Fig 1.
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].
Fig 2.
Lithostratigraphic column for Corumbá Group and section for the upper part of Tamengo Formation (Neoproterozoic) at the Saladeiro quarry.
Detail of the position where Corumbella werneri and other fossils occur. M—mud; S—sand. Modified from Warren et al., 2012, [17]; and Morais, 2013, [49].
Fig 3.
Models for Corumbella werneri.
(A) Reconstruction of Corumbella werneri proposed by Hahn et al. (1982) [4], showing a stalk and polypars (modified by Wilson Soares Jr). (B) Reconstruction of Corumbella werneri as a colonial sessile organism, as interpreted by Babcock et al. (2005) [5] (modified by Abner Santos). Detail of the square symmetry. (C) Reconstruction of Corumbella werneri proposed by Pacheco et al. (2011) [6] and improved in this work (draw by Abner Santos). (D) Detail of the oral region, lateral edges, faces, septa and midline. (E) Aboral region with unisseriated rings on the attachment portion.
Fig 4.
Corumbella werneri, Wood Canyon (USA) and Tamengo Formation (Brazil). Morphology.
(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.
Fig 5.
Corumbella werneri: morphology and modes of life.
(A) GP1E-4216: Corumbella werneri 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 et al. (2011) [6] under a CC BY license, with permission from Luis Alcalá, original copyright 2011.
Fig 6.
Corumbella werneri: ultrastructure of theca.
(A) GP1E-574a: three-dimensional specimen with theca. (B) 3D-rendered microCT of Corumbella theca,flipped by 180° compared to (A): interior view and detail for lamellae microfabric and plates (black arrow). (C) 3D-rendered microCT of Corumbella 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.
Fig 7.
Corumbella werneri: ultrastructure of theca.
(A) SEM of a longitudinal section of a Corumbella 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 Corumbella theca (white arrow). Scale for B: 1mm.
Fig 8.
Corumbella werneri: morphology and modes of life.
(A) GP1E-4089: oral region. (B) GP1E-4077: Inflated tube. Detail of a face with septum (white arrow), midline (black dashed arrow), rings (black dotted arrow) and lateral edge (black arrow) relatively compressed. (C) DGM-5601-I: specimen used in the original description by Hahn et al. (1982). Internal mold, recurved. It is observed the aboral region, uniseriate, without evidente midline in the (incomplete) attachment region. These rings (black dotted arrow) grade to an approximately polyhedral portion, with midline (on the face) (black dashed arrow) and lateral edge (black arrow). Notice a break in the longitudinal mid-distal portion of the fossil. (D) GP1E-4204: tube with longitudinal breakage, where it is evident the septum (white arrow), lateral edge (black arrow) and rings (black dotted arrow). (E) GP1E-3093: internal portion of folded tube, thick exoskeleton, where it is possible to see the septum (white arrow) formed by the inner part of the alternate rings (black dashed arrow). (F) DGM-5606-I: internal mold, three-dimensional, with midline (black dashed arrow), rings (black dotted arrow) and fragments of theca on the lateral edge (black arrow). Scale: 1mm. (A), (B), (C) and (D): reprinted from Pacheco et al. (2011) [6] under a CC BY license, with permission from Luis Alcalá, original copyright 2011.
Fig 9.
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.
Subfigures 2 to 1 correspond to different stages: black arrows show a reconstitution from helical twisting happening when a Corumbella tube becomes partially buried (stage 2) until a possibility of Corumbella life mode (stage 1). Gray arrows point details of twisting until stage 2. Gray circular arrows show possibilities of twisting degrees in tubes.
Table 1.
Revision of morphological terminology and taxonomic affinities of Corumbella werneri.