RCMNS2013-49
The Abrupt Collapse of a Diversity Hotspot? Reconsidering Vallesian (Late Miocene) Diversity in its Type Area P. Anneke Madern l ", Isaac Casanovas-Vilar" David M. Alba l ", Daniel DeMignel" Josep M. Robles" Lars W. van den Hoek Ostende', Salvador Moya-Sola' lInstitut Catalit de Paleontologia Miquel Crusafont, Universitat Autimoma de Barcelona, Edifici ICP, Campus de UAB sin, 08193 Cerdanyola del Valles, Barcelona, Spain. 'Naturalis Biodiversity Center, PO Box 9517, 2300 RA, Leiden, the Netherlands. 3Diparlimento di Scienze delIa Terra, Universitit degli Studi di Torino, Via Valperga Caluso 35,10125 Torino, Italy. ICREA at Institut Catalit de Paleontologia Miquel Crusafont and Unitat d'Antropologia Biologica, Universitat Autonoma de Barcelona. Edifici ICP, Campus de 1a UAB sin, 08193 Cerdanyola del ValIes, Barcelona, Spain.
[email protected] The Miocene was a turbulent time, marked by major faunal turnovers and climate changes. Its mammal faunas showed a succession from less seasonal forests and wooded communities to more seasonal, open woodland communities. In the early Vallesian (11.1-9.7 Ma), the Valles-Penedes Basin (Catalonia, Spain) formed the European area with the highest diversity, representing a true diversity hotspot (Casanovas-Vilar et aI., in press). During the late Vallesian, the distribution of marmnals in Europe seems more even without any apparent diversity hotspots. After the early Vallesian climax, there appears to have been a sudden diversity drop at 9.6 Ma, known as the Vallesian Crisis (Agusti & MoyaSolit, 1990). Initially, this crisis was considered a local event, characterised by the extinction of certain mammal species of Middle Miocene origin in the basin, but more recent works consider the Vallesian Crisis to have affected all European faunas, implying the disappearance of most forest-adapted taxa (Agusti et aZ., 2013). However, contradictorily, doubts have arisen considering the timing of the event and even whether the Crisis can be recognized at all outside the Iberian Peninsula (Casauovas-Vilar et aZ., 2010, in press). Reconstructing past biodiversity is a major goal in palaeontology, but in order to recognise non-random patterns in a chaos of data, biases must be controlled. A common bias is uneven sampling; richer or more intensively sampled sites or time intervals contain more rare taxa and thus show a higher diversity. A peak in data quality could lead to an overestimation of the recorded diversity (Foote, 2000). Robust diversity measures are needed to evaluate such biases, taking into account sample size and the probability of finding a certain taxon at a specific site. To assess the effects of the quality of the large mammal record, we compiled a quantitative database of the Vallesian macromammal record of the Valles-Penedes Basin, where the Vallesian Crisis was first recognized. Our results show that extinction rates in the type area might be overemphasised because of the intensive sampling of the richest locality, the site of Can Uobateres 1, which immediately precedes the crisis. Overall, sampling before the crisis is much better than afterwards, which inflates diversity and exaggerates extinction rates. Therefore, we calculated new diversity estimates independent of sample size using rarefaction and sampling probability (Barry et aI., 2002; Van Dam et ai, 2006; Van der Meulen et aZ., 2005). Our calculations show that many genera that purportedly disappeared during the late Vallesian have a discontinuous record during the early Vallesian and are generally very rare. Since the sampling effort in the late Vallesian sites is comparatively lower, we cannot discount the possibility that at least some of those taxa persisted during the late Vallesian. Thus, the crisis was not a single major event occurring at the earlyllate Vallesian boundary, but a more protracted period of extinctions. Keywords: Late Miocene, Vallesian Crisis, biodiversity hotspot, sampling bias, faunal turnover
References: Agusti, l, Cabrera, L., Garces, M., 2013. The Vallesian Mannnal Turnover: A late Miocene record of decoupled land-ocean evolution Geobios 46, 151-157. Agosti, l, Moyit-Sohl, S., 1990. Mammal extioctions in lbe Val1esian (Upper Miocene). Lecture Notes in Earth Sciences, 30, 425-432. Barry, le., Mbrgar, M.E., Flyar, L.L., Pilbeam, D., Bebrensmeyer, A.K., Mahmood Raza, S., Khan, lA., Badgley, C., Hicks, l, Kelley, l, 2002. Faunal and environmental change in lbe Late Miocene Siwalil
