Decadal–centennial-scale solar-linked climate variations and millennial-scale internal oscillations during the Early Cretaceous

Understanding climate variability and stability under extremely warm ‘greenhouse’ conditions in the past is essential for future climate predictions. However, information on millennial-scale (and shorter) climate variability during such periods is scarce, owing to a lack of suitable high-resolution, deep-time archives. Here we present a continuous record of decadal- to orbital-scale continental climate variability from annually laminated lacustrine deposits formed during the late Early Cretaceous (123–120 Ma: late Barremian–early Aptian) in southeastern Mongolia. Inter-annual changes in lake algal productivity for a 1091-year interval reveal a pronounced solar influence on decadal- to centennial-scale climatic variations (including the ~ 11-year Schwabe cycle). Decadally-resolved Ca/Ti ratios (proxy for evaporation/precipitation changes) for a ~ 355-kyr long interval further indicate millennial-scale (~ 1000–2000-yr) extreme drought events in inner-continental areas of mid-latitude palaeo-Asia during the Cretaceous. Millennial-scale oscillations in Ca/Ti ratio show distinct amplitude modulation (AM) induced by the precession, obliquity and short eccentricity cycles. Similar millennial-scale AM by Milankovitch cycle band was also previously observed in the abrupt climatic oscillations (known as Dansgaard–Oeschger events) in the ‘intermediate glacial’ state of the late Pleistocene, and in their potential analogues in the Jurassic ‘greenhouse’. Our findings indicate that external solar activity forcing was effective on decadal–centennial timescales, whilst the millennial-scale variations were likely amplified by internal process such as changes in deep-water formation strength, even during the Cretaceous ‘greenhouse’ period

Diversification rates in Ctenodactylidae (Rodentia, Mammalia) from Mongolia

Gundis, or comb rats, are rodents of the family Ctenodactylidae. Extant gundis are restricted to Africa and represent a vestige of the diversity that the ctenodactylids attained at both palaeoecological and palaeobiogeographical levels. Here, we present an updated review of the Ctenodactylidae from the Valley of Lakes, Mongolia, based on the study of large collections now available. We have recognised 13 valid species of ctenodactylids grouped into five genera: Karakoromys, Huangomys, Tataromys, Yindirtemys, and Prodistylomys. The ctenodactylids show an initial burst in diversification in the early Oligocene followed by a sequential generic extinction of Karakoromys, Huangomys, and Tataromys. A maximum richness peak at the late Oligocene was followed by a profound diversity crisis. Yindirtemys, the only surviving genus, persisted into the Miocene, joining three Prodistylomys species. These last representatives of the group disappeared coinciding with the late Xiejian faunal reorganisation (Mongolian biozone D).Open access funding provided by Austrian Science Fund (FWF). We acknowledge U. Göhlich (NHMW) for the facilities to study the collections. We thank the support of all Mongolian and European contributors of fieldwork, administration, and scientific work. We are grateful to M.S. Domingo, V. Hernández-Ballarín, and P. López-Guerrero for their advice in the analysis. We would like to thank M. Vianey-Liaud and W. Wessels for their valuable comments. We also thank S. Weber for her help. Our research was granted by several projects of the Austrian Science Fund (P-10505-GEO, P-15724-N06 and P-23061-N19).Peer Reviewe

Reconstructing Krassilovia mongolica supports recognition of a new and unusual group of Mesozoic conifers

Previously unrecognized anatomical features of the cone scales of the enigmatic Early Cretaceous conifer Krassilovia mongolica include the presence of transversely oriented paracytic stomata, which is unusual for all other extinct and extant conifers. Identical stomata arepresent on co-occurring broad, linear, multiveined leaves assigned to Podozamites harrisii, providing evidence that K. mongolica and P. harrisii are the seed cones and leaves of the same extinct plant. Phylogenetic analyses of the relationships of the reconstructed Krassilovia plant place it in an informal clade that we name the Krassilovia Clade, which also includes Swedenborgia cryptomerioides–Podozamites schenkii, and Cycadocarpidium erdmanni–Podozamites schenkii. All three of these plants have linear leaves that are relatively broad compared to most living conifers, and that are also multiveined with transversely oriented paracytic stomata. We propose that these may be general features of the Krassilovia Clade. Paracytic stomata, and other features of this new group, recall features of extant and fossil Gnetales, raising questions about the phylogenetic homogeneity of the conifer clade similar to those raised by phylogenetic analyses of molecular data.Funding for this work was provided by National Science Foundation grants DEB-1748286 to P.S.H., P.R.C. and F.H., and 1348456 to P.R.C. and P.S.H., the Oak Spring Garden Foundation to F.H., and Grants-in-Aid for Scientific Research (21405010 and 24405015) from the Japan Society.</p

Leaves of <i>Podozamites</i> and <i>Pseudotorellia</i> from the Early Cretaceous of Mongolia: stomatal patterns and implications for relationships

<p>Strap-shaped, parallel-veined leaves of <i>Podozamites</i> and <i>Pseudotorellia</i> are among the most common fossils in Late Triassic to Early Cretaceous floras from the Northern Hemisphere. <i>Podozamites</i> is considered to be the leaf of a voltzian conifer, but its cuticle is poorly known, whereas <i>Pseudotorellia</i>, with a thick cuticle and haplocheilic stomata, is commonly considered to be the leaf of a ginkgoalean. Here we describe the leaf morphology, cuticle and stomata of <i>Podozamites</i> and <i>Pseudotorellia</i> based on excellently preserved material from the Early Cretaceous of central Mongolia. <i>Podozamites harrisii</i> sp. nov. has transversely oriented, paracytic (probably syndetocheilic) stomata that are regularly arranged in longitudinal files. <i>Pseudotorellia resinosa</i> sp. nov. and <i>Pseudotorellia palustris</i> sp. nov. have scattered, longitudinally oriented stomata in which the two guard cells are sunken and surrounded by 2–5 specialized lateral subsidiary cells and 1–3 unspecialized polar cells. Association evidence and similarities in cuticular structure suggest that <i>Podozamites harrisii</i> was produced by the same plant as the seed cone <i>Krassilovia</i>. The distinctive stomatal pattern of <i>Podozamites harrisii</i> and <i>Krassilovia</i> is also seen in some species of <i>Swedenborgia</i> and <i>Cycadocarpidium</i>, suggesting these plants may all belong to the same natural group. <i>Cycadocarpidium</i>, <i>Krassilovia</i> and <i>Swedenborgia</i> have previously been treated as conifers, but their transversely oriented, paracytic stomata hint instead at a possible relationship with Bennettitales and Gnetales.</p

Oligocene stratigraphy across the Eocene and Miocene boundaries in the Valley of Lakes (Mongolia)

Cenozoic sediments of the Taatsiin Gol and TaatsiinTsagaan Nuur area are rich in fossils that provide unique evidence of mammal evolution in Mongolia. The strata are intercalated with basalt flows. 40Ar/39Ar data of the basalts frame the time of sediment deposition and mammal evolution and enable a composite age chronology for the studied area. We investigated 20 geological sections and 6 fossil localities of Oligocene and early Miocene deposits from this region. Seventy fossil beds yielded more than 19,000 mammal fossils. This huge collection encompasses 175 mammal species: 50% Rodentia, 13% Eulipotyphla and Didelphomorphia, and 12% Lagomorpha. The remaining 25% of species are distributed among herbivorous and carnivorous large mammals. The representation of lower vertebrates and gastropods is comparatively poor. Several hundred SEM images illustrate the diversity of Marsupialia, Eulipotyphla, and Rodentia dentition and give insight into small mammal evolution in Mongolia during the Oligocene and early Miocene. This dataset, the radiometric ages of basalt I (∼31.5 Ma) and basalt II (∼27 Ma), and the magnetostratigraphic data provide ages of mammal assemblages and time ranges of the Mongolian biozones: letter zone A ranges from ∼33 to ∼31.5 Ma, letter zone B from ∼31.5 to ∼28 Ma, letter zone C from ∼28 to 25.6 Ma, letter zone C1 from 25.6 to 24 Ma, letter zone C1-D from 24 to ∼23 Ma, and letter zone D from ∼23 to ∼21 Ma.Open access funding provided by Austrian Science Fund (FWF). This research was supported by four projects of the Austrian Science Fund (FWF): P-10505-GEO, P-15724-N06, P-23061-N19 to G.D.-H. and a Lise Meitner grant M-1357-B17 to O.M. Travel expenses of G.D.-H. to China and Mogolia were partly covered by the Austrian Academy of Sciences.Peer Reviewe