks appeared, including the huge Megalodon. Grasslands became more common. Mammalian browsers became less common, and grazer species became more common. About 100 species of ape lived at that time, and cetaceans were very common in the seas.[1] The giganic shark Carcharodon megalodon may have preyed on them.

Contents

ClimateEdit

The climate was warm in the Miocene, especially in the first half. The diagram shows that throughout the Oligocene and the first half of the Miocene, climate remained warm.

 
Significant drop off in both temperature and deep sea ocean temperature as measured by delta 18O after the Middle Miocene Climatic Optimum.

This meant that Africa (and elsewhere) was much more forested than today, and that the herbivorous mammals were mainly browsers rather than grazers. In the second half of the Miocene temperatures dropped, and grasslands began to expand.

MediterraneanEdit

Another great event, which undoubtedly affected climate, was the refilling of the Mediterranean basin. The so-called Zanclean flood is thought to have refilled the Mediterranean Sea 5.33 million years ago.[2] This reconnected the Mediterranean Sea to the Atlantic Ocean. It is possible that even before the flood there were partial connections to the Atlantic Ocean.

According to this model, water from the Atlantic Ocean refilled the dried up basin through the modern-day Strait of Gibraltar. The process took up to two years.[3]

The flood may have affected global climate, considering that the much smaller flood triggered when Lake Agassiz drained did result in a cold period.[4]

Related pagesEdit

ReferencesEdit

  1. Alton C. Dooley Jr., Nicholas C. Fraser & Zhe-Xi Luo (2004). "The earliest known member of the rorqual–gray whale clade (Mammalia, Cetacea)" (PDF). Journal of Vertebrate Paleontology 24 (2): 453–463. doi:10.1671/2401. http://www.seaturtle.org/PDF/Dooley_2004_JVertPaleo.pdf. 
  2. Blanc, P.-L. (2002). "The opening of the Plio-Quaternary Gibraltar Strait: assessing the size of a cataclysm". Geodinamica Acta 15 (15): 303–317. doi:10.1016/S0985-3111(02)01095-1. 
  3. M. Roveri (2008). "A high-resolution stratigraphic framework for the latest Messinian events in the Mediterranean area". Stratigraphy 5 (3–4): 323–342. Archived from the original on 21 January 2012. https://web.archive.org/web/20120121052846/http://160.78.38.2/VM_file/PDF/Roveri_2008_Stratigraphy.pdf. 
  4. Garcia-Castellanos, Daniel et al 2009. Catastrophic flood of the Mediterranean after the Messinian salinity crisis. Nature 462 (7274): 778–781. [1]