Palaeogeography, Palaeoclimatology, Palaeoecology 339–341 (2012) 98–113

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Palaeogeography, Palaeoclimatology, Palaeoecology

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Isotopic paleoecology of and the Middle Cooling event in the Basin (Spain)

Laura Domingo a,⁎, Paul L. Koch a, Stephen T. Grimes b, Jorge Morales c, Nieves López-Martínez d a Earth and Planetary Sciences Department, University of California, Santa Cruz, CA 95064, USA b School of Geography, Earth and Environmental Sciences, University of Plymouth, PL4 8AA Plymouth, Devon, United Kingdom c Dept. Paleobiología, Museo Nacional de Ciencias Naturales-CSIC, 28006 Madrid, Spain d Dept. Paleontología, Facultad CC. Geológicas, Complutense de Madrid, 28040 Madrid, Spain article info abstract

Article history: The Middle Miocene underwent profound climatic perturbations detected in worldwide marine and conti- Received 5 January 2012 nental records. The Miocene Climatic Optimum (~17 to 14 Ma), a warm and humid period, was followed Received in revised form 19 April 2012 by the Middle Miocene Cooling (~14–13.8 Ma) characterized by a sharp drop in temperatures and an in- Accepted 25 April 2012 crease in aridity triggered by the reestablishment of the Eastern Antarctica ice sheet. The Madrid Basin, locat- Available online 3 May 2012 ed in the central Iberian Peninsula, has furnished a considerable number of Miocene fossil sites with a very complete succession of localities from the Lower Middle Miocene to the Upper Middle Miocene (Middle Keywords: Carbon and oxygen isotopes and Upper Aragonian, MN5 and MN6, local zones Db to G). Mammalian fossil enamel of different Mammals taxa including , equids, gomphothere, suids and ruminants from 16 fossil sites spanning from ~15.9 Ma to ~13.2 Ma were analyzed for δ13C, δ18O and δ18O values with the aim of determining region- Paleoecology CO3 PO4 Biomes al paleoecological, paleoenvironmental and paleoclimatic changes across this important climate transition. Mean annual precipitation 13 The δ C values vary between −11.9‰ and −6.4‰ (VPDB), indicating a C3 environment ranging from wood- Mean annual temperature lands to more open conditions. The rhinoceros Alicornops simorrense and Hoploaceratherium tetradactylum, the gomphothere Gomphotherium angustidens, the cervid Heteroprox moralesi and the paleomerycid Triceromeryx pachecoi may be regarded as browsers inhabiting more closed environments, whereas the equid Anchitherium, the rhinoceros matritense and the bovid Tethytragus langai show a mixed feeding diet related to more open conditions. Furthermore, the variation in δ13C values across the fossil sites and local zones indicates drier conditions in local zones Db and Dc (~15.9–14.8 Ma), a more humid pe- riod in local zone Dd (~14.8–14.1 Ma), before a return to a drier environment in local zones E, F and G (~14.1–13.2 Ma). The δ18O and δ18O values and calculated δ18O values all track a declining trend CO3 PO4 w – δ18 ‰ from local zones Db to Dd (~15.9 14.1 Ma), with minimum values in local zone E ( OCO3 =26.5±2.1 , δ18 ‰ δ18 − ‰ δ18 – OPO4 =18.4±2.4 , and Ow = 5.3±2.9 ). The minimum in O values in local zone E (~14.1 13.7 Ma) appears to coincide with a drop in temperature at the time of the Middle Miocene Cooling – δ18 δ18 δ18 (~14 13.8 Ma). After this minimum, OCO3, OPO4 and Ow values recover in local zones F and G 13 (13.7–13.2 Ma). The calculation of Δ Cleaf values allowed us to determine plausible biomes that might have existed in the Madrid Basin during the Middle Miocene (i.e., a tropical rain forest, a tropical deciduous forest, a temperate evergreen forest and a xeric woodland–scrubland), although this method was not able to 13 detect more savanna-like environments. Finally, δ Cdiet, meq values were used to infer mean annual precip- itation, with values ranging from ~250 mm/yr (local zone Dc) to ~670 mm/yr (local zone Dd) which are in 13 accordance with the proposed biomes suggested by the Δ Cleaf values and fossil assemblages. © 2012 Elsevier B.V. All rights reserved.

1. Introduction temperatures worldwide and humid tropical and subtropical conditions reaching to middle latitudes (e.g., the presence of crocodiles and palm The Middle Miocene was a period of substantial paleoenvironmental trees in the Vienna Basin; Agustí and Antón, 2002). According to and paleoclimatic change (Flower and Kennett, 1994; Zachos et al., Böhme (2003), who studied ectothermic vertebrates from Central 2001; Böhme, 2003). The Miocene Climatic Optimum (MCO; ~17 to Europe, the lower limit for mean annual temperature (MAT) during 14 Ma) was the warmest period since the Middle Eocene, with high the MCO was 17.4 °C and paleobotanical data and bauxite records point to MAT as high as ~22 °C (Price et al., 1997). This global warming was followed by a sharp and short-term (~200 ka) drop in temperatures – fi ⁎ Corresponding author. Tel.: +1 34 913944875; fax: +1 34 913944849. known as the Middle Miocene Cooling (MMC; 14 13.8 Ma), the rst E-mail address: [email protected] (L. Domingo). step toward the cold climatic regime of the late Neogene (Lear et al.,

0031-0182/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.palaeo.2012.04.026 L. Domingo et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 339–341 (2012) 98–113 99

2000; Zachos et al., 2001; Shevenell et al., 2004). The MMC coincided Farquhar et al., 1989; Ehleringer et al., 1991; Ehleringer and Monson, with the reestablishment of the Eastern Antarctica ice cap; its impacts 1993; Hayes, 2001). Plants following the C3 or Calvin–Benson photosyn- have been recorded in marine and continental sections worldwide thetic pathway (trees, shrubs, forbs and cool-season grasses) strongly 13 (Kennett and Barker, 1990; Flower and Kennett, 1994; Zachos et al., discriminate against Cduringfixation of CO2, yielding tissues with 2001; Shevenell et al., 2004; Lewis et al., 2008; Domingo et al., 2009). δ13C values averaging −27‰ (VPDB) (ranging from −36 to −22‰). This cooling led to a stronger meridional temperature gradient and es- The most negative δ13C values of this range (−36 to −30‰)reflect 13 tablishment of new climatic zonations (Pickford and Morales, 1994; closed-canopy conditions due to recycling of C-depleted CO2 and Böhme, 2003). Estimates of temperature change range from a drop in low irradiance. The highest values (−25 to −22‰) correspond to C3 MAT of more than 7 °C in Central Europe (Böhme, 2003), to a 6 to 7 °C plants from high light, arid, or water stressed environments. C4 plants drop in high-latitude (~55°S) southwest Pacific sea surface tempera- (Hatch–Slack photosynthetic pathway) comprise grasses and sedges tures (Shevenell et al., 2004), to a decline of 8 °C in mean summer tem- from areas with a warm growing season and some arid-adapted dicots. 13 peratures in Antarctica (Lewis et al., 2008). Although more difficult to C4 plants discriminate less against C during carbon fixation, yielding quantify, an increase in aridity accompanied this global cooling. mean δ13C value of −13‰ (ranging from −17‰ to −9‰). Cra- According to palynological studies, a replacement of evergreen forests ssulacean acid metabolism (CAM) is the least common pathway, occur- adapted to humid tropical and subtropical conditions by drought- ring chiefly in succulent plants. CAM plants exhibit δ13C values that adapted vegetation occurred in mid-European latitudes (Agustí and range between the values for C3 and C4 plants. 13 Antón, 2002; Jiménez-Moreno, 2006). While the causes for these pro- Using the expected δ CrangesforC3 and C4 plants and a typical diet- found climatic and environmental changes remain mostly unknown, to-enamel fractionation of +14.1±0.5‰ (Cerling and Harris, 1999), we 13 several mechanisms have been invoked as triggering factors such as a can estimate the expected δ CvaluesforpureC3 feeders in different hab- drawdown in atmospheric pCO2 levels (Kürschner et al., 2008)either itats (closed-canopy, −22 to −16‰; mesic/woodland, −16 to −11‰; via organic carbon sequestration on mid-latitude continental margins open, arid C3, −11 to −8‰)andpureC4 feeders (−3‰ to +5‰). Enam- 13 (“Monterey hypothesis”; Vincent and Berger, 1985; Flower and el δ C values between −8‰ and −3‰ represent mixed C3–C4 diets. Kennett, 1994) or a boost in silicate weathering rates (Raymo, 1994) When considering fossil taxa, however, it is necessary to account for shifts 13 as a consequence of Himalaya uplift. Milankovitch cycles may have in the δ C value of atmospheric CO2 (the source of plant carbon), includ- been also responsible for the drop in temperatures and the enhance- ing anthropogenic modification due to fossil fuel burning, which has de- 13 ment of aridity around the MMC (Shevenell et al., 2004). Finally, tectonic creased the δ C value of atmospheric CO2 from −6.5 to −8‰ since factors and the reorganization of gateway regions may also have played onset of the Industrial Revolution (Friedli et al., 1986; Marino and arole(Pagani et al., 1999; Wang et al., 2006). McElroy, 1991). Using isotopic data from marine foraminifera, Tipple et 13 The relationship between these climate changes and shifts in al. (2010) reconstructed the δ C value of the atmospheric CO2 for the mammalian faunal assemblages is controversial. The MMC triggered Middle Miocene (~15.9–13.2 Ma) as ~−6‰,adifferenceof2‰ relative environmental changes, such as the development of more open, less to the modern value. Accounting for these shifts in baseline, closed- forested habitats. Some authors argued these changes had profound canopy δ13C values would range from −20 to −14‰,mesic/woodland consequences on mammalian terrestrial herbivores, including a from −14 to −9‰, open, arid C3 from −9to−6‰,andpureC4 feeders trend towards a larger body size, more hypsodont teeth, and more from −1‰ to +7‰. elongated distal limb segments (Janis and Damuth, 1990; Agustí and Isotopic studies of ancient C3-dominated ecosystems have provid- Antón, 2002). Other authors have argued that there is no direct rela- ed evidence for niche partitioning among sympatric taxa (Feranec tionship between climatic change and mammalian turnover rates and MacFadden, 2006; Tütken et al., 2006; Domingo et al., 2009; (Costeur et al., 2004; Legendre et al., 2005; Costeur et al., 2007). Tütken and Vennemann, 2009). This is possible because of the wide 13 Costeur et al. (2007) cautioned that this lack of synchroneity might range of δ C values in C3 plants related to microenvironment and be due to flaws in the Mammal Neogene (MN) biochronology and plant functional type. C4 plants have a competitive advantage when urged a revision of the geochronology of some European fossil sites, atmospheric pCO2 levels are low and at higher temperatures, and an issue that has been already dealt with by recent studies (Gómez they have greater water use efficiency (Ehleringer et al., 1991). Unde-

Cano et al., 2011; van der Meulen et al., 2011). niable C4 vestiges have been found in fossil localities as old as ~14 Ma Studies of environmental and climatic fluctuations in long terres- (Nambudiri et al., 1978; Retallack et al., 1990; Morgan et al., 1994), trial sequences are rare in comparison to the more complete sedi- and the C4 plants rose to dominance in different regions asynchro- mentary sequences of the marine record. The Madrid Basin contains nously from the late Miocene to late Pliocene (between ~8 Ma and well preserved Middle Miocene vertebrate localities in continuous ~2.5 Ma) (for a review see Strömberg, 2011). temporal succession. Most of the fossil mammals from this basin cor- Oxygen isotope values have also provenusefulinpaleoenvironmental respond to the Middle Miocene Aragonian continental stage (Daams and paleoecological reconstruction. The δ18O values of both carbonate et al., 1977), spanning from ~17 to 11 Ma. The abundance and variety and phosphate fractions of the bioapatite in mammalian of macromammal taxa in these deposits make the Madrid Basin an are a reflection of the δ18O value of body water, which in turns records ox- ideal location in which to use stable isotope analysis to study pal- ygen uptake (inspired O2 and water vapor, drinking water, dietary water, eonvironmental and paleoecological change in the Middle Miocene. oxygen in food dry matter) and loss (excretion, expired CO2 and water vapor) during tooth development (Bryant and Froelich, 1995; Kohn, 1.1. Isotopic reconstruction of continental environments 1996). Within a taxon, variations in body water δ18O values can be inter- preted as chieflyreflecting changes in the isotopic composition of Analyses of the carbon isotope (δ13C) composition of mammalian ingested water, which varies with mean annual temperature and aridity. tooth enamel have provided information about paleodiets, permitting Briefly, the δ18O values of meteoric water, the ultimate source of drinking reconstruction of habitat preferences and ecological niche dimensions water, and water and oxygen in dry matter in plants, are positively corre- (for a review see Koch, 1998, 2007). The δ13C values of herbivore tooth lated with mean annual temperature. In addition, as aridity increases, this 13 13 18 enamel bioapatite (δ Cenamel)tracktheδ C values of the plants they water (especially the water in plants) becomes O-enriched due to evap- 13 18 consume (δ Cdiet), offset by a consistent +12 to +14‰ due to fraction- oration (Luz et al., 1990; Ayliffe et al., 1992). Within a region, the δ O ations associated with carbonate equilibria and metabolic processes values of herbivore taxa will vary in relation to their physiology of (Cerling and Harris, 1999; Passey et al., 2005). water economy, which determines how much they need to rely upon In terrestrial settings, the dominant control on the δ13C value of drinking water, as well as dietary differences that affect the δ18Ovalue plants is photosynthetic pathway (Bender, 1971; O'Leary, 1988; of water in plants. 100 L. Domingo et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 339–341 (2012) 98–113

In general, there is a contrast between obligate drinkers ( The Madrid Basin extends >10,000 km2 and is filled by Cenozoic that obtain most of their water from drinking, frequently grazers) and terrestrial sediments, ranging in thickness from 3500 m in the west non-obligate drinkers (those obtaining water mainly from plant water to ~2000 m in other areas (Junco and Calvo, 1983). An angular, ero- and metabolic water, frequently browsers) (Kohn, 1996). Levin et al. sive discordance occurs between Paleogene and Neogene sediments. (2006) developed a classification based on the isotopic sensivity to arid- Miocene sediments have the largest outcrop area in the Madrid ity in modern East African mammals. According to this classification, Basin, and most paleontological sites are from this epoch (Alberdi, herbivores can be evaporation insensitive (EI) or evaporation sensitive 1985; Calvo et al., 1993). Miocene sediments can be subdivided into (ES). The first group drinks water daily or consumes nonleafy parts of three depositional units according to tectonic, stratigraphic and sedi- plants (which contain water that has not experienced evaporation); mentological criteria: the Lower Unit (Ramblian–Middle Aragonian, thus, these animals record local meteoric water δ18O values. Evapora- ~20–15 Ma), the Intermediate Unit (Middle Aragonian–Vallesian, tion sensitive (ES) herbivores can survive with little or no drinking ~15–10 Ma), and the Upper Unit (Vallesian–Turolian, ~10–5.3 Ma) water; they obtain most of their water from leaf water, which is prone (Alberdi et al., 1984; Alberdi, 1985; Calvo et al., 1993). to strong evaporative 18O-enrichment. Hence the δ18O values of ES her- A mosaic of continental environments from alluvial fans to bivores increase relative to meteoric water values (as monitored by EI evaporatic lakes are represented by these Neogene deposits. The pa- herbivores) with increasing aridity. leontological sites studied here are from the Lower and Intermediate Units and are Middle Miocene in age (Peláez-Campomanes et al., 2. Geological setting and biochronology 2003). The -Marqués de Monistrol, La Hidroeléctrica, Puente de Toledo, , PAR Peñuelas, Estación Imperial, Paseo The Madrid Basin is part of one of the largest Cenozoic basins in de , 17 and Barajas 3 fossil sites derive from the the Iberian Peninsula, the Tagus Basin. This intracratonic basin is sur- Lower Unit, whereas the Arroyo del Olivar, Somosaguas, Puente de rounded by the Central System to the north, the Iberian Range to the Vallecas, Henares 1, Alhambra-Túneles, Paracuellos 5 and Paracuellos east and the Toledo Mountains to the south. The Tagus Basin, which 3 sites are from the Intermediate Unit. Sites from the Lower Unit formed via compression between the African and European plates occur in the “Peñuelas” facies, which comprise green clays with abun- during the Cenozoic (Andeweg, 2002), can be subdivided into two dant bioturbation and frequent intercalations of carbonate sporadi- smaller basins: the Madrid Basin and the Loranca Basin (Fig. 1). cally associated with flint and sepiolite levels. These deposits have

Fig. 1. The Madrid Basin with the main sediment sources for fluvial fans coming from the Sistema Central and Montes de Toledo (black arrows). The dashed line marks the boundary between detritic rim facies and the lacustrine facies in the Middle and Upper Aragonian (Calvo, 1989). The Cenozoic basins of the Iberian Peninsula are shown in gray in the upper left corner, with a black star for the Madrid Basin. L. Domingo et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 339–341 (2012) 98–113 101 been interpreted as fan-delta environments. Those fossil sites from δ13Cvaluesandδ18O values for both apatite carbonate and phosphate the Intermediate Unit outcrop in coarse- to fine-grained arkosic sand- are reported relative to Vienna Standard Mean Ocean Water (VSMOW). stones indicating intermediate to distal/lacustrine areas in alluvial fan Mammalian tooth enamel samples (n=214) were analyzed for deposits. the carbon and oxygen isotope composition of carbonate in bioapatite 13 18 A revised biochronology of paleontological sites from the Madrid (δ C and δ OCO3, respectively). Approximately 5 mg of enamel was Basin was completed by Peláez-Campomanes et al. (2003). While soaked in 30% H2O2 for 24 h. After 5 rinses with deionized (DI) water, ages for mammalian fossil sites in the basin range from Late Oligocene enamel was soaked for 24 h in a 1 M acetic acid buffered with Ca ac- to Late Miocene–Early Pliocene, all the fossil sites considered in this etate solution to ~pH 5, and again rinsed 5 times with DI water. Sam- study belong to the Middle Miocene (continental stage: Aragonian; ples were freeze-dried at −40 °C and at a pressure of 25×10− 3 Mbar marine stage: Langhian to Serravallian, MN5 and MN6, ~15.9 to for 24 h. Isotopic analyses were conducted at the Stable Isotope Labo- ~13.2 Ma; Fig. 2). Different local zones have been defined for the Ibe- ratory at the University of California Santa Cruz (USA) using a Thermo rian Miocene on the basis of micromammals and designated with MAT253 dual-inlet isotope-ratio mass spectrometer coupled to a Kiel consecutive letters (Hedberg, 1976; Daams et al., 1999; Álvarez IV carbonate device. The standards used were Carrara Marble (CM, Sierra et al., 2003 and references therein). These biozones extend δ13C=1.97‰ and δ18O=−1.61‰, both VPDB), NBS-18 (δ13C= from A (oldest) to M (youngest), with three underlying biozones (X, −5.03‰ and δ18O=−23.01‰, VPDB) and NBS-19 (δ13C=1.95‰ Y and Z) and were defined in the Calatayud and Teruel basins and δ18O=−2.20‰, VPDB). The standard deviations for repeated (Spain). The Lower, Middle and Upper Aragonian comprise local measurements of CM (n=61) and NBS-19 (n=18) were 0.07‰ for zones B and C, D and E, and F and G, respectively (Daams et al., δ13C and 0.05‰ for δ18O. The standard deviations for repeated mea- 1987) and the fossil sites considered in this study are situated in sures of an enamel sample were 0.10‰ for δ13C and 0.30‰ local zones Db, Dc, Dd, E, F and G (Fig. 2). for δ18O (n=17). Duplicate analyses were performed for ~10% of the samples (n=26). The average absolute difference for δ13C and δ18 ‰ ‰ OCO3 was 0.06 and 0.44 , respectively and the standard devia- 3. Material and methods tions of these average differences were 0.16‰ and 0.50‰ for δ13C δ18 and OCO3, respectively. δ18 We analyzed mammalian herbivore tooth enamel from 16 The oxygen isotope values of phosphate in bioapatite ( OPO4) fossil sites located in the Madrid Basin (Spain). Taxa include the were measured on 153 enamel samples. The method of Bassett et al. rhinoceros Alicornops simorrense, Hoploaceratherium tetradactylum (2007) was used to prepare the samples. Between 1.5 and 2 mg of and Hispanotherium matritense, the equids Anchitherium cursor, tooth enamel was weighed out and dissolved in 100 μl of 0.5 M

Anchitherium procerum, Anchitherium matritense, Anchitherium alberdiae HNO3.75μl of 0.5 M KOH was added to neutralize the solution. CaF2 and Anchitherium sp., the gomphothere Gomphotherium angustidens, and other fluorides were precipitated by adding 200 μl of 0.36 M KF. the bovid Tethytragus langai, the cervid Heteroprox moralesi, the suids Samples were then centrifuged for ~7 min, and the supernatant was

Listriodon splendens, Bunolistriodon lockharti, Listriodon retamaensis collected. 250 μl of silver amine solution (0.2 M AgNO3, 0.35 M and Conohyus simorrensis and the paleomerycid Triceromeryx pachecoi NH4NO3, 0.74 M NH4OH) was added to the supernatant after which (Table 1). samples were placed in an oven overnight at 50 °C to promote precip-

A rotary drill with a diamond-tipped dental burr was used to recover itation of yellow crystals of Ag3PO4. Samples were centrifuged and enamel from an area of the tooth as large as possible to avoid seasonal rinsed 5 times with DI water, and then were left in an oven overnight bias in the time of mineralization. The teeth used in this study are ar- at 50 °C. Ag3PO4 crystals were recovered and weighed into pressed — δ18 chived at the Museo Nacional de Ciencias Naturales CSIC (Madrid, silver capsules. OPO4 values were measured using a Thermo Spain) and Museo Geominero—Instituto Geológico y Minero de España Finnigan Delta plus XP isotope ratio mass spectrometer coupled (Madrid, Spain). The carbon and oxygen isotope results are reported in via continuous flow to a high temperature conversion elemental H the δ-notation δ Xsample =[(Rsample −Rstandard)/Rstandard]×1000, where analyzer (TCEA). Repeated measurements of in-house and interna- X is the element, H is the mass of the rare, heavy isotope, and R= 13C/ tional standards are precise to within 0.3‰. The standards used 12Cor18O/16O. Vienna Pee Dee Belemnite (VPDB) is the standard for were Fisher Standard (δ18O=8.4‰), Ellen Gray-UCSC High standard

Fig. 2. The biochronology of the Madrid Basin fossil sites used in this study. Relative temperature and humidity curves for the Aragonian are from δ18O values for the benthic for- aminifer Cibicidoides mundulus from the ODP Site 1171 in the South Tasman Rise (Shevenell et al., 2004), and from assemblages in the Calatayud-Daroca and Madrid Basins (van der Meulen and Daams, 1992; Hernández Fernández et al., 2006a, respectively). The geomagnetic Polarity Time Scale follows Cande and Kent (1995) and provides the main temporal constraints on these strata. European Land Mammal Ages (ELMAs) and Mammal Neogene (MN) units are shown. CC = Casa de Campo, LH = La Hidroeléctrica, PdT = Puente de Toledo, SI = San Isidro, PAR = PAR Peñuelas, EI = Estación Imperial, PdA = Paseo de las Acacias, Bar17 = Barajas 17, Bar3 = Barajas 3, AdO = Arroyo del Olivar, Som = Somosaguas, PdV = , Hen1 = Henares 1, Alh = Alhambra-Túneles, Par5 = Paracuellos 5, Par3 = Paracuellos 3. 102

Table 1 List of fossil sites and taxa from the Madrid Basin selected in this study. R = Rhinocerotidae; E = Equidae; G = Gomphoteriidae; B = Bovidae; C = Cervidae; P = ; S = Suidae.

Fossil sites MN Local R E zone Alicornops Hoploaceratherium Hispanotherium Anchitherium Anchitherium cf. A. Anchitherium Anchitherium Anchitherium cf. A. simorrense tetradactylum matritense cursor cursor procerum matritense matritense

Paracuellos 3 6 G X Paracuellos 5 6 F X X Alhambra-Túneles 6 F X X Henares 1 6 F X Puente de Vallecas 6 F X X .Dmnoe l aaoegah,Pleciaooy aaoclg 339 Palaeoecology Palaeoclimatology, Palaeogeography, / al. et Domingo L. Somosaguas 5 E X Arroyo del Olivar 5 E X Barajas 3 5 Dd Barajas 17 5 Dd Paseo de las Acacias 5 Dc X Estacioń Imperial 5 Dc X X PAR Peñuelas 5 Dc X San Isidro 5 Dc Puente de Toledo 5 Dc X X La Hidroeléctrica 5 DC Casa de Campo-marqueś 5Db X de Monistrol

Table 1 TableList of 1 fossil(continued sites and). taxa from the Madrid Basin selected in this study. R = Rhinocerotidae; E = Equidae; G = Gomphoteriidae; B = Bovidae; C = Cervidae; P = Paleomerycidae; S = Suidae.

Fossil sites E G B C S P

Anchitherium Anchitherium Gomphotherium Tethytragus Heteroprox Listriodon Bunolistriodon Listriodon Conohyus Triceromeryx

alberdiae sp. angustidens langai moralesi splendens lockharti retamaensis simorrensis pachecoi – 4 21)98 (2012) 341 Paracuellos 3 XX Paracuellos 5 X X Alhambra-Túneles Henares 1 –

Puente de Vallecas X 113 Somosaguas X X Arroyo del Olivar X Barajas 3 X Barajas 17 X X Paseo de las Acacias X Estacioń Imperial X PAR Peñuelas X X X San Isidro X Puente de Toledo La Hidroeléctrica X XX Casa de Campo-marqueś XX de Monistrol L. Domingo et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 339–341 (2012) 98–113 103

(δ18O=19.0‰) and Kodak standard (δ18O=18.1‰). Replicate ANOVA detected statistically significant differences among the local δ18 b OPO4 analyses were carried out in~70% of the samples. The average zones (F=8.070, p 0.001). Post-hoc Tukey analyses per taxa, site δ18 ‰ absolute difference for OPO4 was 0.04 and the standard deviation and local zone are provided in the Supplementary data 2. of this average difference was 0.50‰. Means were estimated using all specimens from a site or local zone. Because the number of specimens differs among taxa and sites, and be- cause physiological and ecological differences among taxa may lead to 4. Results differences in δ13C values, it is possible that temporal trends in site or local zone means might be biased by differential taxonomic representa- 4.1. Carbon isotopes tion. We tested for the presence of such biases in two ways. First, Anchitherium and Gomphotherium are abundant and present in most The mean δ13C value (±1 standard deviation [SD]) for all Madrid local zones (both taxa are absent from local zone G; Anchitherium is ab- Basin mammals, irrespective of taxon or level, is −9.5±1.1‰, ranging sent from local zone Db). We constructed site and local zone δ13C value from −11.9 to −6.4‰ (Table 2, Supplementary data 1). The highest curves for these taxa (Supplementary data 3A and B and Supplementary mean δ13C value among the different taxa occurs in the equid data 4A and B). There are significant differences among local zones for Anchitherium sp. from San Isidro (−7.5±1.3‰), whereas the Anchitherium (F=7.657, pb0.001), but not for Gomphotherium lowest mean value occurs in the suid L. splendens from Paracuellos 5 (F=0.932, p=0.457), but in both cases, local zone Dc has the highest (−11.3±0.3‰)(Table 2, Fig. 3). Significant differences occur among δ13C value (Anchitherium: −8.6±1.3‰; Gomphotherium: −9.7± taxa (F=6.292, pb0.001). When comparing among sites, the highest 1.1‰), whereas local zone Dd has the lowest δ13C value (Anchitherium: mean δ13C value occurs at San Isidro (−7.5±1.3‰) and the lowest −10.9‰; Gomphotherium: −10.4±0.3‰) in agreement with the re- mean is from Barajas 3 (−10.4±0.4‰)(Fig. 4A). An ANOVA revealed sults observed when considering all genera altogether. For our second statistically significant differences among the sites (F=5.319, pb0.001). test, we recalculated local zone mean values by a) calculating the aver- LocalzoneDchasthehighestδ13C value (−8.9±1.2‰), whereas local age value for each taxon at each site, b) averaging these taxon means for zone Dd has the lowest δ13Cvalue(−10.4±0.3‰)(Fig. 4B), and an each site to create a site average value, and c) averaging the site means

Table 2 δ13 δ18 δ18 The mean and standard deviation (SD) for C, OCO3 and OPO4 values of the mammalian fossil tooth enamel from the Madrid Basin. n refers to the number of samples. δ13 δ18 δ18 Site MN Local n CCO3 OCO3 SD n OPO4 (‰ VPDB) (‰ VSMOW)

zone Taxa Mean SD Mean (‰ VPDB) Mean (‰ VSMOW) Mean SD

Paracuellos 3 6 G Alicornops simorrense 10 −9.57 0.57 −2.61 28.22 1.34 6 19.42 1.64 Paracuellos 3 6 G Listriodon splendens 4 −10.53 1.01 −0.85 30.03 2.34 4 21.51 1.70 Paracuellos 3 6 G Tethytragus langai 1 −9.15 2.35 24.85 3 23.62 0.84 Paracuellos 5 6 F Gomphotherium angustidens 5 −10.22 1.14 −2.63 28.20 1.82 5 19.93 1.52 Paracuellos 5 6 F Hoploaceratherium tetradactylum 10 −9.90 0.72 −1.27 29.60 0.93 5 20.99 0.89 Paracuellos 5 6 F Anchitherium procerum 9 −9.09 0.69 −1.35 29.52 1.06 5 20.92 1.27 Paracuellos 5 6 F Listriodon splendens 5 −11.25 0.26 −1.69 29.16 0.85 5 21.80 0.80 Alhambra-Túneles 6 F Hoploaceratherium tetradactylum 2 −10.78 0.52 −1.71 29.15 0.09 1 20.23 Alhambra-Túneles 6 F Anchitherium cursor 13 −9.56 0.76 −2.62 28.21 1.24 8 20.59 1.54 Alhambra-Túneles 6 F Bovidae 1 22.06 Henares 1 6 F Hoploaceratherium tetradactylum 3 −9.26 0.20 −1.01 29.87 1.56 3 22.33 2.44 Puente de Vallecas 6 F Hoploaceratherium tetradactylum 2 −10.48 0.43 3.28 34.29 0.40 3 26.85 3.03 Puente de Vallecas 6 F Anchitherium matritense 56 −9.63 0.91 −1.61 29.25 1.57 6 20.19 2.39 Puente de Vallecas 6 F Heteroprox moralesi 2 −10.05 1.29 −3.70 27.09 1.29 4 20.81 1.33 Somosaguas 5 E Gomphotherium angustidens 33 −10.15 0.64 −5.02 25.74 2.29 23 16.94 1.40 Somosaguas 5 E Anchitherium cf. A. cursor 25 −9.85 0.40 −4.38 26.39 1.13 13 16.98 0.85 Somosaguas 5 E Ruminant indet. 14 −9.35 0.67 −5.25 25.37 1.42 8 17.13 1.60 Somosaguas 5 E Conohyus simorrensis 11 −9.67 1.98 −6.22 24.50 2.02 6 16.89 1.98 Arroyo del Olivar 5 E Gomphotherium angustidens 4 −10.26 1.34 −2.89 27.93 0.58 4 19.44 1.06 Arroyo del Olivar 5 E Anchitherium cursor 4 −9.22 1.27 −1.97 28.88 1.99 4 21.78 2.14 Barajas 3 5 Dd Gomphotherium angustidens 6 −10.44 0.35 −2.87 27.95 0.43 5 20.16 1.21 Barajas 17 5 Dd Anchitherium sp. 1 −10.89 −1.45 29.41 5 22.33 0.45 Barajas 17 5 Dd Gomphotherium angustidens 3 −10.24 0.11 −0.95 29.93 1.34 3 21.43 1.48 Barajas 17 5 Dd Rhinoceros 1 −10.23 −2.60 28.23 Barajas 17 5 Dd Palaeomerycidae indet. 1 23.48 Paseo de las Acacias 5 Dc Hispanotherium matritense 2 −8.66 0.24 −0.99 29.89 0.98 4 21.13 0.80 Paseo de las Acacias 5 Dc Anchitherium alberdiae 9 −8.67 0.96 −0.69 30.19 1.09 4 23.60 1.83 Estación Imperial 5 Dc Hispanotherium matritense 2 −9.23 0.35 −0.97 29.91 1.25 2 21.05 2.24 Estación Imperial 5 Dc Anchitherium matritense 3 −8.72 1.67 −0.47 30.42 0.90 6 21.98 1.89 Estación Imperial 5 Dc Bunolistriodon lockharti 2 23.75 1.65 PAR Peñuelas 5 Dc Gomphotherium angustidens 6 −9.64 0.38 −1.34 29.52 0.82 5 21.97 1.22 PAR Peñuelas 5 Dc Hispanotherium matritense 9 −9.02 0.69 −2.38 28.45 1.36 8 20.59 1.79 PAR Peñuelas 5 Dc Anchitherium alberdiae 8 −9.52 0.88 −1.17 29.70 1.01 7 20.15 2.77 San Isidro 5 Dc Anchitherium sp. 4 −7.45 1.29 0.18 31.09 0.81 4 23.74 1.77 Puente de Toledo 5 Dc Hispanotherium matritense 6 −8.37 0.77 −0.47 30.42 0.76 6 22.52 1.37 Puente de Toledo 5 Dc Anchitherium cf. A. matritense 6 −7.87 1.63 0.16 31.07 1.21 4 22.31 2.19 La Hidroeléctrica 5 Dc Gomphotherium angustidens 7 −9.74 1.51 −2.52 28.31 0.74 5 19.93 1.04 La Hidroeléctrica 5 Dc Listriodon retamaensis 2 −10.11 0.60 −2.03 28.82 0.84 2 22.33 La Hidroeléctrica 5 Dc Suid 1 1 19.25 La Hidroeléctrica 5 Dc Triceromeryx pachecoi 2 −11.19 −0.87 30.01 7.08 5 25.59 3.34 Casa de Campo 5 Db Gomphotherium angustidens 3 −9.71 0.93 −0.91 29.97 0.70 4 21.78 0.33 Casa de Campo 5 Db Anchitherium sp. 2 25.17 1.12 Casa de Campo 5 Db Hispanotherium matritense 3 −8.37 0.28 −1.19 29.68 0.46 1 21.52 104 L. Domingo et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 339–341 (2012) 98–113

δ13 ‰ δ18 ‰ Fig. 3. The mean and standard deviation of C( VPDB) versus OCO3 ( VSMOW) for the different mammalian taxa in each local zone. Diamond = Rhinocerotidae; triangle = Equidae; square = Gomphoteriidae; X with vertical = Bovidae; X = Cervidae; circle = Suidae; cross = Palaeomerycidae. to obtain a local zone average value. The difference in local zone δ13C the rhinoceratid H. tetradactylum from Puente de Vallecas (34.3± values between the mean for all specimens and the local zone mean cal- 0.4‰ and 26.9±3.0‰, respectively), whereas the lowest mean value culated to minimize taxonomic biases is trivial (less than 0.2‰ for all occurs in the suid C. simorrensis from Somosaguas (24.5±2.1‰ and local zones). 16.9±1.9‰, respectively) (Table 2, Fig. 3). When comparing among δ18 δ18 sites, San Isidro has the highest mean OCO3 and OPO4 values 4.2. Oxygen isotopes (31.1±0.8‰ and 23.7±1.8‰, respectively), whereas Somosaguas has the lowest values (25.5±1.8‰ and 16.9±1.3‰, respectively) δ18 δ18 (Fig. 4C). When comparing local zones, the maximum δ18O and The mean OCO3 and OPO4 values for all Madrid Basin mammals, CO3 ‰ ‰ δ18 ‰ ‰ irrespective of taxon or level, are 29.1±1.9 and 21.3±2.5 ,respec- OPO4 values occur in local zone Db (29.8±0.6 and 22.7±1.8 ,re- ‰ ‰ δ18 ‰ spectively) and the minimum value occurs in local zone E (26.5±2.2‰ tively ranging from 35.2 to 23.1 for OCO3 and from 29.5 to ‰ δ18 ‰ fi 15.1 for OPO4 (Table 2, Supplementary data 1 and 5). The highest and 18.4±2.4 , respectively) (Fig. 4D). Statistical signi cant differ- δ18 δ18 ences were obtained in three comparisons: taxa (δ18O :F=9.720, mean OCO3 and OPO4 values among the different taxa occur in CO3 L. Domingo et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 339–341 (2012) 98–113 105

b δ18 b δ18 p 0.001; OPO4: F=5.726, p 0.001), sites ( OCO3: F=8.864, 5. Diagenesis b δ18 b δ18 p 0.001; OPO4:F=5.212,p 0.001) and local zones ( OCO3: b δ18 b F=15.390, p 0.001; OPO4: F=8.196, p 0.001). Additional post- When performing isotopic analyses on fossil material, diagenetic hoc Tukey analyses per taxa, site and local zone are provided in the Sup- effects must be addressed. Relative to dentine and bone, tooth enamel plementary data 2. has much larger apatite crystals, a lower content of organic matter, δ13 δ18 δ18 As for C, we tested for taxonomic biases on OCO3 and OPO4 and a low porosity; numerous tests have shown that it is the most re- values in two ways. We constructed site and local zone δ18O values cur- liable bioapatite phase with respect to diagenetic alteration (Kohn ves for Anchitherium and Gomphotherium (Supplementary data 3C and and Cerling, 2002). Oxygen in phosphate has traditionally been reg- D and Supplementary data 4C and D). There are significant differences arded as more reliable than oxygen in carbonate, since P\O bonds δ18 b \ among local zones for Anchitherium ( OCO3:F=8.903,p 0.001; are stronger bonds than C O bond (Kolodny et al., 1983; Longinelli, δ18 δ18 OPO4:F=3.907,p=0.007) and Gomphotherium ( OCO3: F=3.778, 1984; Bryant et al., 1994). Alteration can occur via three processes: δ18 p=0.012; OPO4: F=4.992, p=0.003). Local zone Dc has the highest 1) precipitation of secondary minerals (carbonates, phosphates) on δ18 δ18 ‰ δ18 − 2 − 3 O value for Anchitherium ( OCO3 =30.4±1.2 ; OPO4 =22.1± or between bioapatite crystals; 2) adsorption of CO3 or PO4 from 2.5‰), whereas local zone Db has the highest δ18O value for the solution at surface sites on the crystal lattice; or 3) ion exchange δ18 ‰ δ18 ‰ Gomphotherium ( OCO3 =30.0±0.7 ; OPO4 =21.8±0.3 ). Local during dissolution/reprecipitation or via solid state exchange (Zazzo δ18 zone E has the lowest value for both Anchitherium ( OCO3 =27.6± et al., 2004). Additional material (processes 1 and 2) can be removed ‰ δ18 ‰ δ18 2.0 ; OPO4 =19.7±3.0 )andGomphotherium ( OCO3 =26.8± via acid pretreatments, though preferential removal of new apatite is ‰ δ18 ‰ δ18 fi 2.0 ; OPO4 =18.4±1.7 ). Minimum O values in local zone E dif cult. Zazzo et al. (2004) demonstrated experimentally that bio- pinpointed by Anchitherium and Gomphotherium agree well with mini- apatite carbonate is more susceptible to ion exchange via inorganic mum δ18O values found when considering all genera and maximum processes than bioapatite phosphate (the standard view), whereas δ18O values in local zone Db for Gomphotherium also are in good accor- bioapatite phosphate was more susceptible to microbially-mediated dance with maximum δ18O values in this local zone when considering alteration than bioapatite carbonate. As expected, they determined all taxa. In the case of Anchitherium, this equid could not be sampled that bone is much more susceptible to both inorganic and microbial δ18 in local zone Db. The difference in local zone OCO3 values between alternation, but enamel alteration did occur. δ18 δ18 the mean for all specimens and the local zone mean calculated to min- When both OCO3 and OPO4 values have been determined, −2 imize taxonomic biases were 1.5‰ in local zone G (with higher values tests of diagenetic alteration may take two forms. First, if CO3 and − 3 for the bias-corrected sample) and lower than 0.5‰ at all other local PO4 in bioapatite are cogenetic equilibrium precipitates from body δ18 ‰ zones. The difference for OPO4 values was less than 0.5 for all water at relatively invariant mammalian body temperatures, there δ18 δ18 local zones. should be a consistent difference in OCO3 and OPO4 values

δ13 ‰ δ18 δ18 ‰ δ18 Fig. 4. The mean and standard deviation C( VPDB), OCO3 and OPO4 ( VSMOW) values per site (A and C) and per local zone (B and D). White circles correspond to OPO4 δ18 and black circles correspond to OCO3 values. Fossil site abbreviations as in Fig. 2. 106 L. Domingo et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 339–341 (2012) 98–113

18 18 18 Δ – δ −δ ( OCO3 PO4 = OCO3 OPO4). Several studies of living organisms (H. tetradactylum from Puente de Vallecas) is omitted (Fig. 5C). In 18 Δ – – ‰ fi have observed a OCO3 PO4 of ~8.6 9.1 (Bryant et al., 1996; both cases, no signi cant differences were detected among lines 18 Δ – Iacumin et al., 1996). Obtaining a OCO3 PO4 value near this range (F=0.322, p=0.560 including H. tetradactylum from Puente de for a fossil mammalian bioapatite sample has been viewed as an indi- Vallecas and F=0.430, p=0.387 excluding H. tetradactylum). cation that both phases retain pristine isotopic values (Bryant et al., The results of these tests suggest that our samples have experi- 1996; Fricke et al., 1998; Tütken et al., 2006; Domingo et al., 2009). enced minimal oxygen isotopic alteration of either phosphate or car- δ18 δ18 Second, if OCO3 and OPO4 values are variable, then they should bonate. While there are no comparable tests for carbon isotopes, the exhibit a slope of 1 on a bivariate plot. Because of their asymmetric fact that species cluster in bivariate isotope space, and that the rela- susceptibility to inorganic versus organic alteration, Zazzo et al. tive positions of these clusters are consistent for some taxa, suggests (2004) have argued that if a suite of samples that have experienced that paleobiology is an important driver of isotopic variation. the same diagenetic conditions (i.e., the same temperature and burial fl δ18 δ18 uids), then sample arrays in OPO4 (Y-axis) versus OCO3 (X-axis) plots will have slopes higher than 1 if they have experienced inorgan- 6. Discussion ic diagenesis and slopes lower than 1 if they have experienced micro- bial alteration. 6.1. Paleoecology of the Madrid Basin mammalian taxa 18 Δ – Here, we analyzed only tooth enamel. The mean OCO3 PO4 for all samples is 8.1±1.4‰, which is close to the expected equilibrium We used ~−14‰ as the threshold between closed canopy and difference (Fig. 5A). Iacumin et al. (1996) and Bryant et al. (1996) woodland, ~−9‰ between woodland and open country C3 grass for- δ18 –δ18 − ‰ proposed OCO3 OPO4 equilibrium lines based on modern mam- agers, ~ 6 as the threshold between open country C3 grass for- mal bones and teeth. Fig. 5B and C shows the relationship found agers versus animals from mixed habitats with both C3 and C4 when using only tooth enamel samples from these studies, along plants, and ~−1‰ as the threshold between foragers from these with the line obtained from the Madrid Basin fossil mammals mixed habitats versus those from C4 grasslands. Given the observed (Fig. 5B) and the line when a high value for one anomalous specimen range of δ13C values for Madrid Basin mammals (−11.9 to −6.4‰),

18 18 Δ – ‰ δ Fig. 5. A) OCO3 PO4 ( VSMOW) values for rhinoceros, equids, gomphothere and suids from the Madrid Basin. White circles correspond to OPO4 and black circles correspond to δ18 δ18 δ18 ‰ δ18 δ18 OCO3 values. B) Regression lines between OCO3 and OPO4 ( VSMOW) when considering the entire Madrid Basin dataset. C) Regression lines between OCO3 and OPO4 (‰ VSMOW) when Hoploaceratherium tetradactylum from Puente de Vallecas is omitted. Black circles: this study; white triangles: Iacumin et al. (1996); white squares: Bryant et al. (1996). Illustrations: rhinoceros by O. Sanisidro and the other taxa by M. Antón. L. Domingo et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 339–341 (2012) 98–113 107 the selected taxa might have foraged in woodlands and open habitat beginning of the Late Aragonian. They probably occupied woodlands

C3 environments (Fig. 3). ingesting soft leaves, as indicated by their brachyodont teeth, a fact In those local zones where the equid Anchitherium is present, it that agrees well with their low δ13C values. Given this inferred habi- δ13 δ18 has among the highest C and OCO3 values. The genus tat, the oxygen isotope values are unexpectedly high. It is not likely Anchitherium has been traditionally interpreted as a browser to that this species ingested water from highly evaporated surface mixed-feeder although, depending on the species, it might have water bodies, since this would mean abandoning the protection of a been flexible in its dietary preferences (Hernández Fernández et al., closed environment. A plausible alternative may be that it is an evap- δ13 δ18 2003; Kaiser, 2009; Eronen et al., 2010). Higher C and OCO3 oration sensitive (ES) taxon (sensu Levin et al., 2006) that strongly values in comparison with other taxa are indicative of the consump- relied upon 18O-enriched leaf water to maintain its water balance. tion of a higher proportion of C3 grasses and the occupancy of more Tütken et al. (2006) and Tütken and Vennemann (2009) observed open environments with more evaporated drinking and plant- this same behavior when analyzing the palaeomerycids Palaeomeryx included water. eminens from Steinheim and Germanomeryx fahlbuschi from Sand- Among the rhinoceros, H. matritense has high δ13C and intermedi- elzhausen, respectively. Nevertheless, when considering Middle Mio- δ18 ate OCO3 values. This genus had a hypsodont dentition with cemen- cene mammals, caution must be taken assigning a taxon to one of the tum, long limbs and a slender postcranial skeleton adapted to groups established by Levin et al. (2006), as most mammals of this running. These characteristics may be indicative of a diet based on antiquity do not occur in the same family as their nearest living grasses and the occupancy of more open environments (Cerdeño, relative. 1989; Cerdeño and Nieto, 1995). Hoploaceratherium tetradactylum As far as suids are concerned, the selected taxa belong to two sub- and A. simorrense have intermediate δ13C values. In the local zones families: Listriodontinae (L. retamaensis and L. splendens) and in which they occur, the former has among the highest δ18O values, Tetraconodontinae (C. simorrensis). During the Early and Middle Mio- whereas the latter has among the lowest δ18O values. Eisenmann cene, the dentition of the Listriodontinae shifted from a bunodont and Guérin (1984) considered that H. tetradactylum had features sim- pattern before the MMC to a sub-lophodont to lophodont pattern ilar to those in modern tapirs, which inhabit heavily forested areas after that event. Despite this shift, this subfamily has been considered close to water bodies. The intermediate δ13C values for this rhinocer- as folivorous, dependent to some extent on closed habitats with trees os may be indicative of a diet based on woodland leaves, but the and shrubs (Pickford and Morales, 2003; Orliac et al., 2009). On the values are not as low as expected for an inhabitant of a deep forest/ other hand, the suid C. simorrensis from the Somosaguas site is in- closed canopy habitat (and not in the range of modern tapir, ferred to have inhabited more open environments and to have had DeSantis, 2011), and high δ18O values suggest access to either highly an omnivorous diet, as deduced from its hypertrophid , evaporated surface water sources (more typical of open habitats) or bunodont molars with well-developed pyramidal cuspids and leaf waters that are strongly 18O-enriched. Alicornops simorrense had hyaenoid-type teeth (Sánchez, 2000; van der Made and Morales, morphological features such as brachyodont dentition and short 2003; van der Made and Salesa, 2004). These differences may explain limbs (Cerdeño, 1989) pointing towards humid conditions and its the more negative and less variable δ13C values of the listriodont 18 disappearance has been related to a shift at the end of the Vallesian suids in comparison to C. simorrensis (Fig. 3). The fact that δ OCO3 and the beginning of the Turolian towards increased temperatures values show the opposite relationship, with listriodont suids having and reduced humidity (Cerdeño, 1989). Therefore, A. simorrense higher values than C. simorrensis, may be due to the dependence of may have relied on a higher proportion of leaves in its diet. A low listriodont suids on leaves that may have suffered a higher degree δ18 OCO3 value supplied by this rhinoceros may be linked to the occu- of evaporation. Meanwhile, C. simorrensis, that has been considered pancy of more humid conditions. to be omnivorous, may have obtained most of its water by drinking The gomphothere G. angustidens shows in general low δ13C values. from a less evaporated source of water. This is in good agreement with the fact that it has been regarded as an When comparing δ13Candδ18O values of different sympatric gen- inhabitant of woodland environments and its brachyo-bunodont den- era, it is interesting to consider the pair Hispanotherium–Anchitherium. tition points towards a browsing behavior (Mazo, 2000). The variable These taxa are very abundant from the end of the Early Miocene to δ18 OCO3 values in Gomphotherium may be indicating ingestion of the middle of the Middle Miocene in the Madrid Basin. Morphologi- drinking water in areas with distinct sources and/or distinct rates of cal features observed in the rhinoceros and the equid indicate similar evaporation. ecological niches for these taxa, so that a decrease in the abundance Low to intermediate δ13C values for the cervid H. moralesi is com- of one of these genera is evident in fossil sites where the other is well patible with a browsing to mixed-feeder behavior, a fact supported by represented (Cerdeño, 1989; Cerdeño and Nieto, 1995; Iñigo and its brachyo-selenodont dentition (Rössner, 2010). DeMiguel et al. Cerdeño, 1997). When performing a t-student test, no significant dif- (2011) classified Heteroprox larteti from the MN6 from the Spanish ferences can be drawn between this pair of taxa in the sites where Calatayud-Daroca Basin as a mixed-feeder by means of microwear they coexisted: Puente de Toledo (δ13C: t-student=−0.681, p=0.512; δ18 δ18 − δ13 analyses. Low OCO3 values would be pointing to ingestion of drink- O: t-student= 1.081, p=0.305), PAR Peñuelas ( C: t-student= ing water in woodlands. 1.315, p=0.208; δ18O: t-student=−2.065, p=0.057), Estación Imperial The bovid T. langai has a high δ13C value near the cutoff between a (δ13C: t-student=−0.399, p=0.717; δ18O: t-student=−0.530, p= 13 woodland and an open C3 environment. This result is in accordance 0.633) and Paseo de las Acacias (δ C: t-student=0.016, p=0.988; with Agustí and Antón (2002), who hypothesized that Tethytragus δ18O: t-student=−0.357, p=0.730). Hispanotherium coexisted mainly was an ubiquitous bovid capable of inhabiting different biotopes with A. matritense and A. alberdiae, which have been regarded as with a diet comprising a variety of vegetation, and with DeMiguel et the Anchitherium species more dependent on high humidity levels, al. (2011), who carried out microwear and mesowear analyses on thus, indicating that the ecological niche of these two perissodactyls T. langai from two MN6 fossil sites of the Calatayud-Daroca Basin (rhinoceros and equid) may have not completely overlapped. The and proposed a mixed feeding behavior. In the same way, the very disappearance of Hispanotherium took place at local zone Dd; after- δ18 fi high OCO3 value suggests ingestion of highly evaporated waters in wards rst the rhinoceros Hoploaceratherium and then Alicornops an open environment, or much great reliance on plant water than made their appearance. When comparing the pair Hoploaceratherium– other taxa. Anchitherium,significant differences were found by t-student tests The palaeomerycid T. pachecoi has the lowest δ13C values from at Alhambra-Túneles (δ13C: t-student=−2.149, p =0.049; δ18O: t- local zone Dc. Palaeomerycids are an extinct group of ruminants student=1.005, p =0.022), Paracuellos 5 δ13Cvalues(t-student= that inhabited the Madrid Basin from the Middle Aragonian to the −2.480, p=0.024), and Puente de Vallecas δ18Ovalues(t-student= 108 L. Domingo et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 339–341 (2012) 98–113

5.012, p b0.001), whereas the differences were not significant for Paracuellos 5 δ18O values (t-student=0.165, p =0.871)andPuente de Vallecas δ13Cvalues(t-student=−1.317, p =0.193). Our results suggest that these genera may have partitioned niches, with the rhinoceros better adapted to closed habitats. At the species level, Hoploaceratherium mainly coexisted with A. cursor and A. procerum, which were better adapted to open environments relative to A. matritense and A. alberdiae. Finally, though nearly all Madrid Basin mammal tooth enamel 13 δ C values are in the expected range for a C3 environment, we cannot exclude the possibility that a small percentage of C4 vegetation was present in the diet of taxa with higher δ13C values. This is because ev- idence for C4 vegetation has been detected in the Spanish Middle Miocene (Jiménez-Moreno and Suc, 2007; Urban et al., 2010).

6.2. Changes in the δ13C values in the Madrid Basin: biome change and mean annual precipitation estimation

When comparing δ13C values among the different local zones, two groups can be differentiated by post-hoc Tukey analyses. The local zone Dd (δ13C=−10.4±0.3‰) represented by Barajas 3 and Barajas 17 belongs exclusively to Group 1, whereas local zones Db (δ13C= −9.0±1.0‰) and Dc (−9.0±1.2‰) belong exclusively to Group 2. Local zones E (−9.8±1.1‰), F (−9.7±0.9‰)andG(−9.8±0.8‰) cannot be differentiated from either Group 1 or 2. If δ13C values are interpreted as reflecting moisture levels, generally drier conditions in biozones Db and Dc (Fig. 4B) are followed by wetter conditions in local zone Dd. Aridity increased again in local zone E, with local 13 Fig. 6. The mean and standard deviation (SD) Δ Cleaf (‰ VPDB) values per local zone zones F and G showing similar values. These patterns are also ob- (A) with biomes (following Diefendorf et al., 2010) and mean and standard deviation 13 δ 13 served when looking at C trends showed by Anchitherium and (SD) δ Cdiet, mequ (‰ VPDB) per local zone (B) with mean annual precipitation (after Gomphotherium (Supplementary data 3A and B and Supplementary Kohn, 2010). TRF = tropical rain forest; TSF = tropical seasonal forest; CCEF = Cool- data 4A and B) and therefore, the δ13C curve constructed when con- cold evergreen forest; TDF = tropical deciduous forest; CCMF = cool-cold mixed for- sidering all the taxa is not affected by genus/species metabolism est; XWS = xeric woodland scrubland. MAP is mean annual precipitation in mm/yr. biases. We made biome inferences and estimated mean annual precipita- tion (MAP) following the methods of Diefendorf et al. (2010) and of biomes. According to Hernández Fernández et al. (2003, 2006b), Kohn (2010), respectively. Diefendorf et al. (2010) compiled the the biomes of the Miocene Iberian Peninsula most commonly belonged δ13C values of leaves from woody plants from a broad range of mod- to types II (tropical with summer rains/tropical deciduous woodland) ern C3 biomes. As the fractionation of carbon isotopes during CO2 up- and II/III (transition tropical semiarid/savanna), with a few localities 13 representing biomes V (warm-temperature/temperate evergreen for- take and fixation (Δ Cleaf) varies among biomes (largely due to differences in relative humidity), such data might be used to assess est) and perhaps III (subtropical arid/subtropical desert). The applica- biomes in the past. Kohn (2010) carried out a similar study, but includ- tion of Diefendorf et al. (2010)'s approach to the Madrid Basin ed all types of C3 plants (trees, shrubs and grasses). Kohn (2010) also isotopic data are in agreement with Hernández Fernández et al. reported a correlation between the mean annual precipitation (MAP) (2003, 2006b) in assigning tropical rain forest, tropical deciduous forest, 13 – and modern equivalent carbon isotope values (δ Cdiet, meq, which ac- temperate evergreen forest and xeric woodland scrubland as potential 13 count for the difference in atmospheric δ Cdiet), which could be used Madrid Basin biomes during the Miocene. However, Diefendorf et al. 13 to infer moisture levels at ancient sites. The Δ Cleaf values calculated (2010)'s methodology cannot assign more savanna-like biomes since 13 using mammalian enamel δ C values from the Madrid Basin are these authors only considered woody C3 plant families in their original shown in Fig. 6A and Supplementary data 1 and 6. These values were study. calculated according to the equation: Kohn (2010)'s approach uses the modern equivalent of diet com- position δ13C values, to estimate MAP, albeit with very signif-  diet, meq Δ13 ¼ δ13 −δ13 = þ δ13 = ð Þ icant uncertainty (Freeman et al., 2011)(Fig. 6B; Supplementary data Cleaf CatmCO2 Cleaf 1 Cleaf 1000 1 13 1 and 6). The equation for δ Cdiet, meq values is:

13 13 where δ Cleaf =δ Ctooth −14‰.  13 δ13 ¼ δ13 þ δ13 −δ13 ð Þ Significant differences have been detected in Δ Cleaf values among Cdiet; meq Cleaf Cmodern atmCO2 Cancient atmCO2 2 local zones (F=3.611, p=0.004). As previously inferred from δ13Cre- sults, local zone Dd had slightly wetter conditions than the other local 13 13 zones, while local zone Dc had drier conditions. Inferred biomes for where δ Cleaf is as for Eq. (1), δ Cmodern atmCO2 is −8‰,and 13 each local zone, following the technique outlined in Diefendorf et al. δ Cancient atmCO2 is from Tipple et al. (2010).Significant statistical dif- 13 (2010), are presented in Fig. 6A and Supplementary data 1 and 6. ferences have been obtained in δ Cdiet, meq values among local zones Hernández Fernández et al. (2003, 2006b) also inferred the potential bi- (F=3.604, p=0.004). Inferred MAP ranges from ~250 mm/yr (local omes during the Miocene in the Madrid Basin by analyzing the fossil zone Dc) to ~670 mm/yr (local zone Dd) (Fig. 6B). Local zone MAP mammal assemblages and argued that the type of biomes existing at values (~1000–250 mm/yr) better fit potential precipitation rates in this period of time was very different from those today. These studies dry tropical deciduous woodland (II) and savanna (II/III) biomes to followed the Walter (1970)'s classification, which proposed ten types the very limit of desert (III) biome (Walter, 1970)incomparisonwith L. Domingo et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 339–341 (2012) 98–113 109 separate fossil sites, since local zones contain a wider compilation of Table 3 18 18 Equations used to calculate δ Ow values from mammalian tooth enamel δ OPO taxa than individual localities. 4 values. Overall, these results are in good agreement with existing humidity– aridity curves and intepretations of biome change. Van der Meulen Taxa Equation Reference and Daams (1992) proposed a relative humidity curve based on δ18 δ18 Equids OW (VSMOW) =( OPO4 (VSMOW) - Delgado Huertas et al. the analysis of 59 rodent assemblages in the nearby Calatayud- 22.6)/0.77 (1995) Rhinocerotids δ18O =(δ18O - Tütken et al. (2006) Daroca Basin, whereas Hernández Fernández et al. (2003, 2006a) W (VSMOW) PO4 (VSMOW) conducted a paleoclimatic study based on large mammalian herbi- 25.09)/1.31 δ18 δ18 Proboscideans OW (VSMOW) =( OPO4 (VSMOW) - Ayliffe et al. (1992) vore assemblages of the Iberian Peninsula between the Early and 23.3)/0.94 Late Miocene and a study based on the rodent faunas of the Madrid δ18 δ18 Suids OW (VSMOW) =( OPO4 (VSMOW) - Longinelli (1984) Basin during the Middle Miocene, respectively. The most notable dif- 22.61)/0.85 18 18 Ruminants δ OW (VSMOW) =(δ OPO (VSMOW) - D´Angela and Longinelli ference between these studies is the timing of the aridity peak. This 4 25.53)/1.13 (1990) apparent asynchrony may be caused by differences in mammalian community structure among different basins. Van der Meulen and Daams (1992) situated this peak in the local zone E. Hernández Fernández et al. (2006a) did not detect an especially arid period, relatively small (b2.5‰ in most cases). This is slightly higher than the which is in agreement with our δ13C values from the mammalian range seen in δ18O values for modern terrestrial mammals from a single tooth enamel. region (e.g., Kohn et al., 1996; Clementz and Koch, 2001), but not so In addition, the δ13C results across local zones agree well with the large as to suggest that the equations for any of the taxa are yield highly 18 18 ecological changes proposed for rhinoceros faunas of the Madrid abherent δ Ow values. The δ Ow values drop between local zones Db Basin. According to Cerdeño (1989) and Cerdeño and Nieto (1995), (−0.2±2.5‰) and Dd (−1.9±1.7‰)(Fig. 7B). Unsurprisingly, local 18 H. matritense inhabited open savanna-like environments; they postu- zone E has the lowest δ Ow value (−5.3±3.0‰), followed by a rise lated that its was triggered by a change in environmental in local zones F (−2.5±2.1‰)andG(−2.5±1.7‰), although these re- conditions associated with enhanced humidity in local zone Dd. covered values are not as high as those in local zones Db, Dc and Dd. After this local zone, H. tetradactylum and Alicornops simorrensis These trends could reflect a decrease in the δ18O value of precipi- made their appearance reflecting this slight increase in humidity. tation in local zone E, due to a drop in temperature, which agrees well Although we only analyzed the palaeomerycid T. pachecoi at the La with marine (Zachos et al., 2001; Shevenell et al., 2004) and conti- Hidroeléctrica fossil site, its remains have been recovered at Puente nental records (van der Meulen and Daams, 1992), since during the de Toledo, San Isidro, PAR Peñuelas, Estación Imperial and Paseo de short period of time represented by this local zone, changes in the las Acacias (Peláez-Campomanes et al., 2003). Peláez-Campomanes source of moisture and/or tectonic processes potentially affecting 18 et al. (2003) argued that there was a general trend towards a drop δ Ow values have not been documented. The temperature record of in the abundance of Palaeomerycidae from local zone Dc to local Shevenell et al. (2004) (which is based on δ18O analyses of the ben- zone G. Initially, the drop may have resulted from a climatic trend to- thic foraminifer Cibicidoides mundulus from the ODP Site 1171) fits wards more arid conditions, signaled by the slight increase in δ13C enamel δ18O values from the Madrid Basin well, since they both values in Puente de Toledo and San Isidro (Fig. 4A). Eventually, from have higher temperatures before ~14 Ma, a sudden drop in tempera- PAR Peñuelas, Estación Imperial and Paseo de las Acacias onward, ture at 14 Ma and an increase in temperature after this age, although the decrease in the abundance of palaeomerycids may have been not to temperatures as high as those before 14 Ma. Local zone E is due to competition with cervids. The other taxa did not show notice- represented by the Arroyo del Olivar and Somosaguas fossil sites. 18 able changes across local zones. We found significant differences in δ Ow values between these fos- sil sites (t-student=5.027, p b0.001), with much higher values at δ18 δ18 δ18 − ‰ − ‰ 6.3. Evolution of the OCO3, OPO4 and Ow values in the Madrid Basin Arroyo del Olivar ( 2.6±2.6 )thanSomosaguas( 7.1±1.4 ) (Fig. 7A). The fact that Somosaguas is represented by different taxa δ18 δ18 The OCO3 and OPO4 values show the same trends among fossil (G. angustidens, Anchitherium cf. A. cursor, C. simorrensis and rumi- sites and local zones (Fig. 4C and D). When comparing mean values nants) indicates no bias due to the type of sampled fossil and there- 18 for local zones, post-hoc Tukey analyses reveal two groups: one fore, a reliable average δ Ow value can be assumed. Although the group includes local zones Db, Dc, Dd, F and G, whereas the other is variety of selected taxa from Arroyo del Olivar is lower in compari- δ18 made up exclusively by local zone E which has the lowest OCO3 son with Somosaguas, the fact that a more browser mammal taxa ‰ δ18 ‰ (G. angustidens), occupying woodlands, and a more mixed-feeder mam- (26.5±2.1 ) and OPO4 (18.4±2.4 ) values. Local zone E spans a time of ~14.1–13.7 Ma, coinciding with the MMC event (Flower, mal taxa (A. cursor), occupying more open environments, have been 18 1999; Zachos et al., 2001; Shevenell et al., 2004; Domingo et al., sampled suggests a good average δ Ow value for this site. Hence, differ- 2009). As noted in the Results, similar temporal trends are observed ences may be attributed to a real environmental and climatic shift, when the data is restricted to Anchitherium and Gomphotherium (Sup- represented by the reestablishment of the Eastern Antarctic ice sheet plementary data 3C and D and Supplementary data 4C and D). This that triggered the MMC at the age represented by the Somosaguas site observation demonstrates that the trends are not generated by inclu- (14.1–13.8 Ma) (Flower and Kennett, 1994; Flower, 1999; Zachos et al., sion of different genera (with different physiologies, diets, and habi- 2001; Shevenell et al., 2004; Domingo et al., 2009). tat preferences) in different local zones. Mean annual temperature (MAT) can be estimated using equa- δ18 δ18 δ18 Using tooth enamel OPO4 values, we can estimate the O value tions that relate meteoric water O values to MAT, assuming that 18 18 of the water (δ Ow) ingested by fossil mammals with equations fossil mammalian tooth enamel provides a robust proxy for δ Ow. established for modern mammals (Table 3). The equations used to esti- Most studies taking this approach have relied on equations based 18 mate ingested water come from the closest living analogs of the Mio- on spatial relationships between MAT and δ Ow values from mod- cene taxa, but as noted in our discussion of EI vs. ES taxa, they are ern meteorological data from the areas where fossil sites are cur- rarely from the same family. As such, our understanding of the water rently situated (Tütken et al., 2006; van Dam and Reichart, 2009; 18 economy of the extinct taxa, which can affect the isotopic relationship Matson and Fox, 2010). The MAT and δ Ow correlation is not between drinking water and tooth phosphate, is poor. We are encour- explained by a single process, but rather reflects a complex series 18 aged that the variation in reconstructed δ Ow values for each site and of processes that fractionate oxygen isotopes in water, involving local zone (generated by combining the data from multiple taxa) is evaporation, transport (with water loss through rainout), and 110 L. Domingo et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 339–341 (2012) 98–113

18 Fig. 7. The mean and standard deviation (SD) δ Ow (‰ VSMOW) values per site (A) and per local zone (B). Fossil site abbreviations as in Fig. 2.

condensation and partial equilibration of atmospheric water at each The second equation was constructed using the Global Network of location. Shifts in climate or atmospheric circulation may change the Isotopes in Precipitation (GNIP) database (available at http://nds121. 18 source and transport processes experienced by vapor masses arriv- iaea.org/wiser/) including MAT and weighted δ Ow data from the ing at a site. For example, in the Miocene, climatic belts were ex- likely prevailing biomes II, II/III and III, as well as more rare biomes I panded in such a way tropical and subtropical conditions reached and V (Supplementary Data 7) (Hernández Fernández et al., 2003, higher northern and southern latitudes (Pickford and Morales, 2006b). Using this approach, we calculate the following linear regres- 1994). This is clear in Central Europe where the presence of thermo- sion (±SD): philic ectothermic vertebrates, including crocodilian (Antunes, 1994; Böhme, 2003), and the existence of thermophilous vegetation ÀÁ – o ¼ δ18 þ : ðÞF : ðÞ: ðÞF : 2¼ : : ð Þ (Jiménez-Moreno et al., 2008) point to tropical subtropical condi- MAT C Ow 8 7 0 96 # 0 202 0 04 R 0 3 4 tions at higher latitudes. Ultimately, these complications render this approach to MAT re- construction largely qualitative and heuristic. Yet, we attempted to Finally, in order to compare to the approach taken by other au- δ18 account for uncertainties related to these factors by using three differ- thors, we used modern day MAT and weighted Ow GNIP data ent calibration equations. The first equation, proposed by Yurtsever from Madrid city between 1971 and 2006 to construct the following and Gat (1981), which uses the data from selected worldwide mete- equation (±SD): orological stations, and hence from all existing biomes and climate re- ÀÁ o ¼ δ18 þ : ðÞF : ðÞ: ðÞF : 2¼ : ð Þ gimes, is as follows: MAT C OwðÞ VSMOW 11 2 0 62 # 0 376 0 04 R 0 9 5

Table 4 shows ΔMAT values between consecutive local zones cal- ÀÁ 18 o 18 culated by employing Eqs. (3)–(5), after a correction in δ Ow values MAT C ¼ δ O ðÞþ11:9 0:338: ð3Þ w VSMOW # (0.75‰ for local zones Db and Dc; 0.50‰ for local zone Dd; 0.30‰ for L. Domingo et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 339–341 (2012) 98–113 111

Table 4 cooling (~14.1–13.7 Ma) coincides with the Middle Miocene Cooling ΔMAT (°C) between consecutive local zones calculated using Eqs. (3)–(5). (~14–13.8 Ma), which is detected worldwide in marine and conti- ΔMAT (°C) Eq. (3) Eq. (4) Eq. (5) nental records, stresses the importance of the Madrid Basin mammal fossil site sequence in the study of this global event. Finally, the iso- Zone F to zone G 0.1 0.2 0.1 Zone E to zone F 7.9 13.2 7.1 topic study of the complete mammalian fossil site sequence of the Zone Dd to zone E −10.6 −17.8 −9.6 Madrid Basin (~15.9–13.2 Ma) furnished valuable information about Zone Dc to zone Dd −1.7 −2.8 −1.5 the type of landscape existing through the Middle Miocene, the die- − − − Zone Db to zone Dc 4.1 6.9 3.7 tary behavior and niche occupancy of selected taxa and the variations in paleoenvironmental and paleoclimatic conditions that existed at this local zone E; 0.20‰ for local zones F and G) was applied to account of time. changes in the δ18O value of seawater related to the difference in con- Supplementary data related to this article can be found online at tinental ice volume between today and the Middle Miocene (Lear et http://dx.doi.org/10.1016/j.palaeo.2012.04.026. al., 2000). A progressive decrease in MAT can be observed between local zones Db and E. The MMC event is evident as a strong drop in Acknowledgments MAT values between local zones Dd and E. Subsequently, a recovery of MAT values occurs from local zones E to G. The drop between This study was supported by the UCM, Spanish Ministerio de local zones Dd and E was calculated as 10.6 °C and 9.6 °C, respectively, Educación, Spanish Ministerio de Ciencia e Innovación and Dirección Gen- using Eqs. (3) and (5), and 17.8 °C using Eq. (4). Eqs. (3) and (5) gen- eral de Patrimonio Histórico-CAM (Plan Nacional I+D projects CGL2008- erate a decrease in MAT during the MMC that is comparable to the es- 05813-CO2-01 to J.M. and CGL2009-09000 to N.L-M., a Personal timations suggested by other studies (more than 7 °C in Central Investigador de Apoyo-CAM fellowship and a postdoctoral fellowship Europe (Böhme, 2003), 6 to 7 °C drop in high-latitude southwest Pacific from the Fundación Española para la Ciencia y la Tecnología (FECYT) sea surface temperatures (Shevenell et al., 2004), and 8 °C in mean and Spanish Ministerio de Educación to L.D). This work also received a summer temperatures in Antarctica (Lewis et al., 2008). Eq. (4) yields contribution from the research groups UCM–CAM 910161 “Geologic Re- an unrealistically large drop. A key limitation to Eq. (4) is its low corre- cord of Critical Periods: Paleoclimatic and Paleoenvironmental Factors” lation coefficient (R2 =0.3), which hampers the calculation of accurate and BSCH–UCM 910607 “Evolution of Cenozoic Mammals and Conti- MAT values. This low correlation coefficient is due to climatic factors nental Paleoenvironments”. We thank M.S. Domingo (University of in tropical and subtropical regions that impact precipitation isotope Michigan) for constructive comments in the initial drafts of this values, such as intense precipitation rates (an extreme case is represented manuscript. We acknowledge P. Pérez (Museo Nacional de Ciencias by moonsonal conditions) or high aridity (as observed in biome III). In Naturales de Madrid—CSIC) and S. Menéndez (Museo Geominero, δ18 Instituto Geológico y Minero de España, Madrid) who greatly facilitated any case, it has been observed that the progressive drop in OCO3, δ18 δ18 the sampling of the teeth studied in this research. We are also indebted OPO4 and Ow values, reaching a minimum in local zone E, most like- ly reflects a drop in MAT linked to the MMC and therefore, the Madrid to D. Andreasen, J. Lehman and J. Karr (University of California Santa Basin mammalian fossil sequence has allowed this study to detect this Cruz) for their valuable help with the isotope analyses. M. Antón and event in a continental section. O. Sanisidro kindly provided the illustrations shown in this study. The recovery and study of the Somosaguas fossil material were done by the members and the students of the Somosaguas project, 7. Conclusions UCM (http://investigacionensomosaguas.blogspot.com). The editor P. Kershaw, M. Hernández Fernández (Universidad Complutense de The Madrid Basin (Spain) provides a complete sequence of Middle Madrid) and an anonymous reviewer are acknowledged for valuable Miocene mammal fossil sites spanning ages between ~15.9 Ma and comments that helped to improve the last version of this manuscript. δ13 δ18 δ18 ~13.2Ma. C, OCO3 and OPO4 analyses performed on mammali- N. López-Martínez passed away during the execution of this study. an tooth enamel have allowed us to unveil characteristic dietary and Her wide knowledge and her enthusiasm for paleontology were an climatic features. The δ13C results indicate the equid Anchitherium, inspiration for both colleagues and students. This study constitutes the rhinoceros H. matritense and the bovid T. langai inhabited more a tribute to her, who left too early. open environments, perhaps with a mixed-feeder diet. In constrast, the rhinoceros A. simorrense and H. tetradactylum, the gomphothere References G. angustidens, the cervid H. moralesi and the palaeomerycid T. pachecoi were better adapted to slightly closer habitats and likely were Agustí, J., Antón, M., 2002. Mammoths, Sabertooths and Hominids. Columbia University δ13 Press, New York. browsers. The C values point to an enhancement in humidity in Alberdi, M.T. (Coord.), 1985. Geología y Paleontología del Terciario continental de la local zone Dd (~14.8–14.1 Ma), in agreement with other studies car- provincia de Madrid. Consejo Superior de Investigaciones Científicas. MNCN, 1–105. ried out in the region and with the evolution of rhinoceros faunas in Alberdi, M.T., Hoyos, M., Junco, F., López-Martínez, N., Morales, J., Sesé, C., Soria, M.D., 1984. Biostratigraphy and sedimentary evolution of the continental Neogene in the Madrid Basin with the disappearance of the genus H. matritense, the Madrid area. 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