Scientists
today announced the discovery of a new species of pterosaur from the
Patagonia region of South America. The cranial remains were in an
excellent state of preservation and belonged to a new species of
pterosaur from the Early Jurassic. The researchers have named this new
species 'Allkauren koi' from the native Tehuelche word 'all' for
'brain', and 'karuen' for 'ancient'.
Pterosaurs are an
extinct group of flying reptiles that lived during most of the Mesozoic
Era. This group had an extraordinary adaptation to flight, including
pneumatic bones to lighten its weight, and an elongated digit supporting
a wing membrane. However, pterosaur neuroanatomy is known from only a
few three dimensionally preserved remains and, until now, there was no
information on the intermediate forms. This study therefore provides new
information on the origin, tempo and mode of evolution in this
particular group of flying reptiles.
The fossil of
Allkaruen koi was found in northern central Chubut Province, Patagonia
Argentina and the remains included a superbly preserved and uncrushed
braincase. In order to study the neurocranial anatomy, researchers used
computed tomography to observe, in three dimensions, the cranial
endocast and the inner ear. Subsequently, a comprehensive phylogenetic
analysis of the group was performed, including these cranial data and
other anatomical features. "Allkaruen, from the middle lower jurassic
limit, shows an intermediate state in the brain evolution of pterosaurs
and their adaptations to the aerial environment", said Dr Diego Pol, who
is part of the research team. "As a result, this research makes an
important contribution to the understanding of the evolution of all of
pterosaurs."
An Unusual New Theropod with a Didactyl Manus from the Upper Cretaceous of Patagonia, Argentina
Authors:
Apesteguía et al
Abstract:
Background
Late Cretaceous terrestrial strata of the Neuquén Basin, northern Patagonia, Argentina have yielded a rich fauna of dinosaurs and other vertebrates. The diversity of saurischian dinosaurs is particularly high, especially in the late Cenomanian-early Turonian Huincul Formation, which has yielded specimens of rebacchisaurid and titanosaurian sauropods, and abelisaurid and carcharodontosaurid theropods. Continued sampling is adding to the known vertebrate diversity of this unit.
Methodology/ Principal Findings
A new, partially articulated mid-sized theropod was found in rocks from the Huincul Formation. It exhibits a unique combination of traits that distinguish it from other known theropods justifying erection of a new taxon, Gualicho shinyae gen. et sp. nov. Gualicho possesses a didactyl manus with the third digit reduced to a metacarpal splint reminiscent of tyrannosaurids, but both phylogenetic and multivariate analyses indicate that didactyly is convergent in these groups. Derived characters of the scapula, femur, and fibula supports the new theropod as the sister taxon of the nearly coeval African theropod Deltadromeus and as a neovenatorid carcharodontosaurian. A number of these features are independently present in ceratosaurs, and Gualicho exhibits an unusual mosaic of ceratosaurian and tetanuran synapomorphies distributed throughout the skeleton.
Conclusions/ Significance
Gualicho shinyae gen. et sp. nov. increases the known theropod diversity of the Huincul Formation and also represents the first likely neovenatorid from this unit. It is the most basal tetatanuran to exhibit common patterns of digit III reduction that evolved independently in a number of other tetanuran lineages. A close relationship with Deltadromaeus from the Kem Kem beds of Niger adds to the already considerable biogeographic similarity between the Huincul Formation and coeval rock units in North Africa.
pop sci write up.
Reappraisal of the Early Cretaceous sauropod dinosaur Amargatitanis macni (Apesteguía, 2007), from northwestern Patagonia, Argentina
Authors:
Gallina et al
Abstract:
Amargatitanis macni Apesteguía, 2007 was described as a purported titanosaur sauropod. That referral is significant because Amargatitanis would represent one of the oldest known members of Titanosauria. However, this referral and even the systematic validity of the taxon were questioned. Here, all the available remains of the taxon are evaluated including a description of unpublished elements. The identity of the type material is discussed based on a first-hand examination of the specimens and evaluation of the original field notes as reliable evidence for bone association. The original holotype of Amargatitanis is a chimaera, as pointed out by previous authors. Herein a new, modified holotype for Amargatitanis is proposed. This analysis presents a revised diagnosis for Amargatitanis macni as a valid taxon, and description of unpublished material clarifies the anatomy of this sauropod dinosaur. The inclusion of Amargatitanis macni in an updated phylogenetic analysis revealed the presence of a second species of the family Dicraeosauridae in the La Amarga Formation, suggesting that, at present, there is no record of titanosaur body fossils in Patagonia prior to Cenomanian times.
On The existence of non-microbiotherian Australidelphian marsupials (Diprotodontia) in the Eocene of Patagonia
Authors:
Lorente et al
Abstract:
A diverse assemblage of extinct mammals of early–middle Eocene age (Ypresian–Lutetian boundary) come from the Patagonian localities of La Barda and Laguna Fría around Paso del Sapo in northwestern Chubut Province (Argentina). Metatherians are well represented, mostly by dental remains of ‘Didelphimorphia’, Paucituberculata, Sparassodonta, Microbiotheria, and Polydolopimorphia. Here we analyse three calcanea and one astragalus referable to the same, indeterminate taxon, from La Barda, showing the fusion of their ectal and sustentacular facets. This facet arrangement characterizes the Australidelphia, a marsupial clade represented by Microbiotheria from South America and Antarctica, plus all Australasian lineages. Other australidelphian features shown by these tarsals include: in the calcanea, a reduced peroneal process and a tripartite cuboid facet; in the astragalus, a round, very small astragalar head in relation to the body; a convex trochlea with a half for the tibia and half, in slightly lower position, for the fibula. Their size and other anatomical features suggest that the new tarsals cannot be referred to the Microbiotheria. Phylogenetic analysis suggests that the La Barda taxon lies within the Australidelphia, and that it is either closely related or belongs to, the Diprotodontia. The existence of advanced australidelphians in Patagonia adds further evidence of the close relationship between Patagonia, Antarctica, and Australia during the Late Cretaceous – early Palaeogene.
FIRST GLIMPSE OF THE SILICIFIED HOT SPRING BIOTA FROM A NEW JURASSIC CHERT DEPOSIT IN THE DESEADO MASSIF, PATAGONIA, ARGENTINA
Authors:
Massini et al
Abstract:
Jurassic hot-spring chert deposits in the Deseado Massif, Patagonia, Argentina, have been known for over two decades, but the associated biota has only begun to be documented recently, and thus far only from a small number of localities. Here we report the discovery of a large complex of well-exposed Upper Jurassic epithermal siliceous deposits represented by organic-rich cherts preserved within the geothermal system from La Bajada, Santa Cruz, Argentina. The chert samples analyzed so far contain exceptionally well-preserved, in-situ and transported, tri-dimensionally silicified plants, animals and microorganisms. Plants include equisetaleans (Equisetum thermale), ferns and gymnosperms. Among them, well-preserved in-situ osmundaceous rhizomes in different developmental stages are the dominant component of the taphoflora. Conifers are represented by wood, seeds, leaves and pollen tentatively assigned to the families Araucariaceae and Cheirolepidiaceae. The assemblage also contains vegetative and reproductive structures of fungi, oomycetes, cyanobacteria, algae, testate amoebas, ciliates and numerous remains of unresolved taxonomic affinity. Microorganisms are preserved isolated in the chert matrix or directly associated with plants and other organic remains in mutualistic, parasitic and saprotrophic engagements. Also present are numerous coprolites and arthropod remains that, along with the named microorganisms, are indicative of trophic relationships in the ecosystem. Altogether, this fossil assemblage suggests that distal paleoenvironments within the geothermal system are preserved at La Bajada. The diversity, abundance, and exceptional preservation of fossils in the La Bajada ecosystem provides a unique window into the geological past that offers a substantial contribution to the reconstruction of middle Mesozoic terrestrial ecosystems.
Past population dynamics in Northwest Patagonia: An estimation using molecular and radiocarbon data
Authors:
Ivan Perez et al
Abstract:
Studying demographic changes in past human populations is of great interest due to their role in processes of cultural change as well as the biological evolution of populations. Despite this, a general consensus about the most adequate methodological approach to this end is still lacking. Here, a new approach that combines radiocarbon frequency distributions —uncorrected and corrected by taphonomic bias— and demographic curves independently estimated with modern mitochondrial DNA (mtDNA) is used to estimate population size changes in Northwest Patagonia since the Pleistocene–Holocene transition to recent times. Results based on mtDNA sequences suggest a census size of approximately 3000 individuals (with an estimated female effective size of ca. 750 individuals) by the initial peopling of this region around 10,000 years ago. A strong correspondence between curves based on mtDNA data and those based on archaeological radiocarbon dates (n = 251) was obtained after the effect of taphonomic bias was accounted for. The demographic curves indicate that the population size was relatively stable during the earlier Early Holocene and it increased between 7000 and 5000 years ago, reaching a maximum size around 1000 years ago. Then, the population size declined until present time. We conclude that demographic inferences made on the basis of radiocarbon dates are not necessarily biased but this needs to be evaluated with independent evidence in each specific geographical region.
Tithonian age of dinosaur fossils in central Patagonian, Chile: U–Pb SHRIMP geochronology
Authors:
Suárez et al
Abstract:
Three Tithonian concordant U–Pb SHRIMP zircon ages of 148.7 ± 1.4, 147.9 ± 1.5 and 147.0 ± 1.0 from tuffs intercalated in a clastic sedimentary succession with exceptional dinosaur bones including the new taxon Chilesaurus diegosuarezi gen. et sp. nov. exposed in central Chilean Patagonia (ca. 46°30′S) are reported herein. The fossiliferous beds accumulated in a synvolcanic fan delta reaching a shallow marine basin as indicated by glauconite present in some of the beds, and coeval with the beginning of the transgression of the Aysén Basin.
A new Late Cretaceous (late Campanian to early Maastrichtian) wood flora from southern Patagonia
Authors:
Egerton et al
Abstract:
The Cerro Fortaleza Formation, in southernmost Patagonia (Argentina), contains a unique Late Cretaceous (Campanian) flora and fauna. This formation is characterized by lithified fluvial sands, overbank mud deposits, and paleosols deposited in fluvial, fluvial–palustrine, and coastal plain environments from the northeastern margin of the Austral (Magellanes) Basin. The overlying and underlying formations have been dated as Campanian and Maastrichtian, respectively. Therefore, the Cerro Fortaleza Formation putatively falls within the late Campanian–Maastrichtian. This formation is known for its diverse fauna including dinosaurs, fishes, and turtles. Furthermore, poorly preserved leaf impressions from indeterminate conifers and cycads have also been discovered but not yet described.
Fossil wood taxa from the Cerro Fortaleza Formation yields a diverse flora of gymnosperm wood but only two genera of angiosperm wood. Gymnosperm genera identified in this study include Agathoxylon, Planoxylon, Taxodioxylon, Cupressinoxylon, and Podocarpoxylon; and angiosperm genera identified include Hedycaryoxylon and Nothofagoxylon. This is the first record of Planoxylon, Taxodioxylon, Cupressinoxylon, and Hedycaryoxylon from Argentina. Additionally, this is the oldest occurrence of Nothofagoxylon in Argentina. Both the angiosperm and gymnosperm wood samples possess distinct growth rings, providing strong evidence for seasonal growth regimes in the region. All of the wood genera from the Cerro Fortaleza Formation, except Planoxylon, have also been described from Late Cretaceous sediments of the Antarctic Peninsula. Thus, the presence of these taxa in both regions supports Late Cretaceous plant dispersal between them. Despite sharing the same taxa, the floras from the Cerro Fortaleza Formation and the Antarctic Peninsula exhibit strikingly different relative abundances. The ratio of gymnosperm to angiosperm wood in the Cerro Fortaleza Formation is 75:25; whereas coeval floras from the Antarctic Peninsula are ~ 25:75. The floral differences between these locations may be a relict from a widespread older flora that included Antarctica, regional floristic variations or a result of different depositional and/or taphonomic controls in discrete paleoenvironments.
Early Cretaceous palm pollen tetrads from Patagonia, Argentina
Authors:
Martinez et al
Abstract:
Pollen tetrads and monads of spiny pollen grains with close affinities to palms have been found in several localities from the Lower Cretaceous (Barremian-Albian) of the Austral Basin (Magallanes), Patagonia (Argentina). When found dispersed, spiny and zonasulcate pollen grains, are commonly referred to the fossil genus Spinizonocolpites Muller, with close affinities to the extant palm Nypa. The Patagonian specimens were compared with fossil and extant members of the Arecaceae, showing close similarities in shape and sculpture with the primitive members of the subfamily Calamoideae. Nypa produces tetragonal tetrads different from the tetrahedral tetrads of the Spinizonocolpites-type recovered from Patagonia. The specimens were studied with LM and SEM. The polarity, aperture orientation and tetrad type allow segregating the Patagonian grains from the Nypoideae and relating it to the Calamoideae subfamily. These records suggest an antique origin of monocots and a probably initial diversification of calamoid palms during the Early Cretaceous in high latitudes of Gondwana. The presence of palmae during the Early Cretaceous in southern South America suggests a warm and humid climate, similar to that found in present days at tropics.
Aptian–Albian Cupressaceae (sensu stricto) woods from Cañadón Asfalto Basin, Patagonia Argentina
Authors:
Brea et al
Abstract:
This paper describes the first macrofloristic record from Los Adobes Formation (Chubut Group) in Cañadón Asfalto Basin (Patagonia, Chubut Province, Argentina). The studied fossils were recovered from the Aptian–Albian Bardas Coloradas Member, and consist of silicified woods preserved in fluvial channel deposits. One wood shows homocellular rays with smooth radial and tangential walls, diffuse axial parenchyma, tracheid pitting of the abietinoid type and cross-field pitting cupressoid usually ordered in rows and columns indicating placement within Cupressinoxylon hallei Kräusel. This fossil tree resembles some members of the extant Cupressaceae s.s., as Austrocedrus chilensis (D. Don) Pic. Serm. & Bizzarri, Pilgerodendron uviferum (D. Don) Florin, Fitzroya cupressoide (Molina) I. M. Johnst. and Libocedrus plumosa (D. Don) Druce. Due to poor preservation the other fossil wood specimen was assigned to cf. Cupressinoxylon Göppert 1850 nom. cons. prop. This is the first unequivocal record of C. hallei from the Cretaceous of South America and the oldest reliable record of the Callitroideae, indicating that this subfamily was well established since the mid-Cretaceous in the Southern Hemisphere.
Quasi-static Eocene–Oligocene climate in Patagonia promotes slow faunal evolution and mid-Cenozoic global cooling
Authors:
Kohn et al
Abstract:
New local/regional climatic data were compared with floral and faunal records from central Patagonia to investigate how faunas evolve in the context of local and global climates. Oxygen isotope compositions of mammal fossils between c. 43 and 21 Ma suggest a nearly constant mean annual temperature of 16 ± 3 °C, consistent with leaf physiognomic and sea surface studies that imply temperatures of 16–18 °C. Carbon isotopes in tooth enamel track atmospheric δ13C, but with a positive deviation at 27.2 Ma, and a strong negative deviation at 21 Ma. Combined with paleosol characteristics and reconstructed Leaf Area Indices (rLAIs), these trends suggest aridification from 45 Ma (c. 1200 mm/yr) to 43 Ma (c. 450 mm/yr), quasi-constant MAP until at least 31 Ma, and an increase to ~ 800 mm/yr by 21 Ma. Comparable MAP through most of the sequence is consistent with relatively constant floral compositions, rLAI, and leaf physiognomy. Abundance of palms reflects relatively dry-adapted lineages and greater drought tolerance under higher pCO2. Pedogenic carbonate isotopes imply low pCO2 = 430 ± 300 ppmv at the initiation of the Eocene–Oligocene climatic transition. Arid conditions in Patagonia during the late Eocene through Oligocene provided dust to the Southern Ocean, enhancing productivity of silicifiers, drawdown of atmospheric CO2, and protracted global cooling. As the Antarctic Circumpolar Current formed and Earth cooled, wind speeds increased across Patagonia, providing more dust in a positive climate feedback. High tooth crowns (hypsodonty) and ever-growing teeth (hypselodonty) in notoungulates evolved slowly and progressively over 20 Ma after initiation of relatively dry environments through natural selection in response to dust ingestion. A Ratchet evolutionary model may explain protracted evolution of hypsodonty, in which small variations in climate or dust delivery in an otherwise static environment drive small morphological shifts that accumulate slowly over geologic time.
Climate, dust, and fire across the Eocene-Oligocene transition, Patagonia
Authors:
Selkin et al
Abstract:
The Eocene-Oligocene transition (EOT) is typically interpreted as a time of drastic global cooling and drying associated with massive growth of a glacial icecap in Antarctica and the shift to an "icehouse" climate. The effects of this transition on the terrestrial environments, floras, and faunas of the Southern Hemisphere, however, have been unclear. Here we document simultaneous changes in fire regime and plant community in Patagonia, Argentina. Decreases in the concentration of magnetite in loessites from the Eocene-Oligocene Vera Member of the Sarmiento Formation correlate with decreases in the fraction of burnt palm phytoliths as well as more consistently palm-dominated phytolith assemblages. Association of magnetite and burnt palm phytoliths suggests intense wildfires, which appear to have been suppressed for ∼200 k.y. shortly after the EOT. The disappearance of fire-related characteristics near the EOT is possible if changes in regional wind patterns—consistent with observed changes in sediment particle sizes—caused changes in seasonal precipitation. These results imply a more important role for fire in structuring Eocene-Oligocene landscapes than previously thought.
Purranisaurus potens Rusconi, an enigmatic metriorhynchid from the Late Jurassic–Early Cretaceous of the Neuquén Basin
Authors:
Herrera et al
Abstract:
The Tithonian record from northwestern Patagonia (Neuquén Basin) documents a complete succession of lower, middle, and late Tithonian marine reptiles. From the late Tithonian–early Berriasian of Patagonia, three marine crocodyliforms have been recorded: Dakosaurus andiniensis, Cricosaurus araucanensis, and Purranisaurus potens. Although P. potens includes the first metriorhynchid skull described from Patagonia, no detailed description and/or illustrations have been published. Since the mid-20th century, several authors have discussed the validity of P. potens. Recent preparation of the type material allowed a detailed description as well as exploration of its phylogenetic relationships. We consider P. potens as a valid taxon characterized by a unique combination of characters, such as medial and posterolateral processes of the frontal forming an angle of 60°; supratemporal fossae reaching the minimum interorbital distance, with the dorsal margin of the supratemporal arch being slightly concave in lateral view; thin bony lamina projecting from the lateral and medial alveolar margins of the maxilla; occipital surface ventral to occipital condyle parallel to transverse plane of skull; well-developed crest that extends along the entire height of the supraoccipital; and orbital process of the quadrate very conspicuous and acute, horizontal, and without bony attachment. Phylogenetic analysis recovers P. potens as deeply nested within Geosaurini and, contrary to previous proposals, not closely related to ‘Metriorhynchus’ casamiquelai and ‘M.’ westermanni. Internal relationships within Geosaurini are unresolved. Purranisaurus, as a monotypic genus, is restricted to the late Tithonian–early Berriasian.
Muscular Reconstruction and Functional Morphology of the Hind Limb of Santacrucian (Early Miocene) Sloths (Xenarthra, Folivora) of Patagonia
Authors:
Toledo et al
Abstract:
This article presents a morphofunctional analysis of the hind limb of Santacrucian (Early Miocene) sloths from southernmost Patagonia (Argentina). These fossil sloths were mid sized to large animals, ranging from 40 to 120kg, and their postcranial skeleton was markedly different in shape compared to that of extant tree sloths, which vary from 2 to 10kg. The functional anatomy of the hind limb of Santacrucian sloths was compared with that of living xenarthrans (tree sloths, anteaters and armadillos), which involved reconstruction of the hind limb musculature and comparative and qualitative morphofunctional analyses, and hypotheses on the biological role of the hind limb in terms of preferences in substrate, posture and strategies of locomotion were formulated. The hind limb of Santacrucian sloths bears strong resemblances to that of living South American anteaters in stoutness of skeletal elements, form of the characteristics related to muscular and ligamentous attachments, and conservative, pentadactylous strong-clawed pes. The musculature was very well developed, allowing powerful forces, principally in entire limb adduction, crus flexion and extension, pes extension and toe prehension. These functional features, together with those of the forelimb, are congruent with climbing behavior, and support the hypothesis that Santacrucian sloths were good but slow climbing mammals. However, their climbing strategies were limited, owing principally to their comparatively large body size, and they relied to a large extent on their powerful musculature and curved manual and pedal unguals for both moving and standing on the arboreal supports. This article is protected by copyright. All rights reserved.
Bioerosion trace fossils on bones of the Cretaceous South American theropod Buitreraptor gonzalezorum Makovicky, Apesteguía and Agnolín, 2005 (Deinonychosauria)
Authors:
Gianechini et al
Abstract:
The ichnological record provides valuable information on the lifestyle, behaviour, and other palaeobiological and palaeoecological aspects of the biota. Here, we describe an interesting case of bioerosion trace fossils in bones of Buitreraptor gonzalezorum Makovicky, Apesteguía and Agnolín, 2005, a deinonychosaurian theropod from the fossiliferous locality of La Buitrera, Río Negro, Patagonia, Argentina. The trace fossils are morphologically diverse and preserved in a great percentage of the skeleton, including the jaw, vertebrae and limbs. Four main groups of trace fossils have been informally named as Parallel-Edge Furrows, Overlapped Grooves, Punctures and Lined. Parallel-Edge Furrows are in turn subdivided into four subgroups: isolated furrows, parallel pairs, opposed pairs and a combination of parallel and opposed pairs. The bioerosion trace fossils were probably generated by scavenging activities, and the semi-articulated preservation of the skeleton and the small size of each individual trace indicate small-sized tracemakers. Mammals are the main candidates although some traces may have been generated by crocodyliforms and insects such as dermestids and termites. This evidence provides additional information about palaeoenvironmental conditions, taphonomic processes, taxonomic diversity and ecological relationships that characterised this part of northern Patagonia at Early Cretaceous times.
Late Cretaceous reptilian biota of the La Colonia Formation, central Patagonia, Argentina: Occurrences, preservation and paleoenvironments
Authors:
Gasparini et al
Abstract:
Cropping out on the southeastern margin of the Somún Curá Plateau, the La Colonia Formation (Campanian–Maastrichtian) has yielded, over the last several decades, a varied fossil tetrapod fauna (mammals, ophidians, turtles, dinosaurs, plesiosaurs, anurans). For this study several field trips were carried out specifically to recover reptile remains. Three sections, located on the southeastern slope of the Sierra de La Colonia and in the vicinity of Cerro Bayo, Chubut Province (Argentina), were selected for particular attention. The prospected sections are composed of massive, laminated or heterolithic siltstones and claystones, with scarce and thin intercalations of massive, heterolithic o cross-bedded fine sandstones and of fossiliferous conglomerates. The most abundantly recovered reptiles are terrestrial and freshwater turtles, followed by plesiosaurs and dinosaurs. Among the chelonians, more than 16 specimens of Patagoniaemys gasparinae (Meiolaniformes), three specimens of Yaminuechelys aff. Y. gasparinii (Chelidae), and the remains of a new genus of Chelidae were identified. Among the dinosaurs, theropod metatarsal fragments, an incomplete abelisaurid theropod skeleton, sauropod vertebrae, ankylosaur osteoderms and appendicular fragments of hadrosaurs were found. Among the plesiosaurs there are several well preserved elasmosaurids (including two with associated gastroliths) and a polycotylid (Sulcusuchus erraini). Except for the plesiosaurs, all the reptiles are terrestrial or freshwater taxa. However, analysis of the elasmosaurids indicates they are adult specimens of small body size, which could be related to forms that lived in restricted aquatic environments. Likewise, the polycotylid possesses deep rostral and mandibular grooves, and a conspicuous vascularization and/or innervation, that is consistent with the presence of some associated special sensory structures similar to those known in some cetaceans that inhabit modern rivers and estuaries. Sedimentological analysis suggests that deposition would have been mostly in low-energy restricted environments, like muddy plains, marshes and ponds cut by meandering channels, probably in the central mixed-energy zone within an estuary. This interpretation is consistent with the habitat inferred for the recovered reptiles, as well as with associated foraminifers and with the probable origin of gastroliths found associate with the plesiosaurs.
New abelisaurid remains from the Anacleto Formation (Upper Cretaceous), Patagonia, Argentina
Authors:
Gianechini et al
Abstract:
New theropod remains with abelisaurid affinities from the Upper Cretaceous (Anacleto Formation, lower Campanian), NW Patagonia, Argentina, are here described. The specimen (MPCN-PV 69) consists of a partial premaxilla, fragmentary vertebrae, proximal portion of both humeri, distal portion of the pubis, and an incomplete pedal ungual. Characters linking with Abelisauridae are a premaxilla with a subquadrangular body, externally ornamented, and paradental plates with a striated surface; and humerus with bulbous proximal head, conical internal tuberosity, and reduced greater tubercle. The humerus is similar to those of Carnotaurus and Aucasaurus, due to the presence of a bulbous head and a discontinuity between the head and the internal tuberosity, but also differs from both taxa in the more distal location of the greater tubercle with respect to the internal tuberosity. Aucasaurus also comes from Anacleto Formation, but differences in the humeri suggest that MPCN-PV 69 is a different taxon. The phylogenetic analysis performed supports the affiliation to Abelisauridae, but fails to determinate a more precise relationship with others abelisaurids. However, a majority rule consensus of the analysis shows a position within Brachyrostra. Despite being fragmentary, MPCN-PV 69 probably represents a new abelisaurid from the Anacleto Formation, thus increasing the knowledge and diversity of Late Cretaceous South American abelisaurids.
Fire responses to postglacial climate change and human impact in northern Patagonia (41–43°S)
Authors:
Iglesias et al
Abstract:
Forest/steppe boundaries are among the most dynamic ecosystems on Earth and are highly vulnerable to changes in climate and land use. In this study we examine the postglacial history of the Patagonian forest/steppe ecotone (41–43°S) to better understand its sensitivity to past variations in climate, disturbance, and human activity before European colonization. We present regional trends in vegetation and biomass burning, as detected by generalized additive models fitted to seven pollen and charcoal records, and compare the results with other paleoenvironmental data, as well as archeological and ecological information to (i) estimate postglacial fire trends at regional scales, (ii) assess the evolution of climate–vegetation–fire linkages over the last 18,000 calibrated (cal) years B.P., and (iii) evaluate the role of humans in altering pre-European landscapes and fire regimes. Pollen and charcoal data indicate that biomass burning was relatively low during warm/dry steppe-dominated landscapes in the late glacial/Early Holocene transition and increased as more humid conditions favored forest development after ca. 10,000 cal years B.P. Postglacial fire activity was thus limited by fuel availability associated with sparse vegetation cover rather than by suitable climate conditions. In contrast to extensive burning by European settlers, variations in indigenous population densities were not associated with fluctuations in regional or watershed-scale fire occurrence, suggesting that climate–vegetation–fire linkages in northern Patagonia evolved with minimal or very localized human influences before European settlement.
Reconstruction of a fossil forest reveals details of the palaeoecology, palaeoenvironments and climatic conditions in the late Oligocene of South America
Authors:
Brea et al
Abstract:
This research focuses on the three-dimensional reconstruction of an in situ forest based on fossil wood assemblages recovered in the Rancahué Formation (Upper Oligocene), Neuquén, Argentina. Atherospermataceae, Lauraceae, Nothofagaceae, Eucryphiaceae, Cunoniaceae and Myrtaceae specimens are described. The mapping of a forest floor section and in situ tree diameters enabled the estimation of the following palaeoecological quantitative data: tree density, dominance, basal area, biomass, diametric classes, canopy height, and age classes. Palaeoclimatical data was determined on the basis of physiognomic anatomical features using multivariate anatomical analyses. These results were compared with other proxies including Carlquist's index, Coexistence Approach (CA), Nearest Living Relatives (NLRs), and growth-rings analyses. The structural data from the Aluminé forest inferred from these analyses includes: tree density of 463–701 trees/ha, mean height of 15.22 m, dominance of the genus Nothofagoxylon (89.66 m2/ha), total basal area of 158.20 m2/ha, biomass between 43 and 712 tn/ha and mean age of 223 years (specimens between 31 and 700 years old). These results are comparable to those of mature low-to-middle altitude extant forests dominated by Nothofagus and developed under humid-temperate conditions. Based on the NLRs method, the Aluminé forest has a floristic composition similar to the present-day Valdivian forest. The persistence of Nothofagus as the dominant element in temperate rainforests correlates with regimes where large-scale disturbances, such as volcanism and earthquakes are prevalent. The fossil taxa are closely related to the extant Laurelia, Persea, Eucryphia, Nothofagus, Weinmannia, Myrceugenia and Luma. The forest shows intermixed deciduous and evergreen elements, and taxa with shade-intolerance and intermediate shade tolerance. Also, the majority of these taxa need soils with available water. The integrated analysis of multiple sets of proxy data suggests that the late Oligocene forest grew under temperate and humid climate, while the eco-anatomical features and sedimentary data provide information about the environmental stress conditions of its development and the violent causes of burial.
Mesoproterozoic and Paleoproterozoic subcontinental lithospheric mantle domains beneath southern Patagonia: Isotopic evidence for its connection to Africa and Antarctica
Authors:
Mundl et al
Abstract:
New isotopic studies on mantle xenoliths from Santa Cruz Province, southern Patagonia, Argentina, reveal that at least three discrete subcontinental lithospheric mantle (SCLM) domains—the Deseado Massif, Tres Lagos, and Pali Aike—form the southernmost part of South America. Re-Os systematics yield early Paleoproterozoic (up to 2.5 Ga) SCLM formation ages (rhenium depletion ages, TRD) for Pali Aike spinel peridotites, while samples from the Deseado Massif and Tres Lagos indicate a younger SCLM origin with Neoproterozoic to Mesoproterozoic (0.9–1.3 Ga) and Mesoproterozoic to late Paleoproterozoic (1.3–1.9 Ga) TRD ages, respectively. Hf-Sr-Nd isotopic compositions indicate metasomatic overprinting of the majority of the samples, which, however, has not affected the Os isotopic system. Based on similar formation ages, the geological evolution of the Deseado Massif is most likely connected to the evolution of the Namaqua-Natal belt of South Africa. TRD ages from SCLM domains underneath Tres Lagos and Pali Aike indicate a common origin with crustal sections from Shackleton Range, Antarctica, positioning the southern tip of South America closer to west Antarctica in the reconstructed Rodinia supercontinent than previously assumed.
