Recent fieldwork has extended the distribution of the Daohugou Bed deposits from the Daohugou Village to its several neighboring areas. The fossil-bearing Daohugou deposits uncomformably overlie complex bedrocks, and com- prise three major parts. The red shales in the lower part were misidentified as belonging to the Tuchengzi Formation. Field excavation has indicated that the shales of upper part of the bed are the major fossil-bearing horizon. Due to strong tectonic activities, sediments were often folded with the se- quences inverted in the region. Some newly recognized con- tacts between the Daohugou Bed and the volcanic rocks showed that the ignimbrite of the Tiaojishan Formation (159―164 Ma) underlies the Daohugou deposits, rather than overlying the latter as previously proposed. Thus, the age of the Daohugou deposits should be younger than the age of the ignimbrite, and thus it was incorrect to correlate the Dao- hugou Bed with the Middle Jurassic Jiulongshan Formation. Although biostratigraphic studies based on conchostracans and insects support a Middle Jurassic-early Late Jurassic age for the Daohugou deposits, vertebrate fossils such as Liaoxitriton, Jeholopterus and feathered maniraptorans show much resemblance to those of the Yixian Formation. In other words, despite the absence of Lycoptera, a typical fish of the Jehol Biota, the Daohugou vertebrate assemblage is closer to that of the Early Cretaceous Jehol Biota than to any other biota. We propose that the Daohugou fossil assemblage probably represents the earliest evolutionary stage of the Jehol Biota based on both vertebrate biostratigraphy and the sedimentological and volcanic features which suggest the Daohugou deposit belongs to the same cycle of volcanism and sedimentation as the Yixian Formation of the Jehol Group.
WANG XiaolinZHOU ZhongheHE HuaiyuJIN FanWANG YuanqingZHANG JiangyongWANG YuanXU XingZHANG Fucheng
In the last twenty years,the extraordinary discoveries of vertebrate fossils from the Jehol Biota not only have important impli-cations for studying the evolution of major Mesozoic vertebrate groups,their paleobiostratigraphy and paleoenvironmentology,but also provide critical evidence for understanding the biodiversity changes of the Early Cretaceous ecosystem.Currently,the Jehol Biota in a narrow sense(i.e.,distribution limited to western Liaoning,northern Hebei,and southeastern Inner Mongolia) comprises a vertebrate assemblage of at least 121 genera and 142 species.Among them are 13 genera and 15 species of mammals,33 genera and 39 species of birds,30 genera and 35 species of dinosaurs,17 genera and species of pterosaurs,5 genera and species of squamates,5 genera and 7 species of choristoderes,2 genera and species of turtles,8 genera and species of am-phibians,7 genera and 13 species of fishes as well as 1 genus and species of agnathan.All these known 121 genera are extinct forms,and only a small percentage of them(e.g.,agnathans,some fishes and amphibians) can be referred to extant families.The Jehol vertebrate diversity already exceeds that of the contemporaneous lagersttten such as Santana Fauna from Brazil and the Las Hoyas Fauna from Spain,and is nearly as great as that of the Jurassic Solnhofen Fauna and the Eocene Messel Fauna from Germany.Therefore,The Jehol Biota undoubtedly represents a world class lagerst?tte in terms of both fossil preservation and vertebrate diversity.The success of the Jehol vertebrate diversity had a complex biological,geological,and paleoenviron-mental background.Analysis of the habitat and diet of various vertebrate groups also indicates that the habitat and dietary dif-ferentiation had played a key role in the success of the taxonomic diversity of vertebrates of various ranks.Furthermore,the interactions among vertebrates,plants,and invertebrates as well as the competitions among various vertebrate groups and some key morphological innovations also contributed to the success
