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Flora y paleoclima de la Formación La Meseta (Eoceno medio), isla Marambio (Seymour), Antártida
Abstract
New elements of the La Meseta Formation megaflora are described. This unit crops out on the northern third of Marambio (Seymour) Island, Antarctica. Fossil leaves were collected from the middle part of this formation, dated as middle Eocene. Although the fossils are not well preserved, we identified elements assignable to the following families: Nothofagaceae (at least 3 species), Dilleniaceae, Myricaceae, Myrtaceae, and Lauraceae. However, it was impossible to identify some of the fossils, although all could be recognized as dicotyledonous angiosperms. A palaeoclimatic interpretation based on physiognomic analysis (independent of the taxonomy of the elements) indicates temperate to cool temperate and seasonably moist climate for this formation. This interpretation reinforces the existence of a latitudinal gradient between the Antarctic Peninsula and South America and their progressive migration towards the north as consequence of climatic deterioration during the Eocene-Oligocene.
KEY WORDS. Megaflora. Palaeoclimate. La Meseta Formation. Marambio Island. Antarctica. Middle Eocene.
... In comparison to the west Antarctic Peninsula (South Shetland Islands), a dearth of studies have focussed on Seymour Island Paleogene leaf fossils over the past century. Upchurch and Askin (1989) recovered Late Cretaceous dispersed cuticles, Case (1988), Doktor et al. (1996), Gandolfo et al. (1998aGandolfo et al. ( , 1998b and Friis et al. (2017) studied Eocene leaves and Panti et al. (2012) reviewed araucarian fossil records. Eocene collections have been used as a basis for further investigation of conifers through new imaging techniques (Dawson et al., 2014) and insect herbivory on leaves (McDonald et al., 2007). ...
... Comparison and remarks: Morphotype 18 is distinguished from other morphotypes in the Cross Valley Flora, such as: serrate-margin, mucronate, widely-spaced, distally inclined teeth; semicraspedodromous secondary veins increasing in spacing towards apex, smoothly decreasing in vein angle. However, these characters are not found in other fossil specimens described from the Antarctic Peninsula (Dusén, 1908;Case, 1988;Gandolfo et al., 1998aGandolfo et al., , 1998bTosolini et al., 2013), Patagonia, South America (e.g. Berry, 1937aBerry, , 1937bBerry, , 1938Wilf et al., 2005;Iglesias et al., 2007;Panti, 2018;Vento and Prámparo, 2018) or any modern species. ...
... Valdivian-like broad-leafed and mixed forests thrived in the warm, wet temperate climates, before becoming depauperate by the late Eocene. Evidence of Eocene forest diversity can be seen in floras preserved in the La Meseta Formation on Seymour Island (Askin et al., 1991;Doktor et al., 1996;Gandolfo et al., 1998aGandolfo et al., , 1998bCantrill and Poole, 2005;Pujana et al., 2014;Warny et al., 2019), which will form the subject of a future paper. ...
... Moreover, the fossil floras near Laguna Fria (Paso del Sapo fauna) have a high plant diversity and represent diverse rainforests with Australasian components, including Podocarpaceae and ferns (Wilf et al., 2005;Zamaloa et al., 2006), but Nothofagus has not been reported from there yet [but see Wilf et al. (2005)]. In the Antarctic Peninsula, the palaeoflora suggests a temperate climate with abundant precipitation and marked seasonality (Case et al., 1988;Gandolfo et al., 1998), and even though it is dominated by Podocarpaceae, Nothofagus is widely represented (Pujana et al., 2014). ...
Polydolopidae is a family of Palaeogene marsupials recorded from outcrops in southern South America and the Antarctic Peninsula. They are mostly represented by skull fragments or maxillary, dentary and molar remains. A taxonomic and systematic revision is carried out with the inclusion of a phylogenetic analysis encompassing almost every polydolopid species and five marsupial species found to be related to them in previous analyses (Bonapartherium hinakusijum, Epidolops ameghinoi, Microbiotherium tehuelchum, Prepidolops didelphoides and Roberthoffstetteria nationalgeographica). The Polydolopidae was recovered as a monophyletic group, even though no resolution about its sister-group can be found. The following genera are recovered: Antarctodolops, Amphidolops, Archaeodolops, Eudolops, Hypodolops gen. nov., Kramadolops, Pliodolops, Pseudolops and two unidentified genera (Gen. et sp. indet 1 and 2). One genus and three new species are recognized. The family appeared at the beginning of the Palaeocene and disappeared during the Early Oligocene. The extinction of the group could be related to climatic deterioration in the Early Oligocene, when temperature and the humidity dropped, provoking desertification in the region where Polydolopids evolved.
... Moreover, the fossil floras near Laguna Fria (Paso del Sapo fauna) have a high plant diversity and represent diverse rainforests with Australasian components, including Podocarpaceae and ferns (Wilf et al., 2005;Zamaloa et al., 2006), but Nothofagus has not been reported from there yet [but see Wilf et al. (2005)]. In the Antarctic Peninsula, the palaeoflora suggests a temperate climate with abundant precipitation and marked seasonality (Case et al., 1988;Gandolfo et al., 1998), and even though it is dominated by Podocarpaceae, Nothofagus is widely represented (Pujana et al., 2014). ...
Polydolopidae is a family of Palaeogene marsupials recorded from outcrops in southern South America and the Antarctic Peninsula. They are mostly represented by skull fragments or maxillary, dentary and molar remains. A taxonomic and systematic revision is carried out with the inclusion of a phylogenetic analysis encompassing almost every polydolopid species and five marsupial species found to be related to them in previous analyses (Bonapartherium hinakusijum, Epidolops ameghinoi, Microbiotherium tehuelchum, Prepidolops didelphoides and Roberthoffstetteria nationalgeographica). The Polydolopidae was recovered as a monophyletic group, even though no resolution about its sister-group can be found. The following genera are recovered: Antarctodolops, Amphidolops, Archaeodolops, Eudolops, Hypodolops gen. nov., Kramadolops, Pliodolops, Pseudolops and two unidentified genera (Gen. et sp. indet 1 and 2). One genus and three new species are recognized. The family appeared at the beginning of the Palaeocene and disappeared during the Early Oligocene. The extinction of the group could be related to climatic deterioration in the Early Oligocene, when temperature and the humidity dropped, provoking desertification in the region where Polydolopids evolved.
... Given the century time span since Dusén's report, the dearth of leaf macrofossil-specific research from Seymour Island is surprising. Case (1988) collected new leaf specimens from the Dusén locality, but few other studies of Seymour Island leaf fossils exist: Upchurch and Askin (1989) recovered Late Cretaceous dispersed cuticles, Doktor et al. (1996) and Gandolfo et al. (1998aGandolfo et al. ( , 1998b studied Eocene leaves, and more recently Panti et al. (2012) reviewed araucarian fossil records from Antarctica. Fossil wood from Seymour Island has received more attention, as it was first collected by the Swedish South Polar expedition (Gothan, 1908) and has been the focus of later research and collections from Cretaceous to Paleogene age (e.g. ...
Abstract
Paleocene leaf floras are rare in high latitudes of the Southern Hemisphere, where studies have shown higher taxonomic diversity compared to Northern Hemisphere equivalents. The floras provide valuable insights into biodiversity and forest communities during the Paleocene. The Antarctic Peninsula hosts a wealth of Paleocene–Eocene floras which have been used to interpret climates before, during and after one of the most abrupt and transient warming events known from the geological record. The best-preserved and most diverse Paleocene macrofossils from this region come from the Cross Valley Formation, Seymour Island Group, which have previously provided evidence for warm temperate climates prior to the PETM. Here we present the taxonomy of leaf impressions from the Paleocene Cross Valley Flora for one species and ten new leaf morphotypes of entire-margined angiosperms. The new morphotypes provide evidence of an increased angiosperm diversity within cool-temperate Gondwanan forest inhabiting the east side of the Antarctic Peninsula, which contrasts with a lower floral diversity on the west side of the Peninsula during the late Paleocene.
... The Paleogene forests of the northern Antarctic Peninsula grew under a strongly seasonal climate at ~ 68°S palaeolatitude (Carter et al. 2017). Nevertheless, they incorporated a moderately diverse range of plants dominated by podocarp and araucarian conifers, and nothofagacean, lauracean and cunoniacean angiosperms (Gandolfo et al. 1998a(Gandolfo et al. , 1998bMcDonald et al. 2007). Such forests have been likened to the modern Valdivian rainforests and Magellanic subpolar forests of southern South America (Torres et al. 1994a, b;Poole et al. 2003). ...
An assemblage of permineralized conifer and angiosperm woods collected from Paleogene marine strata on Seymour Island during the Swedish Antarctic expedition of 1901–1903 includes many specimens with internal damage caused by an array of xylophagous organisms. Short, broad, clavate borings referable to Gastrochaenolites clavatus are attributed to pholadid bivalves. Elongate borings with carbonate linings referable to Apectoichnus longissimus were produced by teredinid bivalves. Slender, cylindrical tunnels cross-cutting growth rings and backfilled in meniscoid fashion by frass composed of angular tracheid fragments were probably produced by a terrestrial beetle borer. They are most similar to tunnels generated by modern cerambycid and ptinid coleopterans. Less regular, spindle-shaped cavities and degraded zones flanking growth rings are similar to fungi-generated modern white pocket rot. Larger chambers in the heartwood referable to the ichnotaxon Asthenopodichnium lignorum were produced by an alternative mode of fungal degradation. The biological interactions evident in the fossil woods illustrate additional terrestrial trophic levels enhancing the known complexity of ecosystems on and around the Antarctic Peninsula shortly before the initial pulse of mid-Cenozoic glaciation in Antarctica that caused extirpation of the majority of plants and animals in that region.
Antarctica underwent a complex evolution over the course of the Cenozoic, which influenced the history of the Earth’s climate system. The Eocene-Oligocene boundary is a divide of this history when the ice-free ‘greenhouse world’ transitioned to the ‘icehouse’ with the glaciation of Antarctica.
Prior to this, Antarctica experienced warm climates, peaking during Early Eocene when tropical-like conditions existed at the margins of the continent where geological evidence is present. Climate signals in the geological record show that the climate then cooled, but not enough to allow the existence of significant ice until the latest Eocene. Glacial deposits from several areas around the continental margin indicate that ice was present by the earliest Oligocene. This matches the major oxygen isotope positive shift captured by marine records. On land, vegetation was able to persist, but the thermophylic plants of the Eocene were replaced by shrubby vegetation with the southern beech Nothofagus, mosses and ferns, which survived in tundra-like conditions. Coupled climate–ice sheet modelling indicates that changing levels of atmospheric CO2 controlled Antarctica’s climate and the onset of glaciation. Factors such as mountain uplift, vegetation changes, ocean gateway opening and orbital forcing all played a part in cooling the polar climate, but only when CO2 levels reached critical thresholds was Antarctica tipped into an icy glacial world.
The South American fossil record of Mesozoic mammals and close relatives is one of the best for Gondwana. Early mammals and relatives are found in about a dozen localities in Argentina, Brazil, Bolivia, Chile, and presumably Peru, including a broad sample of non-mammaliaform cynodonts of the Triassic age. Mesozoic mammals span from the latest Early Jurassic to the latest Cretaceous, furthermore some of those archaic lineages unexpectedly survived the end of the Cretaceous period, remaining as minority elements in the Paleocene–Miocene faunal associations. The fossiliferous localities bearing these fossils are presented in this chapter, highlighting the geological setting, age, and their faunal associations.
The sparse record of archaic Mesozoic South American mammals extends from the latest Early Jurassic to the latest Cretaceous, involving about 115 Ma, which can be further extended to about 160 Ma, including the post-K/Pg evidence. We review here the distribution, predicted time of origin, and likely place of origin for the lineages covered in the preceding chapters during that span of time and against the evolving geological backdrop of continental drift and paleogeography. Size, dental diversity, and likely dietary specializations of the Mesozoic South American mammals are discussed in the context of Mesozoic mammals in general. A few of the many surprising advances in comparative genetic and molecular evolution are discussed as part of a holistic view of early mammalian evolution to which fossils can, and should, be integrated. Social, financial, and geographical issues affecting paleontological research in South America, early mammals, in particular, are highlighted. We recognize that we are still in the early stages of development and that much of what we know about Mesozoic South American mammals is likely to be drastically altered by finds in the continent or underrepresented areas from formely Gondwanan landmasses such as Antarctica or Africa. Their scarce mammalian fossil record has hampered their full incorporation into an integrated view of early mammalian evolution. The relatively robust paleontological community present in several South American countries, relatively inexpensive nature of the discipline, and extensive outcrops are likely to ensure continuity of a synergistic research agenda. The potential for novel data, regional strengths in systematics, and the global resurgent importance of time as integral to model-based phylogenies are auspicious signs for the future of Mesozoic mammal research in South America.
Dryolestoids are iconic members of the Mesozoic mammalian associations in South America. They achieved a large taxonomic diversity in this region with disparate dental and cranial morphotypes ranging from the classical role of sharp-toothed insectivores to bunodont, complex dentitions reflecting omnivore/herbivore adaptations. The South American radiation of dryolestoids, the meridiolestidans, are among the most abundant Cretaceous mammals, surviving the K/Pg mass extinction and continuing until the Miocene as minor members of the South American biotas. New specimens have been recently discovered, some of them including associated upper and lower jaws, and exceptionally preserved skulls. These high-quality fossils provide crucial intraspecific dental variation, both along the tooth row and from upper to lower, allowing critical re-interpretation of some taxa originally named on the basis of isolated teeth or very incomplete material. The Cretaceous diversity of meridiolestidans has been grossly overestimated, with taxa based on different dental positions of what was later determinied to be a single taxon. One relatively poorly known Late Cretaceous taxon, Groebertherium, shares many features with the classical Holartic dryolestoids and may represent a Late Jurassic/Early Cretaceous foundational morphology expected for meridiolestidans.
Non-mammaliaform cynodonts, formerly called “mammal-like reptiles,” illustrate earlier states of the morphological architecture in the mammalian lineage. These mammalian forerunners show unique character combinations without direct counterparts among living vertebrates reflecting adaptations long lost along the millions of years of cynodont history. The fossil record from South America, originating mostly from the Middle to Late Triassic of Argentina and Brazil, is one of the most prolific worldwide. SA non-mammalian cynodonts are systematically diverse, including approximately 40 species that present great morphological disparity in skull shape, tooth morphology, pattern of tooth replacement, masticatory mechanisms, and locomotory architectures. In this chapter, we summarize the record of SA non-mammaliaform cynodonts.
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