|Peripatus Home Page Paleontology >> Paleogene Period||Updated: 25-Jun-2018|
AbstractThis page describes the Paleogene Period, including stratigraphy, paleogeography, and famous lagerstätten, followed by a sketched outline of some of the major evolutionary events.
Keywords: Paleogene, Paleogene biota, fossil record, evolution
The Paleogene System does not have a type section, as such, because it was not originally conceived as a unit in its own right. It was instead “cobbled together” from the earliest three of the seven Cenozoic series (epochs) – Paleocene, Eocene, Oligocene, Miocene, Pliocene, Pleistocene and Holocene – “poetically named for relative abundances of modern forms among the fossil shells” (Ogg et al. 2008, p. 129).
Lower (Cretaceous–Paleogene) Boundary
Surely the most widely reported – and the most widely misreported – of all extinction events is that which brought the age of the dinosaurs to an end at the close of the Mesozoic: the “KT” extinction.
Almost all of the popular and “lightly technical” literature published within the past couple of decades is filled with comet or meteorite impact theories, all ultimately traceable to the father and son team of Luis and Walter Alvarez. Indeed, there is a good body of evidence to support the contention that a large extraterrestrial impact did occur at the very end of the Cretaceous.
However, the KT extinction is only one of several such mass extinctions in the Phanerozoic, and by no means the largest. There is no evidence of impacts associated with the other mass extinction events, and very few people try to maintain that argument today. In fact, flood volcanism is the only mechanism which really matches the data. “[L]arge continental flood-basalt volcanic events exhibit a near-perfect stage-level association with marked increases in Mesozoic and Cenozoic extinction intensity. Ten out of the 11 major flood-basalt eruption events of the last 250 million years occur during a stage that contains a local extinction peak (i.e. mass extinction). It is presently unknown whether this association is scale-dependent or extends to smaller events as well” (MacLeod 2002).
“Everyone has a favourite theory for major extinctions, all united by the common theme of attributing dominant importance to physical factors, and playing down the importance of normal biological mechanisms. Our own work strongly favours the diversification of both mammals and birds at least 30 million years before the extinction of dinosaurs – there must be ecological consequences for small dinosaurs from this early diversification” (Penny 2002).
If an impact was the sole cause of the KT extinctions, then that would make the KT different from the several other mass extinctions known, which is not a parsimonious conclusion. However, if an impact did occur at about that time, which seems likely, no doubt it would have added further stress to the already failing ecosystems, and possibly accelerated or even heightened the extinction event in some places.
The GSSP for the base of the Danian Stage (= Cretaceous-Paleogene boundary) was established in 1996 in the clay layer containing the famous “K/T” iridium anomaly and nickel-rich spinels at a section of Oued Djerfane, 8 km west of El Kef, in Tunisia (see Molina et al. 2006).
Upper (Paleogene–Neogene) Boundary
The Paleogene-Neogene boundary is coincident with the base of the Aquitanian Age which in turn defines the base of the Miocene Epoch. The Aquitanian GSSP is formally defined in the Lemme-Carrosio section in northern Italy, located at the 35 m level as measured downward from the top of the section. The horizon corresponds closely with the first appearance of the calcareous nannofossil Sphenolithus capricornutus and with the C6Cn.2n(o) reversal boundary (after Gradstein et al. 2012, p. 925-926).
The Paleogene Period extends from 66.0 Ma to 23.03 Ma (Cohen et al. 2015).
What happened to the Tertiary?
A great deal of the older, particularly European, literature subdivides the Cenozoic into the Teriary and Quaternary Periods, the Tertiary Period comprising the Paleocene through Pliocene Epochs. In fact, this scheme has a very long history, dating back to the earliest attempts to subdivide geological time in the mid-1700s. An alternative subdivision into Paleogene and Neogene was introduced by Hörnes in 1853, and took root, most strongly in America. Initially, the Neogene extended to the present day, i.e., it incorporated the Quaternary Period also.
After some indecision, the ICS eventually adopted a three-fold subdivision of the Cenozoic into Paleogene, Neogene and Quaternary periods. The Paleogene Period comprises the Paleocene through Oligocene epochs, the Neogene comprises the Miocene and Pliocene epochs, and the Quaternary encompasses the Pleistocene and Holocene.
Major Tectonic Events
Land and Sea
Recent phylogenetic analysis suggests that all extant families and subfamilies containing arboreal species originated after the Cretaceous, suggesting that new ecological opportunities shaped anuran diversification as forests rebounded after ... vegetation loss at the K–Pg extinction event” (Xing et al. 2018, p. 1).
Post-Mesozoic Mammalian Evolution
Both abundance and diversity of mammals were reduced severely by the Cretaceous-Tertiary mass extinction event (e.g. in the Hell Creek assemblage, only one out of 28 mammal species survived; Ward 2000, p. 173) with fewer taxa known from the Paleocene than from the Cretaceous.
However, the diversity and range of mammals increased greatly after the Paleocene/Eocene boundary (about 55 million years ago), and new groups appeared on continents throughout the Northern Hemisphere. On the basis of primarily phylogenetic analyses, Asia has been suggested as a likely center of origin (Bowen et al. 2002, p. 2028).
The greatest diversity appears to have been achieved in the Miocene, with a subsequent reduction through to the present day.
Major Biotic Events
Early Primate Evolution
The primate record, generally, and the human record in particular, is very incomplete. The closest living relatives of primates may be the Dermoptera (colugos, arboreal gliding mammals native to Southeast Asia; suggested by genetic studies) or the clade of Dermoptera plus Chiroptera (bats; suggested by morphology). Any common ancestor to the three groups must have lived in the Cretaceous. Probable primate ancestors – genera such as Purgatorius, Plesiadapis and Phenacolemur – date from the earliest Paleogene, approximately 65 Ma. The oldest known true primates occur about 55 Ma (near the Paleocene/Eocene boundary).
Dominican Amber: ?Eocene to Miocene (15-45 Ma); Dominican Republic; small animals, mostly arthropds, and plant fragments preserved in amber; Poinar & Poinar 1999
Grube Messel Shale: Eocene Frankfurt, Germany; lacustrine (lake deposits); fossil plants, vertebrates and insects; Schaal & Ziegler 1992
Monte Bolca (Mt. Bolca): 52 Ma Eocene Near Verona, Italy; tropical marine lagoon. Exceptional preservation of fishes (>200 different kinds), plants, leaves and rare insects. Known since the 17th century. Also see the Musei della Lessinia web page (in Italian). [With thanks to Giorgio Bertoni for this information.]
Green River Formation: Eocene Wyoming; lacustrine (lake deposits); fossil fish (~18 different kinds) and other vertebrates; Grande 1984
New Zealand Occurrences
As Zealandia continued to rift away from Gondwana, the new microcontinent underwent post-rift lithospheric cooling and slowly subsided. The subsidence resulted in extensive marine transgression, with consequent reduction in land area, frequently expressed in the geological record by terrestrial sequences such as coal measures overlain by marine sediments. By the Middle Eocene, “the reduced Zealandia landmass had extensive coastal plains and predominantly fine-grained clastic sediments and carbonates were accumulating in marine sedimentary basins offshore” (Edbrooke 2017, p. 31).
Subsidence of the Zealandia microcontinent reached a maximum between about 35 and 25 Ma, in the Oligocene. This interval of “maximum drowning” saw widespread deposition of limestones as the clastic sediment supply diminished due to the dwindling of emergent land. Some authors have gone so far as to suggest that Zealandia became completely submerged at some time in the late Oligocene, and there is lively on-going debate about this hypothesis. The principal counter-argument is that the diverse and highly endemic present-day New Zealand biota is unlikely to have been able to develop de novo since the end of the Oligocene.
Bowen, G.J.; Clyde, W.C.; Koch, P.L.; Ting, S.; Alroy, J.; Tsubamoto, T.; Wang, Y.; Wang, Y. 2002: Mammalian Dispersal at the Paleocene/Eocene Boundary. Science 295: 2028-2029. Science.
Cohen, K.M.; Finney, S.C.; Gibbard, P.L.; Fan, J.X. 2015: The ICS international chronostratigraphic chart v 2015/01. Episodes 36: 199-204.
Edbrooke, S.W. 2017: The geological map of New Zealand. GNS Science Geological Map 2: 1-183.
Gradstein, F.M.; Ogg, J.G.; Schmitz, M.D.; Ogg, G.M. 2012: The Geologic Time Scale 2012. Elsevier 1-2.
Grande L. 1984: Paleontology of the Green River Formation. Bulletin of the Geological Survey of Wyoming, no. 63: 1-333.
Hörnes, M. 1853: Mitteilung an Prof. Bronn gerichtet: Wien, 3. Okt., 1853. Jahrbuch für Mineralogie, Geognosie, Geologie und Petrefakten-Kunde: 806-810.
Molina, E.; Alegret, L.; Arenillas, I.; Arz, J.A.; Gallala, N.; Hardenbol, J.; von Salis, K.; Steurbaut, E.; Vandenberghe, N.; Zaghbib-Turki, D. 2006: The Global Boundary Stratotype Section and Point for the base of the Danian Stage (Paleocene, Paleogene, “Tertiary”, Cenozoic) at El Kef, Tunesia - Original definition and revision. Episodes 29: 263-273.
Ogg, J.G.; Ogg, G.; Gradstein, F.M. 2008: The Concise Geologic Time Scale. Cambridge: 1-177.
Poinar, G. Jr.; Poinar, R. 1999: The amber forest: A reconstruction of a vanished world. Princeton: 1-239.
Schaal, S.; Ziegler, W. (ed.) 1992: Messel. An insight into the history of life and of the Earth [English translation]. Clarendon Press: 1-322.
Ward, Peter D. 2000: Rivers in Time. Columbia University Press. .
Xing, L.; Stanley, E.L.; Bai, M.; Blackburn, D.C. 2018: The earliest direct evidence of frogs in wet tropical forests from Cretaceous Burmese amber. Nature Scientific Reports 8 (8770): 1-8.
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