By Hofmann, H J O’Brien, S J; King, A F
ABSTRACT- Newly found fossils in the Conception and St. John’s groups of the Bonavista Peninsula considerably extend the known geographic distribution of the Ediacaran fossils in Newfoundland. They occur in deepwater sediments and are preserved as epireliefs, forming census populations underneath volcanic ash layers throughout a more than 1 km thick turbiditic sequence. The exposed fossiliferous units comprise the Mistaken Point, Trepassey, Fermeuse, and Renews Head formations. The remains are tectonically deformed, with long axes of elliptical discs aligned parallel to cleavage strike; shortening of originally circular bedding surface features is on the order of 30-50% (averaging ~35%).
The assemblage includes Aspidella, Blackbrookia, Bradgatia, Charnia, Charniodiscus, Fractofusus, Hiemalora, and Ivesheadia. These occur throughout the succession, with Aspidella being the most common genus, followed by Charnia and Charniodiscus. Four new taxa are described, with candelabra-like fossils with a Hiemalora-like base referred to Primocandelabrum hiemaloranum n. gen. and sp., bush- like fossils to Parviscopa bonavistensis n. gen. and sp., ladder- like fossils to Hadryniscala avalonica n. gen. and sp., and string- like fossils with basal disc to Hadrynichorde catalinensis n. gen. and sp. The remains also include dubiofossils. The stratigraphic ranges of some taxa on the Bonavista Peninsula are longer than previously reported from the Avalon Peninsula, with Fractofusus spindles present in the Trepassey Formation, Bradgatia, Charnia, Charniodiscus, and Ivesheadia reaching as high as the Fermeuse Formation, and Aspidella extending into the middle of the Renews Head Formation. The spindles in the Trepassey Formation are comparable to those found mainly in the stratigraphically older Briscal Formation on the Avalon Peninsula.
INTRODUCTION
THE DISTINCTIVE and problematic Ediacaran fossils of soft-bodied organisms constitute a prominent marker in the history of the Proterozoic biosphere, and a substantial biologic enigma as well. There is no unanimity as to their affinities. Early interpretations placed forms like those found in Newfoundland in the Kingdom Animalia, principally in the Phylum Cnidaria (e.g., Glaessner, 1959, 1984; Anderson, 1978; Fedonkin, 1981), Others have presented different interpretations. Included among these are attributions to a separate extinct Kingdom, Vendozoa (Seilacher, 1989; later Vendobionta, Seilacher, 1992), xenophyophorean protists (Zhuravlev, 1993, Seilacher et al., 2003), lichens (Retallack, 1994), photosynthetic “metacellular” organisms (McMenamin, 1998), colonies of Prokaryota (Steiner and Reitner, 2001), and fungus-like organisms (Peterson et al., 2003). Ediacaran fossils are now thought to be mostly metazoans. For a comprehensive recent review, see Narbonne (2005).
Discoidal remains of this biota were first recognized in the 19th century in the City of St. John’s, Newfoundland and described by Billings (1872) under the name Aspidella terranovica. The black shales in which they were found were subsequently designated the “Aspidella slates” (Murray and Howley, 1881), and the Fermeuse Formation in the more recently constituted St. John’s Group (Williams and King, 1979). Even earlier reports, as far back as 1858, treated somewhat similar ring-like structures from the Charnian of England as possible abiogenic concretions (Ford, 1999, p. 230). Aspidella itself remained controversial as a fossil for more than a century (Hofmann, 1971, p. 16). Modern integrative studies finally established its biogenicity convincingly, if not its biological affinities (Gehling et al., 2000). The Ediacaran biota comprises about ten dozen genera (Waggoner, 1999), exhibiting ample variation of morphology based on simple modes of growth that dominated for a period before becoming extinct at the end of the Proterozoic. Nearly three dozen localities are now known worldwide. The most prominent of these also exhibit the greatest diversity, and are situated in South Australia, Namibia, northern Russia, Ukraine, Newfoundland, and northwestern Canada. The age of the Ediacaran biota is constrained to ~635-542 Ma (Condon et al., 2005), and probably between 580-542 Ma.
The assemblages in the different areas are characterized by disparate sedimentary environments and different preservation styles, as well as distinctive biotic compositions (e.g., Narbonne, 1998; Waggoner, 1999; Grazhdankin, 2004). Ediacaran megafossils in northwestern Canada, Australia, and eastern Europe occur typically as hyporeliefs in shallow water siliciclastics, whereas those in Newfoundland, England, and Finnmark are preserved as epireliefs in deepwater sediments, and those in Namibia commonly are transported entities preserved as endoreliefs in storm-generated sandstone. Some forms such as discs are cosmopolitan, whereas others of more complex morphology have more restricted distribution. For analyses of Ediacaran assemblages, see the reviews by Waggoner (1999, 2003) and Grazhdankin (2004). The forms here described from the Bonavista Peninsula conform to what is known from the Avalon Peninsula- preserved on upper bedding surfaces in deep water turbiditic and shallowing-upward pro-deltaic sediments, below ashfall deposits.
Although the Avalon assemblage has received a great deal of study in recent years (Gehling et al., 2000, Narbonne et al., 2001, Clapham and Narbonne, 2002; Clapham et al., 2003, 2004; Narbonne and Gehling, 2003; Wood et al., 2003; Narbonne, 2004, 2005; Laflamme et al., 2004; Ichaso et al., 2007; Gehling and Narbonne, 2007; Laflamme et al., 2007), much sustained effort will be required to resolve major questions concerning the biological affinities of the elements of this biota. Studies by Narbonne and his associates are continuing to contribute substantially in this regard. Narbonne et al. (2001, p. 28 et seq.) provide a useful summary of the history of research on the Ediacaran biota in Newfoundland.
The objectives of the present study are the description and illustration of new material from the Bonavista Peninsula, now the third area in Newfoundland known to contain this remarkable assemblage (O’Brien and King, 2004a, 2004b, 2005), and, secondly, to relate these occurrences and their context to those on the Avalon Peninsula to the south. Some of the new localities have yielded exceptionally well preserved specimens of several taxa that improve our knowledge on the distribution, environmental setting, morphology, taphonomy, and taxonomic affiliation of specific Ediacaran taxa. One of the significant aspects of the ~570 Ma Avalon assemblage is that no unequivocal trace fossils have yet been recognized. Although here interpreted as body fossils, two of the new taxa in the Bonavista area (Parviscopa n. gen. and Hadrynichorde n. gen.) have some aspects in common with certain trace fossils normally found in rocks younger by 30 million years; these are suitable candidates for further studies to confirm their affinities.
GENERAL GEOLOGIC SETTING
The Bonavista Peninsula of Newfoundland lies within the Appalachian Avalon Zone, a complex and well-preserved Neoproterozoic to Early Paleozoic terrene that records the development of segments of a much larger Precambian orogenic system accreted to the Appalachians during Paleozoic orogenesis (cf. O’Brien et al., 1996). Integral parts of this belt are Ediacaran sedimentary rocks, which are spectacularly preserved along the deeply embayed coast of southeastern Newfoundland
Such Ediacaran rocks are well exposed on the Bonavista Peninsula, where the Spillars Cove-English Harbour fault zone (west of the present map area; see O’Brien et al., 2006, fig. 5) demarcates the boundary of two lithologically contrasting clastic sedimentary domains. Late Neoproterozoic sedimentary rocks west of this brittle structural zone are part of the Musgravetown Group (Hayes, 1948, p. 16-17; O’Brien and King, 2002), a major volcano-sedimentary succession that crops out over large parts of the western Avalon Zone. Similar aged sedimentary strata east of the fault zone, previously included in that group, have recently been remapped and subdivided by O’Brien and King (2002, 2004a, 2004b, 2005) and O’Brien et al. (2006). These rocks are now recognized as correlatives of the upper part of the Conception Group (post-570 Ma), the entire St. John’s Group, and the lower Signal Hill Group, which are major units mapped and defined by Williams and King (1979) and King (1988, 1990) in the Avalon Zone’s type area, Avalon Peninsula, approximately 180 km to the south-southeast. The formational nomenclature is applicable to the units in the Bonavista area, where formations are further subdivided into members as designated in O’Brien and King (2005, figs. 2 and 3). The units are well exposed in the Catalina Dome, a NNE trending elliptical outcrop area approximately 8 x 7 km centered on the towns of Catalina, Port Union, and Melrose (all three now incorporated in the municipality of Trinity Bay North); bedding dips radially around the dome at generally less than 25[degrees] (Fig. 1). Lithostratigraphic correlation of Bonavista and Avalon peninsula rocks is corroborated in a general way by fossil content, although the stratigraphic ranges of individual taxa are not identical in both areas (O’Brien and King, 2002, 2004a, 2005). The Ediacaran strata of eastern Bonavista Peninsula, like their correlatives on the Avalon Peninsula, represent a depositional transition from deepwater basin and slope (Conception Group) to shallowing-upwards basinal, pro- delta and delta front (St. John’s Group), and ultimately alluvial conditions (Signal Hill Group). Large quantities of volcanic ash were brought into this arc-adjacent marine basin throughout its depositional history and were important in the burial and preservation of the Ediacaran biota.
LITHOSTRATIGRAPHY AND PALEOENVIRONMENTS
CONCEPTION GROUP
Drook Formation.-The oldest exposed unit in the map area is the Shepherd Point Member of O’Brien and King (2005), part of the Drook Formation in the Conception Group. This member forms the core of the Catalina Dome (Fig. 1), and is characterized by evenly laminated gray-green siltstone interspersed with numerous thin laminae to thin beds of fine-grained, light gray weathering sandstone, and dark gray- green to black mudstone. Some black mudstones show minute irregular or wavy laminations several millimeters thick; preliminary studies suggest they may represent microbial mats on the sediment surface. Individual centimeter-scale sets of fine sand, silt, and mud are of constant thickness and laterally continuous for several meters, where they pinch out or are terminated by slightly irregular, very low-angle erosional discontinuities. Small scours, small-scale synsedimentary slump folds and faults, and mud rip-up clasts are common and indicate that erosive bottom currents flowed over an unstable slope. Interspersed throughout the member are medium beds of parallel-laminated, poorly sorted, structureless sandstone and rare beds of cross laminated sandstone. This unit has not yet yielded fossils in the study area, but is fossiliferous on the Avalon Peninsula (Narbonne and Gehling, 2003; Clapham et al., 2004).
Mistaken Point Formation.-The overlying Mistaken Point Formation was subdivided by O’Brien and King (2005) into a lower, siliceous Goodland Point Member and an upper, argillaceous Murphy’s Cove Member; both are fossiliferous throughout. The Goodland Point Member is a medium- to thick-bedded siliceous sequence composed of parallel- and cross-laminated sandstone, parallel-laminated siltstone, structureless mudstone and tuff, interpreted as representing Bouma turbidite subdivisions BCDE. The silt, mud, and ash may have been deposited as DE beds or as hemipelagic sediment associated with ash- fall material that was slowly deposited from suspension within the deep sea. Large-scale slump folds (up to several meters in height) are locally preserved and result from gravitational instability of sediment deposited on a slope. This member resembles, and may correlate with, the Middle Cove Member of the Mistaken Point Formation, eastern Avalon Peninsula (King, 1990). Like the soft- bodied Ediacaran fossils on the Avalon Peninsula, the impressions of the organisms on the Bonavista Peninsula are confined to turbiditic siliciclastics and are typically preserved on upper bedding surfaces of interturbidite mudstones, underneath thin water-laid tuffs.
The Murphy’s Cove Member is dominated by medium-bedded, gray and green sandstones and gray, green, and red mudstones. Variegated structureless and laminated mudstones are present at the top of the member and may correlate with the Hibbs Cove Member, uppermost Mistaken Point Formation, at its type locality on the Avalon Peninsula (King, 1990). Fine-grained, white, gray to light brown tuff forms thin beds and laminae throughout the member and commonly preserve Ediacaran fossils underneath.
ST. JOHN’S GROUP
Conception Group strata in the core of the Catalina Dome pass conformably into fossiliferous marine mudrocks and interbedded sandstones of the St. John’s Group (Williams and King, 1979), which consists of, in ascending stratigraphic order, the Trepassey, Fermeuse, and Renews Head formations. These sediments formed initially in a deep basinal slope environment, which, in response to a combination of sea-level changes and to seaward advances of a large prograding delta, shallowed over time and in two major cycles (King, 1980, 1990; O’Brien and King, 2005).
Trepassey Formation.-The Trepassey Formation lies conformably above the Mistaken Point Formation and shows a coarsening- and thickening-upward succession. It is divided into a lower, mud- and silt-rich Catalina Member and an upper, sand-rich Port Union Member (O’Brien and King, 2005). The Catalina Member is a succession of repetitive, thin-to medium-bedded, greenish-gray mudstone, siltstone, and pyritiferous sandstone. The beds are tabular with a sharp base, laterally persistent, and commonly graded, with a basal laminated silty sandstone passing upwards into structureless mudstone and tuff; they are interpreted as Bouma DE turbidites. Ripple cross-lamination and sole marks are rare in these beds. In the upper part of the member, medium beds of cross-stratified sandstone are locally developed. Ediacaran fossils occur below distinctive brown ash layers at several stratigraphic levels in the upper part of the member. The Catalina Member correlates with most of the Trepassey Formation at its type locality in the southern Avalon Peninsula. The upper part of the Catalina Member coarsens and thickens upward and passes transitionally into the Port Union Member. Thick to very thick, 1-3 m tabular beds of fine- to very coarse-grained gray quartzofeldspathic sandstone and granule conglomerate, and interbeds of mudstone, siltstone, agglomerate, and tuff characterize this member. The coarse beds are immature, volcanogenic, and formed under combined rapid downslope subaqueous flow of pre-existing sediment mixed with new pyroclastic debris, which might explain why no fossils have been found within these units. A comparable coarse sandstone facies forms a unit only 5 to 10 m thick at the very top of the Trepassey Formation on the Avalon Peninsula. Other extensive facies within the Port Union Member include thick-bedded fine- to medium-grained sandstone with distinct parallel lamination, associated thick beds of fine- to medium- grained sandstone with a massive or structureless appearance, and intercalated fossiliferous units of thin-bedded mudstones and very fine-grained sandstones that are comparable with those of the underlying Catalina Member.
FIGURE 1-Geologic map of Catalina area, with fossil localities (after O’Brien and King, 2005). Locality 32 is outside map area, near Maberly, 7 km NNE of northeast corner of area, at 48.608[degrees]N 53.009[degrees]W. SHG = Signal Hill Group.
Large-scale slumps and disrupted beds are present throughout the Trepassey Formation, representing periodic rapid burial of the habitat that sustained the organisms in this deep-marine setting. The slumps are of the same composition as their respective members and indicate the presence of a slope on which original sediment deposits became unstable, either because of sediment load or seismic shock; the mass movement was probably slight as the slumped material is near slump scars from which they were derived. The increasing influx up-section of laminated, fine- to medium-grained sand indicates high-energy downslope processes and may reflect shoaling of the basin or sea-level changes.
Fermeuse Formation.-The black-shale-dominated Fermeuse Formation lies in sharp and conformable stratigraphic contact above the Trepassey Formation. The succession studied to date consists primarily of three principal, interbedded lithofacies. Following the terminology of O’Brien et al. (2006), the prominent facies (A-f), seen in the lowermost part of the formation, is dark gray to black shale and mudstone with laminae, and thin to medium interbeds of gray siltstone, fine grained, brown-weathering gray sandstone, and minor tuff. Impoverished current ripples and cross-lamination are locally present but are usually indistinct; rhythmically alternating sand-mud graded units are common. A second, characteristically remobilized facies (B-f) consists of slumped folds of sandstone resedimented in a mud matrix that occur with debris flows. The latter consist of a mixture of sand, mud, and coarse angular to rounded cobble-size fragments of siltstone and sandstone. A third facies (C-f), developed in the upper part of the succession, includes black shales with rare or widely spaced laminae or thin beds of silty sandstone. In general, the proportion of sand increases upwards through the formation. Tuff beds are most common in the lower 300 m of the section and are associated with Ediacaran fossils.
The remobilized facies (B-f) occurs throughout several hundred meters of stratigraphic section and contains repetitive and spectacularly preserved tabular units of synsedimentary folds and disrupted beds of sandstone, each unit commonly several meters thick, interbedded with black shale and silty sandstone. The slumped units are locally capped by sand-rich sedimentary breccias overlain by shale. Thin beds of ash within the shales within facies A-f and B- f preserve a variety of Ediacaran fossils at several stratigraphic levels.
The slumped and disrupted units are attributed to gravitational sliding of poorly consolidated beds of sand and mud on a sloping paleosurface during normal pelagic sedimentation. Huge masses of mixed sand, mud, and coarse clastic debris were transported as debris and other mass flows into deeper parts of a submarine slope and basin. The presence of sharp bedding planes directly above truncated folds of sandstone and coarse breccias at the top of the disrupted unit indicate periods of erosion by intense bottom currents.
Renews Head Formation.-The Renews Head Formation gradationally and conformably overlies the Fermeuse Formation. It differs from the latter by its greater silt and sand content, its pyritic, rusty- weathering lenticular bedding, and the presence of impoverished or starved current ripples, pseudonodules, waterescape structures, and small sand dykes. This formation records another coarsening- and thickening-upward succession. It represents a second major cycle within the group, but one of prograding deltaic sedimentation that passes upward and laterally (above the deep basin and slope) into terrestrial conditions represented by the Gibbett Hill Formation (Signal Hill Group). The Renews Head Formation is divisible into three main lithofacies: (A-r) black shale with numerous laminae of rusty brown-weathering gray silty sandstone, (B-r) thin- to medium- bedded lenticular sandstone intercalated with black shale, and (C- r) distinctive, very thick to extremely thick (>3 m) beds of cross- bedded, laminated, and structureless gray sandstone units interbedded with black shales and thin sandstones. The coarse- grained sandstones are, in places, associated with granule and small pebble layers. Facies (C-r) is commonly incised or present in facies (A-r) and (B-r) and is interpreted as major channelized sand lobes and sheets, which are possible deltafront deposits related to delta- top sedimentation recorded in the overlying Gibbett Hill Formation that crops out beyond the map area (see O’Brien and King, 2004a). Shale-rich units in the formation bear Aspidella terranovica.
PALEONTOLOGY
Fossil assemblage and localities.-In a 1978 reconnaissance mapping and paleontological investigation of eastern Bonavista Peninsula, one of the authors (King) noted that 1) the siliceous rocks of Goodland Point, Catalina, resembled the Mistaken Point Formation, 2) the mudstones of Catalina were comparable with the Trepassey Formation, and 3) the shale sequence of Melrose matched the Fermeuse Formation. At that time, only the shales were found to be fossiliferous, yielding very poorly preserved sphaeromorph acritarchs and nonseptate filamentous microfossils near Port Union (Hofmann et al., 1979). As a result of more recent work, Ediacaran fossils were discovered in this area (O’Brien and King, 2004a).
The main occurrence of the Ediacaran biota on the Bonavista Peninsula is limited to the Catalina Dome (Fig. 1). Discoidal fossils have also been observed at English Harbour, 20 km south of Catalina, and at Maberly, 10 km to the north. The exposed units belong to the Conception and St. John’s groups, with fossiliferous horizons in the Mistaken Point, Trepassey, Fermeuse, and Renews Head Formations.
The general geographic and stratigraphic distributions of the fossiliferous localities were given by O’Brien and King (2004a), as was a summary of their morphologic diversity. The same authors have since provided a more detailed inventory of their occurrence (O’Brien and King, 2005), but the present paper is the first to more fully describe and illustrate the Ediacaran fossils on the Bonavista Peninsula. Figure 2 presents a graphic summary of the more than a dozen constituent elements of this assemblage.
The fossils are best observed on dip slopes of shoreline outcrops. The discovery site, also the one showing the greatest diversity of fossils in the new assemblage, is located in the Murphy’s Cove Member of the Mistaken Point Formation (Locality 5), and is illustrated in Figure 3. The fossils are protected under provincial legislation, but remain exposed to the elements (wave and ice action, cliff collapse, algal and bacterial growth, human activity).
Like the soft-bodied Ediacaran fossils on the Avalon Peninsula, the impressions of the organisms are confined to turbiditic siliciclastics and are typically preserved on upper bedding surfaces of interturbidite mudstones, underneath thin water-laid tuffs (Narbonne et al., 2001, 2005).
Figure 2-Main components of Ediacaran biota on the Bonavista Peninsula. Basal portion of large Charnia Ford, 1958 is conjectural.
All fossils show the effect of Early Paleozoic tectonic deformation and pervasive cleavage development related to the formation of the Appalachian orogenic belt. Originally circular features such as the Aspidella organism were deformed into NNE trending ellipses, in effect constituting built-in strain gauges that provide a quantitative measure of the amount of tectonic shortening, which is on the order of ~35% on average in the study area, but can attain 50% or slightly more locally. This allows for the retrodeformation of not only their images, but also those of associated frondose, bush-like, and other fossils, to reconstruct their morphologies and felling directions at the time of burial (Wood et al., 2003, fig. 5). Most of the illustrations in the plates of the present paper are retrodeformed images of the fossils.
The fossils were studied in situ during the summers of 2004 to 2006, and photographed with digital cameras. Selected important specimens were molded with low viscosity (~7000 cps) black latex which then served to make casts using a dental stone compound, both of which aided the study in the laboratory. Very few actual samples were collected to respect legislation regarding the preservation of the fossil sites. Specimens and casts are deposited at the Newfoundland Museum (NFM) in St. John’s, bearing consecutive numbers from NFM F-457 to NFM F-656. Catalogue numbers of illustrated material are cited in the captions of the respective figures.
We here provide an interim overview of 40 localities while more detailed studies are continuing. The fossils comprise more than a dozen taxa, most of which are also represented on the Avalon Peninsula. The most common and longest-ranging is Aspidella terranovica. Other long-ranging and widespread forms are Bradgatia Boynton and Ford, 1995, Charnia Ford, 1958, Charniodiscus Ford, 1958, Hiemalora Fedonkin, 1982, and Ivesheadia Boynton and Ford, 1996, all of which (excepting Hiemalora) are also characteristic of the Charnwood Forest area in England, from where, in fact, they were first described. Fractofusus is rare in the Mistaken Point and Fermeuse Formations, but abundant at some levels in the Trepassey Formation, and unknown in the Renews Head Formation and in the Charnian of England. Fossils not previously encountered are also described and assigned to four new species and genera.
The fossiliferous exposures extend stratigraphically from near the base of the Mistaken Point Formation in the Conception Group to the middle of the Renews Head Formation in the St. John’s Group (Fig. 4), and thus the range is limited by lack of strata in the lower part of the stratigraphic section as compared to the much more completely exposed sequence on the Avalon Peninsula, where the section also includes the fossiliferous Briscal and Drook Formations below the Mistaken Point Formation. On the other hand, many of the taxa reach stratigraphic levels appreciably higher on the Bonavista Peninsula than on the Avalon (Fig. 5).
The frondose forms Charnia and Chamiodiscus show strong preferred alignment on individual bedding planes, which is attributed to downcurrent felling by bottom currents (Wood et al., 2003). An overall bimodal pattern emerges, with a main mode in a NNE direction, and an opposing secondary mode (Fig. 6); the mean vector show a slight clockwise rotation in ascending the stratigraphic section. The preferred orientation and tripartite organization of basal holdfast disc, stem, and frond indicate that the organisms were erect sessile benthos anchored on the mud, rather than endobenthic (Seilacher, 1992).
DESCRIPTIONS AND DISCUSSIONS OF FOSSILS
Various schemes have been devised to accommodate Ediacaran fossils in a systematic way, but the goal of finding a suitable scheme acceptable to all who work with such remains is still elusive. The most comprehensive and elaborate attempt has been by Fedonkin (in Sokolov and Ivanovskiy, 1985, and Sokolov and Iwanowski, 1990), who arranged the taxa under two main headings, Radialia and Bilateria, with further groupings based on the underlying symmetry of the taxa. Radialia encompass various classes of discoidal coelenterates, whereas the Bilateria comprise various phyla of worm- and arthropod-like fossils, as well as the extinct phylum Petalonamae of frondose forms, some of which, strictly speaking, are not bilateral (e.g., Pteridinium Giirich, 1933). Forms such as Bradgatia, Ivesheadia, Fractofusus, and others do not readily fit into this scheme. Another attempt to classify the Ediacaran biota is that presented in Runnegar and Fedonkin (1992, p. 373).
Inasmuch as the systematic position and phylogeny of many of the forms still need to be worked out (e.g., see Runnegar, 1995 for arguments generally still current), we here use an informal order of presentation that groups the genus-level taxa based on the following broad informal geometric categories and their postulated affinities (Table 1); one kind of dubiofossil is also described. The scheme has its drawbacks. For instance, the discoid forms have traditionally been classified as cnidarians. However, they may be holdfasts of fronds that were not preserved, and they thus could or should be classed as Petalonamae.
Genus ASPIDELLA Billings, 1872
ASPIDELLA TERRANOVICA Billings, 1872
Figure 7.1-7.6
Aspidella terranovica Billings, 1872, p. 478, fig. 14.
FIGURE 3-Discovery locality (Locality 5) in Mistaken Point Formation. 1, Section, looking east. Co-author A. King standing near origin of baseline (0.0 m) on main fossiliferous layer (F7), which extends to white arrow at left. Meter-stick near middle resting on layer F4 with numerous Aspidella Billings, 1872 specimens (see Fig. 7.5). Lighter layers are tuffaceous horizons. Principal fossil levels indicated by F1-F8 in drawn section at right. 2, Composite photo of main bedding surface F7 of eastern part of main ledge at Locality 5, showing location of specimens that provided latex molds. Numbers represent distances in meters east of origin of baseline, and are cited in captions in relevant subsequent figures. Meter scale at center graduated in decimeters. Discoid forms, Spriggia morphs O’BRIEN AND KING, 2004a, fig. 3 D, E; pl. 3A, 3C partim.
For comprehensive synonymy, see GEHLING ET AL., 2000.
Description.-Centimetric elliptical discs on bedding surfaces, with several preservational morphotypes, including small concave epireliefs and larger flat discs, both with distinct narrow raised rim, and others with few to numerous concentric ridges and depressions of low to moderate relief. Dimensions of 84 specimens (long axes) measured at various localities ranging from 0.48 to 12.5 cm (mean 3.72 cm), with a positively skewed, polymodal pattern (Fig. 7); two main modes between 1 and 3 cm and 4 and 5.5 cm.
Occurrence.-Mistaken Point Formation, Localities 1-6, 11, 12, 37, 39; Trepassey Formation, Localities 10, 15, 20, 33, 37, 40, 41; Fermeuse Formation, Localities 16-19, 21-30, 38; Renews Head Formation, Locality 32.
Discussion.-Aspidella terranovica is the taxon with the longest stratigraphic range in the area, and also the most widespread, occurring at 33 of the 41 localities. Despite the basic simple discoid shape, it represents taphonomically quite variable remains, as is the case on the Avalon Peninsula. The polymodal pattern in Figure 7 reflects differences to be expected from measurements on different bedding surfaces and localities. In a comprehensive analysis of discoidal Ediacaran genera worldwide, Gehling et al. (2000) synonymized numerous forms, treated them as preservational variants of Aspidella, and interpreted the discs as casts of the basal impressions of collapsible or hollow bulb-shaped organisms. This action was questioned by Serezhnikova (2005, p. 392), who regarded Ediacaria Sprigg, 1947 and Cyclomedusa Sprigg, 1947 as distinct from Aspidella, and the synonymization as premature, but for our material, we accept the synonymization. Gehling et al. (2000) recognized several morphotypes, including invaginate, flat, and convex types, which are also represented in our area (Fig. 7.1- 7.6). The remains are hardly distinguishable from the basal attachment discs of the frondose taxa such as Charniodiscus, with which they frequently co-occur, and from which they are separated only by the absence of any evidence of an attached frond. In addition, discs in the Catalina Dome area hint at a further relationship to Hiemalora, as non-annulate discs with faint radial processes are associated with close-by Hiemalora (Fig. 7.4).
Figure 4-Simplified stratigraphic section with approximate position of fossil localities. Thicknesses are dip-based estimates. Full circle indicates presence of taxon; empty circle signifies uncertain identification. SHG = Signal Hill Group. Basal portion of taxon 6 (Charnia grandisl) is conjectural.
FIGURE 5-Comparison of stratigraphic ranges of major Ediacaran taxa in eastern Newfoundland. Thicknesses of formations are not to scale. Note the higher ranges on the Bonavista Peninsula (rectangles). Inset map: A-Mistaken Point area on Avalon Peninsula; B-Catalina area on Bonavista Peninsula.
GENUS HIEMALORA Fedonkin, 1982
HIEMALORA STELLARIS (Fedonkin), 1980
Figure 9.1-9.10
Star-shaped forms, ANDERSON AND CONWAY MORRIS, 1982, p. 7-8, text- fig. 3.
Stellate organism, CONWAY MORRIS, 1990, fig. 1c.
Tentaculate discs with possible affinities to Hiemalora, O’BRIEN AND KING, 2004a, p. 209-210, pl. 5b.
?Medusina filamentus [filamentis] SPRIGG, 1949, p. 90, pi. 13, fig. 1, text-fig. 7D.
Pinegia stellaris FEDONKIN, 1980, p. 9, pl. 1, figs. 3-5.
Pinegia stellaris FEDONKIN, 1981, p. 61, pl. 30, figs. 1-3.
Hiemalora stellaris FEDONKIN, 1982, p. 137.
Pinegia cf. stellaris FEDONKIN, 1983, p. 129, 134, pl. 29, fig. 3.
Hiemalora stellaris FEDONKIN, 1984, p. 42-43, pl. 5, fig. 3.
Hiemalora cf. stellaris FEDONKIN, 1984, pl. 5, fig. 5.
Hiemalora stellaris FEDONKIN IN SOKOLOV AND IVANOVSKIY, 1985, v. 1, p. 84, pl. 7, figs. 1, 6, fig. 7A.
Hiemalora stellaris GUREEV, 1988, p. 69, pl. 13, figs. 2, 3.
Hiemalora stellaris FEDONKIN IN SOKOLOV AND IVANOWSKIY, 1990, v. 1, p. 90-91, pl. 7, figs. 1, 6.
?Hiemalora sp. FARMER, VIDAL, MOCZYDLOWSKA, STRAUSS, AHLBERG, AND SIEDLECKA, 1992, p. 189, fig. 5a-b.
Hiemalora stellaris FEDONKIN, 1992, figs. 15-17.
Hiemalora pleiomorphus RUNNEGAR AND FEDONKIN, 1992, p. 387, fig. 7.7.5C.
Hiemalora aff. H. pleiomorphus NARBONNE, 1994, p. 412, fig. 3.1.
Hiemalora stellaris FEDONKIN, 1994, fig. 1A.
Hiemalora cf. stellaris FEDONKIN, 1994, fig. 1C
Hiemalora stellaris SOKOLOV, 1997, p. 134-135, pl. 18, fig. 3.
Hiemalora MARTIN, GRAZHDANKIN, BOWRING, EVANS, FEDONKIN, AND KIRSCHVINK, 2000, p. 843-844, fig. 4D.
Hiemalora NARBONNE, DALRYMPLE, AND GEHLING, 2001, p. 33, 60, 65, 67.
Hiemalora pleiomorpha DZIK, 2003, p. 124, fig. 10B (only).
Description.-Discs on upper bedding surfaces, 0.3-4.8 cm wide (mean = 2.25 cm, n = 27), outlined by a distinct narrow raised rim ~0.5-1 mm wide surrounding a mostly flat disc with or without concentric ring. Attached to rim are numerous outwardly radiating, densely packed to moderately spaced narrow rays or appendages of variable length, generally of the order of the disc diameter or less, but in some specimens attaining double that (maximum observed length 5.2 cm, with average maximum of 3.15 cm for 27 specimens). Rays rectilinear to slightly sinuous, usually unbranched, but bifid and occasional trifid branching observed; rays rarely crossing over one another; 2 mm or less in width, slightly tapering distally to a point (as if descending obliquely into the sediment) or to a bulbous terminus (Fig. 9.1). In Figure 9.6, small specimen sitting on ray of larger specimen. In specimens illustrated in Figure 9.1-9.3, and 9.6, rays exhibiting shallow axial trough with curved semi- elliptical cross sections between narrow, levee-like lateral ridges; possible fusion of two filaments. Central disc bearing faint round outlines 3-5 mm across. Measurements of more complete specimens given in Figure 10.
Occurrence.-Mistaken Point Formation, Localities 2, 3, 5, 11, 35; Fermeuse Formation, Localities 16-18, 21, 24, 26, 29?, 38.
Discussion.-Inasmuch as the terms “tentacles” and “roots” used in the literature for the slender radiating appendages convey quite different anatomical features and functions, depending on one’s interpretation of the body, it seems more appropriate to use the more neutral descriptive labels “rays” or “appendages” until meir function has been more convincingly demonstrated. While appendages in most specimens are unbranched, a few clearly exhibit branching.
FIGURE 6-Circular histograms (radius of wedge) showing azimuths of frond alignments of Charnia and Chamiodiscus Ford, 1958 specimens on Bonavista Peninsula by formation, using 30[degrees] bins for retrodeformed data; mean vector and 95% confidence interval superimposed.
TABLE 1-Postulated affinities of Ediacaran taxa on Bonavista Peninsula.
The affinities of Hiemalora have been problematic. Their shape is not unlike that of the modern colonial cnidarian Obelia Peron and Lesueur, 1810. Fossils of this type from the Vendian (Ediacaran) of the White Sea region were originally referred to Pinegia and compared to solitary polyps of the lower Hydrozoa (Fedonkin, 1980). As the name Pinegia was preoccupied, the fossils were subsequently renamed Hiemalora (Fedonkin, 1982). Without being aware of these publications, Anderson and Conway Morris (1982) considered 3 alternatives for identical fossils in the Mistaken Point Formation- a basal attachment organ, a star-like trace fossil like Heliochone Seilacher and Hemleben, 1966, and a body fossil of unknown affinity. They favored the body fossil interpretation. An attachment organ was discounted, because the smooth ring was viewed as surrounding empty space, and no upward projections were observed. The trace fossil possibility was discarded because of the relationship between the structure and sediment and the mode of preservation. However, while most workers have considered them as cnidarians, the trace fossil interpretation was revisited by Martin et al. (2000). More recently, Dzik (2003, p. 125) regarded the structures as “basal discs of petalonamaeans or related organisms with finger-like protrusions functioning as roots, or possibly, as penetrating organs releasing sulfide from the microbial mat.”
Two species have been formally designated: H. stellaris, originally described from siliciclastics in the northern part of the Russian Platform (Fedonkin, 1980, 1982), and H. pleiomorpha, first recognized in laminated black, bituminous limestone from the Olenek Uplift in Siberia (Vodanyuk, 1989). The latter has a distinguishing presence of an ornamentation on the disc, a pattern of parallel to slightly divergent sets of fine, essentially rectilinear striations on the disc, reminiscent of a delicately folded or stretched membrane. These features may be taphonomic, but may also be related to the presence of appendages that pulled on the membrane under external stress. The distinction between the two species is not always clearcut, as a fair amount of morphologic variability can be observed on a given bedding plane (e.g., Vodanyuk, 1989, fig. 3). Moreover, other specimens from the same formation in the Olenek Uplift seem to lack these features (e.g., Fedonkin, 1984, pl. 4, fig. 6; 1985, pl. 7, fig. 4; Dzik, 2003, fig. 10c; unillustrated specimen in the collection of the Paleontological Institute in Moscow, PIN 3995/252). At least one specimen of undoubted H. stellaris from the Ukraine also bears fine parallel striations on the disc (Fedonkin, 1984, pl. 5, fig.3, PIN 3993/309). Fedonkin (1992, fig. 15), the author of H. stellaris, also has attributed a large specimen with H. pleiomorpha aspect to H. stellaris. The two species may be the end members of biologic and/ or taphonomic spectra. Well preserved Siberian material of Hiemalora is presently under study by Russian colleagues (Serezhnikova and others), so more robust criteria for differentiating the species may be generated. Because of the lack of evidence for the delicate striations in any of our material, and the absence of any distinct multiple clustering of data points (Fig. 10), we assign all our specimens to H. stellaris. FIGURE 7-Outcrop photos of Aspidella terranovica Billings, 1872 (1-6), and Aspidella-like Dubiofossil A (7), from Bonavista Peninsula. All scale bars graduated in cm, except for 5 and 7, which are in dm. Photos in 1-4 are retrodeformed. 1, Multi- ringed, Spriggia-like morph of A. terranovica, Trepassey Formation, Locality 15. 2, Moderately-ringed morph in Fermeuse Formation, Locality 21. 3, Aggregation of small specimens of A. terranovica, some with radial markings (type morph of Gehling et al., 2000). Renews Head Formation, Locality 32. 4, A. terranovica specimens, and discs with faint, Hiemalora-like radial markings extending from raised peripheral rim (a, c). Compare with H. pleiomorpha Vodanyuk, 1989 specimen in Serezhnikova (2005, pl. 4, fig. 3). Gently depressed interiors of discs still retain fine-grained, dark gray tuff covering. The specimens occur on the same bedding surface as the fine Hiemalora (Fedonkin, 1985) specimen illustrated in Figure 9.1. Mistaken Point Formation, Locality 3. NFM catalog numbers: a: NFM F-471; b: NFM F-472; c: NFM F-473; d: NFM F-474; e: NFM F-475; f: NFM F-476; g: NFM F-477. 5, Cluster of A. terranovica specimens of variable size in Mistaken Point Formation Level F4 at Locality 5 (see Fig. 3.1). 6, Large, flat, relatively smooth Spriggia-line morph. Light colored area at center is covering ash layer. Mistaken Point Formation, Level F1 at Locality 4 (see Fig. 3.1). 7, Dubiofossil Type A, a very large ovate structure with concentric rings and very low relief. Mistaken Point Formation, Locality 8.
Figure 8-Size distribution of Aspidella specimens in Bonavista area, based on long diameter of ellipse coincident with cleavage/ bedding lineation. Polymodal pattern reflects different size values for different stratigraphic levels and localities.
Fossils attributed to either species with different degrees of certainty are now known from the Ediacaran in other parts of the world (e.g., Ukraine, Norway, NW and E Canada, Australia; refer to synonymy) (Fig. 11). An early illustration of a disc with branching processes that has caused some workers to compare it to Hiemalora is “Medusina filamentus” from the Rawnsley Quartzite (Sprigg, 1949, p. 90, pi. 30, fig. 1, text-fig. 7d). Sprigg interpreted the form as a medusoid. The illustration of the holotype shows a partial narrow concentric rim surrounding the central disc and the field with the radial processes, at a distance of about 3Vi times the radius of the central disc. This is unlike Hiemalora. The specimen was subsequently ascribed to Pseudorhizostomites Sprigg, 1949, to which it is connected by transitional forms, according to Glaessner and Wade (1966, p. 605).
Specimens of H. stellaris from siliciclastic rocks in the Mogilev Formation of the Ukraine (Gureev, 1988, pi. 13, figs. 2, 3) are comparable to specimens from the White Sea area.
Relatively well preserved specimens from Wales (Gehling et al., 2000, p. 450; J. Gehling photo, personal commun., 2005) closely resemble specimens from Locality 3 in the Catalina area, particularly the processes with levee-like borders and the rounded outlines on the disc.
Farmer et al. (1992, fig. 5a, 5b) illustrated, along with other body fossils, some low epireliefs from the Stappogiedde Formation in Finnmark, northern Norway, and attributed them to Hiemalora sp., but provided no further description. The specimens have a poorly defined central disc ~1 cm across, surrounded by a dense fringe of somewhat ragged-looking, radial appendages.
Narbonne (1994, fig. 3.1) classified a solitary, fragmentary specimen from the Sheepbed Formation in NW Canada as Hiemalora aff. H. pleiomorpha. The specimen is relatively large, has somewhat more relief than typical H. pleiomorpha, has densely packed appendages, some fine striations of uncertain significance on one edge of the central disc, and is preserved in positive hyporelief in turbiditic siliciclastics. It was interpreted as a semiinfaunal polyp impression.
Martin et al. (2000, fig. 4d) illustrated a specimen of Hiemalora from the White Sea coast that very clearly portrays multiple branching, with one or more short branches diverging at angles of 300 -60[degrees] from the main strand. As already stated, the form was interpreted as a trace fossil.
Lastly, De (2003) reported on two questionable Hiemalora specimens from the Upper Vindhyan Bhander Group northwest of Satna, central India. The illustrated specimens are not distinct enough to have confidence in their attribution to this genus, and they are not included in the synonymy.
Material from the Catalina area illustrated in this paper contributes new information on two aspects of the Hiemalora enigma: function and original morphology. It bears on the long-standing question of whether the radiating structures are tentacles, roots, or traces. At least two specimens on the same bedding plane in the Mistaken Point Formation at Locality 5, and another two in the Fermeuse Formation at Localities 21 and 26, show a tripartite arrangement (Fig. 12): a disc with radial appendages that is indistinguishable from Hiemalora, with an attached stalk, which in turn merges distally with an abraded, partially preserved frond. Unfortunately, the detail of the fronds is insufficient to allow their attribution to any of the frondose forms known from Newfoundland or elsewhere. These candelabra-like fossils with a Hiemalora base are next described separately under Primocandelabrum hiemaloranum n. gen. and sp.
It should be noted that Hiemalora individuals without fronds in the Catalina area are, in places, closely associated with, and seem to intergrade with, identical discs that are relatively quite smooth and that bear only a few faint, or no, ray-like radial markings (Fig. 7.4). These structures could be regarded as simple, atypical, unornamented Aspidella.
The second aspect to which the new material contributes is original morphology. Specimens in the Mistaken Point Formation at Locality 3 are remarkably well preserved due to a thin covering layer of black, fine-grained tuffaceous sediment (Fig. 9.1, 9.3). Some specimens suggest that the central organ had significant relief (Fig. 9.10). Others appear to have been flatter, their softbodied parts compacted vertically in such a way that the central organ was compressed without developing a noticeable concentric pattern typically found in Aspidella, which was interpreted as a bulb-like organism or organ by Gehling et al. (2000). The radiating cylindrical appendices or rays were molded in such a way as to suggest collapse of their axial portions, whereas the lateral portions remained elevated and assumed a levee-like aspect. While branching of rays is observed, it is not common. The apparent confluence or fusion of two radial elements in one specimen is intriguing (Fig. 9.1). While it could be due to molding of collapsed tubes, fusion of hyphae is a feature found amongst the fungi, and one may consider whether these fossils could belong to this group. This would support the earlier interpretation by Peterson et al. (2003) that a fungal model may be applicable to particular Ediacaran taxa such as Aspidella, Charnia, and Charniodiscus, although they may not necessarily have been members of the Kingdom Fungi. Additionally, in one instance, a small specimen seems to he over the ray of a larger specimen or be connected with it (Fig. 9.6), while in a second example a round body forms a terminus of fused rays (Fig. 9.1). These juxtapositions may be coincidence, but it is worth considering the possibility that asexual reproduction is represented and search for more examples to strengthen such an interpretation.
Figure 9-Epireliefs of Hiemalora stellaris (Fedonkin), 1980 from Catalina area. All photos retrodeformed; bar scales in cm. 1, Specimen with shallow concave disc filled with fine-grained ash and numerous radiating tubular appendages preserved as rectilinear to curvilinear rays with axial depressions and levee-like margins. Some rays apparently terminating in subcircular structure, and showing confluence (middle right). Mistaken Point Formation, Locality 3. NFM F-478. 2, Specimen with numerous appendages, several exhibiting branching; trifid branch at arrow. Mistaken Point Formation, Locality 3. 3. Specimen with few appendages on same bedding plane as that in 1, located 25.4 cm away. NFM F-479. 4, Specimen with concentrically patterned disc and some relief. Mistaken Point Formation, Locality 5, at 12.2 m E (see Fig. 3.1). NFM F-480. 5, H. stellaris. Mistaken Point Formation, Locality 5 at 32.6 m. 6, Specimen from layer 5.7 cm above layer bearing specimens illustrated in parts 1 and 3 (see also Fig. 15.1). Specimen is cut by small soft- sediment fault scarp (light diagonal band). Note small specimen in upper right (arrow), positioned on ray of larger specimen, possibly representing a case of vegetative reproduction. Mistaken Point Formation, Locality 3. NFM F-467. 7, Small specimen of H. stellaris (NFM F-466) and nearby small Aspidella terranovica (NFM F-465; see also Fig. 15.1). Same slab as part 6. 8, Specimen from Fermeuse Formation, Locality 21, at 23.0 m E, 7.7 m N. NFM F-481. 9, Specimen in Fermeuse Formation, Locality 17. NFM F-482. 10, H. stellaris specimen with high relief and branching appendages. Fermeuse Formation, Locality 24. NFM F-483.
Figure 10-Morphometry data of retrodeformed specimens of Hiemalora in Catalina area. 1, Scatter plot of mean ray length (d) vs. disc diameter (D), and selected ratios of D/d. 2, Scatter plot of number of rays vs. disc diameter. 3, Frequency histogram of D/d ratio; compare with fig. 5 of Serezhnikova (2005).
GENUS PRIMOCANDELABRUM NEW GENUS Type species.-Primocandelabrum hiemaloranum new genus and species (by monotypy).
Diagnosis.-Tripartite, candelabrum-like fossils comprised of basal disc, stem, and variable and incompletely preserved bushlike frond of overall triangular shape, containing coarse, distally diverging branches.
Etymology.-Named for the candelabrum-like shape and its early appearance in the geologic record; primus = L. first.
Discussion.-Hiemalora has not previously been reported as having an attached frond. We here recognize a new genus that is distinct from Hiemalora only by the presence of an attached stem and frondose superstructure. The situation is analogous to the practice of regarding Aspidella and Charniodiscus as separate taxa, depending on the basis of the presence or absence of an identifiable frond, as the genus of frond cannot be guessed from the preservation of only the holdfast; both Aspidella and Hiemalora are viewed as form or organ taxa.
PRIMOCANDELABRUM HIEMALORANUM NEW SPECIES
Figure 12.1-12.4
Diagnosis.-As for genus; basal disc with prominent external radiating processes.
Description.-Tripartite epireliefs characterized by basal discoidal or globular structure attached to a distinct stem that develops distally into an incompletely preserved, bush-like or candelabra-like frond with a general, overall triangular shape. Basal globular or discoidal structure outlined by a narrow raised marginal rim enclosing shallow depression with or without faint concentric markings; numerous (8-30) narrow, straight to slightly sinuous or bent ray-like appendages radiating from disc rim. Diameters of four discs observed 2.5, 3.2, 4.2, and 7.8 cm, length of processes about equal to disc diameter. Stem length (distance between disc center and frond) 3.7, 5.3, 6.0, and 12.4 cm, similar to disc diameter, width uniform, respectively 0.5, 1.6, 0.8, and 3 cm. Fronds incomplete, proximal portion forming acute to approximately right angles, preserved length about double the stem length (minima respectively 8.5, 10.5, 15.0, and 23.5 cm), widths 4.7, 7.0, 7.2, and 20 cm. Frond with poorly defined, coarse, distally diverging ridges and intervening depressions; two depressions in one specimen with faint transverse markings 3 mm wide (Fig. 12.3).
Figure 11-Reported world occurrences of Hiemalora. 1, Sekwi Brook; 2, Avalon; 3, Bonavista; 4, Wales; 5, Tanafjord; 6, White Sea; 7, Podolia; 8, Olenek Uplift; 9, Ediacara; 10, questionable Hiemalora in Vindhyan Supergroup. For references, see synonymy.
Etymology.-Named for its Hiemalora-like base.
Types.-Holotype NFM F-484; paratypes NFM F-485, NFM F-486.
Occurrence.-Mistaken Point Formation at Locality 5, and Trepassey Formation at Localities 21 and 26.
Type locality.-Trinity Bay North, Locality 5, at 37.5 m E (see Fig. 3.2).
Type horizon.-Lower part of Murphy’s Cove Member of Mistaken Point Formation.
Discussion.-The morphology of the basal disc with radiating processes coincides with that of Hiemalora, and the two would be indistinguishable were it not for the presence of an attached stem and frond. The candelabra-like form with the radiating processes on the basal disc thus may have an important bearing on the interpretation of Hiemalora insofar as the radiating appendages in the latter have been explained alternatively as tentacles and as rooting structures. The new Bonavista material supports the case for the latter interpretation, if, indeed the two taxa represent different degrees of preservation of one type of organism. If so, one should look for evidence for the presence of an attached stem in specimens previously referred to Hiemalora. On the other hand, the two taxa may be distinct despite the morphologic resemblance of the ray-bearing discs. The candelabra-like organisms were attached to the seafloor, and were felled in the same direction as nearby Charnia and Charniodiscus specimens. As with specimens of uiese latter frondose genera on the Avalon Peninsula, preservation quality is best for the basal disc and progressively deteriorates towards the distal portion, a taphonomic effect due to diachronous burial of an erect frondose organism (Laflamme et al., 2004, p. 829).
Preservation of local detail in the frond of one specimen, more clearly seen in the latex mold than the specimen in outcrop, shows several oblique divisions spaced equally about 4 mm apart (Fig. 12.3). The pattern is reminiscent of secondary branches in Charnia and Charniodiscus. The shape of the preserved frond portion of this specimen also resembles a stalked specimen of Bradgatia from the Trepassey Formation, but which is without a clearly recognizable Hiemalora-like base (see Fig. 19.4 under Bradgatia).
PRIMOCANDELABRUM sp.
Figure 12.5
“Dusters”, “Feather dusters”, “Tree fronds”, NARBONNE, DALRYMPLE, LAFLAMME, GEHLING, AND BOYCE, 2005, p. 58, 60, 65, 68, figs. 6.3, 6.5, 6.6, 7.3, 7.6.
Description.-Tripartite epireliefs characterized by basal discoidal structure attached to a distinct stem that develops distally into an incompletely preserved, bush-like frond with coarse, distally diverging branching ridges and intervening irregular depressions. Basal disc with or without faint concentric markings. Fronds with overall inverted triangular shape apparently without distinct geometric pattern. Diameters of four discs observed 2.0, 2.2, 3.1, and 5.0 cm. Respective stem length (distance between disc center and frond) 1.9, 2.7, 2.7, and 5.5 cm, similar to disc diameter, stem width respectively 0.3, 0.6, 0.4, and 1.0 cm. Fronds incomplete, proximal portion forming acute to approximately right angles, preserved length respectively 2.4, 4.8, 12.3, and 13 cm, widths approximately 4.0, 5.8, 10, and 10.5 cm. One specimen with faint radial markings on basal disc.
Occurrence.-Mistaken Point Formation, Localities 5, 6; Trepassey Formation, Locality 20: Fermeuse Formation, Localities 21, 26, 29?. Also present in the Mistaken Point Formation on the Avalon Peninsula.
Discussion.-The dimensions and the shape of the bushy superstructure are very similar to those of specimens of P. hiemaloranum, but the ratio of frond width to frond length is slightly higher for Primocandelabrum sp. than for P. hiemaloranum, and the basal discs lack the diagnostic radiating appendices. If originally present, the rays were not preserved, or the attachment disc is preserved at a higher level in the sediment, in which case the form may be a taphomorph of P. hiemaloranum. The fronds of most of these structures show no clear geometric patterns that would allow them to be referred to Charnia, Charniodiscus, or bifoliate rangeomorphs, and thus their affinities are undetermined.
Fronds with rayless discs occur in the Mistaken Point Formation on the Avalon Peninsula, where they have been variably referred to as “dusters”, “feather dusters”, and “tree-fronds.” These are presently under study at Queen’s University.
GENUS CHARNIA FORD, 1958
The Catalina area has yielded fronds of several apparently intergrading morphologic varieties equipped with a short stem emanating from an attachment disc, all broadly attributable to Charnia. The frond patterns range from ones with symmetrical, alternating, acutely diverging primary branches with regular transverse secondary partitions, to ones with a rhomboidal surface pattern, to ones with more asymmetrical and more irregular branches with few or no preserved secondary divisions and presence of rangeomorph elements, allowing for the differentiation of at least 3 morphotypes.
FIGURE 12-Outcrop views of Primocandelabrum hiemaloranum n. gen. and sp. (1-4) and Primocandelabrum sp. (5). All photos retrodeformed; bar scale divisions in cm. 1, Partial frond with well developed rays on basal disc. Mistaken Point Formation, Level F7 at Locality 5 at 37.5 m E (see Fig. 3.2). Holotype NFM F-484. 2, Large partial specimen. Fermeuse Formation, Locality 26. Lighting from right Paratype NFM F-485. 3, Detail view of latex mold made from frond of specimen of Primocandelabrum hiemaloranum n. gen. and sp. in part 2, showing rhythmically spaced transverse markings, probably representing secondary branches. Photo is printed as mirror image to show same orientation as in part 2. Paratype NFM F-485. 4, Abraded frond with faint Hiemalora-like base. Fermeuse Formation, Locality 21. Lighting from right Paratype NFM F-486. 5, Partial frond with Aspidella-like base. Trepassey Formation, Locality 20.
The appreciable morphologic diversity in the Catalina area presents somewhat of a taxonomic dilemma, that is, whether one should assign the forms to different species, or whether the variability represents taphonomic factors or different orientations during burial. For our material, we rely on the regularity of the lobe pattern and transverse divisions, as well as the smaller acute angle at which lobes diverge from the main axis, to assign specimens to C. masoni, and mis includes those with rhomboidal patterns. We distinguish these from specimens with more irregular branching and with higher divergence angles, which we ascribe to Charnia antecedens. Bedding surfaces with numerous individuals of either species show strong preferred orientation, indicating felling from an erect, anchored living position in response to a passing current. A fourth species chacterized by decimetric length is attributed to C. grandis?
The biological affinities of these fossils are uncertain. Charnia has been variously interpreted as algal (Ford, 1958), an octocoral of the extinct order Rangeomorpha (Jenkins, 1985), a pennatulacean cnidarian (Fedonkin, 1992; Jenkins, 1992, 1996; Nedin and Jenkins, 1998), a vendobiont (Seilacher, 1989, 1992), or a fungus (Petersen et al., 2003). Our new material includes fronds with distinct rangeomorph elements within the primary branches of Charnia antecedens, placing them firmly within the Rangeomorpha of the extinct Phylum Petalonamae Pflug, 1972. Glaessner (1979) erected the Family Charniidae based on this genus. CHARNIA MASONI FORD, 1958
Figure 13.1-13.6
Charnia masoni FORD, 1958, p. 212, pl. 13, fig. 1.
Charnia masoni FEDONKIN, 1981, p. 66, pl. 3, figs, 5, 6; pl. 29, fig. 1.
Charnia masoni FEDONKIN, 1985, p. 110, pl. 12, fig. 4; pl. 13, figs. 2-4.
Charnia masoni NEDIN AND JENKINS, 1998, p. 315, fig. 1.
Charnia masoni NARBONNE, DALRYMPLE, AND GEHLING, 2001, p. 32, pl. 1C.
Charnia masoni NARBONNE, DALRYMPLE, LAFLAMME, GEHLING, AND BOYCE, 2005, p. 28, pl. 1I.
Description.-Centimetric to decimetric remains preserved in epirelief, organized in three parts when complete, comprising a basal disc connected by a short stem to a moderately long, bifoliate frond outlined by pattern of narrow vein-like ridges and intervening broader depressions, forming a leaf-like structure that constitutes its most distinctive feature. Frond composed of two opposing series of up to 10 or more contiguous, uniform, parallel, straight to slightly sigmoidal oblique primary branches, diverging at a uniform angle of 150 -50[degrees], in alternate fashion, along zigzag frond axis, with opposing branches offset by half a branch width. Branches in lateral contact or overlapping, divided uniformly into secondary modules of obliquely transverse subrectangular segments generally of uniform orientation, size and shape, and usually numbering between 5 and 12. Some specimens with pattern of regularly spaced and equally distinct, parallel ribs that intersect obliquely with a second set of equally distinct ribs to produce a rhomboidal signature (Fig. 13.5, 13.6). Most specimens incomplete; five specimens yielding partial measurements: where present, basal discs small, 0.5-1.5 cm across; stems 0.5-5.0 cm long, 0.3-0.9 mm wide; fronds 5.7-26.5 cm long, 1.6-5.4 cm wide.
Occurrence.-Mistaken Point Formation, Localities 4-7, 9, 11, and on the Avalon Peninsula (Narbonne et al., 2001); Trepassey Formation, Locality 20; Fermeuse Formation, Localities 17, 18, 26. The species is also found in England (Ford, 1958), the White Sea area (Fedonkin, 1985), Northern Siberia (Fedonkin, 1985), and South Australia (Nedin and Jenkins, 1998).
Discussion.-This species is abundant at several localities, but complete specimens are rare, making it difficult to obtain morphometric data on the overall dimensions and number of branches of the organisms. However, the partial preservation allows the recognition of the systematic, uniform, and symmetrical branching characteristics and uniform secondary modules of C. masoni. Specimens with rhomboidal patterns lack a prominent zigzag axis, and could be interpreted as individuals in an orientation different from the normal felling position, one which resulted in the branches becoming superimposed and concomitantly obscuring the zigzag axis underneath the branches. This kind of preservation has not heretofore been described, and brings up the possibility of the presence of “ventral” and “dorsal” sides of the organisms, elements that need to be explored further. Specimens with apparent long stem (e.g., Fig. 13.3) may represent individuals whose proximal branches were lost due to recent erosion, although another small specimen (Fig. 13.8) has a parallel-sided ridge between the frond and basal disc, indicating that a robust stem is a real biologic feature.
CHARNIA GRANDIS? (Glaessner and Wade, 1966)
Fig. 14
?Charnia sp. GLAESSNER, 1959, p. 1472, text-fig. 1b.
?Rangea? sp. GLAESSNER, IN GLAESSNER AND DAILY, 1959, p. 397, pl. 46, fig. 2.
?Charnia sp. GLAESSNER, 1961, p. 75, text-fig.
?Charnia sp. a GLAESSNER, 1962, p. 484-485, pl. 1, fig. 4.
?Rangea grandis GLAESSNER AND WADE, 1966, p. 616, pl. 100, fig. 5.
?Glaessnerina grandis GERMS, 1973, p. 5, fig. 1D.
Charnia grandis BOYNTON AND FORD, 1995, p. 168, fig. 1.
?Glaessnerina grandis JENKINS, 1996, p. 35, fig. 4.1.
Charnia grandis FORD, 1999, p. 231, fig. 3.
Description.-Incomplete frond preserved as negative epirelief, proximal portion missing; dimensions of retrodeformed specimen approximately 66.5 x 21.1 cm. Single preserved frond portion composed of two series of about 21 partially preserved, upward (forward) curving and distally tapering, parallel primary branches emerging in alternating fashion on each side of medial zigzag axis that is well marked only in the lower portion. Branching angle near 90[degrees] for larger proximal branches, with angles gradually becoming more acute for distal branches, trending towards ~40[degrees]. Width of primary branches (measured near medial axis) gradually decreasing from ~9 mm for branches in proximal region to 3.2 mm for those near apex of frond, and also decreasing distally along branch. Primary branches divided into numerous (up to 13) secondary branches or partitions disposed obliquely at 40- 60[degrees] to primary branches, widths gradually diminishing (in concordance with decrease in primary branch size) from ~10 mm in large proximal branches, to ~3 mm in branches near frond apex, and also distally in individual branches. Lateral inclination of secondary branches with respect to frond axis gradually flattening distally from ~45[degrees] in large proximal primary branches to ~5[degrees] in branches near apex.
Occurrence.-Mistaken Point Formation, Locality 4; Bradgate Formation, Charnwood Forest, England; Ediacara Member, Ediacara, Australia.
Discussion.-Our specimen most closely resembles a 60-cm long specimen from the Bradgate Formation of Charnwood Forest, England, identified as Charnia grandis (Boynton and Ford, 1995, fig. 1; Ford, 1999, fig. 3). Both specimens are more nearly complete than the holotype from the Rawnsley Quartzite in Australia (Glaessner and Wade, 1966, pl. 100, fig. 5), a fragment with dimensions of 16.0 x 7.5 cm showing preservation of five primary branches on one side and seven on the opposing side, and bearing up to 13 se
