Discovery of bilaterian-type through-guts in cloudinomorphs from the terminal Ediacaran Period.
James D Schiffbauer, Tara Selly, Sarah M Jacquet, Rachel A Merz, Lyle L Nelson, Michael A Strange, Yaoping Cai, Emily F Smith
Author Information
James D Schiffbauer: Department of Geological Sciences, University of Missouri, Columbia, MO, 65211, USA. schiffbauerj@missouri.edu. ORCID
Tara Selly: Department of Geological Sciences, University of Missouri, Columbia, MO, 65211, USA. sellyt@missouri.edu. ORCID
Sarah M Jacquet: Department of Geological Sciences, University of Missouri, Columbia, MO, 65211, USA. ORCID
Rachel A Merz: Biology Department, Swarthmore College, Swarthmore, PA, 19081, USA.
Lyle L Nelson: Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, MD, 21218, USA.
Michael A Strange: Department of Geoscience, University of Nevada, Las Vegas, Las Vegas, NV, 89154, USA.
Yaoping Cai: Shaanxi Key Laboratory of Early Life and Environment, State Key Laboratory of Continental Dynamics, and Department of Geology, Northwest University, Xi'an, 710069, China.
Emily F Smith: Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, MD, 21218, USA. ORCID
The fossil record of the terminal Ediacaran Period is typified by the iconic index fossil Cloudina and its relatives. These tube-dwellers are presumed to be primitive metazoans, but resolving their phylogenetic identity has remained a point of contention. The root of the problem is a lack of diagnostic features; that is, phylogenetic interpretations have largely centered on the only available source of information-their external tubes. Here, using tomographic analyses of fossils from the Wood Canyon Formation (Nevada, USA), we report evidence of recognizable soft tissues within their external tubes. Although alternative interpretations are plausible, these internal cylindrical structures may be most appropriately interpreted as digestive tracts, which would be, to date, the earliest-known occurrence of such features in the fossil record. If this interpretation is correct, their nature as one-way through-guts not only provides evidence for establishing these fossils as definitive bilaterians but also has implications for the long-debated phylogenetic position of the broader cloudinomorphs.
