title: Critical appraisal of tubular putative eumetazoans from the Ediacaran Weng'an Doushantuo biota.
abstract: Molecular clock analyses estimate that crown-group animals began diversifying hundreds of millions of years before the start of the Cambrian period. However, the fossil record has not yielded unequivocal evidence for animals during this interval. Some of the most promising candidates for Precambrian animals occur in the Weng'an biota of South China, including a suite of tubular fossils assigned to Sinocyclocyclicus, Ramitubus, Crassitubus and Quadratitubus, that have been interpreted as soft-bodied eumetazoans comparable to tabulate corals. Here, we present new insights into the anatomy, original composition and phylogenetic affinities of these taxa based on data from synchrotron radiation X-ray tomographic microscopy, ptychographic nanotomography, scanning electron microscopy and electron probe microanalysis. The patterns of deformation observed suggest that the cross walls of Sinocyclocyclicus and Quadratitubus were more rigid than those of Ramitubus and Crassitubus. Ramitubus and Crassitubus specimens preserve enigmatic cellular clusters at terminal positions in the tubes. Specimens of Sinocyclocyclicus and Ramitubus have biological features that might be cellular tissue or subcellular structures filling the spaces between the cross walls. These observations are incompatible with a cnidarian interpretation, in which the spaces between cross walls are abandoned parts of the former living positions of the polyp. The affinity of the Weng'an tubular fossils may lie within the algae.
authors.affiliation: School of Earth Sciences, University of Bristol, Life Sciences Building, Tyndall Avenue, Bristol BS8 1TQ, UK Department of Palaeobiology and Nordic Center for Earth Evolution, Swedish Museum of Natural History, Stockholm 10405, Sweden john.cunningham@bristol.ac.uk.
authors.forename: John A
authors.initials: JA
authors.lastname: Cunningham
authors.affiliation: School of Earth Sciences, University of Bristol, Life Sciences Building, Tyndall Avenue, Bristol BS8 1TQ, UK.
authors.forename: Kelly
authors.initials: K
authors.lastname: Vargas
authors.affiliation: Institute of Geology, Chinese Academy of Geological Sciences, 26 Baiwanzhuang Road, Beijing 100037, People's Republic of China.
authors.forename: Liu
authors.initials: L
authors.lastname: Pengju
authors.affiliation: Department of Palaeobiology and Nordic Center for Earth Evolution, Swedish Museum of Natural History, Stockholm 10405, Sweden.
authors.forename: Veneta
authors.initials: V
authors.lastname: Belivanova
authors.affiliation: Swiss Light Source, Paul Scherrer Institute, Villigen 5232, Switzerland.
authors.forename: Federica
authors.initials: F
authors.lastname: Marone
authors.affiliation: School of Earth Sciences, University of Bristol, Life Sciences Building, Tyndall Avenue, Bristol BS8 1TQ, UK Department of Geology, University of Valencia, C/Dr. Moliner 50, Burjassot, Valencia 46100, Spain.
authors.forename: Carlos
authors.initials: C
authors.lastname: Martínez-Pérez
authors.affiliation: Swiss Light Source, Paul Scherrer Institute, Villigen 5232, Switzerland.
authors.forename: Manuel
authors.initials: M
authors.lastname: Guizar-Sicairos
authors.affiliation: Swiss Light Source, Paul Scherrer Institute, Villigen 5232, Switzerland.
authors.forename: Mirko
authors.initials: M
authors.lastname: Holler
authors.affiliation: Department of Palaeobiology and Nordic Center for Earth Evolution, Swedish Museum of Natural History, Stockholm 10405, Sweden.
authors.forename: Stefan
authors.initials: S
authors.lastname: Bengtson
authors.affiliation: School of Earth Sciences, University of Bristol, Life Sciences Building, Tyndall Avenue, Bristol BS8 1TQ, UK.
authors.forename: Philip C J
authors.initials: PC
authors.lastname: Donoghue
mesh_terms: D000818:Animals; D019521:Body Patterning; D002681:China; D000458:Cyanobacteria / Q000145:classification / Q000166:cytology / Q000254:growth & development / Q000648:ultrastructure; D056890:Eukaryota / Q000145:classification / Q000166:cytology / Q000254:growth & development / Q000648:ultrastructure; D005580:Fossils / Q000033:anatomy & histology* / Q000648:ultrastructure; D007448:Invertebrates / Q000033:anatomy & histology* / Q000145:classification / Q000254:growth & development / Q000648:ultrastructure
keywords: Doushantuo; Ediacaran; exceptional fossilization; tubular fossils