Department of Geological Sciences, Stanford University, Stanford, CA, 94305, USA.
Published: February 2023
AI Article Synopsis
Article Abstract
The early Eocene (~ 56-48 million years ago) was marked by peak Cenozoic warmth and sea levels, high CO, and largely ice-free conditions. This time has been described as a period of increased continental erosion and silicate weathering. However, these conclusions are based largely on geochemical investigation of marine mudstones and carbonates or study of intermontane Laramide basin settings. Here, we evaluate the marine coarse siliciclastic response to early Paleogene hothouse climatic and oceanographic conditions. We compile an inventory of documented sand-rich (turbidite) deep-marine depositional systems, recording 59 instances of early Eocene turbidite systems along nearly all continental margins despite globally-elevated sea levels. Sand-rich systems were widespread on active margins (42 instances), but also on passive margins (17 instances). Along passive margins, 13 of 17 early Eocene systems are associated with known Eocene-age fluvial systems, consistent with a fluvial clastic response to Paleogene warming. We suggest that deep-marine sedimentary basins preserve clastic records of early Eocene climatic extremes. We also suggest that in addition to control by eustasy and tectonism, climate-driven increases in sediment supply (e.g., drainage integration, global rainfall, denudation) may significantly contribute to the global distribution and volume of coarse-grained deep-marine deposition despite high sea level.
Shrews are among the most speciose of mammalian clades, but their evolutionary history is poorly understood. Their fossil record is fragmentary and even the anatomy of living groups is not well documented. Here, we incorporate the oldest, most complete fossil shrew yet known into the first phylogenetic analysis of the group to include molecular, morphological and temporal data.
Introduction Raoellidae are small artiodactyls retrieved from the middle Eocene of Asia (ca - 47 Ma) and closely related to stem Cetacea. Morphological observations of their endocranial structures allow for outlining some of the early steps of the evolutionary history of the cetacean brain. The external features of the brain and associated sinuses of Raoellidae are so far only documented by the virtual reconstruction of the endocast based on specimens of the species Indohyus indirae.
Pseudonotherobius kohlsi and Megalomus? coloradensis are newly identified species of lacewings from the early Eocene era, found in Colorado’s Green River Formation.
Pseudonotherobius is characterized by a specific crossvein in its forewings and a uniquely dilated hind wing, which sets it apart within its family.
The genus is tentatively placed within the Carobiinae subfamily, hinting at its similarity to a modern Australian lacewing species.
- A new beetle species, Rhantus villumi sp. nov., has been identified from a single specimen found in the Fur Formation of Denmark, dating back about 55.4 million years to the early Eocene, making it the oldest known member of its genus.
- The discovery aligns with phylogenetic studies and suggests that the presence of this temperate beetle in a typically warm environment indicates potential short-term cooling trends during that period.
- The newly identified species might have fed on mosquito larvae, which have also been found in the same fossil site; however, another Dytiscidae species was noted but remains unidentified due to preservation issues.
Furochrysa alisae gen et sp. nov. is described, and Stephenbrooksia multifurcata Willmann, 1993 and Danochrysa madseni Willmann, 1993 are re-described based on their holotypes and additional specimens from the early Eocene Fur Formation of Denmark.
