The range and extent of the Vallesian Crisis (Late Miocene): new prospects based on the micromammal record from the Vallès-Penedès basin (Catalonia, Spain)

I Casanovas-Vilar,L.W Van Den Hoek Ostende,M Furió,P A Madern

doi:10.5209/rev_jige.2014.v40.n1.44086

I Casanovas-Vilar, L.W Van Den Hoek Ostende + Show 2 more

Open Access

https://doi.org/10.5209/rev_jige.2014.v40.n1.44086

Copy DOI

Abstract

The Vallesian Crisis was initially recognized as a local event, which implied the extinction of certain rodent and artiodactyl genera coincidingwith the early/late Vallesian boundary (at 9.7 Ma). Following works increased the range and extent of this event to encompass allEurope and involve a great number of mammal taxa. Here, we analyze the Vallesian rodent and insectivore record of the Valles-Penedesbasin (Catalonia, Spain), where the crisis was first recognized. We show that the quality of the record before the crisis is comparativelymuch better than afterwards so diversity appears inflated and extinction rates are overrated. Accordingly, we used inferred taxon rangesand rarefaction to calculate new diversity measures independent of sample size. These measures virtually eliminate the Vallesian Crisis,showing that diversity somewhat decreased during the earliest late Vallesian and soon recovered afterwards. This is because it cannot bediscarded that several rare taxa, customarily said to have disappeared during the crisis, are in fact present. Amongst the rodents and insectivores,these taxa include genera that are generally rare and show a discontinuous record during the early Vallesian. These are presumedspecialists adapted to humid forested environments such as flying squirrels, beavers or certain dormice, most of them being only recordedwhen the sample size is large enough. Alternatively, these genera may have been associated to very specific habitats which, for an unknownreason, are not sampled during the late Vallesian. Our results cast serious doubts on the very existence of the Vallesian Crisis suggesting thatrather than an abrupt event a series of extinctions occurred during a longer time span. It has not been evaluated whether the same patternis observed in the case of large mammals and in other areas. However, our results show that biases introduced by the quality of the recordneed to be taken into account when assessing the extent of the event.

Highlights

The Vallesian stage was first proposed by M. Crusafont (1950) for the Late Miocene faunas of the Vallès-Penedès basin (Barcelona, Catalonia, Spain) characterized by the first appearance of the three-toed hipparionine horses (Hipparion s.l.)
Amongst the rodents and insectivores, these taxa include genera that are generally rare and show a discontinuous record during the early Vallesian. These are presumed specialists adapted to humid forested environments such as flying squirrels, beavers or certain dormice, most of them being only recorded when the sample size is large enough
Our results show that the quality of the record in the VallèsPenedès basin during the latest early Vallesian (9.8-9.7 maximum age (Ma)) is much better than afterwards, so a remarkably high number of rare taxa are recorded

Summary

Introduction

The Vallesian stage was first proposed by M. Crusafont (1950) for the Late Miocene faunas of the Vallès-Penedès basin (Barcelona, Catalonia, Spain) characterized by the first appearance of the three-toed hipparionine horses (Hipparion s.l.). Hipparion ( split into several genera) was known to be a characteristic element of the Late Miocene faunas of Pikermi (Greece), which included certain bovids, giraffids and other open-country mammals. The European Middle Miocene sites known to that date included La Grive and Sansan, both in France, which showed a completely different mammal assemblage, dominated by cervids and suids and characteristic of more humid and forested environments. The Vallesian assemblages were intermediate between both faunas, Hipparion and certain eastern immigrants (for example the giraffid Palaeotragus or the felid Machairodus) were present, but coexisted with Middle Miocene elements characteristic of forested environments. The Vallesian faunas and environments would reflect that the changes that occurred during the Late Miocene were gradual (Crusafont, 1950)

Methods

Results

Discussion

Conclusion