La Meseta Research Articles

Biodeterioration of Antarctic fossil penguin bones caused by lichens from the Eocene La Meseta Formation

A large part of the Antarctic surface is covered by lichens since they can withstand extreme environmental conditions. Lichens are primary colonizers and contribute to soil formation by deteriorating rocks through a combination of chemical and physical mechanisms. Therefore, fossil remains found exposed on the surface are usually colonized by epilithic and endolithic lichens. The objective of this work is to determine the biodeterioration generated by lichens on fossil remains and its taphonomic implications. We identified the presence of the euendolithic lichens Lecidea andersonii and Athallia holocarpa growing into fossil penguin bones from Antarctica. The bioerosive damage was evaluated using light and electron microscopic techniques. Pits corresponding to apothecium and sinuous thin fissures remodeled, or in some cases produced, by hyphae were distinguished from the cracks originating from physical weathering. The maximum depth that hyphae extend inside the bone, probably constrained by the light supply, was established to be 2.5 mm. We provided a tool for the reconstruction of the chronology of the taphonomic events, describing the type and magnitude of the damage into the bones.

Probing the Ecology and Climate of the Eocene Southern Ocean With Sand Tiger Sharks Striatolamia macrota.

Many explanations for Eocene climate change focus on the Southern Ocean—where tectonics influenced oceanic gateways, ocean circulation reduced heat transport, and greenhouse gas declines prompted glaciation. To date, few studies focus on marine vertebrates at high latitudes to discern paleoecological and paleoenvironmental impacts of this climate transition. The Tertiary Eocene La Meseta (TELM) Formation has a rich fossil assemblage to characterize these impacts; Striatolamia macrota, an extinct (†) sand tiger shark, is abundant throughout the La Meseta Formation. Body size is often tracked to characterize and integrate across multiple ecological dimensions. †S. macrota body size distributions indicate limited changes during TELMs 2–5 based on anterior tooth crown height (n = 450, mean = 19.6 ± 6.4 mm). Similarly, environmental conditions remained stable through this period based on δ18OPO4 values from tooth enameloid (n = 42; 21.5 ± 1.6‰), which corresponds to a mean temperature of 22.0 ± 4.0°C. Our preliminary ε Nd (n = 4) results indicate an early Drake Passage opening with Pacific inputs during TELM 2–3 (45–43 Ma) based on single unit variation with an overall radiogenic trend. Two possible hypotheses to explain these observations are (1) †S. macrota modified its migration behavior to ameliorate environmental changes related to the Drake Passage opening, or (2) the local climate change was small and gateway opening had little impact. While we cannot rule out an ecological explanation, a comparison with climate model results suggests that increased CO2 produces warm conditions that also parsimoniously explain the observations.

Earliest fossils of giant-sized bony-toothed birds (Aves: Pelagornithidae) from the Eocene of Seymour Island, Antarctica

While pelagornithid or ‘bony-toothed’ bird fossils representing multiple species are known from Antarctica, a new dentary fragment of a pelagornithid bird from the middle Eocene Submeseta Formation on Seymour Island, Antarctica represents a species with a body size on par with the largest known species in the clade. Measurements from the partial ‘toothed’ dentary point to a giant body size for the species, although the spacing among the pseudoteeth differs from that published for other pelagornithids. The discrepancy might suggest that previous techniques are not adequate for examination of incomplete material or that another factor such as phylogeny might impact size estimates and comparisons. Combined with a revised stratigraphic position in the early Eocene La Meseta Formation on Seymour Island for the largest pelagornithid tarsometatarsus known, these Antarctic fossils demonstrate the early evolution of giant body size in the clade (by ~ 50 Ma), and they likely represent not only the largest flying birds of the Eocene but also some of the largest volant birds that ever lived (with an estimated 5–6 m wingspan). Furthermore, the distribution of giant-sized pelagornithid fossils across more than 10 million years of Antarctic geological deposits points to a prolonged survival of giant-sized pelagornithids within the southern seas, and their success as a pelagic predatory component of marine and coastal ecosystems alongside early penguins.

FUNCTIONAL IMPLICATIONS OF A SINGULAR PENGUIN SCAPULA (AVES, SPHENISCIFORMES) FROM THE EOCENE OF ANTARCTICA

Penguins have peculiar modifications in their skeletal anatomy as a consequence of their extremely specialized diving habit. Morphological specialization is particularly evident in the forelimb. However, the kinematics of the pectoral girdle appears to be key to the locomotion of penguins. Penguin scapulae have an unusual morphology among birds. Modern penguins have a very large (especially broad) scapula, whereas this bone is long but narrower in basal fossil species. The recent finding of an incomplete scapula with a singular acromion in the Upper Eocene Submeseta Allomember of the La Meseta Formation in the Antarctic Peninsula reveals a scapula proportionally narrower than those of modern penguins but similar to that of Waimanu and possibly other Eocene species. Osteological comparisons and muscular dissections of modern penguins show that the most striking feature is the curvature of the acromion, and the consequent enlargement of the facies articularis clavicularis. The configuration of the acromion and the corpus scapula reflects a lack of functional optimization in terms of the resistance to forces transverse to the body axis. The scapula´s general morphology suggests it belonged to a medium to large-sized penguin species with no so specialized diving skills.

Additional Pelagornithidae remains from Seymour Island, Antarctica

Two incomplete mandibles are assigned to Pelagornithidae given the presence of a well marked neurovascular furrow and the unique bony projections, or “pseudo-teeth”, along the crista tomialis. Specimens IAA-Pv 175 from Ypresian levels of La Meseta Alloformation (Cucullaea I Allomember), and IAA-Pv 823 from Bartonian beds of the Submeseta Alloformation, in Seymour Island (Antarctic Peninsula, West Antarctica) corresponds to the morpho-type 1, previously proposed for Antarctic pseudo-tooth birds.The intermediate condition of the pseudo-teeth of these specimens reinforces the idea that diet changed from piscivory to molluscivory along the evolutive history of the group.

New mammalian and avian records from the late Eocene La Meseta and Submeseta formations of Seymour Island, Antarctica.

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.

Dinoflagellate cysts of the La Meseta Formation (middle to late Eocene), Antarctic Peninsula: implications for biostratigraphy, palaeoceanography and palaeoenvironment

AbstractDinoflagellate cyst assemblages recovered from the La Meseta Formation cropping out in Seymour Island, Antarctic Peninsula, are studied herein and their distribution is compared with the biostratigraphic scheme available for the Palaeogene of the Southern Ocean and other high-latitude regions. In this way, the La Meseta Formation is dated as middle Lutetian to Priabonian (46.2–36 Ma), which differs from the age provided by other fossils, isotopes and also with the magnetostratigraphic scheme recently performed for the unit. The dinoflagellate cyst data support the proposal of ocean circulation patterns on the South American Shelf prior to the opening of Drake Passage. Assemblages from the La Meseta Formation contain Antarctic-endemic taxa which are also dominant in several circum-Antarctic sites, located south of 45° S. Their distribution reflects an ocean-circulation scheme with wide clockwise gyres surrounding Antarctica that were disrupted as a consequence of the deepening and definitive apertures of the Tasmanian Gateway and Drake Passage towards the Eocene/Oligocene transition. The palaeoenvironmental inference based on the S/D ratio (sporomorphs versus dinoflagellate cysts) and the P/G ratio (peridinioid versus gonyaulacoid dinoflagellate cysts) suggests an overall trend through the section from marine-dominated assemblages with poorly productive waters in the lower part of the section to more terrestrially dominated assemblages with increasing productivity in the upper part of the unit, reflecting a shallowing trend to the top.

Indigenous agglutinated foraminifera from the Eocene La Meseta Formation, Seymour Island, West Antarctica

Indigenous agglutinated foraminifera from the Eocene La Meseta Formation, Seymour Island, West Antarctica

Enamel Microstructure in Eocene Cetaceans from Antarctica (Archaeoceti and Mysticeti)

Modern baleen whales have no adult teeth, whereas dolphins and porpoises have a homodont and polydont dentition, with simplified enamel microstructure. However, archaic cetaceans (archaeocetes and early mysticetes and odontocetes) had a complex and ornamented dentition, with complex enamel microstructure as in terrestrial mammals. This study describes the morphology of teeth and enamel microstructure in two fossil cetaceans from Antarctica: a basilosaurid archaeocete from the La Meseta Formation (middle Eocene); and Llanocetus sp. from the Submeseta Formation (late Eocene), one of the oldest mysticetes known. The two teeth analyzed were lower premolars, with transversely compressed triangular crowns composed of a main cusp and accessory denticles. The enamel microstructure of the basilosaurid and Llanocetus sp. is prismatic with Hunter-Schreger bands (HSB) and an outer zone of radial enamel. In the basilosaurid, the enamel is relatively thin and measures 150–180 μm, whereas in Llanocetus sp. it is considerably thicker, measuring 830–890 μm in the cusp area and 350–380 μm near the crown base. This is one of the thickest enamel layers among cetaceans, extinct and living. Structures resembling enamel tufts and lamellae were observed in both fossils at the enamel-dentine junction (EDJ) and extending along the thickness of the enamel layer, respectively. The presence of HSB and biomechanical reinforcing structures such as tufts and lamellae suggests prominent occlusal loads during feeding, consistent with raptorial feeding habits. Despite the simplification or absence of teeth in modern cetaceans, their ancestors had complex posterior teeth typical of most mammals, with a moderately thick enamel layer with prominent HSB.

Eocene bryozoan assemblages from the La Meseta Formation of Seymour Island, Antarctica

Early to Late Eocene bryozoans from the La Meseta Formation of Seymour Island were collected at two localities within the Cucullaea I Allomember (Telm4 and Telm5) on the northwestern side of the island and in two localities within the Submeseta Allomember (Telm6 and Telm7) on the northeastern side. This fauna is represented by cyclostomes of the suborders Tubuliporina and Cerioporina and suborders of Neocheilostomata, among which nine species have been recognized. The following new species are introduced: Micropora nordenskjoeldi sp. nov., Lunulites marambionis sp. nov., Otionellina antarctica sp. nov. and Otionellina eocenica sp. nov. Some other taxa recognized in the studied material, such as Reticrescis plicatus , Uharella seymourensis and Celleporaria mesetaensis , were previously described from the lowermost (Telm1) or uppermost parts (Telm6–7), thus their stratigraphical ranges within the La Meseta Formation are extended. The diverse growth-forms of the bryozoans include a sole ball-shaped celleporiform colony and reticulated and bilamellar-foliaceous colony, as well as rich encrusting and free-living forms (so-called sand faunas), indicating the existence of locally restricted shallow-marine environments. This is particularly true in the middle and upper parts of the La Meseta Formation (Telm4–7). Reticulated, spheroidal and robust, branched colonies, which thrived in the environmental conditions of the lower part (Telm1), are represented only by a sparse bryozoan biota in the upper part of the La Meseta Formation. Lunulitiforms, such as Lunulites and Otionellina which are warm water, free-living bryozoans, dominate in the siliciclastic sediments of Telm5, but erect folded sheets forming a shell bed composed of ? Goodonia occur in Telm6–7. These three genera are recognized in Antarctica for the first time. The austral genus Otionellina has its earliest fossil record here, showing close biogeographical links with the Late Eocene–Miocene faunas of Australia and New Zealand. The taxonomic composition of the studied fauna together with their growth forms is a very good tool for reconstructing palaeoenvironmental conditions in the middle and upper parts (Telm4–7) of the La Meseta Formation, deposited during the Late Ypresian–Priabonian.

New Metatherian Mammal from the Early Eocene of Antarctica

A new Paleogene metatherian from locality IAA 1/90, Marambio (Seymour) Island in the Antarctic Peninsula is described. Pujatodon ektopos, gen. et sp. nov., is recognized on the basis of a tiny lower left molar recovered from early Eocene (late Ypresian) levels of the Cucullaea I Allomember, La Meseta Formation. The tooth is characterized by its small size, bunoid aspect, short trigonid with closely set paraconid and metaconid, wide and long talonid, the development of an incipient cingulid at the labial base of the crown between the trigonid and talonid, and an expanded posterior cingulid. Body mass estimations for the new taxon range from 83.13 to 153.15 g. Its enamel microstructure shows the earliest evidence among metatherians of aligned prisms, as well as of interprismatic sheets of matrix. The analysis of other parameters, like body mass, molar morphometric index, and wear facets, suggests that the molars of Pujatodon were primarily adapted to the processing of fruits, nuts, seeds, and/or hard insects. Several features suggest the allocation of this specimen among basal polydolopimorphians (Prepidolopidae or, more probably, Glasbiidae). The discovery of the specimen MLP 14-I-10-20 could offer new insights on the origins and early diversification of Australidelphian marsupials in southern (and northern?) continents. It also adds significant information on the diversity of Antarctic Paleogene mammals, their evolution, habits, and historical biogeography.

Cenozoic basin evolution of the Central Patagonian Andes: Evidence from geochronology, stratigraphy, and geochemistry

The Central Patagonian Andes is a particular segment of the Andean Cordillera that has been subjected to the subduction of two spreading ridges during Eocene and Neogene times. In order to understand the Cenozoic geologic evolution of the Central Patagonian Andes, we carried out geochronologic (U-Pb and 40Ar/39Ar), provenance, stratigraphic, sedimentologic, and geochemical studies on the sedimentary and volcanic Cenozoic deposits that crop out in the Meseta Guadal and Chile Chico areas (∼47°S). Our data indicate the presence of a nearly complete Cenozoic record, which refutes previous interpretations of a hiatus during the middle Eocene–late Oligocene in the Central Patagonian Andes. Our study suggests that the fluvial strata of the Ligorio Márquez Formation and the flood basalts of the Basaltos Inferiores de la Meseta Chile Chico Formation were deposited in an extensional setting related to the subduction of the Aluk-Farallon spreading ridge during the late Paleocene–Eocene. Geochemical data on volcanic rocks interbedded with fluvial strata of the San José Formation suggest that this unit was deposited in an extensional setting during the middle Eocene to late Oligocene. Progressive crustal thinning allowed the transgression of marine waters of Atlantic origin and deposition of the upper Oligocene–lower Miocene Guadal Formation. The fluvial synorogenic strata of the Santa Cruz Formation were deposited as a consequence of an important phase of compressive deformation and Andean uplift during the early–middle Miocene. Finally, alkali flood basalts of the late middle to late Miocene Basaltos Superiores de la Meseta Chile Chico Formation were extruded in the area in response to the suduction of the Chile Ridge under an extensional regime. Our studies indicate that the tectonic evolution of the Central Patagonian Andes is similar to that of the North Patagonian Andes and appears to differ from that of the Southern Patagonian Andes, which is thought to have been the subject of continuous compressive deformation since the late Early Cretaceous.

An intertidal balanomorph Hexaminius venerai sp. nov. (Austrobalanidae) colonizing a log of Podocarpoxylon from the La Meseta Formation (Eocene), Seymour Island, Antarctica: a glimpse of Antarctic antiquity

The sessile barnacle Hexaminius venerai sp. nov. (Tetraclitoidea: Austrobalanidae) is described from the middle Eocene La Meseta Formation of Seymour Island, Antarctic Peninsula. Hexaminius venerai sp. nov. is the earliest known record of the genus in the Antarctic, the first occurrence of Hexaminius from outside Australian waters and the first record of a fossil cirripede attached to the substrate from the Antarctic. Exceptional preservation of more than 200 specimens, some of which retain opercula within the shell, is discussed. In life, the cirripedes were attached to a tree trunk tentatively identified as Podocarpoxylon, a South Hemisphere conifer. Hexaminius venerai sp. nov. is a survivor of an early phase in balanid radiation, prior to the development of strong radially-interlocked parietes.https://zoobank.org/urn:lsid:zoobank.org:pub:EAA2EB5C-BC57-41FA-93A0-046AF5FD59EB

Terrestrial and marine floral response to latest Eocene and Oligocene events on the Antarctic Peninsula

ABSTRACTPalynological results from opposite sides of the northernmost Antarctic Peninsula provide insight on terrestrial vegetation and sea-surface conditions immediately before the Eocene–Oligocene transition (EOT), through Early Oligocene glacial conditions and the subsequent Late Oligocene interglacial interval. A latest Eocene sample set from the uppermost La Meseta Formation on Seymour Island, James Ross (back-arc) Basin, records a low-diversity Nothofagus (southern beech)-dominated vegetation with some podocarp conifers similar to Valdivian-type forest found today in Chile and Argentina. Marine organic-walled phytoplankton include leiospheres and Eocene dinoflagellate cysts such as Vozzhennikovia rotunda, V. apertura, Senegalinium asymmetricum and Spinidinium macmurdoense. Immediately before the EOT near the top of the section the decrease in terrestrial palynomorphs, increase in reworked specimens, disappearance of key dinocysts, and overwhelming numbers of sea-ice-indicative leiospheres plus the small dinoflagellate cyst Impletosphaeridium signal the onset of glacial conditions in a subpolar climate. Early to Late Oligocene samples from the Polonez Cove and Boy Point formations on King George Island, South Shetland Islands (magmatic arc), yielded an extremely depauperate terrestrial flora, likely resulting in part from poor vegetation cover during the Polonez Glaciation but also because of destruction of vegetation due to continued regional volcanism. The prevalence of sea-ice-indicative leiospheres in the marine palynomorph component is consistent with polar to subpolar conditions during and following the Polonez Glaciation.

Skates and rays (Elasmobranchii, Batomorphii) from the Eocene La Meseta and Submeseta formations, Seymour Island, Antarctica

Eocene deposits of the famous La Meseta Formation of Seymour Island, Antarctic Peninsula, yielded the most diverse Paleogene fossil elasmobranch association of the Southern Hemisphere. In this assemblage, sharks clearly dominate the fauna, whereas batoids are very rare components. Herein, we describe two new taxa of cold water tolerant skates, Marambioraja leiostemma gen. et sp. nov., and Mesetaraja maleficapelli gen. et sp. nov., two new species of the genus Raja, Raja amphitrita sp. nov. and Raja manitaria sp. nov., as well as remains of warm water adapted myliobatiforms. It is, however, not possible to unambiguously assign these remains either to Myliobatidae or Rhinopteridae, or to any specific genus. Previously reported remains of Raja/Bathyraja sp. are assigned to the new described species Raja manitaria sp. nov. The biogeographic distribution of extant and extinct rays and skates clearly shows that both groups are more widely distributed today than in the past, and additionally seem to have been more diverse in the Northern than the Southern Hemisphere. The occurrence, albeit rare of isolated teeth of skates (Rajidae) and rays (Myliobatidae) in the La Meseta Formation representes a minimum age constraint for their first appearance in the Southern Ocean.http://www.zoobank.org/urn:lsid:zoobank.org:pub:E507D86C-FFEC-4047-A337-AE77606BB1A6

Índice de intensificación agrícola y conservación vegetal en bosques y cafetales colombianos con diferentes estrategias de manejo

Los bosques húmedos premontanos (bh-pm) presentan alto grado de deterioro por efecto de la intervención antrópica, principalmente por actividades agrícolas y ganaderas. Dada la pérdida de conectividad en estos paisajes fragmentados, es prioritario estudiar la contribución de agroecosistemas cafeteros a la diversidad regional. Este estudio evaluó la diversidad florística de cafetales y estimó del índice de intensificación agrícola (IA) en dos estrategias agronómicas de café y en bosques en La Meseta de Popayán, Cauca, Colombia, en altitudes entre 1600 y 1750 m. Se midieron 13 variables de la vegetación tales como riqueza, densidad y estructura arbórea en 20 sitios de muestreo: ocho cafetales a plena exposición, ocho con sombrío y cuatro bosques de referencia. Se determinó que la diversidad florística disminuyó en función del IA, donde las variables relacionadas al componente arbóreo y epífito fueron las que más aportaron a la medición de la IA. La composición arbórea estuvo conformada principalmente por especies pioneras que son relevantes en la conservación y restauración regional. Se concluye que el IA aplicado a estos agroecosistemas ayuda a medir el grado de intervención antrópica; que los cafetales con sombra y parches de bosque son fuente de biodiversidad vegetal, de hábitat y de conectividad entre los paisajes Andinos fragmentados; y que la aplicación del IA en cafetales resulta en una herramienta útil para examinar hipótesis sobre sostenibilidad y conservación.

New carcharhiniform sharks (Chondrichthyes, Elasmobranchii) from the early to middle Eocene of Seymour Island, Antarctic Peninsula

ABSTRACTSeymour Island, Antarctic Peninsula, is known for its wealth of fossil remains. This island provides one of the richest fossiliferous Paleogene sequences in the world. Chondrichthyans seemingly dominate this Eocene marine fauna and offer a rare insight into high-latitude faunas during the Palaeogene. So far, only a few isolated teeth of carcharhinid sharks have been reported from Seymour Island. Bulk sampling in the well-exposed La Meseta and Submeseta formations yielded new and abundant chondrichthyan material, including numerous teeth of carcharhinid and triakid sharks. Here, we present a reevaluation of the previously described carcharhinid remains and a description of new taxa: Meridiogaleus cristatus, gen. et sp. nov., Kallodentis rythistemma, gen. et sp. nov., Abdounia richteri, sp. nov., and Abdounia mesetae, sp. nov. The carcharhiniforms Mustelus sp. and Galeorhinus sp. are reported based on rare material, whereas teeth previously assigned to Scoliodon represent a nomen dubium.https://zoobank.org/urn:lsid:zoobank.org:pub:6FA3D201-3686-4129-BC09-10FC86E3DD34Citation for this article: Engelbrecht, A., T. Mörs, M. A. Reguero, and J. Kriwet. 2017. New carcharhiniform sharks (Chondrichthyes, Elasmobranchii) from the early to middle Eocene of Seymour Island, Antarctic Peninsula. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2017.1371724.

A (tidal-marine) boulder pavement in the late Cenozoic of Seymour Island, West Antarctica: contribution to the palaeogeographical and palaeoclimatic evolution of West Antarctica

AbstractWe report here the discovery of a boulder pavement cropping out at the base of the Hobbs Glacier Formation (Miocene), on the northern sector of Seymour Island (Isla Marambio), West Antarctica, along the contact with the underlying La Meseta Formation (Eocene). The feature described has many points in common with boulder pavements developed in tidal-marine environments. The clasts of the pavement are mostly boulders and bear up to three sets of glacial striae on their bevelled truncated surfaces, but are not elongate parallel to them or bullet shaped. No diamictite body was identified associated with the boulder pavement. These features differ from those of boulder pavements described from terrestrially glaciated Cenozoic deposits and may indicate a shallow glaciomarine environment for the late Cenozoic of Seymour Island.

Eocene squalomorph sharks (Chondrichthyes, Elasmobranchii) from Antarctica

Rare remains of predominantly deep-water sharks of the families Hexanchidae, Squalidae, Dalatiidae, Centrophoridae, and Squatinidae are described from the Eocene La Meseta Formation, Seymour Island, Antarctic Peninsula, which has yielded the most abundant chondrichthyan assemblage from the Southern Hemisphere to date. Previously described representatives of Hexanchus sp., Squalus weltoni, Squalus woodburnei, Centrophorus sp., and Squatina sp. are confirmed and dental variations are documented. Although the teeth of Squatina sp. differ from other Palaeogene squatinid species, we refrain from introducing a new species. A new dalatiid taxon, Eodalatias austrinalis gen. et sp. nov. is described. This new material not only increases the diversity of Eocene Antarctic elasmobranchs but also allows assuming that favourable deep-water habitats were available in the Eocene Antarctic Ocean off Antarctica in the Eocene. The occurrences of deep-water inhabitants in shallow, near-coastal waters of the Antarctic Peninsula agrees well with extant distribution patterns.

Eocene ungulate mammals from West Antarctica: implications from their fossil record and a new species

AbstractHere we describe a new terrestrial mammal from the Eocene of Seymour Island (Isla Marambio) represented by a lower left third molar and assigned to a new species of Sparnotheriodontidae, an ungulate family with a broad palaeobiogeographical distribution in South America. The specimen was found in the Cucullaea I allomember of the La Meseta Formation, in a new mammalian locality (IAA 2/16).Notiolofos regueroisp. nov. shares a brachyodont, lophoselenodont and bicrescentic molar pattern withN. arquinotiensis, recorded for a stratigraphic sequence of 17.5 Ma in Antarctica. The criteria for the species differentiation are the absence of mesial and labial cingulids, the larger paraconid, the wider talonid basin, the accentuated distal projection of the hypoconulid, the centroconid development and the smaller size. Together with the astrapotherianAntarctodon sobrali, they represent the medium to large terrestrial mammals of the early Eocene Antarctic landscape that was mostly dominated by closed forests ofNothofagus. Dental wear facets and differences in their body mass are inferred and discussed as possible evidence of niche differentiation. Additionally, the presence of land mammals with Patagonian affinities in the Eocene of Antarctica reinforces the Cretaceous–Palaeocene presence of the Weddellian Isthmus, a functional land corridor between Antarctica and South America.