Search

The Urbasa-Andia plateau, in the western Pyrenees (North Spain), provides the opportunity to asses in detail the facies types and architecture of a Danian (lower Paleocene) greenhouse ramp to rimmed shelf system, from the slope to the coralgal reefal margin, through to highly restricted evaporitic inner shelf areas, all integrated with a range of porosity forming diagenetic phases associated with highstand and lowstand of sea-level. The detailed nature of the stratal architecture of this greenhouse platform provides an understanding of potential reservoir layering, lateral facies changes and early dolomitization. Significantly, the Danian platform system also allows a whole macroporosity system related to a third order lowstand to be accessed in relative continuity, illustrating how eogenetic karstic porosity can change drastically across a carbonate platform, from the near-massive margin to a layered shelf interior. The outcrops to visit serve as potential analogues for fields in North Africa.

International audience; The Quintanilla la Ojada section (Basque-Cantabrian Region, northern Spain) has yielded two assemblages of Late Cretaceous vertebrates, deposited during the Maastrichtian in coastal environments and related to a transgressive lag at the base of the Valdenoceda Formation. Numerous teeth of Elasmobranchii and Actinopterygii are the most prevailing fossil material, although scarce teeth of marine reptiles (Mosasauridae) and dinosaurs (Hadrosauridae) also occur. The presence of one hadrosaurian tooth, a terrestrial taxon, constitutes the first report of ornithischians in the Valdenoceda Formation. The fossil vertebrate association of Quintanilla la Ojada is similar to that discovered in Albaina (Treviño County, Burgos), also located in the Basque-Cantabrian Region, although relatively younger in age. Both fossil sites are characterised by a mixture of taxa from the northern and southern margins of the Mediterranean Tethys (north-European and north-African outcrops).; La coupe de Quintanilla la Ojada (Région Basco-Cantabrique, Nord de l’Espagne) a livré deux assemblages de vertébrés d’âge Crétacé supérieur, déposés durant le Maastrichtien dans des environnements côtiers et liés à un lag transgressif situé à la base de la Formation Valdenoceda. De nombreuses dents d’Elasmobranchii et d’Actinopterygii sont les plus fréquentes, bien que de rares dents de reptiles marins (Mosasauridae) et de dinosaures (Hadrosauridae) aient aussi été trouvées. La présence d’une dent d’hadrosaure, taxon terrestre, constitue la première mention d’ornithischiens dans la Formation Valdenoceda. L’association de vertébrés fossiles de Quintanilla la Ojada est similaire à celle découverte à Albaina (Comté de Treviño, Burgos), situé également dans la région Basco-Cantabrique, bien que d’âge légèrement plus jeune. Les deux sites fossilifères sont caractérisés par un mélange de taxons des marges nord et sud de la Téthys méditerranéenne (affleurements du Nord de l’Europe et du Nord de l’Afrique).

Los Pirineos occidentales son un territorio con una notable diversidad geológica y un importante registro fósil, que constituye un gran archivo de paleobiodiversidad. En lo que respecta al registro fósil de vertebrados, los Pirineos occidentales (Región Vasco-Cantábrica, Cuenca de Pamplona y sector noroccidental de la Cuenca del Ebro) son relevantes tanto desde el punto de vista de los yacimientos paleontológicos como de las colecciones de fósiles procedentes de ellos. Varios yacimientos de vertebrados forman parte del Inventario de Lugares de Interés Geológico (LIG) con alto o muy alto interés paleontológico en la Comunidad Autónoma del País Vasco. Destacan los yacimientos de peces cretácicos de Zeanuri en Bizkaia, mamíferos eocenos de Zambrana e icnitas miocenas de Salinas de Añana en Álava/Araba y la asociación de vertebrados pleistocenos de Kiputz cerca de Mutriku, en Gipuzkoa. Otros yacimientos notables en el área de estudio deberían ser objeto de iniciativas de geoconservación: es el caso de la cantera de Laño (Condado de Treviño), con asociaciones fi nicretácicas de vertebrados continentales y marinos, los afloramientos con icnitas de aves y mamíferos del Eoceno al Mioceno inferior de Navarra/Nafarroa y la cueva vizcaína de Santa Isabel de Ranero (Pleistoceno), por citar únicamente los ejemplos más sobresalientes. Asimismo, existen colecciones de fósiles de vertebrados en los Pirineos occidentales que destacan por su elevado interés paleontológico, aunque algunos no provengan de LIG reconocidos. Estas colecciones están depositadas en diversos centros e instituciones de Bilbao, Irún, Leioa, Pamplona-Iruñea, y Vitoria-Gasteiz. La valoración de la paleobiodiversidad y el registro fósil es un paso importante para el conocimiento del patrimonio paleontológico de un territorio y la creación de fi guras de geoconservación (e.g., LIG, geosites). Sin embargo, la mera inclusión de los yacimientos paleontológicos en estas fi guras no garantiza su protección y conservación, ni la adecuada gestión de las colecciones de fósiles procedentes de ellos. Por lo tanto, es necesario diseñar estrategias de conservación transversales teniendo en cuenta las particularidades de cada yacimiento y/o colección. La divulgación científi ca y cultural del patrimonio paleontológico de un territorio, como el aquí estudiado, debe contar con una mayor colaboración entre los paleontólogos que han valorado los bienes paleontológicos y los técnicos que los gestionan. Para ello, es necesaria la disposición de partidas presupuestarias específicas que posibiliten el desarrollo de diferentes acciones encaminadas a la investigación, conservación y difusión social de este patrimonio. The western Pyrenees is a territory with a remarkable geodiversity and an important fossil record, which constitutes a large archive of palaeobiodiversity. With respect to the vertebrate fossil record, the western Pyrenees (Basque-Cantabrian Region, Pamplona Basin and the north-western sector of the Ebro Basin) are relevant both from the point of view of palaeontological sites and fossil collections. Several vertebrate fossil sites are integrated into the Inventory of Geological Interest Sites (LIG) with high to very high palaeontological interest of the Autonomous Community of the Basque Country. It is worth highlighting the Cretaceous fish sites of Zeanuri in Biscay, Eocene mammals of Zambrana and Miocene ichnites of Salinas de Añana in Araba, and the Pleistocene vertebrate fossil assemblage of Kiputz near Mutriku, in Gipuzkoa. Other highly significant sites in the study area should be subject to geoconservation initiatives. This is the case of the Laño quarry in the Condado de Treviño, which has provided continental and marine vertebrate fossil assemblages from the latest Cretaceous, Eocene to Early Miocene sites with bird and mammal tracks in Navarre, and the Pleistocene cave deposits of Santa Isabel de Ranero in Biscay, to mention only the most outstanding examples. There are also vertebrate fossil collections in the western Pyrenees that stand out for their high palaeontological interest, although some do not come from recognized LIG. These collections are deposited in several centres and institutions of Bilbao, Irun, Leioa, Pamplona-Iruñea and Vitoria-Gasteiz. The valuation of the palaeobiodiversity and fossil record is an important step for the study of palaeontological heritage of a territory and the set-up of geoconservation designations (e.g., LIG, geosites). However, the mere inclusion of the palaeontological assents in these geoconservation designations does not guarantee either their protection and conservation or the suitable management of the fossil collection. Therefore, it is necessary to design conservation strategies taking into account the particularities of each palaeontological site and/or fossil collection. The scientific and cultural dissemination of the palaeontological heritage of a territory like one studied here should have greater collaboration between the palaeontologists that have valued the palaeontological assets and the technicians and institutions that manage them. This requires the provision of specific budgetary items that enable the development of the different activities of research, conservation and social dissemination of this heritage. Fil: Badiola, Ainara. Universidad del País Vasco; España Fil: Arlegi, Mikel. Universidad del País Vasco; España. Université de Bordeaux; Francia Fil: Astibia, Humberto. Universidad del País Vasco; España Fil: Bardet, Nathalie. Centre National de la Recherche Scientifique; Francia. Muséum National d'Histoire Naturelle; Francia. Université Pierre et Marie Curie; Francia Fil: Berreteaga, Ana. Universidad del País Vasco; España Fil: Corral, J. Carmelo. Museo de Ciencias Naturales de Álava/; España Fil: Díaz Martínez, Ignacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigación en Paleobiología y Geología; Argentina. Universidad Nacional de Río Negro. Sede Alto Valle. Instituto de Investigaciones en Paleobiología y Geología; Argentina Fil: Gómez Olivencia, Asier. Universidad del País Vasco; España. IKERBASQUE. Basque Foundation for Science; España. Universidad Carlos III de Madrid. Instituto de Salud; España Fil: Lopez Horgue, Mikel A.. Universidad del País Vasco; España Fil: Perales Gogenola, Leire. Universidad del País Vasco; España Fil: Pereda Suberbiola, Xabier. Universidad del País Vasco; España

En este trabajo se describen nuevos fósiles de sirenios eocénicos de la Cuenca de Pamplona (Navarra), permitiendo ampliar el registro conocido de estos mamíferos en los Pirineos occidentales. Los fósiles provienen de dos pequeñas localidades cercanas a la capital navarra, Uztarrotz y Ardanatz, ubicadas en formaciones litoestratigráficas diferentes (Margas de Pamplona y Areniscas de Ardanatz), de edad Bartoniense inferior. El material estudiado presenta un buen estado de conservación y consiste en restos de vértebras y costillas, con el aspecto robusto y la estructura compacta del hueso paquiosteosclerótico, característico, aunque no exclusivo, de los sirenios. Morfológica y biométricamente los fósiles de la Cuenca de Pamplona son comparables a las piezas homólogas asignadas por diversos autores a varias especies del género Prototherium en algunas localidades del Eoceno pirenaico y otras áreas del margen norte del Tethys mediterráneo. Algunas de las piezas también son parecidas a las de Halitherium taulannense del Priaboniense de Provenza. Sin embargo, las vértebras de Navarra son notablemente más robustas y presentan otras diferencias con respecto al género Protosiren del margen suroriental del Tethys. Las evidencias morfológicas, biogeográficas y cronológicas actualmente disponibles apuntan a que los restos de la Cuenca de Pamplona pertenecen a un dugónguido basal próximo a Prototherium.

Upper Maastrichtian deposits formed in a nearshore subtidal environment within the Valdenoceda Formation (Castilian Ramp, North Iberian margin) are described together with two recently found selachian assemblages. Rare earth element concentrations (REE) have been used to assess the degree of taphonomic mixing and reworking, observing that it is minor or non-existent, and differences in degree of preservation and ecologic mixing can be explained by biostratinomic processes. The patterns of REE also helped to obtain a better understanding of the depositional environment, including the diagenetic history from burial to final degree of bone preservation. The fossil assemblages here described are close to that of the late Maastrichtian of Albaina (in the enclave of Condado de Trevino, Burgos), both in the Basque-Cantabrian Region, but their age may be slightly older (early late Maastrichtian). In total, the new assemblages consist of 17 taxa, assigned to 11 genera of shallow-water dwellers combined with individuals from the outer shelf. They represent cosmopolitan taxa (Squalicorax pristodontus, Serratolamna serrata and Rhombodus binkhorsti) together with local species (Rhinobatos echavei, Rhinobatos ibericus). Although there are not significant differences between Albaina and Quintanilla la Ojada faunas, the new assemblages add interesting taphonomic and geochemical information to the few existing uppermost Cretaceous deposits with fossil sharks in southwestern Europe.

Here we present the magnetostratigraphic dating of the Laño locality (Condado de Treviño, northern Iberian Peninsula), one of the most noteworthy Campanian-Maastrichtian vertebrate sites of Europe. A composite section of 75 m thickness (Laño quarry) constructed from multiple, overlapping profiles and a continuous one (Faido) have been sampled for magnetostratigraphy. Thermal demagnetization techniques were systematically applied to 161 standard specimens and allowed characterizing the characteristic remanent magnetism, mostly carried out by magnetite. The palaeomagnetic signal is slightly scattered due to variety of lithologies, but the primary character can be guaranteed, since the normal and reverse directions are pseudo antiparallel; 346, 28 (α95: 11.9°, k: 5.3) and 175, −35 (α95: 16.4°, k: 4.6). Reliable samples allowed us to build the local polarity sequence made of eight magnetozones that has been used to correlate to the Global Polarity Time Scale. The age of the lower part of the Laño-village succession is basal late Campanian (Hoplitoplacenticeras marroti ammonite zone) and fits with the long reversed zone that must correlate to Chron C33r. The pattern of magnetozones allows tracking the section up to C30r at the upper part of the profile. In this correlation, the Laño vertebrate site is regarded as latest Campanian in age as it falls within the C32n (≈72–73.5 Ma). The combined lithostratigraphic and magnetostratigraphic analyses have yielded additional conclusions regarding the vertebrate assemblages that are representative of the Late Campanian of the Iberian Peninsula, in addition to highlight an older occurrence in Europe of some vertebrate groups such as salamandrid lissamphians and anguid lizards (or amphisbaenians)., Museo de Ciencias Naturales de Álava, España, Unidad de Zaragoza, Instituto Geológico y Minero de España, España, Departamento de Estratigrafía y Paleontología, Universidad del País Vasco, España, Departamento de Ciencias de la Tierra, Universidad de Zaragoza, España, Departamento de Física, Universidad de Burgos, España

“Lo Hueco” encloses an extraordinary upper Campanian-lower Maastrichtian fossil assemblage, composed mainly of vertebrates but also plants and invertebrates, and concentrated in a sandy channel structure (C), two grey marly mudstone levels (G1 and G2) and the lower part of a red marly mudstone level (R2). Regarding biostratinomy, the C structure (interpreted as a distributary sandy channel) contains numerous highly altered and randomly distributed macrofossils. The G1 level (the proximal part of a flooded muddy plain) preserves several totally or partially articulated specimens, mainly sauropods, with low degree of scattering and preferred orientation with respect to C. The G2 level (the distal part of a flooded muddy plain) and the lower part of the R2 level (the dried part of a muddy plain) contain numerous rarely articulated and randomly scattered macrofossils. Concerning fossil diagenesis, macroscopically, most bones present a first infilling of gypsum in spongy cavities, a ferruginous crust over outer surfaces and a second precipitation of gypsum over outer surfaces and eventually crossing the ferruginous crust and the first infilling of gypsum. Microscopically, most bones from the C structure and the G1 level additionally show radial microcracks in secondary osteons and ferruginous rings in Haversian channels. Given their particular geological and taphonomic characteristics, the C structure, the G1 and G2 levels and the lower part of the R2 level constitute four distinct taphofacies or bonebeds.

We describe a new actinopterygian fauna from the uppermost Cretaceous of Quintanilla la Ojada (Burgos, Spain), in the Villarcayo Sinclynorium of the Basque-Cantabrian Region. It consists mostly of isolated teeth of pycnodontiforms (cf. Anomoeodus sp., Pycnodontoidea indet.), amiiforms (cf. Amiidae indet.) and teleosteans (elopiforms: Phyllodontinae indet., Paralbulinae indet.; aulopiforms: Enchodontidae indet., plus fragmentary fi n spines of Acanthomorpha indet.). Paralbulinae teeth are the most abundant elements in the fossil assemblage. All the remains are disarticulated and show intense post-mortem abrasion. Th e fossil association has been found in dolomite sandstones that are laterally correlated with the Valdenoceda Formation (Lower to basal Upper Maastrichtian) of the Castilian Ramp. Th e observed taphonomic features are coherent with the sedimentological interpretation of the fossiliferous beds as coastal deltaic deposits.

Biostratinomic and bone-diagenesis parameters are used to evaluate the effects of abiotic and biotic processes on the final composition of two late Eocene vertebrate assemblages preserved in a swampy circum-lake environment from the Zambrana site (Basque-Cantabrian Region, northern Iberian Peninsula). No significant transport or bone sorting by fluvial action is observed, and complete and fragmentary bones in the assemblages (Z4 and Z6 beds) show the same biostratinomic features. The attritional bone accumulation in both excavated beds was caused mostly by biotic factors related to routine ecological deaths of population members, probably with some input from predators on the most vulnerable ungulate individuals (autochthonous), although a weak input of small remains by superficial water currents from nearby areas (parautochthonous) cannot be rejected. The vegetation and wet conditions of the swampy environment, together with possible predator and scavenger activity, could have caused the disarticulation and dispersion of some vertebrate remains, mainly those of ungulates. The bones were buried relatively quickly in the phreatic zone under reducing conditions and suffered considerable crushing and fragmentation because of lithostratigraphic compaction. Mineralogic similarities between sedimentary fillings in the fossils and the host sediment, as well as the homogeneous rare earth element (REE) trends of the fossils, are indicative of a uniform and unique diagenetic history and the absence of reworked elements. The fossil bone mineral is well-crystallized francolite (carbonate fluorapatite). The REE enrichment of bones and their calcite and pyrite crusts and fillings were formed during early diagenetic phases. The black coloration of the bones may be explained by their high hydrocarbon (n-alkane components) contents.

A rich variety of vertebrate footprints is known from a number of Upper Eocene to Lower Miocene localities of Navarre (western Pyrenees). The sediments were deposited in a wide range of depositional environments, from marginal marine to diversified terrestrial. Abundant bird tracks have been found in the coastal deposits of the Upper Eocene Liedena Sandstone of the Yesa and Itzagaondoa areas. Ciconiiformes-like (Leptoptilostipus pyrenaicus) and Charadriiformes-like (Charadriipeda ichnospp.) footprints have been recognized. Mammal ichnites have been discovered in the Oligocene and Lower Miocene deposits of Navarre. Equoid perissodactyl ichnites similar to those of Plagiolophustipus occur in the Oligocene fluviatile rocks of the Mues Sandstone of Olexoa and the Rocaforte Sandstone near Oibar and Sada. Trackways of entelodontids (Entelodontipus) are known in fluviatile-palustrine beds of the Oligocene Mues Sandstone of Olkotz. Additionally, bird (Charadriiformes-like) tracks are known in fluviatile-palustrin...

The vertebrate-bearing beds of the Laño quarry (Condado de Treviño) are among the most relevant sites from the Late Cretaceous of Europe. Geologically, Laño and the adjacent region are set on the southern limb of the South-Cantabrian Synclinorium (SE Basque-Cantabrian Region, northern Iberian Peninsula). The Laño sites were discovered in 1984; thousands of bones and teeth, including microfossils, have been collected during the prospection in the field and excavation campaigns. The vertebrate remains occur at two different stratigraphic horizons within a continental to shallow marine succession of Late Campanian-Maastrichtian age. The lower horizon contains the Laño 1 and Laño 2 sites, whereas the upper horizon contains the Albaina site. In the Laño sites, three fossiliferous beds (called L1A, L1B and L2) are known within an alluvial system composed mainly of fluvial sands and silts. The sedimentary structures are consistent with channel areas within an extensive braided river system. Based mainly on stratigraphic correlations, the fluvial beds of Laño are regarded as Late Campanian to Early Maastrichtian in age. These deposits have yielded a very diverse vertebrate assemblage, which consists of nearly 40 species, including actinopterygians, lissamphibians, lepidosaurs, turtles, crocodyliforms, dinosaurs, pterosaurs, and mammals. Seven genera and ten species have been erected to date in Laño. With reference to the marine vertebrate association of Albaina, it consists of at least 37 species, including sharks and rays, actinopterygians, mosasaurids, and plesiosaurs. Two genera and species of rhinobatoids (family indet.) and two new species of rhinobatids have been erected in Albaina. The fossil association indicates a Late (but not latest) Maastrichtian age. Recently, isolated turtle and dinosaur fossils have been discovered in the sublittoral beds of Albaina. The Laño quarry is one of the most noteworthy Campanian-Maastrichtian vertebrate localities of Europe by its taxonomic diversity, and provides useful information about the composition and affinities of both continental and marine vertebrate faunas from the latest Cretaceous of southwestern Europe, Los niveles con fósiles de vertebrados de la cantera de Laño (Condado de Treviño) se cuentan entre los más importantes del Cretácico Superior de Europa. Desde un punto de vista geológico, Laño y la región adyacente forman parte del flanco sur del Sinclinorio Subcantábrico (SE de la Región Vasco-Cantábrica). El descubrimiento de los niveles fosilíferos remonta a 1984; las prospecciones de campo y las campañas de excavación han proporcionado miles de huesos y dientes, incluyendo microfósiles. Los restos de vertebrados aparecen en dos horizontes estratigráficos diferentes formando parte de una sucesión continental a marina litoral de edad Campaniense superior a Maastrichtiense. El horizonte inferior contiene los yacimientos de Laño 1 y Laño 2, mientras que el superior contiene solo uno: Albaina. En los yacimientos de Laño, se reconocen tres niveles fosilíferos (llamados L1A, L1B y L2) formados en el seno de un sistema aluvial compuesto por arenas y limos fluviales. Las estructuras sedimentarias indican áreas de canal dentro de un sistema trenzado muy extendido. Según las correlaciones estratigráficas, los depósitos fluviales de Laño son de edad Campaniense superior a Maastrichtiense inferior. Estos depósitos han proporcionado una asociación muy diversa de vertebrados, que consiste en cerca de 40 especies, incluyendo actinopterigios, lisanfibios, lepidosaurios, tortugas, cocodrilos, dinosaurios, pterosaurios y mamíferos. En Laño se han definido hasta el momento siete géneros y diez especies. Por lo que respecta a la asociación de vertebrados marinos de Albaina, se han reconocido al menos 37 especies, que incluyen tiburones y rayas, actinopterigios, mosasaurios y plesiosaurios. Hasta la fecha se han definido en Albaina cuatro nuevos rinobatoideos: dos especies de rinobátidos y dos géneros y especies cuya familia es indeterminada. La asociación fósil es de edad Maastrichtiense superior no terminal. Recientemente se ha descrito el hallazgo de restos fósiles aislados de tortugas y dinosaurios en los niveles marinos de Albaina. La cantera de Laño es una de las localidades de vertebrados más destacadas del Campaniense-Maastrichtiense por su diversidad taxonómica, y proporciona información relevante sobre la composición y afinidades de las faunas de vertebrados continentales y marinos del Cretácico final del suroeste de Europa, Field research in the Laño quarry has been supported by financial aids of the Ministerio de Economía y Competitividad (MINECO projects CGL2010-18851/BTE and CGL2013-47521-P), Ministerio de Ciencia e Innovación (CGL2007-64061/BTE), Ministerio de Ciencia y Tecnología (CGL2004-02338/BTE, BTE2001-0185-C02-01, BOS2000-1369), Ministerio de Educación y Ciencia (Acción Integrada hispano-francesa 201-B), Diputación Foral de Álava/Arabako Foru Aldundia (93/23, 95/A23), Gobierno Vasco/Eusko Jaurlaritza (IT834-13, IT-320-10, IT-361-07, GV121.310-4/87), Universidad del País Vasco/Euskal Herriko Unibertsitatea (9/ UPV00121.310-15303/2003), Centre National de la Recherche Scientifique (CNRS, France), Institut National des Sciences de l’Univers (INSU), The Dinosaur Society (research grant 1997) and the National Geographic Research (grant #6597-99). This work is part of a palaeontological collaboration (Convenio específico de colaboración) between the Universidad del País Vasco/EHU, the Centre National de la Recherche Scientifique (CNRS, France) and the Muséum National d’Histoire Naturelle (MNHN, Paris). Contribution ISEM n° 2015-049

We report here on new vertebrate fossils from the latest Cretaceous of Albaina (Laño quarry, Condado de Trevño), northern Iberian Peninsula. They consist of an incompletehadrosauroid femur and two partial plates of turtles, one belonging to a Pleurodira(Bothremydidae), the other one to an indeterminate taxon, probably corresponding to aPan-Cryptodira. They are the first dinosaur and turtle remains found in the Late Maas-trichtian sublittoral beds of Albaina. Other components of this shallow marine vertebratefauna are selachians (sharks, rays), actinopterygians (pycnodonts, teleosts) and marine rep-tiles (mosasaurids, plesiosaurs). The Albaina femur is one of the few hadrosauroid remainsfrom the Late Maastrichtian of Europe found in marine environments, and the first onedescribed from this kind of deposits in the Iberian Peninsula. The histological structure ofthe bone indicates that it belongs to an immature individual of small size., Financial support provided by the Ministerio de Economia y Competitividad of Spain (MINECO, projects CGL2010-18851/BTE and CGL2013-47521-P) and by the Gobierno Vasco/Eusko Jaurlaritza (research group IT-834-13). This work is part of a palaeontological collaboration between the UPV/EHU (Bilbao), the CNRS (France) and the MNHN (Paris). The authors thank the Museo de Ciencias Naturales de Alava/Arabako Natur Zientzien Museoa (MCNA) for the support and facilities during the preparation of the fossil specimens. We are also grateful to the reviewers Penelope Cruzado-Caballero and Pascal Godefroit for useful comments and suggestions.

Sirenian vertebrae and ribs have been recently discovered from two Middle Eocene localities of the Pamplona Basin, Navarre (western Pyrenees). These outcrops correspond to different lower Bartonian lithostratigraphic units: the lower part of the Pamplona Marl Formation (Uztarrotz site) and the upper part of the Ardanatz Sandstone (Ardanatz site). The former represents a deep and low-energy sea floor far away from a deltaic slope; the Ardanatz environment probably corresponds to a semi-closed deltaic bay periodically affected by catastrophic floods (i.e., fluvial hyperpycnal flows). The presence of epibiontic activity suggests that the bones were exposed for a while prior to the burial. The histological structures are well preserved except in the peripheral region, where tubular-like microstructures filled by pyrite and iron oxides probably correspond to microbial bioerosion. The major mineral component of the fossil bones is francolite (carbonate fluorapatite). In the Ardanatz samples there is evidence of secondary francolite due to the late replacement of original carbonate fluorapatite through internal fractures. The Ardanatz and Uztarrotz sirenian fossils do not show any evidence of reelaboration. They have similar sum of rare earth elements (REE) concentrations relative to the host rock, but comparatively lower than in other vertebrate fossil bones. This feature may be due to the dense compact structure of pachyosteosclerotic sirenian bones.

Postcranial remains of Sirenia from the early Middle Eocene (late Lutetian) Urbasa-Andia Formation of Navarre (Western Pyrenees) are described. The material consists of two partial atlas vertebrae, one humerus and several dorsal ribs (from Arrasate, Urbasa plateau), and partial dorsal ribs (from Lezaun, Andia plateau). The morphology of the fossils is consistent with referral to Dugongidae, the only sirenian clade known so far in the Middle Eocene of Europe. Moreover, the histological study of the ribs shows that the pachyosteosclerosis of extant Sirenia was definitively present by the early Middle Eocene. The oldest sirenian remains reported to date in the Pyrenean Realm were assigned to the Biarritzian, a regional stage that is currently ascribed either to the middle or to the lower–middle Bartonian. Therefore, the sirenian remains of Lezaun, reliably dated as late Lutetian (SBZ16 zone) in age, are definitively the earliest sirenian fossils known in Western Europe and are among the oldest sea cow records of Europe.