Cretaceous terrestrial biotas of East Asia, with special reference to dinosaur-dominated ichnofaunas: towards a synthesis

This paper represents an “editorial” introduction to this issue, which is one of two special issues of Cretaceous Research on the geology and paleontology of East Asia. This paper makes special reference to the results of joint Japanese, Chinese, and North American expeditions that investigated more than 70 fossil footprint sites and other fossiliferous localities in China, Japan, Korea, Laos, Mongolia, and Thailand. More than 50 of the track sites are considered Cretaceous in age, though in some cases dating is uncertain. We herein present summaries of selected important sites not previously described in detail based on new maps, tracings, and replicas of representative type specimens and related materials that have been assembled in accessible reference collections. Other sites are described in detail elsewhere in this issue and are placed in broader paleoenvironmental context in conjunction with papers that deal with floras, invertebrate and vertebrate body fossils, paleoecosystem reconstruction, and their stratigraphic, sedimentological, and tectonic settings in the second of the two special issues.Preliminary syntheses suggest that Cretaceous vertebrate ichnofaunas of East Asia contain various distinctive elements that are neither typical nor common in other regions. These include an abundance and significant diversity of bird tracks, some with web impressions, various small theropod tracks including diminutive examples (Grallator and Minisauripus) with foot lengths of 2.0–3.0 cm, probable small dromeosaurid tracks (Velociraptorichnus), probable coelurosaurid tracks with bilobed heel impressions (Siampodus), and various small ornithopod tracks that resemble Anomoepus. Giant pterosaur tracks (Haenamichnus) are also unique to this area. A review of the ichnotaxonomy generously accepts about eleven valid ichnogenera of dinosaurs, two of pterosaurs, and nine of birds. At least ten other ichnogenera are dubious and among these several have already been rejected.A preliminary overview of these ichnotaxa in broader context suggests that the dominance of bird and theropod ichnotaxa is a valid reflection of a corresponding dominance of birds and theropod body-fossil taxa. We also note partitioning of ichnofaunas into saurischian-dominated assemblages from low, tropical latitudes and semi-arid, inland basin paleoenvironments, and ornithopod-rich assemblages from higher, more temperate latitudes and humid, coastal paleoenvironments.