Giovanni Bianucci
email: bianucci@dst.unipi.it

Claudio Di Celma

Walter Landini

Klaas Post

Chiara Tinelli

Christian De Muizon

Karen Gariboldi

Elisa Malinverno

Gino Cantalamessa

Anna Gioncada

Alberto Collareta

Rodolfo-Salas Gismondi

Rafael Varas-Malca

Mario Urbina

Olivier Lambert

Distribution of fossil marine vertebrates in Cerro Colorado, the type locality of the giant raptorial sperm whale Livyatan melvillei (Miocene

Keywords: paleontological heritage, marine vertebrates, fossils, Miocene, Peru

ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

The Pisco Formation (middle Miocene -late Pliocene, southern Peru) is known for its exceptional fossil record of marine vertebrates. This is perhaps the most significant record in the world for the Neogene, due to the extraordinary preservation, the elevated concentration of fossils, and their high diversity, including sharks and bony fish, marine turtles and crocodiles, seabirds, baleen and toothed whales, seals, and marine sloths.

Since the 1980s several studies have demonstrated that these fossils are concentrated in some restricted areas, which represent the main vertebrate-bearing fossil localities of the Pisco Formation. Most of the past studies focused on the description of the most significant fossils collected (e.g. Acosta-Hospitaleche, Altamirano-Sierra, [START_REF] Acosta-Hospitaleche | Variaciones morfolo ´gicas del tarsometatarso de los pingu ¨inos (Aves, Sphenisciformes) de la secuencia estratigra ´fica de la Formacio ´n Pisco (Mioceno-Plioceno), Peru ´[END_REF][START_REF] Acosta-Hospitaleche | Nuevos restos de Spheniscidae (Aves, Sphenisciformes) procedentes de la costa del Peru ´[END_REF][START_REF] Altamirano-Sierra | Primer registro de pelı ´cano (Aves:Pelicanidae) para el Mioceno tardio de la formacion Pisco, Peru[END_REF][START_REF] Amson | Osteology and functional morphology of the forelimb of the marine sloth Thalassocnus (Mammalia, Tardigrada)[END_REF]Amson & Muizon, 2014;[START_REF] Amson | Gradual adaptation of bone structure to aquatic lifestyle in extinct sloths from Peru[END_REF][START_REF] Amson | Bone histology as a clue for resolving the puzzle of a dugong rib in the Pisco Formation, Peru[END_REF]Bianucci, Lambert, & Post, 2010;[START_REF] Bisconti | Comparative osteology and phylogenetic relationships of Miocaperea pulchra, the first fossil pygmy right whale genus and species (Cetacea, Mysticeti, Neobalaenidae)[END_REF][START_REF] Bouetel | The anatomy and relationships of Piscobalaena nana (Cetacea, Mysticeti), a Cetotheriidae s.s. from the early Pliocene of Peru[END_REF][START_REF] Cha ´vez | El registro de Pelagornithidae (Aves: Pelecaniformes) y la avifauna neo ´gena del Pacı ´fico sudeste[END_REF][START_REF] Cheneval | L'avifaune Mio-Plioce `ne de la Formation Pisco (Pe ´rou). Etude pre ´liminaire[END_REF][START_REF] Ehret | Origin of the white shark Carcharodon (Lamniformes: Lamnidae) based on the upper Neogene Pisco Formation of Peru[END_REF][START_REF] Go ¨hlich | The oldest fossil record of the extant penguin genus Spheniscus -a new species from the Miocene of Peru[END_REF][START_REF] Lambert | Bony outgrowths on the jaws of an extinct sperm whale support macroraptorial feeding in several stem physeteroids[END_REF][START_REF] Lambert | A new stem-sperm whale (Cetacea, Odontoceti, Physeteroidea) from the latest Miocene of Peru[END_REF][START_REF] Lambert | A new beaked whale (Odontoceti, Ziphiidae) from the Middle Miocene of Peru[END_REF]Lambert, Bianucci, & Post, 2010;[START_REF] Lambert | The giant bite of a new raptorial sperm whale from the Miocene epoch of Peru[END_REF][START_REF] Lambert | A new long-snouted species of the Miocene pontoporiid dolphin Brachydelphis and a review of the Mio-Pliocene marine mammal levels in the Sacaco Basin, Peru[END_REF][START_REF] Lambert | The most basal beaked whale Ninoziphius platyrostris Muizon, 1983: Clues on the evolutionary history of the family Ziphiidae (Cetacea: Odontoceti)[END_REF], 2015;[START_REF] Mcdonald | The cranial anatomy of Thalassocnus (Xenarthra, Mammalia), a derived nothrothere from the Neogene of the Pisco formation (Peru)[END_REF][START_REF] Muizon | Les verte ´bre ´s fossiles de la Formation Pisco (Pe ´rou). Premie `re partie: Deux nouveaux Monachinae (Phocidae, Mammalia) du Plioce `ne de Sud-Sacaco[END_REF][START_REF] Muizon | Les Verte ´bre ´s de la Formation Pisco (Pe ´rou). Deuxie `me partie: Les Odontoce `tes (Cetacea, Mammalia) du Plioce `ne infe ´rieur de Sud-Sacaco[END_REF][START_REF] Muizon | Les Verte ´bre ´s fossiles de la Formation Pisco (Pe ´rou). Troisie `me partie: Les Odontoce `tes (Cetacea, Mammalia) du Mioce `ne[END_REF][START_REF] Muizon | Walrus-like feeding adaptation in a new cetacean from the Pliocene of Peru[END_REF]Muizon & Domning, 2002;[START_REF] Muizon | Odobenocetops peruvianus, the walrus-convergent delphinoid (Cetacea, Mammalia) from the lower Pliocene of Peru[END_REF][START_REF] Muizon | An aquatic sloth from the Pliocene of Peru[END_REF][START_REF] Muizon | A new early species of the aquatic sloth Thalassocnus (Mammalia, Xenarthra) from the ate Miocene of Peru[END_REF]Muizon, McDonald, Salas, & Urbina, 2004a, 2004b;[START_REF] Parham | New sea turtle from the Miocene of Peru and the iterative evolution of feeding ecomorphologies since the Cretaceous[END_REF][START_REF] Pilleri | Neuer spattertiarer cetotherid (Cetacea, Mysticeti) aus der Pisco-Formation Perus[END_REF]Pilleri, -1990;;[START_REF] Stucchi | Una nueva especie de Spheniscus (Aves: Spheniscidae) de la Formacio ´n Pisco, Peru ´[END_REF][START_REF] Stucchi | Los Piqueros (Aves: Sulidae) de la Formacio ´n Pisco, Peru ´[END_REF]Stucchi, , 2008aStucchi, , 2008b;;[START_REF] Stucchi | A new condor (Ciconiiformes, Vulturidae) from the late Miocene/early Pliocene Pisco formation, Peru[END_REF][START_REF] Stucchi | Ramphastosula (Aves: Sulidae): A new avian genus from the early Pliocene of the Pisco formation, Peru[END_REF], 2005a[START_REF] Stucchi | Evidence of a fossil stork (Ciconiidae) from the Late Miocene of the Pisco Formation, Peru[END_REF][START_REF] Stucchi | Una nueva especie de Spheniscidae del Mioceno tardı ´o de la Formacio ´n Pisco, Peru ´[END_REF]Urbina & Stucchi, 2005a[START_REF] Stucchi | Evidence of a fossil stork (Ciconiidae) from the Late Miocene of the Pisco Formation, Peru[END_REF], but data about the diversity of the entire fossil assemblages were published only for some taxonomic groups (e.g. odontocetes in [START_REF] Muizon | Les Verte ´bre ´s de la Formation Pisco (Pe ´rou). Deuxie `me partie: Les Odontoce `tes (Cetacea, Mammalia) du Plioce `ne infe ´rieur de Sud-Sacaco[END_REF][START_REF] Muizon | Les Verte ´bre ´s fossiles de la Formation Pisco (Pe ´rou). Troisie `me partie: Les Odontoce `tes (Cetacea, Mammalia) du Mioce `ne[END_REF]and pinnipeds in Muizon, 1981) or as preliminary faunal lists (e.g. [START_REF] Bianucci | High concentration of long-snouted beaked whales (genus Messapicetus) from the Miocene of Peru[END_REF]. Moreover, these studies generally lack a detailed geological and stratigraphical background, thus leaving unresolved the vertical and horizontal distribution of the fossils in the exposed strata. The first attempt to census the fossil vertebrates in the Pisco Formation was made by [START_REF] Muizon | Geology and paleontology of late Cenozoic marine deposits in the Sacaco area (Peru)[END_REF]. Two decades later, Brand, Esperante and colleagues [START_REF] Brand | Fossil whale preservation implies high diatom accumulation rate in the Miocene-Pliocene Pisco Formation of Peru[END_REF][START_REF] Esperante | Exceptional occurrence of fossil baleen in shallow marine sediments of the Neogene Pisco Formation, Southern Peru[END_REF][START_REF] Esperante | Taphonomy and paleoenvironmental conditions of deposition of fossil whales in the diatomaceous sediments of the Miocene/Pliocene Pisco Formation, southern Peru -a new fossil-lagersta ¨tte[END_REF], evidenced an extraordinary concentration of specimens in several localities of the Pisco Formation, but these papers were limited to baleen whales and, consequently, did not provide any useful information about the faunal diversity of these highly fossiliferous areas. With a different approach, [START_REF] Brand | A high resolution stratigraphic framework for the remarkable fossil cetacean assemblage of the Miocene/Pliocene Pisco Formation, Peru[END_REF] attempted to place some published fossil vertebrates of the Pisco Formation along several measured stratigraphic sections; their work provided a rough indication of the fossil distribution, only reporting a non-exhaustive list of fossils, some of which were not correctly placed along the stratigraphic sections [START_REF] Lambert | A new long-snouted species of the Miocene pontoporiid dolphin Brachydelphis and a review of the Mio-Pliocene marine mammal levels in the Sacaco Basin, Peru[END_REF].

The aim of this work is to present for the first time a detailed map reporting all fossil vertebrates cropping out at Cerro Colorado, the locality where the holotypes of the giant raptorial feeding sperm whale Livyatan melvillei [START_REF] Lambert | The giant bite of a new raptorial sperm whale from the Miocene epoch of Peru[END_REF], the long-snouted beaked whale Messapicetus gregarius [START_REF] Bianucci | High concentration of long-snouted beaked whales (genus Messapicetus) from the Miocene of Peru[END_REF] 2. Geological and stratigraphic setting 2.1. Regional geology The Peruvian margin is generally recognized as a long-lived convergent margin, with the oceanic Nazca Plate subducting approximately eastward below the continental South American Plate. This oblique tectonic collision developed a composite transform-convergent margin characterized by normal and strike-slip faults that formed a number of elongated extensional/pull apart basins along the western margin of Peru [START_REF] Dunbar | Cenozoic marine sedimentation in the Sechura and Pisco basins, Peru[END_REF][START_REF] Leo ´n | Estratigrafı ´a, Sedimentologı ´a y evolucio ´n tecto ´nica de la cuenca Pisco Oriental[END_REF][START_REF] Thornburg | Sedimentary basins of the Peru continental margin: Structure, stratigraphy, and Cenozoic tectonics from 68S to 168 latitude[END_REF][START_REF] Zu ´n ˜iga-Rivero | The hydrocarbon potential of Peru. Lima: BPZ Exploracio ´n[END_REF]). On the central coast of Peru, the (East) Pisco basin formed in the forearc between 13830 ′ and 158S; it is separated from the immediately adjacent West Pisco basin, located on the slope, by a basement high [START_REF] Thornburg | Sedimentary basins of the Peru continental margin: Structure, stratigraphy, and Cenozoic tectonics from 68S to 168 latitude[END_REF]. Its filling succession shows extensive normal and transtensional faulting, which is the result of the strong coupling and prominent oblique convergence between the subducting oceanic slab and the overriding plate (Leo ´n et al., 2008 and references therein). The tectonic structure of the Peruvian margin has not only been affected by the subduction of normal oceanic crust, but also disrupted by collision and subduction of the aseismic Nazca Ridge [START_REF] Hampel | The migration history of the Nazca ridge along the Peruvian active margin: A re-evaluation and some geological implications[END_REF], which produced rapid uplift and inversion of the basin starting from latest Pliocene/earliest Pleistocene time [START_REF] Hsu | Quaternary uplift of the Peruvian coast related to the subduction of the Nazca Ridge: 13.5 to 15.6 degrees south latitude[END_REF][START_REF] Machare | Plio-quaternary vertical motions and the subduction of the Nazca Ridge, central coast of Peru[END_REF][START_REF] Pilger | Plate reconstructions, aseismic ridges, and low-angle subduction beneath the Andes[END_REF].

Stratigraphy

The infill of the Pisco basin is composed of four main stratigraphic units separated by three major breaks of the basin sedimentary record; from the oldest to the youngest, these units are the Paracas Group, the Otuma Formation, the Chilcatay Formation, and the Pisco Formation [START_REF] Devries | Oligocene deposition and Cenozoic sequence boundaries in the Pisco Basin (Peru)[END_REF]. The geological map of the Cerro Colorado study area (Di Celma et al., in press) shows two important angular unconformities in the exposed succession, probably related to a combination of eustatic sea-level changes and regional tectonic movements. The first one is the interformational unconformity between the Oligo-Miocene Chilcatay Formation and the overlying Pisco Formation. The second one is a low-angle intraformational erosional discontinuity that allows the subdivision of the Pisco stratigraphic section, as exposed at Cerro Colorado, into two informal allomembers. The lower allomember is 75 m thick and consists of nearshore conglomerates and thoroughly bioturbated fine-grained sandstones, gradually succeeded by diatomites, diatomaceous mudstones, and minor additions of sandstones, dolomitic horizons, and ash layers. The upper allomember, exceeding 125 m in thickness, is exposed in the upper half of the Cerro Colorado hill and along the eastern portion of the study area; it may be subdivided into two main lithological packages. The lower package, up to 50 m thick, consists of gray and orange, very fine-to medium-grained sandstones displaying abundant evidence of current and wave reworking. The upper package is at least 75 m thick and mostly composed of finely laminated gray-white diatomite with minor interbedded sandstones, dolomitic horizons, and ash layers.

Eight major stratigraphic marker beds, representing a powerful tool to correlate isolated outcrops within the stratigraphic context of the Pisco Formation, have been defined throughout the Cerro Colorado study area. In ascending stratigraphic sequence, they are the Nazca, Tiwanacu, Quechua, Wari, Paracas, Inca, Ica-Chincha, and T17 marker beds. A detailed description of these beds is provided by Di Celma et al. (in press).

Chronostratigraphic framework

Based on the discovery of a rich mollusk level containing the bivalve Anadara sechurana [START_REF] Olsson | Contributions to the Tertiary paleontology of northern Peru: Part 4, The Peruvian Oligocene[END_REF], [START_REF] Bianucci | High concentration of long-snouted beaked whales (genus Messapicetus) from the Miocene of Peru[END_REF] and [START_REF] Lambert | The giant bite of a new raptorial sperm whale from the Miocene epoch of Peru[END_REF] referred to the late middle Miocene (ca 12-13 Ma) the strata containing the holotype of L. melvillei and the specimens of M. gregarius described from Cerro Colorado. The A. sechurana level is here placed by us in the lower allomember, about 47 m above the basal angular unconformity. This age fully agrees with [START_REF] Dunbar | Cenozoic marine sedimentation in the Sechura and Pisco basins, Peru[END_REF] and is just a bit younger than DeVries (1998,2001) in respect to the ones reported for the basal deposits of the Pisco Formation.

The presence of the pontoporiid Brachydelphis mazeasi [START_REF] Muizon | Les Verte ´bre ´s fossiles de la Formation Pisco (Pe ´rou). Troisie `me partie: Les Odontoce `tes (Cetacea, Mammalia) du Mioce `ne[END_REF] and of the ziphiid M. gregarius in the lower allomember of Cerro Colorado further supports the late middle Miocene age for this part of the section, as these species are also described from Cerro la Bruja, a locality where one of the oldest levels (ca 14 -12 Ma) of the Pisco Formation is preserved [START_REF] Bianucci | High concentration of long-snouted beaked whales (genus Messapicetus) from the Miocene of Peru[END_REF][START_REF] Devries | Oligocene deposition and Cenozoic sequence boundaries in the Pisco Basin (Peru)[END_REF][START_REF] Muizon | Les Verte ´bre ´s fossiles de la Formation Pisco (Pe ´rou). Troisie `me partie: Les Odontoce `tes (Cetacea, Mammalia) du Mioce `ne[END_REF].

Otherwise, preliminary biostratigraphical analyses based on diatoms support an early late Miocene age (early Tortonian) for the lower allomember (Di Celma et al., in press). Interestingly, the sister-taxon of M. gregarius is Messapicetus longirostris [START_REF] Bianucci | Messapicetus longirostris, a new genus and species of Ziphiidae (Cetacea) from the late Miocene of 'Pietra Leccese' (Apulia, Italy)[END_REF] which is from the early Tortonian of Italy [START_REF] Bianucci | Relationships of Messapicetus longirostris (Cetacea, Ziphiidae) from the Miocene of South Italy[END_REF]. Nevertheless more detailed biostratigraphic studies and eventually also radiometric dating are needed to better constrain the age of this fossil assemblage.

Study area and methods

An area of approximately 12 km 2 at Cerro Colorado in Ica Region, southern Peru, has been investigated in detail since 2006 during 7 successive field campaigns. Fossils from this area were all found by systematic surface prospecting of the exposures and their exact location was carefully recorded using hand-held global positioning system (GPS) receivers. Detailed taphonomic observations and a preliminary identification of each surveyed fossil specimen were made in the field. On the whole, this area was roughly uniformly investigated, but special attention was given to a restricted area (ca 500 m by 500 m) around the L. melvillei locality, in order to record all exposed isolated shark teeth and bone fragments.

Systematic identifications in the field were made more complicated due to the incompleteness of specimens related to recent erosion (more intense in some areas, such as along steep slopes) and partial burial affecting most specimens.

Several specimens were partially excavated for a more accurate description and identification. At the end of the field observation, these were covered with sediment to avoid further erosion. A few highly significant specimens were collected and deposited in the Museo de Historia Natural de la Universidad Nacional Mayor de San Marcos (MUSM) in Lima for preparation and study.

In the field, special attention was paid to avoid mapping different disarticulated bones of the same animal as belonging to different individuals: size, morphology, fossilization, preservation aspect, and relative position in the stratigraphic column were compared. Bones that were close but originated from different stratigraphic horizons were obviously referred to distinct animals. Isolated bones that were not found in situ and therefore lacked any precise stratigraphical context were not taken into account.

In addition to the completeness of the specimen, the accuracy of the filed systematic determination depends upon the preservation and exposure of diagnostic elements (e.g. for cetaceans, ear bones are often sufficient to identify the family, whereas vertebrae and ribs are much less significant). Determination to species level was possible for several specimens (e.g. the ones referred to M. gregarius), thanks to the collection, laboratory preparation, and detailed study of part of the material.

All fossil specimens were reported on a 1:6500 scale geological map and positioned along the sequence of distinctive marker beds (Di Celma et al., in press) and in a measured stratigraphic section, thus providing a framework for the spatial and temporal placement of all data, observations, samples, and specimens collected during the study. The stratigraphic accuracy for the positioning of specimens along the measured section ranges from + 0.4 to + 3 m. The horizontal and vertical distribution of all recorded fossils is reported in the Main Map.

Concerning the isolated shark teeth, only those belonging to Carcharocles and Cosmopolitodus were reported on the map and along the stratigraphic column. However, unlike the bone remains, they do not necessarily indicate the death of the animal (one shark loses several thousand teeth during its lifetime). Moreover the original concentration of outcropping large shark teeth was observed to decrease over the course of our subsequent field campaigns, due to their continuous illegal collection. In the stratigraphic section, a significant sandy bed displaying an elevated concentration of shark teeth and bones is also reported.

Vertebrate specimens with precise GPS coordinates associated, that were deposited at the MUSM prior to the beginning of this study, were also included in the map. Other previously collected specimens with rough stratigraphic data associated were only taken into account for reconstructing the total vertebrate assemblage of Cerro Colorado.

Being beyond the aim of this work, detailed taphonomic and paleoecological observations are not reported here and will be discussed in a future paper.

Overall composition of the vertebrate assemblage

In total 318 specimens preserved as bone elements were recorded in the vertebrate assemblage of Cerro Colorado. The assemblage is dominated by cetacean remains (81% of the specimens), belonging to mysticetes (39%), odontocetes (23%) and indeterminate cetaceans (19%) (Figure 1).

Among mysticetes, a medium size (5 -8 m) undescribed cetotheriid larger than Piscobalaena nana [START_REF] Pilleri | Neuer spattertiarer cetotherid (Cetacea, Mysticeti) aus der Pisco-Formation Perus[END_REF] is the most common taxon of Cerro Colorado. Furthermore, several complete to incomplete articulated skeletons of this taxon were found. In total, cetotheriid remains represent 18% of the entire vertebrate assemblage, as the indeterminate mysticetes (18%), whereas larger size balaenopteroids are relatively rarer (3%). The odontocete assemblage is more diversified, consisting of stem physeteroids (2%), ziphiids (5%), pontoporiids (9%), kentriodontid-like delphinidans (2%), indeterminate delphinidans (2%), and indeterminate odontocetes (3%). Physeteroids include (1) the holotype of L. melvillei (an almost complete skull, incomplete mandibles, nine detached teeth, and other tooth fragments) [START_REF] Lambert | The giant bite of a new raptorial sperm whale from the Miocene epoch of Peru[END_REF], [START_REF] Muizon | Les verte ´bre ´s fossiles de la Formation Pisco (Pe ´rou). Premie `re partie: Deux nouveaux Monachinae (Phocidae, Mammalia) du Plioce `ne de Sud-Sacaco[END_REF] two specimens related to Acrophyseter (including skulls), and (3) a partial skeleton belonging to an undescribed genus (recently collected for preparation and study). Ziphiids are mainly represented by isolated skulls, in some cases with articulated mandibles, of M. gregarius. The holotype and most of the described referred material (represented by males, females, and one calf) of this species originate from Cerro Colorado [START_REF] Bianucci | High concentration of long-snouted beaked whales (genus Messapicetus) from the Miocene of Peru[END_REF]. After the publication of this material, additional remains of M. gregarius were discovered at Cerro Colorado, including several skulls with associated postcranial remains. The ziphiid record in Cerro Colorado also includes a fragmentary skull, recently collected for preparation and study, showing some affinities with the South African species Nenga nasalis [START_REF] Bianucci | A high diversity in fossil beaked whales (Odontoceti, Ziphiidae) recovered by trawling from the sea floor off South Africa[END_REF]. Kentriodontid-like delphinidans include two well-preserved skulls, belonging to two distinct new genera and species, as well as other more fragmentary remains. Pontoporiids are represented by three specimens referable to an undescribed Pliopontos-like species and several specimens referred to Brachydelphis. Among the latter, some well-preserved short-snouted skulls, sometimes with associate postcranial skeleton, were referred to B. mazeasi, whereas a fragmentary fetus and several isolated periotics could not be identified at the species level.

Non-cetacean marine vertebrates are represented by pinnipeds (4%), sea turtles (4%), longirostrine marine crocodylians (1%), seabirds (4%), sharks and rays (2%, excluding isolated teeth), and bony fish (4%).

The pinniped record consists of a skull with associated vertebral column and ribs, as well as several other fragmentary specimens, including an articulated skeleton, a fragmentary skull with associated mandible, and two isolated mandibles, all belonging to an indeterminate seal (family Phocidae).

Sea turtles are represented by several well-preserved partial skeletons (including skulls) of P. urbinai. Here again the holotype and most of the significant specimens described by [START_REF] Parham | New sea turtle from the Miocene of Peru and the iterative evolution of feeding ecomorphologies since the Cretaceous[END_REF] were found in Cerro Colorado.

Crocodiles are reported on the basis of a partial skeleton embedded in a nodule and some fragmentary postcranial bones.

Seabird remains include some exquisitely well-preserved skulls and/or postcranial skeletons belonging to two undescribed new species of booby (Sula, Sulidae) and other fragmentary bones of indeterminate cormorants (family Phalacrocoracidae) and procellarids.

Significant shark remains include teeth with associated vertebrae of Comopolitodus hastalis and indeterminate carcharinids. More than 3500 isolated elasmobranch teeth, mostly collected from a sandy level with a high concentration in shark teeth and bony fish remains, belong to: (1) carchariniformes (79.5%), represented by carcharinids (78%), and sphyrnids (1.5%); ( 2) lamniformes (14.5%), represented by lamnids (12.5%), odontaspidids (1.5%), and otodontids (0.5%);

(3) myliobatids (6%); and (4) very rare (one tooth for each family) pristids and squatinids (Figure 2). Significant remains of bony fish belong to scombrids (aff. Thunnus sp.) and to an indeterminate sciaenid.

Fossil distribution

Spatial distribution on the ground

On the whole, fossil vertebrates appear not to be uniformly distributed across the mapped area: in some areas, such as at the NE and SW of the Cerro Colorado hill, their concentration is low, whereas fossils are apparently absent at the top of the hill (Figure 3). Such a non-homogenous distribution may be due to: (1) the recent morphological changes of the landscape (on a drop off the fossils exhibit a lower exposition and are subjected to a greater erosion); ( 2) the covering of fossil-bearing outcrops with recent aeolian or landslide deposits; (3) and the non-homogenous vertical and/or horizontal distribution of fossils in the strata. Low fossil concentration at the SW of the Cerro Colorado hill is probably due to 1 and 2, whereas the absence of fossils at the top and the low concentration at the NE of the hill are probably due to 3. The apparently higher concentration of fossils around the L. melvillei locality is at least partly due to the more intense prospecting of this restricted area (see Methods section).

When analyzed separately, odontocetes and mysticetes on the whole display the same distribution pattern as all other vertebrates. However, among mysticetes, balaenopteroid remains are absent in the plain north of the hill, whereas no cetotheriid is recorded on the hill, above the intraformational angular unconformity separating the lower from the upper allomember. Among odontocetes, all physeteroids apart from the Livyatan holotype were discovered to the south of the hill. Considering other vertebrates, pinnipeds are only present on the hill, above the angular unconformity, where bony remains of reptiles, seabirds, bony fish, and sharks were not found. Carcharocles and Cosmopolitodus teeth show a wide distribution.

Stratigraphaic distribution

The stratigraphic distribution of the fossil vertebrates in Cerro Colorado appears highly non-randomly organized, with the highest concentration (88%) of recorded remains in the lower allomember, between 40 and 75 m above the basal unconformity with the Chilcatay Formation (Figure 4). Isolated shark teeth of Carcharocles and Cosmopolitodus are also common in these fossiliferous strata. In this stratigraphic interval, two distinct peaks were identified: the most pronounced between 60 and 65 m (27% of all the fossils found, including the L. melvillei holotype) and the other between 45 and 50 m (15%). A similar distribution is observed when analyzing separately each vertebrate group (excluding the pinnipeds, absent in the lower allomember) with some small differences perhaps due to the low, less statistically representative number of specimens. The above-mentioned 1 m-thick sandy bed is extremely rich in elasmobranch teeth and fish bones are located in this lower allomember, about 59 m above the basal angular unconformity. Another smaller peak (7% of all fossils) is observable in the upper allomember stratigraphic interval, between 130 and 150 m above the basal angular unconformity. As for all the upper allomember, the fossil bone assemblage of this stratigraphic interval consists of pinnipeds and cetaceans. All identified mysticete remains of the upper allomember strata are referred to balaenopteroids; very common in the lower allomember, cetotheriids are apparently absent. Whereas bony remains of reptiles, seabirds, bony fish, and sharks are absent from the upper allomember, isolated shark teeth (but only of Carcharocles and Cosmopolitodus) are found near pinniped and cetacean remains.

Outside these high concentration levels, fossil vertebrates are relatively rare and represent only 5% of the total fossil vertebrate assemblage of the section. More specifically, fossil vertebrates are totally absent in the lower allomember between 5 and 20 m above the basal unconformity and in the whole upper portion of the upper allomember (starting from about 165 m above the basal unconformity).

To interpret the non-uniform distribution of fossil vertebrates in the stratigraphic section, it is necessary to consider the role of the non-homogenous exposure of the strata in the study area.

Where the strata occasionally cross the surface with a high angle in correspondence with the drop off, as noted above, the number of fossils discovered could be lower due to their more limited exposure and greater rate of erosion. Such considerations are certainly applicable for the beds in the lower allomember between 40 and 75 m above the basal unconformity. The high fossil concentration in the areas N and SE of the Cerro Colorado hill corresponds to strata crossing the topography with a low angle, whereas an apparently lower fossil concentration appears on the almost vertical NE and SW slopes of the hill. Instead, fossil vertebrates are almost absent in the lower and upper portions of the stratigraphic section, respectively, to the NE and at the top of the hill, despite the fact that beds crop out almost parallel to the ground in these areas. At least for these cases we can assume that the low number of fossils reported in the section corresponds to a real low concentration in the corresponding strata. Therefore, it is reasonable to propose that the non-uniform distribution of fossil vertebrates in the stratigraphic section is mainly due to vertical changes in fossils concentration.

Conclusion

Focusing on the lower portion (late middle or early late Miocene) of the Pisco Formation cropping out at Cerro Colorado (the locality of the giant raptorial sperm whale L. melvillei), this work provides for the first time a combined quantitative and qualitative evaluation of the fossil vertebrates from a Pisco Formation locality (Figure 5).

Thanks to a detailed geological and stratigraphic study undertaken concomitantly (an important aspect) to the prospection and mapping of fossil vertebrates, all the fossils are reported on a geological map and along the related stratigraphic section. Taken together, these two data-sets provide a detailed and unique overview of the spatial and stratigraphic vertebrate distribution. In particular, an outstandingly elevated concentration (88% of all fossils) is observed from 40 to 75 m above the angular unconformity on the underlying Chilcatay Formation.

The systematic determination of more than 300 specimens preserved as bony elements yielded important information on the composition of the fossil assemblage. Most of these fossils belong to cetaceans (81%), represented by ( 1) mysticetes (39%), including cetotheriids (18%). and balaenopteroids (3%) and ( 2) odontocetes (23%), including kentriodontid-like delphinidans (2%), pontoporiids (9%), indeterminate delphinidans (2%), ziphiids (5%), and physeteroids (2%). Pinnipeds (4%), sea turtles (4%), crocodiles (1%), seabirds (4%), bony fish (4%), and sharks (2%) are also reported. Isolated large teeth of Carcharocles and Cosmopolitodus are common in all the investigated areas of the locality, whereas other shark teeth, most of them referred to carcharinids, are concentrated in one sandy bed.

Data reported in this work represent a unique basis for the development of different research topics: (1) the reconstruction of the ecological structure of the vertebrate assemblage at Cerro Colorado, with a special emphasis on the trophic relationships and the impact of top predators (e.g. Livyatan and Carcharocles) on this ancient marine ecosystem; (2) the taphonomic analysis of the exceptional conservation of this fossil assemblage; and (3) the more punctual systematic studies of significant specimens belonging to new taxa (several cetacean specimens have already been collected and are currently under preparation), in a stratigraphic and geological framework which is more robust than previous work on the vertebrates of the Pisco Formation.

This work represents the first step of a long-term multidisciplinary project foreseeing the realization of similar maps of fossil vertebrates from other localities of the Pisco Formation (e.g. Cerro Los Quesos, see [START_REF] Lambert | A new beaked whale (Odontoceti, Ziphiidae) from the Middle Miocene of Peru[END_REF] and also from the older and seemingly fossiliferous Chilcatay Formation (e.g. Ullujaya, see Bianucci, Urbina, & Lambert, 2014;Lambert, Bianucci, & Urbina, 2014;[START_REF] Lambert | A new archaic homodont toothed whale (Mammalia, Cetacea, Odontoceti) from the early Miocene of Peru[END_REF].

Finally, in order to trigger actions to preserve and promote this extraordinary paleontological heritage, this paper represents the first attempt at compiling highly accurate data on the occurrence of marine vertebrates within the Pisco Formation. Indeed, this comprehensive study may also constitute the first step toward an improved management and conservation of Peruvian paleontological heritage, through: (1) the collection of a large amount of paleontological and geological data demonstrating the richness and uniqueness of the Pisco basin fossil localities as well as their scientific significance, as a means to producing plans for conservation and future research; [START_REF] Muizon | Les verte ´bre ´s fossiles de la Formation Pisco (Pe ´rou). Premie `re partie: Deux nouveaux Monachinae (Phocidae, Mammalia) du Plioce `ne de Sud-Sacaco[END_REF] the implementation of a general database for the paleontological content of Pisco localities. Such a database will be housed at the MUSM and access will be provided to the community for projects involving research, mining, construction, recreation, and tourism in the Pisco Basin area; and (3) collaborative projects with regional and national Peruvian authorities for the application of this conservation model to other paleontological localities in Peru.

Therefore, this work should better be considered as the first step for the future study and conservation of fossil marine vertebrates from the Peruvian southern coast, more than the final result of multiple field campaigns.

Software

The geological map was compiled by scanning hand drafts as black and white TIF files, and then digitizing the linework using the Corel Draw X3 graphics package. By using the GIS Data processing application Global Mapper 12, contour lines for the topographic base map were generated from digital elevation models based on the Shuttle Radar Topography Mission 26 (SRTM), as released by the United States Geological Survey (SRTM3 USGS version 2.1). Positions of fossil specimens were superimposed on the outcrop pattern of distinctive marker bed horizons using Global Mapper 12 to convert a Google Earth kmz file containing their position to Corel Draw.

  the sea turtle Pacifichelys urbinai Parham & Pyenson, 2010 were found.

Figure 1 .

 1 Figure 1. Quantitative composition of the fossil vertebrate assemblage from the Pisco Formation in Cerro Colorado, based on systematic surface prospecting and on a few fossils whose GPS coordinates are unknown. Isolated teeth of Elasmobranchii and fragmentary remains of indeterminate vertebrates are not considered.

Figure 2 .

 2 Figure 2. Quantitative composition of the fossil shark assemblage from the Pisco Formation in Cerro Colorado, based on 3586 isolated teeth.

Figure 3 .

 3 Figure 3. Map of the investigated area of Cerro Colorado showing the whole fossil vertebrate distribution.

Figure 4 .

 4 Figure 4. Stratigraphic distribution of fossil vertebrates in Cerro Colorado.

Figure 5 .

 5 Figure 5. Fossil vertebrates from the Pisco Formation in Cerro Colorado. (a) Partially articulated skeleton of the ziphiid M. gregarius. (b) Complete and articulated skeleton of a kentriodontid-like delphinoid. (c) Skull and mandible of the holotype of the physeteroid L. melvillei. (d), (e), and (f) Complete and articulated skeletons of cetotheriid mysticetes. (g) Skull and partial skeleton of the sea turtle P. urbinai. (h) Several associated shark teeth belonging to the same individual of C. hastalis.

Acknowledgements

We particularly thank W. Aguirre, A. Altamirano-Sierra, E. Dı ´az, M.J. Laime, and M. Stucchi who provided assistance during our stays at the MUSM. We also wish to thank J. Reumer (Natuurhistorisch Museum Rotterdam, NMR) for his participation to the fieldtrip in 2008 and the NMR for supporting the excavation and preparation of the holotype of Livyatan melvillei. We also thank B. Ramassamy (Copenhagen University, Denmark) for his help during one of the 2014 fieldtrips. Constructive comments of the reviewers P.D. Gingerich, B. Jenny, and M. Guimara ˜es Simo ˜es significantly improved both the content and form of this paper.

Disclosure statement

No potential conflict of interest was reported by the authors.

Funding

Research was supported by a grant of the Italian Ministero dell'Istruzione dell'Universita `e della Ricerca [PRIN Project 2012YJSBMK] and by a National Geographic Society Committee for Research Exploration grants [9410 -13].