Determinación de edades en Otariidae y Phocidae (Carnivora) sobre piezas dentarias, técnicas alternativas

The periodic depositing of layers of cement and dentine on the mammal’s teeth it is very useful to determine the absolute age. The different events produced during the life cycle as moult, sexual maturity, nursing and feeding are reflected on the amount and type of cement and dentine deposits on the teeth. The aim of this contribution is to determine through the application of different techniques the age of specimens of Phocidae and Otariidae (Mammalia) housed on different collections in Argentina; in order to compare the results obtained with the use of different techniques and to incorporate a crucial datum to each studied specimen. The different techniques were tested, improved and then were performed on 335 specimens of Arctocephalus gazella, Arctocephalus australis, Otaria byronia, Mirounga leonina, Leptonychotes weddellii, Lobodon carcinophagus e Hydrurga leptonyx. The techniques used were: root external rings counting, dentine and cement line counting, both undecalsified as decalsified. Our results showed that not all techniques are effective for all species and for all teeth, effectiveness depends i.e. on the teeth size,  on the way on the cement is deposited. Finally, we recommend which techniques are more effective for each species. The external ring and dentine line counting techniques with and without decalsification are more suitable for Arctocephalus, the dentine line counting by decalsification is recommendable for O. byronia, while in focids is better to used the line cements counting with previuos decalcificaction in postcanines.La depositación periódica de capas de esmalte, cemento y dentina en los dientes de los mamíferos es de gran utilidad para la determinación de edades absolutas. Los diferentes sucesos que se producen durante la vida del animal como la muda, la madurez sexual, período de lactancia y de alimentación, se reflejan muchas veces en la cantidad y tipo de depósito de dentina en las piezas dentarias. Los objetivos de este trabajo son: determinar, con diferentes técnicas aplicables sobre dientes, las edades absolutas de ejemplares de Phocidae y Otariidae (Mammalia) alojados en diferentes colecciones de la Argentina; comparar los resultados obtenidos con el empleo de las distintas técnicas; y añadir un dato relevante a cada ejemplar estudiado. Se compararon, ajustaron, y aplicaron las técnicas a un total de 335 ejemplares de las siguientes especies: Arctocephalus gazella, Arctocephalus australis, Otaria byronia, Mirounga leonina, Leptonychotes weddellii, Lobodon carcinophagus, e Hydrurga leptonyx. Las tecnicas aplicadas fueron: el conteo de anillos externos de la raíz, el conteo de líneas de dentina y de cemento tanto sin descalcificar como descalcificado. Los resultados mostraron que no todas las técnicas son aplicables a todas las especies, ni para todas las piezas dentarias, dependiendo en parte del tamaño de las piezas y de la forma en que el cemento se deposita. Finalmente recomendamos cuáles técnicas son más efectivas para cada especie estudiada. La técnica de conteo de anillos externos y lineas de dentina con y sin descalcificación es conveniente para los Arctocephalus, mientras que la del conteo de líneas de dentina por descalcificación es recomendable para O. byronia, en los fócidos se recomienda el conteo de líneas de cemento con previa descalcificación en poscaninos

The largest known bear, Arctotherium angustidens, from the early Pleistocene pampeam region of Argentina: with a discussion of size and diet trends in bears

The South American giant short-faced bear (Arctotherium angustidens Gervais and Ameghino, 1880) is one of five described Arctotherium species endemic to South America and it is known for being the earliest, largest, and most carnivorous member of the genus. Here we report an extraordinarily large A. angustidens individual exhumed from Ensenadan sediments (early to middle Pleistocene) at Buenos Aires Province, Argentina. Based on overall size, degree of epiphyseal fusion, and pathologies, this bear was an old-aged male that sustained serious injuries during life. Body mass of the bear is estimated and compared to other ursid species based on a series of allometric equations. To our knowledge, this specimen now represents the largest bear ever recorded. In light of this discovery, we discuss the evolution of body size in Arctotherium (from large-to-small) and compare this to bears that exhibited different evolutionary trajectories. We suggest that the larger size and more carnivorous nature of A. angustidens, compared to later members of the genus, may reflect the relative lack of other large carnivores and abundance of herbivores in South America just after the Great American Biotic InterchangeMuseo de La Plat

Mitochondrial Genomes Reveal an Explosive Radiation of Extinct and Extant Bears near the Miocene-Pliocene Boundary

Background: Despite being one of the most studied families within the Carnivora, the phylogenetic relationships among the members of the bear family (Ursidae) have long remained unclear. Widely divergent topologies have been suggested based on various data sets and methods. Results: We present a fully resolved phylogeny for ursids based on ten complete mitochondrial genome sequences from all eight living and two recently extinct bear species, the European cave bear (Ursus spelaeus) and the American giant short-faced bear (Arctodus simus). The mitogenomic data yield a well-resolved topology for ursids, with the sloth bear at the basal position within the genus Ursus. The sun bear is the sister taxon to both the American and Asian black bears, and this clade is the sister clade of cave bear, brown bear and polar bear confirming a recent study on bear mitochondrial genomes. Conclusion: Sequences from extinct bears represent the third and fourth Pleistocene species for which complete mitochondrial genomes have been sequenced. Moreover, the cave bear specimen demonstrates that mitogenomic studies can be applied to Pleistocene fossils that have not been preserved in permafrost, and therefore have a broad application within ancient DNA research. Molecular dating of the mtDNA divergence times suggests a rapid radiation of bears in both the Old and New Worlds around 5 million years ago, at the Miocene-Pliocene boundary. This coincides with major global changes, such as the Messinian crisis and the first opening of the Bering Strait, and suggests a global influence of such events on species radiations

Mamíferos continentales del Mioceno tardío a la actualidad en la Argentina: cincuenta años de estudios

Ameghiniana was created 50 years ago. During this lapse, the late Cenozoic paleomastozoology developed exponentially in Argentina. Many of the papers dealed with systematics. However, fossil mammals were also used for establish the chronological scale based on a biostratigraphic sequence of faunas mainly from the Pampean area. This scale proved valid for other South American areas. Besides, mammals were used as proxies for understanding the continental climatic evolution and, at the same time, biogeographic studies flourished. In recent years, many paleoecological and morphofunctional studies were carried out. Certainly, the last 50 years were the most productive time in Argentina since the pioneering work of Florentino Ameghino

Mitochondrial genomes reveal an explosive radiation of extinct and extant bears near the Miocene-Pliocene boundary

Background. Despite being one of the most studied families within the Carnivora, the phylogenetic relationships among the members of the bear family (Ursidae) have long remained unclear. Widely divergent topologies have been suggested based on various data sets and methods. Results. We present a fully resolved phylogeny for ursids based on ten complete mitochondrial genome sequences from all eight living and two recently extinct bear species, the European cave bear (Ursus spelaeus) and the American giant short-faced bear (Arctodus simus). The mitogenomic data yield a well-resolved topology for ursids, with the sloth bear at the basal position within the genus Ursus. The sun bear is the sister taxon to both the American and Asian black bears, and this clade is the sister clade of cave bear, brown bear and polar bear confirming a recent study on bear mitochondrial genomes. Conclusion. Sequences from extinct bears represent the third and fourth Pleistocene species for which complete mitochondrial genomes have been sequenced. Moreover, the cave bear specimen demonstrates that mitogenomic studies can be applied to Pleistocene fossils that have not been preserved in permafrost, and therefore have a broad application within ancient DNA research. Molecular dating of the mtDNA divergence times suggests a rapid radiation of bears in both the Old and New Worlds around 5 million years ago, at the Miocene-Pliocene boundary. This coincides with major global changes, such as the Messinian crisis and the first opening of the Bering Strait, and suggests a global influence of such events on species radiations.Facultad de Ciencias Naturales y Muse