Shuhai Xiao, Virginia Polytechnic Institute and State University (United States)
Lin Dong, Virginia Polytechnic Institute and State University (United States)
Bing Shen, Virginia Polytechnic Institute and State University (United States)
Chuanming Zhou, Nanjing Institute of Geology and Palaeontology (China)
Xiaoying Shi, Chinna University of Geosciences (Beijing) (China)
Ganqing Jiang, University of Nevada (United States)
Although the phylogenetic affinities of Horodyskia and Palaeopascichnus are controversial, both genera are characterized by uniserial arrangement of spheroidal or discoidal units. Horodyskia and Palaeopascichnus have previously been known from Mesoproterozoic and Ediacaran rocks, respectively. But our recent studies show that both genera are present in Ediacaran successions in North and South China, they occur in different facies, and they can be preserved as compressed casts in siliciclastic rocks and as three-dimensionally permineralized fossils in early diagenetic cherts. Our continuing work further demonstrates that these two genera are widely distributed in the upper Ediacaran Liuchapo Formation in eastern Guizhou and northern Hunan of South China. The permineralized specimens reveal additional morphological details that are not typically preserved in siliciclastic rocks.
These morphological details, including filaments that connect adjacent units as well as quartz halo surrounding the spheroidal or discoidal units, invite a comparison with agglutinated foraminifers: the units can be compared with cytoplasm-filled chambers, connecting filament with small passage between chambers, and quartz halos with agglutinated tests. The new occurrences of Horodyskia and Palaeopascichnus provide new information about their phylogenetic affinities, evolutionary history, and biostratigraphic significance.