DOI: 10.5061/dryad.cg747g1
title: Data from: Periodic shell decollation as an ecology-driven strategy in the early Cambrian Cupitheca

description: Shell decollation is a growth strategy that has been adopted by a number
 of invertebrate taxa to offset the metabolic and ecological disadvantages
 of shell growth. However, little is known about the origin and evolution
 of this process. We here describe well-preserved specimens of the hyolith,
 Cupitheca decollata sp. nov., preserving the decollation process from the
 early Cambrian Yu’anshan Formation (ca. 518 million years ago) of South
 China. Based on a large number of specimens collectively representing
 different developmental stages, we use high-resolution X-ray
 microtomography and scanning electronic microscopy to reconstruct the
 process of decollation in this taxon. Cupitheca is among the earliest
 known small shelly fossils, and thus our discovery confirmed that periodic
 decollation had evolved by the onset of the Cambrian explosion, reflecting
 the high intensity of the predator-prey arms race in early Cambrian
 ecosystems. A comparison between the decollation processes of Cupitheca
 and other shelly invertebrates suggests that periodic decollation and the
 associated molecular mechanisms of calcium dissolution, uptake,
 allocation, and deposition may have had multiple independent origins.Shell
 decollation is a growth strategy that has been adopted by a number of
 invertebrate taxa to offset the metabolic and ecological disadvantages of
 shell growth. However, little is known about the origin and evolution of
 this process. We here describe well-preserved specimens of the hyolith,
 Cupitheca decollata sp. nov., preserving the decollation process from the
 early Cambrian Yu’anshan Formation (ca. 518 million years ago) of South
 China. Based on a large number of specimens collectively representing
 different developmental stages, we use high-resolution X-ray
 microtomography and scanning electronic microscopy to reconstruct the
 process of decollation in this taxon. Cupitheca is among the earliest
 known small shelly fossils, and thus our discovery confirmed that periodic
 decollation had evolved by the onset of the Cambrian explosion, reflecting
 the high intensity of the predator-prey arms race in early Cambrian
 ecosystems. A comparison between the decollation processes of Cupitheca
 and other shelly invertebrates suggests that periodic decollation and the
 associated molecular mechanisms of calcium dissolution, uptake,
 allocation, and deposition may have had multiple independent origins.
description: FIG. S1. Locality and
 stratigraphy of Changqing section in Huize County, Yunnan Province,
 China.A, location of Yunnan
 Province in China. B, position of Changqing section in Huize County. C,
 stratigraphic column in Changqing section. Abbreviations: SYT, Shiyantou
 Formation; HJS, Hongjingshao Formation.Figure
 S1-166.tifFIG. S2. Morphology and
 decollation structures of Cupitheca decollata sp. nov.A, NIGPAS-HC-018, larval
 shell with a circle of penetrating channels, detail of box shown in G. G,
 enlargement of the penetrating channels, secondarily eroded as a groove.
 B, NIGPAS-HC-019, tubular shell with a belt-like structure, box indicates
 the position of H. H, detail of the belt-like structure along the circle
 of penetrating channels. C, NIGPAS-HC-020, aperturally broken shell with a
 ring, detail of box shown in I. I, enlargement of the ring. D, E,
 NIGPAS-HC-021, 022, tubular shells with rings and micropillar structures,
 boxes indicate the positions of J and L, respectively. J, enlargement of
 the ring and poorly developed micropillars, detail of box shown in K. L,
 enlargement of the ring and the micropillar structure, detail of the
 micropillar structure shown in M. F, NIGPAS-HC-023, apically broken shell
 with a ring and micropillar structure, detail of box shown in N. N,
 enlargement of the deformed ring and micropillar structure, detail of box
 shown in O. K, M, O, vertical micropillars. Scale bars represent: 100 μm
 (A); 200 μm (B-F); 10 μm (G, K, M); 60 μm (H, L); 50 μm (I); 20 μm (J); 40
 μm (N); 12 μm (O).figure
 S2-166.tifFIG. S3. The ring and
 the micropillar structure of Cupitheca decollata sp.
 nov.A, B, NIGPAS-HC-006,
 007, incomplete tubular shells with rings and micropillar structures. C,
 NIGPAS-HC-008, broken tubular shell with a ring. Scale bars represent 200
 μm.figure
 S3-166.tifTable S1. Original
 measurement data.DF-DA, measurements of
 diameter of flange and diameter of aperture. DF-HN, data of diameter of
 flange and height of neck. DR-LDS, data of diameter of ring and length of
 decollated shell. DR-WR, measurements of diameter of ring and width of
 ring.Table
 S1.xlsimage
 stacks-NIGPAS-HC-006The specimen with a ring
 and micropillars on the shell surface was scanned using a
 three-dimensional X-ray microscope, Zeiss Xradia 520 Versa at the Micro-CT
 Lab of Nanjing Institute of Geology and Palaeontology, Chinese Academy of
 Sciences (NIGPAS). The operating voltage of the X-ray source was 60 kV. To
 obtain high resolution, a CCD (charge-coupled device)–based optical
 objectives with 4× was applied in the scan, and voxel size is 1.3455 μm.
 Thin filter LE1 was used to avoid beam hardening artefact. For this scan,
 3201 projections in total were obtained over 360 degrees, and the exposure
 time for each projection was 1.8 s. The volume data were processed using
 VGSTUDIO MAX (3.0 version) software.image
 stacks-NIGPAS-HC-007The specimen with a ring
 and micropillars on the shell surface was scanned using a
 three-dimensional X-ray microscope, Zeiss Xradia 520 Versa at the Micro-CT
 Lab of Nanjing Institute of Geology and Palaeontology, Chinese Academy of
 Sciences (NIGPAS). The operating voltage of the X-ray source was 60 kV. To
 obtain high resolution, a CCD (charge-coupled device)–based optical
 objectives with 4× was applied in the scan, and voxel size is 0.9086 μm.
 Thin filter LE1 was used to avoid beam hardening artefact. For this scan,
 3601 projections in total were obtained over 360 degrees, and the exposure
 time for each projection was 5.5 s. The volume data were processed using
 VGSTUDIO MAX (3.0 version) software.image
 stacks-NIGPAS-HC-008The specimen with a ring
 on the shell surface was scanned using a three-dimensional X-ray
 microscope, Zeiss Xradia 520 Versa at the Micro-CT Lab of Nanjing
 Institute of Geology and Palaeontology, Chinese Academy of Sciences
 (NIGPAS). The operating voltage of the X-ray source was 65 kV. To obtain
 high resolution, a CCD (charge-coupled device)–based optical objectives
 with 4× was applied in the scan, and voxel size is 1.1076 μm. Thin filter
 LE2 was used to avoid beam hardening artefact. For this scan, 3201
 projections in total were obtained over 360 degrees, and the exposure time
 for each projection was 3 s. The volume data were processed using VGSTUDIO
 MAX (3.0 version) software.3D reconstruction
 model3D reconstruction models
 of specimens NIGPAS-HC-006, NIGPAS-HC-007 and NIGPAS-HC-008. The volume
 data were processed using VGSTUDIO MAX (3.0 version)
 software.