The Fezouata Biota: An exceptional window on the Cambro-Ordovician faunal transition

Abstract

Fossil-Lagerstättenwere initially defined as 'bodies of rock unusually rich in palaeontological information' (Seilacher et al., 1985). In the case of the Konservat-Fossil-Lagerstätten (simplified as Lagerstätten thereafter; singular, Lagerstätte), this palaeontological significance resides in the quality of preservation, such deposits yielding remains of entirely soft-bodied organisms. As first pointed out by Allison and Briggs (1993), the Cambrian is unusually rich in Lagerstätten compared to other periods of the Palaeozoic Era. This is particularly fortunate, for these remarkable strata provide unparalleled insights into one of the most critical events of the history of life: the Cambrian Explosion. Virtually every palaeontologist, most geologists, and a significant part of the scientific community, but also many people simply having an interest in natural sciences have heard of the Burgess Shale in the Canadian Rocky Mountains or Chengjiang in South China. Over the last three decades, however, numerous other localities yielding Early Palaeozoic soft-bodied assemblages have been discovered around the world. All are from lower to middle Cambrian rocks, except for a few notable exceptions (e.g.; Briggs et al., 1991, 2015; Aldridge et al., 2001; Lerosey-Aubril et al., 2014), and none really compete with Chengjiang or the Burgess Shale in terms of diversity and abundance (Gaines, 2014). However, with a fauna comprising more than 160 genera - half of them representing soft-bodied organisms (Van Roy et al., 2015a) - the Lower Ordovician Fezouata Shale (undifferentiated Lower and Upper Fezouata formations) of Morocco might well join in a near future these two illustrious localities in the pantheon of Early Palaeozoic Lagerstätten.