Environmental/climatic changes during the Eocene: biotic and geochemical evidences based on the bryozoan fauna (Antarctic Peninsula)

<p>The Paleocene-Eocene bryozoans such as microporoideans, umbonulomorphs, lepraliomorphs as well as cerioporoidean cyclostomes are successful biota inhabited the marine and glacio-marine sequences in Antarctica. Changes in their taxonomic composition, associated faunas, colony growth-forms, biodiversity, skeletal mineralogy and geochemistry are important environmental/climatic indicators.</p><p>The earliest Cenozoic Antarctic bryozoan fossil records (late early Eocene) are well-documented from the shallow-marine–estuarine clastic succession of the lower part (Telm1-2) of the La Meseta Formation of Seymour Island, where the faunas are represented by massive multilamellar colonies, often spectacular in size and dominated by the cyclostome cerioporids and diverse ascophoran cheilostomes. The distinct free-living lunulitiforms, for the first time reported from Antarctica from the Ypresian/Lutetian of the middle part of the La Meseta Fm. (Telm4-6) are represented by the disc-shaped colonies, which are characteristic for the temperate warm, shallow-shelf environment, with the bottom temperature, which are never lower than 10 to 12°C (Hara et al., 2018). The skeletons of the Lunulites, Otionellina, and Uharella are formed by the intermediate-Mg calcite (IMC) with the 4.5 mol% MgCO<sub>3</sub>. The use of the X-ray diffraction (XRD) and the Laser Raman spectroscopy (Hara et al., in preparation) shows that they build the bimineralic skeletons (with the traces of aragonite, calcite and strontium apatite), which are indicative for the temperate shelf environment, sandy and often shifting substrate. Biogeographically, the free-living lunulitiforms (Lunulites and Otionellina) are valuable climatic indicators, inhabited in the Recent the circumtropical, tropical-subtropical to warm-temperate Australasian sand environments.</p><p>Contrary to that, the bryozoans of the Telm6-7 with a scarce lepraliomorphs tentatively assignated to ?Goodonia and accompanied by crustaceans, brachiopods and gadiform fish remains are known from the temperate environments.</p><p>The isotopic analyses of the δ<sup>18</sup>O of the bryozoan skeletons from the lower part of the La Meseta Fm. show the range of the temperature from 13.4°C to 14.6°C (according to the equation given by Anderson & Arthur 1983).</p><p>It is worth pointing that the middle Ypresian/early Lutetian bryozoans, which in the stratigraphical profile of the LMF document the nearly 10 MA evolutionary history of the bryozoans are well-correlated with the MECO event, what is also consisted with the isotopic data based on the macrofaunal marine fossil records (Ivany et al. 2008).</p><p>Anderson T.F., and Arthur M.A.1983<strong>. </strong>Stable isotopes of oxygen and carbon and their application to sedimentologic and paleoenvironmental problems. SEPM Short Course, 10: 1-151.</p><p>Hara U., Mors T., Hagstrom  and Reguero M. A., 2018. Eocene bryozoan assemblages from the La Meseta Formation of Seymour Island. Geological Quarterly, 62: 705-728. </p><p>Hara U., Wrzosek B., and Mors, T. 2020. Calcite and aragonite distribution in the skeletons of bimineralic high-latitude bryozoans in the Raman spectroscopy (in preparation).</p><p>Ivany L.C., Lohmann K. C. Hasiuk F., Blake D.B., Glass A., Aronson R.B., and Moody R.M. 2008. Eocene climate record of the high southern latitude continental shelf: Seymour Island, Antarctica. Geological Society of America Bulletin, v. 120, no. 5-6: 659-678.</p>

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.

Cenozoic bryozoan biota and their response to climatic changes in Antarctica

<p>Antarctic bryozoans are important colonial marine invertebrates in terms of their origin, palaeoenvironment and climatic approaches. The changes of the bryozoan fossil records during the last 55 Ma years  are well-defined by their biodiversity, taxonomic composition and colony growth-forms. The late Early Eocene biota from the shallow-marine–estuarine clastic succession of the lower part (Telm1-2) of the La Meseta Formation of Seymour Island are represented by the prolific, spectacular in size, massive multilamellar colonies dominated by the cerioporids as well as diverse ascophorans  cheilostomes (Hara, 2001). The free-living lunilitiform, disc-shaped colonies, which occur in the middle part of the La Meseta Formation (Telm4-Telm5), are characteristic for the warm, shallow-self environment and bottom temperature, which ranges from 10 to 29°C. The presence of the bimineralic skeletons of this fauna (such as Lunulites, Otionellina, and Uharella) with the traces of aragonite is indicative for the temperate shelf environment, sandy and often shifting substrate. Lunulitids are inhabited by the circumpolar to warm-temperate waters, at the present day. Contrary to that, the bryozoans  from the upper part of the LM (Telm6-7) are  represented by the scarce lepraliomorphs accompanied by the crustaceans, brachiopods and gadiform fish remains. The individuality of the Eocene bryozoan assemblages are well-correlated with the EECO, MECO and EOT climatic events, based on the other marine macrofaunal marine fossil records (see also Ivany et al. 2008). The lower Pliocene bryofauna recently described  from the Cockburn Island Formation  is composed of the rich encrusting shallow-water, membraniporiform zoaria (Hara and Crame, in review, 2020). The biota of thePectenConglomerate are indicative of the interglacial conditions during the deposition of the Cockburn Island Formation. At the present day bryozoans with the preponderance of cheilostomes are the most significant marine benthic community, thriving successfully in cool-water Antarctic  conditions.</p><p>References,</p><p>Hara, U., 2001. Bryozoans from the Eocene of Seymour Island, Antarctic Peninsula, Palaeontogia Polonica , 60:33-155.</p><p>Hara, U., Mors, T., Hagstrom, and Reguero M. A., 2018. Eocene bryozoans  assemblages from the La Meseta Formation of Seymour Island. Geological Quarterly, 62: 705-728. </p><p>Hara., U., and Crame, J.A. 2019. Paleobiodiversity of the Lower Pliocene bryozoan  benthic community and its response to interglacial conditions.  Geological Review (in review).</p><p>Ivany L.C., Lohmann, K. C. Hasiuk, F., Blake D.B., Glass A., Aronson R.B., and Moody R.M. 2008. Eocene climate record of the high southern latitude continental shelf: Seymour Island, Antarctica. Geological Society of America Bulletin, v. 120, no. 5-6: 659-678.</p><p> </p>

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

Dinoflagellate 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.

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

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

Here 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 regueroi sp. nov. shares a brachyodont, lophoselenodont and bicrescentic molar pattern with N. 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 astrapotherian Antarctodon sobrali, they represent the medium to large terrestrial mammals of the early Eocene Antarctic landscape that was mostly dominated by closed forests of Nothofagus. 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.