Identification of the Oligocene to early Miocene loricariid catfish †Taubateia paraiba as a member of the Rhinelepinae

Correct identification of fossil taxa is immensely important for dating molecular phylogenies and understanding when and how quickly modern biodiversity evolved. Fossils that are available for a clade of interest and can be directly incorporated in the phylogenetic analysis are considered primary sources of time calibration, whereas calibrations inferred from other studies are secondary (Arroyave et al., 2013). Studies of taxonomic groups that lack fossils must either expand their analyses to include fossilized outgroup lineages, use secondary calibrations, or use more problematic primary calibrations, e.g., vicariant geologic events. The use of vicariant geologic events to calibrate phylogenies poses the risk of circular reasoning, because the goal of many such studies is to determine how geologic events have affected diversification. Near et al. (2012) argued that fossil calibrations external to clades of interest, but still within the broader Actinopterygian (ray-finned fishes) tree, could be used as means of calibrating a generalized molecular clock, but internal calibrations are still valuable for refining such inferences (Arroyave et al., 2013).

An Early Miocene Lowland on the Northeastern Tibetan Plateau

The northeastern Tibetan Plateau (NE TP) has long been thought to be the last part of the Plateau to be raised, but this assumption has been challenged by recent analyses of fossil leaf energy, which have pointed to the possibility that the present surface altitude of ∼3,000 m above sea level (asl) in the Qaidam Basin (QB) was attained during the Oligocene. Here, for the first time, we present a record of glycerol dialkyl glycerol tetraethers (GDGTs) from a well-dated Cenozoic section in the QB. This record appears to demonstrate that the mean annual average paleotemperature of the QB was 28.4 ± 2.9°C at ∼18.0 Ma. This would suggest that the paleoelevation of the QB was only ∼1,488 m asl at that time and that a ∼1,500 m uplift was attained afterwards, in agreement with the massive shortening of the QB and the rapid drying of inland Asia since the late Miocene.

Submarine volcanic activity and giant amygdale formation along the Panama island arc as a precursor to 6000-year-old agate exploitation on Pedro González Island

An extensive deposit of agate occurs in Pedro González Island in the Gulf of Panama. Previous archaeological research showed that the agate was exploited between 6200 and 5600 cal BP to make stone tools found at the oldest known Preceramic human settlement in the Pearl Island archipelago. We constrain here the origin and geological context of the agate through a geological and geochemical study of the island. We show that it includes primary volcanic breccias, lavas, and tuffaceous marine deposits with sedimentary conglomerates and debris flow deposits, which we define as the Pedro González Formation. This formation records submarine to subaerial volcanic activity along an island arc during the Oligo-Miocene, confirming previous regional models that favour progressive emergence of the isthmus in the early Miocene. The igneous rocks have an extreme tholeiitic character that is interpreted to reflect magmatic cessation in eastern Panama during the early Miocene. The agate is hosted in andesitic lavas in unusually large amygdales up to 20–40 cm in diameter, as well as small amygdales (0.1–1.0 cm) in a bimodal distribution, and in veins. The large size of the agates made them suitable for tool manufacture. Field evidence suggests that the formation of large amygdales resulted from subaqueous lava–sediment interaction, in which water released from unconsolidated tuffaceous deposits at the base of lava flows rose through the lavas, coalesced, and accumulated below the chilled lava top, with subsequent hydrothermal mineralization. These amygdales could therefore be regarded as an unusual result of combined peperitic and hydrothermal processes.