| 1. |
- Bordiga, Manuela, et al.
(författare)
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Reticulofenestra daviesii : Biostratigraphy and paleogeographic distribution across the Eocene-Oligocene boundary
- 2017
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Ingår i: Geobios. - : Elsevier. - 0016-6995 .- 1777-5728. ; 50:5-6, s. 349-358
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Tidskriftsartikel (refereegranskat)abstract
- Improving the biostratigraphy across the Eocene-Oligocene is fundamental to better constrain the timing and causes of an important global climate change of the Cenozoic, the Eocene-Oligocene Transition (EOT; 34-33.5 Ma). Across the EOT, only few nannofossil bioevents are considered globally synchronous and reliable. One of these is the first common occurrence (Bc) of the species Reticulofenestra daviesii that has been proven to be useful for biostratigraphical correlations in the Southern Ocean, but the potential of R. daviesii as a biostratigraphical marker at mid- and low latitudes has not been explored yet in detail. We investigate three deep-sea drill sites located across a N-S transect at mid-low latitudes of the Atlantic Ocean spanning from 34.4 to 33 Ma, reviewing the temporal and geographical distribution together with the intraspecific variability of R. daviesii. Our data quantify the occurrence of R. daviesii in (sub)tropical regions of the Atlantic Ocean, although with lower abundances (similar to 4-12%) compared to Southern Ocean assemblages (40-95%). This suggests that R. daviesii was a cosmopolitan species capable to adapt to a wider range of sea surface temperatures and environmental conditions than previously thought. However, the temporal distributions of R. daviesii at the three studied sites are not comparable to the trends recorded in the Southern Ocean. Its Bc is clearly identifiable only at the equatorial site, occurring similar to 500,000 years before the age estimated in the Southern Ocean (33.705 Ma). Thus, we suggest caution when using the Bc of R. daviesii as a reliable biostratigraphical event at mid- and low latitudes. In addition, our biometrical data reveal that up to 38% of R. daviesii coccoliths is > 8-10 mu m in major axis size, thus bigger than the medium size range (5-8 mu m) originally described. Refining the size range of R. daviesii is important for estimating its cell volume versus surface area and coccolith carbonate mass. (C) 2017 Elsevier Masson SAS. All rights reserved.
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| 2. |
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| 3. |
- Ebbestad, Jan Ove R., 1967-, et al.
(författare)
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An unusual onychochilid mollusc from the Ordovician (Tremadocian) Fezouata Formation, Morocco
- 2015
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Ingår i: Geobios. - : Elsevier BV. - 0016-6995 .- 1777-5728. ; 48:6, s. 427-438
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Tidskriftsartikel (refereegranskat)abstract
- Pelecyogyra fezouataensis nov. gen., nov. sp. is described from the Lower Ordovician (Tremadocian, A. murrayi Biozone) Fezouata Formation at Oued Beni Zoli (locality Z-F5), in the central Anti-Atlas, Morocco. This is the first Onychochilidae Koken in Koken and Perner, 1925 reported from the Ordovician of Morocco. Its stratigraphical position bridges the gap between the late Cambrian and Middle to Upper Ordovician records. This new taxon draws together large specimens, reaching 27 mm in the greatest diameter, with 3 rapidly expanding whorls. All specimens are invariably preserved as dorsoventrally compressed moulds although preservation suggests that the degree of compaction was not great and that the species was generally low spired. A characteristic axe-shaped apertural lip and an ornamentation consisting of fine and dense lirae serve to distinguish the new genus from other onychochilids. The species appears to have been gregarious. In some specimens, small scalloped injuries are preserved along the apertural margins but these are not considered to reflect failed predation. Up to now, twenty-two species and eight genera of Ordovician onychochilids have been documented, being distributed in eight different terranes. The composition of the Onychochilidae is briefly reviewed and updated from the literature, to include Helicotis? Koken in Koken and Perner, 1925, Hyperstrophema Horný, 1964, Invertospira Horný, 1964, Kobayashiella Endo, 1937, Laeogyra Perner, 1903, Matherella Walcott, 1912, Matherellina Kobayashi, 1937, Onychochilus Lindström, 1884, Pelecyogyra nov. gen., Pervertina Horný, 1964, Scaevogyra Whitfield, 1878, Sinistracirsa Cossmann, 1908, Versispira Perner, 1903, and Voskopiella Frýda, 1992. Onychochilidae and Clisospiridae are placed in Mimospirida Dzik, 1983, regarding Hyperstrophina Linsley and Kier, 1984 as a junior synonym.
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| 4. |
- Ebbestad, Jan Ove R., 1967-, et al.
(författare)
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First occurrence of Pterotheca (Gastropoda) from the Silurian (Aeronian) of Spain
- 2017
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Ingår i: Geobios. - : Elsevier BV. - 0016-6995 .- 1777-5728. ; 50:2, s. 97-104
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Tidskriftsartikel (refereegranskat)abstract
- Pterotheca hispanica nov. sp. is described from the basal beds (Stimulograptus sedgwickii graptolite Zone) of the Formigoso Fm., in the Cantabrian Zone of the Iberian Massif, north-western Spain. This specialized bellerophontoid gastropod is for the first time recorded in the Silurian of peri-Gondwana; it is the only Aeronian species known so far. Its most closely allied relatives are from higher beds placed in the Telychian of Scotland. Pterotheca is considered a highly derived genus within the Pterothecinae of the Carinaropsidae, with the strongly reduced to absent coiling and the growth of the septum being synapomorphies. In the present work it is shown that not only the apical angle of the septum can be used to distinguish species, but also the relative length and width of the septum. In some cases, the slit may extend as far back as the anterior part of the internal septum. Silurian species were hitherto only found in marginal Laurentian and Eastern Avalonian settings. Pterotheca is absent from central Laurentia and Baltica, where it could be expected to be present based on its wide Ordovician distribution. In the light of this, the occurrence of the genus in the Aeronian of Spain seems difficult to explain, albeit the genus was present in peri-Gondwana prior to the end-Ordovician extinction. The extreme scarcity of described taxa recorded from Avalonia, Baltica and Iberia during the Early Silurian may explain this patchy distribution.
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| 5. |
- Pole, Mike, et al.
(författare)
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The first Cenozoic Equisetum from New Zealand
- 2017
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Ingår i: Geobios. - Amsterdam : Elsevier. - 0016-6995 .- 1777-5728. ; 50, s. 259-265
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Tidskriftsartikel (refereegranskat)abstract
- Equisetum is described for the first time from Cenozoic deposits of New Zealand. The fossils derive from two early to earliest middle Miocene assemblages in South Island, New Zealand. The fossils are ascribed tentatively to subgenus Equisetum based on their possession of whorled branch scars, but they cannot be assigned with confidence to a formal species. The decline of equisetaleans, otherwise unknown from the Cenozoic of the New Zealand-Australian-Antarctic domain, was possibly a consequence of severe environmental changes – particularly, abrupt shifts in the temperature and soil moisture regime – experienced by this region in the Neogene, coupled with competition from opportunistic angiosperms.
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| 7. |
- Zamora, Samuel, et al.
(författare)
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The Cambrian edrioasteroid Stromatocystites (Echinodermata): Systematics, palaeogeography, and palaeoecology.
- 2015
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Ingår i: Geobios. - : Elsevier BV. - 0016-6995 .- 1777-5728. ; 48:5, s. 417-426
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Tidskriftsartikel (refereegranskat)abstract
- The Cambrian edrioasteroid Stromatocystites is reported and described from Spain, Sweden and Turkey. All previously known occurrences of the genus are critically reviewed, and S. flexibilis is reinterpreted as a junior synonym of S. pentangularis. Stromatocystites was biogeographically widespread and colonized different areas of Baltica, Gondwana (Arabian, eastern and western margins) and Laurentia (western Newfoundland). Stratigraphically, it ranges from Cambrian Series 2, Stage 4 to Cambrian Series 3, Drumian. Stromatocystites lived in quiet water environments with stabilized substrates. It was attached directly to the substrate by its aboral surface. As these environments were widespread throughout Baltica, Gondwana and Laurentia, availability of suitable substrates for larval settlement and oceanic palaeocurrents led to the successful development of Stromatocystites colonies.
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