A microbialite with its entombed benthic community from the Middle Triassic (Anisian-Ladinian) Muschelkalk Group of Germany

Exceptionally preserved non-biomineralised biota occurs within a single microbialite bed in the Muschelkalk Group of Germany. Although their internal structures are barely preserved, morphological features allow assignment to various groups of organisms. Many of the body fossils are preserved as limonitic aggregates within their traces and testify to intimate interaction with the microbial mat. The surface of the mat is scattered with Placozoa, which are reported from the fossil record for the first time. Xenacoelomorpha (Acoela) and Platyhelminthes mainly occur at the termination of their burrows and are accompanied by rare Nematoda. Most of these softbodied invertebrates are Annelida, with representatives of different taxa of Polychaeta preserved within their burrows. The organisms and their traces are systematically described and interpreted, resulting in three new genera and species (Maculicorpus microbialis gen. et sp. nov., Gutticorpus concentrica gen. et sp. nov. and Palaeoscoloplos triassicus gen. et sp. nov.), two new ichnogenera and five new ichnospecies (Foveichnus lobatus igen. et isp. nov., F. canaliculatus igen. et isp. nov., Platyichnus lineatus igen. et isp. nov., Protovirgularia bifurcata isp. nov., and Kimberichnus digitatus isp. nov.). The preservation of this biota is closely related to the development of the microbial mat and interaction with it, which favoured the in-situ entombment of organisms under the development of local dysoxia and anoxia. Rapid burial (obrution), probably by storm deposition, contributed to their preservation. This Fossillagerstätte provides a unique insight into the ecology of a Middle Triassic microbial mat on a mud flat before the onset of the Mesozoic Marine Revolution.