Influence of Tertiary paleoenvironmental changes on the diversification of South American mammals: a relaxed molecular clock study within xenarthrans

BACKGROUND: Comparative genomic data among organisms allow the reconstruction of their phylogenies and evolutionary time scales. Molecular timings have been recently used to suggest that environmental global change have shaped the evolutionary history of diverse terrestrial organisms. Living xenarthrans (armadillos, anteaters and sloths) constitute an ideal model for studying the influence of past environmental changes on species diversification. Indeed, extant xenarthran species are relicts from an evolutionary radiation enhanced by their isolation in South America during the Tertiary era, a period for which major climate variations and tectonic events are relatively well documented. RESULTS: We applied a Bayesian approach to three nuclear genes in order to relax the molecular clock assumption while accounting for differences in evolutionary dynamics among genes and incorporating paleontological uncertainties. We obtained a molecular time scale for the evolution of extant xenarthrans and other placental mammals. Divergence time estimates provide substantial evidence for contemporaneous diversification events among independent xenarthran lineages. This correlated pattern of diversification might possibly relate to major environmental changes that occurred in South America during the Cenozoic. CONCLUSIONS: The observed synchronicity between planetary and biological events suggests that global change played a crucial role in shaping the evolutionary history of extant xenarthrans. Our findings open ways to test this hypothesis further in other South American mammalian endemics like hystricognath rodents, platyrrhine primates, and didelphid marsupials

Sobre los objetivos y resultados de la expedición paleontológica de Handel T. Martin (1903-04) a la Formación Santa Cruz en Patagonia austral

Between January and June 1904, Handel T. Martin (1862-1931), of the University of Kansas (KU), collected fossil vertebrates from the Early Miocene Santa Cruz Formation along the Río Gallegos and the Atlantic Coast of Patagonia, as his own private initiative. In his account of the expedition, Martin stated that when he and his companion, arrived in Buenos Aires, they visited Florentino Ameghino at the Museo Nacional. Martin’s album of photographs shows that he also visited the Museo de La Plata and Ameghino’s home in La Plata. Before heading to Patagonia, Martin assembled his equipment in Bahía Blanca, where his brother had settled. It is not clear if Martin collected a total of 235 or 395 specimens. Clearly, his main goal was to collect fossils to sell, as many specimens were later sold to different institutions in the United States and Europe by Martin himself and through Robert Ferris Damon, a well-known fossil and mineral trader of the time. To date, we have identified only about 170 specimens in formal collections. A large part of the collection – at least 130 of the choicest specimens – remained at KU, which constitutes one of the largest collections of Santacrucian vertebrates outside Argentina (in addition to the ones in the Yale Peabody Museum in New Haven, the Field Museum in Chicago, and the American Museum in New York). Although the collection at KU is largely neglected by paleontologists and has seldom been studied, it contains a good representation of the Santacrucian fauna, with many fine specimens.Entre enero y junio de 1904, Handel T. Martin (1862-1931), de la Universidad de Kansas (KU), colectó vertebrados fósiles de la Formación Santa Cruz (Mioceno temprano) a lo largo del Río Gallegos y la costa atlántica de Patagonia, como una iniciativa privada de Martin. En reporte de la expedición, Martin afirmó que cuando él y su compañero llegaron a Buenos Aires, visitaron a Florentino Ameghino en el (entonces) Museo Nacional. Su álbum de fotografías muestra que también visitó el Museo de La Plata y la casa de Ameghino en La Plata. Antes de dirigirse a la Patagonia, Martin organizó su equipo en Bahía Blanca, donde su hermano se había establecido. No hay certeza de si Martin recogió un total de 235 o 395 ejemplares. Claramente, su principal objetivo fue recoger fósiles para comercializar. Muchos especímenes fueron vendidos a instituciones en los Estados Unidos y Europa por Martin y Robert Ferris Damon, un comerciante de fósiles y minerales. Se han identificado cerca de 170 especímenes en colecciones formales. Gran parte de la colección -unos 130 de los mejores ejemplares- se mantuvo en KU, constituyendo una de las mayores colecciones de vertebrados santacrucenses fuera de Argentina (además de las del Museo Peabody de Yale en New Haven, el Museo Field de Chicago y el Museo Americano de Nueva York). Aunque la colección en KU es en gran medida ignorada por los paleontólogos y poco estudiada, contiene una buena representación de la fauna santacrucenses, con muchos ejemplares de calidad.Facultad de Ciencias Naturales y Muse

The record of the typothere Pachyrukhos (Mammalia, Notoungulata) and the Chinchillid Prolagostomus (Mammalia, Rodentia) in the Santa Cruz Formation (early-middle Miocene) south to the Río Coyle, Patagonia, Argentina

The continental early–middle Miocene Santa Cruz Formation (SCF) from Patagonia is one of the most important stratigraphic units of southern South America in terms of the terrestrial Neogene record. Its fossil content was pivotal for establishing the succession of Cenozoic faunas from Patagonia and formed the basis of the Santacrucian South American Land Mammal Age. Despite the updated knowledge recently achieved, the stratigraphic distribution of many taxa within the SCF remains to be clarified. That is the case with the typothere notoungulate Pachyrukhos and the chinchillid rodent Prolagostomus. New information on the stratigraphy of the SCF along the north bank of the Río Gallegos and Cabo Buen Tiempo (Santa Cruz Province), together with a detailed analysis of the provenance information of the specimens in the principal old museum collections, sheds light on the record of these taxa south to Río Coyle. Our results show that the first recorded occurrence of both taxa in the area was between ~17 Ma and 17.41 Ma, restricted to the upper part of the SCF, including the upper part of the Estancia La Costa Member at Cañadón Las Totoras-Monte Tigre, and the superimposed Estancia La Angelina Member along the Río Gallegos and Cabo Buen Tiempo. Their presence suggests a trend to aridification in the upper part of the SCF south to the Río Coyle. These results are consistent with recent information obtained from other locations of the SCF north to the Río Coyle.La Formación Santa Cruz (FSC; Mioceno temprano–medio de Patagonia) es una de las unidades estratigráficas más importantes de América del Sur austral por su registro del Neógeno terrestre. Su contenido fósil fue fundamental para el establecimiento de la sucesión de faunas del Cenozoico de Patagonia y constituyó la base de la Edad Mamífero Santacrucense de América del Sur. A pesar de la reciente actualización de su conocimiento, la distribución estratigráfica de muchos taxones dentro de la FSC aún no se ha esclarecido. Tal es el caso del notoungulado tipoterio Pachyrukhos y del roedor chinchíllido Prolagostomus. Nueva información sobre la estratigrafía de la FSC en la margen norte del Río Gallegos y en Cabo Buen Tiempo y el análisis de la procedencia de ejemplares en colecciones de museos permitieron esclarecer el registro de esos taxones al sur del Río Coyle. Nuestros resultados indican que el primer registro de ambos taxones en el área sería entre ~17 Ma y 17,41 Ma, restringidos a la parte superior de la FSC, incluyendo la sección más alta del Miembro Estancia La Costa, en Cañadón Las Totoras-Monte Tigre, y el suprayacente Miembro Estancia La Angelina a lo largo del Río Gallegos y en Cabo Buen Tiempo. Su presencia sugiere una tendencia a la aridificación en la parte superior de la FSC al sur del Río Coyle. Estos resultados son consistentes con información reciente de otras localidades de la FSC al norte del Río Coyle.Fil: Vizcaíno, Sergio Fabián. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Paleontología Vertebrados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; ArgentinaFil: Bargo, María Susana. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Paleontología Vertebrados; Argentina. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas; ArgentinaFil: Kay, Richard F.. University of Duke; Estados UnidosFil: Raigemborn, María Sol. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones Geológicas. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Centro de Investigaciones Geológicas; Argentin

Evolution of body size in anteaters and sloths (Xenarthra, Pilosa): phylogeny, metabolism, diet and substrate preferences

Pilosa include anteaters (Vermilingua) and sloths (Folivora). Modern tree sloths are represented by two genera, Bradypus and Choloepus (both around 4–6 kg), whereas the fossil record is very diverse, with approximately 90 genera ranging in age from the Oligocene to the early Holocene. Fossil sloths include four main clades, Megalonychidae, Megatheriidae, Nothrotheriidae, and Mylodontidae, ranging in size from tens of kilograms to several tons. Modern Vermilingua are represented by three genera, Cyclopes, Tamandua and Myrmecophaga, with a size range from 0.25 kg to about 30 kg, and their fossil record is scarce and fragmentary. The dependence of the body size on phylogenetic pattern of Pilosa is analysed here, according to current cladistic hypotheses. Orthonormal decomposition analysis and Abouheif C-mean were performed. Statistics were significantly different from the null-hypothesis, supporting the hypothesis that body size variation correlates with the phylogenetic pattern. Most of the correlation is concentrated within Vermilingua, and less within Mylodontidae, Megatheriidae, Nothrotheriidae and Megalonychidae. Influence of basal metabolic rate (BMR), dietary habits and substrate preference is discussed. In anteaters, specialised insectivory is proposed as the primary constraint on body size evolution. In the case of sloths, mylodontids, megatheriids and nothrotheriids show increasing body size through time; whereas megalonychids retain a wider diversity of sizes. Interplay between BMR and dietary habits appears to be the main factor in shaping evolution of sloth body size.Facultad de Ciencias Naturales y Muse

On the objectives and results of the Handel T. Martin paleontological expedition (1903-04) to the Santa Cruz Formation in southern Patagonia

Entre enero y junio de 1904, Handel T. Martin (1862-1931), de la Universidad de Kansas (KU), colectó vertebrados fósiles de la Formación Santa Cruz (Mioceno temprano) a lo largo del Río Gallegos y la costa atlántica de Patagonia, como una iniciativa privada de Martin. En reporte de la expedición, Martin afirmó que cuando él y su compañero llegaron a Buenos Aires, visitaron a Florentino Ameghino en el (entonces) Museo Nacional. Su álbum de fotografías muestra que también visitó el Museo de La Plata y la casa de Ameghino en La Plata. Antes de dirigirse a la Patagonia, Martin organizó su equipo en Bahía Blanca, donde su hermano se había establecido. No hay certeza de si Martin recogió un total de 235 o 395 ejemplares. Claramente, su principal objetivo fue recoger fósiles para comercializar. Muchos especímenes fueron vendidos a instituciones en los Estados Unidos y Europa por Martin y Robert Ferris Damon, un comerciante de fósiles y minerales. Se han identificado cerca de 170 especímenes en colecciones formales. Gran parte de la colección - unos 130 de los mejores ejemplares - se mantuvo en KU, constituyendo una de las mayores colecciones de vertebrados santacrucenses fuera de Argentina (además de las del Museo Peabody de Yale en New Haven, el Museo Field de Chicago y el Museo Americano de Nueva York). Aunque la colección en KU es en gran medida ignorada por los paleontólogos y poco estudiada, contiene una buena representación de la fauna santacrucenses, con muchos ejemplares de calidad.Between January and June 1904, Handel T. Martin (1862-1931), University of Kansas (KU), collected fossil vertebrates from the Early Miocene Santa Cruz Formation along the Río Gallegos and the Atlantic Coast of Patagonia, as Martin’s private initiative. In the account of the expedition, Martin stated that when he and his companion, arrived in Buenos Aires, they visited Florentino Ameghino at the Museo Nacional. His album of photographs shows that he also visited the Museo de La Plata and Ameghino’s home in La Plata. Before heading to Patagonia, Martin assembled his equipment in Bahía Blanca, where his brother had settled. It is not clear if Martin collected a total of 235 or 395 specimens. Clearly, his main goal was to collect fossils to sell, as many specimens were later sold to different institutions in the United States and Europe by Martin by himself and through Robert Ferris Damon, a well-known fossil and mineral trader of the time. To date, we have identified only about 170 specimens in formal collections. A large part of the collection – at least 130 of the choicest specimens – remained at KU, which constitutes one of the largest collections of santacrucian vertebrates outside Argentina (in addition to the ones in the Yale Peabody Museum in New Haven, the Field Museum in Chicago, and the American Museum in New York). Although the collection at KU is largely neglected by paleontologists and has seldom been studied, it contains a good representation of the Santacrucian fauna, with many fine specimens

First Miocene record of Akaniaceae in Patagonia (Argentina): a fossil wood from the early Miocene Santa Cruz formation and its palaeobiogeographical Implications

Today, Akaniaceae are confined to south-eastern Queensland and north-eastern New South Wales (Australia), southeastern China and northern Vietnam. Akanioxylon santacrucensis gen. and sp. nov. is described as the first fossil wood of Akaniaceae from the early Miocene Santa Cruz Formation (c. 18–16 Ma; Burdigalian) on the Atlantic coast of Santa Cruz Province, Argentina. The diagnostic features are growth rings inconspicuous, with most latewood vessels only slightly narrower than earlywood vessels; diffuse porous wood; mainly solitary vessels, occasionally radial or tangential multiples and clusters; mainly simple, occasionally reticulate and rarely scalariform with many interconnections between bars perforation plates; bordered, minute to small intervessel pits; axial parenchyma scanty paratracheal and apotracheal diffuse; vessel-ray parenchyma pits with much reduced borders to apparently simple; vessel-axial parenchyma pits scalariform or transitional; mainly multiseriate (four to six cells wide) and rare uniseriate rays, heterocellular, occasionally crystals in ray cells; septate and non-septate fibres with simple to minutely bordered pits. These features resemble the extant Akania and Bretschneidera. The eco-anatomical analysis suggests that this fossil wood grew under temperate to warm-temperate and semi-arid climatic conditions. This record of Akania/Bretschneidera-like wood in South America reinforces the existence of an old relationship with the Australasia flora. The discovery of Akaniaceae in the Santa Cruz Formation extends the record of the taxon in South America c. 30 Ma and 10°S in latitude and suggests that the family was widespread in Patagonia as a component of forests developed in a frost-free humid biome in South American at mid to high latitudes.Facultad de Ciencias Naturales y Muse

Fossil localities of the Santa Cruz Formation (Early Miocene, Patagonia, Argentina) prospected by Carlos Ameghino in 1887 revisited and the location of the Notohippidian

Between January and September of 1887 Carlos Ameghino carried out his first geologic and paleontological expedition to the Río Santa Cruz, Patagonia. Based on the fossils and geologic information compiled, in 1887 and 1889, Florentino Ameghino named more than 120 new species of extinct mammals and his Formación Santacruceña and Piso Santacruceño (Santacrucian stage). Data published by both brothers state that the specimens were collected in outcrops by the Río Santa Cruz, between 90 and 200 km west of its mouth. However, information in the posthumously published letters and Travel Diary of C. Ameghino allows us to recognize a fourth locality, Río Bote, at about 50 km further southwest. In 1900, 1902, F. Ameghino divided the Piso Santacruceño in a younger étage Santacruzienne and older étage Notohippidéen, restricting the geographical distribution of the latter to Kar Aiken locality, northeast of Lago Argentino. However, 15 of the 54 species that F. Ameghino listed as exclusively Notohippidian stage already had been named on specimens collected South to the Río Santa Cruz in 1887, two year prior to C. Ameghino's first visit to Kar Aiken. Based on historical information and several expeditions to the Río Santa Cruz and its environs, in this contribution we establish the geographical locations of the 1887 localities, formalize their names, evaluate the stratigraphic position of the fossil-bearing levels, and analyze the geographic extension of the Notohippidian, inferring that Río Bote is where C. Ameghino first collected species that came to define the Notohippidian.Facultad de Ciencias Naturales y Muse

Sobre los objetivos y resultados de la expedición paleontológica de Handel T. Martin (1903-04) a la Formación Santa Cruz en Patagonia austral

Between January and June 1904, Handel T. Martin (1862-1931), of the University of Kansas (KU), collected fossil vertebrates from the Early Miocene Santa Cruz Formation along the Río Gallegos and the Atlantic Coast of Patagonia, as his own private initiative. In his account of the expedition, Martin stated that when he and his companion, arrived in Buenos Aires, they visited Florentino Ameghino at the Museo Nacional. Martin’s album of photographs shows that he also visited the Museo de La Plata and Ameghino’s home in La Plata. Before heading to Patagonia, Martin assembled his equipment in Bahía Blanca, where his brother had settled. It is not clear if Martin collected a total of 235 or 395 specimens. Clearly, his main goal was to collect fossils to sell, as many specimens were later sold to different institutions in the United States and Europe by Martin himself and through Robert Ferris Damon, a well-known fossil and mineral trader of the time. To date, we have identified only about 170 specimens in formal collections. A large part of the collection – at least 130 of the choicest specimens – remained at KU, which constitutes one of the largest collections of Santacrucian vertebrates outside Argentina (in addition to the ones in the Yale Peabody Museum in New Haven, the Field Museum in Chicago, and the American Museum in New York). Although the collection at KU is largely neglected by paleontologists and has seldom been studied, it contains a good representation of the Santacrucian fauna, with many fine specimens.Entre enero y junio de 1904, Handel T. Martin (1862-1931), de la Universidad de Kansas (KU), colectó vertebrados fósiles de la Formación Santa Cruz (Mioceno temprano) a lo largo del Río Gallegos y la costa atlántica de Patagonia, como una iniciativa privada de Martin. En reporte de la expedición, Martin afirmó que cuando él y su compañero llegaron a Buenos Aires, visitaron a Florentino Ameghino en el (entonces) Museo Nacional. Su álbum de fotografías muestra que también visitó el Museo de La Plata y la casa de Ameghino en La Plata. Antes de dirigirse a la Patagonia, Martin organizó su equipo en Bahía Blanca, donde su hermano se había establecido. No hay certeza de si Martin recogió un total de 235 o 395 ejemplares. Claramente, su principal objetivo fue recoger fósiles para comercializar. Muchos especímenes fueron vendidos a instituciones en los Estados Unidos y Europa por Martin y Robert Ferris Damon, un comerciante de fósiles y minerales. Se han identificado cerca de 170 especímenes en colecciones formales. Gran parte de la colección -unos 130 de los mejores ejemplares- se mantuvo en KU, constituyendo una de las mayores colecciones de vertebrados santacrucenses fuera de Argentina (además de las del Museo Peabody de Yale en New Haven, el Museo Field de Chicago y el Museo Americano de Nueva York). Aunque la colección en KU es en gran medida ignorada por los paleontólogos y poco estudiada, contiene una buena representación de la fauna santacrucenses, con muchos ejemplares de calidad.Facultad de Ciencias Naturales y Muse

Herramientas conceptuales y metodológicas para el estudio de la morfología y paleobiología de vertebrados

La paleobiología reconstruye la historia de vida de taxones extintos. Una forma de estudiar la paleobiología de vertebrados es asumir que existe una estrecha relación entre forma y función, de manera que la última puede inferirse a partir de la primera (principio de correlación forma-función). Este enfoque integrador combina la biología de vertebrados actuales (morfología, filogenia, desarrollo e historia de vida, comportamiento, metabolismo y fisiología, etc.), la física e ingeniería (biomecánica, física de materiales), la química (análisis isotópicos de tejidos animales) y las matemáticas y estadísticas (modelado, métodos probabilísticos o permutacionales, etc.), entre otros aspectos y disciplinas. Un protocolo básico para estudios paleobiológicos basado en la correlación forma-función identifica tres atributos biológicos esenciales para cada taxón: tamaño corporal, preferencia y uso de sustrato y alimentación. Las herramientas metodológicas más generalizadas son la morfología funcional, la biomecánica y la ecomorfología. Nuestro grupo ha estudiado mayormente las implicaciones funcionales del esqueleto y la morfología dental y sus consecuencias sobre el rol biológico que los vertebrados extintos de América del Sur desempeñaron en sus paleoecosistemas. El estudio de otros rasgos, como la audición y la visión, mejorará la discriminación de nichos en ecosistemas pasados

Evolution of body size in anteaters and sloths (Xenarthra, Pilosa): phylogeny, metabolism, diet and substrate preferences

Pilosa include anteaters (Vermilingua) and sloths (Folivora). Modern tree sloths are represented by two genera, Bradypus and Choloepus (both around 4–6 kg), whereas the fossil record is very diverse, with approximately 90 genera ranging in age from the Oligocene to the early Holocene. Fossil sloths include four main clades, Megalonychidae, Megatheriidae, Nothrotheriidae, and Mylodontidae, ranging in size from tens of kilograms to several tons. Modern Vermilingua are represented by three genera, Cyclopes, Tamandua and Myrmecophaga, with a size range from 0.25 kg to about 30 kg, and their fossil record is scarce and fragmentary. The dependence of the body size on phylogenetic pattern of Pilosa is analysed here, according to current cladistic hypotheses. Orthonormal decomposition analysis and Abouheif C-mean were performed. Statistics were significantly different from the null-hypothesis, supporting the hypothesis that body size variation correlates with the phylogenetic pattern. Most of the correlation is concentrated within Vermilingua, and less within Mylodontidae, Megatheriidae, Nothrotheriidae and Megalonychidae. Influence of basal metabolic rate (BMR), dietary habits and substrate preference is discussed. In anteaters, specialised insectivory is proposed as the primary constraint on body size evolution. In the case of sloths, mylodontids, megatheriids and nothrotheriids show increasing body size through time; whereas megalonychids retain a wider diversity of sizes. Interplay between BMR and dietary habits appears to be the main factor in shaping evolution of sloth body size.Facultad de Ciencias Naturales y Muse