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New records of Burgess Shale-type taxa from the middle Cambrian of Utah

Published online by Cambridge University Press:  01 October 2015

Simon Conway Morris ,
Paul A. Selden ,
Glade Gunther ,
Paul G. Jamison  and
Richard A. Robison
Simon Conway Morris
Affiliation:
Department of Earth Sciences, University of Cambridge, Cambridge, CB2 3EQ, UK
Paul A. Selden
Affiliation:
Department of Geology, University of Kansas, Lawrence, Kansas 66045-7594, USA ; Natural History Museum, London, SW7 5BD, UK
Glade Gunther
Affiliation:
Brigham City, Utah 84302, USA
Paul G. Jamison
Affiliation:
JPS Inc., Logan, Utah 84321, USA
Richard A. Robison
Affiliation:
Department of Geology, University of Kansas, Lawrence, Kansas 66045-7594, USA ;
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Abstract

Cambrian strata of the Laurentian craton contain numerous examples of Burgess Shale–type faunas. Although displaying a more or less concentric distribution around the cratonal margin, most faunal occurrences are in present-day western North America, extending from the Northwest Territories to California. Nevertheless, the soft-bodied and lightly skeletalized fossils in most of these Lagerstätten are highly sporadic. Here, we extend knowledge of such Middle Cambrian occurrences in Utah with reports of four taxa. An arthropod from the Marjum Formation, Dytikosicula desmatae gen. et sp. nov., is a putative megacheiran. It is most similar to Dicranocaris guntherorum, best known from the younger Wheeler Formation, but differs primarily in the arrangement of pleurae and overall size. Along with a specimen of ?Yohoia sp, a new species of Yohoia, Y. utahana sp. nov., is described. It differs from the type and only known species, Y. tenuis, principally in its larger size and shorter exopods; it is the first description of this genus from outside the Burgess Shale. A new species of a stem-group lophotrochozoan from the Spence Shale, Wiwaxia herka sp. nov., possesses a palisade of dorso-lateral spines that are more robust and numerous than the type species of Wiwaxia, W. corrugata. Another notable taxon is Eldonia ludwigi from the Marjum Formation, which is interpreted as a primitive ambulacrarian (assigned to the cambroernids) and a new specimen of the ?cnidarian Cambrorhytium from the Wheeler Shale is illustrated.

Information

Type
Articles
Information
Journal of Paleontology , Volume 89 , Issue 3 , May 2015 , pp. 411 - 423
Copyright
Copyright © 2015, The Paleontological Society 

Introduction

The soft-bodied and lightly skeletalized fossils of the Burgess Shale–type biotas have had a profound impact on our understanding of the major radiations of the early metazoans, an event colloquially referred to as the Cambrian “explosion” (e.g., Conway Morris, Reference Conway Morris1998; Marshall, Reference Marshall2006). To date, only three occurrences are especially prolific. These are the type locality in British Columbia, Canada (and adjacent outcrops, see Collins et al., Reference Collins, Briggs and Conway Morris1983), the Chengjiang localities around Kunming, Yunnan, China (e.g., Chen and Zhou, Reference Chen and Zhou1997; Zhang et al., Reference Zhang, Liu and Zhao2008), and Sirius Passet, Peary Land, North Greenland (e.g., Conway Morris and Peel, Reference Conway Morris and Peel1995, Reference Conway Morris and Peel2008; Reference Conway Morris and Peel2010; Budd, Reference Budd2011; Daley and Peel, Reference Daley and Peel2010; Ineson and Peel, Reference Ineson and Peel2011; Peel and Ineson, Reference Peel and Ineson2011). This is not to say that other localities do not have very considerable potential: most notable in this respect are faunas from the Emu Bay Shale of South Australia (e.g., Paterson et al., Reference Paterson, Edgecombe, García-Bellido, Jago and Gehling2010, Reference Paterson, García-Bellido, Lee, Brock, Jago and Edgecombe2011; Edgecombe et al., Reference Edgecombe, García-Bellido and Paterson2011) and in South China both the Kaili deposits from Guizhou, (e.g., Zhao et al., Reference Zhao, Yuan, Zhu, Yang and Peng2003, Reference Zhao, Zhu, Babcock, Yuan, Parsley, Peng, Yang and Wang2005; Lin, Reference Lin2006; Yang et al., Reference Yang, Zhao, Yang, Da and Wu2011) and new assemblages (Guanshan, Xiaoshiba) adjacent to Kunming (e.g. Hu et al., Reference Hu, Zhu, Steiner, Luo, Zhao and Liu2010; Yang et al., Reference Yang, Ortega-Hernández, Butterfield and Zhang2013).

Although these localities rightly enjoy the lion’s share of attention, in terms of present-day geography, the lower and middle Cambrian Burgess Shale-type faunas (broadly construed: Conway Morris, Reference Conway Morris1989; Butterfield, Reference Butterfield1995) are widely distributed, with records from western Canada (e.g., Copeland, Reference Copeland1993; Butterfield and Nicholas, Reference Butterfield and Nicholas1996; Randell et al., Reference Randell, Liebermann, Hasiotis and Pope2005; Johnston et al., Reference Johnston, Johnston and Powell2009; Caron et al., Reference Caron, Gaines, Mángano, Streng and Daley2010; Kimmig and Pratt, Reference Kimmig and Pratt2015), eastern United States (e.g., Skinner, Reference Skinner2005; Schwimmer and Montante, Reference Schwimmer and Montante2007; Conway Morris and Peel, Reference Conway Morris and Peel2010), Russia (e.g., Repina and Okuneva, Reference Repina and Okuneva1969; Friend et al., Reference Friend, Zhuravlev and Solov’ev2002; Ivantsov et al., Reference Ivantsov, Zhuravlev, Leguta, Krassilov, Melnikova and Ushatinskaya2005), Australia (e.g., Jago and Anderson, Reference Jago and Anderson2004; Ortega-Hernandez et al., Reference Ortega-Hernández, Braddy, Jago and Baillie2010), Europe (e.g., Conway Morris and Robison, Reference Conway Morris and Robison1986; Chlupáč and Kordule, Reference Chlupáč and Kordule2002; García-Bellido et al., Reference García–Bellido, Alvarez, Gamez Vintaned, Liñán and Gozalo2011; Gámes Vintaned et al., Reference Gámes Vintaned, Liñán and Zhuravlev2011), and China (e.g., Steiner et al., Reference Steiner, Hu, Liu and Keupp2012; Xiao et al., Reference Xiao, Hu, Yuan, Parsley and Cao2005; Zhang and Hua, Reference Zhang and Hua2005; Liu, Reference Liu2013; Sun et al., 2013).

It remains the case, however, that in a significant number of these latter Burgess Shale–type localities, the quality of preservation may be impressive, but the range of material is relatively limited and has only been obtained as the result of intensive and protracted seasons of collecting. This applies, for example, to a series of localities in the western United States, most of which are in Utah. Outcrops in the Latham Shale (Gaines and Droser, Reference Gaines and Droser2002), Poleta Formation (English and Babcock, Reference English and Babcock2010), Pioche Formation (e.g., Webster et al., Reference Webster, Gaines and Hughes2008), Spence Shale (e.g., Conway Morris and Robison, Reference Conway Morris and Robison1988; Liddell et al., Reference Liddell, Wright and Brett1997; Gaines and Droser, Reference Gaines and Droser2005; Garson et al., Reference Garson, Gaines, Droser, Liddell and Sappenfield2012), Wheeler Formation (e.g., Conway Morris and Robison, Reference Conway Morris and Robison1986; Gaines et al., Reference Gaines, Kennedy and Droser2005; Halgedahl et al., Reference Halgedahl, Jarrard, Brett and Allison2009; Stein et al., Reference Stein, Church and Robison2011), Marjum Formation (e.g., Gaines and Droser, Reference Gaines and Droser2010), and Weeks Formation (e.g., Bonino and Kier, Reference Bonino and Kier2010; Robison and Babcock, Reference Robison and Babcock2011; Lerosey-Aubril et al., Reference Lerosey-Aubril, Ortega-Hernandez, Kier and Bonino2013) have yielded a series of Burgess Shale-type fossils. These include non-trilobite arthropods, priapulids, sponges and chancelloriids, as well as several taxa, notably the medusiform Eldonia and cataphract Wiwaxia, whose systematic positions have been more contentious. To the existing literature on these localities scattered across the Great Basin (e.g., Rigby, Reference Rigby1983; Gunther and Gunther, Reference Gunther and Gunther1981; Briggs and Robison Reference Briggs and Robison1984; Robison, Reference Robison1991; Conway Morris and Robison, Reference Conway Morris and Robison1986, Reference Conway Morris and Robison1988; Rigby et al., Reference Rigby, Gunther and Gunther1997; Waggoner and Hagadorn Reference Waggoner and Hagadorn2004; Briggs et al., Reference Briggs, Lieberman, Halgedahl and Jarrard2005; Cartwright et al., Reference Cartwright, Halgedahl, Hendricks, Jarrard, Marques, Collins and Lieberman2007; Halgedahl et al., Reference Halgedahl, Jarrard, Brett and Allison2009; Moore and Lieberman, Reference Moore and Lieberman2009; Conway Morris and Peel, Reference Conway Morris and Peel2010; Gaines and Droser, Reference Gaines and Droser2010) we now add some significant new finds. These include an articulated specimen of a new species of Wiwaxia (Spence Shale), arthropods in the form of Dytikosicula desmatae gen. et sp. nov. (Marjum Formation), as well as specimens of ?Yohoia sp. and Yohoia utahana sp. nov. (Spence Shale), and a large specimen of Eldonia (Marjum Formation). In passing, we also draw attention to a specimen of the questionable cnidarian Cambrorhytium (Wheeler Formation).

Methods

Specimens were photographed with Canon 5D MkII and MkIII cameras (Canon U.S.A. Inc., Melville, NY) mounted on Leica MZ12.5 and MZ16 stereomicroscopes, either dry or under 70% ethanol, and in cross-polarized light using a ring light and/or low-angle illumination with polarizing filters, and a polarizing filter in front of the objective lens. For each specimen, several photographs were taken at different levels of focus and then stacked using Adobe Photoshop CS6 (Adobe Systems Inc., San Jose, CA) to ensure all parts of each specimen were in focus. For some larger specimens, a mosaic of photographs was taken and these were then merged using Photoshop (see Selden, Reference Selden2014 for further details). Drawings were made using camera lucida attachments to the microscopes and digitized using iDraw 2.4 (www.indeeo.com).

Systematic paleontology

Specimens are housed in the University of Kansas Natural History Museum, Lawrence, Kansas (KUMIP prefix) and the Sedgwick Museum, University of Cambridge (SM prefix).

Phylum Arthropoda von Siebold, Reference von Siebold1848

Family Yohoiidae Henriksen, Reference Henriksen1928

Genus Yohoia Walcott, Reference Walcott1912

Type species

Yohoia tenuis Walcott, Reference Walcott1912.

Yohoia utahana new species

Figure 1.1–1.4

Diagnosis

Relatively large (approximately 30 mm), tergites 10–13 bear tergopleurae, expods short with large spines, and mostly covered by tergopleurae.

Description

Large Yohoia, body length 30.9 mm (including telson, excluding great appendage); straight trunk; head shield with median smooth portion, and large lateral area with strongly curved margins divided into three regions. Anterior border of median part of head shield expanded slightly anteriorly, beyond procurved line (Fig. 1.1, 1.2). Pair of eyes situated anteriorly beyond anterior margin of head shield. Great appendage consisting of proximal element emerging from beneath anterior head shield between eyes, extending downwards not beyond lateral edges of head shield, followed by distal element extending upwards. Trunk of 13 segments, increasing in length from approximately 1.0 mm (1), through approximately 1.5 mm (5–9) to approximately 2.0 mm (11–13), and telson. Tergites show slight posterior imbrication. Tergopleura of tergite 1 lobate, narrower (transversely) than other tergites, partly covered by posterior margin of head shield. Tergopleurae 2–9 lobate, with recurved anterior margin, curved tip, procurved posterior margin (Fig. 1.1, 1.2). Curvature of anterior and posterior margins increases posteriorly, so tergopleurae of more posterior tergites appear more swept back. Tergopleura 10 with recurved anterior margin, short pointed posterior angle. Tergopleurae 11–13 narrower (transversely), with short sharply pointed posterior angles. Trunk limbs with exopod and endopodal rami. At least 6 endopods, associated with trunk segments 1–5, 8 (Fig. 1.3, 1.4); exopods on trunk segments 1–9, not seen on segments 10–13. Endopods slender, at least distally where seen protruding from beneath head shield or tergopleurae, tapering distally. Exopods appear as fan of stout bristles, connected by organic material (?setules), curving backwards and downwards, extending only slightly beyond margins of tergopleurae. Telson spatulate, lineations on surface, straight posterior margin bearing zigzag pattern of short spines.

Figure 1

Yohoia utahana sp. nov., holotype, KUMIP 357406. (1) photograph of part; (2) interpretative camera-lucida drawing of part; (3) photograph of counterpart; (4) interpretative camera-lucida drawing of counterpart. e, eye; ex1, ex2, etc. exopods; en1, en2, etc., endopods; ga, great appendage; tp, tergopleura. Grey areas indicate possible gut trace; black shows black particles within possible gut (Fig. 1.2). Dashed lines on Figure 1.4 indicate outline of darker color representing organic material between exopod spines. Scale bars represent 5 mm.

Holotype

KUMIP 357406, only known specimen (collected by PMJ), part and counterpart.

Etymology

After Utah, the state in which the specimen was found.

Occurrence

Spence Shale Member, Langston Formation (Hintze, Reference Hintze1988, Chart 15), lower Middle Cambrian, polymerid Glossopleura Zone (Robison, Reference Robison1976). Locality is about 35 m above base of Spence Shale, Miner’s Hollow, Wellsville Mountain, Box Elder County, Utah.

Remarks

Terminology follows Haug et al. (Reference Haug, Waloszek, Maas, Liu and Haug2012). It is not straightforward differentiating morphology from abiogenic marks in the matrix, such as with a scattering of darker patches, particularly near the anterior of the specimen. A suboval patch near the apex of the head shield resembles an eye. However, in cross-polarized light, the putative eye shows a slightly different coloration, indicating that the suboval patch is matrix. Similarly, matrix patches align with the endopods but these, too, are not thought to be part of the animal.

The body is laterally compressed. Anteriorly, however, the head region has rotated longitudinally. Previous reconstructions of Yohoia (Whittington, Reference Whittington1974; Haug et al., Reference Haug, Waloszek, Maas, Liu and Haug2012) show the eyes to be near the top of the head shield, adjacent to the base of the lateral area of the head shield. In this specimen, the eye position is similarly adjacent to the base of the lateral area of the head shield, but the head shield extends further dorsally from the eye than would be the case if it were strictly a lateral compression. At the opposite end of the animal, the telson also presents a dorso-ventral aspect, similarly suggesting a degree of rotation.

The body is straight with neither curvature nor a distinct bend which would indicate a tail region. In life, however, it was clearly flexible because adjacent tergites imbricate. Cephalic appendages include a poorly preserved great appendage and a pair of eyes. With respect to the former the great appendage is poorly preserved, but appears to show a downward part emerging from the anterior of the head between the eyes, and beyond this an upward-sweeping part (the claw element). In the case of the eyes one is located between the great appendage and the head shield; the other eye is less obvious but on the part is superimposed on the base of the great appendage (Fig. 1.1, 1.2). Scattered black patches along the trunk (most obvious on segments 3–9) may be remains of the gut; the line of these coincides with the junction between the main part of each tergite and its tergopleura (Fig. 1.1, 1.2). A similar line of dark patches can be seen in the Yohoia specimens figured by Haug et al. (Reference Haug, Waloszek, Maas, Liu and Haug2012; fig. 3).

Interpretation of the tergopleurae and exopods is problematic. The part (Fig. 1.1, 1.2) shows lateral tergopleurae which extend at least the same distance from their junction with main tergite as the width of the latter. In contrast, in the type species the tergopleurae are relatively shorter than the large, flap-like structures that extend beyond the tergite edges and have been interpreted as exopods (Whittington, Reference Whittington1974; Haug et al., Reference Haug, Waloszek, Maas, Liu and Haug2012). On the counterpart (Fig. 1.3, 1.4) radiating lines resemble the fringing setae of the exopods, but they are much sparser and stouter. Moreover, rather than forming a fringe they are almost completely covered by the tergopleurae. Thus, in the new species, the exopods are shorter than in Y. tenuis (see Haug et al., Reference Haug, Waloszek, Maas, Liu and Haug2012, fig. 9). In Y. utahana, the tips of the tergopleurae do not extend beyond the lateral edge of the head shield, as do the ends of the radiating lines. The tergopleurae (in the part; Fig. 1.1, 1.2) seem, therefore, to be real, whereas the underlying radiating lines (in the counterpart, Fig. 1.3, 1.4) likely represent exopodal spines. On the counterpart (Fig. 1.3, 1.4), the matrix shows a darker hue between the exopodal spines (outlined in dashed lines on the drawing), which possibly represents organic material—perhaps masses of setules—connecting the exopodal spines.

Compared with the type and only known species of Yohoia (Y. tenuis Walcott, Reference Walcott1912), this is larger, with a body length of 30.9 mm. Length of tergites 3–5 (l1 of Haug et al., Reference Haug, Waloszek, Maas, Liu and Haug2012) is 4.2 mm, length of the head shield (l2 of Haug et al., Reference Haug, Waloszek, Maas, Liu and Haug2012) is 4.6 mm. Plotting l1/l2 (Fig. 2) on the graph of similar measurements for Y. tenuis (Haug et al., Reference Haug, Waloszek, Maas, Liu and Haug2012, fig. 2) shows Y. utahana to lie well beyond the scatter of points, at more than twice the mean for both measurements of the type species. The lateral areas of the head shield show strongly curved margins, in which respect it differs from the type species, in which these lateral areas are subquadrate (Whittington, Reference Whittington1974, text-fig. 2; Haug et al., Reference Haug, Waloszek, Maas, Liu and Haug2012). As in Y. tenuis, the lateral area is divided into three parts, and the trunk consist of 13 segments and a telson which is almost indistinguishable from that of Y. tenuis (Whittington, Reference Whittington1974).

Figure 2

Scatterplot of lengths of tergites three to five (l1) versus length of head shield (l2) of: ● Yohoia tenuis Walcott, Reference Walcott1912, and ★ Yohoia utahana sp. nov. Yohoia tenuis data from Haug et al. (Reference Haug, Waloszek, Maas, Liu and Haug2012, fig. 2).

Related genera (Stein et al., Reference Stein, Budd and Peel2013) from the Lower Cambrian Chengiang biota of China include Fortiforceps Hou and Bergström, Reference Hou and Bergström1997, which has somewhat similar exopods but lacks tergopleurae and has 20 tergites, and Jianfengia Hou, Reference Hou1987, which has even more (22) tergites. On the other hand Haikoucaris Chen, Waloszek and Maas, Reference Chen, Waloszek and Maas2004 has the same number of postcephalic tergites as Yohoia (13) and possibly similar exopods (albeit on all trunk segments), but lacks tergopleurae and has a distinct telson. Yohoia differs from all of these related genera in its distinctive head shield with the large, tripartite, lateral area, and spatulate telson composed of a single plate.

?Yohoia species indeterminate

Figure 3

Description

Single specimen occurs in dorso-ventral aspect. Most obvious feature is trunk, with at least nine segments, and prominent tergopleurae (Fig. 3). Largest of these at mid-point, and decrease markedly in size toward the presumed posterior. Broad central strand may represent gut trace. It has slight relief, and may be sediment-filled. Alternatively (considering Yohoia is not known to have a sediment-filled gut), the specimen may have split at level of tergopleurae but below level of arched dorsum, revealing matrix beneath. Both ends of specimen indistinct, but presumed anterior (head shield) approximately quadrate. Opposite end smaller and appears to be approximately circular. No appendages preserved.

Figure 3

?Yohoia sp., SM X.50206; photograph under ethanol. Scale bar represents 5 mm.

Material

SM X.50206, collected by PMJ, part only.

Occurrence

Spence Shale Member, Langston Formation, (Hintze, Reference Hintze1988, Chart 15), lower middle Cambrian, polymerid Glossopleura Zone (Robison, Reference Robison1976). Locality is approximately16 m above base of Spence Shale, as float, Miner’s Hollow, Wellsville Mountain, Box Elder County, Utah.

Remarks

Attribution to Yohoia (see Whittington, Reference Whittington1974) is provisional. Apart from size, its principal similarities are the prominent tergopleurae, and possibly the head-shield. Unlike Yohoia, however, the tergopleurae are prominent to the last (visible) trunk segment

Genus Dytikosicula new genus

Diagnosis

As for the species.

Type species

Dytikosicula desmatae new species.

Etymology

Based on the Greek west (dytikos) and small dagger (sicula), and is a combined reference to both the geographical area and the recurved paratergal extensions.

Remarks

This new taxon is similar to Dicranocaris (Briggs et al., Reference Briggs, Lieberman, Hendricks, Halgedahl and Jarrard2008). Phylogenetic relationships of Cambrian arthropods are not fully resolved but Dicranocaris appears to be a megacheiran (Ortega-Hernández et al., Reference Ortega-Hernández, Legg and Braddy2013; see also Hendricks and Lieberman, Reference Hendricks and Lieberman2008).

Dytikosicula desmatae new species

Figures 4.1–4.2, 5.1–5.2

1981 ?Molaria-like trilobitomorph, Gunther and Gunther, pl. 48B.

1991 ?Alalcomenaeus cf. cambricus (Simonetta); Robison, p. 86, fig. 7.10.

2008 ?Dicranocaris guntherorum Briggs et al., p. 245, figs 5.4–9 [non figs. 5.1–3].

Diagnosis

Subcircular head shield and trunk with at least six tergites, all with prominent pleurae. It differs from Dicranocaris by trunk segment one bearing pleura, and pleurae more arcuate. Head shield similar, but dorsal outline more circular.

Description

Single specimen (Figs. 4, 5) preserved in dorsal aspect, lacks posterior section. Head shield suboval in outline, with smooth margins and gently concave posterior margin abutting first thoracic segment. No evidence for eyes. Trunk undifferentiated, but bears six rather prominent pleural extensions, quite strongly recurved posteriorly and well separated. Posterior end incomplete. No appendages preserved.

Figure 4

Dytikosicula desmatae gen. et sp. nov., holotype, SM X.50203. (1) photograph dry in low-angle light; (2) photograph under ethanol. Scale bars represent 5 mm.

Figure 5

Interpretative camera-lucida drawing of Dytikosicula desmatae gen. et sp. nov., compare Figure 4. hd, head shield; pl 1, pl 2, etc., pleurae 1–6. Scale bar represents 5 mm.

Holotype

SM X.50203, holotype and only known specimen, part only. Specimen originally collected by Robert Drachuk, and donated by Charlie Magovern.

Etymology

Refers to the proposed link (Greek, desmos, bond or chain) to other Cambrian megacheirans.

Occurrence

Marjum Formation, middle Cambrian. Locality is west of Delta, House Range, Utah.

Remarks

Specimen shows characteristic Burgess Shale-type preservation (e.g. Briggs et al., Reference Briggs, Lieberman, Hendricks, Halgedahl and Jarrard2008). Otherwise parts of the fossil have a brownish mineral adhering which may represent the original skeleton, apparently uncalcified. Associated with part of the thorax are granular areas, probably representing diagenetic mineral growth (?pyrite). These are not obviously consistent with any soft-part anatomy, but may have resulted from decaying tissue.

This new taxon is most similar to the megacheiran Dicranocaris guntherorum Briggs et al., Reference Briggs, Lieberman, Hendricks, Halgedahl and Jarrard2008, best known from the Wheeler Formation but is also recorded from the Marjum Formation. Detailed comparisons are hindered because the best preserved specimen of D. guntherorum is more complete than the sole specimen of D. desmatae, and is buried at an oblique angle in comparison to the dorso-ventral attitude of the specimen described here. The most obvious difference is that whereas in D. guntherorum the pleural extensions of the trunk are limited to segments 2 to 5, in D. desmatae each of the preserved segments bears pleura. In addition and making allowances for the different angles of burial, the head of D. desmatae appears to be somewhat more circular. Deciding whether Dytikosicula desmatae is a distinct taxon, or better interpreted as another species of Dicranocaris is to some extent a matter of judgement. Generic distinction, however, is warranted not only by the differences noted, but also the conspicuously larger size of the holotype. In this context it is tentatively suggested that other material (albeit from the Wheeler Formation) and attributed questionably to D. guntherorum by Briggs et al. (Reference Briggs, Lieberman, Hendricks, Halgedahl and Jarrard2008; figure 5.4–9; see also Gunther and Gunther, Reference Gunther and Gunther1981; Robison, Reference Robison1991) not only falls into the same size range of D. desmatae but may be better accommodated in this taxon. Thus despite poor preservation these specimens (all in lateral view) show some evidence for a pleuron on the first trunk segment (see also Gunther and Gunther, Reference Gunther and Gunther1981, pl. 48; the precise interpretation of these structures diverged amongst the authors contributing to Briggs et al. (Reference Briggs, Lieberman, Hendricks, Halgedahl and Jarrard2008)).

It is also worth noting a possible relationship to the arthropod Serracaris lineata Briggs, Reference Briggs1978, which is known only from the Lower Cambrian Kinzers Formation of Pennsylvania. All specimens of this taxon are incomplete, but available material consists of an elongate trunk consisting of at least fifteen tergites with recurved extensions. The most obvious differences are that in Serracaris these tergal extensions on either side appear to be double. In addition, one segment towards the anterior end has conspicuously larger extensions, although there they appear to have been single. Briggs (Reference Briggs1978, Pl. 1, fig. 4) drew attention to a possible anterior carapace. Because of its unique occurrence he regarded it, however, as probably fortuitous. It does, however, have some similarity to the head shield of Dytikosicula, but in Serracaris it appears proportionally larger and possibly wider. Although the posterior end of the unique specimen of D. desmatae is not preserved, Briggs et al. (Reference Briggs, Lieberman, Hendricks, Halgedahl and Jarrard2008) drew attention in D. guntherorum to “the unique morphology of the telson” (p. 245) with its terminal bifurcation. Although these authors made no comparison, Serracaris also possesses a bifurcate telson (Briggs, Reference Briggs1978). Serracaris is, of course, stratigraphically somewhat older than Dytikosicula. From the Eldon Formation of British Columbia Briggs (Reference Briggs1978, text fig. 2a, b) described a more nearly contemporaneous form to D. desmatae as Serracaris?. The unique specimen is poorly preserved, and appears to have had more spinose tergal projections.

Stem-group Lophotrochozoa

Remarks

Current consensus regards the wiwaxiids as having a molluscan affinity (e.g. Yang et al., Reference Yang, Smith, Lan, Hou and Zhang2014). Our material throws no further light on this question, and we prefer to take a more agnostic view of their wider relationships, placing them within the lophotrochozoans but not shoe-horning them into a specific phylum.

Family Wiwaxiidae Walcott, Reference Walcott1911a;

Remarks

Wiwaxiids are best known from articulated material of Wiwaxia corrugata (Matthew, Reference Matthew1899) from the Phyllopod Bed of the Burgess Shale (Conway Morris, Reference Conway Morris1985). Also occurring in this deposit in moderate abundance are isolated sclerites (and rarely partial associations), detached from the cataphract scleritome either by deciduous action or upon death and post-mortem scattering (see also Butterfield, Reference Butterfield1990; Mankiewicz, Reference Mankiewicz1992). Sclerites are also known from the Lower and Middle Cambrian of northwestern Canada (e.g. Butterfield and Nicholas, Reference Butterfield and Nicholas1996), South China (e.g. Y-L. Zhao et al., Reference Zhao, Qian and Li1994, Reference Zhao, Zhu, Babcock, Yuan, Parsley, Peng, Yang and Wang2005; Harvey et al., Reference Harvey, Ortega-Hernández, Lin, Zhao and Butterfield2012; Sun et al., Reference Sun, Zhao, Peng and Yang2014; Yang et al., Reference Yang, Smith, Lan, Hou and Zhang2014; F-C. Zhao et al., Reference Zhao, Smith, Yin, Zeng, Hu, Li and Zhu2015), Utah (Conway Morris and Robison, Reference Conway Morris and Robison1988), Australia (Porter, Reference Porter2004), Czech Republic (Fatka et al., Reference Fatka, Kraft and Szabad2011) and Siberia (Ivantsov et al., Reference Ivantsov, Zhuravlev, Leguta, Krassilov, Melnikova and Ushatinskaya2005). These records collectively indicate that the individual sclerites were probably robust and relatively resistant to decay. In contrast, articulated wiwaxiids are very rare. Apart from the Burgess Shale examples (Conway Morris, Reference Conway Morris1985) and recent discoveries from the Xiaoshiba Lagerstätte (Yang et al., Reference Yang, Smith, Lan, Hou and Zhang2014) and the Kaili Formation (Zhao et al., Reference Zhao, Qian and Li1994, Reference Zhao, Zhu, Babcock, Yuan, Parsley, Peng, Yang and Wang2005, Pl. II, fig. 2; also Sun et al., 2013, fig. 6) in China, our report is the only known occurrence of an articulated specimen from Laurentia.

Genus Wiwaxia Walcott, Reference Walcott1911a

Type species

Wiwaxia corrugata (Matthew, Reference Matthew1899).

Wiwaxia herka new species

Figure 6.1–6.8

Diagnosis

A wiwaxiid with a prominent palisade of recurved and stout dorso-lateral spines. Differs from type species in larger number of spines and their degree of robustness.

Description

Single articulated specimen (Fig. 6.1, 6.2) preserved in approximately lateral view, shows a fairly pronounced dorso-ventral curvature (cf., Conway Morris, Reference Conway Morris1985, figs. 82, 83, 88). Most obvious feature is palisade of dorso-lateral spines. These are quite stout, posteriorly recurved, closely spaced. Those on the right-hand side (in the part) are clearest, with a total of 13 visible. Near the anterior end, a few spines of the opposite side are visible at a lower level. Three anterior-most spines are somewhat shorter (about half the length of others), whereas remainder longer and sub-equal length, except at posterior where again last one or two shorter. Remaining sclerites, that mantled dorsal and lateral regions of the body, only moderately well preserved, but components of the lateral and ventro-lateral series are identifiable. In addition to the articulated specimen, six isolated sclerites are available. Based on the characteristic recurved shape, three (KUMIP 286300, 286302) are identified as ventro-lateral (equivalent to siculate; see Conway Morris and Peel, Reference Conway Morris and Peel1995 [Fig. 6.3, 6.7, 6.8]). Another two sclerites (KUMIP 286300, 286301), one of which is poorly preserved, are more elongate and probably represent lateral (=cultrate) sclerites (Fig. 6.4, 6.5). Finally, one sclerite (KUMIP 286301) may be from the dorsal region (Fig. 6.6).

Figure 6

Wiwaxia herka sp. nov. (1) holotype, KUMIP 287449; (2) holotype, interpretative camera-lucida drawing, compare Figure 6.1 Fine lines represent striations on sclerites; other lines partial outlines of compressed sclerites. Hachure on lower side is edge of excavated sediment. ant, anterior; l sl, lateral sclerites; v-l sl, ventro-lateral sclerites. Dorso-lateral spines numbered consecutively from anterior; numbers with asterisks refer to left side, others more complete series on right side; (3–5) KUMIP 286300: (3) isolated ventro-lateral sclerite (part only); (4) isolated ?lateral sclerite, part; (5) isolated ?lateral sclerite, counterpart; (6) KUMIP 286301 isolated ?dorsal sclerite (part only); (7) KUMIP 286302 isolated ventro-lateral sclerite, part; (8) KUMIP 286302, isolated ventro-lateral sclerite, counterpart. All photographs taken dry under cross-polarized illumination. Scale bars represents 5 mm (1, 2), 1 mm (3–8).

Holotype

KUMIP 287449, holotype, part and counterpart (Fig. 6.1, 6.2), collected by Glade Gunther. Paratypes, KUMIP 286300 (part with two sclerites, counterpart with opposite side of ?lateral sclerite only) (Fig. 6.3–6.5), 286301 (Fig. 6.6), 286302 (part and counterpart) (Fig. 6.7, 6.8), donated by Lloyd Gunther.

Etymology

From herka (Greek, fence), in reference to the palisade of spines.

Occurrence

Spence Shale Member, Langston Formation (Hintze, Reference Hintze1988, Chart 15), lower Middle Cambrian, polymerid Glossopleura Zone (Robison, Reference Robison1976). Locality is approximately 3 m below top of Spence Shale, south side of Antimony Canyon on west side of Wellsville Mountain; NW¼ sec. 31, T. 10 N., R. 1 W.; approximately 4 km north of Brigham City, Box Elder County, Utah. Other biota from the same locality, mostly collected by members of the Lloyd Gunther family, include trilobites Amecephalus idahoense (Resser, Reference Resser1939a), Athabaskia wasatchensis (Resser, Reference Resser1939b), Glossopleura gigantea ? Resser, Reference Resser1939a, Glossopleura sp., Kootenia mendosa Resser, Reference Resser1939a, and Zacanthoides idahoensis Walcott, Reference Walcott1908; other arthropods Meristosoma paradoxum Robison and Wiley, Reference Robison and Wiley1995, Hurdia indet. sp. (Daley et al., Reference Daley, Budd and Caron2013) and an undetermined taxon with large axial spine on rear shield; undetermined articulate brachiopods; echinoderms Ctenocystis utahensis Robison and Sprinkle, Reference Robison and Sprinkle1969, and Gogia sp. nov.; a hemichordate (see Loduca et al., Reference Loduca, Caron, Schiffbauer, Xiao and Kramer2013) Yuknessia simplex Walcott, Reference Walcott1919; hyolith Hyolithes carinatus Babcock and Robison, Reference Babcock and Robison1988; sponge Vauxia gracilenta? Walcott, Reference Walcott1920; worms Ottoia prolifica Walcott, Reference Walcott1911a, and Selkirkia sp.; other animal taxa, Eldonia ludwigi Walcott, Reference Walcott1911b, and Scenella sp.; large coprolites (cf. Conway Morris and Robison, Reference Conway Morris and Robison1988, fig. 32); and algae Marpolia spissa Walcott, Reference Walcott1919.

Remarks

Erection of new species Wiwaxia herka is based on a single articulated specimen, seems justified on account of the distinctiveness of its dorso-lateral spines. In contrast to W. corrugata (Conway Morris, Reference Conway Morris1985) spines are more densely arrayed (approximately 12 versus an average of approximately 8) and less elongate. On the unproven assumption that the isolated sclerites (Fig. 6.3–6.8) derive from the same species, the ventro-lateral ones appear similar to those of W. corrugata, whereas the ?lateral and ?dorsal sclerites appear to be more elongate. W. herka is evidently closely related to W. corrugata, but differs more obviously from other lower Cambrian taxa from China (Zhao et al., Reference Zhao, Qian and Li1994; Yang et al., Reference Yang, Smith, Lan, Hou and Zhang2014) in being substantially larger and possessing spines (also absent in juvenile W. corrugata: Conway Morris Reference Conway Morris1985).

This new species confirms the basic arrangement of the wiwaxiid scleritome, but does not throw further light on their phylogenetic position within the lophotrochozoans. One approach is to treat wiwaxiids as stem-group annelids. This is on the dual supposition of the similarities of the sclerite microstructure to annelidan chaetae (Butterfield, Reference Butterfield1990; see also Conway Morris and Peel, Reference Conway Morris and Peel1995) and the inferred transformation of the scleritome into parapodial bundles capable of locomotion and defense (Conway Morris and Peel, Reference Conway Morris and Peel1995; Struck, Reference Struck2011). Arguments, especially on the nature of the radula-like mouth-parts (Smith, Reference Smith2012) and similarities to Odontogriphus (Caron et al., Reference Caron, Scheltema, Schander and Rudkin2006) on the other hand point to a molluscan affinity (see also Smith, Reference Smith2014). By itself, W. herka can add nothing material to this discussion, but it is worth emphasizing that if the wiwaxiids belong to a stem-group identified as the halwaxiids (Conway Morris and Caron, Reference Conway Morris and Caron2007) then shoe-horning them into a given phylum may serve to obscure how crucial anatomical transitions were achieved among which end-results are the setae of annelids (and brachiopods) or radula of mollusks.

Superphylum Ambulacraria Metschnikoff Reference Metschnikoff1881

Stem-group Cambroernids

Remarks

The cambroernids is an un-ranked informal stem group (Caron et al., Reference Caron, Gaines, Mángano, Streng and Daley2010).

Family Eldoniidae Walcott, Reference Walcott1911b

Genus Eldonia Walcott, Reference Walcott1911b

Type species

Eldonia ludwigi Walcott, Reference Walcott1911b.

Eldonia ludwigi Walcott, Reference Walcott1911b

Figure 7.1–7.2

Description

New specimen, part and counterpart, incomplete with slightly more than half disc preserved. Maximum width approximately 80 mm. Principal features (Fig. 7) visible are part of gut (and associated coelomic cavity) and disc. Latter consists of two fairly distinct regions. Inner zone traversed by series of widely spaced radial lines, which are probably on surface of disc. Outer region bears semi-continuous groove (in part) and otherwise subdued concentric wrinkles. Half of disc, which might have shown the feeding apparatus, not preserved.

Figure 7

Eldonia cf ludwigi Walcott 1911, SM X.50204.1; (1) photographed dry in low-angle light; (2) photographed under ethanol. Scale bars represent 10 mm.

Material

SM X.50204.1 (part) and SM X.50204.2 (counterpart), collected by Paul Jamison.

Occurrence

Middle part of Marjum Formation, mid-middle Cambrian, Ptychagnostus punctuosus Zone. Locality is Marjum Pass, House Range, Millard County, Utah.

Remarks

Specimen from the same stratigraphic horizon was described by Conway Morris and Robison (Reference Conway Morris and Robison1988, figs. 28, 29). To first approximation new specimen is similar, but preserves outer parts of the disc more clearly.

The medusiform eldoniids (and rotadiscids) are a characteristic component of Burgess Shale-type faunas. In addition to their type occurrence in the Burgess Shale (Walcott, Reference Walcott1911b; Durham, Reference Durham1974; Friend, Reference Friend1995), this group is recorded from other Lower (e.g., Chen et al., Reference Chen, Zhu and Zhou1995; Chen and Zhou, Reference Chen and Zhou1997) and Middle Cambrian localities in China (Zhao and Zhu, Reference Zhao and Zhu1994; Dzik et al., Reference Dzik, Zhao and Zhu1997), Siberia (Friend et al., Reference Friend, Zhuravlev and Solov’ev2002), Poland (Masiak and Zylińska, Reference Masiak and Żylińska1994), and Utah (Conway Morris and Robison, Reference Conway Morris and Robison1988) Taxonomic affinities of the eldoniids have remained controversial (e.g., Zhu et al., Reference Zhu, Zhao and Chen2002). One suggestion has been to link them to the lophophorates (e.g., Dzik et al., Reference Dzik, Zhao and Zhu1997). More popular has been to pursue a relationship either to the echinoderms (e.g., Friend, Reference Friend1995) or a more specific proposal that they are actual holothurians, an idea that stems back to the time of C.D. Walcott (e.g., Clark, Reference Clark1912) and has received recurrent support (e.g., Durham, Reference Durham1974; Hou and Bergström, Reference Hou and Bergström2003). The description of the related Herpetogaster collinsi from British Columbia (Caron, Conway Morris and Shu, Reference Caron, Conway Morris and Shu2010; see also Caron et al., Reference Caron, Gaines, Mángano, Streng and Daley2010) suggests, however, that this taxon, along with Eldonia and Phlogites, are stem-group ambulacrarians forming an informal group known as the cambroernids that lies close to the echinoderm-hemichordate divergence.

Wider significance

While these finds augment existing knowledge of otherwise rare taxa, it is worth reviewing some wider implications of this work. First, as noted, Dytikosicula desmatae gen. et sp. nov. appears to be a megacheiran, closely related to Dicranocaris guntherorum. In the wider context of Cambrian arthropod evolution (e.g., Budd and Telford, Reference Budd and Telford2009; Edgecombe, Reference Edgecombe2010) the overall diversity of known taxa is striking, and reports of more poorly preserved material (e.g., Halgedahl et al., Reference Halgedahl, Jarrard, Brett and Allison2009; Johnston et al., Reference Johnston, Johnston and Powell2009; Caron et al., Reference Caron, Gaines, Mángano, Streng and Daley2010) that in at least some cases represent new forms (e.g. Legg, Reference Legg2013) suggest that our documentation of arthropod morphospace is incomplete. Thus, in the context of the description of Dytikosicula and its phylogenetic proximity to Dicranocaris, this indicates a relatively densely occupied area of morphospace, but a cursory glance at other Cambrian megacheirans (see Hendricks and Liebermann, 2008) suggests otherwise a considerable disparity. So too the identification of a new species of Yohoia hints at another more densely populated area of arthropod morphospace.

While the collection of Burgess Shale-type fossils from Middle Cambrian localities in the western United States has proved to be a relatively slow process, these new finds serve two useful purposes. First, they confirm that the diversity of these faunas remains incompletely documented. Second, they reinforce the notion of a Burgess Shale–type fauna that arguably is typical of Cambrian shelf seas, although this is not to dispute environmental controls on the make-up of particular assemblages. In general, however, the Burgess Shale-type faunas differ more in the details rather than general aspect. Although the majority of assemblages were deposited in offshore, even deeper water, and in conditions of low oxygen (e.g., Gaines and Droser, Reference Gaines and Droser2010), shallower water locales are also known (e.g., Copeland, Reference Copeland1993; Schwimmer and Montante, Reference Schwimmer and Montante2007; Gehling et al., Reference Gehling, Jago, Paterson, García-Bellido and Edgecombe2011; see also Masiak and Zylińska, Reference Masiak and Żylińska1994). Collectively, these confirm a broad faunal identity characterized by arthropods, sponges, priapulids as well as eldoniids (and less frequently groups such as chordates, polychaetes and vetulicolians), along with a variety of typical Cambrian shelly taxa (trilobites, hyoliths, brachiopods). Despite this common identity, subtle distinctions may ultimately reveal paleoenvironmental controls that may in turn refine our understanding of the ecological preferences of at least some taxa. A useful test case involves the arthropod Marrella. Known from an incomplete specimen from the Lower Cambrian Balang Formation of Hunan (Liu, Reference Liu2013) and slightly more abundantly from the lower Middle Cambrian Kaili Fossil-Lagerstätte of Guizhou (Zhao et al., Reference Zhao, Yuan, Zhu, Yang and Peng2003), prior to these reports Marrella was effectively known only from the Phyllopod bed of the Burgess Shale (Whittington, Reference Whittington1971) and immediately adjacent areas (García-Bellido and Collins, Reference García–Bellido and Collins2006), where it occurs in extraordinary abundance (e.g. García-Bellido and Collins, Reference García–Bellido and Collins2006; Caron and Jackson, Reference Caron and Jackson2008). It remains conjectural what specific environmental conditions favor the occurrences of Marrella, or indeed other highly sporadic occurrences in the Burgess Shale-type faunas, such as the annelids, chordates, or halkieriids.

Conclusions

This report augments our knowledge of Cambrian arthropods, notably in the form of Yohoia utahana sp. nov. and Dytikosicula desmatae gen. et sp. nov., and illustrates a new species of Wiwaxia. It also amplifies the occurrences of Eldonia. Finally, we also note briefly a specimen (collected by PMJ) of the tubicolous ?cnidarian Cambrorhytium (see Conway Morris and Robison, Reference Conway Morris and Robison1988) from the upper Wheeler Shale (Fig. 8) of the Drum Mountains, Millard County, Utah. The specimen (part and counterpart) is relatively small (approximately 1 cm) and at its proximal end shows relatively coarse growth lines (Fig. 8). No associated soft parts are evident.

Figure 8

Cambrorhytium sp., SM X.50205.2. Scale bar represents 5 mm.

Acknowledgments

We thank Sandra Last and Vivien Brown for technical assistance, and Martin Smith for a review of the manuscript, and referees Allison Daley and Diego Garcia-Bellido. We also thank Charlie Magovern for the gift of the holotype of Dytikosicula desmatae.

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Figure 0

Figure 1 Yohoia utahana sp. nov., holotype, KUMIP 357406. (1) photograph of part; (2) interpretative camera-lucida drawing of part; (3) photograph of counterpart; (4) interpretative camera-lucida drawing of counterpart. e, eye; ex1, ex2, etc. exopods; en1, en2, etc., endopods; ga, great appendage; tp, tergopleura. Grey areas indicate possible gut trace; black shows black particles within possible gut (Fig. 1.2). Dashed lines on Figure 1.4 indicate outline of darker color representing organic material between exopod spines. Scale bars represent 5 mm.

Figure 1

Figure 2 Scatterplot of lengths of tergites three to five (l1) versus length of head shield (l2) of: ● Yohoia tenuis Walcott, 1912, and ★ Yohoia utahana sp. nov. Yohoia tenuis data from Haug et al. (2012, fig. 2).

Figure 2

Figure 3 ?Yohoia sp., SM X.50206; photograph under ethanol. Scale bar represents 5 mm.

Figure 3

Figure 4 Dytikosicula desmatae gen. et sp. nov., holotype, SM X.50203. (1) photograph dry in low-angle light; (2) photograph under ethanol. Scale bars represent 5 mm.

Figure 4

Figure 5 Interpretative camera-lucida drawing of Dytikosicula desmatae gen. et sp. nov., compare Figure 4. hd, head shield; pl 1, pl 2, etc., pleurae 1–6. Scale bar represents 5 mm.

Figure 5

Figure 6 Wiwaxia herka sp. nov. (1) holotype, KUMIP 287449; (2) holotype, interpretative camera-lucida drawing, compare Figure 6.1 Fine lines represent striations on sclerites; other lines partial outlines of compressed sclerites. Hachure on lower side is edge of excavated sediment. ant, anterior; l sl, lateral sclerites; v-l sl, ventro-lateral sclerites. Dorso-lateral spines numbered consecutively from anterior; numbers with asterisks refer to left side, others more complete series on right side; (3–5) KUMIP 286300: (3) isolated ventro-lateral sclerite (part only); (4) isolated ?lateral sclerite, part; (5) isolated ?lateral sclerite, counterpart; (6) KUMIP 286301 isolated ?dorsal sclerite (part only); (7) KUMIP 286302 isolated ventro-lateral sclerite, part; (8) KUMIP 286302, isolated ventro-lateral sclerite, counterpart. All photographs taken dry under cross-polarized illumination. Scale bars represents 5 mm (1, 2), 1 mm (3–8).

Figure 6

Figure 7 Eldonia cf ludwigi Walcott 1911, SM X.50204.1; (1) photographed dry in low-angle light; (2) photographed under ethanol. Scale bars represent 10 mm.

Figure 7

Figure 8 Cambrorhytium sp., SM X.50205.2. Scale bar represents 5 mm.