ARTICLE Download: 28| View: 166| Comments: 0
Subject: Earth Sciences, Palaeontology Keywords: chordates; vetulicolians; cephalochordates; vertebrates; tunicates; Cambrian; Chenjiang Biota; Burgess Shale; Banffia; Vetulicolia; Myllokunmingia; Metaspriggina; agnathans; deuterostomes; all-trans-retinoic acid (ATRA); morphogen gradients
Online: 3 July 2019 (11:01:11 CEST)
Deuterostomes make a sudden appearance in the fossil record during the Early Cambrian. Two deuterostome groups, the chordates and the vetulicolians, are of particular interest for understanding the evolutionary dynamics of the Cambrian evolutionary event. Lagerstätten in China and elsewhere have dramatically improved our understanding of the range of variation in these ancient animals. Cephalochordate and vertebrate body plans are well established at least by Cambrian Series 2. Taken together, roughly a dozen chordate genera and fifteen vetulicolian genera document an explosive radiation of deuterostomes at the base of the Cambrian. A new vetulicolian (••• nov. gen. nov. sp.) with a polygonal anterior section and a narrow, unsegmented posterior region (‘tail’) bearing possible myotomes provides new insight into the affinities of the various body plans that emerged during the Early Cambrian. It seems clear that the advent of deuterostomes near the Cambrian boundary involved both a reversal of gut polarity and a two-sided retinoic acid gradient, with a gradient discontinuity at the midpoint of the organism that is reflected in the sharp division of vetulicolians into anterior and posterior sections.
Mon, 6 August 2018
ARTICLE Download: 162| View: 208| Comments: 0 | doi:10.20944/preprints201808.0102.v1
Subject: Earth Sciences, Palaeontology Keywords: global warming and environmental change; Late Quaternary paleoenvironments; Termination I; sea-water paleotemperature; marine microfossils; North Atlantic; stable isotopes
Online: 6 August 2018 (08:56:58 CEST)
The micropaleontological study (radiolarians and foraminifera) of the sediment core AMK-340, Reykjanes Ridge, North Atlantic, combined with the radiocarbon dating and Oxygen/Carbon isotopic record, provided data for the reconstruction of the summer paleotemperature on the water depth of 100 m, and paleoenvironments during the Termination I in the age interval of 14.5–8 ka. The response of the main microfossil species on the paleoceanographic changes within the Bølling-Allerød (BA) warming, the Younger Dryas (YD) cold event, and final transition to the warm Holocene was different. The BA warming was well reflected in the radiolarian and benthic but not planktic foraminiferal record. The high abundances of the cold-water radiolarian species Amphimelissa setosa as the Greenland/Iceland Sea indicator marked a cooling at the end of the BA and within the start of the YD at 13.2–12.3 ka. The micropaleontological and isotopic data together with the paleotemperature estimates for the Reykjanes Ridge at 60° N document that, after the warm BA, the middle YD ca. 12.5–12.2 ka was the next significant step toward the Holocene warming. Start of the Holocene interglacial conditions was reflected in abundant occurrence of the microfossils being indicators of the open boreal North Atlantic environments and lower oxygen isotope values indicating increasing warmth.
Tue, 31 July 2018
ARTICLE Download: 209| View: 181| Comments: 0 | doi:10.20944/preprints201807.0610.v1
Subject: Earth Sciences, Palaeontology Keywords: ichnite; Skye; Yorkshire; footprints; dinosaur; sauropod; theropod; ornithopod
Online: 31 July 2018 (06:40:24 CEST)
Despite the Hebrides and Cleveland basins being geographically close, research has not previously been carried out to determine faunal similarities and assess the possibility of links between the dinosaur populations. The palaeogeography of both areas during the Middle Jurassic shows that there were no elevated landmasses being eroded to produce conglomeratic material in the basins at that time. The low-lying landscape and connected shorelines may have provided connectivity between the two dinosaur populations. The dinosaur fauna of the Hebrides and Cleveland basins has been assessed based primarily on the abundant ichnites found in both areas as well as their skeletal remains. In the two basins the dinosaur faunas are very similar, consisting of non-neosauropod eusauropods, a possible basal titanosauriform, large and small theropods and ornithopods and europodan thyreophorans. The main difference in the faunas is in the sizes. In the Cleveland Basin the ichnites suggest that there were medium and large theropods alongside small to medium sized ornithopods whereas in the Hebrides Basin the theropods were from small to large and the ornithopods were medium to large. It is suggested that migrations could have taken place between the two areas during the Middle Jurassic. A tentative food chain from the herbivorous dinosaurs to the top predators can be inferred from the footprints.
Wed, 24 January 2018
ARTICLE Download: 947| View: 406| Comments: 0 | doi:10.20944/preprints201801.0229.v1
Subject: Earth Sciences, Palaeontology Keywords: Mid Miocene Climatic Optimum (MMCO); nannoplankton; temperature changes; Cibulakan Formation
Online: 24 January 2018 (18:50:42 CET)
Global climatic event on Middle Miocene triggered by geology activity is called by Mid- Miocene Climatic Optimum (MMCO). This event was widely distributed and associated with increasing temperature and CO2 content in the atmosphere. The effect of MMCO was widely known the mid-latitude region, but still limited information in low latitude sediments. This study try to perform the effect of MMCO at Cibulakan Formation in which deposited in the low latitude basin, Bogor Basin. Fifty eights samples from Cileungsi River were taken at Cibulakan Formation and quantitative nannoplankton analysis was carried out for this study. Nannoplankton shows the sensitive response with sea surface temperature changes. Increasing of total population nannoplankton indicates the rising of temperature and dropping temperature is marked by decreasing population. The effect of sea surface temperature changes relates with salinity changes as the effect of evaporation. Helicosphaera carteri and Umbilicosphaera jafari were counted to know the salinity trend at Cibulakan Formation. Sea surfaces temperature changes was observed on Early Miocene which was influenced by small scale Early Miocene glaciation and active tectonic during this period. Warming temperature taken place on Middle Miocene as the effect of warm and open sea during Mid Miocene Climatic Optimum. Afterwards, hot temperature continued on Late Miocene triggered by global increasing temperature at Pacific Ocean and widely distribution of clean water at North West Java Basin.