Carbonaceous macrofossils from the Ediacaran–Cambrian lower shale member of the Soltanieh formation, Northwestern Iran

Abstract

The Ediacaran–lower Cambrian Soltanieh Formation exposed in the Soltanieh Mountains of northwestern Iran is a mixed siliciclastic-carbonate succession that hosts skeletal animals, metazoan trace fossils, and macroalgal compressions, in addition to a well-resolved C isotopic record. Here we attempt to clarify the systematic paleontology of carbonaceous compression macrofossils found at the base of the Lower Shale Member of this formation, close to the Ediacaran–Cambrian boundary, and discuss their implications for our understanding of the early evolution of complex multicellular organisms. We identified five distinct morphological groups: (1) small discoidal fossils (chuarids), (2) branching thalli (Eoholynia corumbensis), (3) large discoidal fossils (Doulia rara), (4) simple ribbon-like compressions, and (5) chuarid-like discoidal structures with an attached filament. These fossils display limited diversity but include representatives of the three groups that dominate Ediacaran–Cambrian macrophyte diversity globally. All are present at the stratigraphic level in which Cambrian animals and trace fossils first appear, providing broader biological context for understanding early animal diversification.