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Paleogeography and biogeography of the Gondwanan final breakup and its terrestrial vertebrates: New insights from southern South America and the “double Noah’s Ark” Antarctic Peninsula
Abstract
The Mesozoic plate tectonic and paleogeographic history of the final break up of West Gondwana had a profound effect on the distribution of terrestrial vertebrates in South America. As the supercontinent fragmented into a series of large landmasses (South America, Antarctica, Australia, New Zealand, the Indian subcontinent, and
Madagascar), particularly during the Late Jurassic and Cretaceous, its terrestrial vertebrates became progressively isolated, evolving into unique faunal assemblages. The episodic nature of South American mammalian Cenozoic faunas became apparent in its modern formulation after George Gaylord Simpson’s seminal works on this topic. Two aspects add complexity to this generally accepted scheme: first, the fact that South America is not (and was not) a biogeographic unit, as the Neotropical Region does not include its southernmost tip (the Andean Region, including Patagonia and the southern Andes). Second, and intimately linked with the first one, that South America was not an island continent during the Late Cretaceous and the beginning of the Cenozoic, being
its southernmost portion closely linked with West Antarctica up to the late Paleocene at least. Here we stress on this second aspect; we summarize a series of recent, detailed paleogeographical analyses of the continental breakup between Patagonia (including the Magallanes Region) and the Antarctic Peninsula crustal block, beginning with the opening of the Atlantic Ocean in the Early Cretaceous and running up to the Early Paleogene
with the expansion of the Scotia Basin. In second place, we comment on the implications of these distinct paleogeographic and paleobiogeographic scenarios (before and after their geographic and faunistic isolation) for the evolution of South American terrestrial mammalian faunas. Summarizing, (1) we recognize a West Weddellian terrestrial biogeographic unit with the assemblage of the southern part of South America (Patagonia and the Magallanes Region) and the Antarctic Peninsula (and probably Thurston Island) crustal block of West Antarctica, spanning from the Late Cretaceous (Campanian) through the Early Paleogene (Paleocene); (2) we suggest that the Antarctic Peninsula acted as a double "Noah’s Ark” regarding, first, the probable migration of some non-therian lineages into southern South America; later, the migration of metatherians to Australasia.
... In contrast, the South American Episode is primarily distinguished by Paleocene to Recent endemic therian mammals whose ancestors migrated from the Laurasian North American continent (Goin et al., 2012;Pascual and Ortiz-Jaureguizar, 2007), but also of likely native lineages such as xenarthrans. Interestingly, the faunal evolution in each Episode was marked by distinctive tectonic and paleogeographic histories (Reguero and Goin, 2021). Here, we will focus on the South American Episode, which gave rise to the continent's modern mammal communities. ...
... However, the history of this continent is likely more complex, as it is now accepted that SA was intermittently connected with other landmasses during the Cenozoic. For instance, the southernmost extreme of South America remained connected to the present Antarctic Peninsula until about 40 Ma (Lagabrielle et al., 2009;Reguero and Goin, 2021). Additionally, it is hypothesized that South America might have been partially connected to Africa during the Paleogene to early Miocene via the Walvis Ridge-Rio Grande Rise passage (Agnolin, 2024;Carvalho et al., 2019) and the Greater Antilles (and even Central and North America) during the late Eocene? to early Miocene? ...
... To address this situation, we will focus on regional-scale macroevolutionary processes by analyzing only fossils from southern South America (hereafter SSA), defined as the region south of 15°S (Ortiz-Jaureguizar and Cladera, 2006). SSA has a richer fossil record of notoungulates than northern SA and likely shares a common biogeographic and evolutionary history (Morrone, 2002;Ortiz-Jaureguizar and Cladera, 2006;Reguero and Goin, 2021). ...
Unraveling the biotic and abiotic drivers likely influencing clades' diversification dynamics (differential speciation and extinction rates) is crucial for understanding life on Earth. Here, we present a comprehensive analysis of the diversification dynamics of notoungulates (Mammalia: Notoungulata), the most diverse and widespread Cenozoic herbivore mammals that evolved in South America (SA) but are now entirely extinct. Employing fossil occurrences restricted to the southern part of the SA and a Bayesian framework, we examined the historical speciation and extinction rates across all notoungulates, subor-ders, and three body size categories and tested whether these dynamics could be driven by biotic (e.g., diversity dependence, competition) and abiotic (e.g., Andean uplift and temperature changes) factors. Our findings reveal significant variability in diversification rates over time and groups driven by biotic and abiotic factors. We observed an increase in notoungulate speciation rates correlated with lower group self-diversity, likely related to limited environmental productivity and more extensive emerged continental areas that can provide increased environmental and ecological heterogeneity. In contrast, elevated extinction rates were correlated with intensified Andean uplift events, which can trigger landscape modifications and the arrival of placental carnivores after the Great American Biotic Interchange, probably due to notoungulate vulnerability to novel predation pressures. Furthermore, sparassodont diversity appears to increase speciation and extinction rates of notoungulates, although the direct mechanism relating them remains uncertain. The heterogeneity in the observed patterns of speciation and extinction across distinct size categories and taxonomic clades provides valuable perspectives on how ancient global and regional changes impacted the diversification dynamics of mammals and underscores the intricate interplay between environmental changes and biological interactions in shaping the evolution of life on Earth. Ó
... 3). Gondwanan separation occurred in two predominant phases: Phase 1 (southern Gondwanan disarticulation), which involved the separation of southern South America, southern Africa, Australia-Antarctica, and Madagascar-India, beginning approximately 180 mya and largely completed by 120 mya (Jokat et al. 2003), and Phase 2 (western Gondwanan disarticulation), involving the separation of South America and Africa, which was completed 80 mya (Reguero and Goin 2021). At the split between the Austroboletoidae and Time-calibrated phylogeny of Boletaceae using 1461 BUSCO genes. ...
... The closest relatives of these Chilean boletes occurred in geographic regions as disjunct as North America, lowland tropical northern South America, and Australia. Boletus loyita and Gastroboletus valdivianus were most closely related to extant Australian taxa, suggesting an origin prior to southern Gondwanan disarticulation (phase 1 separation) (Reguero and Goin 2021). Close relationships between southern Gondwanan Australian and southern South American taxa have been documented elsewhere (Feng et al. 2017). ...
... are endemic to Africa. India separated from Africa and Madagascar ~120 mya (Reguero and Goin 2021) and at 40 mya was already in contact with Asia (Aitchison et al. 2007;Hu et al. 2016). If B. alliaceus and P. africanus are indeed sister lineages of Boletus s. str., then the arrival and subsequent diversification of true porcini in Asia must have been a dispersal event, because the separation of India from mainland Africa (~180-170 mya ;Hankel 1994) or Madagascar (83.6-91.6 mya; Storey 1995) occurred long before our estimated age of the Boletus s. str. ...
The porcini mushroom family Boletaceae is a diverse, widespread group of ectomycorrhizal (ECM) mushroom-forming fungi that so far has eluded intrafamilial phylogenetic resolution based on morphology and multilocus data sets. In this study, we present a genome-wide molecular data set of 1764 single-copy gene families from a global sampling of 418 Boletaceae specimens. The resulting phylogenetic analysis has strong statistical support for most branches of the tree, including the first statistically robust backbone. The enigmatic Phylloboletellus chloephorus from non-ECM Argentinian subtropical forests was recovered as a new subfamily sister to the core Boletaceae. Time-calibrated branch lengths estimate that the family first arose in the early to mid-Cretaceous and underwent a rapid radiation in the Eocene, possibly when the ECM nutritional mode arose with the emergence and diversification of ECM angiosperms. Biogeographic reconstructions reveal a complex history of vicariance and episodic long-distance dispersal correlated with historical geologic events, including Gondwanan origins and inferred vicariance associated with its disarticulation. Together, this study represents the most comprehensively sampled, data-rich molecular phylogeny of the Boletaceae to date, establishing a foundation for future robust inferences of biogeography in the group.
... Here, we will use the term "subantarctic" in the physiographic sense, as it refers to the territories immediately north of the Antarctic convergence and roughly south 46°S (the southern limit of Chubut, central Patagonia). The arrival of duck-billed dinosaurs into southern Patagonia and the Antarctic Peninsula is documented by unnamed partial remains that are currently assumed to belong to hadrosaurids like those of central and northern Patagonia (10)(11)(12)(13). At the time, southern Patagonia and the Antarctic Peninsula retained close geographic proximity to each other, with intermittent formation of land bridges and similar biotic components that have led to the suggestion of a distinct West Weddelian Terrestrial Biogeographic Province (10). ...
... The arrival of duck-billed dinosaurs into southern Patagonia and the Antarctic Peninsula is documented by unnamed partial remains that are currently assumed to belong to hadrosaurids like those of central and northern Patagonia (10)(11)(12)(13). At the time, southern Patagonia and the Antarctic Peninsula retained close geographic proximity to each other, with intermittent formation of land bridges and similar biotic components that have led to the suggestion of a distinct West Weddelian Terrestrial Biogeographic Province (10). These territories may have also become at least partially isolated from the rest of South America due to marine transgressions, such as the Kawas Sea (14). ...
... (I) CPAP 5360, distal end of the right femur in distal view, showing a deep intercondylar extensor groove, in which the condyles nearly meet anteriorly(9). In addition, the condyles are posteriorly welldeveloped(10). (J) CPAP 5362, left tibia in proximal view in which the posteromedial condyle is wider than the lateral condyle (11). ...
In the dusk of the Mesozoic, advanced duck-billed dinosaurs (Hadrosauridae) were so successful that they likely outcompeted other herbivores, contributing to declines in dinosaur diversity. From Laurasia, hadrosaurids dispersed widely, colonizing Africa, South America, and, allegedly, Antarctica. Here, we present the first species of a duck-billed dinosaur from a subantarctic region, Gonkoken nanoi, of early Maastrichtian age in Magallanes, Chile. Unlike duckbills further north in Patagonia, Gonkoken descends from North American forms diverging shortly before the origin of Hadrosauridae. However, at the time, non-hadrosaurids in North America had become replaced by hadrosaurids. We propose that the ancestors of Gonkoken arrived earlier in South America and reached further south, into regions where hadrosaurids never arrived: All alleged subantarctic and Antarctic remains of hadrosaurids could belong to non-hadrosaurid duckbills like Gonkoken. Dinosaur faunas of the world underwent qualitatively different changes before the Cretaceous-Paleogene asteroid impact, which should be considered when discussing their possible vulnerability.
... Recent studies have established a well-constrained stratigraphic framework for the valley (Manríquez et al., 2019George et al., 2020), and identified potential preservation of continuous deposition across the K/Pg boundary (George et al., 2020). This locality has produced a wealth of fossil discoveries that have greatly expanded our understanding of the diversity of vertebrates and plants at southern high latitudes during the end of the Cretaceous (Alarcón-Muñoz et al., 2020;Goin et al., 2020;Trevisan et al., 2020;Martinelli et al., 2021;Soto-Acuña et al., 2021;Suazo Lara and Gomez, 2022), and help elucidate biogeographic patterns during final Gondwanan breakup (reviewed in Reguero and Goin, 2021). While some of these notable discoveries represent partially articulated specimens (i.e., Stegouros elengassen, Soto-Acuña et al., 2021), most vertebrate fossils recovered from the locality are isolated or fragmentary. ...
... Here we consider records from South America, Antarctica, and Australia, as they were the last Gondwanan continents to maintain intermittent connectivity throughout the end of the Mesozoic (Poblete et al., 2016;Reguero and Goin, 2021). Of these southern landmasses, South America has the most abundant theropod record from the Bauru, Salta, Cañadón Asfalto, Neuquén, and Magallanes-Austral Basins. ...
... Remains from Campanian and Maastrichtian deposits on Seymour, James Ross, and Vega islands include isolated bones of non-avian and avian theropods (Acosta Hospitaleche et al., 2019;Lamanna et al., 2019) and partial skeletons of the paravian Imperobator antarcticus (Case et al., 2007;Ely and Case, 2019) and ornithurines V. iaai (Clarke et al., 2005(Clarke et al., , 2016 and P. gregorii (Chatterjee, 2002;Acosta Hospitaleche et al., 2019). Notably, populations during the latest Cretaceous of the Magallanes-Austral Basin and James Ross Basin would have been the last cross-continental Gondwanan populations to maintain connectivity during the end Cretaceous, as changes in sea level intermittently exposed connections to the Antarctic Peninsula (Poblete et al., 2016;Reguero and Goin, 2021), leading to similarities in the taxa found in both. ...
The end Cretaceous mass extinction was marked by a dramatic change in biodiversity, and the extinction of all non-avian dinosaurs. To understand the diversity of dinosaur clades prior to this event, as well as recovery by avian dinosaurs (birds), we need a better understanding of the global fossil record. However, the fossil record from southern localities, particularly southernmost (>60°S) South America, has only recently begun to be described. Discoveries from Patagonia are important to accurately assess global trends in dinosaur diversity, particularly during the latest Cretaceous before the Cretaceous/Paleogene (K/Pg) mass extinction event. Here we describe new theropod dinosaur specimens, representing both associated material and isolated elements, from Upper Cretaceous (Campanian-Maastrichtian) deposits of the Río de las Chinas Valley, Magallanes-Austral Basin, Chile. These discoveries include the southern-most known occurrences of several theropod clades outside of Antarctica, including megaraptorids, unenlagiines, enantiornithines and ornithurines. Notably, these remains provide much needed time-constrained records of smaller theropods, including birds, which are less often recovered from Upper Cretaceous deposits. While fragmentary, these fossils are the first records of theropods from Chilean Patagonia, and provide insight into the distribution of avian and non-avian theropods in southern high latitude ecosystems prior to the K/Pg mass extinction event. Sampling from this region is still sparse, and more fossils from age-controlled sections are needed to accurately assess global extinction dynamics through the end Cretaceous.
... 8 It is generally assumed that metatherians arrived in Australasia during the early Paleogene from South America via Antarctica. 9,10 Most probably, by the latest Cretaceous metatherians arrived in South America from North America in one or more migratory waves. It has been suggested that they arrived through an island filter route, the Aves Ridge, at the eastern edge of the Caribbean Plate. ...
... 16 These episodes include marine and nonmarine extinctions, sea-level oscillations, continental flood-basalt eruptions, ocean anoxic events, pulses of intra-plate magmatism and changes in sea floor spreading rates. Episodes were centered at around 10,34,63,95,122,141,184,201,217, and 255 Ma. We find significant coincidences between (at least) the last four of these dates (10,34,63, and 95 Ma) and major events in metatherian evolution (as metatherians most probably originated by the Late Jurassic or Early Cretaceous, the 184, 201, 217 and 255 Ma dates are not relevant in our consideration): from older to younger, (1) a major radiation by Cenomanian (early Late Cretaceous) times of marsupialiform metatherians in North America, (2) the first radiation in the Danian (early Paleocene) of metatherians in South America, quite distinct both in the northern (Neotropical) and southern (Andean) portions of this continent (see below); (3) major extinctions and faunal turnovers by the latest Eocene-earliest Oligocene (the ''Patagonian Hinge'' event), 14 and (4) several extinctions by the late Miocene (Messinian), concomitant with the beginning of the ''Age of the Southern Plains'' in South America. ...
... Episodes were centered at around 10,34,63,95,122,141,184,201,217, and 255 Ma. We find significant coincidences between (at least) the last four of these dates (10,34,63, and 95 Ma) and major events in metatherian evolution (as metatherians most probably originated by the Late Jurassic or Early Cretaceous, the 184, 201, 217 and 255 Ma dates are not relevant in our consideration): from older to younger, (1) a major radiation by Cenomanian (early Late Cretaceous) times of marsupialiform metatherians in North America, (2) the first radiation in the Danian (early Paleocene) of metatherians in South America, quite distinct both in the northern (Neotropical) and southern (Andean) portions of this continent (see below); (3) major extinctions and faunal turnovers by the latest Eocene-earliest Oligocene (the ''Patagonian Hinge'' event), 14 and (4) several extinctions by the late Miocene (Messinian), concomitant with the beginning of the ''Age of the Southern Plains'' in South America. 17 All these four dates are also coincident with major warming or cooling events at the global scale. ...
A noticeable aspect of metatherian evolution in South America is the influence of climatic oscillations in their macroevolutionary patterns, involving major radiations during warming phases, and extinctions and functional turnovers during cooling phases. Two aspects explain why southern metatherians were more successful than their Northern Hemisphere counterparts: a well-established presence previous to the arrival of eutherians and warm climates on a continental scale. Living South American marsupials reach a maximum species richness at the edges of tropical biomes, in areas of contact between tropical and subtropical biomes, or between subtropical and temperate biomes. Three biomes concentrate 80.6% of the records of living marsupials in South America, with tropical and subtropical moist broadleaf forests including the majority of them. South American marsupials are expected to suffer great losses of suitable habitat due to climate change and land conversion. Land exploitation will continue in the immediate future, probably being more disruptive to South American biomes than the current trend in global warming. We suggest that conservation efforts focusing on stenotopic species, such as those of Caenolestidae and Microbiotheriidae, should be given high priority.
... The samples from the upper section of the SMF (S9, S10, S11, and S12) show marked negative Eu anomalies (and lower concentrations of total REE) which can be assumed to be a response to some event of volcanism, such as an orogenic arc. Such a process, which was already operating in the area alongside the fracturing of Gondwana in the Late Cretaceous (Reguero & Goin, 2021), generated a connection between southern South America (Patagonia and Magellanic Regions) and the AP. ...
... This connection involved the Weddelian Isthmus associated with an epicontinental sea and occurred towards the late Paleocene Reguero & Goin, 2021). ...
Trace elements, particularly rare earth elements (REE), are widely used as proxies to reconstruct paleoenvironmental and taphonomic conditions. We traced these elements in fossil penguin bones collected along the Paleogene sequence exposed in Seymour Island (=Isla Marambio) to test them as indicators of the tectonic changes to which this region was exposed. The results indicated the contents of REE in thirteen samples of the analyzed bone tissues. The negative europium anomaly in the samples from Bartonian and Priabonian beds reflects regional events. This signal coincides in time with the opening of the Drake Passage, and with the tectonic changes that occurred between the end of the Eocene and the beginning of the Oligocene, between the western margin of South America and the Antarctic Peninsula.
... The Antarctic continent, today isolated from any other landmass due to the Antarctic Circumpolar Current, was part of the supercontinent Gondwana at the beginning of the Mesozoic (McLoughlin, 2001). During the Gondwanan breakup, starting in the Late Jurassic, South America, Africa, India, Australia, New Zealand, Madagascar, East and West Antarctica, and South America began to rift apart (e.g., Reguero & Goin, 2021). West Antarctica (including the Antarctic Peninsula) was connected to southern South America until the Drake Passage was completely formed. ...
... Additionally, the rain shadow effect caused by uplift of the Andes Mountains also contributed to this expansion. Evidence for this is given by Reguero et al. (2014) and Reguero and Goin (2021). ...
The concept of seasonal forests groups structural types of vegetation that are related to climatic seasonality in the tropics of South America. Consequently, this determines the physiognomy of the vegetation, from semi‐deciduous to strongly deciduous. The strongest link between seasonally dry tropical forests (SDTFs) is their floristic composition, where Leguminosae and Anacardiaceae dominate the woody flora. The fossil records of the Neogene of northwestern Argentina reveal a list of species found in various locations and formations of the Miocene–Lower Pleistocene obtained from studies of pollen, woods (logs), cuticles, impressions of leaves and fruits. The analysis of sediments and woody structures from the Tapebicuá, Toropí/Yupoí and El Palmar Formations (Upper Pleistocene) of the Mesopotamia region allowed us to identify several pollen taxa and silicified wood fragments (mineralized). The woody and shrubby association whose current relatives characterize the SDTF is composed of the 16 fossil species described here belonging to seven families. In our samples, Anadenanthera colubrina and Myracrodruon balansae are the most significant members of the families Leguminosae and Anacardiaceae, which are dominant in the SDTF. The paleobotanical species described in this study confirm the extension of the SDTF to the province of Corrientes, coinciding with various climatic events (dry subtropical, semi‐desert and warm‐humid climate) that would have favored the development of these forests during the Pleistocene in this region. The absolute dates obtained for the Toropí/Yupoí and Tapebicuá Formations confirm their synchronicity and correlation to Marine Isotope Stage 5. The palynological analysis, the presence of Menendoxylon and the sedimentological data allow us to infer the existence of a seasonally dry humid paleoclimate in northeastern Argentina during the Late Pleistocene favorable to the development of the SDTF.
... Additionally, the rain shadow effect caused by uplift of the Andes Mountains also contributed to this expansion. Evidence for this is given by Reguero et al. (2014) and Reguero and Goin (2021). ...
... Considered a sub-basin of the Larsen Basin (del Valle et al., 1992;Macdonald et al., 1988), its sediments are currently exposed in the Northwestern zone of the Antarctic Peninsula. At the same time, the James Ross Basin (or sub-Basin) was in close contact with the Magallanes (Austral) Basin in South Patagonia at the end of the Cretaceous (Jordan et al., 2020;Reguero and Goin, 2021). ...
The first dinosaur discovered in the Antarctic continent was the ankylosaur Antarctopelta oliveroi in the 1980s.
Nevertheless, since then several hypotheses of phylogenetical relationships have been proposed because these have been
depended on how the skeletal remains have been interpreted. The main obstacle for clarifying its phylogenetic position is that
many portions of the skeleton remain unknown, in addition to the presence of unknown characters in typical ankylosaurs.
Considered an ankylosaurid, nodosaurid, or even a chimaera, a recent proposal based on mostly complete material of a new
ankylosaur from Chilean Patagonia provided support for a novel phylogenetic hypothesis: Antarctopelta and other southern
ankylosaurs are an early branching clade, the Parankylosauria, whose origin probably dates to the Late Jurassic. In the light of
this new view, a redescription of the available skeletal remains is provided together with a new reconstruction of the first
Antarctic dinosaur known to the science community.
... Possibly for that reason, the representatives of Clinocera clade A are found in all biogeographical regions (Sinclair, 2000(Sinclair, , 2003a(Sinclair, , 2008Sinclair & Plant, 2022 in the C. fuscipennis group (Sinclair, 2008). The direct connection between South America and Africa lasted until Late Cretaceous ($100 Mya, Reguero & Goin, 2021;or 90 Mya, White, 1994), but it could have been connected longer via islands that were used as stepping-stones (Sinclair, 2003a). All this is indicating that Clinocera clade A and possibly clade B were well established prior to the separation within Gondwanaland. ...
This study presents the first molecular phylogenetic analysis of the Clinocerinae, challenging the traditionally accepted monophyly of this subfamily. DNA was extracted from fresh and museum specimens representing all biogeographical regions. Maximum likelihood (ML) and Bayesian inference (BI) phylogenetic analyses were performed based on sequences from two mitochondrial genes, cytochrome c oxidase subunit I (COI) and cytochrome β , and three nuclear genes, carbomoylphosphate synthase domain of rudimentary, elongation factor‐1α and isocitrate dehydrogenase. Through molecular data and morphological examination, our results reveal a division within Clinocerinae, distinguishing ‘typical’ or Clinocerinae (s.s.) from several genera, specifically Afroclinocera Sinclair, Asymphyloptera Collin and Proagomyia Collin, possibly lending support for a reclassification of these genera outside Clinocerinae. Bergenstammia Mik is proposed as a junior synonym of Phaeobalia Mik, syn. n. , and the following new combinations are recognized: Phaeobalia albanica (Wagner) comb. n. , Phaeobalia aurinae (Pusch & Wagner) comb. n. , Phaeobalia carniolica (Horvat) comb. n. , Phaeobalia frigida (Vaillant) comb. n. , Phaeobalia glacialis (Palaczyk & Słowińska) comb. n. , Phaeobalia multiseta (Strobl) comb. n. , Phaeobalia nudimana (Vaillant) comb. n. , Phaeobalia nudipes (Loew) comb. n. , Phaeobalia pulla (Vaillant & Wagner) comb. n. , Phaeobalia pyrenaica (Vaillant & Vinçon) comb. n. , Phaeobalia slovaca (Wagner) comb. n. and Phaeobalia thomasi (Vaillant & Vinçon) comb. n. Re‐evaluation of the genus Roederiodes resulted in the following new combinations: Clinocerella macedonicus (Wagner & Horvat) comb. n. and Clinocerella montenegrinus (Wagner & Horvat) comb. n. The origins of Clinocerinae (s.s.) are traced back to the Holarctic region, Laurasian origin, with a likely complex history of dispersal events into the Southern Hemisphere. Based on current knowledge, the greatest generic and species richness is confined to the Palaearctic Region. These findings provide valuable insights into the evolutionary relationships and distribution patterns of Clinocerinae (s.s.), challenging existing taxonomic classifications and shedding light on their historical biogeography.
... This process resulted in the separation of Africa and South America, and in the opening of the Atlantic Ocean. Fossil records and phylogeographic studies show important diversification processes during this period in different biological groups, for example, mammals (Reguero andGoin 2021), birds (Feduccia 2003), amphibians (Frazão et al. 2015), fish (Cioffi et al. 2019; for details, see Chap. 21) and angiosperms (McLoughlin 2001). ...
... This process resulted in the separation of Africa and South America, and in the opening of the Atlantic Ocean. Fossil records and phylogeographic studies show important diversification processes during this period in different biological groups, for example, mammals (Reguero andGoin 2021), birds (Feduccia 2003), amphibians (Frazão et al. 2015), fish (Cioffi et al. 2019; for details, see Chap. 21) and angiosperms (McLoughlin 2001). ...
Phylogeography is the study of the spatial distribution of genealogical lineages, especially those found within and among closely related species. The discipline was originally considered a bridge between population genetics (microevolutionary processes) and phylogenetic systematics (macroevolutionary patterns). Therefore, phylogeographic studies are paramount to understanding the assembly of the world’s biota, especially in the Neotropics, one of the most biodiversity-rich regions in the world, harboring approximately one-third of all global species. Throughout this chapter, we show how phylogeography can provide information on the fine-scale genetic diversity of species/populations in the Neotropics. We briefly review the main hypotheses concerning neotropical diversification in terrestrial and freshwater organisms, which illustrate the complexity of processes responsible for the outstanding biodiversity levels in the region. We also present the main methodological approaches to assess these underlying diversification processes, and advocate that they should take this complexity into account to provide insightful guidance for biodiversity protection policies in the Neotropics at multiple evolutionary scales.KeywordsDemographic historyDiversification processesEvolutionary significant unitsHypotheses testsLandscape evolutionPhylogenyPopulation genetics
... The new Patagonian species Acmopyle grayae is the only known reliable record of the genus reported in South America (Table 1). Climatic cooling, increased seasonality, and isolation of South America as consequences of the deepening and widening of the Drake Passage that began just following~50 Ma caused the biogeographic isolation of South America and extirpation of the genus from Patagonia after the early Eocene (Lawver et al., 2011;Dunn et al., 2015;Barreda et al., 2020;Reguero and Goin, 2021;van de Lagemaat et al., 2021). Like many paleo-Antarctic lineages , Acmopyle survived in Australia at least until the middle to late Eocene (Hill and Carpenter, 1991; Table 1; Figure 1) and potentially in New Zealand from the Miocene to the early Quaternary (Pole, 1997(Pole, , 2007 Figure 1) by tracking its preferred high-rainfall habitats. ...
Premise:
Acmopyle (Podocarpaceae) comprises two extant species from Oceania that are physiologically restricted to ever-wet rainforests, a confirmed fossil record based on leaf adpressions and cuticles in Australia since the Paleocene, and a few uncertain reports from New Zealand, Antarctica, and South America. We investigated fossil specimens with Acmopyle affinities from the early Eocene Laguna del Hunco site in Patagonia, Argentina.
Methods:
We studied 42 adpression leafy-shoot fossils and included them in a total evidence phylogenetic analysis.
Results:
Acmopyle grayae sp. nov. is based on heterophyllous leafy shoots with three distinct leaf types. Among these, bilaterally flattened leaves uniquely preserve subparallel, linear features that we interpret as accessory transfusion tissue (ATT, an extra-venous water-conducting tissue). Some apical morphologies of A. grayae shoots are compatible with the early stages of ovuliferous cone development. Our phylogenetic analysis recovers the new species in a polytomy with the two extant Acmopyle species. We report several types of insect-herbivory damage. We also transfer Acmopyle engelhardti from the middle Eocene Río Pichileufú flora to Dacrycarpus engelhardti comb. nov.
Conclusions:
We confirm the biogeographically significant presence of the endangered West Pacific genus Acmopyle in Eocene Patagonia. Acmopyle is one of the most drought-intolerant genera in Podocarpaceae, possibly due to the high collapse risk of the ATT, and thus the new fossil species provides physiological evidence for the presence of an ever-wet rainforest environment at Laguna del Hunco during the Early Eocene Climatic Optimum.
... Diversification of several groups of organisms distributed in the southern hemisphere has been attributed to the breakup of Gondwanan (for example, marsupials (Reguero and Goin, 2021)). The Gondwanan fragmentation is well-documented, and concordant with geographic distributions of many taxa (reviewed in Sanmartíin and Ronquist (2004)). ...
The miniature orb weaving spiders (symphytognathoids) are a group of small spiders (< 2 mm), including the smallest adult spider Patu digua (0.37 mm in body length), that have been classified into five families. The species of one of its constituent lineages, the family Anapidae, build a remarkable diversity of webs (ranging from orbs to sheet webs and irregular tangles) and even include a webless kleptoparasitic species. Anapids are also exceptional because of the extraordinary diversity of their respiratory systems. The phylogenetic relationships of symphytognathoid families have been recalcitrant with different classes of data, such as, monophyletic with morphology and its concatenation with Sanger-based six markers, paraphyletic (including a paraphyletic Anapidae) with solely Sanger-based six markers, and polyphyletic with transcriptomes. In this study, we capitalized on a large taxonomic sampling of symphytognathoids, focusing on Anapidae, and using de novo sequenced ultraconserved elements (UCEs) combined with UCEs recovered from available transcriptomes and genomes. We evaluated the conflicting relationships using a variety of support metrics and topology tests. We found support for the phylogenetic hypothesis proposed using morphology to obtain the "symphytognathoids'' clade, Anterior Tracheal System (ANTS) Clade and monophyly of the family Anapidae. Anapidae can be divided into three major lineages, the Vichitra Clade (including Teutoniella, Holarchaea, Sofanapis and Acrobleps), the subfamily Micropholcommatinae and the Orb-weaving anapids (Owa) Clade. Biogeographic analyses reconstructed a hypothesis of multiple long-distance transoceanic dispersal events, potentially influenced by the Antarctic Circumpolar Current and West Wind Drift. In symphytognathoids, the ancestral anterior tracheal system transformed to book lungs four times and reduced book lungs five times. The posterior tracheal system was lost six times. The orb web structure was lost four times independently and transformed into sheet web once.
... Sadly, we only have a few tantalising cues as to how marsupials radiated across Gondwana, owing to difficulties of obtaining fossils from Antarctica (Gelfo et al. 2019). However, by the late Cretaceous, Gondwana had all but broken apart and South America was probably fully isolated from the remainder of Antarctica (Reguero and Goin 2021). This deep separation is also reflected in the split of living marsupials into two major groups, the American Ameridelphia and the mostly Australian Australidelphia. ...
The metatherians (crown-clade marsupial mammals and their fossil relatives) originated in the Late Jurassic or Early Cretaceous of Laurasia, and have since spread worldwide with diversification in South America and Australasia during the Cenozoic. Despite this long evolutionary history, paleoneurology is known for a few taxa from the Americas and Australia, with most work being published in the last 40+ years. Here, we contextualise research on metatherian paleoneurology with traditional tenets that marsupials are developmentally constrained in their brain size and advanced cognitive and sensorimotor capabilities. We summarize recent research on marsupial neuromorphology with a perspective on how these insights apply to extinct species. We describe a digital cranial endocast of the didelphid Caluromys philander to compare with endocasts of crown and stem marsupials. Although endocasts of basal metatherians morphologically resemble those of didelphids, there is significant variation in brain shape and cerebrum gyrification among marsupials, possibly due to differences in how neural tissue is distributed within limited braincase space. Lastly, we examined existing endocranial volume and body mass estimates for crown and stem marsupials. The earliest metatherians have substantially smaller relative brain sizes than recent species, although this may relate to errors in estimating metatherian mass and endocast volumes.
... nov. (Madagascar), Cladonotini (Asia), and Choriophyllini (Caribbean) is evident, so it is reasonable to hypothesize that those characters represent homologies and reflect the common ancestry on the ancient continent of Gondwana, which is a pattern that has been observed in numerous other taxa (Turner 2004;Gray et al. 2009;Reguero and Goin 2021). Cladonotinae are polyphyletic; their taxonomy is still far from resolved (Zhang et al. 2020). ...
Only two leaf-like pygmy grasshopper species and specimens are known from Madagascar: the Leatherback Pygmy Grasshopper (Lepocranus fuscus Devriese, 1991) —which has a relatively low median carina of the pronotum; and the Malagasy Litterhopper (Valalyllum folium gen. et. sp. nov.), herein described — which has a high median carina. Lepocranus fuscus is known from the rainforests around Tampolo, Manakambahiny, and Mahavelona (Foulpointe). The new taxon, Valalyllum folium gen. et. sp. nov. is known only from the Belanono forest. Both species inhabit northeastern Madagascar. The new species could be rare or not-easy-to-spot in the rainforest leaf litter, where it most probably lives. A new tribe, Valalyllini trib. nov., is described for the two mentioned genera because its members are different from the Caribbean leaf-like Choriphyllini Cadena Castañeda & Silva, 2019, from the African leaf-like Xerophyllini Günther, 1979, and from the Asian leaf-like Cladonotini Bolívar, 1887. A tabular key to the tribes of Cladonotinae with leaf-like representatives is provided, together with photographs of type specimens of both species belonging to the newly described tribe. The holotype of the new species belongs to the Muséum national d’Histoire naturelle Orthoptera collection, Paris.
... The specimen was considered a Caenolestidae (=Caenolestinae in Reig, 1955;Patterson and Marshall, 1978;Marshall, 1980) but this assignation was questioned by Abello (2007) based on the poor available evidence to verify diagnostic features. However, more recently Reguero and Goin (2021) mentioned this taxon in a faunal list as a Pichipilidae. Considering the available information, P. guaraniticus is smaller than MJHG-NCP 277 and differs from it by its more gracile morphology, proportionally longer and narrower tooth, paraconid and metaconid separated by a deep valley, trigonid with sharp and high cuspids (Patterson and Marshall, 1978), entoconid lacking an obvious flat surface as seen in MJHG-NCP 277 (according to the drawing in Ameghino´s contributions). ...
The Paleogene terrestrial faunal succession and its associated bearing volcaniclastic deposits has been exhaustively studied in central Patagonia, but there is still no acceptable litho-bio-chronostratigraphic ordering for the extra-Andean North Patagonia. The only references on Paleogene mammals bearing deposits north to Chubut River are imprecise and contradictory. West to Ingeniero Jacobacci (Río Negro Province, Argentina), the paleontologist and archaeologist Rodolfo Casamiquela reported a fossiliferous succession with Casamayoran or Mustersan (Eocene) and Deseadan (Oligocene) mammals from rocks currently mapped as the Las Chacras Formation. This unit includes acid to intermediate tuffs, ignimbrites, paleosols, conglomerates, and basalts originated in a perivolcanic fluvial system, under a seasonal subhumid-humid climate according to predominant pedogenic features. As a result of our fieldworks and fossil collection in the area of Ingeniero Jacobacci, and the revision of the materials collected by Casamiquela in the forties and fifties (with well-known stratigraphic origin), we identified a single mammal association from the lower section of the Las Chacras Formation (here named the Lower Las Chacras fauna) composed by: Plesiofelis schlosseri Roth, 1903 (Sparassodonta), Trigonostylops Ameghino, 1897, Astraponotus Ameghino, 1901 (Astrapotheria), Propyrotherium Ameghino, 1901 (Pyrotheria), Pseudhyrax eutrachytheroides Ameghino, 1901, Eohegetotherium priscum Ameghino, 1901, Puelia sigma (Ameghino, 1901), Periphragnis Roth, 1899 (Notoungulata), Isutaetus depictus Ameghino, 1902 (Cingulata), and a new member of Adianthidae (Litopterna) and probably of Pichipilidae (Paucituberculata). This assemblage is closer to that derived from the Rosado Member of the Sarmiento Formation at Gran Barranca, central Patagonia (type locality of the Mustersan Land Mammal Age) dated in ca. 38 Ma (late middle Eocene). A pyroclastic flow associated to the bearing deposits of Ingeniero Jacobacci was dated (K-Ar) in 39.2±2 Ma, value compatible with the Mustersan age here inferred for the Lower Las Chacras fauna. The alleged occurrence of Deseadan mammals in these levels was based on remains of an isotemnid notoungulate incorrectly identified as a leontinid. The presence of the Tinguirirican (early Oligocene) notoungulate Eohegetotherium priscum, with more apomorphic dental traits than in its Eocene allies, and of an astrapotheriid more derived than Astraponotus suggests that some advanced faunal elements would have been established in North Patagonia earlier than in central Patagonia.
... Combined with the flattened distal caudal centra, we infer that Antarctopelta had a similar weapon. A close relationship of Antarctopelta with Stegouros is plausible given their similar age, palaeogeographical proximity, and evidence of intercontinental dispersal of flora and fauna between the Antarctic peninsula and southern South America during the late Cretaceous 5,29 . ...
Armoured dinosaurs are well known for their evolution of specialized tail weapons—paired tail spikes in stegosaurs and heavy tail clubs in advanced ankylosaurs1. Armoured dinosaurs from southern Gondwana are rare and enigmatic, but probably include the earliest branches of Ankylosauria2–4. Here we describe a mostly complete, semi-articulated skeleton of a small (approximately 2 m) armoured dinosaur from the late Cretaceous period of Magallanes in southernmost Chile, a region that is biogeographically related to West Antarctica5. Stegouros elengassen gen. et sp. nov. evolved a large tail weapon unlike any dinosaur: a flat, frond-like structure formed by seven pairs of laterally projecting osteoderms encasing the distal half of the tail. Stegouros shows ankylosaurian cranial characters, but a largely ancestral postcranial skeleton, with some stegosaur-like characters. Phylogenetic analyses placed Stegouros in Ankylosauria; specifically, it is related to Kunbarrasaurus from Australia6 and Antarctopelta from Antarctica7, forming a clade of Gondwanan ankylosaurs that split earliest from all other ankylosaurs. The large osteoderms and specialized tail vertebrae in Antarctopelta suggest that it had a tail weapon similar to Stegouros. We propose a new clade, the Parankylosauria, to include the first ancestor of Stegouros—but not Ankylosaurus—and all descendants of that ancestor. Stegouros elengassen, an ankylosaur from the late Cretaceous of Chile, has a large tail weapon, named a macuahuitl after the Aztec club, with a frond-like structure formed by seven pairs of laterally projecting osteoderms encasing the distal half of the tail.
... Floras document a strong increase in diversity by the early Eocene (Fig. 2), including many Australasian elements (e.g. Eucalyptus, Gymnostoma, Akania, and Agathis), supporting the strong southern biogeographic connection (Gandolfo and Zamaloa, 2021;Reguero and Goin, 2021). Patagonian land faunas were diverse in the early Eocene, being largely represented by small insectivorous (e.g. ...
The fossil record from Cenozoic sediments provides a great deal of information that has direct bearing on the early assembling of modern Patagonian ecosystems. In this synthesis, we revise selected fossil marine and terrestrial records from the last 66 Ma with the aim of understanding major shifts of Patagonian biotas. From the Paleocene to the mid Eocene this region supported outstandingly diverse terrestrial assemblages that show strong connections to modern-day Australasia (e.g. gum trees, casuarinas, monotremes). Nearshore marine biotas confirm peak warmth conditions, with tropical species with Tethyan affinities. The late Eocene and early Oligocene marks the onset of a period of overall regional cooling, drying, and increasingly variable ecological conditions. The rise of palm-dominated flammable biomes in hinterlands and the prevalence of Gondwanan gallery forest (e.g. southern beeches and podocarps) along river-sides supported the existence of mosaic habitats maintained by edaphic and regional climatic conditions. This shift in landscapes reflects the evolution of a wide range of herbivorous mammals (e.g. Notoungulata, Litopterna, and Astrapotheria). The late Oligocene and early-to-mid Miocene witnessed a dramatic modification of landscapes including the incursion of high sea-level episodes, the emergence of specialized coastal (i.e. salt-marsh) plant taxa and the expansion of large herbivorous mammals with predominantly high-crowned teeth (e.g. Notoungulata: Hegetotheriidae, Interatheriidae, and Mesotheriidae). The cooling trend of this interval was interrupted by a mid-Miocene transient warming event, with the dispersion of terrestrial (e.g. platyrrhine monkeys, palms) and marine (e.g. Tuberculodinium vancampoae) elements with tropical affinity into southernmost South American regions. Seasonally-dry conditions increased towards the end of the Miocene, yet subtropical species persisted either in terrestrial (e.g. malpighs, passion vines, capybaras), and marine (e.g. Subtropical and Caribbean molluscs) environments. The increasing aridity caused by the Andean uplift wiped out most of the forest species and promoted the diversification of open-habitat species; the emergence of the current grass-dominated Patagonian Steppe occurred later on, probably during the Quaternary.
... Moving to terrestrial environments, Reguero and Goin (2021) explored the response of South American and Antarctic terrestrial vertebrates to the final break up of West Gondwana. They recognized a major biogeographic province; the West Weddellian terrestrial unit that includes mammalian faunas from southern South America and the Antarctic Peninsula spanning the Late Cretaceous to the Paleocene. ...
Dinosaurs potentially originated in the mid-palaeolatitudes of Gondwana 245–235 million years ago (Ma) and may have been restricted to cooler, humid areas by low-latitude arid zones until climatic amelioration made northern dispersals feasible ca 215 Ma. However, this scenario is challenged by new Carnian Laurasian fossils and evidence that even the earliest dinosaurs had adaptations for arid conditions. After becoming globally distributed in the Early–Middle Jurassic (200–160 Ma), dinosaurs experienced vicariance driven by Pangaean fragmentation. Regional extinctions and trans-oceanic dispersals also played a role, and the formation of ephemeral land connections meant that older vicariance patterns were repeatedly overprinted by younger ones, creating a reticulate biogeographic history. Palaeoclimates shaped dispersal barriers and corridors, including filters that had differential effects on different types of dinosaurs. Dinosaurian biogeographic research faces many challenges, not the least of which is the patchiness of the fossil record. However, new fossils, extensive databasing and improved analytical methods help distinguish signal from noise and generate fresh perspectives. In the future, developing techniques for quantifying and ameliorating sampling biases and modelling the dispersal capacities of dinosaurs are likely to be two of the key components in our modern research programme.
Ever since the discovery of Macrauchenia patachonica by Charles Darwin in 1834, the affinities of litopterns—a group of extinct South American Native Ungulates (SANUs)—have been elusive. In particular, the interfamilial relationships and timing of the familial diversification within the order Litopterna have not been addressed with adequate taxon and character sampling, and modern phylogenetic methods. We address these issues using a new morphological matrix of 703 dental and mandibular characters, scored for the earliest litopterns alongside early SANUs of other orders (Astrapotheria, Notoungulata, Pyrotheria, and Xenungulata). We also included members of families that have been often included within Litopterna, such as Didolodontidae, Protolipternidae, Indaleciidae, and Notonychopidae, the last two sometimes grouped in the order Notopterna. We conducted maximum parsimony and undated and tip-dated Bayesian phylogenetic analyses. Our results indicate that (1) didolodontids, protolipternids, and kollpaniines should be considered early SANUs, but not particularly closely related to any order, (2) Indaleciidae and Notonychopidae usually form a monophyletic group (Notopterna), and (3) Litopterna is a monophyletic unit composed of four families [Adianthidae, Anisolambdidae (subfamilies Anisolambdinae and Sparnotheriodontinae), Macraucheniidae, Proterotheriidae], and tentatively the notoptern families Indaleciidae and Notonychopidae with a probable origin ~64.0 Mya in the Early Palaeocene.
Dryolestoid mammals are classical members of the Jurassic faunas of Laurasia but mostly absent during the Cretaceous. The reverse is true in Gondwana in general and South America in particular, where meridiolestid dryolestoids are dominant in the Late Cretaceous. We describe here 21 new mammalian specimens from the Upper Cretaceous locality Cerro Tortuga (Allen Formation, Patagonia, Argentina) collected via screenwashing, which we identify as meridiolestid dryolestoids. We recognize a new species of meridiolestid and reassign a previously described specimen to the new taxon. The morphology of these new remains represents a new morphotype in the spectrum of meridiolestid diversity, recording a broadening of trophic adaptations from the ancestral insectivory to the more derived herbivory observed among the later and more derived members of the group. The novel dental morphology helps bridge the anatomy of the plesiomorphic sharp-toothed meridiolestidans with that of the more derived and bunodont mesungulatoids. The new taxon suggests that development of both broad cingulids and complex crown morphology precede the development of the wide compressed roots, bunodonty, and thickened enamel characteristic of derived mesungulatids. Other specimens from the collection are referable to taxa previously known from the same locality. These provide new information about tooth positioning, dental formula, and overall dental morphology. The new material suggests that Groebertherium, previously regarded as a dryolestid taxon, is in fact a likely member of Meridiolestida.
Where Did They Come From? The Origins of South American Fauna offers a fascinating journey into the origins of South American flora and fauna. Exploring life on the continent before and after the breakup of Gondwana, it delves into how creatures arrived in South America, be it through drifting across oceans or traversing land bridges. From birds and reptiles to mammals and fish, this book provides a comprehensive compendium of biological diversity, discussing their origins and evolutionary paths. Readers will gain insights into the mechanisms of animal dispersal, evolution, and the impact of the Great Biotic Interchange. The book also lists references for further exploration of the subject.
The book is structured into five parts:
Building South America: Covers tectonic movements, climate changes, and breaching isolation.
Shaping South America: Explores the landforms and diverse biomes across the continent.
Vertebrates within South America: Discusses unique amphibians, reptiles, fish, mammals, and birds that evolved on the continent.
Vertebrates immigrating to South America: Examines exotic reptiles, birds, and mammals that found their way to the continent. The author also lists the families of almost all genera of South American animals, while giving knowledge of their origins.
Recent Arrivals - the Great Biotic Interchange: Explores the significant interchange of various species that occurred later.
Ideal for students, biologists, and anyone curious about the natural world, this book is a captivating read that uncovers the incredible history of South American fauna and its evolutionary tapestry.
Where Did They Come From? The Origins of South American Fauna offers a fascinating journey into the origins of South American flora and fauna. Exploring life on the continent before and after the breakup of Gondwana, it delves into how creatures arrived in South America, be it through drifting across oceans or traversing land bridges. From birds and reptiles to mammals and fish, this book provides a comprehensive compendium of biological diversity, discussing their origins and evolutionary paths. Readers will gain insights into the mechanisms of animal dispersal, evolution, and the impact of the Great Biotic Interchange. The book also lists references for further exploration of the subject.
The book is structured into five parts:
Building South America: Covers tectonic movements, climate changes, and breaching isolation.
Shaping South America: Explores the landforms and diverse biomes across the continent.
Vertebrates within South America: Discusses unique amphibians, reptiles, fish, mammals, and birds that evolved on the continent.
Vertebrates immigrating to South America: Examines exotic reptiles, birds, and mammals that found their way to the continent. The author also lists the families of almost all genera of South American animals, while giving knowledge of their origins.
Recent Arrivals - the Great Biotic Interchange: Explores the significant interchange of various species that occurred later.
Ideal for students, biologists, and anyone curious about the natural world, this book is a captivating read that uncovers the incredible history of South American fauna and its evolutionary tapestry.
Levantamento das ocorrências dos dinossauros ornitísquios gondwânicos e as condições ambientais que implicaram na distribuição do grupo no supercontinente.
Monotremata is a clade of egg-lying mammals, represented by the living platypus and echidnas, which is endemic to Australia, and adjacent islands. Occurrence of basal monotremes in the Early Cretaceous of Australia has led to the consensus that this clade originated on that continent, arriving later to South America. Here we report on the discovery of a Late Cretaceous monotreme from southern Argentina, demonstrating that monotremes were present in circumpolar regions by the end of the Mesozoic, and that their distinctive anatomical features were probably present in these ancient forms as well.
The Snow Hill Island Formation (SHIF; late Campanian-early Maastrichtian) crops out in the northeast of the Antarctic Peninsula and constitutes the basal part of the late Campanian-early Maastrichtian sedimentary succession of the James Ross Basin (NG Sequence). Its major exposures occur at the James Ross and Vega islands. Several fossil-bearing localities have been identifi ed in the SHIF providing a valuable fauna of invertebrates and vertebrates, and fl ora. Our study focuses on the vertebrate fauna recovered at Gamma and Cape Lamb members of the SHIF. The marine vertebrate assemblages include chondrichthyans, actinopterygians, and marine reptiles (elasmosaurid plesiosaurs and mosasaurs). A diverse terrestrial vertebrate as semblage has been reported being characterized by dinosaurs (sauropod, elasmarian ornithopods, nodosaurid ankylosaur, and a paravian theropod), pterosaurs and birds. Most SHIF dinosaurs share close affi nities with penecontemporaneous taxa from southern South America, indicating that at least some continental vertebrates could disperse between southern South America and Antarctica during the Late Cretaceous. The Snow Hill Island Formation provides the most diverse Late Cretaceous marine and continental faunas from Antarctica. The present study summarizes previous and new vertebrate fi ndings with the best actualized stratigraphical framework, providing a more complete fauna association and analyzing further perspectives.
The Upper Cretaceous (Cenomanian) Mata Amarilla Formation in western Central Santa Cruz Province of Argentina has yielded fragmentary teeth of a large ?docodontan, an australosphenidan, a meridiolestidan (Amarillodon meridionalis gen. et sp. nov.), and a stem dryolestid (Treslagosodon shehuensis gen. et sp. nov.). These represent the first possible records for docodontans, Cretaceous australosphenidans, and stem dryolestids in South America. Both ?docodontan tooth fragments are unusually large and exhibit potential durophagous adaptation. The Amarillodon gen. nov. lower (?deciduous) posterior premolar has a trigonid angulation of 100° and is autapomorphic by a large and exoedaenodont distolabial accessory cusp on the distal cingulid. Both the mesial and distal cingulid are shelf-like. The mesiolabial upper molar fragment of the ausktribosphenid australosphenidan is similar to an upper M1 of aff. ?Bishops from the lower Albian (Lower Cretaceous) of Australia by its large stylar cusp ?C and breached paracone. The lower molar of the new stem dryolestid is characterized by a large talonid cusp d and a mesio-distally strongly compressed mesial root that is weaker than the distal one. The australosphenidan, if corroborated, suggests faunal interrelationships between Australia and South America by the late Early/early Late Cretaceous.
Lizards of the clade Iguanidae (sensu lato) are primarily a New World group. Thus, the remarkable presence of an endemic lineage of iguanas (family Opluridae) on the isolated Indian Ocean island of Madagascar has long been considered a biogeographic anomaly. Previous work attributed this disjunct extant distribution to: (1) vicariance at about 140-165 Ma, caused by the breakup of Gondwana and the separation of South America, Africa, and Madagascar (with subsequent extinction of iguanas on Africa, and potentially other Gondwanan landmasses), (2) vicariance at about 80-90 Ma, caused by the sundering of hypothesized land-bridge connections between South America, Antarctica, India, and Madagascar, or (3) long-distance overwater dispersal from South America to Madagascar. Each hypothesis has been supported with molecular divergence dating analyses, and thus the biogeographic origin of the Opluridae is not yet well resolved. Here we utilize genetic sequences of ultraconserved elements for all Iguania families and the majority of Iguanidae (s.l.) genera, and morphological data for extant and fossil taxa (used for divergence dating analyses), to produce the most comprehensive dataset applied to date to test these origin hypotheses. We find strong support for a sister relationship between the Opluridae (Madagascar) and Leiosauridae (South America). Divergence of the Opluridae from Leiosauridae is dated to between the late Cretaceous and mid-Paleogene, at time when Madagascar was already an island and was isolated from all other Gondwanan landmasses. Consequently, our results support a hypothesis of long-distance overwater dispersal of the Opluridae lineage, either directly from South America to Madagascar or potentially via Antarctica or Africa, leading to this radiation of iguanas in the Indian Ocean.
In the last decades, several discoveries have uncovered the complexity of mammalian evolution during the Mesozoic Era, including important Gondwanan lineages: the australosphenidans, gondwanatherians, and meridiolestidans (Dryolestoidea). Most often, their presence and diversity is documented by isolated teeth and jaws. Here, we describe a new meridiolestidan mammal, Orretherium tzen gen. et sp. nov., from the Late Cretaceous of southern Chile, based on a partial jaw with five cheek teeth in locis and an isolated upper premolar. Phylogenetic analysis places Orretherium as the earliest divergence within Mesungulatidae, before other forms such as the Late Cretaceous Mesungulatum and Coloniatherium , and the early Paleocene Peligrotherium . The in loco tooth sequence (last two premolars and three molars) is the first recovered for a Cretaceous taxon in this family and suggests that reconstructed tooth sequences for other Mesozoic mesungulatids may include more than one species. Tooth eruption and replacement show that molar eruption in mesungulatids is heterochronically delayed with regard to basal dryolestoids, with therian-like simultaneous eruption of the last premolar and last molar. Meridiolestidans seem endemic to Patagonia, but given their diversity and abundance, and the similarity of vertebrate faunas in other regions of Gondwana, they may yet be discovered in other continents.
Gondwanatheria is an enigmatic mammaliaform clade distributed in the Cretaceous and Paleogene of South America, Africa, Madagascar, India and Antarctica. The Mesozoic record in South America is restricted to the Latest Cretaceous of Río Negro and Chubut provinces, Argentina and Magallanes Region of southern Chile. The aim of the present contribution is to describe a new specimen of gondwanatherian mammaliaforms from beds belonging to the Maastrichtian Chorrillo Formation, cropping out 30 km SW of El Calafate, Santa Cruz Province, Argentina. It is represented by a single molariform referable to the species Magallanodon baikashkenke with which it shares a unique combination of characters. Analysis of the unique combination of characters exhibited by Magallanodon shed doubts on the monophyly of Ferugliotheriidae and suggest that South American taxa may be closely related to each other. The wide geographical distribution and occurrence of gondwanatherians on geological units of diverse origins suggest that they were capable of facing disparate environmental conditions.
The Cretaceous-Paleogene (K/Pg) extinction appears to have been geographically heterogeneous for some organismal groups. Southern Hemisphere K/Pg palynological records have shown lower extinction and faster recovery than in the Northern Hemisphere, but no comparable, well-constrained Southern Hemisphere macrofloras spanning this interval had been available. Here, macrofloral turnover patterns are addressed for the first time in the Southern Hemisphere, using more than 3500 dicot leaves from the latest Cretaceous (Maastrichtian) and the earliest Paleocene (Danian) of Argentine Patagonia. A maximum ca. 90% macrofloral extinction and ca. 45% drop in rarefied species richness is estimated across the K/Pg, consistent with substantial species-level extinction and previously observed extir-pation of host-specialized leaf mines. However, prior palynological and taxonomic studies indicate low turnover of higher taxa and persistence of general floral composition in the same sections. High species extinction, decreased species richness, and homogeneous Danian macrofloras across time and facies resemble patterns often observed in North America, but there are several notable differences. When compared with boundary-spanning macrofloras at similar absolute paleolatitudes (ca. 50°S or 50°N) from the Williston Basin (WB) in the Dakotas, both Maastrichtian and Danian Patagonian species richnesses are higher, extending a history of elevated South American diversity into the Maastrichtian. Despite high species turnover, our analyses also reveal continuity and expansion of leaf morphospace, including an increase in lobed and toothed species unlike the Danian WB. Thus, both Patagonian and WB K/Pg macro-floras support a significant extinction event, but they may also reflect geographically heterogeneous diversity, extinction, and recovery patterns warranting future study.
We describe Magallanodon baikashkenke gen. et. sp. nov., a new gondwanatherian mammal from the Late Cretaceous of the Magallanes Region in southern Chile (Río de Las Chinas Valley, Estancia Cerro Guido, north of Puerto Natales city, Última Esperanza Province). The mammal-bearing layer is placed within the Late Campanian-Early Maastrichtian levels of the Dorotea Formation (Magallanes/Austral Basin). The new remains constitute the southernmost record of a Mesozoic gondwanatherian mammal, as well as the frst Mesozoic mammal from Chile. This taxon is comparable in size to the hypsodont-toothed Gondwanatherium (Late Cretaceous) and Sudamerica (Early Paleocene) but with noticeably brachyodont molariforms supported by four to fve roots. As in other gondwanatherians, it has at least one hypertrophied, rodent-like incisor in the upper jaw. The new taxon is here diagnosed and described, and is regarded as a possible ferugliotheriid (?Ferugliotheriidae). If confrmed, it would represent the largest known taxon for this family. Its molariform occlusal crown pattern, after wear, resembles that of other gondwanatherians, particularly ferugliotheriids and that of the sudamericid Gondwanatherium. This adds new evidence on the phylogenetic proximity of ferugliotheriid and sudamericid gondwanatherians. An analysis of the enamel microstructure of the upper incisor of Magallanodon was performed demonstrating several crucial similarities with the pattern shown by Gondwanatherium (Sudamericidae). We discuss the signifcance of Magallanodon for understanding the acquisition, within gondwanatherians, of a lophed molariform pattern. Finally, we discuss the signifcance of the new fnding in the context of southern biotas, including those of Patagonia and Antarctica.
West Antarctica has formed the tectonically active margin between East Antarctica and the Pacific Ocean for almost half a billion years, where it has recorded a dynamic history of magmatism, continental growth and fragmentation. Despite the scale and importance of West Antarctica, there has not been an integrated view of the geology and tectonic evolution of the region as a whole. In this Review, we identify three broad physiographic provinces and present their overlapping and interconnected tectonic, magmatic and sedimentary history. The Weddell Sea region, which lays furthest from the subducting margin, was most impacted by the Jurassic initiation of Gondwana break-up. Marie Byrd Land and the West Antarctic rift system developed as a broad Cretaceous to Cenozoic continental rift system, reworking a former convergent margin. Finally, the Antarctic Peninsula and Thurston Island preserve an almost complete magmatic arc system. We conclude by briefly summarizing the geologic history of the West Antarctic system as a whole, how it provides insight into continental margin evolution and what key topics must be addressed by future research.
A remarkable diversity of plant-eating mammals known as South American native ungulates (SANUs) flourished in South America for most of the Cenozoic. Although some of these species likely filled ecological niches similar to those of modern hoofed mammals, others differed substantially from extant artiodactyls and perissodactyls in their skull and limb anatomy and probably also in their ecology. Notoungulates and litopterns were the longest-lived and most diverse SANU clades and survived into the Quaternary; astrapotheres went extinct in the late Miocene, whereas other SANU groups were restricted to the Paleogene. Neogene notoungulates were quite specialized in craniodental structure, but many were rather unspecialized postcranially; in contrast, litopterns evolved limb specializations early in their history while maintaining more conservative dentitions. In this article, we review the current understanding of SANU evolutionary relationships and paleoecology, provide an updated compilation of genus temporal ranges, and discuss possible directions for future research. ▪ South American native ungulates (SANUs) were a diverse, long-lived, and independent radiation of mammals into varied terrestrial plant-eater niches. ▪ We review origins, evolution, and paleoecology the major SANU clades: Notoungulata, Litopterna, Astrapotheria, Xenungulata, and Pyrotheria. ▪ At their peak, during the Eocene and Oligocene, more than 40 genera of native ungulates inhabited South America at any one time. ▪ SANUs ranged from <1 kg to several tons and evolved many combinations of diet and locomotor adaptations not seen in living ungulates.
Expected final online publication date for the Annual Review of Earth and Planetary Sciences, Volume 48 is May 29, 2020. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
The middle-late Eocene of Antarctica was characterized by dramatic change as the continent became isolated from the other southern landmasses and the Antarctic Circumpolar Current formed. These events were crucial to the formation of the permanent Antarctic ice cap, affecting both regional and global climate change. Our best insight into how life in the high latitudes responded to this climatic shift is provided by the fossil record from Seymour Island, near the eastern coast of the Antarctic Peninsula. While extensive collections have been made from the La Meseta and Submeseta formations of this island, few avian taxa other than penguins have been described and mammalian postcranial remains have been scarce. Here, we report new fossils from Seymour Island collected by the Antarctic Peninsula Paleontology Project. These include a mammalian metapodial referred to Xenarthra and avian material including a partial tarsometatarsus referred to Gruiformes (cranes, rails, and allies). Penguin fossils (Sphenisciformes) continue to be most abundant in new collections from these deposits. We report several penguin remains including a large spear-like mandible preserving the symphysis, a nearly complete tarsometatarsus with similarities to the large penguin clade Palaeeudyptes but possibly representing a new species, and two small partial tarsometatarsi belonging to the genus Delphinornis. These findings expand our view of Eocene vertebrate faunas on Antarctica. Specifically, the new remains referred to Gruiformes and Xenarthra provide support for previously proposed, but contentious, earliest occurrence records of these clades on the continent.
The Austral-Magallanes is an oil-producing basin located in southern Argentina and Chile, containing a siliciclastic stratigraphic record ranging from the Late Jurassic to late Cenozoic. This short paper finalize the two special volumes of the Latin American Journal of Sedimentology and Basin Analysis dedicated to the basin, and aims to provide a comprehensive synthesis based on the current knowledge about the chronology of deposition, stratigraphy, and tectonic events that shaped this basin. During the breakup of Gondwana in the Jurassic, an extensional phase was responsible for the beginning of accumulation of volcaniclastic material within grabens, which subsequently were covered by widespread Lower Cretaceous shallow and deep marine deposits that conforms the main hydrocarbon system. From Late Cretaceous onward, the subduction-related compressive regime associated to Andean uplift and fold and thrust belt migration was responsible for the onset of the foreland stage. During the Late Cretaceous, the foredeep zone accumulated a thick pile of deep marine deposits that graded upward to shallow marine and terrestrial deposits. During the Cenozoic, the foredeep was less marked and shallow marine and terrestrial sediments accumulated in wide areas, punctuated by important unconformities associated to foreland uplift. Future developments should focus on: i) improving the age-controlled stratigraphy; ii) joining the information provided by subsurface and outcrop studies; and iii) developing source to sink models to address the Andean impact in the sedimentation of the basin. ARTICLE INFO Article history
The first fossil remains of vertebrates, invertebrates, plants and palynomorphs of the Chorrillo Formation (Austral Basin), about 30km to the SW of the town of El Calafate (Province of Santa Cruz), are described. Fossils include the elasmarian (basal Iguanodontia) Isasicursor santacrucensis gen. et sp. nov., the large titanosaur Nullotitan glaciaris gen. et sp. nov., both large and small Megaraptoridae indet., and fragments of sauropod and theropod eggshells. The list of vertebrates is also composed by the Neognathae Kookne yeutensis gen. et sp. nov., two isolated caudal vertebrae of Mammalia indet., and isolated teeth of a large mosasaur. Remains of fishes, anurans, turtles, and snakes are represented by fragmentary material of low taxonomical value, with the exception of remains belonging to Calyptocephalellidae. On the other hand, a remarkable diversity of terrestrial and freshwater gastropods has been documented, as well as fossil woods and palinological assemblages. The Chorrillo Formation continues south, in the Las Chinas River valley, southern Chile, where it is called Dorotea Formation. Both units share in their lower two thirds abundant materials of titanosaurs, whose remains cease to appear in the upper third, registering only elasmarians (Chorrillo Formation) and hadrosaurs (Dorotea Formation). Above both units there are levels with remains of invertebrates and marine reptiles. It is striking that the dinosaurs of the lower two thirds of the Chorrillo and Dorotea formations are represented by large basal titanosaurs and Megaraptoridae coelurosaurs, being the Saltasaurinae and Aeolosaurinae sauropods and Abelisauridae theropods totally absent. In contrast, these taxa are dominant components in sedimentary units of central and northern Patagonia (e.g., Allen, Los Alamitos, La Colonia formations). Such differences could reflect, in part, a greater antiquity (i.e., late Campanian-early Maastrichtian) for the Chorrillo fossils, or, more probably, different environmental conditions. Thus, knowledge of the biota of the southern tip of Patagonia is expanded, particularly those temporarily close to the K-Pg boundary.
The fossil record of terrestrial mammals in Antarctica is temporally and geographically constrained to the Eocene outcrops of La Meseta and Submeseta formations in Seymour (Marambio) Island in West Antarctica. The faunal assemblage indicates a clear South American imprint since all the groups have a close phylogenetic relationship with Cretaceous and Paleogene mammals from Patagonia. Despite the presence of several mammalian taxonomic groups: Dryolestida, Gondwanatheria, Eutheria and Metatheria, the presence of other major mammalian taxa should be expected and will probably be confirmed by new findings. Placental mammals with an inferred body mass between 10 to 400 kg in size, are represented by xenarthrans, and two groups of the so called South American native ungulates: Astrapotheria and Litopterna. The Metatheria are the smaller (less than 1 kg) and most abundant components of the fauna. Marsupials are represented by derorhynchid ameridelphians, several microbiotherian australidelphians (both microbiotheriids and woodburnodontids), and ?glasbiid prepidolopod and polydolopid polydolopimorphians. Plus, there are remains of several mammalian teeth of indeterminate phylogenetic affinities. The present knowledge of the Southern Hemisphere mammalian evolution and paleogeographic change through time, indicates that Antarctica played a major role for land mammals, at least since the Jurassic. The actual representation of Paleogene terrestrial mammals in Antarctica is most probably biased, as all the evidence indicates that australosphenidan mammals should be present in this continent since the Jurassic.
The Paleocene (66-56 Ma) was a critical time interval for understanding the geological history in high palaeolatitudes after the end of Cretaceous event (recovery from mass extinction, palaeoclimate, global sea level changes, among others). The sedimentary succession from Seymour Island (Antarctic Peninsula) provides key reference material from this important phase of the early Cenozoic. A detailed age model is proposed for the López de Bertodano Formation (LBF), Sobral Formation (SF) and Cross Valley-Wiman Formation (CVWF) based on a new magnetostratigraphic section which integrates previous dinoflagellate cyst biostratigraphy, Iridium anomaly (K-Pg boundary), U-Pb zircon dating (airfall tuff) and strontium isotope values from macrofossils. The new composite magnetostratigraphic section, which includes the Cretaceous-Paleogene boundary, has been correlated to the GPTS from C29r up to C24r. The top of the LBF is confirmed as latest Maastrichtian to earliest Danian (~65.4 Ma) in age. The overlying SF is mostly Danian in age (~65.2-~63 Ma) and CVWF is Selandian-Thatenian (~61.3-56.9 Ma). LBF, SF and CVWF are unconformity-bounded units (alloformations) that record the geological evolution of the James Ross Basin during a period of relative decreasing tectonism but coeval with volcanic activity. Unconformity based internal units have been recognized, dividing each formation into allomembers (LBF: Molluscan and Cenozoic; SF: A, B and C; CVWF: Dí az, Arañado, Bahí a Pingüino). The new age model allows correlation of base-level changes with eustatic sea-level fluctuations. The bases of the SF and CVWF are correlated with the 65.3 and 61.5 Ma sea level lowstands.
Although the fossil record of non-avian dinosaurs from the Cretaceous of Antarctica is the poorest of any continent, fossils representing at least five major taxonomic groups (Ankylosauria, early-diverging Ornithopoda, Hadrosauridae, Titanosauria, and Theropoda) have been recovered. All come from Upper Cretaceous (Coniacian–Maastrichtian) marine and nearshore deposits belonging to the Gustav and Marambio groups of the James Ross Basin at the northern tip of the Antarctic Peninsula. The majority of these finds have come from the Campanian–Maastrichtian Snow Hill Island and López de Bertodano formations of James Ross and Vega islands. Given the rarity of Antarctic Cretaceous non-avian dinosaurs, discoveries of any fossils of these archosaurs, no matter how meager, are of significance. Here we describe fragmentary new ornithischian (ankylosaur and ornithopod) material from the upper Campanian–lower Maastrichtian Cape Lamb Member of the Snow Hill Island Formation and the Maastrichtian Sandwich Bluff Member of the López de Bertodano Formation. One of these specimens is considered to probably pertain to the holotypic individual of the early-diverging ornithopod Morrosaurus antarcticus. We also provide an up-to-date synthesis of the Late Cretaceous non-avian dinosaur record of the James Ross Basin and analyze the biostratigraphic occurrences of the various finds, demonstrating that most (including all named taxa and all reasonably complete skeletons discovered to date) occur within a relatively condensed temporal interval of the late Campanian to early Maastrichtian. Most or all James Ross Basin dinosaurs share close affinities with penecontemporaneous taxa from Patagonia, indicating that at least some continental vertebrates could disperse between southern South America and Antarctica during the final stages of the Mesozoic.
The living tree sloths Choloepus and Bradypus are the only remaining members of Folivora, a major xenarthran radiation that occupied a wide range of habitats in many parts of the western hemisphere during the Cenozoic, including both continents and the West Indies. Ancient DNA evidence has played only a minor role in folivoran systematics, as most sloths lived in places not conducive to genomic preservation. Here we utilize collagen sequence information, both separately and in combination with published mitochondrial DNA evidence, to assess the relationships of tree sloths and their extinct relatives. Results from phylogenetic analysis of these datasets differ substantially from morphology-based concepts: Choloepus groups with Mylodontidae, not Megalonychidae; Bradypus and Megalonyx pair together as megatherioids, while monophyletic Antillean sloths may be sister to all other folivorans. Divergence estimates are consistent with fossil evidence for mid-Cenozoic presence of sloths in the West Indies and an early Miocene radiation in South America.
The Flat Rocks locality in the Wonthaggi Formation (Strzelecki Group) of the Gippsland Basin, southeastern Australia, hosts fossils of a late Barremian vertebrate fauna that inhabited the ancient rift between Australia and Antarctica. Known from its dentary, Qantassaurus intrepidus Rich and Vickers-Rich, 1999 has been the only dinosaur named from this locality. However, the plethora of vertebrate fossils collected from Flat Rocks suggests that further dinosaurs await discovery. From this locality, we name a new small-bodied ornithopod, Galleonosaurus dorisae n. gen. n. sp. from craniodental remains. Five ornithopodan genera are now named from Victoria. Galleonosaurus dorisae n. gen. n. sp. is known from five maxillae, from which the first description of jaw growth in an Australian dinosaur is provided. The holotype of Galleonosaurus dorisae n. gen. n. sp. is the most complete dinosaur maxilla known from Victoria. Micro-CT imagery of the holotype reveals the complex internal anatomy of the neurovascular tract and antorbital fossa. We confirm that Q. intrepidus is uniquely characterized by a deep foreshortened dentary. Two dentaries originally referred to Q. intrepidus are reassigned to Q. ? intrepidus and a further maxilla is referred to cf. Atlascopcosaurus loadsi Rich and Rich, 1989. A further ornithopod dentary morphotype is identified, more elongate than those of Q. intrepidus and Q. ? intrepidus and with three more tooth positions. This dentary might pertain to Galleonosaurus dorisae n. gen. n. sp. Phylogenetic analysis recovered Cretaceous Victorian and Argentinian nonstyracosternan ornithopods within the exclusively Gondwanan clade Elasmaria. However, the large-bodied taxon Muttaburrasaurus langdoni Bartholomai and Molnar, 1981 is hypothesised as a basal iguanodontian with closer affinities to dryomorphans than to rhabdodontids.
UUID: http://zoobank.org/4af87bb4-b687-42f3-9622-aa806a6b4116
Two timelines for extinction
The Cretaceous-Paleogene extinction that wiped out the nonavian dinosaurs 66 million years ago was correlated with two extreme events: The Chicxulub impact occurred at roughly the same time that massive amounts of lava were erupting from the Deccan Traps (see the Perspective by Burgess). Sprain et al. used argon-argon dating of the volcanic ash from the Deccan Traps to argue that a steady eruption of the flood basalts mostly occurred after the Chicxulub impact. Schoene et al. used uranium-lead dating of zircons from ash beds and concluded that four large magmatic pulses occurred during the flood basalt eruption, the first of which preceded the Chicxulub impact. Whatever the correct ordering of events, better constraints on the timing and rates of the eruption will help elucidate how volcanic gas influenced climate.
Science , this issue p. 866 , p. 862 ; see also p. 815
The Mesozoic plate tectonic and paleogeographic history of Gondwana had a profound effect on the distribution of terrestrial vertebrates. As the supercontinent fragmented into a series of large landmasses (South America, Africa-Arabia, Antarctica, Australia, New Zealand, the Indian subcontinent, and Madagascar), particularly during the Late Jurassic and Cretaceous, its terrestrial vertebrates became progressively isolated, evolving into unique faunal assemblages. We focus on four clades that, during the Mesozoic, had relatively low ability for dispersal across oceanic barriers—crocodyliforms, sauropod dinosaurs, nonavian theropod dinosaurs, and mammals. Their distributions reveal patterns that are critically important in evaluating various biogeographic hypotheses, several of which have been informed by recent discoveries from the Late Cretaceous of Madagascar. We also examine the effects of lingering, intermittent connections, or reconnections, of Gondwanan landmasses with Laurasia (through the Caribbean, Mediterranean, and Himalayan regions) on the distributions of different clades. Expected final online publication date for the Annual Review of Earth and Planetary Science Volume 47 is May 30, 2019. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
Two paleomagnetic poles of 80 and 75 Ma have been computed from 191 to 123 paleomagnetic samples, respectively, of the marine sedimentary units of the Upper Cretaceous Marambio Group exposed in the James Ross Island, Antarctic Peninsula. Paleomagnetic behaviors during stepwise thermal demagnetization and rock magnetic analyses indicate that magnetization is likely primary and carried by SD-PSD detrital titanomagnetite. Application of an inclination shallowing correction by the elongation-inclination method yielded a significant inclination shallowing affecting the older (ca. 80 Ma) succession exposed in the northwest area of the island. However, the paleomagnetic directions computed from the younger (ca. 75 Ma) succession outcropping in the southeast corner of the island yielded an indeterminate result using the same analysis. The inclination shallowing-corrected 80 Ma paleopole position plus previous ones of ca.110, 90 and 55 Ma were used to construct the Apparent Polar Wander Path (APWP) for the Antarctic Peninsula during the Late Cretaceous-Paleocene. This path confirms that oroclinal bending of the Antarctic Peninsula as well as relative displacement with respect to East Antarctica are negligible since 110 Ma. Comparison with the apparent polar wander path for South America for the 130-45 Ma period suggests that this continent and the Antarctic Peninsula kept a very similar relative paleogeographic position since 110 Ma until 55 Ma, which likely meant a physical link between both continental masses. During that period, both continents underwent a relatively fast southward displacement of around 7° and a clockwise rotation relative to the Earth spin axis that can be bracketed between around 100 and 90 Ma. Oroclinal bending of the Fuegian Andes was likely due to tectonic interactions between the Patagonian-Fuegian Andes and the Antarctic Peninsula promoted, at least partially, by such displacements. By 55 Ma the Antarctic Peninsula probably was starting or about to start its final separation from South America.
The Río Chico Group in the San Jorge Basin of central Patagonia (Argentina) preserves some of South America’s most significant Paleogene records of biotic and climatic change. Three of its constituent formations, the Peñas Coloradas, Las Flores, and Koluel-Kaike, host vertebrate faunas referred to the “Carodnia faunal zone,” the Itaboraian South American Land Mammal Age (SALMA), and the Riochican SALMA. However, the precise absolute ages of these units, and thus their associated faunas and paleoclimate records, are poorly resolved. Herein, we report new paleomagnetic and geochronologic results from these formations in south-central Chubut Province, Argentina. U-Pb dating of four volcanic ashes, using both laser ablation–multicollector–inductively coupled plasma–mass spectrometry and high-resolution chemical abrasion–isotope dilution–thermal ionization mass spectrometry, indicates ages of igneous crystallization of 51.403 ± 0.037 (0.045) [0.071] Ma for a level within the middle Las Flores Formation and 46.714 ± 0.012 (0.026) [0.057] Ma, 44.579 ± 0.013 (0.026) [0.054] Ma, and 42.856 ± 0.017 (0.027) [0.054] Ma for levels in the lower, middle, and upper Koluel-Kaike Formation, respectively. Combining these with previous isotopic ages in our new magnetostratigraphic framework, we correlate the Peñas Coloradas Formation to chrons C27n-26r (ca. 62.5 to ca. 61.6 Ma; late Danian) and the section from the middle Las Flores to the uppermost Koluel-Kaike to chrons C23n to C19r (ca. 51.4–42.2 Ma; mid Ypresian–late Lutetian). We combine these data with other recently published chronostratigraphic results from Paleogene units in Patagonia to better constrain the ages of noteworthy Paleogene plant and mammal fossil sites in Patagonia and to develop a revised temporal calibration of the Las Flores, Vacan, and “Sapoan” faunas.
One of the most intriguing paleobiogeographical phenomena related to the final stage of Gondwanan breakup is the close similarities and, in most cases, inferred sister-group relationships, of a number of terrestrial and marine/coastal vertebrate taxa recovered from Paleogene deposits of West Antarctica with those from other continents (South America, Australia). These continents are today separated by large and deep ocean floors, which was not the case in the geological past. However, the inferred timing of continental separation does not always match with the inferred time of vertebrate dispersals.
The relationships between sequence stratigraphy and evolutionary succession on land mammal communities of Paleocene beds in coastal Patagonia (45º S) are analyzed. We found that there exists a harmonic correspondence between the discontinuities in strata and mammal sequences. More specifically, we conclude that: (1) each of the Patagonian Paleocene "fauna! zones" recognized by Simpson represent discrete episodes in South American mammal evolution ; (2)
those mammals recently recovered from the "Banco Negro Inferior" of the Salamanca Group at Punta Peligro represent fourth, older, and more distinct Paleocene episode than assemblages previously described from this area; (3) the mammals characterizing each of the theses episodes were recovered from discrete strata packages bounded by complex surfaces irregularly shaped after subaerial incisions, coastal abrasion and marine scouring; (4) we think that the implicit discontinuities that separate both the mammals evolutionary episodes (turnovers) and the sedimentary sequences (unconformities) were developed concurrently, and both consequently may have been linked to global eustatic changes; (5) three of the four episodes previously had been considered to characterize discrete SALMAs, from older to younger, Tiupampian (Peligran?), Itaboraian ("Kibenikhoria fauna! zone"), and Riochican ("Ernestokokenia fauna! zone"). The fourth episode ("Carodnia fauna! zone"), between Tiupampian and Itaboraian, have not been distinguished previously as a SALMA, and although it seems to characterize a discrete one, the
present evidence is not sufficient to warrant building a new SALMA; (6) as for other SALMAs based on Patagonian faunas, it could be difficult to distinguish these SALMAs in areas outside this region.
During the Cenozoic Patagonia acted as a distinct paleogeographic region (particularly during the Paleogene) and it is difficult to assert if all the determinants evolutionary processes affecting these
faunas occurred just in Patagonia; and (7) the high endemic diversity of marsupials during the Tiupampian SALMA, when the endemic radiation of placentals showed only their first steps, supports the hypothesis of a previous immigration of marsupials to South America.
The origins of South America’s exceptional plant diversity are poorly known from the fossil record. We report on unbiased quantitative collections of fossil floras from Laguna del Hunco (LH) and Río Pichileufú (RP) in Patagonia, Argentina. These sites represent a frost‐free humid biome in South American middle latitudes of the globally warm Eocene. At LH, from 4,303 identified specimens, we recognize 186 species of plant organs and 152 species of leaves. Adjusted for sample size, the LH flora is more diverse than comparable Eocene floras known from other continents. The RP flora shares several taxa with LH and appears to be as rich, although sampling is preliminary. The two floras were previously considered coeval. However, 40Ar/39Ar dating of three ash‐fall tuff beds in close stratigraphic association with the RP flora indicates an age of \landscape $47.46\pm 0.05 Ma, 4.5 million years younger than LH, for which one tuff is reanalyzed here as \landscape $51.91\pm 0.22 Ma. Thus, diverse floral associations in Patagonia evolved by the Eocene, possibly in response to global warming, and were persistent and areally extensive. This suggests extraordinary richness at low latitudes via the latitudinal diversity gradient, corroborated by published palynological data from the Eocene of Colombia.
Resolving the role of longitudinal versus transverse sediment dispersal in ancient sedimentary basins is paramount for understanding filling history and the timing of source area exhumation. The southern Patagonian Andes provide a unique opportunity for constraining these relationships because Upper Cretaceous shallow- and deep-marine strata that record the longitudinal filling history of the Magallanes-Austral foreland basin are exposed along a 500+ km outcrop belt. New stratigraphic, sedimentologic, and facies analyses of the Cenomanian-aged Lago Viedma Formation indicate a protracted phase of a dominantly shoreface and foreshore depositional setting at the northern end of the basin (Austral basin sector), whereas 200 km to the south, age-equivalent strata of the Punta Barrosa Formation are characterized by southward-flowing deep-water fan systems. New sandstone compositional data from both formations are rich in intermediate volcanic grains and suggest an un-dissected to transitional volcanic arc source. However, detrital zircon populations from the shallow-marine Lago Viedma Formation are dominated by arc sources (126-75 Ma), whereas deep-water strata of the Punta Barrosa Formation contain much greater abundances of Jurassic (199-161 Ma) and pre Jurassic (>200 Ma) ages. This indicates that deep-water fan systems were not linked to a shelfal sediment dispersal system by a simple northward point-source model, despite consistent southward-directed paleocurrents in deep-water strata. Time-transgressive provenance variations continue southward (along strike), where lithostratigraphic equivalents in the Ultima Esperanza and Fuegian sectors of the basin contain a mix of arc and pre Jurassic metamorphic basement sources and a paucity of Jurassic ages. We interpret these along-strike provenance variations to be the result of significant local sediment contributions from transverse sources. The influence of transverse tributaries during the early history of the Magallanes-Austral foreland basin suggests that the diachronous onset of coarse clastic deposition in the basin was likely due to the progressive delivery (and initiation) of more locally derived coarse clastic sediment. We attribute this to southward-progressing thrust-belt development associated with progressive north to south collision (or suturing) of the parautochthonous Patagonian arc with attenuated continental crust of South America.
Australian dinosaurs have played a rare but controversial role in the debate surrounding the effect of Gondwanan break-up on Cretaceous dinosaur distribution. Major spatiotemporal gaps in the Gondwanan Cretaceous fossil record, coupled with taxon incompleteness, have hindered research on this effect, especially in Australia. Here we report on two new sauropod specimens from the early Late Cretaceous of Queensland, Australia, that have important implications for Cretaceous dinosaur palaeobiogeography. Savannasaurus elliottorum gen. et sp. nov. comprises one of the most complete Cretaceous sauropod skeletons ever found in Australia, whereas a new specimen of Diamantinasaurus matildae includes the first ever cranial remains of an Australian sauropod. The results of a new phylogenetic analysis, in which both Savannasaurus and Diamantinasaurus are recovered within Titanosauria, were used as the basis for a quantitative palaeobiogeographical analysis of macronarian sauropods. Titanosaurs achieved a worldwide distribution by at least 125 million years ago, suggesting that mid-Cretaceous Australian sauropods represent remnants of clades which were widespread during the Early Cretaceous. These lineages would have entered Australasia via dispersal from South America, presumably across Antarctica. High latitude sauropod dispersal might have been facilitated by Albian–Turonian warming that lifted a palaeoclimatic dispersal barrier between Antarctica and South America.
Determining both short-and long-term sedimentation rates is becoming increasingly important in geomorphic (exhumation and sediment flux), structural (subsidence/flexure) and natural resource (predictive modelling) studies. Determining sedimentation rates for ancient sedimentary sequences is often hampered by poor understanding of stratigraphic architecture, long-term variability in large-scale sediment dispersal patterns and inconsistent availability of absolute age data. Uranium– Lead (U-Pb) detrital zircon (DZ) geochronology is not only a popular method to determine the provenance of siliciclastic sedimentary rocks but also helps delimit the age of sedimentary sequences, especially in basins associated with protracted volcanism. This study assesses the reliability of U-Pb DZ ages as proxies for depositional ages of Upper Cretaceous strata in the Magallanes-Austral retro-arc foreland basin of Patagonia. Progressive younging of maximum depositional ages (MDAs) calculated from young zircon populations in the Upper Cretaceous Dorotea Formation suggests that the MDAs are potential proxies for absolute age, and constrain the age of the Dorotea Formation to be ca. 82–69 Ma. Even if the MDAs do not truly represent ages of contemporaneous volcanic eruptions in the arc, they may still indicate progressive-but-lagged delivery of increasingly younger vol-canogenic zircon to the basin. In this case, MDAs may still be a means to determine long-term (≥1– 2 Myr) average sedimentation rates. Burial history models built using the MDAs reveal high aggra-dation rates during an initial, deep-marine phase of the basin. As the basin shoaled to shelfal depths, aggradation rates decreased significantly and were outpaced by progradation of the deposystem. This transition is likely linked to eastward propagation of the Magallanes fold-thrust belt during Campa-nian-Maastrichtian time, and demonstrates the influence of predecessor basin history on foreland basin dynamics.
Even though ammonites are not very abundant in Patagonia, a large number of specimens were collected by geologists from the Empresa Nacional del Petroleo (ENAP), Chile, during the course of several years of field work in the Magallanes Basin. This study describes the ammonite family Kossmaticeratidae present in that collection, which is a typical element of most southern hemisphere Late Cretaceous assemblages. The species described include: Kossmaticeras ( Kossmaticeras ?) fasciculatum n. sp., K. ( Karapadites ) constrictus n. sp., K. ( Natalites ) cecioni n. sp., K. ( Natalites ) hauthali (Paulcke), K. ( Natalites ) sp., Neograhamites kiliani Spath, N. taylori Spath, Gunnarites elegans n. sp., G. bhavaniformis (Kilian and Reboul), Grossouvrites gemmatus (Huppe), and Maorites densicostatus (Kilian and Reboul).
The stratigraphic information on this fauna indicates that it is distributed in four assemblages. The oldest (assemblage A), possibly late Santonian to early Campanian in age, includes the species Kossmaticeras ( Kossmaticeras ?) fasciculatum, Neograhamites taylori , and possibly N. kiliani. This is followed by assemblage B (possibly middle to late Campanian), with K. ( Karapadites ) constrictus, K. ( Karapadites ) centinelaense (Blasco, Nullo, and Proserpio), K. ( Natalites ) hauthali, K. ( Natalites ) cecioni, Neograhamites morenoi Riccardi, N. taylori, N. kiliani, K. ( Natalites ) sp., Gunnarites elegans, G. bhavaniformis , and possibly Pseudokossmaticeras paulckei Collignon. The third assemblage (C), possibly late Campanian to early Maastrichtian in age, contains G. elegans, G. bhavaniformis, Grossouvrites gemmatus , and K. ( Natalites ) hauthali . The youngest assemblage (D) is possibly late Maastrichtian in age and is composed of the species Maorites densicostatus and Grossouvrites gemmatus .
The upper Mesozoic to lower Cenozoic sequence is the only exposed marine succession of that age in Antarctica. Sedimentary facies include proximal submarine fans, shelf settings, and deltaic environments. Sea-floor anomaly data from the Pacific Ocean suggest that development of Upper Mesozoic to Cenozoic fore-arc, magmatic arc, and back-arc terrains of the Peninsula resulted from the subduction of the Phoenix Plate until the early Tertiary, and, after reorganization of spreading centers in Late Cretaceous time, subduction of the Aluk Plate. Strata in the James Ross Island region constitute the sedimentary and volcanic fill of an ensialic back-arc basin developed on the Weddell Sea flank of the Antarctic Peninsula. -from Author
ABSTRACT. We describe an isolated molariform tooth excavated from ?Eocene deposits
at Santa Rosa, Peru´ . The specimen most probably belongs to a mammal, and it
may correspond to a left upper last molar. Analysis of its enamel and dentine microstructure
leads to no definite conclusion as to its relationships, or even as to its enamel–
dentine structural patterns. Taphonomic processes, for example, digestion of the specimen
by a predator, might be involved in some of its peculiar characteristics. Its unique
gross morphology prevents us from assigning it to any known mammal group with
confidence. Several features of its cusp and crest morphology resemble the general pattern
of Late Cretaceous–Eocene gondwanatherian mammals, especially that of Ferugliotherium
windhauseni (Ferugliotheriidae).
ABSTRACT: NEW PALlNOLOGIC DESCRIPTIOKS FROM THE SALAMANCA AND BORORÖ FORMATIONS (PALEOCENE), CHUBUT PROVINCE, ARGENTINE REPUBLIC.
The material was collected from several sectíons of the Salamanca Formation (Cerro Abigarr:ido, Puerto Visser, Bajada de Hansen) and from otHer sections of the Bororó Forrnation. Samples from
one subsurface core have been studíed too. The groups here described include monocolpate, tricolpate
and tricolporate grains. The following new species are proposed . Liliacidites vermireticulatus, Spillizollocolpites hialinus, Rousea microreticulata, Rousea minuscula, Striatopollis exignus, Tricolpites bibaculatus, Psilatricolporites salamanquensis and Ericipites microtectatum-
This book summarizes the most relevant published paleontological information, supplemented by our own original work, on the record of Mesozoic mammals’ evolution, their close ancestors and their immediate descendants. Mammals evolved in a systematically diverse world, amidst a dynamic geography that is at the root of the 6,500 species living today. Fossils of Mesozoic mammals, while rare and often incomplete, are key to understanding how mammals have evolved over more than 200 million years. Mesozoic mammals and their close relatives occur in a few dozen localities from Argentina, Brazil, Chile, Bolivia, and Peru spanning from the Mid- Triassic to the Late Cretaceous, with some lineages surviving the cataclysmic end of the Cretaceous period, into the Cenozoic of Argentina. There are roughly 25 recognized mammalian species distributed in several distinctive lineages, including australosphenidans, multituberculates, gondwanatherians, eutriconodonts, amphilestids and dryolestoids, among others. With its focus on diversity, systematics, phylogeny, and their impact on the evolution of mammals, there is no similar book currently available.
Andinodelphys cochabambensis Marshall & Muizon, 1988 is one of the best preserved metatherian species from the early Palaeocene fauna of Tiupampa (Bolivia). It is represented by five almost complete skulls, three of them being securely associated to sub-complete to partial skeleton. Four skulls could be extracted from a block including several intermingled skeletons. The present paper provides a thorough description of the dental, cranial, and dentary anatomy of A. cochabambensis. The cranial anatomy of A. cochabambensis is similar to that of Pucadelphys andinus. The skull of Andinodelphys however differs from that of Pucadelphys in its larger size and proportionally longer rostrum. Other differences include the presence, in Andinodelphys, of large anteriorly protruding I1s, small palatal vacuities, a transverse canal, and a small hypotympanic sinus. Andinodelphys has the same dental formula as Pucadelphys (I 5/4, C 1/1, P 3/3, M4/4), the plesiomorphic condition for metatherians. Furthermore, both genera share the lack a tympanic process of the alisphenoid, a deep groove for the internal carotid artery at the anterior apex of the promontorium, a small prootic canal perforating the lateral edge of the petrosal and opening laterally in the deep sulcus for the prootic sinus, and a vestigial anterior lamina of the petrosal. Dentally Andinodelphys closely resembles Pucadelphys, the two genera differing in the larger size of the former and in the inconstant presence in the former of a twinned stylar cusp C. Although 25% smaller, the cheek teeth of Andinodelphys closely resemble those of Itaboraidelphys camposi from the early Eocene of Itaboraí (Brazil). As far as dental morphology is concerned, both genera are likely to have diverged from a direct common ancestor, probably Andinodelphys-like, with Itaboraidelphys displaying more derived dental structures. Two isolated petrosal from Itaboraí (Type 2 petrosals) are morphologically close to those of Andinodelphys but distinctly larger. In this paper, a previous interpretation including the teeth of Itaboraidelphys and these petrosals in the same taxon is followed. A phylogenetic analysis retrieved Itaboraidelphys as a sister taxon of the clade Pucadelphys + Andinodelphys, thus lending support to inclusion of the former in the Pucadelphyidae. Three sets of parsimony analyses were performed. A first set of analyses (with all characters) retrieved a strict consensus tree with a clade as follows: (pucadelphyids, (deltatheroidans (stagodontids, Gurlin Tsav skull-GTS), sparassodonts)). An implied weighting analysis with the same data matrix placed the stagodontids in an early diverging position but retained a clade (pucadelphyids, (deltatheroidans, (GTS, sparassodonts))), the deltatheroidans, being therefore inserted in the pucadelphydans. This result implies an independent arrival of pucadelphyids and sparassodonts to South America, which consequently must have been present in North America in the Late Cretaceous. Possible North American sparassodonts could be the poorly known genera Atokatheridium and Olklatheridium (currently referred to deltatheroidans) and the pucadelphyids may have been present in the Late Cretaceous of North America with the genus Aenigmadelphys. However, this hypothesis is less parsimonious (with regard to palaeobiogeography) than a single southward migration of an ancestral Pucadelphyda (Pucadelphyidae + Sparassodonta). Because the result of this first set of analyses may have been induced by heavily homoplastic dental characters related to hypercarnivory, a second set of analyses was performed excluding all the dental characters. The strict consensus is poorly resolved but retains monophyletic Marsupialia and Sparassodonta. An implied weighting analysis retrieved a monophyletic Pucadelphyda but split the deltatheroidans, the polyphyly of which is regarded as a possible artefact related to the lack of dental characters. The GTS is sister taxon to Pucadelphyda. Because the polyphyly of deltatheroidans contradicts all previous hypotheses, a third set of analyses has been performed excluding only those molar characters that supported the close relationships of the hypercarnivorous clades (deltatheroids, stagodontids, and sparassodonts). The strict consensus tree retrieved monophyletic deltatheroidans, Marsupialia and sparassodonts. An implied weighting analysis resulted in deltatheroidans forming a paraphyletic stem assemblage of Metatheria and monophyletic Pucadelphyda. The GTS was no longer related to sparassodonts but was the sister taxon of a clade including the North American taxa of the data matrix, Asiatherium, and Marsupialia. This topology, which is favoured here, supports (as well as that of the second set of analyses) a single pucadelphydan southward migration, probably in the Late Cretaceous, with a Tiupampian radiation of South American carnivorous metatherians.
The Kibenikhoria and Ernestokokenia local faunas were described in the 1930s by George G. Simpson, who defined them as two chronologically consecutive faunas based on a comparison with the Casamayoran South American Land Mammal Age (SALMA). Later, in the 1980?s, both faunas were respectively the basis of the Itaboraian and Riochican SALMAs, a scheme broadly accepted since more than eight decades. However, a systematic revision of their native ungulates is still lacking. In this contribution, we study several collections performed in the classic localities of Cañadón Hondo and Bajo Palangana (southeastern South America), and discuss the systematic status of the mammals listed in their faunas. Our results allow to: (1) assert that the beds containing the mammal associations in Cañadón Hondo and Bajo Palangana locate in the the upper Las Flores Formation and are essentially contemporaneous, (2) improve the knowledge for Kibenikhoria get and Henricosbornia lophodonta, (3) propose H. waitehor and?Peripantostylops orehor are synonymous names of H. lophodonta, and (4) recognize Shecenia ctirneru, Seudenius cteronc, and Pospithecus as Trigonostylopidae aff. Trigonostylops. The Kibenikhoria and Ernestokokenia faunas have six genera in common; five of them are shared with the lower levels of the Sarmiento Formation, whereas K. get, Isotemnus ctalego, Pliodolops winecage, and Gasternia ctalehor are exclusive taxa. Here, the Riochican sensu stricto from Marshall is used to include both local faunas, which represents a distinct and more derived fauna than that from the Itaboraí Formation, but witha less advanced evolutive stage than the lower Sarmiento Formation.
Megaraptorid theropods thrived in South America and Australia during the mid-Cretaceous. Their Australian record is currently limited to the upper Barremian–lower Aptian upper Strzelecki Group and the upper Aptian–lower Albian Eumeralla Formation of Victoria, the Cenomanian Griman Creek Formation of New South Wales, and the Cenomanian–lowermost Turonian Winton Formation of Queensland. The latter has produced Australovenator wintonensis, the stratigraphically youngest and most complete Australian megaraptorid. The Eric the Red West (ETRW) site on Cape Otway, Victoria (Eumeralla Formation; lower Albian), has yielded two teeth, two manual unguals, and a right astragalus that are almost identical to the corresponding elements in Australovenator. Herein, we classify these as Megaraptoridae cf. Australovenator wintonensis. We also reappraise the ‘spinosaurid’ cervical vertebra from ETRW and suggest that it pertains to Megaraptoridae. Three other theropod elements from ETRW—a cervical rib (preserving a bite mark), a caudal vertebra, and a non-ungual manual phalanx—are also described, although it is not possible to determine their phylogenetic position more precisely than Tetanurae (non-Maniraptoriformes). All elements were found in a fluvial deposit, associated with isolated bones of other theropods, ornithopods, and turtles, amongst others; consequently, no two can be unequivocally assigned to the same theropod individual. The new specimens from ETRW demonstrate that a megaraptorid theropod morphologically similar to Australovenator lived during the late Early Cretaceous in Victoria, at a higher paleolatitude than its northern counterpart. Moreover, they attest to the success of megaraptorids in late Barremian–early Turonian faunas throughout eastern Australia.
The Magallanes-Austral foreland basin preserves an important record of orogenesis and landscape evolution in the Patagonian Andes of Chile and Argentina. Throughout the retroarc foreland basin, a regional disconformity with little to no angular discordance separates Upper Cretaceous–lower Paleocene strata from overlying deposits of diachronous Eocene to Miocene age. Here we report detrital zircon U-Pb geochronological results for 11 sandstone samples, and vitrinite reflectance data for 6 samples of organic matter from a fossiliferous dinosaur-bearing marine and nonmarine clastic succession in the Río de las Chinas valley (50–51°S) of central-southern Patagonia to: (1) determine the timing and duration of the unconformity using U-Pb maximum depositional age constraints, (2) reconstruct sediment provenance and dispersal patterns, (3) assess possible temporal variations in arc magmatism, (4) evaluate the amount of sedimentary overburden removed during unconformity development, and (5) confirm the presence of a fossiliferous southern hemisphere Cretaceous–Paleogene (K/Pg) boundary site. Samples from the Dorotea Formation yield maximum depositional ages spanning Maastrichtian to Danian time (with ages as young as ∼65–63 Ma), confirming preservation of the K/Pg boundary in a section with recently discovered fossils of dinosaurs, other terrestrial vertebrates, and plants. Samples from directly above the unconformity in the Man Aike Formation, yield middle Eocene maximum depositional ages (with a prominent 45–40 Ma age cluster), indicating a long-lived ∼20 Myr hiatus representative of nondeposition or erosion. Analyses of organic matter preserved in multiple coal horizons of the uppermost Dorotea Formation show consistently low vitrinite reflectance values, requiring limited sedimentary burial, consistent with nondeposition or sediment bypass rather than deposition and later erosional removal of a previously proposed thick package of Paleocene to middle Eocene clastic material. On the basis of regional trends in the age and geometry of the unconformity, timing of arc magmatism, and temporal variations in sediment provenance, we consider a range of potential mechanisms for unconformity genesis, including (1) shortening-related uplift of the frontal fold-thrust belt, (2) cratonward advance of a flexural forebulge, (3) accommodation changes driven by regional or eustatic variations in sea level, (4) ridge collision and slab-window genesis, (5) isostatic rebound during tectonic quiescence (or minor extension), or (6) regional foreland uplift during flat-slab subduction.
Living sloths represent two distinct lineages of small-sized mammals that independently evolved arboreality from terrestrial ancestors. The six extant species are the survivors of an evolutionary radiation marked by the extinction of large terrestrial forms at the end of the Quaternary. Until now sloth evolutionary history has mainly been reconstructed from phylogenetic analyses of morphological characters. Here we used ancient DNA methods to successfully sequence 10 extinct sloth mitogenomes encompassing all major lineages. This includes the iconic continental ground sloths Megatherium, Megalonyx, Mylodon, and Nothrotheriops, and the smaller endemic Caribbean sloths Parocnus and Acratocnus. Phylogenetic analyses identify eight distinct lineages grouped in three well-supported clades and whose interrelationships are markedly incongruent with the currently accepted morphological topology. We show that recently extinct Caribbean sloths have a single origin but comprise two highly divergent lineages that are not directly related to living two-fingered sloths, which instead group with Mylodon. Moreover, living three-fingered sloths do not represent the sister-group to all other sloths but are nested within a clade of extinct ground sloths including Megatherium, Megalonyx, and Nothrotheriops. Molecular dating also reveals that the eight newly recognized sloth families all originated between 36 and 28 million years ago (Mya). The early divergence of recently extinct Caribbean sloths around 35 Mya is consistent with the debated GAARlandia hypothesis postulating the existence at that time of a biogeographic connection between northern South America and the Greater Antilles. This new molecular phylogeny has major implications for reinterpreting sloth morphological evolution, biogeography, and diversification history.
The stratigraphic architecture and environmental evolution of the Cerro Guido-Rio de las Chinas Valley Complex contains the upper Cretaceous to Eocene record of the Magallanes/Austral Basin, located in southernmost Chile. This retroarc foreland basin contains a significant record of early Cretaceous to Miocene biogeographic and environmental changes that occurred in high paleolatitudes after the break-up of Gondwana. Using 37 stratigraphic sections, we generated a 1390 m thick stratigraphic column, which was used to developed sedimentary facies and an analysis of sequence stratigraphy. Results show, in general, aggradation composed of six third-order depositional sequences each delimited by an erosive surface. A lowstand systems tract developed above each surface, represented by alluvial environments similar to braided fluvial systems, and coastal plain environments, with the development of meandering fluvial and lacustrine systems. Above the lowstand tract, the transgressive systems tract is composed of a shallow marine environment with foreshore, shoreface, and offshore systems. A highstand systems tract was observed in one sequence, and is represented by shallow marine facies. The extensive outcrop in the studied area contains a diverse and voluminous fossil record, containing fossilized invertebrates (bivalves, gastropods, bryozoans, and brachiopods), vertebrates (hadrosaurs, ornithischians, sauropods, theropods, birds, mammals, frogs, turtles, plesiosaurs, mosasaurs, and sharks), and plants (wood, leaves impressions, flowers, pollen, and spores). Thus, this study broadens the understanding of the South American-Antarctic connection during the late Cretaceous-Paleogene, through a diverse fossil record and study of the paleoenvironmental evolution of this high-latitude basin.
The mid-Cretaceous Griman Creek Formation (GCF), which crops out near the town of Lightning Ridge in the Surat Basin of north-central New South Wales, Australia, is noteworthy for its opalised vertebrate fauna. The fossil assemblage comprises remains of aspidorhynchid teleosts, lamniform chondrichthyans, dipnoans, chelid and possible meiolaniform turtles, leptocleidid-like and possible elasmosaurid plesiosaurians, anhanguerian pterosaurs, titanosauriform sauropods, megaraptoran theropods, ankylosaurians, several forms of non-iguanodontian and iguanodontian ornithopods, crocodylomorphs, enantiornithine birds, and stem and true monotremes, making it one of the most diverse mid-Cretaceous terrestrial vertebrate faunas in Australia. A detailed stratigraphic survey of twenty subterranean opal mines provides new information on the geology, age and palaeoenvironment of the main fossil-bearing beds. Vertebrate remains derive from the ‘Finch Clay facies’ laterally-extensive but discontinuous lenses of claystone that likely accumulated relatively rapidly in near-coastal but freshwater embayments (i.e. lagoonal conditions), and probably represent a single, roughly contemporaneous fauna. U-Pb age dating of detrital zircons extracted from a distinct layer of volcanogenic claystone immediately overlying one of the opalised fossil-bearing layers yields a maximum depositional age of 100.2–96.6 Ma. These new dates confirm an early to mid-Cenomanian age for the fauna, rather than Albian, as has been reported previously. The GCF at Lightning Ridge is therefore equivalent to the middle part of the Winton Formation (Queensland) and several million years older than the sauropod-dominated fauna at Winton.
The Sierra Baguales, situated north of the Torres Del Paine National Park in the Magallanes region of southern Chile, shows a well-exposed stratigraphic sequence ranging from the Late Cretaceous to late Pliocene, which presents a unique opportunity to study the evolution of sedimentological styles and trends, palaeoclimate changes, and tectonic events during this period. The depositional environment changed from a continental slope and shelf during the Cenomanian-Campanian (Tres Pasos Formation) to deltaic between the Campanian-Maastrichtian (Dorotea Formation) and estuarine in the Lutetian-Bartonian (Man Aike Formation). During the Rupelian, a continental environment with meandering rivers and overbank marshes was established (Río Leona Formation). This area was flooded in the early Burdigalian (Estancia 25 de Mayo Formation) during the Patagonian Transgression, but emerged again during the late Burdigalian (Santa Cruz Formation). Measured palaeocurrent directions in this Mesozoic-Cenozoic succession indicate source areas situated between the northeast and east-southeast during the Late Cretaceous, east-southeast during the middle Eocene, and southwest during the early Oligocene to early Miocene. This is confirmed by detrital zircon age populations in the different units, which can be linked to probable sources of similar ages in these areas. The east-southeastern provenance is here identified as the Antarctic Peninsula or its northeastern extension, which is postulated to have been attached to Fuegian Patagonia during the Eocene. The southwestern and western sources were exhumed during gradual uplift of the Southern Patagonian Andes, coinciding with a change from marine to continental conditions in the Magallanes-Austral Basin, as well as a decrease in mean annual temperature and precipitation indicated by fossil leaves in the Río Leona Formation. The rain shadow to the east of the Andes thus started to develop here during the late Eocene-early Oligocene (~ 34 Ma), long before the “Quechua Phase” of Andean tectonics (19–18 Ma) that is generally invoked for its evolution at lower latitudes.
The processes of orocline formation are a topic of debate in geosciences. The Patagonian orocline has been a case in point for over a century. Large anomalous paleomagnetic pole rotations show that the orocline started to form at the same time as mid-Cretaceous closure of the Rocas Verdes Basin, today known from ophiolitic and basin fill remnants in the Patagonian and Fuegian Andes. Some studies therefore present bending of the Andes and closure of the basin as shared consequences of rotation of a small plate that was driven by subduction-related forces at the Pacific margin of Gondwana. An alternative view of the orocline is as a product of Cretaceous to Paleogene-aged sinistral oblique convergence at the plate-boundary scale. Geological data from Tierra del Fuego have been interpreted in support of both views. Here, I test these suggestions by comparing the Rocas Verdes Basin's tectonostratigraphy to predictions of a plate kinematic model for fragmentation of the western interior of Gondwana. The model is sufficient to explain the known history of basin opening to a width of ~ 100–300 km during the period 152–141 Ma and later closure in oblique plate convergence. As this convergence occurred by motion around a distant Euler pole, it could not have produced the Patagonian orocline by rotation of a lithospheric plate on its Pacific flank. The large anomalous paleomagnetic rotations of Tierra del Fuego, instead, are likely to have occurred within the crust by rotation and deformation of regional strike-slip faults and the intervening rocks to accommodate oblique convergence of the South American and Antarctic plates between Albian and Paleocene times.
Diversity, dietary, and body mass analyses suggest that the early Eocene represents the major radiation event in South America metatherian evolutionary history. During this period, representatives of all orders typical of the Paleogene reached their greatest diversity (i.e., “basal ameridelphians”; Polydolopimorphia Polydolopiformes, and Bonapartheriiformes Bonapartherioidea); frugivory was the dominant trophic niche. By the middle late Eocene occurs a functional and taxonomic turnover. Among the Polydolopimorphia, frugivore types declined and were replaced by larger-sized frugivores/folivores (Polydolopiformes) and smaller-sized granivores (Bonapartheriiformes). The Sparassodonta showed a diversity increase and occupied the large-sized hypercarnivore niches. The Eocene–Oligocene boundary constitutes another extinction and turnover event marked by the disappearance of “basal ameridelphians”, the Polydolopiformes and Bonapartheriiformes Bonapartherioidea. Lineages that survive into the Deseadan are the Sparassodonta, Paucituberculata, Microbiotheria, and Bonapartheriiformes Argyrolagoidea. Dominant trophic types were those of carnivores and granivores. Environmental factors probably modeled the Paleogene metatherian faunal dynamics in South America. Mean annual temperatures (MAT) and precipitations seem the main factors modeling the taxonomic and trophic diversity, respectively. The adaptive radiation of the early Eocene seems associated with the maximum thermal event of the late Paleocene-early Eocene. The turnover event of the late Eocene seems associated with a sharp drop in the rainfall regime. The extinction and turnover event of the Eocene–Oligocene boundary also seem associated with a strong drop in ambient temperatures. The diversity in evolution of Paleogene metatherians shows a pattern similar to that of living marsupials at the latitudinal level. For a given mean temperature, the number of species in extinct associations is very close to that of the living ones.
The southernmost Andes of Patagonia and Tierra del Fuego present a prominent arc-shaped structure: the Patagonian Bend. Whether the bending is a primary curvature or an orocline is still matter of controversy. New paleomagnetic data have been obtained south of the Beagle Channel in 39 out of 61 sites. They have been drilled in Late Jurassic and Early Cretaceous sediments and interbedded volcanics and in mid-Cretaceous to Eocene intrusives of the Fuegian Batholith. The anisotropy of magnetic susceptibility was measured at each site and the influence of magnetic fabric on the characteristic remanent magnetizations (ChRM) in plutonic rocks was corrected using inverse tensors of anisotropy of remanent magnetizations. Normal polarity secondary magnetizations with west-directed declination were obtained in the sediments and they did not pass the fold test. Thesecharacteristic directions are similar to those recorded by mid Cretaceous intrusivessuggesting a remagnetization event during the normal Cretaceous superchron and describea large (>90°) counterclockwise rotation. Late Cretaceous to Eocene rocks of the FueguianBatholith, record decreasing counterclockwise rotations of 45° to 30°. These paleomagneticresults are interpreted as evidence of a large counterclockwise rotation of the FueguianAndes related to the closure of the Rocas Verdes Basin and the formation of the DarwinCordillera during the Late Cretaceous and Paleocene.The tectonic evolution of the Patagonian Bend can thus be described as theformation of a progressive arc from an oroclinal stage during the closure of the RocasVerdes basin to a mainly primary arc during the final stages of deformation of theMagallanes fold and thrust belt. Plate reconstructions show that the Antarctic Peninsulawould have formed a continuous margin with Patagonia between the Early Cretaceous andthe Eocene, and acted as a non-rotational rigid block facilitating the development of thePatagonian Bend.