scholarly journals Widespread loss of mammalian lineage and dietary diversity in the early Oligocene of Afro-Arabia

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Dorien de Vries ◽  
Steven Heritage ◽  
Matthew R. Borths ◽  
Hesham M. Sallam ◽  
Erik R. Seiffert
Keyword(s):  
Dietary Diversity ◽  
Late Eocene ◽  
Early Oligocene ◽  
Mammalian Lineage ◽  
Global Cooling ◽  
Evolutionary Trajectories ◽  
Cooling Phase ◽  
Potential Impact ◽  
The Antarctic ◽  
Major Reduction

AbstractDiverse lines of geological and geochemical evidence indicate that the Eocene-Oligocene transition (EOT) marked the onset of a global cooling phase, rapid growth of the Antarctic ice sheet, and a worldwide drop in sea level. Paleontologists have established that shifts in mammalian community structure in Europe and Asia were broadly coincident with these events, but the potential impact of early Oligocene climate change on the mammalian communities of Afro-Arabia has long been unclear. Here we employ dated phylogenies of multiple endemic Afro-Arabian mammal clades (anomaluroid and hystricognath rodents, anthropoid and strepsirrhine primates, and carnivorous hyaenodonts) to investigate lineage diversification and loss since the early Eocene. These analyses provide evidence for widespread mammalian extinction in the early Oligocene of Afro-Arabia, with almost two-thirds of peak late Eocene diversity lost in these clades by ~30 Ma. Using homology-free dental topographic metrics, we further demonstrate that the loss of Afro-Arabian rodent and primate lineages was associated with a major reduction in molar occlusal topographic disparity, suggesting a correlated loss of dietary diversity. These results raise new questions about the relative importance of global versus local influences in shaping the evolutionary trajectories of Afro-Arabia’s endemic mammals during the Oligocene.

scholarly journals Links between CO<sub>2</sub>, glaciation and water flow: reconciling the Cenozoic history of the Antarctic Circumpolar Current

2014 ◽  
Vol 10 (3) ◽  
pp. 2397-2416 ◽  
Author(s):  
J.-B. Ladant ◽  
Y. Donnadieu ◽  
C. Dumas
Keyword(s):  
Antarctic Circumpolar Current ◽  
Ice Sheet ◽  
Late Eocene ◽  
Early Oligocene ◽  
History Of ◽  
Potential Impact ◽  
Circumpolar Current ◽  
Set Up ◽  
The Antarctic ◽  
Exact Timing

Abstract. The timing of the onset of the Antarctic Circumpolar Current (ACC) is a crucial event of the Cenozoic because of its cooling and isolating effect over Antarctica. It is intimately related to the glaciations occurring throughout the Cenozoic from the Eocene–Oligocene (EO) transition (≈34 Ma) to the middle Miocene glaciations (≈13.9 Ma). However, the exact timing of the onset remains debated with evidence for a late Eocene set up contradicting others data pointing to an occurrence closer to the Oligocene–Miocene (OM) boundary. In this study, we show the potential impact of the Antarctic ice sheet on the initiation of a proto-ACC at the EO boundary. Our results reveal that the regional cooling effect of the ice sheet increases the sea ice formation, which disrupts the meridional density gradient in the Southern Ocean and leads to the onset of a circumpolar current and its progressive strengthening. We also suggest that subsequent variations in atmospheric CO2, ice sheet volumes and tectonic reorganizations may have affected the ACC intensity after the Eocene–Oligocene transition, which in turn may provide an explanation for the second initiation of the ACC at the Oligocene–Miocene boundary and may reconcile evidence supporting both early Oligocene and early Miocene onset of the ACC.

scholarly journals Links between CO<sub>2</sub>, glaciation and water flow: reconciling the Cenozoic history of the Antarctic Circumpolar Current

2014 ◽  
Vol 10 (6) ◽  
pp. 1957-1966 ◽  
Author(s):  
J.-B. Ladant ◽  
Y. Donnadieu ◽  
C. Dumas
Keyword(s):  
Antarctic Circumpolar Current ◽  
Middle Miocene ◽  
Ice Sheet ◽  
Late Eocene ◽  
Early Oligocene ◽  
History Of ◽  
Potential Impact ◽  
Circumpolar Current ◽  
The Antarctic ◽  
Exact Timing

Abstract. The timing of the onset of the Antarctic Circumpolar Current (ACC) is a crucial event of the Cenozoic because of its cooling and isolating effect over Antarctica. It is intimately related to the glaciations occurring throughout the Cenozoic from the Eocene–Oligocene (EO) transition (&amp;approx; 34 Ma) to the middle Miocene glaciations (&amp;approx; 13.9 Ma). However, the exact timing of the onset remains debated, with evidence for a late Eocene setup contradicting other data pointing to an occurrence closer to the Oligocene–Miocene (OM) boundary. In this study, we show the potential impact of the Antarctic ice sheet on the initiation of a strong proto-ACC at the EO boundary. Our results reveal that the regional cooling effect of the ice sheet increases sea ice formation, which disrupts the meridional density gradient in the Southern Ocean and leads to the onset of a circumpolar current and its progressive strengthening. We also suggest that subsequent variations in atmospheric CO2, ice sheet volumes and tectonic reorganizations may have affected the ACC intensity after the Eocene–Oligocene transition. This allows us to build a hypothesis for the Cenozoic evolution of the Antarctic Circumpolar Current that may provide an explanation for the second initiation of the ACC at the Oligocene–Miocene boundary while reconciling evidence supporting both early Oligocene and early Miocene onset of the ACC.

The youngest record of fossil land mammals from Antarctica; its significance on the evolution of the terrestrial environment of the Antarctic Peninsula during the late Eocene

1997 ◽  
Vol 71 (2) ◽  
pp. 348-350 ◽  
Author(s):  
S. F. Vizcaino ◽  
M. Bond ◽  
M. A. Reguero ◽  
R. Pascual
Keyword(s):  
Antarctic Peninsula ◽  
Present Note ◽  
Late Eocene ◽  
South American ◽  
Terrestrial Environment ◽  
Shallow Marine ◽  
Early Oligocene ◽  
La Meseta Formation ◽  
The Antarctic ◽  
Seymour Island

The record of fossil land mammals from Antarctica has been restricted previously to the middle levels of the Eocene-?early Oligocene La Meseta Formation in Seymour Island, Antarctic Peninsula. This mostly shallow-marine sequence was divided informally into seven subunits (Tertiary Eocene La Meseta or TELM 1 to 7) by Sadler (1988). Land mammals, representing South American lineages of marsupials, edentates, and ungulates were recovered from TELM 3, 4, and 5 (Marenssi et al., 1994; Vizcaíno et al., 1994). The purpose of the present note is to report the discovery of a well-preserved ungulate tooth from the uppermost level of the La Meseta Formation (TELM 7) and to discuss its paleoenvironmental implications.

Southern high latitude vegetation change across the Drake Passage region linked to prolonged intervals of climate cooling during the early Oligocene

2021 ◽  
Author(s):  
Nick Thompson ◽  
Ulrich Salzmann ◽  
Adrián López Quirós ◽  
Carlota Escutia ◽  
Peter Bijl ◽  
...  
Keyword(s):  
Antarctic Peninsula ◽  
Vegetation Change ◽  
Drake Passage ◽  
Late Eocene ◽  
Mean Annual Temperature ◽  
Temperature And Precipitation ◽  
Early Oligocene ◽  
Terrestrial Environments ◽  
The Antarctic

&lt;p&gt;The possible causes of the onset of Antarctic glaciation around the Eocene-Oligocene Transition (EOT), approximately 34 million years ago (~34Ma), are poorly understood. Uncertainties particularly remain over the role of the Drake Passage opening on the development of the Antarctic Circumpolar Current (ACC), and how this affected both marine and terrestrial environments. A major obstacle in understanding the role of the opening Drake Passage and ACC in Cenozoic climate changes has been the lack of continuous records spanning the EOT from the region. Here we present new palynomorph data from ODP Leg 113 Site 696 Hole B, recording changes in terrestrial environments and paleoclimate across the EOT. The sporomorph assemblage reveals the presence of Nothofagus-dominated forests with secondary Podocarpaceae and an understory of angiosperms and cryptogams growing across much of the Northern Antarctic Peninsula and South Orkney Microcontinent during the late Eocene (~37.60-34.95 Ma). Palaeoclimate reconstructions show that these forests grew under wet temperate conditions, with mean annual temperature and precipitation around 12&amp;#176;C and 1650mm, respectively. Today, similar temperate Nothofagus-dominated mixed-podocarp forests occur in the temperate Valdivian region of southern Chile. At the onset of the EOT, the palynomorph assemblage indicates an unusual expansion of gymnosperms and cryptogams, accompanied by a rapid increase in taxa diversity between ca. 34 and 32 Ma. Sporomorph based climate reconstructions do not provide evidence for an abrupt cooling at the EOT but reveal the onset of prolonged cooling phases throughout the early Oligocene. A contemporaneous increase in reworked Mesozoic sporomorphs at the EOT is likely to be linked to frequent glacial advances from the Antarctic Peninsula and South Orkney Microcontinent, although iceberg-rafted debris from Antarctica cannot be ruled out. We conclude that climate instability and glacial related disturbance at the onset of the EOT facilitated the suppression of Nothofagus and the expansion of a more diverse vegetation with many pioneer taxa that were able to quickly colonise during glacial retreat cycles.&lt;/p&gt;

Review of fossil penguins from Seymour Island

1971 ◽  
Vol 178 (1053) ◽  
pp. 357-387 ◽  
Keyword(s):  
New Zealand ◽  
Indirect Evidence ◽  
Late Eocene ◽  
Valid Species ◽  
The North ◽  
Early Oligocene ◽  
North Eastern ◽  
The Antarctic ◽  
Early Late ◽  
Seymour Island

Two collections of fossil penguins have been made from Seymour Island, off the north-eastern end of the Antarctic Peninsula, one by a Swedish expedition in 1901-1903 and the other by a British expedition in 1946. The age has usually been considered early Miocene but is probably earlier, late Eocene now seeming most likely but still uncertain. Wiman in 1905 based six then new generic and specific names on the Swedish collection Anthropornis nordenskjoeldii and Delphinornis larsenii are considered valid. Pachypteryx grandis is a valid species but is transferred to Anthropornis. Eosphaeniscus gunnari is a valid species transferred to Palaeeudyptes , a genus otherwise known from New Zealand and Australia. Orthopteryx gigas and Ichtyopteryx gracilis are considered essentially indeterminate, as are two groups of bones not named by Wiman. Marples named genus and species Notodyptes wimani from the British collection. The species is accepted but transferred to the New Zealand genus Archaeospheniscus. Wimanornis seymourensis , new genus and species, is based on a British specimen. This penguin fauna is essentially similar to the early (late Eocene and early Oligocene) faunas known from New Zealand. In the probable absence of species in common, geographic proximity is not indicated. The ecological similarity and some indirect evidence suggest that despite the presence of relative gigantism these penguins lived in considerably warmer waters than those of the present Antarctic coast.

The Eocene-Oligocene planktic foraminiferal transition: extinctions, impacts and hiatuses

1993 ◽  
Vol 130 (4) ◽  
pp. 483-499 ◽  
Author(s):  
Eustoquio Molina ◽  
Concepción Gonzalvo ◽  
Gerta Keller
Keyword(s):  
Thermohaline Circulation ◽  
Middle Eocene ◽  
Species Abundance ◽  
Late Eocene ◽  
Cool Temperature ◽  
Early Oligocene ◽  
Major Species ◽  
Global Cooling ◽  
Impact Events ◽  
Species Extinctions

AbstractBiostratigraphic study and re-examination of 22 late Eocene to early Oligocene sections provides data in support of three and possibly a fourth late Eocene impact events in the G. index Zone during a period of about 1 Ma of the middle Priabonian between 34.7 and 35.7 Ma. No major species extinctions or significant species abundance changes directly coincide with these impact events. Species extinctions are gradual and selective, affecting primarily cool-temperature-intolerant surface dwellers. These extinctions began with the onset of global cooling during the early middle Eocene and culminated near the Eocene/Oligocene boundary. The global cooling was associated with the isolation of Antarctica as Australia moved northward, the development of a circum-Antarctic circulation, growth of Antarctic ice sheet beginning by late middle Eocene time and a change from a thermospheric to thermohaline circulation. We find no evidence that the multiple late Eocene impact events directly contributed to the climatic deterioration already in progress.

Global cooling accelerated by early late Eocene impacts?

Geology ◽  
2000 ◽  
Vol 28 (8) ◽  
pp. 687-690 ◽  
Author(s):  
Hubert B. Vonhof ◽  
Jan Smit ◽  
Henk Brinkhuis ◽  
Alessandro Montanari ◽  
Alexandra J. Nederbragt
Keyword(s):  
Late Eocene ◽  
Global Cooling ◽  
Early Late

Falcatifolium (Podocarpaceae) macrofossils from paleogene sediments in south-eastern Australia: a reassessment

1998 ◽  
Vol 11 (6) ◽  
pp. 711 ◽  
Author(s):  
Robert S. Hill ◽  
Leonie J. Scriven
Keyword(s):  
Leaf Morphology ◽  
Middle Eocene ◽  
Late Eocene ◽  
South Eastern ◽  
Early Oligocene ◽  
Extant Species ◽  
Eastern Australia ◽  
South Eastern Australia

A re-investigation of macrofossils previously referred to the extantpodocarpaceous genus Falcatifolium Laubenfels shows thatno records can be sustained. Falcatifolium australisD.R.Greenwood from Middle Eocene sediments in Victoria bears littleresemblance to extant species in the genus and is transferred to the newfossil genus Sigmaphyllum R.S.Hill & L.J.Scriven.Specimens from Early Oligocene sediments in Tasmania previously assigned toFalcatifolium are described as a second species ofSigmaphyllum, S. tasmanensisR.S.Hill & L.J.Scriven, and specimens from mid to late Eocene sediments inTasmania previously assigned to Falcatifolium do notbelong to that genus, although their true generic affinities are uncertain.Dispersed cuticle specimens from Late Eocene–Oligocene sediments inSouth Australia referred to Falcatifolium are notreliable records of the genus and require further investigation. However,Dacrycarpus eocenica D.R.Greenwood, from Middle Eocenesediments in Victoria is transferred to Falcatifolium,and is similar to the extant species F. angustumLaubenfels, which has a leaf morphology unusual for the genus.Falcatifolium eocenica (D.R.Greenwood) R.S.Hill & L.J.Scriven is the only reliable record of the genus in the Australian fossilrecord to date.

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