There are significant geographic gaps in our knowledge of marine mammal evolution because most fossils have been found and described from Northern Hemisphere localities and a few other high-latitude ...areas in the Southern Hemisphere. Here, we describe fossil cetacean remains from five geological units in the South American tropics (Urumaco, Codore, Castilletes, Cantaure, and Querales formations) generally representing marginal marine depositional environments (estuaries, deltas, and tidal flats). While fossil cetaceans from Venezuelan Neogene localities have been previously studied, this paper includes the first descriptions of fossil cetaceans from Colombia, including a diverse assemblage of mysticetes and odontocetes. We identified and provisionally referred fragmentary remains to the iniid
Ischyrorhynchus vanbenedeni
and to the platanistid
Zarhachis flagellator
. The latter suggests the presence of Platanistidae in the eastern coast of South America during the early-middle Miocene, representing the second record of Platanistidae in South America and the first record of Platanistidae in eastern South America. Other less-diagnostic specimens are characterized by features commonly seen in longirostrine odontocetes such as Iniidae, Platanistidae, Pontoporiidae, Lipotidae, Eoplatanistidae, and Squalodelphinidae.
The two extant genera of strictly freshwater dolphins Inia and Platanista are the result of convergent evolution to freshwater environments with reduced visibility. Characterized by their long snout ...and small melon, these extant taxa are clustered into two clades, Iniidae in South America and Platanistidae in Southern Asia. Their evolutionary history leading to freshwater environments remains mostly unknown, because many of their related fossil species have been found in marine environments. Here, we report riverine dolphin remains (two rostral fragments and a periotic) from two stratigraphic levels of the late middle Miocene (ca. 12.5 Ma) from La Venta, Colombia. The periotic has a reduced cochlear aqueduct mediodorsally oriented, the anterior process is relatively thin, and the dorsal opening of the facial canal is located lateral to the spiral cribriform tract. The rostral fragments are dorsoventrally flattened; the mandible features two longitudinal ventral grooves, and the premaxilla-maxilla suture of the rostrum is located in a deep lateral groove. These characteristics indicate that the specimens belong to Platanistidae, the lineage of the Ganges river dolphin Platanista. Platanistids had also been recorded on coeval strata from the Fitzcarrald arch, Peru. The occurrence of middle Miocene platanistids in both the La Venta and Fiztcarrald localities suggests that members of this lineage moved into freshwater environments in South America earlier than the ancestors of the modern Amazon river dolphin Inia. The subsequent collapse of the Pebas ecosystem could have played a role in the extinction of non-marine Platanistoidea in South America.
Este trabajo analiza estrategias de disuasión de entrada en una secuencia de subastas tipo inglesa, con venta de múltiples derechos de producción. Esto, motivado por intentos de entrada infructuosos ...observados en algunas de las subastas anuales de derechos de pesca ocurridas desde inicios de los años 1990 en la pesquería industrial del Bacalao de Profundidad en Chile. Se analizan condiciones paramétricas bajo las cuales las firmas incumbentes podrían haber logrado disuadir entrada en forma no cooperativa, o bien habrían requerido coludirse para tal fin. Se desarrolla un modelo con dos etapas de competencia. En la primera etapa se subastan secuencialmente múltiples derechos de pesca; en la segunda etapa, esos derechos se usan para competir en un mercado Cournot de bien homogéneo. El análisis se focaliza en la relación entre número de incumbentes, fuentes de ventaja competitiva para éstos y el número y tamaño productivo de múltiples derechos de pesca en venta. El énfasis está en analizar cómo la divisibilidad del objeto en venta afecta las posibilidades de los incumbentes para disuadir la entrada de nuevos rivales.
The systematic value of the middle-ear ossicles, in particular the malleus, has been long recognized for diverse groups. We present systematic work on the characters of the middle-ear ossicles of ...pinnipeds, focusing on until now poorly studied Southern Hemisphere species. Mallei were extracted from 16 specimens of pinnipeds belonging to five austral and one boreal species of Phocidae and two austral species of Otariidae. Several characters used in this study have been described previously, and some were here modified. Three new characters are here defined and analysed. All characters were mapped onto the phylogeny. Our character analysis shows the transformations that have occurred in the evolution of middle ear ossicles in pinnipeds and identifies diagnostic features of many of its clades. Beyond the identification of specific changes within eachclade, our study of pinniped ossicle evolution documents the occurrence of anatomical convergences with other groups of mammals that live in an aquatic environment, as has occurred in other organ systems as well.
One of the best-known faunal assemblages that characterizes the past ecosystems from South America comes from the Santa Cruz Formation in Argentina. This assemblage is formed by an endemic fauna, ...which included ground sloths, glyptodonts, native ungulates, terror birds (phorusrhacids), among others. The Santacrucian South American Land Mammal Age is dated 18.0–15.6 Ma, late early Miocene. Current curatorial efforts revealed a large collection of over 1100 fossil remains from the Santa Cruz Formation, donated in 2007 to the Paleontological Museum, University of Zurich, Switzerland. The fossils were brought to Switzerland in the late 1880s by Theodor Allemann, an engineer and amateur collector. The collection includes skulls, isolated teeth, mandibles, and isolated postcranial elements. Postcranials are mainly represented by astragali, calcanei, and osteoderms. The study of the remains allowed us to recognize 20 families of mammals, one of birds, and one of amphibians: Abderitidae, Palaeothentidae (Paucituberculata); Hathliacynidae (Sparassodonta); Dasypodidae, Peltephilidae, and Glyptodontidae (Cingulata); Megatheriidae and Megalonychidae (Tardigrada); Astrapotheriidae (Astrapotheria), Protherotheriidae and Macraucheniidae (Litopterna); Toxodontidae, Homalodotheriidae, Hegetotheriidae and Interatheriidae (Notoungulata); Dasyproctidae, Dinomyidae, Neoepiblemidae, Chinchillidae, Erethizontidae, Echimyidae and Eocardidae (Rodentia); Phorusrhacidae (Cariamiformes); and Calyptocephalellidae (Anura). Among them, we identified 28 genera and 9 species. Reference to the previous work on the Santa Cruz fauna and the good preservation of the material allow us to achieve taxonomic resolution in the identifications. We discuss the potential usefulness of this collection for studying the paleobiology of specimens/species of this fauna.
An iniid fossil (Cetacea, Odontoceti) is reported based on a periotic found in the Codore Formation (late Miocene to middle Pliocene) of northwestern Venezuela. The marine sediments where the Codore ...dolphin was collected have yielded another cetacean and a diverse elasmobranch fauna. Cladistic analysis indicates a close relationship between the Codore dolphin and the extant Amazon River dolphin (Inia geoffrensis); key characteristics include a large cochlear portion that is dorsoventrally compressed and the extremely small size of the posterior process. High-resolution micro-computed tomography scans were used for the description and analysis of the bony labyrinth endocast. Geometric morphometric analysis of the bony labyrinth endocast places the Codore dolphin as intermediate between the La Plata dolphin (Pontoporia blainvillei) and Inia geoffrensis (principal component 1), but distinctive from both extant species (principal component 2). Comparisons of the depositional environment with cladistically informed reconstructions and inferences based on cochlear. and vestibular anatomy suggest that the Codore dolphin had the flexibility to enter marine, brackish, and fluvial environments as some extant cetaceans do today (e.g., Pontoporia blainvillei).
Este trabajo analiza estrategias de disuasión de entrada en una secuencia de subastas tipo inglesa, con venta de múltiples derechos de producción. Esto, motivado por intentos de entrada infructuosos ...observados en algunas de las subastas anuales de derechos de pesca ocurridas desde inicios de los años 1990 en la pesquería industrial del Bacalao de Profundidad en Chile. Se analizan condiciones paramétricas bajo las cuales las firmas incumbentes podrían haber logrado disuadir entrada en forma no cooperativa, o bien habrían requerido coludirse para tal fin. Se desarrolla un modelo con dos etapas de competencia. En la primera etapa se subastan secuencialmente múltiples derechos de pesca; en la segunda etapa, esos derechos se usan para competir en un mercado Cournot de bien homogéneo. El análisis se focaliza en la relación entre número de incumbentes, fuentes de ventaja competitiva para éstos y el número y tamaño productivo de múltiples derechos de pesca en venta. El énfasis está en analizar cómo la divisibilidad del objeto en venta afecta las posibilidades de los incumbentes para disuadir la entrada de nuevos rivales.
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