DOUSHANTUO-TYPE MICROFOSSILS IN EARLIEST CAMBRIAN ROCKS OF MONGOLIA

Doushantuo-Pertatataka-type acanthomorphic acritarchs and embryo-like microfossils are found globally in early Ediacaran rocks. Phosphorites within the Kheseen Formation, northern Mongolia, have previously been reported to contain a Doushantuo-Pertatataka-type dominated microfossil assemblage that is earliest Cambrian in age. The Kheseen Biota is, therefore, one of the youngest Doushantuo-Pertatataka-type assemblages described. Here we report an expanded Kheseen Biota that includes the newly identified taxa Appendisphaera grandis, A. tenuis, Asterocapsoides wenganensis, Knollisphaeridium maximum and Mengeosphaera reticulata, alongside potential new species of Appendisphaera, Sinosphaera and Variomargosphaeridium. The phosphorites also preserve further species of the embryo-like taxon Megasphaera. The biota shows that many Doushantuo-Pertatataka-type taxa did not go extinct in the late Ediacaran, and extends the temporal range of several species by tens of millions of years. Notably, several taxa in the Kheseen Biota are shared with the iconic phosphatized Weng’an assemblage. Given that the evolution of animals had occurred by the Cambrian, the absence of definitive animals in the Kheseen Biota indicates that animal fossils may be excluded from such deposits for reasons other than their non-evolution (e.g., ecology, taphonomy). Given the taxonomic and taphonomic similarities between Kheseen and Weng’an, our work thus questions the use of Weng’an as a maximum age calibration for crown animals.