The Burgess Shale

Zacanthoides romingeri

Zacanthoides romingeri (figure 3) illustrated by Rominger (1887) as Embolimus spinosa.

Taxonomy:

Class: Trilobita (Order: Corynexochida)
Remarks:

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

Species name: Zacanthoides romingeri
Described by: Rominger
Description date: 1887
Etymology:

Zacanthoides – probably from the Greek z(a), “very,” and akanthion, “thistle” or “porcupine” or “hedgehog,” and oides, “resembling;” thus, very thistle- or porcupine-like.

romingeri – after Carl Rominger, a Michigan paleontologist who in 1887 published the first descriptions of trilobites from Mount Stephen.

Type Specimens: Type status under review – UMMP 4871 (2 specimens), University of Michigan Museum of Paleontology, Ann Arbor, Michigan, USA.
Other species:

Burgess Shale and vicinity: Zacanthoides sexdentatus, Z. submuticus, Z. longipygus, Z. planifrons, Z. divergens, all from older and younger Middle Cambrian rocks on Mount Stephen, Mount Odaray, and Park Mountain (Rasetti, 1951).

Other deposits: other species elsewhere in North America.

Age & Localities:

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

The Trilobite Beds on Mount Stephen.

History of Research:

Brief history of research:

In 1887 Carl Rominger published an engraving of a nearly complete and markedly spiny trilobite and named it Embolimus spinosa. In 1908 Charles Walcott introduced the combination Zacanthoides spinosus for the Mount Stephen species and for a similar trilobite from Nevada. The next change came in 1942, when Charles Resser at the United States National Museum asserted that the Mount Stephen species was sufficiently distinct that it required a new name. Resser chose to honour the man who first formally described many of the common Mount Stephen trilobites, and Zacanthoides romingeri remains the combination in use today.

Description:

Morphology:

Hard parts: adult dorsal exoskeletons can reach up to 6 cm in length, tapering back from a large crescentic cephalon through a thorax of nine segments, to a relatively small rounded-triangular pygidium with long marginal spines.

The wide free cheeks bear strong genal spines; short, thorn-like intragenal spines mark the posterior corners of the fixed cheeks. The glabella is long and narrow, slightly expanded forwards. There are four pairs of lateral glabellar furrows; the anterior two pairs are weaker and angled to the front, the stronger posterior two are angled back. Very long narrow eyes that bow strongly outward are located far back on the cephalon. The occipital ring extends rearward into a strong, broad-based spine. Long, blade-shaped terminal spines on the wide pleurae curve progressively more backwards. A slender needle-like spine arises from the axial ring of the eighth thoracic segment. There are four pygidial axial rings; five pairs of marginal spines, each successively shorter, are directed rearwards and extend beyond the tip of the pygidium.

Unmineralized anatomy: not known.

Abundance:

Zacanthoides romingeri is moderately abundant at the Mount Stephen Trilobite Beds but absent from Fossil Ridge. Complete trilobites with the free cheeks in place are very scarce, and this species is mostly found as disarticulated sclerites. Its distinctive characteristics, however, usually allow even isolated pieces to be readily identified.

Maximum Size:
60 mm

Ecology:

Ecological Interpretations:

Zacanthoides romingeri adults very likely walked along the sea bed. The overall spinosity of this species may have served as a deterrent to predators, or possibly helped to break up the visual outline of the animal, making it harder to see on the sea floor (Rudkin, 1996).

References:

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

RESSER, C. E. 1942. Fifth contribution to nomenclature of Cambrian trilobites. Smithsonian Miscellaneous Collections, 101 (15): 1-58.

ROMINGER, C. 1887. Description of primordial fossils from Mount Stephens, N. W. Territory of Canada. Proceedings of the Academy of Natural Sciences of Philadelphia, 1887: 12-19.

RUDKIN, D. M. 1996. The Trilobite Beds of Mount Stephen, Yoho National Park, p. 59-68. In R. Ludvigsen (ed.), Life in Stone – A Natural History of British Columbia’s Fossils. UBC Press, Vancouver.

RUDKIN, D. M. 2009. The Mount Stephen Trilobite Beds, p. 90-102. In J.-B. Caron and D. Rudkin (eds.), A Burgess Shale Primer – History, Geology, and Research Highlights. The Burgess Shale Consortium, Toronto.

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. D. 1888. Cambrian fossils from Mount Stephens, Northwest Territory of Canada. American Journal of Science, Series 3, 36: 163-166.

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

Other Links:

Yohoia tenuis

3D animation of Yohoia tenuis.

ANIMATION BY PHLESCH BUBBLE © ROYAL ONTARIO MUSEUM

Taxonomy:

Class: Unranked clade Megacheira? (stem group arthropods)
Remarks:

Yohoia was originally considered to be a branchiopod crustacean (Walcott, 1912; Simonetta, 1970), but was also described as being closely related to the chelicerates (Briggs and Fortey, 1989; Wills et al., 1998; Cotton and Braddy, 2004). Other analyses suggest that Yohoia belongs in the group of “great appendage” arthropods, the Megacheira, together with LeanchoiliaAlalcomenaeus and Isoxys (Hou and Bergström, 1997; Budd, 2002). The megacheirans have been suggested to either be stem-lineage chelicerates (Chen et al. 2004; Edgecombe, 2010), or stem-lineage euarthropods (Budd, 2002).

Species name: Yohoia tenuis
Described by: Walcott
Description date: 1912
Etymology:

Yohoia – from the Yoho River, Lake, Pass, Glacier, Peak (2,760 m) and Park, British Columbia, Canada. “Yoho” is a Cree word expressing astonishment.

tenuis – from the Latin tenuis, “thin,” referring to its slender body.

Type Specimens: Lectoype –USNM57699 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, Raymond and Collins Quarries on Fossil Ridge.

History of Research:

Brief history of research:

Yohoia was first described by Walcott (1912), who designated the type species Y. tenuis based on six specimens, and a second species, Y. plena, based on one specimen. Additional specimens of Y. tenuis were described by Simonetta (1970), and a major redescription of Yohoia tenuis was then undertaken by Whittington (1974), based on over 400 specimens of this species. Whittington (1974) invalidated Y. plena, upgrading it to its own genus, Plenocaris plena, leaving Y. tenuis as the only species of YohoiaYohoia has since been included in several studies on arthropod phylogeny and evolution (e.g., Briggs and Fortey, 1989; Hou and Bergström, 1997; Wills et al., 1998; Budd, 2002; Chen et al., 2004; Cotton and Braddy, 2004).

Description:

Morphology:

The body of Yohoia consists of a head region encapsulated in a cephalic shield and 14 body segments, ending in a paddle-shaped telson. The dorsal head shield is roughly square and extends over the dorsal and lateral regions of the head. There is a pair of great appendages at the front of the head. Each appendage consists of two long, thin segments that bend like an elbow at their articulation, with four long spines at the tip. Three pairs of long, thin, segmented appendages project from beneath the head shield behind the great appendages.

The body behind the head consists of ten segments with tough plates, or tergites, that extend over the back and down the side of the animal, ending in backward-facing triangular points. The first of these body segments may have an appendage that is segmented and branches into two (biramous), with a segmented walking limb bearing a flap-like extension. The following nine body segments have only simple flap-shaped appendages fringed with short spines or setae. The next three body segments have no appendages, and the telson is a paddle-shaped plate with distal spines.

Abundance:

Over 700 specimens of Yohoia are known from the Walcott Quarry, comprising 1.3% of the specimens counted (Caron and Jackson, 2008) but only few specimens are known from the Raymond and Collins Quarries.

Maximum Size:
23 mm

Ecology:

Ecological Interpretations:

Yohoia is thought to have used its three pairs of cephalic appendages, and possibly the biramous limb on the first body segment, to walk on the sea floor. The animal could also swim by waving the flap-like appendage on the body trunk. The setae on these appendages may have been used for respiration. The pair of frontal appendages were likely used to capture prey or scavenge food particles from the sea floor.

References:

BRIGGS, D. E. G. AND R. A. FORTEY. 1989. The early radiation and relationships of the major arthropod groups. Science, 246: 241-243.

BUDD, G. E. 2002. A palaeontological solution to the arthropod head problem. Nature, 417: 271-275.

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

CHEN, J. Y., D. WALOSZEK AND A. MAAS. 2004. A new ‘great-appendage’ arthropod from the Lower Cambrian of China and homology of chelicerate chelicerae and raptorial antero-ventral appendages. Lethaia, 37: 3-20.

COTTON, T. J. AND S. J. BRADDY. 2004. The phylogeny of arachnomorph arthropods and the origin of the Chelicerata. Transactions of the Royal Society of Edinburgh: Earth Sciences, 94: 169-193.

EDGECOMBE, G. D. 2010. Arthropod phylogeny: An overview from the perspectives of morphology, molecular data and the fossil record. Arthropod Structure and Development, 39: 74-87.

HOU, X. AND J. BERGSTRÖM. 1997. Arthropods of the Lower Cambrian Chengjiang fauna, southwest China. Fossils and Strata, 45: 1-116.

SIMONETTA, A. M. 1970. Studies on non trilobite arthropods of the Burgess Shale (Middle Cambrian). Palaeontographia Italica, 66 (New series 36): 35-45.

WALCOTT, C. D. 1912. Cambrian Geology and Paleontology II. Middle Cambrian Branchiopoda, Malacostraca, Trilobita and Merostomata. Smithsonian Miscellaneous Collections, 57(6): 145-228.

WHITTINGTON, H. B. 1974. Yohoia Walcott and Plenocaris n. gen. arthropods from the Burges

Other Links:

None

Worthenella cambria

Worthenella cambria (USNM 57643) – Holotype, part and counterpart. Left, plate 22 of Walcott (1911), showing a retouched image of the original specimen described (figure 2) together with other “worms.” Right, images of the same specimen. Specimen length = 60 mm. Specimen wet – direct light (left column), dry – polarized light (right column). Walcott Quarry.

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

Taxonomy:

Class: Unranked clade (stem group arthropods)
Remarks:

This animal is related to arthropods, but its systematic status within this group is unknown (Briggs and Conway Morris, 1986).

Species name: Worthenella cambria
Described by: Walcott
Description date: 1911
Etymology:

Worthenella – Possibly after the American palaeontologist Amos Henry Worthen, who died in 1888, just as Walcott’s career was taking off.

cambria – from the Welsh Cambria meaning Wales, in reference to the age of the fossil.

Type Specimens: Holotype –USNM57643 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:

Worthenella was first described by Walcott from a single specimen in a 1911 monograph dealing with various Burgess Shale worms. Walcott interpreted this animal as a polychaete annelid (or bristle worm), in the same family as the animal Wiwaxia (which is now interpreted as a primitive mollusc). However, this interpretation was questioned (Conway Morris, 1979), and the affinities of Worthenella have remained difficult to establish because this singular fossil is too poorly known (Briggs and Conway Morris, 1986).

Description:

Morphology:

The animal is elongate with a small head and bears at least 46 segments of similar dimensions. Appendages or tentacles are present beneath the head, but their preservation is poor and it is difficult to know their precise nature and arrangement. The anterior 34 segments seem to bear filamentous branches on their ventral sides, with the following 8 segments equipped with longer appendages. The gut is straight and the anus is terminal.

Abundance:

This animal is known from a single specimen.

Maximum Size:
60 mm

Ecology:

Ecological Interpretations:

Not enough is known about this organism to interpret its ecology.

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.

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

Other Links:

None

Thelxiope palaeothalassia

Thelxiope palaeothalassia (GSC 74990). Articulated specimen (close up to the right), associated with several individuals of the arthropod Canadaspis perfecta. Specimen length = 29 mm. Specimen dry – polarized light. Walcott Quarry.

© GEOLOGICAL SURVEY OF CANADA. PHOTOS: JEAN-BERNARD CARON

Taxonomy:

Class: Unranked clade (stem group arthropods)
Remarks:

The affinity of Thelxiope has not been considered in detail because the appendages are unknown.

Species name: Thelxiope palaeothalassia
Described by: Simonetta and Delle Cave
Description date: 1975
Etymology:

Thelxiope – from the Greek thelx meaning “enchanting,” and ops, meaning “voice,” referring to the muse-like appearance of the animal.

palaeothalassia – from the Greek palaios, meaning “ancient,” and thalassios, meaning “marine,” in reference to the age and environment where the animal lived.

Type Specimens: Holotype –USNM144914 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 (1912) figured two fragmentary specimens as Mollisoniarara; these were first reinterpreted by Simonetta (1964) within a new genus Parahabelia rara, along with three additional specimens that he thought were related. However, Simonetta and Delle Cave (1975) considered that among those five specimens, the two originally figured by Walcott as M? rara had to be synonymized with M. symmetrica and the other three had to be placed within a new genus and species called Thelxiope palaeothalassia, a name in use since then.

Description:

Morphology:

This species has a relatively wide cephalon and seven segments and resembles Habelia in overall shape. However, in T. palaeothalassia, each segment bears a single prominent spine pointing dorsally. The last segment is armed with a very long pointed telson.

Abundance:

Thelxiope is extremely rare, with only four known specimens.

Maximum Size:
43 mm

Ecology:

Ecological Interpretations:

Thelxiope is too poorly known to allow detailed studies of its ecology.

References:

SIMONETTA, A. M. 1964. Osservazioni sugli arthropodi non trilobiti della “Burgess Shale” (Cambriano medio). Monitore Zoologico Italiano, 72 (3-4: III Contributo: I Generi MolariaHabeliaEmeraldellaParahabelia (Nov.) Emeraldoides (Nov.): 215-231.

SIMONETTA, A. M. AND L. DELLE CAVE. 1975. The Cambrian non-trilobite arthropods from the Burgess shale of British Columbia: A study of their comparative morphology, taxonomy and evolutionary significance. Palaeontographia Italica, 69: 1-37.

WALCOTT, C. 1912. Cambrian Geology and Paleontology II. Middle Cambrian Branchiopoda, Malacostraca, Trilobita and Merostomata. Smithsonian Miscellaneous Collections, 57(6):145-228.

Other Links:

None

Tegopelte gigas

Tegopelte gigas (USNM 189201) – Holotype. Complete specimen showing antennae and appendages partially prepared near the back. Specimen length = 270 mm. Specimen dry – direct (top) and polarized light (bottom). Walcott Quarry.

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

Taxonomy:

Class: Unranked clade (stem group arthropods)
Remarks:

Tegopelte is usually compared to the soft-bodied “trilobites” such as Naraoia and Saperion, but the exact relationships of these taxa to the mineralized trilobites is uncertain (Whittington, 1977). The tegopeltids and other trilobite-like arthropods are sometimes referred to as Trilobitoidea, which when grouped together with the trilobites form the Lamellipedians (Hou and Bergström, 1997; Wills et al., 1998; Edgecombe and Ramsköld, 1999). This group has been variously placed in the upper stem lineage of the arthropods (Budd, 2002), or in the stem lineage of either the mandibulates (Scholtz and Edgecombe, 2006) or the chelicerates (Cotton and Braddy, 2004).

Species name: Tegopelte gigas
Described by: Simonetta and Delle Cave
Description date: 1975
Etymology:

Tegopelte – from the Greek tegos, “tile,” and pelte, “leather-shield,” referring to the shape of the dorsal body covering.

gigas – from the Greek gigas, “giant,” referring to the large size of the animal.

Type Specimens: Holotype –USNM189201 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:

Tegopelte was first described by Simonetta and Delle Cave (1975) to include only two relatively large specimens. This original description showed Tegopelte to have a cephalon with six or seven pairs of walking appendages, a thorax of four tergites each bearing five appendages, and a tail segment with ten appendages. Whittington (1985) re-examined the animal, reducing the number of head appendages to three, and describing the thorax as having only three tergites with three appendages each. The tail in Whittington’s (1985) reconstruction had two segments with a total of 20 appendages. Later re-examination by Ramsköld et al. (1996) suggested that the body has no tergites, but instead consists of an undivided dorsal shield. Tegopelte has been grouped together with the Chengjiang taxon Saperion to form the Tegopeltidae (Ramsköld et al., 1996; Hou and Bergström, 1997), a clade later confirmed by cladistic analysis (Edgecombe and Ramsköld, 1999; Hendricks and Lieberman, 2008).

Description:

Morphology:

The dorsal morphology of Tegopelte consists of an elongated oval-shaped dorsal shield that is featureless and undivided. The length of the two known specimens is 25.7 cm and 27.0 cm, making it one of the largest arthropods in the Burgess Shale. The ventral morphology consists of a pair of multi-segmented antennae at the front of the body, followed by a series of identical limbs that are segmented and branch into two (biramous), totaling approximately 33 along the entire body. The biramous limbs have a walking branch made up of six segments with a pair of spines on the terminal segment, and a filamentous branch where numerous elongated oval blades attach to a central shaft. The biramous limbs decrease in size towards the posterior end of the body.

Abundance:

Tegopelte is extremely rare, with only two known specimens.

Maximum Size:
270 mm

Ecology:

Ecological Interpretations:

Tegopelte probably spent much of its time walking on the seafloor, based on the presence of many appendages. It used the segmented branches of its biramous appendages for walking, and it is likely that the filamentous branches were used for oxygen exchange, and to propel the animal through the water during short bursts of swimming. The antennae would have been used to sense the environment. The lack of eyes, gut glands and feeding appendages make it difficult to allocate a feeding strategy to Tegopelte.

References:

BUDD, G. E. 2002. A palaeontological solution to the arthropod head problem. Nature, 417: 271-275.

COTTON, T. J. AND S. J. BRADDY. 2004. The phylogeny of arachnomorph arthropods and the origin of the Chelicerata. Transactions of the Royal Society of Edinburgh: Earth Sciences, 94: 169-193.

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.

EDGECOMBE, G. D. and L. RAMSKÖLD. 1999. Relationships of Cambrian Arachnata and the systematic position of Trilobita. Jounral of Paleontology, 73: 263-287.

HENDRICKS, J. R. AND B. S. LIEBERMAN. 2008. New phylogenetic insights into the Cambrian radiation of arachnomorph arthropods. Journal of Paleontology, 83: 585-594.

HOU, X. AND J. BERGSTRÖM. 1997. Arthropods of the Lower Cambrian Chengjiang fauna, southwest China. Fossils and Strata, 45: 1-116.

RAMSKÖLD, L., J. CHEN, G. D. EDGECOMBE AND G. ZHOU. 1996. Preservational folds simulating tergite junctions in tegopeltid and naraoiid arthropods. Lethaia, 29: 15-20.

SIMONETTA, A. M. AND L. DELLE CAVE. 1975. The Cambrian non-trilobite arthropods from the Burgess shale of British Columbia: A study of their comparative morphology, taxonomy and evolutionary significance. . Palaeontographia Italica, 69: 1-37.

WHITTINGTON, H. B. 1977. The Middle Cambrian trilobite Naraoia, Burgess Shale, British Columbia. Philosophical Transactions of the Royal Society of London, B, 280: 409-443.

WHITTINGTON, H. B. 1985. Tegopelte gigas, a second soft-bodied trilobite from the Burgess Shale, Middle Cambrian, British Columbia. Journal of Paleontology, 59: 1251-1274.

WILLS, M. A., D. E. G. BRIGGS, R. A. FORTEY, M. WILKINSON AND P. H. A. SNEATH. 1998. An arthropod phylogeny based on fossil and recent taxa, p. 33-105. In G. D. Edgecombe (ed.), Arthropod fossils and phylogeny. Columbia University Press, New York.

Other Links:

None

Stanleycaris hirpex

Stanleycaris hirpex (ROM 59944) – Holotype, part and counterpart. Individual claw. Specimen length = 29 mm. Specimen dry – polarized light. Stanley Glacier.

© ROYAL ONTARIO MUSEUM. PHOTOS: JEAN-BERNARD CARON

Taxonomy:

Class: Dinocarida (Order: Radiodonta, stem group arthropods)
Remarks:

Stanleycaris is an anomalocaridid closely related to Hurdia and Laggania. Anomalocaridids have been variously regarded as basal stem-lineage euarthropods (e.g., Daley et al., 2009), basal members of the arthropod group Chelicerata (e.g., Chen et al., 2004), and as a sister group to the arthropods (e.g., Hou et al., 2006).

Species name: Stanleycaris hirpex
Described by: Caron et al.
Description date: 2010
Etymology:

Stanleycaris – from Stanley Glacier, 40 kilometres southeast of the Burgess Shale in Kootenay National Park, where the fossils come from and the Latin caris, meaning “shrimp.” The name Stanley was given after Frederick Arthur Stanley (1841-1908), Canada’s sixth Governor General.

hirpex – from the Latin, hirpex, meaning “large rake,” in reference to the rake-like aspect of the appendage.

Type Specimens: Holotype –ROM59944 in the Royal Ontario Museum, Toronto, Canada.
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 Stanley Glacier in Kootenay National Park.

History of Research:

Brief history of research:

The first fossils of this species were collected by the Royal Ontario Museum in 1996 from talus slopes, but it was not until 2008, during a larger expedition, that specimens were discovered in their proper stratigraphic context. A description of this new genus and species soon followed (Caron et al., 2010).

Description:

Morphology:

Stanleycaris is known from paired or isolated grasping appendages and disarticulated assemblages. The entire animal might have reached 15 centimetres in total length. The grasping appendages range in length from 1.2 cm to 3 cm and have eleven segments (or podomeres), with five spinous ventral blades on the second to sixth segments. Double-pointed dorsal spines are particularly prominent from the second to the sixth segment, decreasing in size towards the distal end of the appendage. The longest of these robust spines is typically two to three times shorter than the ventral blades. The last segment has three curved terminal spines. Mouthparts are represented by circlets of plates bearing teeth around a central square opening. Assemblages are poorly preserved, and the best example consists of a pair of grasping appendages, a mouth part, and remnants of what might represent parts of a carapace or gill structures.

Abundance:

This species is relatively rare and only found near Stanley Glacier.

Maximum Size:
150 mm

Ecology:

Ecological Interpretations:

Stanleycaris is considered a predator or a scavenger, based on the morphology of its frontal appendages and mouth parts. The comb-like ventral blades might have been useful for searching small prey items or disturbing carcasses at the water-sediment interface and within the flocculent level of the mud.

References:

CARON, J.-B., R. GAINES, G. MANGANO, M. STRENG AND A. DALEY. 2010. A new Burgess Shale-type assemblage from the “thin” Stephen Formation of the Southern Canadian Rockies. Geology, 38(9): 811-814.

CHEN, J. Y., L. RAMSKÖLD AND G. Q. ZHOU. 1994. Evidence for monophyly and arthropod affinity of Cambrian giant predators. Science, 264: 1304-1308.

CHEN, J. Y., D. WALOSZEK AND A. MAAS. 2004. A new ‘great-appendage’ arthropod from the Lower Cambrian of China and homology of chelicerate chelicerae and raptorial antero-ventral appendages. Lethaia, 37: 3-20.

DALEY, A. C., G. E. BUDD, J. B. CARON, G. D. EDGECOMBE AND D. COLLINS. 2009. The Burgess Shale anomalocaridid Hurdia and its significance for early euarthropod evolution. Science, 323: 1597-1600.

HOU, X., J. BERGSTRÖM AND P. AHLBERG. 1995. Anomalocaris and other large animals in the Lower Cambrian Chengjiang fauna of Southwest China. GFF, 117: 163-183.

Other Links:

http://geology.geoscienceworld.org/cgi/content/full/38/9/811?ijkey=ZQFY537sTggAw&keytype=ref&siteid=gsgeology

Skania fragilis

Skania fragilis (ROM 60752) – Part and counterpart (first and second rows). Complete specimen showing antennae. Specimen length = 11 mm. Specimen dry – polarized light (left column) and wet (right column). Raymond Quarry.

© ROYAL ONTARIO MUSEUM. PHOTOS: JEAN-BERNARD CARON

Taxonomy:

Class: Unranked clade (stem group arthropods)
Remarks:

The affinity of Skania is controversial, but most agree it is related to the arthropods. It is similar to Primicaris (Lin et al., 2006; Zhang et al., 2007), and both taxa have been compared to soft-bodied trilobites like Naraoia (Walcott, 1931; Zhang et al., 2007; Hou and Bergström, 1997). Other researchers suggest these taxa are related to the enigmatic Ediacaran taxon Parvancorina (Delle Cave and Simonetta, 1975; Gehling, 1991; Conway Morris, 1993; Simonetta and Insom, 1993), with all three taxa forming a clade in sister group position relative to the trilobites (Lin et al., 2006).

Species name: Skania fragilis
Described by: Walcott
Description date: 1931
Etymology:

Skania – from Skana, the name of a glacier near Mount Robson, British Columbia, Canada.

fragilis – from the Latin fragilis, “brittle,” referring to the delicate nature and small size of the animal.

Type Specimens: Holotype –USNM83950 in the National Museum of Natural History, Smithsonian Institution, Washington, DC, USA.
Other species:

Burgess Shale and vicinity: none.

Other deposits: Skania sundbergi Lin et al. 2006 from the Kaili Formation, China.

Age & Localities:

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

The Walcott and Raymond Quarries on Fossil Ridge.

History of Research:

Brief history of research:

Skania fragilis was first described by Walcott (1931) in a posthumous monograph published by his assistant Charles Resser. Resser compared Skania to the trilobites and Naraoia. However in a redescription by Delle Cave and Simonetta (1975), it was suggested instead that Skania was closely related to the Ediacaran taxon Parvancorina minchami Glaessner 1958. This affinity has been much discussed (Gehling, 1991; Conway Morris, 1993; Simonetta and Insom, 1993; Lin et al. 2006), and Skania has also been compared extensively with Primicaris Zhang et al. 2003. Skania and Primicaris have also been interpreted as juveniles (protaspides) of naraoiids (Hou and Bergström, 1997).

Description:

Morphology:

Skania has a single, undifferentiated, soft dorsal shield that is roughly kite-shaped. The dorsal shield is rounded at the front of the head, and tapers towards the posterior of the body, ending in a pair of short margin spines at the posterior end. At the point of maximum width there are sharp genal spines directed posteriorly. The posterior margin of the head is delineated by a narrow rim that is strongly arched forward, with the cephalic region occupying one-quarter of the exoskeletal length. A midgut is preserved in the axial region of the body trunk. Appendages are poorly preserved but consist of a pair of anterior antennae and ten or more paired body limbs.

Abundance:

Skania fragilis is known from fewer than 40 specimens in total.

Maximum Size:
17 mm

Ecology:

Ecological Interpretations:

The ecology of Skania is poorly known because the details of its morphology remain enigmatic. The form of the appendages is assumed to be biramous based on the overall similarity with Primicaris, which possesses biramous appendages, meaning that both animals may have walked on the seafloor, using their filamentous appendages for oxygen exchange and occasional swimming. Skania lacks eyes, so it likely used its antennae to sense the environment. The feeding strategy is unknown.

References:

CONWAY MORRIS, S. 1993. Ediacaran-like fossil in Cambrian Burgess Shale-type faunas of North America. Palaeontology, 36: 593-635.

DELLE CAVE, L. AND A. M. SIMONETTA. 1975. Notes on the morphology and taxonomic position of Aysheaia (Onycophora?) and of Skania (undetermined phylum). Monitore Zoologico Italiano New Series, 9: 67-81.

GEHLING, J. G. 1991. The case for Ediacaran fossil roots to the metazoan tree, p. 181-223. In B. P. Radhakrishna (ed.), The world of Martin F. Glaessner. Geological Society of India, Bangalore.

HOU, X. AND J. BERGSTRÖM. 1997. Arthropods of the Lower Cambrian Chengjiang fauna, southwest China. Fossils and Strata, 45: 1-116.

LIN, J., S. M. GON III, J. G. GEHLING, L. E. BABCOCK, Y. ZHAO, X. ZHANG, S. HU, J. YUAN M. YU AND J. PENG. 2006. A Parvancorina-like arthropod from the Cambrian of South China. Historical Biology, 18: 33-45.

SIMONETTA, A. M. AND E. INSOM. 1993. New animals from the Burgess Shale (Middle Cambrian) and their possible significance for the understanding of the Bilateria. Bolletino di Zoologia, 60: 97-107.

WALCOTT, C. D. 1931. Addenda to descriptions of Burgess Shale fossils. Smithsonian Miscellaneous Collections, 85: 1-46.

ZHANG, X., D. SHU AND D. H. ERWIN. 2007. Cambrian naraoiids (Arthropoda): morphology, ontogeny, systematics, and evolutionary relationships. Palaeontological Society Memoir, 68: 1-52.

Other Links:

None

Sidneyia inexpectans

3D animation of Sidneyia inexpectans.

ANIMATION BY PHLESCH BUBBLE © ROYAL ONTARIO MUSEUM

Taxonomy:

Class: Unranked clade (stem group arthropods)
Remarks:

Sidneyia is usually considered to be closely related to the chelicerates, but its exact position relative to this group remains unclear (Budd and Telford, 2009). Sidneyia has been variously placed as the sister group to the chelicerates (Hou and Bergström, 1997), close to the crown on the chelicerate stem lineage (Bruton, 1981; Edgecombe and Ramsköld, 1999; Hendricks and Lieberman, 2008), or basal in the chelicerate stem lineage (Briggs and Fortey, 1989; Wills et al., 1998; Cotton and Braddy, 2004).

Species name: Sidneyia inexpectans
Described by: Walcott
Description date: 1911
Etymology:

Sidneyia – after Walcott’s son Sidney, who discovered the first specimen in August of 1910.

inexpectans – from the Latin inexpectans, “unexpected,” since Walcott did not expect to find such a fossil in strata older than the Ordovician.

Type Specimens: Lectotype –USNM57487 (S. inexpectans) in the National Museum of Natural History, Smithsonian Institution, Washington, DC, USA.
Other species:

Burgess Shale and vicinity: none.

Other deposits: A single specimen from the Chengjiang Fauna in China was used to describe a second species, Sidneyia sinica (Zhang et al. 2002), however this was later shown to be incorrectly attributed to Sidneyia (Briggs et al. 2008).

Age & Localities:

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

Burgess Shale and vicinity: The Walcott, Raymond and Collins Quarries on Fossil Ridge, Mount Field and Mount Stephen – Tulip Beds (S7) and other smaller localities – Odaray Mountain and Stanley Glacier.

Other deposits: Sidneyia has been described from the Wheeler Formation (Briggs and Robison, 1984) and the Spence Shale (Briggs et al. 2008) in Utah, and the Kinzers Formation in Pennsylvania (Resser and Howell, 1938).

History of Research:

Brief history of research:

Sidneyia was the first fossil to be described by Walcott (1911) from the Burgess Shale. Further details were added by Walcott the following year (Walcott, 1912), and Strømer (1944) and Simonetta (1963) made minor revisions to Walcott’s reconstruction. A large appendage found in isolation was originally suggested to be the large frontal appendage of Sidneyia (Walcott, 1911), but this was later found to belong to the anomalocaridid Laggania (Whittington and Briggs, 1985). A major study by Bruton (1981) redescribed the species based on the hundreds of available specimens.

Description:

Morphology:

Sidneyia has a short, wide head shield that is convexly domed and roughly square. The two front lateral corners are notched to allow an antenna and a stalked eye to protrude. Other than the pair of antennae, which are long and thin with at least 20 segments, there are no cephalic appendages. The hemispherical and highly reflective eyes are above and posterior to the antennae.

The thorax of Sidneyia has nine wide, thin body segments that widen from the first to the fourth segment and then get progressively narrower posteriorly. The first four thoracic segments bear appendages with a large, spiny basal segment (the coxa) and 8 thinner segments, ending in a sharp claw. The next five thoracic appendages have a similar appendage but also have flap-like filaments in association with the limbs.

The abdomen consists of three circular rings that are much narrower than the thorax, with a terminal, triangular telson. The last segment of the abdomen has a pair of wide flaps that articulate with the telson to form a tail fan. A trace of the straight gut can be seen in some specimens extending from the anterior mouth to the anus on the telson, and pieces of broken trilobites are sometimes preserved in the gut.

Abundance:

Sidneyia is a relatively common arthropod in the Walcott Quarry, comprising 0.3% of the specimens counted (Caron and Jackson, 2008). Hundreds of specimens have been collected from the Walcott Quarry (Bruton, 1981) and in other nearby localities.

Maximum Size:
160 mm

Ecology:

Ecological Interpretations:

Sidneyia walked and swam above the sea floor. Its anterior four thoracic appendages were used for walking, and the spiny basal coxa would crush food items and move them towards the mouth. The posterior five thoracic appendages were used for swimming, with the flap-like filaments undulating through the water column to create propulsion. These filaments were also likely used for breathing, like gills.

The predatory nature of Sidneyia is indicated by its spiny coxa used to masticate food, and the presence of crushed fossil debris in its gut. Sidneyia would have walked or swam above the sea floor, using its eyes and antennae to seek out prey, which it would capture and crush with its anterior appendages.

References:

BRIGGS, D. E. G. AND R. A. FORTEY. 1989. The early radiation and relationships of the major arthropod groups. Science, 246: 241-243.

BRIGGS, D. E. G. AND R. A. ROBISON. 1984. Exceptionally preserved non-trilobite arthropods and Anomalocaris from the Middle Cambrian of Utah. The University of Kansas Paleontological Contributions, 111: 1-24.

BRIGGS, D. E. G., B. S. LIEBERMAN, J. R. HENDRICKS, S. L. HALGEDAHL AND R. D. JARRARD. 2008. Middle Cambrian arthropods from Utah. Journal of Paleontology, 82(2): 238-254.

BRUTON, D. L. 1981. The arthropod Sidneyia inexpectans, Middle Cambrian, Burgess Shale, British Columbia. Philosophical Transactions of the Royal Society of London B, 295: 619-653.

BUDD, G. E. AND M. J. TELFORD. 2009. The origin and evolution of arthropods. Nature, 457(7231): 812-817.

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

CARON, J.-B., R. GAINES, G. MANGANO, M. STRENG, AND A. DALEY. 2010. A new Burgess Shale-type assemblage from the “thin” Stephen Formation of the Southern Canadian Rockies. Geology, 38: 811-814.

COTTON, T. J. AND S. J. BRADDY. 2004. The phylogeny of arachnomorph arthropods and the origin of the Chelicerata. Transactions of the Royal Society of Edinburgh: Earth Sciences, 94: 169-193.

EDGECOMBE, G. D. AND L. RAMSKÖLD. 1999. Relationships of Cambrian Arachnata and the systematic position of Trilobita. Jounral of Paleontology, 73: 263-287.

HENDRICKS , J. R. AND B. S. LIEBERMAN. 2008. Phylogenetic insights into the Cambrian radiation of arachnomorph arthropods. Journal of Paleontology, 82: 585-594.

HOU, X. AND J. BERGSTRÖM. 1997. Arthropods of the Lower Cambrian Chengjiang fauna, southwest China. Fossils and Strata, 45: 1-116.

RASSER, C. E. AND B. F. HOWELL. 1938. Lower Cambrian Olenellus zone of the Appalachians. Bulletin of the Geological Society of America, 49: 195-248.

SIMONETTA, A. M. 1963. Osservazioni sugli artropodi non trilobiti della Burgess Shale (Cambriano medio). II. Contributo: I Generai Sidneyia ed Amiella Walcott 1911. Monitore Zoologico Italiano, 70: 97-108.

STØMER, L. 1944. On the relationships and phylogeny of fossil and recent Arachnomorpha. Norsk Videnskaps-Akademi Skrifter I. Matematisk-Naturvidenskaplig Klasse, 5: 1-158.

WALCOTT, C. D. 1911. Middle Cambrian Merostomata. Cambrian geology and paleontology II. Smithsonian Miscellaneous Collections, 57: 17-40.

WALCOTT, C. D. 1912. Cambrian Geology and Paleontology II. Middle Cambrian Branchiopoda, Malacostraca, Trilobita and Merostomata. Smithsonian Miscellaneous Collections, 57(6): 145-228.

WHITTINGTON, H. B. AND D. E. G. BRIGGS. 1985. The largest Cambrian animal, Anomalocaris, Burgess Shale, British-Columbia. Philosophical Transactions of the Royal Society of London Series B-Biological Sciences, 309: 569-609.

WILLS, M. A., D. E. G. BRIGGS, R. A. FORTEY, M. WILKINSON AND P. H. A. SNEATH. 1998. An arthropod phylogeny based on fossil and recent taxa, pp. 33-105. In G. D. Edgecombe (ed.), Arthropod fossils and phylogeny. Columbia University Press, New York.

ZHU, X., H. JIAN AND S. DEGAN. 2002. New occurrence of the Burgess Shale arthropod Sidneyia in the Early Cambrian Chengjiang Lagerstätte (South China), and revision of the arthropod Urokodia. Alcheringa: An Australasian Journal of Palaeontology, 26: 1-18.

Other Links:

http://paleobiology.si.edu/burgess/sidneyia.html

Sarotrocercus oblita

Reconstruction of Sarotrocercus oblita.

© MARIANNE COLLINS

Taxonomy:

Class: Unranked clade (stem group arthropods)
Remarks:

The phylogenetic affinity of Sarotrocercus is uncertain because its morphology is too poorly known to make a definitive designation. Fryer (1998) suggested it was the most primitive of all arthropods, and it was placed within the Arachnomorpha by Cotton and Braddy (2004). Sarotrocercus has also been aligned with Megacheiran taxa such as Yohoia (e.g. Briggs and Fortey, 1989) and Leanchoilia (e.g., Wills et al. 1995; 1998).

Species name: Sarotrocercus oblita
Described by: Whittington
Description date: 1981
Etymology:

Sarotrocercus – from the Greek sarotes, “sweeper”, and kerkops, “a long tailed-monkey”, in reference to the feathery aspect of the tail.

oblita – from the Latin oblitus, “forgotten”, perhaps in reference to the fact that the few specimens of this species were described as part of another species.

Type Specimens: Holotype –USNM144890 (part) and UNSM 272171 (counterpart) 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:

The genus Sarotrocercus was erected by Harry Whittington in 1981 based on seven specimens originally included within Molaria spinifera (Simonetta and Delle Cave, 1975). No further research has been performed on the fossil material since then, although Sarotrocercus has been included in many studies of arthropod relationships (e.g. Briggs and Fortey, 1989; Wills et al., 1995; Fryer, 1998).

Description:

Morphology:

Sarotrocercus has an oval body consisting of a head shield and nine overlapping trunk segments; a cylindrical posterior segment carries a relatively short, narrow spine ending in a fan-shape cluster of small spikes. The whole animal was about 1.5 cm long. Although the head shield was not very strongly developed, it did bear a pair of large, stalked eyes that poked out from beneath the margin, and a pair of jointed appendages. Each of the nine body segments bore a pair of lobate appendages, with comb-like fringes which might have functioned as gills.

Abundance:

S. oblita is rare in the Burgess Shale. It was originally described on the basis of 7 specimens (Whittington, 1981), and 28 further specimens have been recovered from the Walcott Quarry representing less than 0.1% of the community (Caron and Jackson, 2008).

Maximum Size:
16 mm

Ecology:

Ecological Interpretations:

The absence of walking limbs combined with an inferred flexibility of the body imply that the organism swam, probably in an inverted position, using its paddle-like appendages and long tail. Its rarity in the Burgess Shale suggests that it may have spent much time in the water column, thus avoiding submarine landslides that trapped animals living on the sea floor. The absence of sediment in its gut suggest that Sarotrocercus was a filter feeder (Briggs and Whittington, 1985; Whittington, 1981).

References:

BRIGGS, D. E. G. AND R. A. FORTEY, 1989. The Early radiation and relationships of the major arthropod groups. Science, 246: 241-243.

BRIGGS, D. E. G. AND H. B. WHITTINGTON, 1985. Modes of life of arthropods from the Burgess Shale, British Columbia. Transactions of the Royal Society of Edinburgh. Earth Sciences, 76(2-3): 149-160.

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

COTTON, T. J. AND S. J. BRADDY, 2004. The phylogeny of arachnomorph arthropods and the origin of the Chelicerata. Transactions of the Royal Society of Edinburgh, 94(03): 169-193.

FRYER, G. 1998. A defence of arthropod polyphyly, p. 23. In R. A. Fortey and R. H. Thomas (eds.), Arthropod relationships. Springer, London.

SIMONETTA, A. M. AND L. DELLE CAVE, 1975. The Cambrian non-trilobite arthropods from the Burgess shale of British Columbia: A study of their comparative morphology, taxonomy and evolutionary significance. Palaeontographia Italica, 69: 1-37.

WHITTINGTON, H. B. 1981. Rare arthropods from the Burgess Shale, Middle Cambrian, British Columbia. Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences, 292(1060): 329-357.

WILLS, M. A., D. E. G. BRIGGS, R. A. FORTEY AND M. WILKINSON, 1995. The significance of fossils in understanding arthropod evolution. Verhandlungen den deutschen zoologischen Gesellschaft, 88: 203-216.

WILLS, M. A., D. E. G. BRIGGS, R. A. FORTEY, M. WILKINSON AND P. H. A. SNEATH, 1998. An arthropod phylogeny based on fossil and recent taxa, p. 33-105. In G. D. Edgecombe (ed.), Arthropod fossils and phylogeny. Columbia University Press, New York.

Other Links:

None

Ptychagnostus praecurrens

Ptychagnostus praecurrens (USNM 116212). Complete individual originally interpreted as the holotype of Triplagnostus burgessensis by Rasetti (1951). Specimen length = 8 mm. Specimen dry – direct light. Walcott Quarry.

© Smithsonian Institution – National Museum of Natural History. Photo: Jean-Bernard Caron

Taxonomy:

Class: Trilobita (Order: Agnostida)
Remarks:

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

Species name: Ptychagnostus praecurrens
Described by: Westergård
Description date: 1936
Etymology:

Ptychagnostus – from the Greek ptycho, “pleated” (some species have pleat-like furrows on the cephalon), and agnostos, for “unknown” or “unknowable.”

praecurrens – from the Latin prae, “before,” and currens, “to run,” in reference to the old age of this fossil

Type Specimens: Holotype – SGU611; in the Geological Survey of Sweden (Sveriges geologiska undersökning – SGU), Uppsala, Sweden (Westergård, 1936)
Other species:

Burgess Shale and vicinity: none.

Other deposits: other species occur throughout the world in Middle Cambrian rocks.

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:

Trilobites currently assigned to this genus and species have been described under several name combinations. Originally, Rasetti (1951) described it as Triplagnostus burgessensis, but subsequently (Rasetti, 1967) considered T. burgessensis to be a synonym of Ptychagnostus praecurrens (Westergård, 1936), a name retained by Peng and Robison (2000), despite numerous interim variations.

Description:

Morphology:

Hard parts: adult dorsal exoskeletons reach about 8 mm in length. The semicircular cephalon has a narrow marginal rim around the front and sides and sharply rounded the genal angles. There are no dorsal eyes and no facial sutures. The narrow glabella comes to an ogival point, with a median furrow extending across the short preglabellar field to the anterior margin; a transverse furrow crosses the glabella just in front of a low tubercle located behind the midpoint. Two short thoracic segments carry lateral nodes on the axial rings. A narrowly rimmed pygidium, the same size and general shape as the cephalon, has abruptly angled anterolateral corners. The pygidial axis is broader than the glabella, but of similar outline, with a median tubercle between two transverse furrows. The pointed tip of the axis reaches almost to the rim posteriorly, without a median furrow.

Unmineralized anatomy: not known

Abundance:

Very common in the Walcott Quarry on Fossil Ridge, where it is the most abundant trilobite (Caron and Jackson, 2008).

Maximum Size:
10 mm

Ecology:

Ecological Interpretations:

Adult agnostine trilobites have often been regarded as pelagic organisms that swam or drifted in the water column. Evidence now suggests that most were members of the mobile benthic epifauna, possibly micrograzers or particle feeders, preferentially occupying colder, deeper, offshore waters.

References:

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

PENG, S. C. AND ROBISON, R. A. 2000. Agnostoid biostratigraphy across the middle-upper Cambrian boundary in Hunan, China. Paleontological Society Memoir, no. 53 (supplement to Journal of Paleontology), 74(4), 104 pp.

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

RASETTI, F. 1967. Lower and Middle Cambrian trilobite faunas from the Taconic Sequence of New York. Smithsonian Miscellaneous Collections, 152(4): 112 pp.

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.

WESTERGÅRD, A. H. 1936. Paradoxides oelandicus beds of Oland: with the account of a diamond boring through the Cambrian at Mossberga. Sveriges Geologiska Undersökning. Series C, no. 394, Årsbok 30, no. 1: 1-66.

Other Links: