The Burgess Shale

Burlingia hectori

Burlingia hectori (ROM 48449). Complete individual. Specimen length = 5.1 mm. Specimen dry – direct light. Trilobite Beds on Mount Stephen (Burlingia locality).

© Royal Ontario Museum. Photo: Jean-Bernard Caron

Taxonomy:

Class: Trilobita (Order: Uncertain)
Remarks:

Trilobites are extinct euarthropods, probably stem lineage representatives of the Mandibulata, which includes crustaceans, myriapods, and hexapods (Scholtz and Edgecombe, 2006).

Species name: Burlingia hectori
Described by: Walcott
Description date: 1908
Etymology:

Burlingia – after Lancaster Burling, then with the United States National Museum, who discovered the first specimens on Mount Stephen in 1907; Burling was later employed by the Geological Survey of Canada to work on Cambrian strata and fossils in the Rockies.

hectori – after Sir James Hector, surgeon and geologist on the Palliser Expedition (1857-1860), and the man at the heart of the apocryphal tale according to which Kicking Horse Pass and the Kicking Horse River received their names.

Type Specimens: Lectotype –USNM53418 in the National Museum of Natural History, Smithsonian Institution, Washington, DC, USA (Rasetti, 1951).
Other species:

Burgess Shale and vicinity: none.

Other deposits: Burlingia ovata from the Middle Cambrian of China; three species of Schmalenseeia from the early Middle to early Upper Cambrian of Sweden, China, Australia, Siberia, England, and Newfoundland (Whittington, 1994).

Age & Localities:

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

Found originally at a single locality just north of the Trilobite Beds on Mount Stephen, the species has since been identified from the Middle Cambrian of Öland, Sweden (ex-Burlingia laevis – see Whittington, 1994).

History of Research:

Brief history of research:

The first three specimens of this strange little trilobite were found by Lancaster Burling when he accompanied Charles Walcott on his first visit to Mount Stephen in 1907. These were named and described the following year (Walcott, 1908a) and the best specimen was re-illustrated in Walcott’s popular account (1908b) in the Canadian Alpine Journal. Its tiny size and very odd morphology immediately set Burlingia apart from all other trilobites except for another diminutive form, Schmalenseeia amphionura, which had been described just 5 years earlier from the Upper Cambrian of Sweden. Species of both genera are now known to occur as rare elements in Cambrian faunas around the world, however, despite a thorough redescription (Whittington, 1994), burlingiids have consistently proven difficult to fit into any current trilobite phylogeny.

Description:

Morphology:

Hard parts: the largest of the known Mount Stephen specimens of Burlingia hectori is only 8 mm in length; other complete individuals are 5-6 mm long. Dorsal shields vary from nearly circular to elongate ovoid in outline and specimens appear almost flat due to mechanical distortion and compression of the very thin exoskeleton. The cephalon has a semicircular to rounded triangular shape with the genal corners acutely angled, but not drawn out into spines.

Burlingia has proparian facial sutures, meaning both branches of the suture lie anterior of the genal angle and are directed obliquely forward, setting off small trapezoidal free cheeks. The narrow, forward-tapering glabella has very little independent relief, and extends over the posterior two-thirds of the cephalic mid-length. Low crescentic eye lobes lie close to the glabella at about cephalic mid-length, bounded by the proparian sutures. The thorax consists of 14 segments, with only a slight change in slope setting off the low axial lobe from the flat, unfurrowed pleurae. The overlapping pleurae, with acutely angled tips, curve progressively more strongly to the rear; the last pair extend directly backwards past the notched tip of the tiny parallel-sided pygidium.

Unmineralized anatomy: not known.

Abundance:

Exceedingly rare, present only at the Mount Stephen Burlingia locality.

Maximum Size:
8 mm

Ecology:

Ecological Interpretations:

The small adult size, peculiar morphology, thin exoskeleton, and wide geographical distribution of burlingiids have all been considered suggestive of a planktonic mode of life, but this hypothesis has not met with universal agreement (Whittington, 1994), and the lifestyle of Burlingia hectori remains enigmatic.

References:

RASETTI, F. 1951. Middle Cambrian stratigraphy and faunas of the Canadian Rocky Mountains. Smithsonian Miscellaneous Collections, 116 (5): 1-277.

SCHOLTZ, G. AND G. D. EDGECOMBE. 2006. The evolution of arthropod heads: reconciling morphological, developmental and palaeontological evidence. Development Genes and Evolution, 216: 395-415.

WALCOTT, C. 1908a. Cambrian Geology and Paleontology I. Cambrian trilobites. Smithsonian Miscellaneous Collections, 53(2): 13-52.

WALCOTT, C. D. 1908b. Mount Stephen rocks and fossils. Canadian Alpine Journal, 1: 232-248.

WHITTINGTON, H. B. 1994. Burlingiids: small proparian Cambrian trilobites of enigmatic origin. Palaeontology, 37: 1-16.

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Marpolia spissa

3D animation of Marpolia spissa.

ANIMATION BY PHLESCH BUBBLE © ROYAL ONTARIO MUSEUM

Taxonomy:

Class: Cyanophyceae (Order: Oscillatoriales?)
Remarks:

Walcott (1919) considered this species to be a cyanobacterium, but Walton suggested a relationship to red algae instead (Walton, 1923). More recent studies concurred with Walcott’s original interpretation (Conway Morris and Robison, 1988).

Species name: Marpolia spissa
Described by: Walcott
Description date: 1919
Etymology:

Marpolia – from Mount Marpole (2,997 m), a peak located near the Burgess Shale, northwest of Emerald Lake in Yoho National Park.

spissa – from the Latin spissus, “crowded,” in reference to the bush-like aspect of this cyanobacteria.

Type Specimens: Lectotype –USNM35403 (M. spissa); holotype –USNM35412 (M. aequalis) in the National Museum of Natural History, Smithsonian Institution, Washington, DC, USA.
Other species:

Burgess Shale and vicinity: M. aequalis Walcott 1919 from the Trilobite Beds on Mount Stephen (known from a single specimen).

Other deposits: Marpolia (possibly represented by different species) is common in various Cambrian exceptional fossil deposits, in particular from the Middle Cambrian Spence Shale and Wheeler Formation in Utah (Conway Morris and Robison, 1988) and the Middle Cambrian Kaili Formation in China (Yang et al., 2001).

Age & Localities:

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

The Walcott Quarry on Fossil Ridge, the Tulip Beds (S7) on Mount Stephen, and other smaller localities on Mount Field, Mount Stephen and Monarch Cirque.

History of Research:

Brief history of research:

Walcott described Marpolia in 1919 and named two species from the Burgess Shale, M. spissa from the Walcott Quarry and M. aequalis from the Trilobite Beds. M. spissa was compared to the modern Oscillatorialesin an unpublished thesis (Satterthwait, 1976), an interpretation followed by Conway Morris and Robison (1988) based on the study of fossil material from various Utah deposits. M. spissa is commonly found in thin sections (Mankiewicz, 1992) and can be isolated by acid maceration (Butterfield, 1990). A recent taphonomic study demonstrated that the preservation style of Marpolia is similar to other Burgess Shale organisms (Butterfield et al., 2007).

Description:

Morphology:

Marpolia forms dense tufts up to 5 cm in length composed of numerous filaments. Filaments tend to branch near the base of the tuft. Each filament averages about 40 microns in width. Filaments are composed of an outer sheath and one to four strands of inner cells. Each cell is about 2 microns in length. M. aequalis has a central stem and stronger branching structures than M. spissa.

Abundance:

Estimating the abundance of Marpolia is difficult since some bedding planes have large tangled masses of this cyanobacterium, and many could represent fragments of the same colony. M. spissa is rare and represents only 0.07% of the Walcott Quarry community (Caron and Jackson, 2008).

Maximum Size:
50 mm

Ecology:

Ecological Interpretations:

The absence of an attachment structure suggests that Marpolia may have been free-living, floating in large masses (i.e., planktonic). It may have attached to other floating objects as free-living cyanobacteria do today. It is also possible that the lack of attachment structure is taphonomic (a structure that is lost during deposition), due to detachment from the sediment during transport (caused by having been swept up in mud flows) prior to burial.

References:

BUTTERFIELD, N. J. 1990. Organic preservation of non-mineralizing organisms and the taphonomy of the Burgess Shale. Paleobiology, 16: 272-286.

BUTTERFIELD, N. J., U. BALTHASAR AND L. WILSON. 2007. Fossil diagenesis in the Burgess Shale. Palaeontology, 50: 537-543.

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. AND R. A. ROBISON. 1988. More soft-bodied animals from the Middle Cambrian of Utah and British Columbia. University of Kansas Paleontological Contributions, 122 p.

MANKIEWICZ, C. 1992. Obruchevella and other microfossils in the Burgess Shale: preservation and affinity. Journal of Paleontology, 66: 717-729.

SATTERTHWAIT, D. F. 1976. Paleobiology and Paleoecology of Middle Cambrian Algae from Western North America. Unpublished PhD thesis, California, Los Angeles, 120 p.

WALCOTT, C. D. 1919. Middle Cambrian Algae. Cambrian Geology and Paleontology IV. Smithsonian Miscellaneous Collections, 67(5): 217-260.

WALTON, J. 1923. On the structure of a Middle Cambrian alga from British Columbia (Marpolia spissa Walcott). Proceedings of the Cambridge Philosophical Society-Biological Sciences, 1: 59-62.

YANG, R., J. MAO, Y. ZHAO, X. CHEN AND X. YANG. 2001. Branching macroalgal fossils of the Early-Middle Cambrian Kaili Formation from Taijiang, Guizhou Province, China. Acta Geologica Sinica, 75: 433-440.

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