Fabiana María Martin

Revising the recent evolutionary history of equids using ancient DNA

The rich fossil record of the family Equidae (Mammalia: Perissodactyla) over the past 55 MY has made it an icon for the patterns and processes of macroevolution. Despite this, many aspects of equid phylogenetic relationships and taxonomy remain unresolved. Recent genetic analyses of extinct equids have revealed unexpected evolutionary patterns and a need for major revisions at the generic, subgeneric, and species levels. To investigate this issue we examine 35 ancient equid specimens from four geographic regions (South America, Europe, Southwest Asia, and South Africa), of which 22 delivered 87–688 bp of reproducible aDNA mitochondrial sequence. Phylogenetic analyses support a major revision of the recent evolutionary history of equids and reveal two new species, a South American hippidion and a descendant of a basal lineage potentially related to Middle Pleistocene equids. Sequences from specimens assigned to the giant extinct Cape zebra, Equus capensis, formed a separate clade within the modern plain zebra species, a phenotypicically plastic group that also included the extinct quagga. In addition, we revise the currently recognized extinction times for two hemione-related equid groups. However, it is apparent that the current dataset cannot solve all of the taxonomic and phylogenetic questions relevant to the evolution of Equus. In light of these findings, we propose a rapid DNA barcoding approach to evaluate the taxonomic status of the many Late Pleistocene fossil Equidae species that have been described from purely morphological analyses.

TAFONOMÍA DE LA INTERACCIÓN ENTRE PUMAS Y GUANACOS EN EL PARQUE NACIONAL TORRES DEL PAINE, CHILE

A taphonomic study of the interaction between pumas and guanacos at Torres del Paine National Park is presented. Previous biological studies, transects and longitudinal observations on carcasses resulting from puma predation were used to attain this goal. Carnivore marks, disarticulation, burial and other markers were recorded in different visits to the carcasses. The archaeological relevance of this observations is fi nally discussed.

Synergistic roles of climate warming and human occupation in Patagonian megafaunal extinctions during the Last Deglaciation

Patagonian megafaunal extinctions reveal synergistic roles of climate change and human impacts. The causes of Late Pleistocene megafaunal extinctions (60,000 to 11,650 years ago, hereafter 60 to 11.65 ka) remain contentious, with major phases coinciding with both human arrival and climate change around the world. The Americas provide a unique opportunity to disentangle these factors as human colonization took place over a narrow time frame (~15 to 14.6 ka) but during contrasting temperature trends across each continent. Unfortunately, limited data sets in South America have so far precluded detailed comparison. We analyze genetic and radiocarbon data from 89 and 71 Patagonian megafaunal bones, respectively, more than doubling the high-quality Pleistocene megafaunal radiocarbon data sets from the region. We identify a narrow megafaunal extinction phase 12,280 ± 110 years ago, some 1 to 3 thousand years after initial human presence in the area. Although humans arrived immediately prior to a cold phase, the Antarctic Cold Reversal stadial, megafaunal extinctions did not occur until the stadial finished and the subsequent warming phase commenced some 1 to 3 thousand years later. The increased resolution provided by the Patagonian material reveals that the sequence of climate and extinction events in North and South America were temporally inverted, but in both cases, megafaunal extinctions did not occur until human presence and climate warming coincided. Overall, metapopulation processes involving subpopulation connectivity on a continental scale appear to have been critical for megafaunal species survival of both climate change and human impacts.

Mitochondrial genomes reveal the extinct Hippidion as an outgroup to all living equids

Hippidions were equids with very distinctive anatomical features. They lived in South America 2.5 million years ago (Ma) until their extinction approximately 10 000 years ago. The evolutionary origin of the three known Hippidion morphospecies is still disputed. Based on palaeontological data, Hippidion could have diverged from the lineage leading to modern equids before 10 Ma. In contrast, a much later divergence date, with Hippidion nesting within modern equids, was indicated by partial ancient mitochondrial DNA sequences. Here, we characterized eight Hippidion complete mitochondrial genomes at 3.4–386.3-fold coverage using target-enrichment capture and next-generation sequencing. Our dataset reveals that the two morphospecies sequenced (H. saldiasi and H. principale) formed a monophyletic clade, basal to extant and extinct Equus lineages. This contrasts with previous genetic analyses and supports Hippidion as a distinct genus, in agreement with palaeontological models. We date the Hippidion split from Equus at 5.6–6.5 Ma, suggesting an early divergence in North America prior to the colonization of South America, after the formation of the Panamanian Isthmus 3.5 Ma and the Great American Biotic Interchange.

Ground sloths and humans in southern Fuego-Patagonia: taphonomy and archaeology

Abstract An evaluation of Late Pleistocene interactions between ground sloths and humans in the Fuego-Patagonia of Chile and Argentina is presented. Aspects of ground sloth taphonomy are explored, particularly the difficulties of using cut-mark and breakage evidence to recognize human exploitation. Selective transport of large animal bones is also reviewed in regards to its use as a marker of human exploitation of ground sloths. An evaluation of the relevant archaeological and paleontological records for the individual taxon Mylodon sp. is presented. It is concluded that there is little to no evidence for active human hunting of ground sloths and that scavenging is the only form of interaction that can be defended.

Ancient mitochondrial DNA reveals convergent evolution of giant short-faced bears (Tremarctinae) in North and South America

The Tremarctinae are a subfamily of bears endemic to the New World, including two of the largest terrestrial mammalian carnivores that have ever lived: the giant, short-faced bears Arctodus simus from North America and Arctotherium angustidens from South America (greater than or equal to 1000 kg). Arctotherium angustidens became extinct during the Early Pleistocene, whereas Arctodus simus went extinct at the very end of the Pleistocene. The only living tremarctine is the spectacled bear (Tremarctos ornatus), a largely herbivorous bear that is today only found in South America. The relationships among the spectacled bears (Tremarctos), South American short-faced bears (Arctotherium) and North American short-faced bears (Arctodus) remain uncertain. In this study, we sequenced a mitochondrial genome from an Arctotherium femur preserved in a Chilean cave. Our molecular phylogenetic analyses revealed that the South American short-faced bears were more closely related to the extant South American spectacled bear than to the North American short-faced bears. This result suggests striking convergent evolution of giant forms in the two groups of short-faced bears (Arctodus and Arctotherium), potentially as an adaptation to dominate competition for megafaunal carcasses.

EXPLORANDO LA VARIABILIDAD DEL REGISTRO ARQUEOLÓGICO Y TAFONÓMICO EN PALI-AIKE (CHILE) A TRAVÉS DE LA BÚSQUEDA DE REGISTROS PLEISTOCENOS A CIELO ABIERTO

The search design and preliminary results of a study focused in evaluating the existence of open air fi ni-Pleistocene sites or partially exposed places, but scarcely explored by archaeologists, in the Pali- Aike Volcanic Zone, Chile, is presented. This research was oriented towards humid environments of rivers Chico and Gallegos Chico, as much as to dry locations in old scoria locations and volcanic features. Evidence retrieved indicates the existence of mechanisms that work as bone collector tramps in both environments, nevertheless, the chronology of these fi ndings is restricted - for the moment - to Holocene times.

PRESENCIA DE RHEIDAE EN TIERRA DEL FUEGO DURANTE LA TRANSICIÓN PLEISTOCENO-HOLOCENO. IMPLICANCIAS BIOGEOGRÁFICAS Y PALEOECOLÓGICAS

*** ABSTRACT Preliminary information related with a taxon-date of 9.960 ± 50 years BP for Rheidae will be introduced in this paper. This date was obtained on a Rheidae first phalanx from the Tres Arroyos 1 site, north of Tierra del Fuego, Chile. Biogeographical, palaeoecological and archaeological implications are discussed.

First Record of Smilodon Lund (Felidae, Machairodontinae) in Tierra del Fuego Island (Chile)

In this contribution we describe the first record of Smilodon for Tierra del Fuego Island, and discuss its relevance.