The Guiyang biota is an exceptionally preserved Early Triassic (approximately 250.8 million years ago) fossil assemblage from the Daye Formation near Guiyang (China), discovered between 2015 and 2019 and first reported in 2023. It is the oldest known Mesozoic lagerstätte, and it provides evidence of the existence of a complex marine ecosystem shortly after the Permian–Triassic extinction event. Palaeogeography The Guiyang biota comes from the northern margin of the Nanpanjang Basin, that was a Triassic equatorial foreland basin on the eastern side of the Tethys Ocean. Age The Guiyang biota belongs to the late Dienerian, a subsection of the Induan period of early Triassic.The biostratigraphy evidenced by the Radioceras ammonoids and the Neospathodus cristagalli and Neospathodus dieneri conodonts is consistent with the Dienerian, and U-Pb zircon dating confirms the strata span about 110,000 years, between 250.83 and 250.72 millions of years ago, 1.08 millions of years after the Permian extinction. Species The biota is rich in bony fishes. Teeth of chondrichthyes are also present. Two coelacanth species, ranging between 50 and 100 cm, are the largest animals so far identified; the presence of these relatively large predators suggests the ecosystem was fully functional. Actinopterygii are represented by ten species in six orders: Palaeonisciformes,Ptycholepiformes, Acipenseriformes, Perleidiformes, Polzbergiiformes and Parasemionotiformes. Most Guiyang fossils are crustaceans. Decapoda are represented, among others, by two of the oldest shrimps ever found: one a species of the genus Anisaeger and the other an undetermined member of Aegeridae. A lobster was also present. Other crustaceans are ostracods and Cyclida, one of the latter similar but not identical to Yunnanocyclus nodosus. Among molluscs, two ammonoids have been reported, Pseudosageceras and Radioceras. References Lagerstätten Triassic life