Sheinwoodian (uppermost Lower Silurian) - GeoScienceWorld

Sheinwoodian (uppermost Lower Silurian) Radiolaria from the Cape Phillips Formation, Nunavut, Canada M. K. Jones and P. J. Noble Department of Geological Sciences and Engineering, University of Nevada Reno, MS 172, Reno, Nevada, 89557-0138, USA email: [email protected]

ABSTRACT: Radiolarians from the C. perneri-M. opimus graptolite Zone (Sheinwoodian; Wenlock) are described from a section in the Cape Phillips Formation, Nunavut, Canada, with a focus on the spherical radiolarian component (Archaeospicularia, Entactinaria, and Spumellaria). Three new genera, Involutentactinia, Perforentactinia, and Franklinia are described and the genera Labyrinthospahera, Gyrosphaera, and Haplotaeniatum are emended. Ten new species are described: Involutentactinia eccentra n. sp., containing two varieties; Involutentactinia eccentra n. sp. sensu strictu, and I. eccentra cupressa n. var.; Magnentactinia ostentata n. sp., Perforentactinia excepta n. sp., Plussatispila aethra n. sp., Franklinia tricae n. sp., F. dipulvisphaera, n. sp., Haplotaeniatum vertigospongum, n. sp., Gyrosphaera cavea n. sp., Labyrinthosphaera lancia, n. sp., and Labyrinthosphaera ? lenzi n. sp. Haplotaenitaumiids and entactiniids are dominant and respectively, comprise as much as 35% and 20% percent of the fauna in some samples. Secuicollactines represent a small but persistent component. Inaniguttids, formerly thought to be a dominant portion of upper Sheinwoodian faunas, are represented by only one inaniguttid species, P. aethra, which makes up between 0.5 to 18% of the fauna. This first detailed glimpse at the upper Sheinwoodian revises the ranges of two biostratigraphically important taxa: the first appearance of Inanihella tarangulica group taxa occurs above the C. perneri-M. opimus Zone and the last appearance of Haplotaeniatum is within the C. perneri-M. opimusZone. Revisions to the existing radiolarian biozonation of Noble and Aitchison are proposed; the Long-spined inaniguttid 2 zone now extends through the C. perneri –M. opimus Zone encompassing this fauna, and the base of the Long-spined inaniguttid 3 Zone is redefined and moved to the base of the Homerian.

INTRODUCTION A new radiolarian fauna from the Sheinwoodian (Lower Silurian) has been recovered from a section within the Cape Phillips Formation, Nunavut, Canada. This assemblage contains four new genera and ten new species that add to the knowledgebase of Paleozoic radiolarians. This and other Paleozoic taxonomic works strive to expand the biostratigraphic potential of radiolarians. Silurian radiolarian biostratigraphy is in its infancy. Recent work has demonstrated the utility of Silurian radiolarians for both local and global biostratigraphic purposes. Studies from Eurasia (Nazarov and Ormiston 1993), the Canadian Arctic (Goodbody 1981, 1982, 1986; MacDonald 1998, 1999, 2003, 2004, 2006), Japan (Furutani 1990, Wakamatsu et al. 1990), the United States (Noble 1994; Won et al. 2002; Noble et al. 1998) and Sweden (Noble and Maletz 2000) demonstrate a global distribution of some Silurian radiolarians. The aforementioned studies, utilized for biostratigraphic work, are constrained by the small number of field sites worldwide and known to contain sufficiently well-preserved radiolarians with continuous stratigraphic coverage. There remain many stratigraphic gaps within the Silurian from which there are no data. In order to fully develop Silurian radiolarian biostratigraphy, more data are needed from stratigraphic sections that are well dated by independent means and that contain well-preserved faunas with stratigraphically continuous coverage. The best preserved and most stratigraphically continuous sequence of radiolarian-bearing rocks occurs in the Canadian Arctic, specifically within the Llandovery and Wenlock sections of the Cape Phillips Formation (Goodbody 1981, 1982, 1986; Renz 1988; MacDonald 1998, 1999, 2003, 2004, 2006).

Well-preserved radiolarians are found largely in calcareous concretions, and to a lesser extent, in bioclastic limestone beds. Graptolites are abundant and provide tight age control for the sections. The field site at Rookery Creek, Cornwallis Island (text-fig. 1) contains pristinely preserved radiolarians that were collected at 0.5-1m intervals. The radiolarians recovered in the current study occur within the upper Sheinwoodian Stage of the Silurian, an interval that had not previously been examined in great detail. The study interval is confined to one graptolite zone, the Cyrtograptus perneri- Monograptus opimus Zone of Lenz and Melchin (1991) which coincides with the lower portion of the Long-spined inaniguttid Zone 3 of Noble and Aitchison (2000) (text-fig. 2). Regional Setting The Cape Phillips Formation was deposited within the Franklinian basinal province, a mildly deformed deep-water province that existed along the trailing margin of the Arctic platform from Cambrian through Early Devonian (Trettin 1989). The Cape Phillips Formation is a calcareous fine-grained shale unit rich in graptolites. It crops out on a number of islands in the Canadian Arctic Archipelago, including Cornwallis, Little Cornwallis, Devon, Bathurst, and Truro Islands, and is laterally equivalent to shelfal facies strata of the Allen Bay through Barlow Inlet Formations. The shelf break separating the Cape Phillips from its platform facies equivalents transects Cornwallis Island from the southwest to the northeast (text-fig. 1). The age of the Cape Phillips Formation is well established by graptolite biostratigraphy (Lenz 1988, 1990, 1993, 1995; Melchin 1989, 1994; Lenz and Melchin 1989, 1990, 1991) and ranges from Upper Ordovician through Lower Devonian.

micropaleontology, vol. 52, no. 4, pp. 289-315, text-figures 1-8, plates 1-7, table 1, 2006

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M. K. Jones and P. J. Noble: Sheinwoodian (uppermost Lower Silurian) Radiolaria from the Cape Phillips Formation, Nunavut, Canada

TEXT-FIGURE 1 Map showing the location of the Rookery Creek field site on Cornwallis Island. Dotted line demarcates the boundary between the graptolitic facies (dark grey area) and the shallower shelf facies.

The section collected at Rookery Creek is part of Member C of the Cape Phillips Formation (Thorsteinsson 1958). The strata are well exposed along an incised stream valley that runs westward to the ocean. A series of sections were measured in 2001 by Noble and Lenz and radiolarian samples were collected from all beds containing calcareous concretions. The exposure sampled, section 01-RC3c, occurs in the middle of member C and is a 21m thick section of interbedded calcareous and dolomitic shale that dips shallowly to the southwest (text-fig. 3). The base of section 01-RC3c is located at N75°22'0.2"/W95°44'10". Compressed graptolites are common throughout the section and Lenz provided supporting age control with field identifications. MATERIAL AND METHODOLOGY The samples from section 01-RC3c at Rookery Creek consist of 1 to 2 kg of concretion fragments, commonly from one or two concretions in a given bed. Well-preserved radiolarians were recovered from fifteen samples (text-fig. 3). Each sample was digested in dilute HCl (~5%). Residues were sieved using 63µm, 180-µm, and 500-µm sieves. The 63-µm and 180µm residues were stored in denatured alcohol as coarse and fine residues. Residues containing high amounts of organic material were cleaned by heating them in a 30% hydrogen peroxide solution. Samples containing abundant calcareous silt were heated in 30% HCl for several minutes. These procedures dramatically increased picking efficiency by removing organic clots and encrustations of silt. 290

TEXT-FIGURE 2 Chart showing the Arctic graptolite zones (Melchin, 1989; Lenz, 1990; Lenz and Melchin, 1991; Lenz, 1995) for the Llandovery through Ludlow and the unrevised radiolarian zones of Noble and Aitchison (2000) for the Silurian. The C. perneri-M. opimus graptolite zone (shaded)

is the interval studied herein.

Radiolarians were picked from fine and coarse residues using reflected light microscopy. Inititally, 200 radiolarians were picked from each fine and coarse residue, and additional specimens of each species were later picked for taxonomic study. Table 1 lists the relative abundance of each taxon per 200 count of the coarse residue. Preliminary assignments of species were made using reflected light microscopy and later substantiated and revised with the aid of transmitted light microscopy that revealed internal structures. A useful technique for examining radiolarian internal structures is thin sectioning. This “slicing” technique was developed by P. Dumitrica and is described in De Wever et al. (2001). This procedure is slightly modified herein. Radiolarian specimens were embedded in Aroclor medium for the sectioning procedure. Aroclor is a brittle resin material with a refractive index of 1.662. It melts at a low temperature, and solidifies without becoming sticky. Individual radiolarians were placed on a melted lens of Aroclor on a glass slide. The slide was heated until the radiolarian sank into the medium. After the Aroclor cooled, the surface was scraped with a razor blade under a reflected light microscope until the internal structures could be seen. The scratched surface of the medium was then smoothed by heating

Micropaleontology, vol. 52, no. 4, 2006

TABLE 1

Taxon occurrence chart showing relative abundance of radiolarians based on counts of 200 specimens in the coarse residue fraction. v = very rare (1% to 3% to 10%).

the slide on a hot plate for approximately three seconds until the surface re-melted. This method allows one or both sides of a specimen to be sectioned with minimal breakage and has revealed important internal radiolarian structures, such as the presence of internal spicules and spiraliform coiling patterns, that are used to classify radiolarians at the family and genus levels. Radiolarian Biostratigraphy

The employment of Silurian radiolarians in biostratigraphy has been attempted locally from several places in the world, including Japan (Furutani 1990; Wakamatsu et al. 1990), west Texas (Noble 1994), and more recently the Canadian Arctic (MacDonald 2003). In addition, two attempts at synthesis have been made, relying on data from all available global localities. Data, largely from Eurasia, and secondarily from North America were combined, resulting in the recognition of two assemblages of temporal significance in the Silurian (Nazarov 1988; Nazarov and Ormiston 1993), although the first and last appearances of distinctive taxa comprising these two assemblages had yet to be precisely established. A later attempt at a global biozonation by Noble and Aitchison (2000) incorporated additional range data from west Texas, Japan, and preliminarily from the Arctic. Noble and Aitchison based their radiolarian zones on the ranges of distinct morphotypes left in open nomenclature and of genera and species that were robust and comprised a dominant fraction of the assemblages. The intention was to create a practical zonation that can be applied to chert faunas with only moderate preservation. As such, it relies on gross and obvious differences between the main constituents of radiolarian assemblages, as was known from the existing literature. This zonation remains useful as a crude first-order dating tool that can distinguish poorly preserved Llandovery faunas from post Llandovery faunas, but falls short when applied to sections with good preservation. Furthermore, the zonal boundaries were defined and placed on the basis of limited data and need to be more precisely defined.

One boundary in particular that requires re-examination is that between the Long-spined inaniguttid Zone 2 (LSI-2) and Long-spined inaniguttid Zone 3 (LSI-3) (text-fig. 2). The data originally used to define this boundary (Noble and Aitchison, 2000; Noble 2000) came from three reconnaissance samples from the C. perneri-M. opimus Zone, and an additional three from the overlying Cyrtograptus lundgreni Zone at Snowblind Creek located approximately 60 km southeast of the Rookery Creek section. The more detailed treatment of the radiolarians from the C. perneri-M. opimus Zone herein clearly shows that the ranges of the defining taxa for the LSI-2 and LSI-3 zones need revision. The LSI-3 Zone (text-fig. 2) is a very generalized and longranging biozone that spans the upper Sheinwoodian through the rest of the Wenlock and much of the Ludlow, and encompasses eight graptolite zones (text-fig. 2). The base of the LSI-3 Zone is defined by the first appearance datum (FAD) of Ceratoikiscum, and the top defined by the last appearance datum (LAD) of the rotasphaerids. Secondarily, the zone is recognized by the first appearance of Inanihella tarangulica group taxa near the base of the zone, a species group that is a dominant and persistent component of the LSI-3 fauna. The Inanihella tarangulica group taxa comprise several morphologically similar species of large thick-walled inaniguttids with many long robust spines, and include Inanihella tarangulica Nazarov and Ormiston 1984, I. perarmata Nazarov and Ormiston 1993, I. legiuncula Nazarov and Ormiston 1993, Oriundogutta ? kingi Noble 1994, and Aciferopylorum admirandum Nazarov and Ormiston 1993. Common components of the LSI-3 Zone are the Inanihella tarangulica group, Ceratoikiscum, rotasphaerids, Magnentactinia (Cenosphaera) hexagonalis (Aberdeen 1940), Palaeoscenidiidae, and “labyrinthine spumellarians” of unknown affinity. The base of the LSI-3 Zone approximately corresponds the base of the C. perneri-M. opimus Zone, thus the data herein should correspond to the lowest part of LSI-3 zone. Although the Rookery Creek section 01-RC3c contains Ceratoikiscum, the taxon whose FAD defines the base of LSI-3, 291


other components of the fauna bear closer resemblance to those in LSI-2. Inanihella tarangulica group taxa are entirely absent from section 01-RC3c and make their first appearance in the overlying C. lundgreni Zone. In fact, the inaniguttid component of the fauna is very small, comprising only one species, Plussatispila aethra n. sp., which is large and distinct, but represents less than 5% of the entire fauna. The haplotaeniatumid genera Labyrinthosphaera and Gyrosphaera, typically large components of LSI-2 faunas, are a significant component of the section 3c fauna (up to 35%). The haplotaeniatumid genus Haplotaeniatum, which was thought to have become extinct at or near the top of the Llandovery, is seen to persist in low numbers through the C. perneri-M. opimus Zone. The presence of the new genus Franklinia presents another departure from the original diagnosis of LSI-3. Franklinia dominates the samples from the Sheinwoodian Rookery Creek samples, but it (or similar taxa) has not been noted, even informally, from other localities worldwide. It persists into the Homerian with decreased abundance, and thus appears to be confined to the lower part of the Wenlock. Lastly, there is a significant component of entactiniids in the faunas described herein (up to 20%), including two new genera containing three new species. In many ways, the Rookery Creek section 3c data seem to match better with the description of the underlying Zone, LSI-2, which is characterized by Gyrosphaera, Labyrinthosphaera, long-spined inaniguttids of the I. penrosei morphotype (i.e. Plussatispila), rotasphaerids, entactiniids with cylindrical spines (e.g. Perferoentactinia n. gen. and Involutentactinia n. gen.), palaeoscenidiids, and Magnentactinia Won 1997a (= Cenosphaera hexagonalis in Noble and Aitchison, 2000). Again, the only significant departure is the presence of Ceratoikiscum, which does not occur in the LSI-2 Zone and, in fact, whose FAD corresponds to the top of that zone. In summary, the preliminary zonation of Noble and Aitchison (2000) can be updated with the new data herein. Revisions move the LSI-2/LSI-3 boundary from the middle of the Sheinwoodian up to the base of the Homerian. The FAD of Ceratoikiscum should no longer define the base of LSI-3 and the top of LSI-2. Instead, the FAD of I. tarangulica group taxa, or possibly the first abundance of Inaniguttidae, should be the defining feature. In addition, the base of the LSI-2 Zone must be revised because it is presently defined as the LAD Haplotaeniatum, which is shown herein to persist into the upper Sheinwoodian. These revisions more accurately reflect the ranges of the dominant corporeal faunas for each zone and thus could still be applicable to assigning ages to moderately well-preserved chert faunas, provided the dominant spumellarian components remain relatively consistent between marginal basin facies and more oceanic chert facies. More work is needed in the underlying lower Sheinwoodian to determine the FAD of taxa characteristic of Rookery Creek section 3c, including Plussatispila, Magnentactinia, and Franklinia. Once these data are available, they may be tied into work in progress in the Llandovery (MacDonald, in press) and Homerian (Noble, unblished data) to build a detailed radiolarian biozonation based largely on species ranges for the Lower Silurian of the Canadian Arctic. TEXT-FIGURE 3 Stratigraphic column representing the lithology of Rookery Creek section 01-RC3c showing location of samples. Lithologic key: 1 = calcareous shale, 2 = dolomite, 3 = dolomitic shale, black ovals = concretions.

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TEXT-FIGURE 4 Illustrations of the wall structures common to the taxa described herein.

SYSTEMATIC PALEONTOLOGY Terminology Diagnostic terminology for this report follows that of taxonomic treatments of De Wever et al. (2001), Won (1997a, 1997b), and MacDonald (1998, 1999, 2006). The following is a brief discussion of the terms commonly used herein. Terms describing the wall structure, or construction of the radiolarian shell are especially important in distinction among spumellarian genera. Various types of wall structures observed in Silurian spumellarians are illustrated in figure 4. They are distinguished on the basis of shell thickness, pore diameter, and pore frame morphology. The pore frame is the skeletal structure surrounding the vacant pores. Thin, two-dimensional shell walls with a regular array of pores are described as latticed (text-fig. 4). Most latticed shells from the Upper Paleozoic and younger strata show a regularity of both pore shape and pore size. Lower Paleozoic “latticed” forms differ by having less regular pore shape and size, a seeming contradiction to the term lattice. Many of the two-dimensional thin-walled forms in this study show a great range of pore shape and size, indicating that a term other than latticed should be employed. The term irregularly porous is used herein to describe thin two-dimensional shell walls with pores of various sizes and shapes (text-fig. 4). Gossamer is a term used to describe the very delicate “lacy” outer cortical shell, for example, the outermost shell of P. aethra (plate 5, fig. 1). Thick shell walls with a complex array of irregularly shaped pores dominate most of the taxa and present the biggest descriptive challenge. Labyrinthine wall structure is composed of a random array of individual bars of silica that form a maze-like polygonal pore frame (text-fig. 4). This term was used to describe a similar wall structure in Carboniferous stauraxon radiolarians (Cheng 1986), with the exception that the Carboniferous taxa have hollow silica bars. The shell can appear loosely or densely labyrinthine depending on the diameter of the pores. Pore frame width is generally uniform so that differences in shell density are a function of pore size.

Internal structures are important diagnostic features at the family level and higher because they are believed to be the most conservative developmentally and evolutionarily (De Wever et al. 2001). Three distinct internal structures are observed herein: an entactiniid spicule, a proloculus, and a small medullary shell, and are characters used to define the larger clades (i.e. family level or higher rank). An entactiniid spicule (Foreman 1963, p. 269 figs. 1-4) is an internal structure that gives rise to the primary spines in entactiniids (eg. plate 2, figs. 2, 3 and 7). All spicules observed herein are bar-centered, where the rays attach at either end of a rod of silica. Rays of the entactiniid spicule are rods of silica that protrude through the outer shell and become primary spines. The proloculus of the Haplotaeniatumidae (Won et al. 2002) is a tiny network of bars at the center of the radiolarian from which beams protrude (text-fig. 5). Beams are thin silica rods that travel through the shell and become primary spines once outside of the shell. In the case of the Inaniguttidae, the internal diagnostic feature is a small round to polygonal medullary shell (Nazarov and Ormiston 1984) that may be single- or double-walled (Furutani 1990). Primary spines extend inward as beams and attach directly to the first medullary shell in the Inaniguttidae and the first medullary shell is then enveloped in one or more concentric shells. Following the terminology of De Wever et al. (2001), the inner shells are called medullary shells and the outermost shell or shells are called the cortical shell (text-fig. 6). The medullary shell or shells are separated from the cortical shell by a wide space. The term apophysis is used widely by Nazarov (e.g. Nazarov 1988; Nazarov and Ormiston 1993) and refers to projections from spines or beams that, in some cases, connect to form an enveloping shell or partial shell. Won (1997a; 1997b) discusses apophyses in the Retentactiniinae and defines inner apophyses as any branching of the spicular rays. These branchings, where present, form complex N-frames, or network frames (text-fig. 7; plate 2, fig 3b). The Retentactiniinae are defined by the pres293


tions and are assigned UCMP specimen numbers. The section 01-RC3c is assigned UCMP field locality number MF7026. Additional material from this section is housed at the University of Nevada Reno. SYSTEMATIC DESCRIPTIONS Class ACTINOPODA Calkins 1909 Subclass RADIOLARIA Müller 1858 Superorder POLYCYSTINA Ehrenberg 1838 Order ARCHAEOSPICULARIA Dumitrica, et al. 2000 Superfamily ROTASPHAERACEA Noble 1994

Synonymy: Secuicollactacea DUMITRICA et al. 2000, p. 564 and 567. – DE WEVER et al. 2001, p. 87.

Family ROTASPHAERIDAE Noble 1994, emend. Noble and Maletz 2000

Type genus: Rotasphaera Noble 1994 Synonymy: Secuicollactidae DUMITRICA ET AL. 2000, p. 565 and 568. – DE WEVER ET AL. 2001, p. 89. TEXT-FIGURE 5 General structure of Gyrosphaera, a haplotaeniatumid, illustrating

the proloculus.

ence of an N-frame, which is a complex three-dimensional internal structure formed by apophyses connecting to the rays of the central spicule (Won 1997a, 1997b). The three-dimensional complexity of the N-frame makes it extremely difficult to observe, however a portion of it, called the R-frame, is often more obvious (text-fig. 7). The R-frame is a plane through the N-frame that is seen in cross-section as a ring around the spicule (plate 6, fig. 4). Won’s outer apophyses (1997a; 1997b) are branchings on the spines external to the outermost fully developed (cortical) shell. Outer apophyses that branch at an angle from the spine to the shell are herein referred to as cypress tree structures because the base of the spine is observed to spread out like the roots of a cypress tree (text-fig. 6). Members of superfamily Rotasphaeracea Noble 1994 possess latticed shells constructed of rotasphaerid structures (Noble and Maletz 2000). A rotasphaerid structure is an angular arrangement of straight rods and bars that converge upon a single point in a radiating pattern like the spokes of a wheel. The rotasphaerid structure is a general term that includes two different structures: 1) an ectopic spicule sensu Nazarov and Ormiston (1984) where the radiating rods (called basal rays) continue to form prominent spines (called basal spines) on the outer shell and are roughly perpendicular to an apical spine (text-fig. 8; MacDonald 1998; Noble and Maletz, 2000), and 2) primary units, sensu MacDonald (1998) where the radiating rods (called primary bars) fuse into the shell and do not become spines. Won et al (2002) note that not all primary units appear to have a spine emanating from the center. Spines that emanate from the center of a primary unit are called primary spines, whereas spines of lesser size not emanating from a primary unit are called secondary spines. Repository

All holotype and paratype specimens are housed inthe University of California Museum of Paleontology Microfossil collec294

Remarks: See MacDonald (1998), Noble and Maletz (2000), and MacDonald (2003) for a discussion of the Rotasphaeridae. We follow the systematic scheme proposed by Noble and Maletz (2000). Won et al. (2002) discuss the variability in primary units, and similar to MacDonald (1998), point out that some units lack a spine protruding from the center. Won et al. (2002) furthermore propose emendations to Rotasphaeridae that we do not adopt because they would restrict its definition to exclude the genera Diparvipila MacDonald 1998 and Rotasphaera Noble 1994. Dumitrica et al (2000) treat Rotasphaeridae as a junior synonym to Secuicollactidae, apparently based on an incorrect attribution of Secuicollactidae to Nazarov and Ormiston 1984. Nazarov and Ormiston (1984), when erecting the genus Secuicollacta, placed it within the Haplentactinidae Nazarov 1980, subfamily Secuicollactinae Nazarov and Ormiston 1984. Won et al. (2002) states that the family Secuicollactidae “seems to have been informally established by Nazarov and Ormiston, 1984 in the newsletter of Eurorad IV”, suggesting that this was the source of the wrong attribution. Won et al. (2002) also point out, subsequent work by Nazarov (1988) and Nazarov and Ormiston (1993) continue to place Secuicollacta within the Haplentactiniidae. Aside from the Eurorad conference volume (includes Nazarov and Ormiston 1984), we have been unable to locate any other 1984 Eurorad newsletter, and the 1985 Eurorad newsletter, while containing an abstract by Nazarov and Ormiston, (Radiolaria vol. 9, p. 66) makes no mention of Secuicollactidae. To our knowledge, the first printed appearance of the term Secuicollactidae, whether formal or informal, is in Dumitrica et al. (2000). In our examination of the International Code of Zoological Nomenclature, we can find no basis to support priority for Secuicollactidae nor to give attribution of this name to Nazarov and Ormiston 1984. The Principle of Coordination (ICZN, 2000, article 36.1), which provides for the simultaneous erection of other names within the family group rank based on the stem of the nominal genus, does not seem applicable because the genus and subfamily were assigned to the Haplentactiniidae. Furthermore, article 35.5 (ICZN 2000), regarding precedence for names in use at higher rank, states that after 1999 an older name of lower rank (i.e. Secuicollactinae) should not displace the younger name of higher rank in prevailing usage (i.e.


Rotasphaeridae). Alternatively, had the intention been merely to elevate rank of subfamily Secuicollactinae Nazarov and Ormiston 1984 to the family level, Dumitrica et al. (2000) would have needed to emend the diagnosis because the one given by is essentially that of Rotasphaeridae. The attribution in the case of such a rank elevation should have appeared as Secuicollactidae Nazarov and Ormiston emend. Noble 1994. We continue to use the subfamily as a means of distinguishing rotasphaerids with an ectopic spicule from those without (see Noble and Maletz 2000; MacDonald 2003), and thus treat Secuicollactidae as a junior synonym and attribute it to Dumitrica et al. (2000). Subfamily SECUICOLLACTINAE Nazarov 1984 emend. MacDonald 1998 Genus Secuicollacta Nazarov and Ormiston 1984, emend. MacDonald 1998

Type species: Secuicollacta cassa Nazarov and Ormiston 1984 Synonymy: Parasecuicollacta WON, BLODGETT and NESTOR 2002, p. 953. Remarks: This genus was defined as a coarsely meshed spumellarian possessing an ectopically placed spicule with five to seven straight rays emanating from one perpendicular spine, and thought to be equivalent to Holdsworth’s (1977) “rotasphaerids” (Nazarov and Ormiston 1984; Nazarov 1988). The ectopic spicule of Secuicollacta was interpreted to be one of several more or less identical rotasphaerid structures by subsequent workers (i.e., Wakamatsu et al. 1990; Furutani 1990; Noble 1994), because the original description seemingly ignored the presence of multiple rotasphaerid structures and the ectopic spicule was not obvious in the photos of the type species, S. cassa. These workers were influenced by specimens from moderately preserved chert faunas that seemed to lack ectopic spicules. Noble (1994) mistakenly removed the ectopic spicule as a defining character in her emended diagnosis of Secuicollacta because the spicule appeared to be one of a number of rotasphaerid structures she termed “primary spine units” (= primary unit herein). This emendation is not currently adopted because, although multiple rotasphaerid structures exist in Secuicollacta, one of the rotasphaerid structures possesses basal rays and is the ectopic spicule (MacDonald 1998). The similarity in appearance between the ectopic spicule and other rotasphaerid structures, termed “primary units” (MacDonald 1998), cannot be denied. Won et al. (2002) dispute the distinctness of the ectopic spicule, describing it as a “prominent primary unit”. MacDonald (2003) notes that the ectopic spicule is not necessarily more “prominent”, but can be distinguished on the basis of basal spines/rays emanating from the apical spine. Dumitrica et al. (2000) and De Wever et al. (2001) define the ectopically placed spicule of Secuicollacta as a peculiar primary unit. Noble and Maletz (2000) acknowledge the presence of an ectopic spicule in the secuicollactines and consider both the ectopically placed spicule and the primary units as types of “rotasphaerid structures”. This similarity is best seen in comparing the genera Secuicollacta and Rotasphaera, which differ only in that Rotasphaera lacks an ectopic spicule. Even when an ectopic spicule can be identified in Secuicollacta, it is difficult to pick out with the untrained eye and may be easily be obscured by poor preservation. For this reason, absence of an ectopic spicule in Rotasphaera may be more a function of shell growth and preservation than of different phylogeny (see Noble

TEXT-FIGURE 6 General structure and terminology used herein for Plussatispila.

and Maletz 2000 for further discussion). Should the variable presence of an ectopic spicule ever be verified interspecifically, then the genus Rotasphaera would become a junior synonym to Secuicollacta. Macdonald (1998; 2003) maintains that he consistently observes an ectopic spicule in specimens assigned to species of Secuicollacta, and never sees it in specimens of species assigned to Rotasphaera. The two genera thus remain separate and assigned to separate subfamilies, for the time being. Won et al. (2002) describe a new genus Parasecuicollacta which differs from Secuicollacta by being more robust-walled and having a lumpy or ragged surface outline due to a spinose or pseudospongy outer layer. MacDonald (2003) argues that the basic skeletal elements of Parasecuicollacta are the same as Secuicollacta and the thin labyrinthine (= Won’s pseudospongy) outer layer is a function of secondary spine development and insufficient to warrant a new genus. We concur with MacDonald (2003) and list Parasecuicollacta as a junior synonym. Secuicollacta malevola MacDonald 1998

Plate 1, figures 1-3 Description: Angular pore frame, with irregular, loose, open structure of robust bars and struts derived from seven to ten hexatine primary units. More than twenty secondary spines occur per hemisphere approximately half length of primary spines, and variably preserved. Basal rays of ectopic spicule are equivalent size to secondary spines and more robust than primary bars emanating from primary units. Lattice surrounding base of ectopic spicule usually more open than lattice around other spines. Primary spines long, robust, round in cross section, taper to sharp point, and length shorter than diameter of shell. Remarks: Although the spines of Secuicollacta malevola from Rookery Creek have shorter, more robust spines than those de295


scribed by MacDonald (1998; 2003), they are still assigned to this species. This taxon bears some resemblence to S. multispinosa (Won et al. 2002) but differs in having a lesser development of secondary spines and a thinner shell wall. This species is rare at Rookery Creek, comprising from 0% to 3.5% of the fauna. Secuicollacta resodiosae MacDonald 1998

Plate 1, figures 4-6 Description: Single, thin, latticed cortical shell. Angular pores very small. Five to ten primary units present. Ectopic spicule often difficult to recognize, but may be distinguishable by robust basal rays that emerge as short robust basal spines. Spinose, with over thirty spines per hemisphere, giving shell “fuzzy” appearance. Primary spine length commonly equal to diameter of shell, and secondary spine length may be equal to half shell diameter. All spines circular in cross section, and taper to sharp point. Remarks: There is a great deal of variation in the number and length of secondary spines. Specimens assigned to S. malevola with uncharacteristically long secondary spines (pl. 1, fig. 1) may appear superficially similar to S. resodiosae. The secondary spines of S. resodiosae are typically more numerous and much longer than those of S. malevola. This species is rare at Rookery Creek, comprising between 0% to 2.5% of the fauna. Secuicollacta parvitesta Won Blodgett and Nestor 2002

Plate 1, figure 7 Description: Small spherical shell (60-70µm diameter), commonly four to five primary units whose primary bars form loose, angular pore frame. Angular pores approximately two to three times larger than width of pore frame. Pentactine ectopic spicule usually obvious because of large pores. Primary spine length commonly equal to diameter of shell. Typically five to seven robust primary spines, but in some specimens as many as 12. Spines round in cross section, and taper to sharp point. Remarks: Specimens are very small and delicate with nearly all spines forming from the spicule only. Large specimens have some primary spines attached at the centers of primary units. This species is common in two samples at Rookery Creek (Table 1), reaching a maximum abundance of 8% in sample 01-RC3c 5m, but is rare in other samples, comprising no more than 1.5% of the fauna. Order ENTACTINARIA Kozur and Mostler 1982 Family ENTACTINIIDAE Riedel 1967 emend Won 1997a

Remarks: Systematic treatment of the Entactiniidae is problematic with various authors claiming priority of different names and disagreeing as to whether shell structure or number of rays should be a primary consideration in its subdivision. See Won (1997a) for a detailed history of Nazarov’s treatment of the Entactinidae. Kozur and Mostler (1981; 1982) argue that Entactiniidae is a junior synonym to Triposphaeridae Vinassa de Regny (1898), however De Wever et al. (2001) considers the type species, Triposphaera peachii Hinde 1890, nominum oblitum, and Aitchison and Stratford (1997) conclude that Triposphaera Hinde 1890 may instead be an inaniguttid. Aitchison and Stratford (1997) consider the nominal genus, Entactinia Foreman 1963, to be a junior synonym to Stigmosphaerostylus Rüst 296

1892, yet retain the name Entactiniiade at the family level. Entactiniidae has been under continued use since it was proposed by Riedel (1967) and its concept is widely recognized by radiolarian workers. Won (1997a, 1997b) abandons Nazarov’s subdivision of the Entactiniidae and argues that instead of the number of primary spines, the presence of apophyses and cortical shell construction should be the primary basis for subdivision into two subfamilies, the Entactiniinae Nazarov 1975 and the Rentactiniinae Won 1997. Although Won’s revisions are based largely on her observations of the Devonian Gogo faunas (Won 1997a; 1997b), we find her classification compatible with the Silurian entactiniids described herein and adopt her classification. Subfamily RETENTACTINIINAE Won 1997b Remarks: The most obvious diagnostic feature of this subfamily is the presence of an R-frame, which is a planar cut through the N-frame and appears as a “halo” around the internal spicule. In the Rookery Creek material, the N-frame can be virtually undetectable, unless it is very robust. Apophyses may attach directly to the shell wall or, in other cases, hang free from the spines. Outer apophyses are not to be confused with points of connection of the outer shell to the spines. Nazarov’s (1988) subdivision of the Entactiniidae into the subfamilies Entactininnae Nazarov 1975 and Astroentactininnae Nazarov 1975 was based largely on the number of rays emanating from the spicule, whereas Won (1997a) believes that wall structure and presence of apophyses are a more important criterion. She emends the Entactiniinae, and abandons the use of Astroentactininae. Astroentactininae is not available for emendation because the nominal genus Astroentactinia Nazarov 1975 is treated as a junior synonym to Entactinia Foreman 1963. The Retentactiniinae Won 1997b is proposed as a sister subfamily to the Entactininnae. Spongentactinia Nazarov 1975 is included in the Retentactiniinae and its definition emended by Won (1997b) to more accurately reflect the type species, which does not have a medullary and cortical shell, but instead has a latticed base upon which spongy layers are developed. The terms medullary and cortical shells are generally used only when there is a notable gap separating the shells (Won 1997a; De Wever et al. 2001). De Wever et al (2001) treat Retentactiniinae as a junior synonym to the tribe Spongactiniini Nazarov 1975 which they treat as a separate sister family (i.e. Spongentactiniidae) to the Entactiniiade. The tribe Spongentactiniini while used by Nazarov and Ormiston (1983) in their description of the Late Devonian Gogo Formation fauna, seems to have been abandoned later by Nazarov (1988). We recommend that the Retentactiniinae be retained and do not consider it synonymous to Spongentactiniini, which is more narrowly defined (De Wever et al. 2001), and might appropriately be considered a tribe within the Retentactiniinae. Genus Involutentactinia Jones and Noble n. gen.

Type species: Involutentactinia eccentra Jones and Noble n. sp. Diagnosis: Spherical to subspherical shell consisting of three to four layers of weakly spiraliform labyrinthine material. Six-rayed bar-centered spicule occurs eccentrically within the inner shell. Apophyses on rays are present at inner spine/whorl intersections. Remarks: The presence of apophyses places this genus in subfamily Retentactiniinae. The wall structure, however, is best described as labyrinthine as opposed to spongy.


This is a distinct entactiniid genus due to the spiraliform nature of the shell construction. No other genus within family Entactiniidae exhibits this character. Polyentactinia Foreman 1963 differs by possessing a single latticed shell with an angular mesh. Syntagentactinia Nazarov 1980 is probably the closest genus morphologically but lacks the spiraliform shell and also differs by possessing a massive spicule with two partial to completely formed spongy shells. Species included: Involutentactinia eccentra n. sp. Range and occurrence: lower Wenlock; upper Sheinwoodian (C. perneri-M. opimusZone), Canadian Arctic, as far as known. Etymology: Latin, involuta - rolled up Involutentactinia eccentra Jones and Noble n. sp.

Plate 1, figures 8-11; Plate 6, figures 1-3 Diagnosis: Loose labyrinthine spiraliform shell composed of three whorls. Pore frames highly angular and irregular. Six primary spines extend from eccentric six-rayed bar-centered spicule. Description: Robust R-frame present. External angle of primary spines reflects position of entactiniid spicule. Median bar of spicule short. Pore frame very loose and pores larger on each successive whorl. Pores in outermost whorl show rough hexagonal shape. Primary spines circular in cross section, taper to a point, and slightly shorter in length than diameter of shell. Short needle-like secondary spines are present and on average, are about ¼ length of primary spines. Remarks: Two varieties are recognized within this species, I. eccentra n. sp. sensu strictu, as described, forms the typologic base for the species. A second variety, I. eccentra var. cupressa, has only two whorls and is described separately below. Externally, I. eccentra sensu strictu appears more robust than I. eccentra var. cupressa (compare plate 1, figs. 8-11 with plate 1, fig. 12 and plate 2, fig. 1) and in cross section, the spiraliform wall structure is more defined (compare plate 6, figs. 1-3 with plate 6, fig. 4). I. eccentra n. sp. sensu strictu is the less common of the two varieties (Table 1).When present, it comprises