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The biota of the Upper Cretaceous site of Lo Hueco (Cuenca, Spain).

1. Introduction

The Upper Cretaceous (Campanian-Maastrichtian) marly mudstone fossil site of Lo Hueco is located near the village of Fuentes, Cuenca Province, Spain (Fig. 1). It was discovered in 2007 during the cutting of a little hill for installation of the Madrid-Levante train railway. The paleontological intervention in Lo Hueco was not a preventive or routine excavation. There was no previous evidence of the presence of a fossil bed there, so the discovery occurred after the onset of the activity of civil works. When the paleontological activity began, the fossil beds had already been partially affected by the earthworks and the presence of a huge amount of macrofossils in the site was evident. Under these conditions, both paleontological excavation and civil work planning significantly conditioned each other.

The evaluation phase started in July 2007, confirming the existence of a rich fossil site and characterizing the fossil beds and their size as comprising approximately ten hectares. At least two of these hectares were included in the area affected by the civil work. The first phase consisted in a single excavation campaign affecting near 100,000 cubic meters of sediments. This excavation involved the combination of various techniques: paleontological monitoring of the mechanical removal of levels, topographical and stratigraphic control of the extraction of fossils, systematic sampling of excavation grids and systematic collection of sediment samples for the analysis of the microfossils (Fig. 2). As a result, more than 10,000 fossil remains and 25 tons of rocks were collected. This constitutes one of the largest collections of vertebrate remains from the Upper Cretaceous of Europe. Currently, the collection of Lo Hueco is housed in a 1,000 [m.sup.2] facility provided by the Museo de las Ciencias de Castilla-La Mancha in Cuenca, where a preparation laboratory has been established. The management of such a large and complex collection substantially makes the research activity of some taxonomic groups difficult, with particular requirements of conservation and preparation. Recently, the systematic preparation of this material has been intensified, particularly the one corresponding to the sauropod remains.

We consider that the study and interpretation of this fossil site will represent a relevant contribution to the knowledge of the southwestern European Upper Campanian-Lower Maastrichtian record. The present paper outlines the still very preliminary results obtained to date by the multidisciplinary group working on the analysis of the Lo Hueco collection.

2. Geological context

The fossil site of Lo Hueco is located in the southwestern branch of the Iberian Ranges, on the Arcas-Fuentes Syncline. It includes an interval in the "Garumn" facies, which is the informal term for the marls, clays and gypsums, mainly reddish, deposited in shallow marine, coastal or continental environments of south-western Europe during the last part of the Cretaceous and the early Paleogene (Leymerie, 1862). These beds belong to the upper part of the "Margas, Arcillas y Yesos de Villalba de la Sierra" Formation (Vilas et al., 1982) (Fig. 1). A stratigraphic succession of green (V), grey (G1), red (R1), grey (G2), red (R2) and brown (M) beds of marly mudstones, separated by gradual boundaries, is identified in Lo Hueco. A sharp boundary partially modified the succession by a first sulphatic interval (S1) that cuts Bed V and by a second sulphatic interval (S2) that distorts at least part of Level G2. In addition, an erosive surface modified it by a sandy channel structure (C) that interrupts Levels V, G1 and R1 (Barroso-Barcenilla et al., 2009a, 2010; Carenas et al., 2011; Cambra-Moo et al., 2012) (Fig. 1).

Four of these stratigraphic lithosomes have yielded the main part of the fossils from Lo Hueco: Structure C, Levels G1 and G2, and the lower part of Level R2. Lithosome C, interpreted as the deposits of a distributary sandy channel, is composed of sandy conglomerates and breccias, with a relatively high proportion of clasts (mainly pebbles of silica and phosphatic bone fragments, but also soft clasts of clays and carbonates) and a low proportion of matrix and cement (<20%), sandstones, and sandy mudstones. It exhibits numerous erosive surfaces and tractive deposits and has in its sandy mudstone fraction relevant proportions of quartz (3025%), calcite (20-15%), feldspar (10-5%), and clay minerals (55-40%) (Barroso-Barcenilla et al., 2009a, 2010; Gonzalez-Acebron et al., 2010).

Bed G1 corresponds to the proximal part of a flooded muddy plain, close to the distributary channels. Bed G2 and the lower part of Bed R2, are respectively interpreted as the distal part of a flooded muddy plain (distant from the distributary channels) and the partially or totally dried part of a muddy plain. All of them are composed of marly mudstones, with a relatively high proportion of clay minerals (>85%), moderate proportion of gypsums (<15%), and low proportion (10-5%) of calcium carbonates (calcite). These beds show mainly planar or parallel bedding and locally wavy and massive bedding, and some thin sandy interbeds with cross-bedding (especially in the upper part of Beds G1 and G2). Their clay minerals include illite (65-30%), kaolinite (50-20%), smectite (25-0%), and chlorite (2.5-0%) (Barroso-Barcenilla et al., 2009b, 2010; Coruna et al., 2011). All the stratigraphic lithosomes of this site contain a significant quantity of gypsum, but this mineral is especially abundant in the S1 and S2 intervals (Barroso-Barcenilla et al., 2009a, 2010; Carenas et al., 2011; Gonzalez-Acebron et al., 2014).

3. Taphonomy

Concerning the fossil assemblage of Lo Hueco, several modes of preservation can be described (Fig. 3). Plants, mainly represented by fragments of wood, herbaceous stems and leaves, and roots, appear mostly as carbonified fossils (Fernandez-Lopez, 2000). Specifically, woody plants (tree trunks and some branches) usually maintain their original volume in part, with the interior partially or totally infilled or replaced by gypsum. Other plant specimens show resinous material in the lumen of their well-preserved tracheids and parenchyma cells (Cambra-Moo et al., 2013). Invertebrates appear preserved as internal moulds of marly mudstones (bivalves) or gypsum (gastropods). Vertebrates, which constitute the largest part of the fossil assemblage, are represented by hard parts such as bones, teeth, plates, osteoderms and scales that mainly retain the original structure finely preserved in their interior with moderate diagenetic modifications. All of the vertebrate remains were restricted to Lithosome C, Beds G1 and G2, and the lower part of Bed R2, which has permitted us to define them, on the basis of their geological and taphonomic description, as taphofacies or bonebeds (sensu Rogers et al., 2007; Cambra-Moo et al., 2012). On the one hand, taking into account the biostratinomic description, it can be highlighted that Taphofacies C generally contains highly altered macrofossils (of centimetric size, fragmented and with signs of mechanical erosion processes, such as abrasion, see Fig. 3) that appear always disarticulated, scattered, and randomly distributed (Barroso-Barcenilla et al., 2009a; Cambra-Moo et al., 2009, 2012). On the other hand, the taphofacies G1, G2 and R2 have larger (of decimetric size, see Fig. 2) and slight or no eroded macrofossils. Specifically, Taphofacies G1 preserves an important number of totally or partially articulated specimens, mainly sauropod dinosaurs (the largest macroremains), with a low degree of scattering and a mainly parallel and perpendicular orientation to Taphofacies C. Taphofacies G2 and R2, by contrast, contain macrofossils that are rarely articulated and randomly scattered (Barroso-Barcenilla et al., 2009a; Cambra-Moo et al., 2009, 2012).

Regarding diagenetic modifications, most macrofossils (especially bones) macroscopically have, from inside to outside: a first infilling of gypsum (in inner cavities), a ferruginous crust (outer surfaces, usually thicker in the fossils from Taphofacies C and G1 than in those from Taphofacies G2 and R2), and a second growth of gypsum crystals (covering outer surfaces and eventually crossing the ferruginous crust and first gypsum infilling). Some fossils, frecuently from the darkest deposits of Taphofacies G1 and, mostly, G2 present microcrystalline pyrite formed inside their intimal structure (Barroso-Barcenilla et al., 2009a; Cambra-Moo et al., 2009, 2012).

4. Fossil record

The Lo Hueco site has yielded fossil remains representing both micro and macro plants and animals. The macroscopic invertebrate remains are relatively scarce and generally represented by gastropods and bivalves. The uniqueness of the site lies in the richness and abundance of vertebrate fossils (Ortega et al., 2008). The main recognized groups are fishes, turtles, squamates, crocodilians, and non-avian dinosaurs. Among these, turtles, crocodiles and dinosaurs (ornithopods, theropods, and sauropods) are the best represented. The most abundant record of dinosaurs in Lo Hueco consists of thousands of titanosaur specimens that can be attributed to, at least, two distinct taxa. Albeit they are less abundant, the diversity of theropods is the greatest among the dinosaurs represented at Lo Hueco. Moreover, some groups mentioned in previous papers (e.g. Ortega et al., 2008), such as amphibians, some squamates, or possible remains of pterosaurs, are so poorly represented that it is not possible, at present, to provide further information.

4.1. Palynomorphs

The preliminary analysis of the spore/pollen content revealed a relatively rich palynoflora, mainly integrated by terrestrial palynomorphs (Peyrot et al., 2013). The palynological assemblage is characterized by the dominant angiosperms, and subordinate spores and gymnosperms. The angiosperm component accounted for about 80 % of the pollinic sum and was represented by more than 20 taxa, including the common Upper Cretaceous monocolpates (Arecipites, Liliacidites, and Monocolpopollenites). Tricolpate and triporate pollen grains (including Normapolles representatives) were common but rarely reached dominance. Monoporate pollen grains related to modern representatives of Sparganiaceae, Restionaceae, and Thyphaceae were, however, well represented. The gymnospems were mainly integrated Inaperturopollenites and bisaccate pollen grains related to Cupressaceae-Taxodiaceae and Pinaceae, respectively. Cryptogams included Leptolepidites, Deltoidospora, and Polypodiaceoisporites. The coenobial green algae Pediastrum spp. were consistently recorded in the samples. As a whole, the palynofloras suggest the presence of a tropical near-coast palaeovegetation integrated by swamp or local wetland vegetation with subordinate arboreal component (i.e. Fagales, gymnosperms). The palynofloras of the site revealed different micro-environments probably related to water availability within a near-coast environment. The presence of a high number of pollen grains related to Typhaceae, distinguishes the assemblages of Lo Hueco from other Late Cretaceous European palynofloras (Walbec, Maastricht, Campo, Tercis) (Peyrot et al., 2013).

4.2. Meso and mega plant remains

Fossil plants from Lo Hueco consist of millimetric (meso-) to pluricentric (mega-) remains. They are preserved as impressions and compressions, and include charred debris and cuticles (Fig. 4). Several specimens show yellow to orange iron oxide deposits on their surfaces and inside the structures. Some others have infillings of gypsum or are contained inside gypsum.

Spirally-arranged leaved conifers include shoots of Brachyphyllum type, with the length of free part of appressed leaf equal or shorter than the leaf cushion, and of Pagiophyllum type with the free part longer than the leaf cushion.

Large leaf laminae suggest that several types of angiosperms are present (Fig. 4). Among these are specimens that closely resemble the freshwater free-floating fossil Limnobiophyllum (Stockey et al., 1997). The extremely short, stocky stem, the single-developed, sessile, entire-margined, orbicular leaf, the campylodromous venation with 10 or 11 primary veins, the longitudinal elongated meshes of higher order veins, and the numerous simple adventitious roots of the specimen HUE-08091 (Fig. 4D, E) are features that definitively fall within the range of the genus diagnosis emended by Stockey et al. (1997). The specimen HUE-07484 (Fig. 4) is laterally compressed, and shows five leaves with fainter venation pattern. Due to the resemblance with living plants such as the freshwater Spirodela Schleiden, Kvacek (1995) and Stockey et al. (1997) placed Limnobiophyllum in Lemnaceae within Arales. However, considering the most recent phylogeny, Limnobiophyllum must be now included in Lemnoideae of Araceae and within Alismatales. Some specimens correspond to angiosperm reproductive organs. A globular inflorescence shows numerous units (flowers?) radiating from the centre (Fig. 4H). There are several types of seeds (Fig. 4I-M). Cuticles were extracted using maceration of bulk sediments in a dilute solution of hydrogen peroxide, washed and sieved under tap water, and prepared and examined under light microscope and scanning electron microscope (SEM). Stumps, roots, logs, and branches are also present and those preserved as charcoals were studied under SEM.

4.3. Molluscs

The Lo Hueco taphonomic conditions for the fossilization of carbonated remains justify the low number of collected specimens, biasing the real abundance and diversity of these invertebrates in the palaeoenvironment.

Molluscs are mainly preserved as internal casts of marly mudstones without hinge details (bivalves), or of gypsum (most of gastropods), and have been kept in open nomenclature until additional discovery of more complete specimens. Bivalves are recorded as freshwater unionids assigned to Margaritiferidae (?Margaritifera) and Unionidae (?Anodonta), and as heterodontids from Corbiculidae (?Corbicula) and Pisidiidae (?Pisidium). Gastropods are known after at least two species of possible Melanopsidae (?Faunus) (Callapez et al., 2011, 2013). Due to poor preservation, these taxonomic identifications are tentatively based on the overall shape and details of external ornamentation visible in the composite moulds. Both bivalve and gastropod taxa are widely known from the Upper Cretaceous and Cenozoic freshwater environments. The occurrence of Melanopsidae can also be related to some influence of moderately brackish conditions. All bivalves have been found disarticulated, a fact that can be related to energetic episodes in the aquatic depositional environment. Therefore, although their presence at the site is rare, these aquatic molluscs provide additional data that improve our knowledge about the reconstruction of the original Cretaceous palaeoenvironment and its ecosystem.

4.4. Fishes

Fossil fishes from Lo Hueco have been collected from screenwashing and picking of fossil micro-remains. Most of the specimens consist of isolated fish remains (Fig. 5), and mainly correspond to ganoid scales and teeth (Torices et al., 2010a, 2011; Serrano et al., 2012). Most of the scales present the general morphology of those of the lepisosteids (Actinopterygii, Lepisosteidae): rhomboidal contour and cross section composed of two layers, an upper ganoid layer and a basal bony one. Lepisosteids are a very abundant freshwater neopterigian group from the Upper Cretaceous and Cenozoic continental deposits worldwide (Wiley, 1976; Grande, 2010). However, nowadays they are restricted to the Eastern portion of North America and Central America.

The technique used for studying ganoid scales follows the methodology proposed by Gayet and Meunier (1986), who analyzed and compared the differences in the ornamental pattern among the different groups of actinopterigian fishes with ganoid scales. The scale ornamentation consists of micrometric ganoid tubercles spread over the scale surface. According to these authors, the size of these tubercles and the distance between them are constant not only within each lineage, but also within each genus (Gayet and Meunier, 1986; Gayet et al., 2002).

The analysis of the scale micro-ornamentation under SEM observation (Fig. 5) assigns the scales from Lo Hueco to Atractosteus, in contrast to previous works that assigned them to Lepisosteus (Serrano et al., 2012). The presence of Atractosteus in the Iberian Peninsula was also documented in the Upper Campanian-basal Maastrichtian of Lano (Condado de Trevino, Burgos), based on an isolated supracleithrum (Cavin, 1999).

Other lepisosteid remains recovered are teeth with plicidentine, skull bones, and opisthocoelic vertebrae. These vertebrae are unique to this lineage within Actinopterygii (Wiley, 1976; Grande, 2010). Less abundant are teeth assigned to other actinopterigian fishes: Pycnodontoidea, Amiidae, and Albulidae (Torices et al., 2010a, 2011). Numerous amphicoelic vertebrae have also been collected, which can be only considered for the time as corresponding to unidentified Actinopterygii members.

4.5. Turtles

The first identified and described articulated remains of Bothremydidae in the Spanish record came from Lo Hueco (Perez-Garcia et al., 2009a). The abundant material recovered (Fig. 6A-D) is providing relevant information to increase the knowledge of this clade of Pleurodira. A high percentage of the turtle specimens identified corresponds to Bothremydidae. Prior to the study of this material, Polysternon was regarded as the unique representative of Bothremydidae whose presence was confirmed in the Spanish record (Lapparent de Broin and Murelaga, 1999). Some articulated specimens of Lo Hueco show that other bothremydid taxa also inhabited the Iberian Peninsula in the Late Cretaceous. In addition, some plates recognized from other localities are similar to those of the bothremydids of Lo Hueco (Perez-Garcia et al., 2010). In this sense, "Elochelys" convenarum, a taxon so far only recognized by its holotype, a relatively complete shell from the Maastrichtian of Haute-Garonne (France) (Laurent et al., 2002a), is identified in Lo Hueco. The information on the morphological variability of the European bothremydids is so far very limited. The comparison between the material known of Elochelys perfecta and the specimens identified as "Elochelys" convenarum open the discussion of the validity of the two species of the genus, allowing the possibility to expand the known range of intraspecific variation in both species. However, given the criteria used for the identification of other members of Bothremydidae, the combination of characters that distinguish these two species justifies their assignation to two distinct genera. The species present in Lo Hueco was assigned to the new genus Iberoccitanemys (Perez-Garcia et al., 2012a).

A second member of Foxemydina within Bothremydidae is present in Lo Hueco (Fig. 6). The current state of knowledge allows its identification as an indeterminate taxon belonging to the clade of Polysternon and Foxemys. This identification is the first evidence that robustly demonstrates the sympatric coexistence of two different members of Bothremydidae in a Late Cretaceous ecosystem of Europe (Perez-Garcia et al., 2013). The identification of a member of Bothremydidae naturally leads to the assignment of the other specimens found in the same locality to the same taxon. However, the recognition of two taxa in the same site shows that the revision of many of the previous identifications is necessary. In fact, many of them should be reassigned to Bothremydidae indet. or to Foxemydina indet.

Besides members of Bothremydidae, a second clade of turtles, whose record is very rare, is identified in the site of Lo Hueco. It is attributed to an indeterminate representative of Pan-Cryptodira (Perez-Garcia et al., 2009b). It is a large turtle, with a carapace at least one metre in length. Despite the abundance of members of Solemydidae (stem Testudines) and Dortokidae (stem Pleurodira) in the southwestern European Late Cretaceous record (Lapparent de Broin and Murelaga, 1999; Perez-Garcia et al., 2012b), none of them has been collected in Lo Hueco.

4.6. Squamates

Squamate remains are relatively rare at Lo Hueco, but the specimens are recognized as highly diverse when compared to the available record from the Late Cretaceous of Europe. Some Spanish sites have yielded squamate remains that mostly do not have a precise identification. For example, some remains of lacertilians and madtsoiid snakes at Lano (Rage, 1999), Anguidae and Lacertoidea at Aren (Lopez-Martinez et al., 2001; Blain et al., 2010), and some unindentified cranial fragments and isolated vertebrae in Chera, Valencia (Company, 2004) have been reported. Some unindentified forms (including varanoids) have also been described in Aveiro, Viso, and Taveiro, Portugal (Antunes and de Broin, 1988). In southern France, several squamates have been reported in Champ-Garimond (Iguanidae indet., Lacertilia indet.), Cassagnau (Varanoidea indet.), and Cruzy (Varanoidea indet. and Lacertilia indet.) (Buffetaut et al., 1996, 1999; Sige et al., 1997; Garcia et al., 1999, 2000; Laurent et al., 2002b).

At Lo Hueco, a set of cranial elements that were preliminary assigned to Lacertoidea (a mandibular fragment and an isolated tooth) and Iguania (several maxillary and mandibular remains with some tricuspid teeth) (Narvaez and Ortega, 2010; Torices et al., 2010a) have been recognized.

Various vertebrae, probably belonging to a new genus of Varanoidea, have also been collected. Their anatomical and microanatomical features reveal that these vertebrae probably belong to a non-marine "pythonomorph-lizard" (Houssaye et al., 2013).

Most of the micro and macro remains, currently under study, correspond to taxa hitherto unpublished for the Iberian record. Therefore, the diversity of the Upper Cretaceous Iberian squamate fauna is clearly higher than recognized presently.

4.7. Crocodyliforms

Crocodyliformes are one of the most abundant and better-preserved vertebrate groups represented at Lo Hueco. Abundant isolated and articulated cranial and postcranial bones have been found (Fig. 6E-F). Presently, a set of ten skulls has been collected and identified, in a preliminary analysis, as belonging to at least two different taxa of non-Crocodylia eusuchians.

The first is a medium-sized crocodyliform with a relatively wide and round rostrum (Fig. 6E-F). It has characteristic large teeth, separated by narrow interalveolar spaces. Although this taxon has a close relationship with Allodaposuchus, it shows remarkable differences that suggest that it is a new genus (Narvaez and Ortega, 2012; Narvaez et al., 2013). The second crocodyliform is also a medium-sized animal that has a more elongate snout and a slender rostrum. It also exhibits features that suggest a close relationship with the Iberian Allodaposuchus, but, again, it has characters that distinguish it from the known representatives of this genus and from the other crocodile represented at the site.

Members of two groups probably compose the European record of non-crocodylian eusuchians. The first is Hylaeochampsidae, a monophyletic group represented by small forms as Hylaeochampsa, from the Barremian of the Isle of Wight (Clark and Norell, 1992); Pietraroiasuchus, from the Albian of Italy (Buscalioni et al., 2011); Iharkutosuchus, from the Santonian of Hungary (Osi et al., 2007); and Acynodon from the Campanian-Maastrichtian of Spain, France and Italy (Buscalioni et al., 1997, 1999; Martin, 2007; Delfino et al., 2008). Specimens from Romania, France and Spain compose a second non-crocodylian eusuchian group (Buscalioni et al., 2001; Puertolas-Pascual et al., 2014) generally assigned to Allodaposuchus.

Other taxa from the Upper Cretaceous of Europe, such as the supposed alligatoroids Massaliasuchus and Musturzabalsuchus, from France and Spain (Buscalioni et al., 1997, 1999; Martin and Buffetaut, 2008) or the putative Spanish crocodyloid Arenysuchus from Spain (Puertolas et al., 2011), are probably also close to these basal groups (Narvaez and Ortega, 2011). Most recent phylogenetic analyses (Buscalioni et al., 2011, Puertolas-Pascual et al., 2014) place Allodaposuchus as the sister clade of Hylaeochampsidae.

The preliminar study of Lo Hueco taxa indicates that they are related to forms close to Allodaposuchus and phylogenetically situated at the base of Eusuchia. This supports the hypothesis of the existence of a group of basal non-crocodylian eusuchians formed exclusively by European taxa, and shows a complex distribution of these forms in the Upper Cretaceous European Archipelago (Narvaez et al., 2013).

4.8. Ornithischian dinosaurs

Although some preliminary works indicated the possible presence of ankylosaur remains (Ortega et al., 2008), the presence of thyreophorans is not certain at Lo Hueco. Consequently, the ornithischians at Lo Hueco are presently restricted to the basal iguanodontian Rhabdodontidae. This group of ornithopod dinosaurs is considered as both endemic from the Late Cretaceous of Europe (Weishampel et al., 2003; Osi et al., 2012) and having a more complicated evolutionary history given the controversial systematic position of the Australian genus Muttaburrasaurus (McDonald, 2012). The clade includes three genera, each containing two species, ranging from the Santonian to the Maastrichtian. In southern France and the Iberian Peninsula, only Rhabdodon is recognized, whereas in Austria, Hungary and Romania two genera (Mochlodon and Zalmoxes) have been described (Osi et al., 2012).

The rhabdodontid remains of Lo Hueco include cranial and postcranial bones (Fig. 7A-B). The cranial remains consist of isolated dentary and maxillary teeth and a right dentary (Escaso et al., 2009). Both maxillary and dentary teeth are similar to those of rhabdodontids in having a well-developed and central primary ridge. Moreover, the isolated maxillary teeth bear parallel ridges as in other rhabdodontids. The general morphology of the dentary is similar to that of other rhabdodontids and it shares with Rhabdodon and Zalmoxes a rostroventrally-inclined symphysis. A recent work on the rhabdodontid postcranial remains of Lo Hueco described two femora and an ischium of three different individuals (Escaso et al., 2012). This work concluded that the femora are robust as in Rhabdodon individuals, differing from Mochlodon and Zalmoxes, in which the femora are more lightly constructed (Osi et al., 2012). The morphology of the ischium is similar to that of Zalmoxes (Weishampel et al., 2003) and Rhabdodon (Pincemaille-Quillevere, 2002).

In conclusion, the rhabdodontids of Lo Hueco show a character combination that is not conclusive, but that is congruent with the described morphological variation of Rhabdodon. Thus, it is preferred provisionally to refer these ornithopods to Rhabdodon sp.

4.9. Theropod dinosaurs

The theropod remains mainly consist of teeth and scarcer postcranial material (Fig. 7C-K). The diversity at the site is constituted by a medium-size primitive form, whose characters are congruent with abelisaurid ceratosaurians previously described from the Iberoccitanian Upper Cretaceous (Astibia et al., 1990; Le Loeuff, 1992; Tortosa et al., 2014), and remains of maniraptoran theropods representing various members of Paraves, whose analysis is still in progress. Presently, theropod diversity at Lo Hueco has been established on the basis on teeth whose analysis identifies five morphotypes. Two of the morphotypes present a very similar morphological blade-like shape with similar height, FABL (fore-aft basal length), and width. In both, posterior denticles density is 2.5-6 denticles per millimetre (measured in the middle of the carina) and the anterior denticle density is 3-6 denticles per millimetre. These characters are comparable quantitatively and qualitatively with those described in dromaeosaurid teeth. However, a morphotype presents posterior and anterior square denticles, while the other presents denticles that are slightly pointed towards the top of the tooth. Based on these differences, the first is attributed to Dromaeosaurinae (Fig. 7F) whereas the second is attributed to Velociraptorinae (Fig. 7G) (Torices et al., 2012).

A small tooth represents the third morphotype (Fig. 7D). The general morphology of the tooth resembles an isosceles triangle and its denticles are small. Morphological and morphometric characters are similar to those of the teeth attributed to Richardoestesia, and so, are identified as cf. Richardoestesia (Torices et al., 2010b, 2012).

The fourth morphotype is represented by a small tooth with longitudinal ridges along the labial and lingual flanks (Fig.7E). These longitudinal ridges are similar to those of the teeth of Paronychodon from the Upper Cretaceous of North America (Torices et al., 2012).

The fifth morphotype belongs to a larger, medium-size theropod (Fig. 7C). Unfortunately, it is badly preserved and the enamel has disappeared. Its general morphology is bladelike, laterally-compressed and it is possible to observe the trace of denticles that have been eroded. For this reason it can only be identified as Theropoda indet. (Torices et al., 2012).

The abundance of theropod teeth (nearly one hunded and fifty recovered teeth) makes the record of Lo Hueco one of the richest in Europe. The composition of this carnivorous fauna is similar to others described for the same age in the Iberian Peninsula and Europe with the presence of different taxa of dromeosaurids, a large theropod, and taxa similar to the North Americans Richardoestesia and Paronychodon (Torices et al., in press).

4.10. Sauropod dinosaurs

The presently known diversity of titanosaurian sauropods from the Upper Cretaceous of Europe is so far composed of five genera. However, new evidence indicates that it was probably higher. There are two valid genera described in southern France: Ampelosaurus atacis (Le Loeuff, 1995) and Atsinganosaurus velauciensis (Garcia et al., 2010). Two additional titanosaurs are known from Transylvania (now central Romania): Magyarosaurus dacus (Huene, 1932) and Paludititan nalatzensis (Csiki et al., 2010). In northern Spain, the Upper Cretaceous site of Lano yielded material referred to the only Iberian titanosaur described to date: Lirainosaurus astibiae (Sanz et al, 1999).

So far, Lo Hueco has yielded more than 10,000 fossils of which nearly half corresponds to titanosaurian remains (Fig. 2). There are more than twenty sets representing partial skeletons of several individuals. These partial skeletons frequently preserve parts of the series of caudal vertebrae that can be articulated with elements of the pelvic girdle, appendicular remains, and even with part of the dorsal vertebrae series. The analysis of the distribution of the isolated remains in the fossil site will establish the relationship between them and several of the partial skeletons, providing a relatively complete sampling of some of the represented taxa. For the moment, preliminary comparisons indicate the presence of at least two titanosaur morphotypes based on two types of cranial morphologies, appendicular bones, and teeth.

Despite the wealth of sauropod bones collected from Lo Hueco, only few cranial specimens have been retrieved. Among them, are two types of braincases. One (Fig. 8E-F) presents some similarities with the braincase of Ampelosaurus atacis from the Upper Campanian-Lower Maastrichtian of France. However, there are also many differences that suggest its consideration as Ampelosaurus sp. (Knoll et al., 2013a). The other is a short and deep skull in overall morphology. It also presents a flat occiput that is a phylogenetically restricted character within titanosaurs. This same condition is found in both Ampelosaurus and Jainosaurus septentrionalis, the latter from the Maastrichtian of India. Nevertheless, this second morphotype presents a dorsoventrally elliptical foramen magnum that differentiates it from Ampelosaurus. It appears close to the "Jainosaurus morph" braincase and a phylogenetic proximity with Jainosaurus is likely (Knoll et al, 2013b).

The analysis of the sauropod tooth morphology at Lo Hueco (Fig. 8A-B) also identifies two morphotypes that can be correlated to those of other European titanosaurs (Diez Diaz et al., 2013). The first (Fig. 8A) has the same morphology as the robust spatulated teeth found in Fox-Amphoux-Metisson, southern France (Diez Diaz et al., 2012a) and Massecaps (Diez Diaz et al., 2013). The second morphotype (Fig. 8B) is similar to the gracile spatulated teeth of Atsinganosaurus (Diez Diaz et al., 2014). The microwear patterns on the apical wear facets of both morphotypes of teeth support the hypothesis of a non-selective diet on soft stems, such as herbaceous plants. However, the microwear differences also suggest niche partition for both species (Diez Diaz et al., 2014).

Titanosaurian osteoderms are commonly found at Lo Hueco (Fig. 8P-T). All these osteoderms are variations of the described bulb and root morphotype (Csiki, 1999; D'Emic et al. 2009). They are large osteoderms with an amygdaloid outline, one or more visceral keels and two well differentiated regions: a round end (the bulb), and a more elongated and irregularly ornamented region (the root). These osteoderms display a high variability ranging from rounded osteoderms, whose roots are a just little bit longer than the bulb (Fig. 8P, Q, T), to elongated osteoderms, whose roots are up to five times longer than the bulb (Fig. 8R-S). One titanosaurian individual (specimen HUE-EC-3) was found associated with two osteoderms: one very elongated and a rounded one. This supports the idea that the variability of osteoderms found at Lo Hueco represents intra-individual variability (Vidal et al., 2014).

The study of the axial and appendicular remains (Fig. 8GO) is in a preliminary stage, but it also confirms the presence of two types of titanosaurs (Ortega et al., 2008). Although based on partial results, the phylogenetic assignment of Lo Hueco titanosaurs and their relationships with the other titanosaur described in Europe is not well understood yet. At present there are not shared morphologies between Lo Hueco morphotypes and Lirainosaurus astibiae. However, some Lo Hueco cranial remains and tooth morphologies can be recog nized in sites from southern France supporting the hypothesis of a broader distribution of some titanosaurs throughout the Ibero-Armorican Realm.

The presence of two titanosaurian taxa in Lo Hueco that can be distinguished from the well-known species Lirainosaurus astibiae corroborates the rise of the sauropod diversity from the Late Cretaceous of the Iberian Peninsula, as suggested by some previous studies on the biota of Lo Hueco (Diez Diaz et al., 2012b).

The simultaneous presence of two titanosaurian taxa is relatively common in others Upper Campanian-Lower Maastrichtian sites, such as Bellevue, Velaux, Massecaps or FoxAmphoux-Metisson in southern France, which produces a high level of uncertainty in the attribution of isolated remains that appear together in these sites.

5. Stable isotope analyses

Stable isotope analyses ([[delta].sup.18][O.sub.PO4], [[delta].sup.13]C, and [[delta].sup.18][O.sub.PO3]) carried out on the Lo Hueco multi-taxa terrestrial vertebrate assemblage have provided valuable information about climatic and environmental conditions that existed in Iberia during the Late Campanian-Early Maastrichtian (Late Cretaceous). [[delta].sup.18][O.sub.H2O] and temperature values estimated from dinosaurs, crocodyliforms, turtles and lepisosteids (mean [[delta].sup.18][O.sub.H2O] = -3.0 [+ or -] 1.2 [per thousand]; mean temperature = 22.0 [+ or -] 4.4[degrees]C) are in good agreement with subtropical [[delta].sup.18]O precipitation values observed today and with temperatures estimated in other studies for the Lo Hueco latitude (~31[degrees]N) during the Late Campanian-Early Maastrichtian (Amiot et al., 2004; Sellwood and Valdes, 2006; Domingo et al., 2013). Seasonal thermal varibility was estimated as the difference between temperature of the warmest months (TWMs), yielded by crocodyliforms and turtles, whose bioapatite mineralizes during the warm season, and mean annual temperature (MAT), supplied by theropods that record ingested water throughout the year. Lo Hueco DTWMs-MAT results (ranging from 2.2 [+ or -] 0.1[degrees]C to 7.4 [+ or -] 0.2[degrees]C) do not indicate a significant greater seasonal thermal variability when compared to seasonal studies of Cretaceous Tethyan rudists (Steuber et al., 2005) and modern subtropical conditions.

From a paleoecological standpoint, [[delta].sup.13]C values of the Lo Hueco sauropods (-10.5 [+ or -] 0.8 [per thousand]) point to consumption of pure [C.sub.3] vegetation, a fact supported by bulk organic matter [[delta].sup.13]C values (-25.1 [+ or -] 1.4 [per thousand]) from Lo Hueco sediments. The estimated fractionation value between sauropod enamel and diet ([[DELTA].sup.13][C.sub.enamel-diet]) is ~15 [per thousand], lower than other fractionation values

calculated for sauropods (~16 [per thousand]; Tutken et al, 2011) and ornithischians (~18 [per thousand]; Fricke and Pearson, 2008; Fricke et al., 2008), and probably points to differences in metabolic and/ or physiological processes or different utilization of plant organic compounds and/or plant parts. Although the Lo Hueco crocodyliform material remains under study and no paleoecological remarks have been attained yet from a morphological perspective, isotopic results indicate that these crocodyliforms may have incorporated food items from brackish

waters as indicated by their [[delta].sup.13]C values, whereas they avoided ingesting saline water and preferentially consumed freshwater, as suggested by their [[delta].sup.18][O.sub.CO3] values when compared with isotopic values of modern crocodyliforms inhabiting subtropical regions. Finally, the Lo Hueco turtles record the lowest [[delta].sup.13]C and [[delta].sup.18][O.sub.CO3] values of the vertebrate assemblage likely indicating a diet based on a mixture of aquatic and terrestrial [C.sub.3] vegetation and/or invertebrates and ingestion of water with an inland source, a fact that agrees well with their taxonomic designation (Bothremydidae).

6. Prospective

Scientific interest in Lo Hueco Konzentrat-Lagerstatt lies in the large number of fossils found and the excellent conditions of preservation of the specimens. The site contains an unusual abundance of individuals of continental tetrapods, particularly titanosaur sauropods, crocodiles, and turtles. Moreover, in the case of titanosaurs, the site yielded multiple partial skeletons in articulation or with a low dispersion of its elements. Given these factors, the Konzentrat-Lagerstatt of Lo Hueco (Cambra-Moo et al., 2013) is unique not only for the Spanish record but also for the entire Upper Campanian-Lower Maastrichtian record of Europe.

The biota identified at Lo Hueco presents a particular association of species, including the presence of new taxa and new records for the Iberian Peninsula of relatively common taxa in the European realm. In addition, this diversity reflects the absence of taxa frequently encountered in the Iberoccitanian Upper Cretaceous (even in the Campano-Maastrichtian record), constituting a bias that may depend on ecological factors.

The taphonomic analysis together with the geological context and the flora and fauna provide an approach to ecological and paleoenvironmental reconstruction of the Lo Hueco wetland ecosystem with some singularities. Noticeable among them is the presence of unusual patterns of preservation such as the first remains of fossilized wood in gypsum for the Upper Cretaceous (Cambra-Moo et al., 2013), or the recognition of the oldest evidence of wetland vegetation under stressful conditions showing characteristics of a modern community of plants (Peyrot et al., 2013).

The conditions of preservation of the fossil remains of Lo Hueco contain other uniquenesses of which at least two are especially relevant to Late Cretaceous faunas. The discovery of large terrestrial tetrapods with skeletons in articulation or high association with good histological preservation of individuals at various stages of growth will provide for the possibility of ontogenetic studies in some lineages of reptiles.

The combination of information from skeletal sets, abundance of remains for some taxa, and the possible ontogenetic series analysis facilitate the evaluation of the sources of both intra and interespecific variability of some taxa. This reassessment of the evolutionary history of some lineages of reptiles from the Late Cretaceous of Europe, especially titanosaurian sauropods, eusuchian crocodyliforms, and pleurodiran bothremyidid turtles will appear in future studies.

http://dx.doi.org/10.5209/rev_JIGE.2015.v41.n1.48657

Acknowledgments

The fieldwork at Lo Hueco (2007-2009) was funded by ADIF (the state-owned company that administrate the Spanish railway infrastructures) through the company awarded the civil works (Ferrovial). The authors acknowledge the involvement and commitment to this task to the more-than-one-hundred technicians and assistants. The paleontological excavation was authorized by the Direccion General de Patrimonio y Museos de la Junta de Comunidades de Castilla-la Mancha whose acronym is 04.0392-P11. The excavation also received support from different estates of the Government of the Autonomous Community of Castilla-La Mancha (Presidencia de la JCCM, Consejeria de Cultura, Consejeria de Medio Ambiente, Delegacion de la JCCM en Cuenca) and the City Council of Fuentes. Research at Lo Hueco was financed by the Spanish Ministerio de Ciencia e Innovacion: CGL2009-12008, CGL2011-25894, CGL2009-10766, CGL2009-12143, and currently the proyect CGL2012-35199: "Estudio paleoambiental, faunistico y floristico del yacimiento del Cretacico Superior de Lo Hueco (Fuentes, Cuenca)". Part of this research has been also financed within the projects PEII11-0237-7926 of the Junta de Comunidades de Castilla-La Mancha. L.D. acknowledges a PICATA contract of the UCM-UPM Moncloa Campus of International Excellence (Spain). Preparation of the material has been partially developed by the Employment Workshop of Paleontological Restoration of Lo Hueco funded by the Fondo Social Europeo, Junta de Comunidades de Castilla-La Mancha, Spanish Ministerio de Empleo y Seguridad Social, and the Diputacion Provincial de Cuenca. We thank Jean Le Loeuff (Musee des Dinosaures, Esperaza) and Bernat Vila (Universidad de Zaragoza) for comments and suggestions on the manuscript, and David B. Weishampel (Johns Hopkins University, Baltimore) for their thorough editing of the manuscript.

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F. Ortega (1) *, N. Bardet (2), F. Barroso-Barcenilla (3,4), P.M. Callapez (5), O. Cambra-Moo (6), V. Daviero-Gomez (7), V. Diez Diaz (8), L. Domingo (4,9,10,11), A. Elvira (1), F. Escaso (1), M. Garcia-Oliva (1), B. Gomez (7), A. Houssaye (12), F. Knoll (13,14), F. Marcos-Fernandez (1), M. Martin (1), P. Mocho (15), I. Narvaez (1), A. Perez-Garcia (1,16), D. Peyrot (4), M. Segura (3), H. Serrano (1), A. Torices (17), D. Vidal (15), J.L. Sanz (15)

(1) Grupo de Biologia Evolutiva, Facultad de Ciencias, UNED, Paseo de la Senda del Rey, 9, 28040 Madrid, Spain.

(2) Sorbonne Universites, CR2P CNRS-MNHN-UPMC Paris 6, Departement Histoire de la Terre, Museum National d'Histoire Naturelle, CP 38, 57 rue Cuvier, 75005 Paris, France.

(3) Grupo de Investigacion IBERCRETA, Universidad de Alcala de Henares, 28871 Alcala de Henares, Spain.

(4) Departamento de Paleontologia. Facultad de Ciencias Geologicas. Universidad Complutense de Madrid. 28040 Madrid, Spain.

(5) CGUC, Departamento de Ciencias da Terra, Universidade de Coimbra, 3000-272 Coimbra, Portugal.

(6) Laboratorio de Poblaciones del Pasado (LAPP), Departamento de Biologia, Facultad de Ciencias, Universidad Autonoma de Madrid, 28049 Madrid, Spain.

(7) Centre National de la Recherche Scientifique, Unite Mixte de Recherche 5276, Laboratoire de Geologie de Lyon-Terre, Planetes, Environnement, Universite Lyon 1 (Claude Bernard), 69622 Villeurbanne Cedex, France.

(8) Departamento de Estratigrafia y Paleontologia, Universidad del Pais Vasco/Euskal Herriko Unibertsitatea (UPV/EHU), Facultad de Ciencia y Tecnologia, Apartado 644, 48080 Bilbao, Spain.

(9) Instituto de Geociencias IGEO (CSIC, UCM), c. Jose Antonio Novais, 12, 28040 Madrid, Spain.

(10) Departamento de Ingenieria Geologica, Universidad Politecnica de Madrid, 28003 Madrid, Spain.

(11) Earth and Planetary Sciences Department, University of California, Santa Cruz, CA 95064, USA.

(12) UMR 7179 CNRS/Museum National d'Histoire Naturelle, DepartementEcologie et Gestion de la Biodiversite, 57 rue Cuvier CP-55, 75005 Paris, France.

(13) Departamento de Paleobiologia, Museo Nacional de Ciencias Naturales-CSIC, 28006 Madrid, Spain

(14) University of Manchester, Oxford Road, Manchester M13 9PL, U.K.

(15) Unidad de Paleontologia, Departamento de Biologia, Facultad de Ciencias, Universidad Autonoma de Madrid, 28049 Madrid, Spain.

(16) Centro de Geologia, Faculdade de Ciencias da Universidade de Lisboa (FCUL), Edificio C6, Campo Grande, 1749-016 Lisbon, Portugal

(17) Department of Biological Sciences, Faculty of Science, CW405 Biological Sciences Building, University of Alberta, Edmonton, Alberta T6G 2E9, Canada.

e-mail addresses: fortega@ccia.uned.es (F.O., Corresponding autor); bardet@mnhn.fr (N.B.); fbarroso@geo.ucm.es (F.B.-B.); callapez@dct. uc.pt (P.M.C.); oscar.cambra@uam.es (O.C.); veronique.daviero@univ-lyon1.fr (V.D.-G.); diezdiaz.veronica@gmail.com (VD.-D.); lauradomingo@geo.ucm.es (L.D.); aelviramartin@gmail.com (A.E.); fescaso@ccia.uned.es (F.E.); paleomau@gmail.com (M.G.-O.); bernard. gomez@univ-lyon1.fr (B.G.); houssaye@mnhn.fr (A.H.); knoll@mncn.csic.es (F.K.); fmarcos03@gmail.com (F.M.-F.); bwalkeri@hotmail. com (M.M.); p.mochopaleo@gmail.com (P.M.); inarvaez@ccia.uned.es (I.N); paleontologo@gmail.com (A.P.-G); daniton@gmail.com (D.P.); manuel.segura@uah.es (M.S.); geo.humberto.serrano@gmail.com (H.S.); torices@ualberta.ca (A.T.); rickraptor@me.com (D.V.); dinoproyecto@gmail.com (J.L.S)

Received: 24 December 2013 / Accepted: 18 December 2014 / Available online: 25 March 2015
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Title Annotation:texto en ingles
Author:Ortega, F.; Bardet, N.; Barroso-Barcenilla, F.; Callapez, P.M.; Cambra-Moo, O.; Daviero-Gomez, V.; D
Publication:Journal of Iberian Geology
Date:Jan 1, 2015
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