Origin and paleo-environment of the first modern mammals in China during the Paleocene-Eocene Thermal Maximum ‘Paleo-environment’

Description :

Context and objectives

True primates appeared suddenly on all three northern continents at the beginning of the Eocene Epoch, about 55.5 million years before present. They make their first appearance exactly during the Paleocene-Eocene Thermal Maximum (PETM), a 100.000 years-lasting abrupt global warming event that represents the warmest period of the last 65 million years. Teilhardina, the oldest primate, is now known on all three continents in association with the Carbon Isotope Excursion (CIE) that marks the PETM. Relative positions within the CIE indicates that Chinese Teilhardina asiatica is the oldest, Belgian T. belgica is younger, and North American T. brandti and T. americana are the youngest. Analysis of morphological characteristics in scanning electronic microscopy of all four species supports an Asian origin and a westward Asia-to-Europe-to-North America dispersal for Teilhardina.
High-resolution isotope stratigraphy indicates that this happened in an interval of about 25.000 years (Smith et al, 2006, PNAS). The fossil record indicates that primates are not the only modern mammal group that appears during the PETM. This is also the case for the first rodents, modern ungulates (artiodactyls, perissodactyls), and modern carnivores. The PETM climate changes obviously also affected the contemporaneous floras. These floral changes and the interaction of floral and faunal changes are still almost completely unknown. Only recently, the first transitional flora was published, and floral changes were suggested to be comparable to those in postglacial periods and those predicted for an anthropogenic global change.
What are the ancestors of the modern mammal orders? How did the PETM affect paleofloras? Is the global PETM event the driving mechanism for the dispersal of modern cosmopolitan mammals and for the progressive extinction of endemic archaic mammals on all the continents?
Identification of Late Paleocene and Early Eocene Chinese mammal faunas and their environment and characterisation of the remarkable paleoclimate during the PETM are keys in the understanding of the appearance and success of the first modern mammals 55 million years ago.


Methodology

Exploratory missions, excavations and multidisciplinary analyses are done in several Chinese localities from the Late Paleocene and Early Eocene (60 to 50 million years ago). This includes the famous early Eocene Wutu coal mine (Shandong province), and the Paleocene-Eocene transition Lingcha Formation (Hunan province) that has yielded the oldest primate Teilhardina asiatica. Diversity analysis of mammal faunas mainly based on dental remains and comparison with Europe (especially the Belgian Earliest Eocene Dormaal fauna, the reference-level for Europe), North America and India allow to analyse the paleobiogeography of mammal groups, and to distinguish the endemic groups of each continent from the groups that made intercontinental migrations around the PETM.
This is combined with the identification of the associated floras based on palynology and macrofossils (seeds, leafs and wood anatomy) to characterise both the paleo-environment of the mammals, and the paleo-climate that evolved very quickly around the PETM. Isotopic analyses of the carbon (δC13) of the organic matter from the sediment in the different sections allow high resolution dating of the fossils, by a geochemical technique developed by a Belgium team including FUNDP and RBINS.

Results

Exploration missions: among the localities visited until now by a team of RBINS-IBCAS during four international expeditions between 2008 and 2010 some sites have been considered important for collecting:
- Macrofossils (vertebrates and plant remains) and paleopalynological samples at Wutu coalmine in the Changle County of Shandong Province.
- Geological samples for Carbon isotopic analysis from Lingcha Formation at Hengyang in Paleocene-Eocene transition of Hunan Province.
- Palynological samples from Late Cretaceous through Early Eocene Qiuba, Gaoyugou and Dazhang Formations in the Tantou area of Henan Province.
- Vertebrates from the late Paleocene of Anhui province.
 

Documentation :

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