Mario Alberto Cozzuol

Formation of the Isthmus of Panama

Independent evidence from rocks, fossils, and genes converge on a cohesive narrative of isthmus formation in the Pliocene. The formation of the Isthmus of Panama stands as one of the greatest natural events of the Cenozoic, driving profound biotic transformations on land and in the oceans. Some recent studies suggest that the Isthmus formed many millions of years earlier than the widely recognized age of approximately 3 million years ago (Ma), a result that if true would revolutionize our understanding of environmental, ecological, and evolutionary change across the Americas. To bring clarity to the question of when the Isthmus of Panama formed, we provide an exhaustive review and reanalysis of geological, paleontological, and molecular records. These independent lines of evidence converge upon a cohesive narrative of gradually emerging land and constricting seaways, with formation of the Isthmus of Panama sensu stricto around 2.8 Ma. The evidence used to support an older isthmus is inconclusive, and we caution against the uncritical acceptance of an isthmus before the Pliocene.

Repeated mass strandings of Miocene marine mammals from Atacama Region of Chile point to sudden death at sea

Marine mammal mass strandings have occurred for millions of years, but their origins defy singular explanations. Beyond human causes, mass strandings have been attributed to herding behaviour, large-scale oceanographic fronts and harmful algal blooms (HABs). Because algal toxins cause organ failure in marine mammals, HABs are the most common mass stranding agent with broad geographical and widespread taxonomic impact. Toxin-mediated mortalities in marine food webs have the potential to occur over geological timescales, but direct evidence for their antiquity has been lacking. Here, we describe an unusually dense accumulation of fossil marine vertebrates from Cerro Ballena, a Late Miocene locality in Atacama Region of Chile, preserving over 40 skeletons of rorqual whales, sperm whales, seals, aquatic sloths, walrus-whales and predatory bony fish. Marine mammal skeletons are distributed in four discrete horizons at the site, representing a recurring accumulation mechanism. Taphonomic analysis points to strong spatial focusing with a rapid death mechanism at sea, before being buried on a barrier-protected supratidal flat. In modern settings, HABs are the only known natural cause for such repeated, multispecies accumulations. This proposed agent suggests that upwelling zones elsewhere in the world should preserve fossil marine vertebrate accumulations in similar modes and densities.

A new species of tapir from the Amazon

Abstract All known species of extant tapirs are allopatric: 1 in southeastern Asia and 3 in Central and South America. The fossil record for tapirs, however, is much wider in geographical range, including Europe, Asia, and North and South America, going back to the late Oligocene, making the present distribution a relict of the original one. We here describe a new species of living Tapirus from the Amazon rain forest, the 1st since T. bairdii Gill, 1865, and the 1st new Perissodactyla in more than 100 years, from both morphological and molecular characters. It is shorter in stature than T. terrestris (Linnaeus, 1758) and has distinctive skull morphology, and it is basal to the clade formed by T. terrestris and T. pinchaque (Roulin, 1829). This highlights the unrecognized biodiversity in western Amazonia, where the biota faces increasing threats. Local peoples have long recognized our new species, suggesting a key role for traditional knowledge in understanding the biodiversity of the region. Resumo Todas as espécies conhecidas de antas viventes são alopátricas: 1 no sudeste da Ásia e as 3 na América Central e América do Sul. Entretanto, o registro fóssil para antas é mais amplo geograficamente, incluindo Europa, Ásia, América do Norte e do Sul, encontrados desde o Oligoceno tardio, tornando a distribuição atual um relicto da original. Descrevemos aqui uma nova espécie de Tapirus vivente da floresta amazônica, a primeira desde T. bairdii Gill, 1865, e o primeiro novo Perissodactyla em mais de 100 anos, a partir de caracteres morfológicos e moleculares. O novo táxon é menor em estatura do que T. terrestris (Linnaeus, 1758) com morfologia distinta do crânio, sendo basal ao clado formado por T. terrestris e T. pinchaque (Roulin, 1829). Esta descoberta destaca a biodiversidade oculta no oeste da Amazônia, onde a biota enfrenta ameaças crescentes. Alguns povos locais há muito tempo reconheceram esta nova espécie, sugerindo um papel fundamental para o conhecimento tradicional na compreensão da biodiversidade da região.

The South American Gomphotheres (Mammalia, Proboscidea, Gomphotheriidae): Taxonomy, Phylogeny, and Biogeography

The taxonomic history of South American Gomphotheriidae is very complex and controversial. Three species are currently recognized: Amahuacatherium peruvium, Cuvieronius hyodon, and Notiomastodon platensis. The former is a late Miocene gomphothere whose validity has been questioned by several authors. The other two, C. hyodon and N. platensis, are Quaternary taxa in South America, and they have distinct biogeographic patterns: Andean and lowland distributions, respectively. South American gomphotheres became extinct at the end of the Pleistocene. We conducted a phylogenetic analysis of Proboscidea including the South American Quaternary gomphotheres, which resulted in two most parsimonious trees. Our results support a paraphyletic Gomphotheriidae and a monophyletic South American gomphothere lineage: C. hyodon and N. platensis. The late Miocene gomphothere record in Peru, Amahuacatherium peruvium, seems to be a crucial part of the biogeography and evolution of the South American gomphotheres.

THE OLDEST SPECIES OF DIDELPHIS (MAMMALIA, MARSUPIALIA, DIDELPHIDAE), FROM THE LATE MIOCENE OF AMAZONIA

Abstract The oldest known species of the genus Didelphis (Mammalia, Marsupialia, Didelphidae) is described here. The holotype and only known specimen comes from the late Miocene deposits of the Solimões Formation at Patos, Acre River, Brazil. The new species is one of only a few marsupials known from this assemblage. The new species differs from other known species by its smaller size, low mandibular ramus, smaller molars relative to premolars, and p3 with inflated crown. The last feature suggests more frugivorous habits than in other species of the genus.

Giant-toothed white sharks and cetacean trophic interaction from the Pliocene Caribbean Paraguaná Formation

The role of the extinct giant-toothed white sharkCarcharodon megalodon (Agassiz) in the Caribbean Neogene is discussed based on new evidence of predation on cetaceans from the Lower Pliocene Paraguaná Formation in Venezuela. Large sharks have occupied the highest trophic level in the marine environment. However, based on the recovery of a giant white shark tooth piercing a cetacean lumbar vertebra, the predator-prey relationship is discussed under the hypothesis of initial shark attack, subsequent floating transport of the cetacean carcass, and scavenging prior to deposition on the bottom. The scarce Caribbean fossil records of both giant-toothed sharks and cetaceans suggest that these species were transients during the Pliocene on the Venezuelan coast.KurzfassungDie Rolle des ausgestorbenen RiesenweißhaiesCarcharodon megalodon (AGASSIZ) im Neogen der Karibik wird anhand eines neuen Predationsbefundes aus der unter-pliozänen Paraguaná-Formation in Venezuela diskutiert. Große Haie haben die höchste trophische Ebene im marinen Milieu besetzt. Hier wird ein Zahn eines Riesenweißhaies dokumentiert, der noch in einem Lumbarwirbel eines Wales steckt, was für ein Räuber-Beute-Verhältnis spricht. Die Befunde sprechen für einen Angriff des Räubers, gefolgt von Transport des Walkadavers, Aasfressen und schließlich Ablagerung am Boden des Meeres. Riesenweißhaie und Cetaceen waren im Pliozän in den Küstenregionen von Venezuela vorhanden.

The antiquity of riverine adaptations in Iniidae (Cetacea, Odontoceti) documented by a humerus from the late Miocene of the Ituzaingó Formation, Argentina.

“River dolphins” are a paraphyletic group of toothed whales (Odontoceti) that represent independent secondary invasions of freshwater habitats. Different “river dolphin” lineages display suites of convergent morphological specializations that commonly reflect adaptations to riverine and freshwater environments, such as longirostry, reduced orbits, and wide, paddle‐like flippers. One lineage, the Iniidae, is presently endemic to South America, and includes several extinct Neogene taxa along with their sole extant genus, Inia (the Amazon River dolphin). We report here a humerus recovered from the late Miocene deposits of the Ituzaingó Formation in the Paraná Basin of Argentina. The specimen exhibits diagnostic features of the family Iniidae, including a scapular‐sternal joint of the humerus, which is a unique anatomical connection among mammals. This joint permits enhanced parasagittal adduction of the flipper as a control surface, relative to other odontocetes, providing Inia with a high degree of maneuverability in its structurally complex and heterogenous riverine habitat. This unique anatomical connection, here documented from the late Miocene (∼9 million years–6.5 million years old), not only provides the oldest diagnostic record for Iniidae, but it also indicates a similar habitat use for this lineage, a finding coincident with the current paleoenvironmental interpretation for the Ituzaingó Formation. Anat Rec, 297:1096–1102, 2014.

A new beaked whale (Cetacea, Odontoceti) from the Late Miocene of Patagonia, Argentina

ABSTRACT A new genus and species of Ziphiidae, Notoziphius bruneti, gen. et sp. nov., from the late Miocene of Patagonia, is described on the basis of a well-preserved skull and partial left and right dentaries. It can be diagnosed by large, triangular, and markedly asymmetric nasals that strongly point anteroventrally, the ascending process of the maxilla not expanded posteriorly, supraoccipital strongly sloped posteroventrally; elliptical fossa on the nasal process of the premaxilla, small and anterolaterally directed premaxillary crest, and the presence of well-defined alveoli in the maxilla. A phylogenetic analysis including 25 ziphiid genera and 31 characters shows Notoziphius as nested within Ziphiidae in a basal clade with Aporotus, Beneziphius, Messapicetus, and Ziphirostrum. This clade is diagnosed by medial fusion of the premaxillae that closes the mesorostral groove, lateral margin of prenarial basin formed by a thick strip of maxilla, premaxillary crest anterolaterally directed, and reduced contact between nasal and premaxillary crest. The presence of Notoziphius in the Miocene of Patagonia increases our knowledge of ziphiid diversity in South America. Notoziphius bruneti and other Miocene records of ziphiids reinforce the idea that during the Miocene ziphiids were widely distributed and diverse.

The aquatic sloth Thalassocnus (Mammalia, Xenarthra) from the late Miocene of North-Central Chile: biogeographic and ecological implications

JHOANN CANTO,1 RODOLFO SALAS-GISMONDI,*2 MARIO COZZUOL,3 and JOSE YANEZ4; 1Museo Nacional de Historia Natural, Secci6n Paleontologfa, Casilla 587, Santiago, Chile, jcanto@paleontologica.org; 2Departamento de Paleontologia de Vertebrados, Museo de Historia Natural, UNMSM, Av. Arenales 1256, Lima 14, Peru, rodsalasgis@yahoo.com; 3Laboratorio de Paleontologia. Museu de Ciencia e Tecnologia-PUCRS, Porto Alegre, RS, Brasil, mario.cozzuol@pucrs.br; 4Zoologia Secci6n, Museo Nacional de Historia Natural, Casilla 787, Santiago, Chile, jyanez@mnhn.cl

A MIOCENE CUSK-EEL (OPHIDIIFORMES: OPHIDIIDAE) FROM PENINSULA VALDES, ARGENTINA

Abstract Genypterus valdesensis, sp. nov. from the Puerto Madryn Formation in Península Valdés, Argentina is the first fossil ophidiid reported from South America and represents the first well preserved record of the genus worldwide. The specimen consists of a nearly complete articulated skull and some disarticulated postcranial elements. A thorough description is given of the osteological features of the species, which can be used to recognize it as a distinct taxon. The fossil species is characterized by the presence of a foramen on infraorbital 3 and by the square-shape of infraorbital 4. An array of morphological features taken in combination contribute to further differentiate G. valdesensis from the Recent species. This specimen also provides unequivocal evidence of the presence of the Ophidiiformes in the southwestern Atlantic Ocean 14 MA.