30 March 2024, Volume 35 Issue 1

    

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Foreword
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  Foreword

  Advances in Polar Science. 2024, 35(1): 0-0.

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Contents
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  Contents

  Advances in Polar Science. 2024, 35(1): 1-1.

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Reviews
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  Review of the Cretaceous avian diversity of Antarctica: a changing scenario for the evolution of early Neornithine birds

  Carolina ACOSTA HOSPITALECHE, Facundo IRAZOQUI, Paula BONA, Ariana PAULINA-CARABAJAL

  Advances in Polar Science. 2024, 35(1): 1-13. https://doi.org/10.12429/j.advps.2023.0025

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  The worldwide record of Cretaceous Neornithes and Neornithine-like birds is both controversial and poorly understood. However, in recent years, the Antarctic continent has yielded a substantial number of Maastrichtian avian specimens, contributing significantly to our understanding of the early evolution of this group. Simultaneously, the keen interest and collaborative efforts of various paleornithologists have resulted in a wealth of knowledge, which we have thoroughly reviewed, updated, and discussed in the context of recent discoveries.
Articles
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  Middle Eocene chondrichthyan fauna from Antarctic Peninsula housed in the Museo de La Plata, Argentina

  Martina CHARNELLI, Soledad GOUIRIC-CAVALLI, Marcelo A. REGUERO, Alberto L. CIONE

  Advances in Polar Science. 2024, 35(1): 14-47. https://doi.org/10.12429/j.advps.2023.0035

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  In recent years, the taxonomy and systematics of the cartilaginous fish taxa from the Eocene La Meseta Formation of Seymour (Marambio) Island, Antarctica have been extensively discussed in a series of papers, resulting in a complete revision of the Antarctic Eocene ichthyofauna housed in the Vertebrate Paleontology collection of the Museo de La Plata, Argentina. This collection constitutes one of the largest and taxonomically most diverse in the world, with approximately 20000 specimens, which provides a solid database used for the analysis of qualitative and quantitative chondrichthyan taxonomic composition. The information provided herein might be useful to understand the sudden decline in chondrichthyan taxonomic diversity towards the top of La Meseta Formation as well as its potential relationship with environmental changes during the Eocene. 
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  Contributions to the knowledge of Antarctodon sobrali (Mammalia: Astrapotheria) from the Eocene of Antarctica

  Javier N. GELFO

  Advances in Polar Science. 2024, 35(1): 48-62. https://doi.org/10.12429/j.advps.2023.0031

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  The Astrapotheria constitutes one of the five orders of extinct South American native ungulates, with a fossil record that also extends to the Eocene of the Antarctic Peninsula. In contrast to the abundant specimens known for litoptern Sparnotheriodontidae and metatherians, astrapotheres are represented by scant remains assigned to the endemic Antarctodon sobrali and indeterminate astrapotheres, restricted to levels 35Cu0 and 35n of the Cucullaea I Allomember of the La Meseta Formation. The discovery of a lower molar assignable to this species in the Eocene levels of Seymour (Marambio) Island, enables a revision of the diagnosis and the homologies of the dental characters used to describe this taxon. A reanalysis of its phylogenetic relationships reveals the nearly simultaneous presence of basal astrapotheres in the early Eocene of Itaboraí (Brazil), Patagonia, and West Antarctica. These taxa are characterized by lacking dental specializations usually associated with more abrasive diets like terminal forms of Uruguaytheriinae and Astrapotheriinae. Antarctodon appears to have thrived on the Antarctic continent during the Early Eocene Climatic Optimum within the paleoclimatic context of a hot-house world. Unlike present conditions in Antarctica where no terrestrial mammals inhabit, the early Eocene climate was characterized by warmer temperatures and a biologically diverse environment rich in primary producers, dominated by Nothofagus forests, encompassing both deciduous and evergreen forests, which supported a diverse assemblage of continental vertebrates.
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  The first record of dermochelyid turtles in the Eocene of Tierra del Fuego: new insights on the evolution of the Weddellian faunas

  Paula BONA, Juliana STERLI, Marcelo Saúl de la FUENTE, Eduardo OLIVERO, Marta S. FERNÁNDEZ, Marcelo REGUERO

  Advances in Polar Science. 2024, 35(1): 63-77. https://doi.org/10.12429/j.advps.2023.0026

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  The Antarctic Paleogene marine fossil record has been the key to reconstructing the evolution of the Weddellian Sea and final dismemberment of Southern Gondwana. In this context, Eocene marine vertebrates from Seymour (Marambio) Island have provided valuable information. We present the first Eocene record of marine reptiles from the southern Atlantic Coast of South America. This corresponds to several postcranial turtle remains represented by a proximal end of the right humerus, three caudal and one thoracic vertebrae, a fragment of the left pubis, and ten ossicles of the dorsal carapace, coming from the Leticia Formation (late-mid Eocene) at Cabo Tiburones, Tierra del Fuego, Argentina. These materials show several features such as the size and general morphology of the humerus and vertebrae, and the presence of relatively small, irregular, smooth, and unkeeled ossicles, which allow us to assign them to Dermochelyidae indet. Dermochelyids are a cosmopolitan group of cryptodiran turtles, registered from the late Cretaceous up to the recent, with some physiological-biological peculiarities (e.g., endothermy and an exclusive jellyfish-based diet) and characterized by the presence of an osseous carapace formed by ossicles. The new finding from the Leticia Formation is an addition to the scarce and extremely fragmentary record of Eocene dermochelyids from the southern seas like those from the La Meseta and Submeseta formations (Antarctica) and the Waihao and Burnside formations (New Zealand). This new information allows us to discuss the presence of these turtles in such high latitudes in the past and its implication in the evolution of the Weddellian fauna.
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  A new look at the first dinosaur discovered in Antarctica: reappraisal of Antarctopelta oliveroi (Ankylosauria: Parankylosauria)

  Sergio SOTO ACUÑA, Alexander O. VARGAS, Jonatan KALUZA

  Advances in Polar Science. 2024, 35(1): 78-107. https://doi.org/10.12429/j.advps.2023.0036

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  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.
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  Environmental changes affect picoplanktonic composition in Antarctic Peninsula ponds

  Micaela DÍAZ, Leonardo LAGOMARSINO, Gabriela MATALONI, Marianela BELTRÁN, Marcela LIBERTELLI, Paulina FERMANI

  Advances in Polar Science. 2024, 35(1): 108-122. https://doi.org/10.12429/j.advps.2023.0018

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  Antarctic Peninsula is experiencing one of the largest global warming events worldwide. Shallow water bodies generated by the melting of snow in summer are numerous, and they might act as sentinels of climate change due to their rapid response and ability to integrate catchment information. Shifts in climate can influence the structure of microbial communities which dominate these freshwaters ecosystems. Here, we characterize three ponds at Cierva Point (Antarctic Peninsula) by examining their physico-chemical and morphological characteristics and we explored how different factors modify the structure of the microbial community. We studied the abundance and biomass of heterotrophic bacteria, picocyanobacteria and picoeukaryote algae during January and February of two consecutive summers (2017 and 2018). We found that ponds had different limnological characteristics, due to their location, geomorphological features and presence of the surrounding flora and fauna. Physico-chemical parameters as well as microbial community differed between ponds, months and years. In 2017, most ponds were oligo to mesotrophic states. The larger accumulated rainfall (as a result of environmental changes on the Antarctic Peninsula) during 2018, particularly in February, causes nutrient runoff into water bodies. This affects those ponds with the highest seabird circulation, such as gentoo penguin, increasing eutrophication. As a result, picoplanktonic abundances were higher, and the community structure shifts to a largely heterotrophic bacteria dominated one. These results suggest that these communities could act as sentinels to environmental changes, anticipating a future with mostly hypertrophic ponds.
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  Impact of transparent exopolymer particles on the dynamics of dissolved organic carbon in the Amundsen Sea, Antarctica

  HU Ji, XUE Siyou, ZHAO Jun, LI Dong, ZHANG Haifeng, YU Peisong, ZHANG Cai, YANG Xufeng, PAN Jianming

  Advances in Polar Science. 2024, 35(1): 123-131. https://doi.org/10.12429/j.advps.2023.0012

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  The Southern Ocean is an important carbon sink pool and plays a critical role in the global carbon cycling. The Amundsen Sea was reported to be highly productive in inshore area in the Southern Ocean. In order to investigate the influence of transparent exopolymer particles (TEP) on the behavior of dissolved organic carbon (DOC) in this region, a comprehensive study was conducted, encompassing both open water areas and highly productive polynyas. It was found that microbial heterotrophic metabolism is the primary process responsible for the production of humic-like fluorescent components in the open ocean. The relationship between apparent oxygen utilization and the two humic-like components can be accurately described by a power-law function, with a conversion rate consistent with that observed globally. The presence of TEP was found to have little impact on this process. Additionally, the study revealed the accumulation of DOC at the sea surface in the Amundsen Sea Polynya, suggesting that TEP may play a critical role in this phenomenon. These findings contribute to a deeper understanding of the dynamics and surface accumulation of DOC in the Amundsen Sea Polynya, and provide valuable insights into the carbon cycle in this region.
Letter & Trend
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  Long-term trends in the abundance and breeding performance in Adélie penguins: the Argentine Ecosystem Monitoring Program

  Mariana A. JUÁRES, Anahí M. SILVESTRO, Brenda C. ALFONSO, M. Mercedes SANTOS

  Advances in Polar Science. 2024, 35(1): 132-140. https://doi.org/10.12429/j.advps.2023.0027

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  In this work, we report long-term trends in the abundance and breeding performance of Adélie penguins (Pygoscelis adeliae) nesting in three Antarctic colonies (i.e., at Martin Point, South Orkneys Islands; Stranger Point/Cabo Funes, South Shetland Islands; and Esperanza/Hope Bay in the Antarctic Peninsula) from 1995/96 to 2022/23. Using yearly count data of breeding groups selected, we observed a decline in the number of breeding pairs and chicks in crèche at all colonies studied. However, the magnitude of change was higher at Stranger Point than that in the remaining colonies. Moreover, the index of breeding success, which was calculated as the ratio of chicks in crèche to breeding pairs, exhibited no apparent trend throughout the study period. However, it displayed greater variability at Martin Point compared to the other two colonies under investigation. Although the number of chicks in crèche of Adélie penguins showed a declining pattern, the average breeding performance was similar to that reported in gentoo penguin colonies, specifically, those undergoing a population increase (even in sympatric colonies facing similar local conditions). Consequently, it is plausible to assume a reduction of the over-winter survival as a likely cause of the declining trend observed, at least in the Stranger Point and Esperanza colonies. However, we cannot rule out local effects during the breeding season affecting the Adélie population of Martin Point.
Annoucements
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  SCAR 2024

  Advances in Polar Science. 2024, 35(1): 141-141.

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  Acknowledgements

  Advances in Polar Science. 2024, 35(1): 142-142.

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