Oxygen isotopes of East Asian dinosaurs reveal exceptionally cold Early Cretaceous climates

Abstract

Early Cretaceous vertebrate assemblages from East Asia and particularly the Jehol Biota of northeastern China flourished during a period of highly debated climatic history. While the unique characters of these continental faunas have been the subject of various speculations about their biogeographic history, little attention has been paid to their possible climatic causes. Here we address this question using the oxygen isotope composition of apatite phosphate (δ ) from various reptile remains recovered from China, Thailand, and Japan. δ values indicate that cold terrestrial climates prevailed at least in this part of Asia during the Barremian-early Albian interval. Estimated mean air temperatures of about 10 ± 4 °C at midlatitudes (∼ 42 °N) correspond to present day cool temperate climatic conditions. Such low temperatures are in agreement with previous reports of cold marine temperatures during this part of the Early Cretaceous, as well as with the widespread occurrence of the temperate fossil wood genus Xenoxylon and the absence of thermophilic reptiles such as crocodilians in northeastern China. The unique character of the Jehol Biota is thus not only the result of its evolutionary and biogeographical history but is also due to rather cold local climatic conditions linked to the paleolatitudinal position of northeastern China and global icehouse climates that prevailed during this part of the Early Cretaceous.

Fig. 1.

Palaeogeographic map of eastern Asia in the Early Cretaceous modified from ref. . Number refers to the following horizons and localities: 1: Napai Fm., Guangxi, China, Aptian?; 2: Sao Khua Fm., Thailand, Barremian? (43); 3: Khok Kruat Fm., Thailand, Aptian (43); 4: Xinmingbao Fm., Gansu, China, Aptian-Albian (44); 5: Yixian Fm., Liaoning, China, Barremian-early Aptian (6); 6: Shahai and 7:Fuxin formations, Liaoning, China, Aptian-Albian (45); and 8: Kuwajima Fm., Japan, Barremian-early Aptian (46). Palaeolatitude of each locality was calculated using the Apparent Polar Wander Path (APWP) of refs. , . Abbreviations refer to major tectonic divisions: EUR, Europe; INC, Indo-China; IND, India; J, Japan; JUN, Junggar; K, Korea; KAZ, Kazakhstan; LH, Lhassa; MON, Mongolian; NCB, north China; QI, Qiangtang; SCB, south China; SH, Shan Thai; SIB, Siberian; and TAR, Tarim.

Fig. 2.

Latitudinal variations in δ values of dinosaurs, crocodilians, and turtles compared to expected latitudinal variations in δ values of present day endotherms and ectotherms drawn using δ and mean air temperature values of IAEA (International Atomic Energy Agency)/WMO (World Meteorological Organization) (27), and the following equations : δ-26.44 [endotherms; (15)] and T = 113.3 - 4.38∗ (δ) [ectotherms; (12)].

Fig. 3.

Calculated mean meteoric water δ gradient during the Early Cretaceous of eastern Asia vs. absolute latitudes. The Early Cretaceous thermal gradient was calculated using fossil vertebrate δ values and published equations (15). The present day continental temperature gradient for low altitude localities and the calculated Late Campanian—Middle Maastrichtian gradient are given for comparison.

Fig. 4.

Estimated mean annual temperatures during the Early Cretaceous of eastern Asia vs. absolute latitudes. The Early Cretaceous thermal gradient was calculated using fossil vertebrate δ values and published equations (15). The present day continental temperature gradient for low altitude localities and the calculated Late Campanian—Middle Maastrichtian gradient (15) are given for comparison.