Geologica Acta: an international earth science journal ISSN: 1695-6133 [email protected] Universitat de Barcelona España DOMINGO, L.; LÓPEZ-MARTÍNEZ, N.; GRIMES, S.T. Trace element analyses indicative of paleodiets in Middle Miocene mammals from the Somosaguas site (Madrid, Spain) Geologica Acta: an international earth science journal, vol. 10, núm. 3, septiembre, 2012, pp. 239-247 Universitat de Barcelona Barcelona, España Available in: http://www.redalyc.org/articulo.oa?id=50524523003 How to cite Complete issue Scientific Information System More information about this article Network of Scientific Journals from Latin America, the Caribbean, Spain and Portugal Journal's homepage in redalyc.org Non-profit academic project, developed under the open access initiative Geologica Acta, Vol.10, Nº 3, September 2012, 239-247 DOI: 10.1344/105.000001746 Available online at www.geologica-acta.com Trace element analyses indicative of paleodiets in Middle Miocene mammals from the Somosaguas site (Madrid, Spain) 1, 2, 3 2, 3, † 4 L. DOMINGO N. LÓPEZ-MARTÍNEZ S.T. GRIMES 1 Earth and Planetary Sciences Department, University of California Santa Cruz, CA 95064 (USA). E-mail: [email protected]; Fax: +34 913944849 2 Departamento de Paleontología, Facultad CC. Geológicas, Universidad Complutense de Madrid-Instituto de Geología Económica (CSIC) 28040 Madrid, Spain 3 Unidad de Investigación de Paleontología, Instituto de Geología Económica (CSIC) 28040 Madrid, Spain 4 School of Geography, Earth and Environmental Sciences, University of Plymouth Drake Circus, Plymouth, Devon, PL4 8AA, United Kingdom. E-mail: [email protected]; Fax: +44 (0)1752 584776 † Deceased, December 2010 ABS TRACT Trace element analysis of fossil bone and enamel constitutes a useful tool to characterize the paleoecological behavior of mammals. Up to now, most trace element studies have focused on Plio-Pleistocene fossils. Here, we show that paleodietary inferences based on trace element analyses can be also obtained from ~14Ma old Miocene mammals, in a period of time when important paleoclimatic changes took place due to the development of the East Antarctic ice sheet. Trace element ratio (Ba/Ca, Sr/Ca) analyses have been performed on herbivore tooth enamel (gomphothere Gomphotherium angustidens, equid Anchitherium cf. A. cursor, suid Conohyus simorrensis and ruminants) across three stratigraphic levels from the Somosaguas site (Middle Miocene, Madrid Basin, Spain). Previous scanning electron microscope, rare earth element and stable isotope analyses suggested minimal diage- netic alteration of the tooth enamel samples. Trace element analyses reported here show different paleoecological behavior among the studied fossil taxa. Anchitherium cf. A. cursor shows higher Ba/Ca and Sr/Ca ratios than Gomphotherium angustidens, indicating the equid was a mixed-feeder, while the gomphothere was a browser. The enrichment in Ba/Ca and Sr/Ca ratios in the ruminants is attributed to differences in their gastrointestinal tracts and to a more grazing diet. A high variability in trace element values characterizes the suid Conohyus simorrensis, which is believed to be connected to some degree of omnivory. KEYWORDS Geochemistry. Tooth enamel. Diagenesis. Paleoecology. Herbivores. INTRODUCTION malian paleoecological behavior (Sillen, 1986, 1992; Ne- din, 1991; Gilbert et al., 1994; Safont et al., 1998; Spon- The last couple of decades have witnessed an increase heimer et al., 2005; Sponheimer and Lee-Thorp, 2006). In in the use of trace elements as a tool to characterize mam- particular, strontium and barium have been used to infer 239 L . D O M I N G O e t a l . Mammalian paleodiets in the Middle Miocene paleodiets (Gilbert et al., 1994; Safont et al., 1998) as mam- ~14Ma, is well preserved and not significantly altered by mals discriminate against these elements (biopurification of diagenetic processes (Domingo et al., 2009). calcium) in such a way that a decrease in Sr/Ca and Ba/Ca ratios up the food chain has been detected (Elias et al., Here, we apply a suite of trace element analyses for 1982; Sillen and Kavanagh, 1982; Burton et al., 1999; the first time to Miocene mammalian paleoecology. We Blum et al., 2000) with carnivores providing the low- show that differences in trace element patterns are con- est values (Fig. 1). Therefore, trace element analyses in sistent in different mammalian species and are congruent recent and fossil material allow the distinction between with their expected paleodiets across the Middle Miocene different types of diet; herbivory (grazing vs. browsing), stratigraphic succession from the Somosaguas site (Madrid carnivory and omnivory (Balter et al., 2002; Palmqvist Basin, Spain), during a critical span of time when the rees- et al., 2003; Sponheimer et al., 2005; Sponheimer and tablishment of the East Antarctic ice cap brought about a Lee-Thorp, 2006). The concentration of trace elements sharp decrease in temperature and strengthening of aridity. in fossil teeth and bones may also provide an indica- tion of the proportion of these elements in the soil and groundwater which in turn will control the trace GEOLOGICAL SETTING element content in plants (Bowen and Dymond, 1955; Wallace and Romney, 1971). Furthermore, different Somosaguas is a Middle Miocene vertebrate paleon- plant parts may show different trace element concen- tological site situated in the Universidad Complutense de trations (Runia, 1987; Burton et al., 1999). Caution is Madrid Campus in the locality of Pozuelo de Alarcón (Ma- recommended when making comparisons between trace drid Basin, Spain, Fig. 2A). It has been systematically ex- element concentrations from fossil taxa from different cavated since 1998 and up to now, two different sites have paleontological sites situated far away from each other been discovered: North Somosaguas (recording mainly as different lithologies may exist at each site ultimately macro-mammal remains) and South Somosaguas (record- affecting the tooth enamel geochemical signal (Sil- ing micro-mammal remains) separated by a distance of len and Kavanagh, 1982; Sponheimer and Lee-Thorp, 60m. To date, a total of 29 vertebrate species, 24 of which 2006). Therefore, when making paleoecological com- are mammals, have been found (Hernández Fernández et parisons among taxa, it is desirable to select trace ele- al., 2006; Perales et al., 2009). An analysis of the verte- ment data from taxa coming from a single site (Nedin, brate assemblage suggests a tropical or subtropical savan- 1991; Sponheimer and Lee-Thorp, 2006). nah paleoenvironment around a temporal/seasonal lake, with isotopic analyses of bioapatite and inorganic carbona- Previous studies have concentrated on Plio-Pleistocene tes across the ~5meters-thick section suggesting a paleo- and Holocene fossil and sub-fossil material (Sillen, 1986, climatic shift towards a cooler and more arid environment 1992; Gilbert et al., 1994; Safont et al., 1998; Palmqvist et (López-Martínez et al., 2000; Hernández Fernández et al., al., 2003; Sponheimer et al., 2005; Sponheimer and Lee- 2006; Carrasco et al., 2008; Domingo et al., 2009) as a con- Thorp, 2006). Older fossils were thought to be unsuitable sequence of the reestablishment of the ice cap in Antarctica. for such paleoecological studies because of diagenesis giving rise to the loss of the original geochemical signals The majority of the paleontological mammal record of due to intensive chemical interactions within the burial the Madrid Basin is placed in the Aragonian continental environment. However, time is not directly related to the degree of geochemical alteration, as the signals of pristine preservation can be detected even in very old fossil mate- rial (Kolodny and Luz, 1991; Botha et al., 2005; Fricke et al., 2008). In this sense, Eberle et al. (2009) have demon- strated that trace element analyses can shed light on the dietary behavior of different Early Oligocene mammalian taxa from North America. Following Reynard et al. (1999) and Lécuyer et al. (2003), rare earth element (REE) patterns can be used to verify the degree of diagenetic alteration in fossil bones and teeth and thus, determine if original paleoecological information is preserved in their chemical composition. Previous scanning electron microscopy (SEM), REE, and FIGURE 1 Trophic pyramid showing that Ba/Ca ratio decreases up stable isotope analyses supported the notion that the the food chain with grasses having the highest values and carnivores Somosaguas mammalian tooth enamel, which is as old as the lowest ones. Geologica Acta, 10(3), 239-247 (2012) 240 DOI: 10.1344/105.000001746 L . D O M I N G O e t a l . Mammalian paleodiets in the Middle Miocene stage (~17-11Ma) as defined by Daams et al. (1977). Luis paleontological sites (Toots and Voorhies, 1965; Sillen, and Hernando (2000) re-evaluated the Somosaguas site 1986; Gilbert et al., 1994; Palmqvist et al., 2003). Howev- on the basis of the micromammals and proposed an age er, it is well known that bone is more susceptible to under- range from 14.1 to 13.8Ma (Biozone E, MN 5, Late Middle go diagenetical alteration compared to the more resistant Aragonian, Middle Miocene). dental enamel (Lee-Thorp and van der Merwe, 1987, 1991; Ayliffe et al., 1994; Wang and Cerling, 1994; Sponheimer Three different stratigraphic units (T1, T2, T3) made and Lee-Thorp, 1999; Hoppe et al., 2003; Lee-Thorp and up of arkosic and micaceous sands and clays have been Sponheimer, 2003; Tütken et al., 2008). Due to this issue, recognized in Somosaguas (Fig. 2B): T1, T2 and T3 have Sponheimer et al. (2005) and Sponheimer and Lee-Thorp all been identified as middle to distal facies of alluvial fans (2006) began to perform trace element analyses on the arriving northwards from the Sistema Central Range. Only enamel of different mammalian taxa. T1 and T3 have provided vertebrate remains. T2 pinches out to the North, so that T3 lies directly over T1 at North Due to the scarcity and value of the carnivore remains Somosaguas (Mínguez-Gandú, 2000). at the Somosaguas site, only herbivore tooth enamel was considered in this study.