The largest freshwater odontocete: A South Asian river dolphin relative from the proto-Amazonia.

Several dolphin lineages have independently invaded freshwater systems. Among these, the evolution of the South Asian river dolphin Platanista and its relatives (Platanistidae) remains virtually unknown as fossils are scarce. Here, we describe Pebanista yacuruna gen. et sp. nov., a dolphin from the Miocene proto-Amazonia of Peru, recovered in phylogenies as the closest relative of Platanista. Morphological characters such as an elongated rostrum and large supraorbital crests, along with ecological interpretations, indicate that this odontocete was fully adapted to fresh waters. Pebanista constitutes the largest freshwater odontocete known, with an estimated body length of 3 meters, highlighting the ample resource availability and biotic diversity in the region, during the Early to Middle Miocene. The finding of Pebanista in proto-Amazonian layers attests that platanistids ventured into freshwater ecosystems not only in South Asia but also in South America, before the modern Amazon River dolphin, during a crucial moment for the Amazonian evolution.

A heavyweight early whale pushes the boundaries of vertebrate morphology.

The fossil record of cetaceans documents how terrestrial animals acquired extreme adaptations and transitioned to a fully aquatic lifestyle1,2. In whales, this is associated with a substantial increase in maximum body size. Although an elongate body was acquired early in cetacean evolution3, the maximum body mass of baleen whales reflects a recent diversification that culminated in the blue whale4. More generally, hitherto known gigantism among aquatic tetrapods evolved within pelagic, active swimmers. Here we describe Perucetus colossus-a basilosaurid whale from the middle Eocene epoch of Peru. It displays, to our knowledge, the highest degree of bone mass increase known to date, an adaptation associated with shallow diving5. The estimated skeletal mass of P. colossus exceeds that of any known mammal or aquatic vertebrate. We show that the bone structure specializations of aquatic mammals are reflected in the scaling of skeletal fraction (skeletal mass versus whole-body mass) across the entire disparity of amniotes. We use the skeletal fraction to estimate the body mass of P. colossus, which proves to be a contender for the title of heaviest animal on record. Cetacean peak body mass had already been reached around 30 million years before previously assumed, in a coastal context in which primary productivity was particularly high.

Bridging two oceans: small toothed cetaceans (Odontoceti) from the Late Miocene Chagres Formation, eastern Caribbean (Colon, Panama).

Fossil cetaceans are often found in Miocene marine outcrops across the globe. However, because this record is not homogeneous, the dissimilar increase in occurrences, along with the sampling bias has created regions with extensive records and others with great scarcity. Among these, the Caribbean has remained enigmatic due to the lack of well-preserved cetacean fossils. Here, we report new Caribbean fossil cetaceans from the Upper Miocene Chagres Formation exposed along Piña beach, Eastern Panama, including a scaphokogiine kogiid, an Acrophyseter-like physeteroid and the phocoenid Piscolithax. Along with previous records of the iniid Isthminia panamensis and the kogiine Nanokogia isthmia, the Chagres cetacean fauna shows some similarities with other Late Miocene cetacean communities such as the Californias in the North Pacific, although their closest affinities lie with the eastern South Pacific Pisco Formation, Peru. Such findings indicate that though deep and intermediate Caribbean-Pacific water interchange was reduced by the Middle Miocene due to the shallowing of the Central American Seaway, shallow waters marine connection that persisted until the Pliocene might have facilitated the dispersal of coastal species across both sides of the Isthmus.

Sperm whales (Physeteroidea) from the Pisco Formation, Peru, and their trophic role as fat sources for late Miocene sharks.

Shark-cetacean trophic interactions, preserved as bite marks in the fossil record, mostly correspond to isolated or fragmentary findings that bear limited information about major trophic patterns or roles. Here, we provide evidence of focalized foraging by sharks in the form of tooth bite marks over physeteroids fossil bones from the late Miocene of Peru. These findings indicate that sharks were targeting the forehead of coeval physeteroids to actively feed on their lipid-rich nasal complexes. Miocene physeteroids displayed a broad diversity, including giant predatorial forms, small benthic foragers and suction feeders. Like their extant relatives, these animals exhibited enlarged fatty forehead organs responsible for their sound production capabilities, thus evolving taxon-specific cranial architecture. Bite marks are found on the cranial bones where these structures were attached, indicating that sharks actively targeted this region; but also, in areas that would only be accessible following the consumption of the surrounding soft tissues. The shape of the bite marks and their distribution suggests a series of consecutive scavenging events by individuals of different shark species. Similar bite patterns can be recognized on other Miocene physeteroids fossils from across the globe, suggesting that sharks actively exploited physeteroid carcasses as fat sources.

Late middle Miocene caviomorph rodents from Tarapoto, Peruvian Amazonia.

Miocene deposits of South America have yielded several species-rich assemblages of caviomorph rodents. They are mostly situated at high and mid- latitudes of the continent, except for the exceptional Honda Group of La Venta, Colombia, the faunal composition of which allowed to describe the late middle Miocene Laventan South American Land Mammal Age (SALMA). In this paper, we describe a new caviomorph assemblage from TAR-31 locality, recently discovered near Tarapoto in Peruvian Amazonia (San Martín Department). Based on mammalian biostratigraphy, this single-phased locality is unambiguously considered to fall within the Laventan SALMA. TAR-31 yielded rodent species found in La Venta, such as the octodontoid Ricardomys longidens Walton, 1990 (nom. nud.), the chinchilloids Microscleromys paradoxalis Walton, 1990 (nom. nud.) and M. cribriphilus Walton, 1990 (nom. nud.), or closely-related taxa. Given these strong taxonomic affinities, we further seize the opportunity to review the rodent dental material from La Venta described in the Ph.D. volume of Walton in 1990 but referred to as nomina nuda. Here we validate the recognition of these former taxa and provide their formal description. TAR-31 documents nine distinct rodent species documenting the four extant superfamilies of Caviomorpha, including a new erethizontoid: Nuyuyomys chinqaska gen. et sp. nov. These fossils document the most diverse caviomorph fauna for the middle Miocene interval of Peruvian Amazonia to date. This rodent discovery from Peru extends the geographical ranges of Ricardomys longidens, Microscleromys paradoxalis, and M. cribriphilus, 1,100 km to the south. Only one postcranial element of rodent was unearthed in TAR-31 (astragalus). This tiny tarsal bone most likely documents one of the two species of Microscleromys and its morphology indicates terrestrial generalist adaptations for this minute chinchilloid.

A stem delphinidan from the Caribbean region of Venezuela.

The dense Miocene record of cetaceans is known from localities along the coasts of all continents, mostly in the northern Atlantic or the eastern Pacific regions, but Antarctica. Fossils from the Caribbean region are few and include of a couple of findings from Panama and Venezuela. Here, we report a partly complete skull from the Caujarao Formation (middle Miocene), Falcon State, Caribbean region of Venezuela. Our phylogenetic analyses indicate that the Caujarao specimen is a 'stem delphinidan', a group that includes several taxa of early diverging odontocetes whose phylogenetic affinities remain a matter of debate. The fossil record has shown that this group of stem delphinidans was taxonomically diverse, but displayed a somewhat homogeneous cranial patterning, with most of the variations being found within the mandible or tympanoperiotic characters. As other stem delphinidans the Caujarao odontocete displays an enlarged temporal fossa and a fairly symmetrical cranium. Because the skull is missing several key diagnostic characters due to the preservation state of the specimen, a more precise taxonomic identification is not possible. Despite this, the finding of this specimen highlights the importance of the fossil record from the Neogene of Venezuela, and the importance of the area to understand cetacean evolution in the proto-Caribbean.

New record of Neosaimiri (Cebidae, Platyrrhini) from the late Middle Miocene of Peruvian Amazonia.

The Honda Group of La Venta, Colombia, has yielded a wide array of crown platyrrhine primates, documenting the late Middle Miocene epoch (ca. 13.1-12.6 Ma, Laventan South American Land Mammal Age). Although exceptional, this record represents only a snapshot of the evolutionary history of New World monkeys because virtually none of the primate taxa recorded at La Venta had so far been found elsewhere. We describe here few dental remains of a cebine platyrrhine discovered from Laventan deposits in the San Martín Department of Peru (Peruvian Amazonia). The primate dental specimens from that new fossil-bearing locality (TAR-31) are strongly reminiscent morphologically of the teeth of Neosaimiri fieldsi from La Venta. However, given that several aspects of the dental variability from TAR-31 are unknown, we prefer to provide an assignment with open nomenclature (i.e., N. cf. fieldsi), instead of formally referring these remains to N. fieldsi, pending the discovery of additional specimens. The occurrence of Neosaimiri in Peru, in coeval deposits of La Venta, thus represents a second and southernmost record of that low-latitude genus in the Neotropics, thereby demonstrating its wide distribution along the northwestern edge of the Pebas Mega-Wetland System, in tropical western South America.

La hiperdiversificación de Physeteroidea (Cetacea: Mammalia) del Mioceno tardío en el Pacifico Sur, nuevos fósiles del área de Sacaco, Arequipa, Perú / Physeteroidea (Cetacea: Mammalia) hyper-diversification from late Miocene of South Pacific, new fossils from the Sacaco area, Arequipa, Peru

Resumen Los cachalotes (Physeteroidea) son un grupo de cetáceos con una ecología restringida en la actualidad. Las tres especies actuales son el remanente de un grupo que alcanzó su máxima diversificacion durante el Mioceno, incluyendo cinco especies simpátricas descritas en la Formación Pisco, Ica-Arequipa, Perú. Entre estas se incluyen formas piscívoras, bénticas, así como carnívoros de tamaño medio e hipercarnívoros. Se reportan dos dientes aislados provenientes del Mioceno superior de las localidades de Sacaco y Sacaco sur, que corresponden con la morfología típica de Physeteridae. Esta morfología dentaria es similar a la de taxones presentes en el hemisferio norte como Orycterocetus o Aulophyseter del Mioceno medio. Debido a esto se presume que los restos corresponderían a physetéridos con hábitos piscívoros, que quizás poseyeron un desarrollo incipiente de la capacidad de succión. La presencia de este linaje indicaría que a fines del Mioceno los parientes de los modernos Physeter y Kogia compartieron el mar peruano con formas extintas, sin solapamiento de nichos debido a la morfología altamente derivada de cada grupo. Este nuevo registro expande la comunidad de cetáceos fósiles de Sacaco, que se vio favorecida por la gran diversidad de ambientes poco profundos que dominaron el litoral peruano hasta el establecimiento final del Sistema Humboldt.

Abstract Sperm whales (Physeteroidea) are a group of cetaceans with a restricted modern ecology. The three extant species are a remnant of a group that reached its diversity peak during the Miocene, including five already-described species from the Pisco Formation, Ica-Arequipa, Peru. We report two isolated teeth from the upper Miocene localities of Sacaco and Sud-Sacaco, which correspond with the typical morphology of Physeteridae. This morphology is similar to the one present in northern hemisphere taxa as Orycterocetus or Aulophyseter. Because of this the remains could be related to physeterids with piscivorous habits, so there would not be a niche overlap with other coeval sperm whales. This new registry expands the fossil cetacean community of Sacaco, which was favored by the great diversity of shallow environments that dominated the Peruvian coast until the final establishment of the Humboldt System.