The European ruminants during the "Microbunodon Event" (MP28, Latest Oligocene): impact of climate changes and faunal event on the ruminant evolution.

Bastien Mennecart,Brian Lee Beatty

doi:10.1371/journal.pone.0116830

Abstract

The Earth already experienced numerous episodes of global warming and cooling. One of the latest impressive events of temperature rising was the Late Oligocene Warming that occurred around 25 Mya. An increase of the marine temperature of 2 to 4°C has been observed in a short time interval. In Europe, this major climatic event can be correlated to the continental faunal turnover “Microbunodon Event”. This event is marked by a huge faunal turnover (40% of the ungulate fauna during the first 500k years) and environmental changes. Drier conditions associated to the appearance of the seasonality lead to new environmental conditions dominated by wooded savannahs. This is correlated to a major arrival of Asiatic immigrants. Moreover, from a homogenous fauna during the main part of the Oligocene, local climatic variations between the European Western coast and the more central Europe could have provided faunal regionalism during the latest Oligocene and earliest Miocene. Considering the ruminants, this event is the major ever known for this group in Europe. A total renewal at the family level occurred. Thanks to a precise stratigraphic succession, major evolutionary elements are highlighted. Typical Oligocene species, mainly Tragulina, were adapted to wooded environments and were leaves/fruits eaters. They disappeared at the end of MP27 or the early MP28. This corresponds to the appearance of the Asiatic immigrants. The Tragulina (Lophiomerycidae, Bachitheriidae) and stem Pecora gave way to more derived stem and maybe crown Pecora (e.g. “Amphitragulus”, Babameryx, Dremotherium). These newcomers were adapted to more open environments and mixed feeding. The disappearance of the Tragulina is probably linked to environmental and vegetation changes, and competition. They give way to more derived ruminants having a more efficient metabolism in drier conditions and a better assimilation of less energetic food.

Highlights

Nowadays, the comprehension of the current global warming event is a major asset to prevent extinctions [1]
This study presents first or new descriptions of fossil material from Western Europe localities, dated to MP28
Bachitherium lavocati was only known in the Pech Desse locality [17], [20]

Summary

Introduction

The comprehension of the current global warming event is a major asset to prevent extinctions [1]. The cooling event from the Terminal Eocene Event (a decrease of around 6°C recorded in Northern Atlantic organisms, [6]) concluded to the formation of a permanent ice sheet in Antarctica [6] and the dry out of the Turgai straits in Asia [5] It permitted the immigration of Asiatic animals into Europe and the extinction of European endemic fauna with a faunal renewal of 60% [4,5,6,7]. A rise of the temperature of 2 to 4°C is observed in marine organisms from North Sea and Northern Atlantic [10], [11] This faunal turnover is observed among the entire group of vertebrates and plants (terrestrial plants [12]; charophyta [13]; booid snakes [14]; micromammals [15]; and large mammals, especially the ruminant, which the fauna is totally renewed [8], [9], [16]–[19]).

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Conclusion