Insights into the Skeletonization, Lifestyle, and Affinity of the Unusual Ediacaran Fossil Corumbella

The Ediacaran fossil Corumbella is important because it is hypothesized to be a scyphozoan\ud cnidarian, and thus might be one of the rare examples of bona fide Neoproterozoic nimals.\ud Unfortunately, its mode of life, style of skeletonization, and taxonomic affinity have been very controversial. Here, we use X-ray micro-CT, SEM, and taphonomic analysis to compare preservational modes of Corumbella, in order to better understand the symmetry, mode of construction, preservational style, and taxonomy of this group. Results suggest that articulated and disarticulated specimens of Corumbella from the Ediacaran of Brazil, Paraguay, and the United States, although sometimes preserved very differently, represent\ud the same taxon—Corumbella werneri. Corumbellids had a thick but flexible theca and probably lived with their basalmost part anchored in the sediment, much like Conotubus. When considered together, these results suggest that Corumbella was one of the first animals to build a skeleton, employing a lamellar microfabric similar to conulariids.FAPESP (Proc. 2009/02312-4)NAPAstrobio (PRP-USP)FAPESP (Proc. 2011/50242-5)CNPq (562143/ 2010-6, 458555/2013-4)CAPES.Astrobiology Laboratory (AstroLab, IAG-USP)LNNano/CNPEMNP-BioMa

Lithostratigraphic column for Corumbá Group and section for the upper part of Tamengo Formation (Neoproterozoic) at the Saladeiro quarry.

<p>Detail of the position where <i>Corumbella werneri</i> and other fossils occur. M—mud; S—sand. Modified from Warren <i>et al</i>., 2012, [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0114219#pone.0114219.ref017" target="_blank">17</a>]; and Morais, 2013, [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0114219#pone.0114219.ref049" target="_blank">49</a>].</p

Corumbella werneri: ultrastructure of theca.

<p>(A) GP1E-574a: three-dimensional specimen with theca. (B) 3D-rendered microCT of <i>Corumbella</i> theca,flipped by 180° compared to (A): interior view and detail for lamellae microfabric and plates (black arrow). (C) 3D-rendered microCT of <i>Corumbella</i> theca (A) without flipping in C1 and C2, with details of rings (white arrow). (D) compression and fragmentation along theca. D1 shows a transversal section in the fossil structure. Flipped by 180° of it produces D2, with details of small breakages (white arrow). (E) Details of lamellar plates by SEM (black arrow) and (F) pores in plates (black dashed arrow). Scale: 1mm.</p

Simplified map of South America (A) with detail of the geological map of the Paraguay Belt (B), and Corumbá Group (C) Modified from Oliveira, 2010, [48].

<p>Simplified map of South America (A) with detail of the geological map of the Paraguay Belt (B), and Corumbá Group (C) Modified from Oliveira, 2010, [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0114219#pone.0114219.ref048" target="_blank">48</a>].</p

Corumbella werneri: morphology and modes of life.

<p>(A) GP1E-4216: <i>Corumbella werneri</i> and (B) attachment region evidenced by (C) 3D-rendered microCT. (C1) shows a transverse-lateral section of (B). In (C1), it is possible to observe the conical morphology of the final attachment region, obliterated by the rock matrix in (B) (black arrow). (C2) is a detail of the attachment region in transversal section. (C3) is a lateral view of the final attachment region. (D) GP1E-4109: external mold of (E), GP1E-4210: internal mold with prismatic geometry and almost square in cross section. Note lateral edge (black arrow), midline (white arrow) and the alternate disposition of rings (black dashed arrow) across midline, on the face. (F) Zoom of specimen (E) to observe the “u” alternate disposition of rings across midline (white arrow), rings (black dashed arrow) and the continuity of rings on the lateral edges (black arrow). (G) and (H) MicroCT of (E). (G) Transversal section (black dashed line) showing a folded polyhedral tube in (H). Details of the rings (black dotted line), lateral edges (black dashed line) and open folded lateral edge (black line). Scale: 1mm. (A), (B) and (E): reprinted from Pacheco <i>et al</i>. (2011) [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0114219#pone.0114219.ref006" target="_blank">6</a>] under a CC BY license, with permission from Luis Alcalá, original copyright 2011.</p

Simplified model for the mechanical origin of the torsion observed on the Corumbella specimen from USA (LACMNH 12802), which is dependent of the physical conditions of the animal and/or of the external forces.

<p>Subfigures 2 to 1 correspond to different stages: black arrows show a reconstitution from helical twisting happening when a <i>Corumbella</i> tube becomes partially buried (stage 2) until a possibility of <i>Corumbella</i> life mode (stage 1). Gray arrows point details of twisting until stage 2. Gray circular arrows show possibilities of twisting degrees in tubes.</p

Corumbella werneri: ultrastructure of theca.

<p>(A) SEM of a longitudinal section of a <i>Corumbella</i> theca. Dashed circle marks a detail of a sectioned ring. (B) EDS mapping of (A). Here it is possible to observe higher concentration o calcium in fragments of theca (represented by white dots) in comparison to the rock matrix and molds of fossil without fragments. (C) and (D) are details of the white dashed circle in (A), showing micro layers in <i>Corumbella</i> theca (white arrow). Scale for B: 1mm.</p

Corumbella werneri, Wood Canyon (USA) and Tamengo Formation (Brazil). Morphology.

<p>(A) LACMNH 12802 (Wood Canyon Formation). Polyhedral specimen, covered with desert varnish. Observe rings (black dashed arrow) alternately converging on the midline (marked with an “X” in the draw), in continuity with the lateral edges. Detail of the helical twist (black arrow). (B) Draw representing (A) with detail of the rings (black dashed arrow); midline (marked with an “X” in the encounter of two rings in the face) and torsion (black arrow). (C) and (D) GP1E-5808b (Tamengo Formation). Note torsion in the two-dimensional tube (black arrow) (C) and detail of the helical twist represented in (D) (black dashed lines). (E) LACMIP loc. 17130 (Wood Canyon Formation). End section quadrangular pressed torsional in (A). Observe lateral edges (white curved arrow) and septa (black curved arrow). (F) LACMNH 12802. Quadrangular section untwisted end in (A). See lateral edge (white curved arrow) (G) LACMNH loc. 17130. Aboral region. Detail for lateral continuity of the rings (black dotted arrow). Scale: 1 mm.</p