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Chancelloriids of the Cambrian Burgess Shale

Stefan Bengtson and Desmond Collins

Plain Language Abstract

The Burgess Shale in the Canadian Rocky Mountains was discovered by Charles Doolittle Walcott in 1909. The shale features a diverse fossil biota, about 505 million years old, with soft tissues of animals and algae preserved in delicate detail. The Burgess Shale has become the iconic, if no longer unique, window onto the "Cambrian explosion," the evolutionary event that produced the profusion of multicellular life characterizing the modern type of biosphere.

Among the most enigmatic of the Burgess Shale animals are the cactus-like chancelloriids. These have sessile, bag-shaped bodies covered in aggregates of hollow, calcareous spines. Walcott interpreted them as sponges with a spicular skeleton, but subsequent work showed that chancelloriid spines are dermal sclerites of an external skeleton, quite different from sponge spicules. Instead, the chancelloriid sclerites show a number of similarities to spine- and scale-shaped sclerites of bilaterally symmetrical animals that are also found in the Cambrian biota.

In this article we investigate old and new collections of chancelloriids from the Burgess Shale. There are three species present, Chancelloria eros, Allonnia tintinopsis, and Archiasterella coriacea. Chancelloriids were anchored to shells or lumps of debris in the muddy bottom, or to sponges, or to other chancelloriids. They had a radially symmetrical body and central mouth-like opening surrounded by a palisade of modified sclerites. There is no evidence of minute body openings, as in sponges, or internal organs, such as a gut. The body seems to have been able to contract from the attached end to expel waste material through the central opening.

Resumen en Español

Chancelóridos del Cámbrico de Burgess Shale

Se revisan los chancelóridos con forma de cactus del Cámbrico Medio de Burgess Shale a partir de las colecciones originales de Walcott (1920) y de nuevos materiales que contienen varios cientos de especímenes recolectados por las expediciones del Royal Ontario Museum, de 1975 a 2000. La interpretación de Walcott de los chancelóridos como esponjas se basaba en la interpretación errónea de los coeloscleritos dérmicos como espículas embebidas del tipo presente en las esponjas, una interpretación que condujo además a la aglutinación de tres taxones distintos en una sola especie, Chancelloria eros Walcott, 1920. Aquí se separan de C. eros los otros dos taxones y se describen como Allonnia tintinopsis n. sp. y Archiasterella coriacea n. sp., todos ellos pertenecientes a la familia Chancelloriidae Walcott, 1920. Los chancelóridos eran animales sedentarios, anclados a conchas o trozos de restos en el fondo fangoso, o a esponjas, o a otros chancelóridos. Tenían un cuerpo con simetría radial y un orificio apical rodeado por una empalizada de escleritos modificados. Los tegumentos bien conservados en Al. tintinopsis y Ar. coriacea no muestran ninguna apertura tipo ostium. Tampoco hay evidencia de órganos internos, como un tubo digestivo. Los especímenes parcialmente estrechados sugieren que el cuerpo se contrajo periódicamente desde el extremo de fijación para expulsar material de desecho de la cavidad corporal. Los chancelóridos eran cercanos a los cnidarios en cuanto a su organización, pero compartían el carácter de poseer coeloscleritos con los bilaterales halkiéridos y sifogonuquítidos. Lo más probable es que el taxón Coeloscleritophora sea parafilético.

Palabras clave: Cámbrico; Burgess Shale; Chancelloriida; Coeloscleritophora; Metazoa; nuevas especies

Traducción: Enrique Peñalver

Résumé en Français

Les chancelloriides des schistes de Burgess du Cambrien

Les chancelloriides ressemblant à des cactus provenant des schistes de Burgess du Cambrien moyen sont révisées en utilisant comme base les collections originales de Walcott (1920) et de nouveaux matériaux contenant plusieurs centaines de spécimens collectés par des expéditions sur le terrain par le Musée Royal de l'Ontario entre 1975 et 2000. L'interprétation de Walcott que les chancelloriides étaient des éponges était fondée sur une interprétation erronée que les coelosclérites dermiques étaient des spicules intégrés de type éponge, une interprétation qui en outre conduit au regroupement de trois taxons distincts dans une espèce, Chancelloria eros Walcott, 1920. Les deux autres taxons sont ici séparés de C. eros et décrit sous le nom d'Allonnia tintinopsis n.sp. et d'Archiasterella coriacea n.sp., appartenant toutes à la famille Chancelloriidae Walcott, 1920. Les chancelloriides étaient des animaux sédentaires, ancrés à des coquilles ou des morceaux de débris dans de fond boueux, ou des éponges, ou à d'autres chancelloriides. Ils avaient un corps à symétrie radiale et un orifice apical entouré d'une palissade de sclérites modifiés. Les téguments bien conservés chez Al. tintinopsis et Ar. coriacea ne montrent pas les ouvertures d'ostium. Et il n'y a aucune preuve d'organes internes, comme un intestin. Des spécimens partiellement rétrécies suggèrent que le corps se contractait périodiquement à partir de l'extrémité attachée pour expulser les déchets de la cavité du corps. Les chancelloriides étaient proches dans leur organisation des cnidaires, mais partageaient le caractère de coelosclérites avec les bilatériens halkieriides et siphogonuchitides. Le taxon Coeloscleritophora est probablement paraphylétique.

Mots-clés: Cambrien; Schistes de Burgess; Chancelloriida; Coeloscleritophora; métazoaires; nouvelles espèces

Translator: Kenny J. Travouillon

Deutsche Zusammenfassung

Chancelloriiden aus dem kambrischen Burgess Shale

Die Kaktus-artigen Chancelloriiden aus dem mittelkambrischen Burgess Shale werden auf der Basis von Walcotts (1920) Originalsammlungen und neuem Material aus Feldexkursionen (von 1975 bis 2000) des Royal Ontario Museums, das mehrere hundert Stücke umfasst, revidiert. Walcotts Interpretation von Chancelloriiden als Schwämme basierte auf einer Fehlinterpretation der dermalen Coelosclerite als eingebettete Schwamm-typische Spiculae, eine Interpretation die überdies zur Zusammenfassung von drei deutlich abgegrenzten Taxa in eine Art führte, Chancelloria eros Walcott, 1920. Die anderen beiden Taxa werden hier von C. eros separiert und als Allonnia tintinopsis n.sp. und Archiasterella coriacea n.sp. beschrieben, alle zugehörig zur Familie Chancelloriidae Walcott, 1920. Chancelloriiden waren sesshafte Tiere, die auf Schalen oder Geröllklumpen des schlammigen Bodens verankert waren, oder auf Schwämmen oder andern Chancelloriiden. Sie hatten einen radialsymmetrischen Körper und eine apikale Öffnung, die mit einer Palisade von modifizierten Scleriten umgeben war. Gut erhaltene Integumente bei Al. tintinopsis und Ar. coriacea zeigen keine Ostium-artigen Öffnungen. Ebenso gibt es keinen Hinweis auf interne Organe, wie beispielsweise einen Darm. Teilweise verengte Stücke deuten darauf hin, dass sich der Körper periodisch vom angewachsenen Ende aus zusammenzog um Abfallstoffe aus der Körperhöhle auszustoßen. Chancelloriiden waren in ihrer Organisation den Cnidaria ähnlich, teilten jedoch das Merkmal Coelosclerite mit den bilateralen Halkieriiden und Siphogonuchitiden. Das Taxon ist höchstwahrscheinlich paraphyletisch.

Schlüsselwörter: Kambrium; Burgess Shale; Chancelloriida; Coeloscleritophora; Metazoa; neue Art

Translator: Eva Gebauer

Arabic

498 arab

Translator: Ashraf M.T. Elewa

 

 

FIGURE 1.  Chancelloria eros Walcott, 1920, lectotype, USNM 66524. Figured by Walcott (1920) as pls 86:2 and 88:1f. 1. Wet. 2. Dry, coated with ammonium chloride. Detail of 1 (position marked by frame). 3. Dry, coated with ammonium chloride. Detail of 2 (position marked by frame). Top arrow (grey): 4+0 sclerite. Middle arrow (black): 7+1 sclerite, preserved in negative relief (ascending ray towards the viewer). Bottom arrow (white): 7+1 sclerite, preserved in positive relief (ascending ray pointing away from the viewer).

figure 1 

 

FIGURE 2. Allonnia tintinopsis n.sp., USNM 66526 (specimen figured as Chancelloria eros by Walcott, 1920, pl. 88:1, 1a, and by Briggs et al., 1994, figure 176). 1. Wet. 2, 3. Details of 1 (positions marked by frames), dry.

figure 2

 

FIGURE 3. Allonnia tintinopsis n.sp., USNM 66528, upper part of body (specimen figured as Chancelloria eros by Walcott, 1920, pl. 88:1d, 1e). 1. Wet. 2. Detail of 1 (position marked by frame), wet. 3. Detail of 2 (position marked by frame), wet. figure 3

 

FIGURE 4. Archiasterella coriacea n.sp. USNM 66527 (specimen figured as Chancelloria eros by Walcott,1920, pl. 88:1c, and de Laubenfels, 1955, figure 76). 1. Dry. 2. Detail of 1 (position marked by frame), dry.

figure 4

 

FIGURE 5. Chancelloria eros Walcott, 1920. 1. ROM 62538, ST talus, wet. Arrow points to empty area that may represent an apical orifice. 2. Detail of 1 (position marked by frame), wet. 3. ROM 62535A, BW -300, dry.

figure 5

 

FIGURE 6. Chancelloria eros Walcott, 1920. ROM 62539, BW -320. 1. Dry. 2. Detail of 1 (position marked by frame), wet. figure 6

 

FIGURE 7. Chancelloria eros Walcott, 1920. ROM 62588B, BW -320. 1. Dry. 2. Detail of 1 (position marked by frame), dry. 3. Detail of 1 (position marked by frame), wet.

figure 7

 

FIGURE 8. Chancelloria eros Walcott, 1920. 1, 2. ROM 49580, ST. 1. Dry. 2. Detail of 1 (position marked by frame), dry. 3. ROM 62590, ST, dry. figure 8

 

FIGURE 9. Chancelloria eros Walcott, 1920. 1 - 3. ROM 57604, BW -130. Specimens of the lingulate brachiopod Acrothyra gregaria appear to be attached to the spines of the Chancelloria. The brachiopods are concentrated to what is interpreted as the apical part of the chancelloriid body. 1. Wet. 2. Detail of 1 (position marked by frame), dry. 3. Detail of 2 (position marked by frame), dry. 4. ROM 63055, ST, dry. figure 9

 

FIGURE 10. Chancelloria eros Walcott, 1920. ROM 62534, RT. 1. Wet. 2. Detail of 1 (position marked by frame), wet. Note the common presence of 3+0 Allonnia -type sclerites (arrows) in a scleritome dominated by 5–7+1 Chancelloria-type sclerites. figure 10

 

FIGURE 11. Chancelloria eros Walcott, 1920. ROM 49599A, RQ 8.0. Arrows point to examples of 3+0 sclerites. 1. Dry. 2. Detail of 1 (position marked by frame), dry. figure 11

 

FIGURE 12. Allonnia tintinopsis n.sp. intergrown with or superimposed on Chancelloria eros Walcott, 1920. 1 - 3. ROM 49605(2) (intergrown with a specimen of Vauxia), RQ 9.2. 1. Same as figure 12B in Bengtson, 2000; see that paper for details on settings. 2, 3. Details of 1 (positions marked by frames), dry. 4 - 6. ROM 62537B, RQ 8.4. 4. Wet. 5, 6. Details of 4 (positions marked by frames), dry. Net-like patches are fragments of Micromitra shells. figure 12

 

FIGURE 13. Chancelloria eros Walcott, 1920. 1. ROM 49578, ST, dry. 2. ROM 43126, ST, dry.

figure 13

 

FIGURE 14. Chancelloria eros Walcott, 1920 (1, 2), and C. cf. eros (3-5), ST. 1. ROM 49574, dry. 2. ROM 49572, dry. 3 - 5. ROM 49576, dry. Items 4 and 5 show details of the upper and lower portions, respectively, of 3.

figure 14

 

FIGURE 15. Life reconstruction of Chancelloria eros, Walcott, 1920. Artwork Pollyanna von Knorring.

 figure 15

FIGURE 16. Allonnia tintinopsis n.sp., ROM 62527, part (1, 2) and counterpart (3), BW -110. 1. The larger specimen to the right in 1 is the holotype (ROM 62527[1]). 2. Holotype, detail of apical part (position marked in 1), with tuft. 3. Detail of lower part of body of holotype (counterpart; position on part marked in 1), showing morphology and arrangement of sclerites. Small letters at mid right denote lateral (L) and ascending (A) rays of selected sclerites. All pictures taken wet. figure 16

 

FIGURE 17. Allonnia tintinopsis n.sp. Apical tufts and concentration gradient of pyrite. 1. ROM 62524A (also in Figure 21.1), RQ 8.7, wet. 2. ROM 62516B, RQ 8.8, wet. 3. ROM 62519B, RQ 8.2, wet. 4. ROM 62586, wet. 5. ROM 62517, RQ 8.8, wet. figure 17

 

FIGURE 18. Ray length against distance from base in Allonnia tintinopsis n.sp. ROM 49610A, RQ 11.4 (left; white squares) and ROM 49607A, RQ 10.7 (right; black circles). figure 18

 

FIGURE 19. Allonnia tintinopsis n.sp. with stalk-like constriction. ROM 49573, ST. 1. Complete specimen, dry. 2. Detail of 1 (position marked by frame), dry, showing lower part of stalk with densely packed sclerites and debris.

figure 19

 

FIGURE 20. Allonnia tintinopsis n.sp. with stalk-like constrictions. 1. ROM 49616B, RQ 9.1, dry. 2. ROM 49596A, RQ 8.4, dry. 3, 4. ROM 49603, RQ 8.9. 3, Dry/pol. 4 . Detail of 3 (position marked by frame), dry/pol.

figure 20

 

FIGURE 21. Allonnia tintinopsis n.sp. Apical tufts and orifices. 1. ROM 62524A (also in Figure 17.1), RQ 8.7, dry. 2. ROM 49608a, RT, dry/pol. 3. ROM 49608b, RT, dry/pol. 4. ROM 49607A, RQ 10.7, wet/pol. 5. ROM 62525B, RQ 8.4, dry. 6. ROM 62525B, RQ 8.4, dry/pol. 7. ROM 62520B (also in Figure 24.3), RQ 9.0, wet. 8, 9. ROM 62587, RQ 8.4, wet/pol (8), wet (9). 10. ROM 49614B, RQ 9.0, dry/pol. 11, 12. ROM 49620B (counterpart to the upper right specimen in Figure 27.3), RQ 9.0, 11. Dry/pol. 12. Detail of 11 (position marked by frame), dry/pol. Scale bars in all pictures equal 1 mm.

figure 21

 

FIGURE 22. Allonnia tintinopsis n.sp. ROM 49612A, RQ 9.8, dry/pol. 1. Apical part of body, with tuft. 2, 3. Details of 1 (positions marked by frames). figure 22

 

FIGURE 23. Allonnia tintinopsis n.sp. Apical tufts. 1. ROM 49605(1), RQ 9.2, wet/pol. 2, 3. ROM 62591, UE. 2. Wet. 3. Detail of 2 (position marked by frame), wet. figure 23

 

FIGURE 24. Allonnia tintinopsis n.sp. intergrown with Vauxia (1, 2) and having Micromitra attached to the spines (1, 3, 4). 1. ROM 49588B, RQ 9.0, wet/pol. 2. ROM 49606, RQ 8.9, wet. 3. ROM 62520B (also in Figure 21.7), RQ 9.0, wet. 4. ROM 62515B, RQ 8.8, wet.

figure 24 

 

FIGURE 25. Allonnia tintinopsis n.sp. associated with Vauxia. 1. ROM 49587B, RQ 8.3, dry. 2. ROM 49584A, RQ 8.1, wet.

 figure 25

 

FIGURE 26. Allonnia tintinopsis n.sp. ROM 57574, RQ 8.5. Apical tuft and orifice. 1. Dry. 2 - 4. Details of preceding pictures (positions marked by frames), dry.

figure 26 

 

FIGURE 27. Allonnia tintinopsis n.sp., attachment to Vauxia. 1 - 2. ROM 62523A, RQ 8.4. 1. Wet. 2. Detail of 1 (position marked by frame), wet. 3. ROM 49620A (upper right-hand specimen is part to the one in Figure 21.11-12), RQ 9.0, wet. figure 27

 

FIGURE 28. Allonnia tintinopsis n.sp., two specimens on the same slab showing probable attachment to hyoliths ( 1 , wet) and Vauxia ( 2, wet). ROM 62518A, RQ 8.2. Inset in 2 (dry) shows blowup of isolated, probably extraneous, Chancelloria -like sclerite in Allonnia scleritome. figure 28

 

FIGURE 29. Intergrowths of Allonnia tintinopsis n.sp. and Vauxia. Part, ROM 62526A (2) and counterpart, ROM 62526B (1, 3), RQ 8.4. 1. Wet. 2. Detail of part (position marked by frame in 1), wet. 3. Detail of 1 (position marked by frame), wet.

figure 29 

 

FIGURE 30. Allonnia tintinopsis n.sp, apical orifice with pyrite concentration. 1. ROM 49609A, RQ 9.0, dry. 2. ROM 62536, BW -400, wet/pol. 3. ROM 49582B, RQ 9.0, wet/pol. 4. ROM 49601A, RQ 9.7 (figure 1A2 in Bengtson, 2000; see that paper for details on settings).

figure 30 

 

FIGURE 31. Integument structure of Allonnia and Archiasterella. 1. Allonnia tintinopsis n.sp. ROM 62514B, RQ 9.8, dry. 2, 3. Allonnia tintinopsis n.sp., ROM 49600A, UE. 2. Dry. 3. Detail of 2 (position marked by frame), dry. 4. Archiasterella coriacea n.sp., holotype, ROM 62531A, BW -130, dry. figure 31

 

FIGURE 32. Allonnia tintinopsis n.sp. 1. ROM 49615A, WT, dry/pol. 2. ROM 49621, UE, dry. figure 32

 

FIGURE 33. Association of Allonnia tintinopsis n.sp., bodies and attachments, on bedding slab. ROM 62585, RQ 8.4. 1. Part; arrow points to specimen represented by counterpart in 3, dry. 2. Tracing of bodies (red; darker tones toward the apex) and root bulbs (grey), based on both part and counterpart. 3. Counterpart of specimen with root bulb marked by arrow in 1, dry.
figure 33

 

FIGURE 34. Two Allonnia tintinopsis n.sp. associated with a Vauxia. Ottoia to the right. ROM 49589A, RQ 9.0, wet.
 figure 34

 

FIGURE 35. Intergrowth of Allonnia tintinopsis n.sp. with Vauxia. ROM 62521B, RQ 8.4. 1. Dry. 2. Detail of 1 (position marked by frame), dry.
 figure 35

 

FIGURE 36. Allonnia tintinopsis n.sp. together with Micromitra shells and carapace of Isoxys. ROM 49602B, RQ 8.7, dry.

figure 36

 

FIGURE 37. Life reconstruction of Allonnia tintinopsis, n.sp., growing on the sponge Vauxia. Artwork Pollyanna von Knorring.

 figure 37

 

FIGURE 38. Archiasterella coriacea n.sp., holotype, ROM 62531A (same specimen as in Figures 31.4 and 39), BW -130. 1. Complete specimen showing alignment of sclerites, wet. 2. Detail of 1 (position marked by frame) showing the apical tuft, wet. 3. Detail of 1 (position marked by frame) showing the attitude of sclerites relative to the body wall, wet.

 figure 38

 

FIGURE 39. Archiasterella coriacea n.sp., holotype, ROM 62531A, BW -130, superposition of sclerites from two sides of body. △ - basal side down; ▼ - basal side up. Cf. Figures 31.4 and 38.

figure39
 

 

FIGURE 40. Archiasterella coriacea n.sp, ROM 57573, WQ -130. 1. Wet. 2, 3. SEM stereographs (red/blue anaglyphic images) of latex casts taken of counterpart to show structure of integument. Frames show positions of details 2 and 3.

figure 40

 

FIGURE 41. Archiasterella coriacea n.sp. 1, 2. ROM 62529B, BW -130. 1. Dry. 2. Detail of 1 (position marked by frame), wet/pol. 3. ROM 62530A, BW -130, wet. 4. ROM 62532, BW -130, apical part, wet.

figure 41

 

FIGURE 42. Archiasterella coriacea n.sp. 1, 2. ROM 62528A, RQ 8.4. 1. Showing distribution of sclerites, wet. 2. Showing integument, wet/pol. 3. ROM 62533A, BW -130, wet. 4. ROM 49583B, RQ 9.0, wet. Specimen attached to a Vauxia.

figure 42

 

FIGURE 43. Archiasterella coriacea n.sp. ROM 49617B, RQ 13.8. 1. Complete specimen, wet. 2. Detail of upper specimen in 1 (position marked by frame), wet. 3. Detail of 1 (position marked by frame), wet, showing stalk uniting upper and lower specimen.

figure 43

 

FIGURE 44. Archiasterella coriacea n.sp. 1. ROM 49619A, RQ, wet. 2. ROM 49567A, UE, wet. Arrow points to tuft.

figure 44

 

FIGURE 45. Life reconstruction of Archiasterella coriacea, n.sp. Artwork Pollyanna von Knorring. 

figure 45

 

bengtsonStefan Bengtson
Department of Palaeobiology and Nordic Center for Earth Evolution
Swedish Museum of Natural History
Box 50007
SE-104 05 Stockholm
Sweden
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Stefan Bengtson is emeritus Professor of Palaeozoology at the Swedish Museum of Natural History. His main interests concern the origins and early evolution of multicellular organisms, including animals. This involves working with various kinds of fossils (and colleagues) in the Proterozoic and early Phanerozoic. Stefan's early studies focused on Cambrian 'small shelly fossil' (SSFs; they are commonly neither small nor shelly, but the expression has stuck like glue) and the focus has now widened (some say blurred) to include Proterozoic and Cambrian embryos, embryo-like fossils, algae, and fungi, using the revelatory technique of X-ray tomographic microscopy.

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collinsDesmond Collins
501−437 Roncesvalles Ave.
Toronto, Ontario M6R 3B9
Canada
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Desmond Collins served as Curator of Invertebrate Palaeontology and Head of Palaeobiology at the Royal Ontario Museum. His earlier career as an expert on fossil cephalopods took a turn in 1972 during a brief visit to Walcott's Quarry on an IGC field excursion where he saw talus specimens which were of better quality than the ones in the ROM collection being assembled for a new gallery display. He finally got permission to collect talus specimens for display, in 1975. At the time, there was no intention to collect specimens for research. Surprisingly, specimens of new and rare species were collected, indicating that there were probably other fossil-bearing levels still to be discovered on Fossil Ridge.

Thus began a series of another 17 field seasons of reconnaissance and excavation from 1981 to 2000, mostly on Fossil Ridge and Mount Stephen, yielding a collection of over 150,000 specimens, the largest collection of Burgess Shale fossils in the world.

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