UNIQUE PALEOARCTIC VERTEBRATE ASSEMBLAGES FROM LATE TRIASSIC AND EARLY JURASSIC LACUSTRINE STRATA OF THE JUNGGAR BASIN (NW CHINA)

The Junggar Basin in Xinjiang is famous for its Late Jurassic tetrapods, particularly dinosaurs. However, until very recently Late Triassic and Early Jurassic strata have produced little in the way of vertebrates save two dinosaur footprints (1) (Badaowan Fm, E. Jurassic), and, more recently, the chondrostean fish Saurichthys from Late Triassic strata (2). Recently (3), we very briefly outlined some new vertebrate assemblages from Junggar Late Triassic and Early Jurassic great lake sequences, focusing on the empirical evidence for seasonal freezing (lake-ice-rafted-debris) and the underappreciated Arctic paleolatitude of this coal-bearing area (3). Collected during NIGPAS-led stratigraphic studies in the 2015-2017 field seasons, the new assemblages include: 1) large sculptured palaeonisciform cranial elements, small associated palaeonisciforms, possible sauropterygian teeth, large-dinosaur dinoturbation, and additional as yet unidentified small vertebrate bones from the Haojiagou Fm (?late Norian-Rhaetian); 2) medium-sized brontozoid dinosaur footprints from the Badaowan Fm (Hettangian-?Sinemurian)]; and 3) the hybodont shark egg case Palaeoxyris [the second from the Early Jurassic of China (4)], numerous associated and fragmentary small palaeonisciform fish elements including one articulated skull and several small skeletons, and various dinosaur footprints and dinoturbation from the Sangonghe Fm (?Sinemurian-Toarcian). A possible ash associated with the aforementioned lower Sangonghe fish skull has produced a LA-ICP-MS age of roughly 193 Ma, consistent with a Sinemurian age (5). These are the only continental paleoarctic vertebrate assemblages known [the only other contender being Arctosaurus from Nunavut, Artic Canada (6), at 40°-50°N during the Triassic]. We are optimistic that there will be many additional discoveries in Early Mesozoic strata of the Junggar basin, the importance of which cannot be overemphasized.

1. Xing et al (2014) Vert. PalAsia. 52:40–348; 2. Fang & Wu (2022) Hist. Bio.:1-11; 3. Olsen et al (2022) Sci. Advances 8:eabo6342; 4. Fu (2018) 12^th Nat. Cong. Chinese. Soc. Paleont. & 29^th Ann. Acad. Conf.; 5. Lampert et al (2020) AGU Fall Mtg. Abst. T009-0013; 6. Sues (2017) Can. Jour. Earth Sci. 54:129-133.