Cambios en la riqueza taxonómica y en las tasas de primera y última aparición de los Proterotheriidae (Mammalia, Litopterna) durante el Cenozoico

The Proterotheriidae have been recorded from Upper Paleocene until Holocene [«Land-mammal Ages» (= SALMAs) Itaboraian-Lujanian]. They are mainly braquiodonts, with cursorial habits, small to medium sized, and an early tendency toward the monodactily. The objectives of this paper are: 1) to analyze the changes in the diversity and faunistic exchange rates of these South American «ungulates» (at genus and species levels) throughout the biochron of the family; and 2) to relate these changes with the principal changes in climatic-environmental conditions. The results show that Proterotheriidae suffered marked changes in the generic and specific diversity during the Itaboraian-Lujanian SALMAs, with four diversity peaks: two minors in the Casamayoran and Laventan SALMAs, and two majors in the Santacrucian and Huayquerian ones. These peaks were interrupted by two hiatuses in the fossil record, the first in the Divisaderan-Tinguirirican SALMAs, and the second in the Mayoan SALMA. In general, Proterotheriidae show an elevated exchange rate during its biochron, both at genus as well as species levels. This elevated exchange rate indicates that the family possesses a higher biochronological value. Both the fluctuations in taxonomic richness as well as exchange rates are related with the climatic-environmental changes occurred during the Cenozoic. As a rule, higher diversity is observed in those SALMAs in which there is a relatively equalized relation between forests and grasslands. On the other hand, diversity markedly falls when the environments change from wet and closed to most open and arid. The last Proterotheriidae species (Neolicaphrium recens) was confined to the Pleistocene of north-eastern Argentina and western Uruguay, where an ecotone between forests and grasslands is recorded.Los Proterotheriidae han sido registrados desde el Paleoceno Superior hasta el Holoceno [«Edadesmamífero (= SALMAs) Itaboraiense-Lujanense]. Son mayoritariamente braquiodontes, cursoriales, de tamaño pequeño a mediano, que muestran una temprana tendencia hacia la monodactilia. Los objetivos del presente trabajo son: 1) analizar los cambios en la diversidad y las tasas de recambio de estos «ungulados» sudamericanos (tanto a nivel de especies como de géneros) a lo largo de todo su biocrón; y 2) vincular estos cambios con las principales variaciones en las condiciones climático-ambientales. Los resultados muestran que durante el lapso comprendido entre las SALMAs Itaboraiense-Lujanense, los Proterotheriidae sufren grandes cambios en la diversidad genérica y específica, con cuatro picos de diversidad (dos menores en las SALMAs Casamayorense y Laventense y dos mayores en las SALMAs Santacrucense y Huayqueriense). Estos picos están interrumpidos por dos hiatos en el registro fósil, en las SALMAs Divisaderense-Tinguiririquense y en la SALMA Mayoense, respectivamente). En líneas generales, los Proterotheriidae muestran durante su biocrón una elevada tasa de recambio tanto a nivel de géneros como de especies, razón por la cual esta familia puede ser considerada de gran valor biocronológico. Las fluctuaciones en la riqueza taxonómica y las tasas de recambio taxonómico guardan relación con los cambios climático-ambientales acaecidos durante el Cenozoico. Asimismo, la mayor diversidad se observa en aquellas SALMAs en las que hay una relación relativamente equilibrada entre bosques y pastizales, declinando marcadamente la diversidad a medida que los ambientes se tornan más abiertos y áridos. La última especie de Proterotheriidae (Neolicaphrium recens) queda restringida al NE de la Argentina y al O de Uruguay, donde es registrado un ecotono entre bosques y pastizales

First evidence for a massive extinction event affecting bees close to the K-T boundary

Bees and eudicot plants both arose in the mid-late Cretaceous, and their co-evolutionary relationships have often been assumed as an important element in the rise of flowering plants. Given the near-complete dependence of bees on eudicots we would expect that major extinction events affecting the latter would have also impacted bees. However, given the very patchy distribution of bees in the fossil record, identifying any such extinctions using fossils is very problematic. Here we use molecular phylogenetic analyses to show that one bee group, the Xylocopinae, originated in the mid-Cretaceous, coinciding with the early radiation of the eudicots. Lineage through time analyses for this bee subfamily show very early diversification, followed by a long period of seemingly no radiation and then followed by rapid diversification in each of the four constituent tribes. These patterns are consistent with both a long-fuse model of radiation and a massive extinction event close to the K-T boundary. We argue that massive extinction is much more plausible than a long fuse, given the historical biogeography of these bees and the diversity of ecological niches that they occupy. Our results suggest that events near the K-T boundary would have disrupted many plant-bee relationships, with major consequences for the subsequent evolution of eudicots and their pollinators.Sandra M. Rehan, Remko Leys, Michael P. Schwar

Bone histology provides insights into the life history mechanisms underlying dwarfing in hipparionins

Size shifts may be a by-product of alterations in life history traits driven by natural selection. Although this approach has been proposed for islands, it has not yet been explored in continental faunas. The trends towards size decrease experienced by some hipparionins constitute a good case study for the application of a life history framework to understand the size shifts on the continent. Here, we analysed bone microstructure to reconstruct the growth of some different-sized hipparionins from Greece and Spain. The two dwarfed lineages studied show different growth strategies. The Greek hipparions ceased growth early at a small size thus advancing maturity, whilst the slower-growing Spanish hipparion matured later at a small size. Based on predictive life history models, we suggest that high adult mortality was the likely selective force behind early maturity and associated size decrease in the Greek lineage. Conversely, we infer that resource limitation accompanied by high juvenile mortality triggered decrease in growth rate and a relative late maturity in the Spanish lineage. Our results provide evidence that different selective pressures can precipitate different changes in life history that lead to similar size shifts

Paleoecología y evolución de la fauna de mamíferos de América del Sur durante la «edad de las planicies australes» (Mioceno superior-Plioceno superior)

In this paper, the paleoecology and evolution of the South American land-mammal fauna during the «Age of the Southern Plains» are studied. Chronologically, the «Age of the Southern Plains» encompasses the Chasicoan, Huayquerian, Montehermosan and Chapadmalalan South American Land-Mammal Ages. Changes on the taxonomic richness, first and last appearance rates, and trophic types were considered, taking as a model the fossil record of the Pampean Region (Argentina). A gradual increase of the taxonomic richness is observed during the «Age of the Southern Plains». Caviomorpha and Cingulata were the most diversified taxonomic groups. First appearance rates are higher that those of the last appearances excepting the Chapadmalalan, in which both rates reach a balance. From a trophic point of view, grazer mammals were predominant. This last characteristic corroborates the hypothesis of an existing similarity between the «Age of the Southern Plains» and the North American Clarendonian Chronofauna.<br><br>En este trabajo se estudian la paleoecología y la evolución de la fauna de mamíferos de América del Sur durante la denominada «edad de las planicies australes», un período que abarca las «Edades-mamífero» Chasiquense, Huayqueriense, Montehermosense y Chapadmalalense. Para ello se consideran los cambios en la riqueza taxonómica, en las tasas de primera y última aparición y en los tipos tráficos, tomando como modelo el registro de la Región Pampeana de la República Argentina. Durante la «edad de las planicies australes» se observa un paulatino incremento en la riqueza taxonómica, con un predominio de los Caviomorpha y los Cingulata. Las tasas de primera aparición son más altas que las de última aparición con la excepción de la «Edad-mamífero» Chapadmalalense, en la cual ambas tasas alcanzan un equilibrio. Desde un punto de vista trófico, predominan los mamíferos pastadores. Esta última característica corrobora la similitud existente entre la fauna de la «edad de las planicies australes» y la Cronofauna Clarendoniana de América del Norte

Análisis cladístico, paleoecología y extinción de la subfamilia Pichipilinae (Marsupialia, Caenolestidae)

The extinct subfamily Pichipilinae is a monophyletic group that comprise three genera and six species of small marsupials that lived on Southern South America from early Colhuehuapian (early Miocene) to Montehermosan (late Pliocene) land-mammal «ages». A cladistic analysis of the Pichipilinae was carried out using sixteen dental characters, and the six species considered as terminal taxa. Apomorphic character states were identified using the subfamily Caenolestinae as outgroup. The analysis yielded one cladogram, with 16 steps, a consistency index of 0.93, and a retention index of 0.83. In this cladogram: 1) Phonocdromus gracilis is the sister group to the other Pichipilinae species; 2) Pichipilus halleuxi + Pliolestes tripotamicus and Pichipilus rigssi + Pichipilus centinelus + Pichipilus osborni are two sistergroups, and 3) the relationship among Pichipilus rigssi + Pichipilus centinelus + Pichipilus osborni is unresolved. The results of the cladistic analysis support the previous hypothesis of a close phylogenetic relation between Pliolestes tripotamicus and Pichipilus halleuxi. It is probably that new and more complete fossil specimens of Pichipilus halleuxi allow: a) to include this species in Pliolestes; or b) to include Pliolestes tripotamicus in Pichipilus. It is possible to infer that Pichipilinae were scansorial, nocturnal and insectivorous- frugivorous mammals, that lived on wet and warm-temperate climatic conditions. Probably, its extinction was related to the climatic-environmental changes occurred on Southern South America during the middle Miocene-late Pliocene span.La subfamilia Pichipilinae es un grupo monofilético que comprende tres géneros y seis especies de pequeños marsupiales extinguidos, que habitaron el extremo austral de América del Sur desde la «Edad-mamífero» Colhuehuapense (Mioceno temprano) hasta la Montehermosense (Plioceno tardío). Se realizó un análisis cladístico de los Pichipilinae empleando dieciséis caracteres dentales, y las seis especies conocidas fueron consideradas como taxones terminales. Los caracteres apomórficos fueron identificados utilizando a la subfamilia Caenolestinae como grupo externo. El análisis produjo un cladograma, con 16 pasos, un índice de consistencia de 0,93 y un índice de retención de 0,83. En este cladograma: 1) Phonocdromus gracilis es el grupo hermano de las restantes especies de Pichipilinae; 2) Pichipilus halleuxi + Pliolestes tripotamicus y Pichipilus rigssi + Pichipilus centinelus + Pichipilus osborni son dos grupos hermanos y 3) la relación entre Pichipilus rigssi + Pichipilus centinelus + Pichipilus osborni no está resuelta. Los resultados del análisis cladístico soportan la hipótesis previa de una estrecha relación filogenética entre Pliolestes tripotamicus y Pichipilus halleuxi. Es posible que nuevos y más completos especímenes fósiles de Pichipilus halleuxi permitan: a) incluir esta especie en Pliolestes; o b) incluir a Pliolestes tripotamicus en Pichipilus. Es posible inferir que los Pichipilinae fueron mamíferos escansoriales e insectívoro-frugívoros, que vivieron bajo condiciones climático-ambientales húmedas y templado-cálidas. La extinción de estos marsupiales estuvo relacionada probablemente con los cambios climático-ambientales ocurridos en la porción austral de América del Sur durante el lapso Mioceno medio-Plioceno

A multivariate approach to the association pattern of reciprocal translocations induced by chemicals and ionizing radiation in mouse germ cells

The degree of similarity between chemical and physical agents in their capacity to induce reciprocal translocations was analyzed by means of multivariate analysis techniques. The effect of three different doses of gamma rays, four doses of X-rays and different doses of adriamycin, mitomycin C, thio-tepa and bleomycin was analyzed. Data were arranged in a basic matrix by two methods: cluster analysis and ordination. Two main groups were found, one including doses of 9 and 10 Gy and the other including the remaining lower doses of ionizing radiation and the other chemicals. Various subgroups were found within the second group. Accordingly, using presence/absence data there was not a specific pattern of chromosomal damage induction for physical and chemical agents. The increase in the frequencies of reciprocal translocation observed with 9 and 10 Gy was due to an increase in the kind of multivalent configurations. This variability could be dose dependent. Likewise, the similarity observed in the second group between the chemicals and the lower doses of ionizing radiation could also be dose dependent

First ? cimolodontan multituberculate mammal from South America

We describe a Cretaceous ?cimolodontan multituberculate p4 from South America, for which we erect the new genus and species Argentodites coloniensis. This new taxon is represented by an isolated ?left p4 from the Upper Cretaceous (?Campanian or Maastrichtian) La Colonia Formation of Patagonia (Fig. 1). It has a strongly convex anterior margin and prismatic enamel, which attest to its cimolodontan nature, while the previously known p4 (MACN−RN 975) from the Late Cretaceous Los Alamitos Formation is roughly rectangular, suggesting “plagiaulacidan” affinity. The presence of normal prismatic enamel in Argentodites suggests similarities to Ptilodontoidea. However, it differs from the Late Cretaceous and Paleocene Laurasian cimolodontans (including Ptilodontoidea) in having a long, straight posterior margin, a nearly straight dorsal margin, characteristic of some “Plagiaulacida”, and in having the lingual side close to the mirror image of the labial side, the character that poses difficulties in establishing whether it is a right or left tooth. Because of these differences we assign Argentodites to ?Cimolodonta, tentatively only, superfamily and family incertae sedis