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:

Class: Graptolithina (Order: Dithecoidea, stem group hemichordates)
Remarks:

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

Species name: Chaunograptus scandens
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:

Period:
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:

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:

None

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:

Class: Non applicable
Remarks:

The position of Oesia is uncertain. Originally described as an annelid worm by Walcott (1911), a recent reinterpretation as a chaetognath (Szaniawski, 2005, 2009) has been vigorously rejected, and a position closer to the hemichordates proposed instead (Conway Morris, 2009).

Species name: Oesia disjuncta
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 appearance of this species.

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:

Period:
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:

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). However, a recent interpretation as a chaetognath (Szaniawski, 2005, 2009) has spurred new debate (Conway Morris, 2009, Szaniawski, 2009) with a view that a hemichordate relationship might be possible (Conway Morris, 2009). A thorough restudy of other hemichordate-like organisms from the Burgess Shale will be required to confirm this new hypothesis.

Description:

Morphology:

The body of Oesia is elongate with an anterior section which appears to be swollen. There is no evidence of grasping spines. The presence of fine transverse striations on the body has been interpreted as transverse muscle bands, but other features, such as fins and internal organs, are contentious.

Abundance:

Walcott recognized nine specimens of this species, but Oesia is probably more abundant than previously thought. Oesia and another similar hemichordate-like form (“Ottoia tenuis”) represent about 2.2% of the Walcott Quarry community (Caron and Jackson, 2008).

Maximum Size:
90 mm

Ecology:

Ecological Interpretations:

The vermiform aspect of this fossil and apparent lack of fins suggest a benthic lifestyle, but its mode of feeding is unknown.

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.

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

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.

WALCOTT, C. 1911. Cambrian Geology and Paleontology II. Middle Cambrian annelids. Smithsonian Miscellaneous Collections, 57(5): 109-145.

SZANIAWSKI, H. 2005. Cambrian chaetognaths recognized in Burgess Shale fossils. Acta Palaeontologica Polonica, 50(1): 1-8.

SZANIAWSKI, H. 2009. Fossil Chaetognaths from the Burgess Shale: A Reply to Conway Morris (2009). Acta Palaeontologica Polonica, 54(2): 361-364.

Other Links:

None