Small mammal (rodents and lagomorphs) European biogeography from the Late Oligocene to the mid Pliocene

Abstract

Aim To analyse the fossil species assemblages of rodents and lagomorphs from the European Neogene in order to assess what factors control small mammal biogeography at a deep-time evolutionary time-scale.Location Western Europe: 626 fossil-bearing localities located within 31 regions and distributed among 18 successive biochronological units ranging from c . 27 Ma (million years ago; Late Oligocene) to c . 3 Ma (mid Pliocene).Methods Taxonomically homogenized pooled regional assemblages are compared using the Raup and Crick index of faunal similarity; then, the inferred similarity matrices are visualized as neighbour-joining trees and by projecting the statistically significant interregional similarities and dissimilarities onto palaeogeographical maps. The inferred biogeographical patterns are analysed and discussed in the light of known palaeogeographical and palaeoclimatic events.Results Successive time intervals with distinct biogeographical contexts are identified. Prior to c . 18 Ma (Late Oligocene and Early Miocene), a relative faunal homogeneity (high interregional connectivity) is observed all over Europe, a time when major geographical barriers and a weak climatic gradient are known. Then, from the beginning of the Middle Miocene onwards, the biogeography is marked by a significant decrease in interregional faunal affinities which matches a drastic global climatic degradation and leads, in the Late Miocene ( c . 11 Ma), to a marked latitudinal pattern of small mammal distribution. In spite of a short rehomogenization around the Miocene/Pliocene boundary (6-4 Ma), the biogeography of small mammals in the mid Pliocene ( c . 3 Ma) finally closely reflects the extant situation. Main conclusionsThe resulting biogeographical evolutionary scheme indicates that the extant endemic situation has deep historical roots corresponding to global tectonic and climatic events acting as primary drivers of long-term changes. The correlation of biogeographical events with climatic changes emphasizes the prevalent role of the climate over geography in generating heterogeneous biogeographical patterns at the continental scale.

Palaeoecology and palaeoenvironment of the Aquitanian locality Ulm-Westtangente (MN2, Lower Freshwater Molasse, Germany)

“…Ulm-Westtangente fills in a gap towards eastern Europe and allows completing the picture. It attests to the same basic faunal context with few differences to other European regions (Costeur et al 2004;Maridet et al 2007). The MN2 richest faunas in Europe (Montaigu-le-Blin, Laugnac, Cetina de Aragon, La Chaux 7) do indeed indicate a faunal homogeneity albeit also showing some sort of east-west diversity gradient.…”

“…The European continent showed a more fractured shape than today; western Europe was continental with a partially open Rhine Graben separating the western part from the rest of the continent to the east. This geographic configuration did not, however, yield particularly high levels of regional endemism for mammals (Maridet et al 2007;Costeur 2009). This led credence to the hypothesis that the Aquitanian relative climatic stability and homogeneity allowed species to settle down in several regions without creating strong faunal heterogeneities.…”

“…Additionally, crocodile remains found in Ulm-Westtangente (Heizmann et al 1989) tend to exclude the existence of a true temperate climate (involving cold winters), and rather coincide with the proximity of some warm-temperate extant faunas in the PCA. Considering that changes of community structures are long-term processes (Montuire and Girard 1998;Maridet et al 2007), the composition of the UlmWesttangente fauna and the number of cricetid species suggest a temperate-inherited community structure. This implies an ongoing (and progressive) climatic evolution from temperate to subtropical conditions, and Ulm-Westtangente reflecting somehow an intermediate stage in this transition.…”

“…The Aquitanian is an interesting period framed by the Late Oligocene global warming (Zachos et al 2001;Dallai and Burgess 2011) and the late Early/early Middle Miocene climatic optimum (Zachos et al 2001;Böhme 2004). Europe seemed to be marked by a period of climatic stability associated with few faunal changes, many genera being inherited from the Late Oligocene and constantly present throughout the Aquitanian (Maridet et al 2007;Costeur and Legendre 2008b;Maridet and Costeur 2010). The whole fauna is progressively replaced by immigrant species from other continental domains (Mein 1999).…”

Small mammals and stratigraphic position of the “Großberg-Bank” (lower Oberrad Formation, MN1, early Miocene) at Laubenheim Quarry in the Mainz Basin, SW Germany, and their implications for early Miocene biostratigraphy

“…However, according to Mödden (1996) a faunal exchange at least between the Swiss Molasse and the Mainz Basin alongside the Upper Rhine Graben is very likely. Also, according to more recent studies (Maridet et al 2007;Costeur 2009;Costeur et al 2012) during the Aquitanian, especially rodents show very little regional endemism all over Europe despite the Rhine Graben acting as a geographical barrier between its Western and Eastern parts. Description From the mandible the top half is preserved, including the m2 (Fig.…”