The Burgess Shale

Chaunograptus scandens

Chaunograptus scandens (ROM 61106). A single stem with several small thecae on both sides, next to the arthropod Waptia fieldensis and the sponge Leptomitus lineatus. Specimen length = 14 mm. Specimen wet – direct light (both images). Walcott Quarry.

© Royal Ontario Museum. Photos: Jean-Bernard Caron

Taxonomy:

Kingdom: Hemichordata
Phylum: Hemichordata
Higher Taxonomic assignment: Graptolithina (Order: Dithecoidea, stem group hemichordates)
Species name: Chaunograptus scandens
Remarks:

This species belong to a primitive group of graptolites called the dithecoids, a sister group to dendroids and graptoloids (Rickards and Durman, 2006).

Described by: Ruedemann
Description date: 1931
Etymology:

Chaunograptus – from the Greek chaunos, “loose,” and graptos, “inscribed,” in reference to the general outline of the animal.

scandens – from the Latin scandens, “to climb,” in reference to the presence of this species on the surface of sponges.

Type Specimens: Holotype – UNSM 83484 in the National Museum of Natural History, Smithsonian Institution, Washington, DC, USA.
Other species:

Burgess Shale and vicinity: none.

Other deposits: Several species of this genus occur in the Cambrian (Rickards and Durman, 2006; Ruedemann, 1947).

Age & Localities:

Age:
Middle Cambrian, Bathyuriscus-Elrathina Zone (approximately 505 million years ago).
Principal localities:

The Walcott Quarry on Fossil Ridge.

History of Research:

Brief history of research:

Described by Ruedemann in 1931, Chaunograptus was originally interpreted as a hydroid (which is now considered an obsolete group) within the Class Hydrozoa (see also Ruedemann, 1947). The hydrozoans include jellyfish and corals today. Graptolites are now convincingly interpreted as a primitive group of pterobranchs within Hemichordates (see references in Urbanek, 1986).

Description:

Morphology:

Chaunograptus scandens is a small colonial organism comprised of several very slender and straight stems that branch near the base. Short conical structures (thecae) are attached to either side of each stem at regular intervals.

Abundance:

About a dozen specimens are known from the Walcott Quarry, comprising only 0.021% of the specimens counted (Caron and Jackson, 2008).

Maximum Size:
25 mm

Ecology:

Life habits: Hemichordata
Feeding strategies: Hemichordata
Ecological Interpretations:

Like modern rhabdopleurid forms, Chaunograptus was probably attached to substrates in order to filter the water for particulate organic matter. The original description suggests that Chaunograptus might have been climbing on the sponge Leptomitus lineata (“Tuponia lineata” in Ruedemann, 1931).

References:

CARON, J.-B. AND D. A. Jackson, 2008. Paleoecology of the Greater Phyllopod Bed community, Burgess Shale. Palaeogeography, Palaeoclimatology, Palaeoecology, 258: 222-256.

RICKARDS, R. B. AND P. N. DURMAN, 2006. Evolution of the earliest graptolites and other hemichordates, p. 5-92. In M. G. Bassett and V. K. Deisler (eds.), Studies in Palaeozoic Palaeontology. National Museum of Wales Geological Series 25. National Museum of Wales, Cardiff.

RUEDEMANN, R. 1931. Some new Middle Cambrian fossils from British Columbia. Proceedings of the United States National Museum, 79: 1-25.

RUEDEMANN, R. 1947. Graptolites of North America. Geological Society of America Memoir, 19: 652.

URBANEK, A. 1986. The enigma of graptolite ancestry: lesson from a phylogenetic debate, p. 184-226. In A. Hoffman and M. H. Nitecki (eds.), Problematic Fossil Taxa (Oxford Monographs on Geology and Geophysics N°5). Oxford University Press and Clarendon Press, Oxford.

Other Links:

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Oesia disjuncta

Oesia disjuncta (USNM 57630) – Lectotype, part and counterpart. Complete specimen. Specimen length = 85 mm. Specimen wet – direct light (top row), wet – polarized light (bottom row). Walcott Quarry.

© SMITHSONIAN INSTITUTION – NATIONAL MUSEUM OF NATURAL HISTORY. PHOTO: JEAN-BERNARD CARON

Taxonomy:

Kingdom: Hemichordata
Phylum: Hemichordata
Higher Taxonomic assignment: Enteropneusta
Species name: Oesia disjuncta
Remarks:

Oesia is considered a stem-group enteropneust (acorn worms) and has the characteristic three-part anatomy of the group, consisting of a proboscis, collar and trunk (Nanglu et al. 2016; Nanglu et al. 2020).

Described by: Walcott
Description date: 1911
Etymology:

Oesia — from Lake Oesa, a small lake located a few kilometres southeast of the Burgess Shale.

disjuncta — from the Latin prefix dis, to signify a negation, and junctus, “joined.” The name is probably in reference to the crooked or bent shape of the early discovered specimens of Oesia.

Type Specimens: Lectotype –USNM57630 in the National Museum of Natural History, Smithsonian Institution, Washington, DC, USA.
Other species:

Burgess Shale and vicinity: none.

Other deposits: none.

Age & Localities:

Age:
Middle Cambrian, Wuliuan stage, Burgess Shale Formation (around 507 million years old).
Principal localities:

Marble Canyon (Kootenay National Park), the Walcott Quarry on Fossil Ridge.

History of Research:

Brief history of research:

Walcott (1911) described this species as a polychaete worm, but this view was challenged by Lohman (1920) who suggested a tunicate (chordate) affinity instead. Conway Morris (1979) rejected both interpretations, and this animal was later regarded as a problematic organism of unknown affinity (Briggs and Conway Morris, 1986). Szaniawski suggested a chaetognath affinity in 2005, which was argued against by Conway Morris in 2009. Nanglu et al. formally redescribed Oesia as an enteropneust (hemichordate) in 2016.

Description:

Morphology:

Oesia ranged in length from 2.4mm – 120mm, with an average length of 53mm. The anteriormost region is an oval or “acorn” shaped proboscis, which gives the acorn worms (Enteropneusta) their common name. The proboscis is frequently preserved with a darker, more dense carbon content than surrounding tissues, suggesting that it was highly muscular as the proboscis is in modern acorn worms. Behind the proboscis was a short cylindrical region called the collar, which enclosed the mouth. Behind the collar was a long, cylindrical region called the trunk, which maintain a roughly even width throughout. Unlike in modern acorn worms or its contemporary Spartobranchus, the trunk of Oesia was not divided into a pharynx and a posterior trunk. Instead, the collagenous gill bars that define the pharynx continue throughout the entire length. This gives Oesia a relatively inflexible appearance. At the posterior end of Oesia was a bilobed shaped attachment structure. The interior of this structure also preserved highly concentrated carbon relative to surrounding tissue which, along with its shape, suggests that this appendage was for grasping. Oesia is often found inside another fossil previously described as the alga Margaretia dorus, but which is now recognized as the secreted dwelling of Oesia, which was likely used for feeding as a pre-filtration device. This tube was typically twice the width of Oesia and could reach nearly 50 cm in total length. The tube contained a series of spirally arranged pores and could bifurcate into branches as many as 5 or 6 times (although 1 or 2 bifurcations is more common).

Abundance:

Oesia is relatively rare at the Walcott Quarry, but is abundant at Marble Canyon where it represents the third most abundant species with 3,373 specimens (Nanglu et al. 2020).

Maximum Size:
120 mm.

Ecology:

Life habits: Hemichordata
Feeding strategies: Hemichordata
Ecological Interpretations:

Oesia was likely a suspension feeder, owing to its extended pharynx laden will gill bars. These gill bars would have been covered in small hair-like structures called cilia which would move to create a flow of water towards the mouth and into the body. Excess water would then be expelled through pores, while food was passed through the gut. The large tubes of Oesia would have projected from the muddy seafloor into the water, with the pores allowing for water to move in and out of the tube. This would allow for fresh water for Oesia to feed on and refresh the tube with oxygenated water.

References:

 

  • BRIGGS, D. E. G. AND S. CONWAY MORRIS. 1986. Problematica from the Middle Cambrian Burgess Shale of British Columbia, p. 167-183. In A. Hoffman and M. H. Nitecki (eds.), Problematic fossil taxa (Oxford Monographs on Geology and Geophysics No. 5). Oxford University Press & Clarendon Press, New York.
  • CONWAY MORRIS, S. 1979. The Burgess Shale (Middle Cambrian) fauna. Annual Review of Ecology and Systematics, 10(1): 327-349.
  • CONWAY MORRIS, S. 2009. The Burgess Shale animal Oesia is not a chaetognath: A reply to Szaniawski (2005). Acta Palaeontologica Polonica, 54(1): 175-179.
  • LOHMANN, H. 1920. Oesia disjuncta Walcott, eine Appendicularie aus dem Kambrium. Mitteilungen aus dem Zoologischen Staatsinstitut und Zoologischen Museum in Hamburg, 38: 69-75.
  • NANGLU, K., CARON, J.-B., CONWAY MORRIS, S.C., AND C. B. CAMERON. 2016. Cambrian suspension-feeding tubicolous hemichordates. BMC Biology 14: 1-9.
  • NANGLU, K., J.-B. CARON, AND C. B. CAMERON. 2020a. Cambrian tentaculate worms and the origin of the hemichordate body plan. Current Biology 30 (21): 4238-4244
  • NANGLU, K., CARON, J.-B. and GAINES, R. R. 2020b. The Burgess Shale paleocommunity with new insights from Marble Canyon, British Columbia. Paleobiology, 46, 58-81.
  • SZANIAWSKI, H. 2005. Cambrian chaetognaths recognized in Burgess Shale fossils. Acta Palaeontologica Polonica, 50(1): 1-8.
  • WALCOTT, C. 1911. Cambrian Geology and Paleontology II. Middle Cambrian annelids. Smithsonian Miscellaneous Collections, 57(5): 109-145.
Other Links:

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