Low dinosaur biodiversity in central China 2 million years prior to the end-Cretaceous mass extinction

Abstract

Whether or not nonavian dinosaur biodiversity declined prior to the end-Cretaceous mass extinction remains controversial as the result of sampling biases in the fossil record, differences in the analytical approaches used, and the rarity of high-precision geochronological dating of dinosaur fossils. Using magnetostratigraphy, cyclostratigraphy, and biostratigraphy, we establish a high-resolution geochronological framework for the fossil-rich Late Cretaceous sedimentary sequence in the Shanyang Basin of central China. We have found only three dinosaurian eggshell taxa (Macroolithus yaotunensis, Elongatoolithus elongatus, and Stromatoolithus pinglingensis) representing two clades (Oviraptoridae and Hadrosauridae) in sediments deposited between ∼68.2 and ∼66.4 million y ago, indicating sustained low dinosaur biodiversity, and that assessment is consistent with the known skeletal remains in the Shanyang and surrounding basins of central China. Along with the dinosaur eggshell records from eastern and southern China, we find a decline in dinosaur biodiversity from the Campanian to the Maastrichtian. Our results support a long-term decline in global dinosaur biodiversity prior to 66 million y ago, which likely set the stage for the end-Cretaceous nonavian dinosaur mass extinction.

Keywords: dinosaur eggshells; east Asia; end-Cretaceous mass extinction; magnetostratigraphy.

Fig. 1.

Location and geology of the Shanyang Basin in East Qinling, central China (A). Four studied stratigraphic sections (Sigou, Dongbeigou, Juanlingcao, and Niupanggou) are shown with red lines. Most dinosaur eggshells in this study were found in the layers from site a to site b within the Niupanggou section (B). The lithology refers to Fig. 2. The topographic maps are based on the digital elevation database from https://srtm.csi.cgiar.org and https://www.google.com/maps.

Fig. 2.

Lithostratigraphy, biostratigraphy, and magnetostratigraphy of the Shanyang Basin sedimentary sequence. (A−C) Juanlingcao section; (D−F) Sigou section; (G−I) Dongbeigou section. GPTS (J) is the geomagnetic polarity timescale (GPTS 2020) (19). VGP latitudes are for sample ChRM directions converted to VGPs. Positive (northerly) and negative (southerly) VGP latitudes correspond to normal and reverse polarities, delineated in the polarity column by filled and open bars, respectively. Green open circles are accepted sample data with maximum angular deviation (MAD) values of 15° or less (SI Appendix). The proposed correlation constrains the Shanyang Basin sedimentary sequence to an interval from ∼71.7 Ma to ∼64.6 Ma, based on the occurrences of the Danian fossil Bemalambda and the Cretaceous dinosaur fossils (labeled open triangles). The thick conglomerate layer (labeled solid triangles), together with the overlying pelitic siltstone embedded a mass of reduction spots, are performed as a marker layer to correlate different sections.

Fig. 3.

Ages of the dinosaur eggshells and bones in the Shanyang Basin. The integrated lithology (A and B) refers mainly to the Juanlingcao section for its integrity and continuity. The high-resolution magnetic susceptibility data (D) were acquired from the Sigou section. The labels e7–e33 in D represent the 100,000-y short eccentricity cycles extracted with Gaussian band-pass filters using the software of Analyseries 2.0.8 (52). The ages in red (black) are the astronomical timescale (GPTS) (C). Dinosaur bone fossils in E refer to Xue et al. (18). Layer I: dinosaur species undetermined. Layer II: Shanyangosaurus niupanggouensis. Layer III: Shantungosaurs cf. giganteus, Tyrannosauridae, Sauropoda; Layer IV: dinosaur species undetermined. (SI Appendix). The relative thicknesses of the Sigou section and Niupanggou section are converted to the thickness of the integrated section based on their polarities and lithology (e.g., conglomerate layers). The δ¹⁸O values (F and G) are from the tropical Pacific (ODP 1209, ODP 1210B) (42, 55), Walvis Ridge in the South Atlantic (ODP 1262) (43), and Boreal Chalk Sea in Denmark (Stevns-1 core) (56). The δ¹⁸O values of the ODP cores were measured from benthic foraminifera. The δ¹⁸O values of the Stevns-1 cores were measured from the bulk carbonate of Stevns-1. Abbreviations: KPB, Cretaceous-Paleogene boundary; MMWE, Middle Maastrichtian warming event; LMWE, Late Maastrichtian warming event; and DT, Deccan Traps.

Fig. 4.

Sedimentary facies in the Juanlingcao–Niupanggou area. Similar lithology and sedimentary structures were observed in the Juanlingcao section and Niupanggou section. The tectonic evolution of the Shanyang Basin refers to Yu and Li (57). The SAR (sediment accumulation rate) in the different stages was calculated by the age model and the thickness of the sediments (SI Appendix, Fig. S8). The warm and cool climate intervals refer to Fig. 3.

Fig. 5.

Paleogeography of the Shanyang Basin in the stage of the Maastrichtian meandering river system. The depositional center is in the eastern part of the basin (18), and its sediment provenances are mainly from the southern and northwestern denudation areas (57). Most dinosaur eggshells buried in situ were discovered in the eastern part of the basin (e.g., the Niupanggou area), indicating that the dinosaurs primarily laid their eggs in this area. The slow subsidence of the hanging wall block and the developed meandering river system provide an excellent taphonomic environment for dinosaur egg preservation.

Fig. 6.

The Late Cretaceous dinosaur bones and eggshells through time (A) in the East Qinling basins (B) and the global distribution of the Late Cretaceous dinosaur occurrences (C). The materials and data in A are from the basins in the East Qinling region (B) (, –29). The ranges of the basins in East Qinling (B) are the coverage area of the sediments currently seen. The fossil ages and the ranges of the same basin are presented in the same color (e.g., the Shanyang Basin is presented in black). The global dataset of the Late Cretaceous dinosaur refers to Condamine et al. (7). The topographic maps (B) are based on the digital elevation database from https://www.google.com/maps. The plate tectonic map 66.0 Ma is produced by the ODSN Plate Tectonic Reconstruction Service (https://www.odsn.de/odsn/services/paleomap/paleomap.html). See SI Appendix, Table S12 for the source of dinosaur images. Abbreviations: Cen., Cenomanian; Tur., Turonian; Con., Coniacian; San., Santonian; Cam., Campanian; and Maa., Maastrichtian.