Carolina Castillo

Small vertebrate taphonomy of La Cueva del Llano, a volcanic cave on Fuerteventura (Canary Islands, Spain). Palaeoecological implications

Abstract Cueva del Llano is a volcanic tube of Pleistocene age on Fuerteventura Island. A strand of it (Ramal Nuevo) contains a complex sedimentary infill which has been divided into three sedimentary units and contains at least eight fossiliferous levels of Holocene age. The taphonomic analysis of small vertebrates found in the sediments revealed a scatological origin for the vertebrate assemblage, and that the barn owl (Tyto alba) is the main agent responsible for this concentration of bone remains. Furthermore, the taphonomic analysis allows to reconstruct the changes in the palaeodiet of barn owls during the Holocene of Fuerteventura (Canary Islands) and infer the alterations produced in the vertebrate comunity during that time. In the upper units of the sedimentary infill, the appearance of the house mouse (Mus musculus) is observed. This immigration is correlated that is associated to a decrease of the lava mouse (Malpaisomys insularis) proportions in the fossil assemblage. Also, the study of small vertebrate accumulation in Ramal Nuevo shows that volcanic tubes can be referred to as very useful concentration trap for taphonomic studies.

Testing limiting similarity in Quaternary terrestrial gastropods

Abstract The hypothesis of limiting similarity, which postulates that morphologically and/or ecologically similar species will differ enough in shape, size, or other variables to minimize competition, has been controversial among ecologists and paleoecologists. Many studies have reported the occurrence of limiting similarity in modern environments or in time-averaged fossil deposits; however, empirical high-resolution time series demonstrating limiting similarity over longer time scales are lacking. We have integrated radiocarbon-calibrated amino acid dating techniques, stable isotope estimates, and morphometric data to test the hypothesis of limiting similarity in late Quaternary land snails from the Canary Islands over a period of 42,500 years. We tested for both ecological character displacement (two closely related species will differ in size in order to minimize competition in sympatry and these differences will be minimized in allopatry) and community-wide character displacement (overdispersion of body size among competitors in a guild). Multiple proxies of body size consistently show that two endemic congeneric pulmonate gastropod species (Theba geminata and T. arinagae) maintained a difference in size from ∼42,500 b.p. through the last occurrence of T. arinagae 14,900 b.p., with a concomitant trend of a decreasing body size. Theba geminata body size did not converge on that of T. arinagae and variation in T. geminata body size did not increase significantly following the extinction of T. arinagae; therefore, ecological character displacement and release did not occur. Community-wide character displacement was found in only one time bin over the last 42,500 years. These results suggest that limiting similarity is a transient ecological phenomenon rather than a long-term evolutionary process. This study not only demonstrates the problems inherent in biological “snapshot” studies and geological studies of time-averaged deposits to test limiting similarity adequately, but it also presents a more adequate research protocol to test the importance of interspecific competition in the history of life.

Marine-continental magnetobiostratigraphic correlation of the Dolomys subzone (middle of Late Ruscinian): implications for the Late Ruscinian age

Abstract Lacustrine deposits, which form part of a continental unit cropping out in many localities of the Jerez Basin (SW Spain), have for the first time been dated. These deposits are attributed to the lower part of the Dolomys subzone, the upper part of the MN 15 Neogene Mammal Unit (late Ruscinian). This continental unit unconformably overlies a marine unit. Since the isochrony of the unconformity is not precisely established, the biostratigraphic results and palaeomagnetic data give two possibilities in correlating the Dolomys subzone with the marine magnetobiostratigraphy: (1) it can be correlated with the C2Ar reversed-polarity chron, or (2) with the C2An.2r reversed-polarity subchron (or C2An.1r ?). Therefore, the lower boundary of the MN 15 would be at the base of the C2Ar or at the very top of the Early Pliocene, respectively. In any case, considering the magnetobiostratigraphy correlation carried out in other Pliocene continental basins of the southeastern Spain, the top of MN 15 seems to be within the Late Pliocene.

The submarine volcanic succession of the basal complex of Fuerteventura, Canary Islands: A model of submarine growth and emergence of tectonic volcanic islands

Three lithostratigraphic units have been distinguished in the volcanic succession of the basal complex of Fuerteventura Island. These units are, from bottom to top: the submarine volcanic group, the transitional volcanic group, and the subaerial volcanic group. These three groups record the submarine growth and emergence of the island. The volcanism is represented by ultra-alkaline and strongly alkaline igneous series. The igneous activity was due to the presence of an anomalous zone in the sublithospheric mantle, the low density of which also caused uplift of the Mesozoic oceanic crust. Two extensional phases and an intervening contractional phase developed coeval to the generation of the volcanic succession. The submarine volcanic group was deposited in the hanging wall basin of a large listric extensional detachment directed toward the SSW. The transitional volcanic group was syntectonic with respect to a late inversion of the listric detachment. Finally, the subaerial volcanic group resulted from a second episode of WNW extension. This study of the evolution of the basal complex of Fuerteventura serves as the basis for a tectonic model of submarine growth and emergence of volcanic islands.