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SMITHSONIA N CONTRIBUTION S T O PALEOBIOLOG Y • NUMBE R 9 4 

Middle Proterozoic (1.5 Ga) Horodyskia moniliformis 

Yochelson and Fedonkin, the Oldest Known 

Tissue-Grade Colonial Eucaryote 

Mikhail A. Fedonkin 

and Ellis L. Yochelson 

Smithsonian Institution Press 

Washington, D.C. 

2002 
ABSTRAC T 

Fedonkin, Mikhail A., and Ellis L. Yochelson. Middle Proterozoic (1.5 Ga) Horodyskia 

moniliformis Yochelson and Fedonkin, the Oldest Known Tissue-Grade Colonial Eucaryote. 

Smithsonian Contributions to Paleobiology, number 94, 29 pages, frontispiece, 19 figures, 

2002.— "Problematic bedding-plane markings" discovered by the late R.J. Horodyski from the 

Appekunny Formation in Glacier National Park, Montana, and dated at approximately 1.5 

giga-annum (Ga), were never formally named. We are convinced the specimens are biogenic 

and have placed them within Linnaean nomenclature as Horodyskia moniliformis Yochelson 

and Fedonkin. An apt description of the locally abundant fossils is "string of beads." On each 

string, beads are of nearly uniform size and spacing; proportionally, bead size and spacing 

remain almost constant, regardless of string length or size of individual beads. They may not be 

related to any other known fossil, and their position within highest levels of the taxonomic 

hierarchy is enigmatic. We judge they were multicellular, tissue-grade, colonial eucaryotes. 

Similar strings have been reported from Western Australia, but nowhere else. The general geologic setting in Montana, details of sedimentation, and taphonomy suggest the organisms were 

benthonic, growing upward about 1 cm through episodically deposited eolian dust. During life, 

specimens were stiff and relatively strong, but show no evidence of a mineralized skeleton. 

They lived in poorly oxygenated water with the body progressively subjected to anaerobic conditions. Their energy source is obscure; their mode of growth and several features of interpreted environment lead us to speculate that Horodyskia likely lived primarily by ingesting 

chemosynthetic bacteria rather than by photosynthesis. This notion should be tested by searching red, fine-grained, subaqueous arenites of approximately the same age throughout the world 

for additional occurrences. 

OFFICIAL PUBLICATION DATE is handstamped in a limited number of initial copies and is 

recorded in the Institution's annual report, Annals of the Smithsonian Institution. SERIES COVER 

DESIGN: The trilobite Phacops rana Green. 

Fedonkin, M. A. (Mikhail Aleksandrovich) 

Middle Proterozoic (1.5 Ga) Horodyskia moniliformis Yochelson and Fedonkin, the oldest known tissue-grade 

colonial eucaryote / Mikhail A. Fedonkin and Ellis L. Yochelson. 

p. cm. — (Smithsonian contributions to paleobiology ; no. 94) 

Includes bibliographic references. 

1. Horodyskia moniliformis—Montana. 2. Paleontology—Proterozoic. 3. 

Fossils—Montana. I. Yochelson, Ellis Leon, 1928- II. Title. III. Series. 

QE701.S56no. 94 

[QE719.6] 

560s-dc21 

[561'.9] 2001049570 

® The paper used in this publication meets the minimum requirements of the American 

National Standard for Permanence of Paper for Printed Library Materials Z39.48—1984. 
Contents 

Page 

Introduction 1 

Acknowledgments 1 

Geologic Setting 2 

Collecting Localities 3 

Material and Methods 4 

Previous Investigations 4 

Organic Versus Inorganic Origin 5 

Systematic Paleontology 5 

Domain EUCARYA 5 

Kingdom Uncertain 5 

Phylum Uncertain 5 

Horodyskia Yochelson and Fedonkin 6 

Horodyskia moniliformis Yochelson and Fedonkin 6 

Comparison to Trace Fossils 6 

Specimen Characteristics 6 

Abundance and General Shape 6 

Bead Shape 9 

Associated Biota 9 

Details of Matrix 12 

Lithology 12 

Depositional Environment 14 

Preservation 15 

Taphonomy of Upper Bedding-Plane Surfaces 15 

Taphonomy of Sole Surfaces 16 

Hypotheses 21 

Paleoenvironmental Considerations 21 

Mode of Life 22 

Growth 23 

Single Organism Versus Colonial Organism 25 

Integument 25 

Feeding and Possible Food Supply 26 

Discussion 26 

Literature Cited 28 

in 
FRONTISPIECE.—A dark gray slab from the Appekunny Formation, showing several strings of black-colored 

beads of varying lengths and configurations on the sole surface. A lighter-colored halo accentuates the beads. 

The curved strand trending left to right in the upper part of the photograph is designated as holotype. Several 

beads to the lower left where two strands cross show the inner ridges, but they are too small to be seen in this 

illustration. Above the scale, two beads are on a fragment of another sole surface and may be the upper parts of 

the string to their right. A similar view of this slab was figured in Yochelson and Fedonkin (2000). The corner 

insert is one of the beads from the holotype, indicated by an arrow, the upper surface of which is intact and standing slightly in positive relief; xlO; see also Figure 17c. USNM 508100; Rising Wolf Mountain. 
Middle Proterozoic (1.5 Ga) 

Horodyskia moniliformis Yochelson and 

Fedonkin, the Oldest Known TissueGrade Colonial Eucaryote 

Mikhail A. Fedonkin 

and Ellis L. Yochelson 

Introduction 

The rise of biological complexity is a fundamental problem 

that has been attacked by a wide variety of scientific disciplines. Models derived from various approaches are not always 

consistent. Even within one general approach, for example molecular biology, different models have been developed. At the 

core of some debates is the time of origin of the eucaryotic cell 

and the subsequent appearance of multicellular organisms. 

The aim of this paper is to describe a new form, significantly 

older than presumed multicellular organisms heretofore reported in the literature. To support our interpretation that this 

taxon is of tissue-grade complexity, we have considered sedimentary environment, taphonomic effects, and paleoecology, 

among other points. The paleontology of the Proterozoic is still 

poorly known, and demonstrating that a multicellular form 

does occur in ancient rocks may help resolve the paradox between molecular clock models that predict an early rise of complex life forms and the relatively late appearance of such 

megafossils. 

Mikhail A. Fedonkin, Paleontological Institute, Russian Academy of 

Sciences, Profsoyuznaya ui 123, Moscow 117647 Russia. Ellis L. 

Yochelson, Research Associate, Department of Paleobiology, National 

Museum of Natural History, Smithsonian Institution, Washington, 

D.C. 20560-0137 USA. 

Review Chairperson: John Pandolfi, Department of Paleobiology, 

National Museum of Natural History, Smithsonian Institution, Washington, D.C. 20560-0121. 

Reviewers: Douglas Erwin, Department of Paleobiology, National 

Museum of Natural History, Smithsonian Institution, Washington, 

D.C. 20560-0137; Andrew Knoll, Museum of Botany, Harvard University, Cambridge, Massachusetts 02138. 

The late Robert J. Horodyski devoted his career to the study 

of Proterozoic life and was particularly zealous in field work. 

In 1992, we spent 10 days with him in Glacier National Park, 

Montana, mostly at Apikuni Mountain (Figure 1). The Appekunny Formation, Belt Supergroup, was named before the 

spelling of the mountain's name was changed to Apikuni. At 

this locality, Horodyski (1982:884) found "problematic bedding plane markings"; these are now described in detail and are 

discussed below. Other markings, possibly indicative of former 

megascopic forms of life, are associated with this form (Fedonkin et al., 1994). Following Dr. Horodyski's unexpected 

death on 9 September 1994, part of his collection was donated 

to the National Museum of Natural History (NMNH), Smithsonian Institution, and, combined with the Yochelson-Fedonkin 

material, forms the basis for this study. 

ACKNOWLEDGMENTS 

This project could not have been completed without the assistance of many persons. Ronald Parsley, Department of Geology, Tulane University, had the difficult task of organizing and 

distributing collections after the death of R.J. Horodyski. Authorities at Glacier National Park permitted our collecting of 

specimens. In 1992, Donald Winston, Department of Geology, 

University of Montana, introduced us to stratigraphy of the 

Belt Supergroup and has continued to share his wide experience with us. In particular, he pointed out the low hummock 

cross-bedding in the Appekunny Formation and the unique nature of this subaqueous red bed. Visits to Washington, D.C, by 

M.A. Fedonkin in 1992 and 1996 were made possible by the 

Office of Fellowships and Grants, Smithsonian Institution, and 

in 1999 by support from the Walcott fund. Fieldwork during 
SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY 

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FIGURE 1.—Outline map of boundary of Glacier National Park (GNP) and principal roads. The three collecting 

localities are indicated: (1) Apikuni Mountain; (2) Going-to-the-Sun Road; and (3) Rising Wolf Mountain. 

1992 was supported by National Science Foundation SGER 

grant from P. Kelly, based on proposal number 9115583. 

We are grateful to T.A. Ivanovskaya, Geological Institute, 

Russian Academy of Sciences, Moscow, for her comments 

concerning glauconite. Eugene Jarosavich (retired), Department of Mineral Sciences, NMNH, performed microprobe 

analyses at our request. Donald Dean, Department of Paleobiology, NMNH, made polished and thin sections. Walter Brown, 

head of the Scanning Electron Microscope (SEM) Laboratory, 

NMNH, aided our SEM inquiries. We are particularly indebted 

to Victor Krantz (retired), Office of Photographic Services, 

NMNH, for the outstanding photographs of exceedingly difficult material. Figures 18 and 19 were prepared by E. Tokareva 

and S. Rozhnov, respectively, artists at the Paleontological Institute, Russian Academy of Sciences. 

Early drafts were read by Donald Winston and F.M. Bayer, 

Department of Invertebrate Zoology, NMNH. Their suggestions improved the manuscript, which later also benefitted dramatically from critical reading by D. Erwin, Department of Paleobiology, NMNH, and A. Knoll, Museum of Botany, Harvard 

University, Cambridge Massachusetts. 

Geologic Setting 

The Proterozoic Belt Supergroup covers a vast region in 

Montana, Idaho, and Washington and is in excess of 16 km 

thick. Winston and Link (1993:495) summarized the regional 

setting and stratigraphic correlations. Glacier National Park 

(GNP) is at the eastern edge of the Belt outcrop. Near the 

northeastern GNP boundary, the oldest unit exposed is the Altyn Formation (Figure 2). That carbonate unit contains prominent and abundant stromatolites, particularly Biacalia Krylov 

(Horodyski, 1983, 1989a) in its upper portion. The Altyn is 

thrust eastward over Cretaceous beds; its thickness is unknown, 

but about 150 m are exposed at Apikuni Falls. Whipple (1992) 

noted the contact with the overlying Appekunny Formation is 

disconformable, showing up to 2 m of relief. 
NUMBER 94 

top not exposed 

Shepard Formation 

(>270 m) 

Snowslip Formation 

(385 m) 

Siyeh Formation 

(780 m) 

Grinnell Formaton 

(605 m) 

Appekunny Formation 

(-700 m) 

Altyn Formation 

(>150m) 

base not exposed 

FIGURE 2.—Units of the Belt Supergroup exposed in the northwest part of 

GNP. Both the lower and upper parts of the section are cut off by faults. The 

thicknesses are taken from sections measured by others in the Swiftcurrent Valley-Logan Pass area. The position of the Pursell Lava is indicated by an arrow. 

The Appekunny Formation is 530-690 m thick on the eastern edge of GNP and is divided into five informal members 

(Whipple et al., 1984). On the west side of GNP, the formation 

is thin and only the uppermost informal member can be identified; members 1-4 grade laterally into the upper part of the 

Pritchard Formation (Winston, in litt., 1997). The Pritchard 

contains microfossils, but no megafossils have been reported 

(Horodyski, 1993, appendix). The Appekunny Formation is the 

approximate temporal equivalent of the Greyson Shale in the 

Big Belt Mountains. There is no evidence that the two formations were interconnected, although a connection through the 

Highland Range is plausible (Winston, in litt., 1997); both microfossils and megafossils occur in the Greyson (Horodyski, 

1993, appendix). 

Overlying the Appekunny Formation within the Swiftcurrent 

Valley-Logan Pass area near the center of GNP are the Grinnell, Helena (= Siyeh), Snowslip, and Shepard formations, totaling about 2000 m in thickness. In the southwest part of GNP, 

west of the Blacktail fault, the Mt. Shield, Bonner, and McNamara formations outcrop. The Helena and Shepard are carbonate units. The Helena, like the Altyn, contains stromatolites, being particularly noted for several cycles of alternating 

growths oiBiacalia Krylov and Conophyton Maslov. The other 

formations are argillites, siltstones, and sandstones that are 

characteristically red-colored. 

Based on the literature, Fedonkin et al. (1994:202) suggested 

an age of about 1.4 billion years for the Appekunny Formation. 

Recent age determinations (U/Pb) on the Purcell Lava, between 

the Snowslip and Shepard formations, range from 1508 to 1845 

Ma(Aleinikoffetal, 1996:376). 

The Appekunny Formation is primarily variegated siltstone, 

weathering into slabby layers 1-10 cm thick. As previously 

noted, Whipple et al. (1984:38-39) divided the formation into 

five informal units. The specimens of interest are in the lower 

portion of the section. "The lowest member, member 1, is 

about 450 ft thick and consists of alternate successions of palemaroon and grayish-green siltite and minor argillite." A key 

marker mentioned by Whipple (1992) is a sand-sized quartz 

arenite about 175 ft above the base. We did not observe it during field work; Winston (in litt., 1997) noted that most fossils 

occur below it. 

"Member 2 closely resembles member 1, except in the absence of maroon beds, it is about 550 ft. thick. Thin beds of 

arenite, 1 to 3 in. thick are common in the lower part and laminae are generally thicker in member 2 than in 1" (Whipple et 

al., 1984). Member 3 is given as about 550 ft of interbedded pyritic arenite, grayish green siltite, and minor argillite. The 

poorly exposed member 4 was measured by Whipple et al. 

(1984) at about 450 ft of "thin to very thin laminae of olive siltite accompanied by thin lenticular beds of rusty-brown arenite." 

Member 5 is a bright green argillite about 200 ft thick, containing mud-chip breccia, fluid-escape structures, and shrinkage 

cracks, features that occur less commonly in member 3. In brief 

text accompanying his GNP map, Whipple (1992) mentioned 

the members, but they were not mapped. Harrison et al. (1998) 

mentioned, but did not map, the five informal units and mentioned them intertonguing with the Prtichard Formation. 

During the 1992 season, Fedonkin et al. (1994:204) arbitrarily designated three units at Apikuni Mountain on the basis 

of color. Examination of lithology by sawn and natural cross 

sections now suggests our collections and Horodyski's may be 

confined to member 1 of Whipple et al. (1984), but this can 

only be confirmed by further field work. Distinction between 

members 1 and 2 is based primarily on color of the weathered 

rock and may not be as significant as differences in overlying 

units. The range of fossils through member 1 was not determined in 1992, but they are present though some meters of 

rock thickness. 

COLLECTING LOCALITIES 

A broad glacial valley occurs above the carbonate Altyn Formation, the upper ledges of which form Apikuni Falls. Apikuni 

Mountain is the east flank of the valley, with strata of the Appekunny Formation dipping at a low angle toward the valley een-
SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY 

ter. The lower part of the mountain slope is only slightly 

steeper than the dip, and large rock surfaces are well exposed. 

All Appekunny units weather into slabs. Slabs from members 

1 and 2 commonly are 1-3 cm thick, thinner than those from 

higher units. Most bedding planes appear flat, but within members 1 and 2 are low, nearly imperceptible hummocks, many 

less than 1 cm high with 1-2 dm between hummocks (Winston 

et al., 1989:91) (Figure 6c). Limited field observations suggest 

these hummocks, which superficially resemble ripple marks, 

are more abundant and larger in the higher members. 

In the 1992 season, specimens were collected at two other localities (Fedonkin et al., 1994:206) (Figure 1). The first is 

about 16 km south of Apikuni Mountain, along Going-to-theSun Road, U.S. Highway 89, the GNP east-west route. Outcrops only along small road cuts and a steep dip restrict collecting. Winston (in litt., 1997) noted hummocks are larger in these 

beds than in the equivalent member 1 at Apikuni Mountain. 

The second locality is about 45 km south of Apikuni Mountain, on the southern flank of Rising Wolf Mountain near Two 

Medicine Campground (Figure 1). The section is primarily 

dark-colored strata; red or green beds are rare. Because of the 

steep mountain slope and the dip, only a relatively small outcrop is available, and we obtained few fossiliferous slabs. Several Horodyski slabs have a 1991 date, which is presumably 

when he found this locality. 

Winston (pers. comm., 1996) judged that the Rising Wolf 

Mountain locality occurs within member 1. At Apikuni Mountain, dark-colored beds are rare, although Winston reported 

they are persistent. It is also possible the strata at Rising Wolf 

Mountain extend up into member 2, which further reinforces 

Winston's opinion that the differentiation of member 1 and 2 

may not be significant. One small piece in the Horodyski collection is from Otokomi Mountain (Figure I4d), which is between Apikuni Mountain and Going-to-the-Sun Road. It is 

about 6 km north and slightly east of the highway site. We have 

no further information on this occurrence. In 1993, Winston 

and Yochelson briefly examined the Appekunny Formation 

near the GNP southern boundary and in Waterton Lakes National Park in southern Alberta. No indication of Proterozoic 

life was seen at either location. 

MATERIAL AND METHODS 

About 120 slabs in the Horodyski collection show specimens 

of interest. Almost one-third of these bear 1992 collecting 

dates, about one-third have a 1991 date, and seven were collected in 1993. Fifteen numbered slabs were keyed to his 1983 

notebook. Most of this material is from Apikuni Mountain. 

Some Horodyski slabs have no associated locality data or field 

number. We assume these unmarked slabs probably came from 

Apikuni Mountain, as Horodyski's notes indicate he visited 

that locality most field seasons. For the illustrated specimens of 

uncertain provenance, the locality is given as "Apikuni Mountain" to note this minor uncertainty. 

The 1992 collection of Fedonkin and Yochelson is smaller 

than that of Horodyski and includes material not directly germane to this investigation. We concentrated on collecting other 

indications of possible biogenic origin, for there was a tacit understanding that Horodyski would study this common form. 

Still, about 75 slabs show this fossil. Among this material, a 

few slabs show early growth stages, as do several specimens in 

the Horodyski collection. Post-larval, tiny specimens are difficult to find. Once that size range is passed, strings of smaller 

beads are more common on the outcrop than larger ones. 

In 1993, Yochelson and Winston spent one day at Apikuni 

Mountain to collect a few additional slabs. Figure captions 

omit year and collector; this data can be obtained from museum 

labels. 

Although specimens are abundant, good ones are not common. Mechanical weathering is severe in GNP, and few specimens show surface details. Coating with glycerine, water, or 

ammonium chloride were inferior to photographs of dry slabs. 

The illustrated slabs include a centimeter scale to show size. 

Several slabs are shown in entirety, but for economy most have 

been trimmed. Most large slabs show a number of specimens. 

About 5% of specimens we examined in the laboratory are illustrated herein. 

Specimens have been cataloged, and their numbers are preceded by the acronym USNM (collections of the NMNH, which 

include those of the former United States National Museum). 

Previous Investigations 

Horodyski (1982:884) described and illustrated "problematic 

bedding-plane markings" from Apikuni Mountain. He provided 

no formal description and called them "string of beads" because of their appearance on the outcrop. So apt an informal descriptive term is used herein without quotation marks. Nevertheless, it is not meant to imply that the fossils were spherical. 

The strings of beads were illustrated and briefly noted the 

following year (Horodyski, 1983:399-^100). Along with a later 

reillustration, Horodyski (1989b: 11-13) mentioned several 

trace fossils, but said: "The Appekunny specimens are not demonstrably biogenic. Work is in progress on studying the internal structure of these markings; but at present, the mode of formation of these structures remains uncertain. At present, they 

are best regarded as dubiofossils." 

Horodyski's work in GNP emphasized studying stromatolites and sampling for microfossils. He took a cautious approach toward recognition of any higher life forms in the Belt 

Supergroup. At one time Horodyski (1986) questioned the organic nature of all forms from the Belt described as fossils by 

Walcott (1899). 

Following report of GNP string of beads, Grey and Williams 

(1987) noted occurrences from Western Australian beds of 

about the same age. Susbsequently, they illustrated material 

that appears remarkably similar to that described herein (Grey 

and Williams, 1990). Their work strongly reinforced the biologic nature of the string of beads, but despite comprehensive 
NUMBER 94 

description and careful analysis, they also did not provide a 

taxonomic name. 

Photographs of Horodyski's material were published twice in 

The Proterozoic Biosphere (Schopf and Klein, 1992). Fedonkin 

and Runnegar (1992:394) noted them as "puzzling beddingplane markings." Hofmann (1992a:418^119) compared them 

to the trace fossil Neonereites Seilacher, acknowledged the 

work of Grey and Williams, but considered them dubiofossils. 

The book has become a basic reference for those involved in 

Proterozoic studies; although the illustrations did not add new 

data, they introduced the strings to a wide audience of geologists who normally do not follow paleontologie literature. It 

may be significant that despite continued study of Precambrian 

sediments by many geologists, no further occurrences of the 

strings have been published. 

Horodyski (1993:562-563) remarked that the 1990 paper by 

Grey and Williams led him "to conclude that the Belt specimens truly are fossils," and in a figure caption he wrote, "These 

structures are interpreted as megafossils, possibly having eukaryotic algal affinities." Fedonkin et al. (1994) illustrated several specimens but did not include a detailed discussion. 

Early workers on the Precambrian named presumed biogenic 

structures that later turned out to be spurious. This "Precambrian syndrome" has properly made present-day workers skeptical of formalizing a name for a structure obtained from older 

Proterozoic rocks, and it may have influenced Horodyski's delay of detailed study. Proterozoic paleontologists have concentrated on carbonate rocks bearing stromatolites and on microfossils preserved in cherts. Siliclastic units have been little 

investigated, perhaps because Proterozoic paleontologists 

"know" they do not yield organic remains. 

Organic Versus Inorganic Origin 

Recognizing the need for caution, we judge enough information is available to confirm that the string of beads are fossils 

and that they are distinctive enough to be formally named. 

They are not dubiofossils or pseudofossils. In light of Horodyski's reluctance to name the specimens and his later concerns 

as to their nature, it is appropriate to explain our view from two 

aspects. 

First, we are unfamiliar with any phenomenon of sedimentation, subsequent compaction, or lithification that might produce such a shape as the string of beads (Frontispiece, Figures 

6a, 14c, J). They are not raindrop impressions, for otherwise 

slabs would be covered with them. The strings are not gas escape structures, for otherwise beads would be randomly distributed; the beads are not concretions or nodules. Winston (pers. 

comm., 1993) noted the low hummocky structures show no evidence of mud cracks or other indicators of exposure. That effectively rules out other terrestrial phenomena, such as salt 

crystal molds, which occur higher in the Belt. 

The beads are not produced by recent weathering. Lichens 

are abundant on exposed surfaces, but their growth commonly 

forms irregular spots larger than the largest beads. Lichen-produced patches are surface phenomena, whereas a few strings 

were collected from freshly split bed rock. Questionable forms, 

scrubbed off the rock with a stiff brush, were eliminated from 

this study. 

Second, the definite arrangement in strings is a feature of at 

least some later forms of colonial life. Although the size of 

beads varies among strings, all beads on a single string are virtually the same size. In our interpretation, the nearly uniform 

spacing of beads on a string, regardless of bead size, is another 

indication of coherent growth (Figures 8b, \2d). 

In documenting "bedding-plane markings" in Australia, 

Grey and Williams (1990:319-320) discussed possible inorganic origin in detail and concluded the strings of beads were 

probably biogenic. Hofmann (1992a) commented on similarity 

to strings of "millet seed" gypsum casts from the Balbirini Dolomite, MacArthur Basin, Northern Territory, Australia (Jackson et al., 1987:139) and considered them dubiofossils. From 

the illustrations provided, comparison to these rare secondarily 

silicified gypsum nodules is not convincing to us. Grey and 

Williams (1990) saw no need to make such a comparison in 

their comprehensive discussion. The Appekunny Formation 

shows no evidence of evaporites. 

Systematic Paleontology 

Domain EUCARYA 

Kingdom Uncertain 

Phylum Uncertain 

DISCUSSION.—The classic Linnaean subdivisions of Animal, 

Vegetable, and Mineral are long discarded, but for much of the 

nineteenth century, the prevailing concept was of plant and animal as the only two kingdoms. Coordinate with ever more sophisticated microscopy, classification has expanded in the 

twentieth century. Taxonomic increase at high systematic levels is the order of the day. Textbooks recognize five living 

kingdoms: bacteria, protists, fungi, plants, and animals. Kingdoms proposed from the fossil record need not be noted here. 

Some workers divide modern algae among several kingdoms. 

Recently, bacteria have been placed into two divisions. To a 

large extent these changes are based on molecular criteria rather 

than on the morphologic criteria traditional to paleontology. 

We suggest the organism described below was a multicellular eucaryote. If its growth and other points discussed are correctly interpreted, the life cycle was far more complex than 

clumping of single cells, such as in the modern Volvox. The 

fossil has no obvious morphologic relationship to Phanerozoic 

or Vendian taxa considered to be animals. The algal record is 

less well known, but again there is no close comparison to any 

Vendian taxa. Eventually, this fossil may be recognized as distinct at the phylum level. 
SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY 

Horodyskia Yochelson and Fedonkin 

Horodyskia Yochelson and Fedonkin, 2000:844. 

TYPE SPECIES.—Horodyskia moniliformis Yochelson and Fedonkin. 

DIAGNOSIS.—Cones spaced along a horizontal tube. 

DESCRIPTION.—Presumed colonial organisms of small vertically oriented cones, hemispherical on their upper surface, 

growing with essentially uniform spacing from an elongated 

horizontal stolon. 

DISCUSSION.—To our knowledge this genus does not closely 

resemble other living or fossil forms. Observation on taphonomy and other points bearing on morphology are discussed in 

other sections of this work before the general discussion. 

Even by standards of the Phanerozoic, Horodyskia is a locally common fossil. Although negative information may be 

destroyed in an instant of collecting, the active investigation of 

Middle Proterozoic in the western United States has not 

yielded any other occurrences. The taxon occurs only in siliclastic rocks and is limited in time. Such restrictions support 

interpretation of a highly specialized life habitat. 

At the time this manuscript was prepared, we had not seen 

any specimens reported by Grey and Williams (1990). On the 

basis of one color transparency, we were tempted to assign the 

Australian specimens to the genus, but it seemed more prudent 

to leave open the question of whether those forms are congeneric, let alone conspecific. That material was originally 

known from three localities, but it now has been found in outcrops stretching several hundred kilometers in Western Australia (Grey, in litt., 1998). Winston and Link (1993:503) 

showed several reconstructions of Proterozoic paleogeography, one of which would place Antarctica and Australia close 

to Montana. 

Horodyskia moniliformis Yochelson and Fedonkin 

FRONTISPIECE, FIGURES 3,4,6-176 

Horodyskia moniliformis Yochelson and Fedonkin, 2000:844, fig. 1. 

DIAGNOSIS.—Proportionally uniform spacing of cone at all 

growth stages. 

DESCRIPTION.—A series of tiny spherical bodies growing 

from a thin horizontal stolon and elongating with growth. Size 

and spacing between bodies remaining nearly uniformly proportional for every individual series. During growth, spheroidal 

shape becoming ellipsoidal and oriented with the long axis vertical, while size of the bodies and spacing between them proportionally increases. Tubes relatively short, with general 

shape like a wide ice cream cone. Upper surface hemispherical 

in early stages and probably at maturity, although slight invagination cannot be ruled out. 

DISCUSSION.—Horodyski (1982) suggested that distinct 

large and small forms occurred. We judge all specimens are 

one species represented by various growth stages. Horodyski 

also indicated that several specimens were branched. We reexamined his original material and a few other strings that superficially appear to branch. They are all interpreted as closely adjacent strings or, rarely, as two strings crossing. 

We are satisfied that only one species is present at the three 

GNP localities. What differences exist are best interpreted as 

slightly different taphonomic histories. 

The holotype selection presents some concerns. The first issue is whether a string on a bedding plane or a sole surface 

should be selected. A sole surface better illustrates bead spacing, yet more details of the individuals can be seen on some upper surfaces. The second issue is selection of the type locality. It 

is easy to obtain specimens at Apikuni Mountain if one has a 

collecting permit from the National Park Service. Material from 

Rising Wolf Mountain is scarce, but it shows more of the morphology, and in the final analysis, that is more significant. The 

Frontispiece illustrates most of the slab that bears the holotype. 

HOLOTYPE.—USNM 508100. 

PARATYPES.—USNM 508101-508131. Only the figured material is formally designated as paratypes; the bulk of the collections contributed to the interpretations given, but to declare 

all material as paratypes would not have been good museum 

policy. 

ETYMOLOGY.—The generic name marks the contributions of 

Robert J. Horodyski to the study of Proterozoic life. The specific name alludes to the appearance of the fossils as a string of 

beads or a necklace. 

Comparison to Trace Fossils 

Several workers have compared Horodyskia to trace fossils, 

but we judge this approach to be spurious. The closest similarity in appearance is to Hormosiroidea Schaffer (see Hantzchel, 1975:69-71), which looks like hemispherical or spherical bodies aligned on a string, but Hormosiroidea does not 

show the mode of growth of Horodyskia. The mode of growth 

and cone-like shape of beads distinguishes Horodyskia from 

Neonereites Seilacher, interpreted as a string of fecal pellets. 

In Phycodes Richter, vertical outlets in the burrow system 

arise from a horizontal shaft, and where these shafts are preserved on an upper bedding plane they may mimic a string of 

beads. They are unlike traces known from the Vendian (Fedonkin, 1981). 

Specimen Characteristics 

ABUNDANCE AND GENERAL SHAPE 

At Apikuni Mountain Horodyskia is extremely abundant 

(Figure 6a); one outcrop of about 0.5 m2 includes more than 12 

strings. If the restricted collecting areas on Going-to-the Sun 

Road and on Rising Wolf Mountain are considered, specimens 

may be equally common at those localities. At Rising Wolf 

Mountain slabs are generally small, yet several bear two 

strings. 
NUMBER 94 

FIGURE 3.—a. An exceptionally long string of beads in a sigmoidal pattern on a gray sole surface, with the beads 

in shallow negative relief. The axes of ovals of the beads vary along the string. Several beads above the scale and 

to the right show a dark spot within the bead. USNM 508101; Apikuni Mountain, b, A long string of relatively 

large beads on a grayish tan sole surface of essentially no relief. A wide halo of iron oxide occurs around each 

bead. A shorter string of smaller beads to the upper right shows much smaller halos around several beads. Two 

isolated beads of the same size occur below this string. The larger beads are irregular in outline, whereas the 

smaller ones approach a circular shape. USNM 508102; Apikuni Mountain. 

Because the sediment is arenite, any bottom may have provided a firm substrate for early growth. The rain of sediment 

was slow enough that many organisms were not smothered at an 

early stage. Settling of an initial stage could have been more or 

less continuous. Adjacent occurrences of strings with different 

sizes of beads supports the interpretation of continuous settling. 
SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY 

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FIGURE 4.—a, A long string, which undergoes an abrupt bend, in slight negative relief on a gray sole surface. In 

color, this matrix approaches that of slabs from Rising Wolf Mountain, but these beads are of white silica and 

some are accentuated by small halos. USNM 508103; Apikuni Mountain, b, A long string in positive relief on a 

greenish gray upper bedding-plane surface. The curve to the right forms a shape like a reverse question mark, 

which is appropriate for this enigmatic fossil. USNM 508104; Apikuni Mountain. 

Some strings were collected that grew on hummock surfaces (Figures 6c, lc), and a relationship may exist between 

slight bedding-plane depressions and more abundant strings. 

It is equally possible that collecting bias is involved, for 

strings in prominent swales are easier to see in the field. Some 

strings cross hummocks from trough to crest; others are oblique to slope. 

Strings of fewer than six beads are exceedingly rare. Slabs 

with only one or two beads are broken across a string or have a 

parting plane cutting obliquely across the string. The shape of 
NUMBER 94 

strings varies widely. Straight or nearly straight strings are uncommon (Figure 5). Gently curved arcs (Figure Sb), distinct U 

shapes (Figure 3b), sigmoidal (Figure 4a), and irregular 

shapes (Figure 4b) all occur. We cannot find any correlation of 

bead size with shape of a string or number of beads. Variation 

in string shape and length are judged to be primary growth 

features. 

Smaller beads are closely and uniformly spaced, and larger 

beads are more widely, but still uniformly, spaced (Figures 

%a,b, 12c; Table 1). Horodyski (1982:887) plotted the relationship between length and spacing of beads on 10 strings. Grey 

and Williams (1990:312) added more data from 20 strings and 

produced a scatter diagram using both data sets. It confirms a 

relationship between bead size and spacing; no further discussion of this feature is necessary. 

Grey and Williams (1990:313) used mean bead size and its 

standard deviation for comparison to various organisms and inorganic objects. In our view, tiny individuals are rare due to 

difficulty of preservation and collecting; large individuals are 

rare due to general considerations of population growth. Most 

beads are in a narrow size range, mainly because of the ease of 

seeing them on the outcrop. Size distribution seemingly has no 

deeper significance. 

TABLE 1.—Measurements of selected specimens of Horodyskia moniliformis. 

5 cm 

FIGURE 5.—Tracings, from a multiple number of slabs, of the course of 21 

strings of beads. The strings do not touch the edges of a slab and seemingly are 

complete. The beads are of a variety of growth sizes, but bead size does not 

correlate with either string length or string orientation. Growth in a nearly 

straight line almost never occurred, and even slight curvature was an exception. 

Number of beads 

5 

6 

7 

8 

8 

8 

10 

12 

21 

22 

23 

29 

Average diameter 

ofbeads 

4.5 

9.2 

5.0 

4.6 

4.9 

4.5 

6.3 

4.4 

4.1 

3.6 

2.7 

2.1 

Spacing ofbeads 

4.6 

14.2 

4.6 

5.2 

4.3 

4.9 

3.7 

3.9 

3.8 

4.5 

2.5 

2.0 

BEAD SHAPE 

Reference 

Figure lc 

Figure Sa 

Figure 126 

Figure lb 

Figure 86 

Frontispiece 

Figure lie 

Figure 14c 

Figure 4a 

Figure Ab 

Figure 8b 

Figure 6c 

Although a few beads, especially smaller ones, are nearly circular in outline, they are the exception. On many strings bead 

shape changes along the length. Bead outlines may be elongated 

ovals or, especially larger ones, irregular. This observation 

seems consistent with mechanical properties of objects under 

compaction—the smaller the diameter, the greater the durability. Beads surrounded by an aureole show a greater diversity of 

shape. On slabs that show current shadows or scour patterns, 

change in shape is more consistent; this is interpreted as specimens having been tilted slightly by a unidirectional current. 

Hemispheres on bedding-plane surfaces are essentially circular in outline and reflect the upper portion of vertical tubes, 

which is further support that during life the cross section was 

nearly circular. The negative impressions seen rarely on both 

the bedding-plane and sole surfaces are triangular to quadrangular. We interpret them as an approximate impression of the 

lengthened bead. We reconstruct the shape as similar to a low, 

quite wide cone with a rounded scoop of ice cream on top. 

Original tube length cannot be determined, but we surmise 

from observing both lower and upper layers of integument on 

the sole surface that there was little shortening by compaction. 

Our best guess is that the tallest beads grew about 1 cm. 

ASSOCIATED BIOTA 

Sphaeromorphs in the Appekunny (Horodyski, 1993) are too 

poor for any generic assignment, but their range of cell size is 

within that of procaryotes. Horodyski (1993) also indicated the 

formation contained spiral impressions up to 10 cm in diameter 

and oval depressions about 2 cm in diameter bordered by elevated rims; both may be inorganic structures. Fedonkin et al. 

(1994) reported a variety of bedding-plane traces from member 

1. We now interpret "tiny trails" as stolons of Horodyskia. Several other traces have been ruled out as sedimentological phenomenon or fragments of bacterial film. Reexamination of this 

material still suggests that other biota may have been present. 

Good specimens of faint traces are rare and are subject to different interpretations. 
10 SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY 

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FIGURE 6.—a, Several strings, all with beads of nearly the same size, in positive relief on a greenish gray upper bedding-plane surface. All beads are 

nearly the same size, and the differences in string length and curvature suggest random orientation of the earliest growth stages. USNM 508105; 

Apikuni Mountain, b, Part and counterpart of a string ofbeads broken off at 

both ends. To the left is the gray sole surface, with the upper bedding-plane 

surface to the right. The beads preserved in negative relief on the sole surface 

are accentuated by infilled current crescents standing in relief as arcuate 

ridges. This specimen confirms the surface assignment for most of the loose 

slabs. USNM 508106; Apikuni Mountain, c, A hummocky surface bearing 

several strings ofbeads. To the right of the scale, a short string ofbeads occupies a depression in the center of the photograph, and a string of larger beads 

is above them; because of the lighting, the surface topography appears in 

reverse relief. Above the scale is another string of poorly preserved beads on 

a crest, trending more or less parallel to the others. To the left, nearly at right 

angles to the strings of larger beads, a long string of very small beads crosses 

the crest of a hummock and a trough. Current crescents are well developed 

around some of the larger beads. The more obscure crescents associated with 

smaller strings suggest that bead size was a factor in the formation of these 

features. The degree of development of the crescents also may reflect various 

declinations of individuals originally in vertical position within the sediment, 

but shifted slightly because of the irregular surface of the hummock and, perhaps, may reflect slight differential compaction of the sediment. USNM 

508107; Apikuni Mountain. 
NUMBER 94 

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FIGURE 7.—a, Large beads preserved in positive relief on a grayish green upper bedding-plane surface. The large 

concentration ofbeads demonstrates high population density and makes the various strings difficult to differentiate. Beads vary in shape, but many are oval. USNM 508108; Apikuni Mountain, b, Strings preserved in positive 

relief, like a series of rounded knolls, on a dark green upper bedding-plane surface. Several sizes are present: 

large beads to the left are in two strings, each curved at the end and nearly touching so as to appear as a U within 

a shallow trough; small beads to the center trend across a hummock and trough; to the upper right are beads intermediate in size between those on the other two strings. At the upper right one string trends more or less horizontally with a "kink" near the center; above it is another string, which thereby gives a superficial impression of 

branching. USNM 508109; "Apikuni Mountain." c, A hummocky, green upper bedding-plane surface showing 

numerous strings in positive relief. The few large beads to the left trend obliquely up the crest of a low hummock. The string of smaller beads directly above it go through a trough and up toward a crest. There are a variety 

of sizes, lengths, and orientations among the other strings, all of which show essentially uniform proportional 

spacing. USNM 508110; Apikuni Mountain. 
12 SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY 

bj 

FIGURE 8.—a, A string of the largest beads known to date, with the widest spacing between beads. Above the 

scale is a bead so faint that it hardly appears on the photograph; another faint bead is between the two that are to 

the right. USNM 508111; Apikuni Mountain, b. Strings of several sizes on a dark green sole surface. The large 

beads above the scale show very shallow current crescents preserved as ridges; they mimic the outlines of halos. 

To the center right, two strings of smaller beads cross. Still smaller beads occur to the lower right of the crossed 

strings. USNM 508112; Apikuni Mountain. 

One organic form that is not so open to argument is bacterial 

mats. These produce a crinkled surface on bedding planes, 

aptly described informally as "elephant skin" texture. The 

wrinkles may represent upper-surface relief of a mat after degradation under a layer of sediment (Figure 9b,d). Evidence of 

some mats at Apikuni Mountain was documented by Fedonkin 

et al. (1994), and at least one specimen of Horodyskia was covered by a mat (Figure 9b). 

Having mentioned that, it must be noted that such mats are 

an exception, and few specimens were found at Apikuni Mountain. The sediment below modern mats is strongly anaerobic. 

The paucity of mats in the formation might be related to greater 

depths rather than to shallower water. 

Details of Matrix 

LlTHOLOGY 

At Apikuni Mountain, individual beds weather to red, green, 

tan, or gray. Specimens of Horodyskia moniliformis occur in all 

rock colors with no differences in morphology. Sawn cross sections show no obvious differences among the different colored 

siltstones, and they show that most of the grays, browns, and 
NUMBER 94 13 

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FIGURE 9.—a, Thin section through the impression of a flattened, white-colored bead marked on the sole surface 

by two lines. USNM 508113 (x7.5); Apikuni Mountain, b, A string of large beads preserved in negative relief on 

a presumed sole surface. The microrelief of the surface is interpreted as the impression of a bacterial mat that 

grew over the beads. USNM 508114; Apikuni Mountain, c, Thin section across at least three cycles of graded 

bedding. At the base and near the top of the thin section are microripples. The fine lamination could reflect participation of bacterial films in binding of sediment surfaces under conditions of very low sedimentation rate. 

USNM 508115 (x5); Apikuni Mountain, d. Enlargement of a portion of b to show the "elephant skin" texture of 

the bacterial mat (x4). 

greens are a result of surface weathering. Most fossiliferous 

slabs from this locality are green to greenish gray. Most of the 

material from Going-to-the-Sun Road is in a dark red matrix, 

but the strings are no different. The surface color at all localities is mentioned in the figure captions, primarily because the 

color of the matrix affects the quality of the illustrations. 

As shown well in thin sections, the rock is laminated on a 

delicate scale (Figure 9a, c). Commonly four to six laminae oc-
14 SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY 

cur within 1 mm, yet all show graded bedding of silt-sized to 

clay-sized particles. Very low-angle cross bedding on a 1-2 

mm scale occurs in some layers and is so slight as to be hardly 

apparent to the naked eye (Figure 9c). 

Petrographic examination indicates that the rocks are composed almost entirely of angular grains of quartz and smaller 

amounts of angular feldspar. Extremely rare black grains showing right angles are iron oxide, but they originally may have 

been disseminated pyrite. If any clay minerals were present, 

they are not obvious. No mica or glauconite was observed. 

One tan weathering bed was examined by microprobe. Analysis made with a 20 micron-wide beam and 100 microns spacing was run parallel to the laminae. The results, normalized to 

100% for each spot analyzed and averaged, are as follows: 

Si02, 73.03%; A1203, 12.76%; FeO, 2.87%; MgO, 2.55%; 

CaO, 1.93%; K20, 4.51%; Ti02, 0.57%; MnO, 0.05%; Na20, 

1.46%. A run across coarser and finer laminae at the same spacing gave similar results: Si02, 74.53%; A1203, 9.60%; FeO, 

3.08%; MgO, 3.72%; CaO, 4.11%; K20, 3.03%; Ti02, 0.98%; 

MnO, 0.07%; Na20, 0.85%. A third probe, also at right angles 

to laminations, through a shorter distance with a 10 micron 

beam at 40 microns spacing, produced virtually the same results: Si02 , 72.96%; A1203, 12.73%; FeO, 3.91%; MgO, 

3.91%; CaO, 2.99%; K20, 3.95%; Ti02, 0.50%; MnO, 0.03%; 

Na20, 0.4%. These analyses support the results of the petrographic determination that the grains are silica and feldspar. 

Iron and manganese oxides may come mainly from coatings on 

silica grains. 

Microprobe analysis showed no obvious differences between 

beads and matrix. Beads examined from Apikuni Mountain are 

now formed of white silica (Figure \3b). Beads from Rising 

Wolf Mountain are black on a dark gray matrix (Figurel3#). 

This rock is also finely laminated, but material is limited, and 

we have not sacrificed any for more detailed study. Whether 

the dark color represents organic components originally 

present is a problem for future study. 

DEPOSITIONAL ENVIRONMENT 

Key lithologic features in member 1 of the Appekunny are 

the microscopically thin laminations and the tiny size of grains 

constituting them. This ultrafine lamination appears unique 

within the Belt Supergroup (Winston, in litt., 1997) The "microlamination sediment type" described by Winston (1989:53) 

from the Belt is different and is an alternation of silt and clay 

on a millimeter scale. 

It is not clear how these delicate laminations formed. Whether 

an external mechanism, such as diurnal or lunar, influenced formation is uncertain. Glacial varves is an unlikely mechanism, 

and there is no evidence of glaciation within the Belt. The episodic lamination resembles modem sedimentation in the central 

basin of large lakes (Reineck and Singh, 1980:250-251). 

In our view, the sediment source was probably wind-borne 

dust. Darwin (1962:5) commented on a dust cloud far at sea 

during his first few days on H.M.S. Beagle. In that example, the 

dust was composed primarily of microscopic-sized organisms, 

but fine volcanic ash has been documented on ships far from a 

volcano. Differential settling of larger and smaller particles 

would provide graded bedding on a microscopic scale. Huebschman (1973:697) proposed that silt in the Pritchard Formation was wind-blown in origin. 

Intermittent wind provides an ideal mechanism for finescale, graded bedding. Even a gentle breeze would have stirred 

shallow water enough to insure laminae were widespread. Most 

sediment settled below the fair-weather wave base. The regional distribution of the Appekunny Formation implies it was 

on a shelf rather than at great depth, but there is no evidence of 

emergence. Thus, a depth range of more than 2-3 m, and less 

than 100 m, is a reasonable guess. The fine laminations and 

small grain size indicate low energy conditions at the basin 

floor and thereby support an implication of greater rather than 

shallower depth. 

Member 1 of the Appekunny Formation shows another novel 

sedimentological feature in that individual grains are coated 

with hematite (Winston, in litt., 1997). Red color occurs 

through the Belt, especially in some younger units, but those 

beds show mud cracks, salt crystal molds, and other indicators 

of terrestrial deposition. This is the only subaqueous red unit 

within the Belt Supergroup. 

Since the pioneering efforts of Walcott (1899), arguments 

have raged over whether portions of the Belt were deposited 

in marine waters or were deposited in lakes. One may interpret the depositional environment as analogous to a modern 

playa lake having a slight bathymetric gradient (Winston and 

Link, 1993:505-506). The adjacent terrestrial sedimentsource area was low-lying on a stable platform; most sediment was produced mechanically. In the absence of land vegetation, eolian erosion and eolian transport were significant 

and were augmented by unconfined and sheet-like flow of water (Winston and Link, 1993:503). Proterozoic paleogeographic reconstructions are less certain than those for the 

Phanerozoic, but some schemes place the Belt depositional 

basin near the equator. Such a warmer region would accelerate formation of hematite and would have a climate in which 

variable winds would be common. 

In the fossiliferous part of member 1, most slabs are 2 to 3 

cm thick; bedding planes may imply episodic sedimentation. It 

is plausible that each slab represents a major storm that formed 

the low hummocks, although any relationship between hummocks and bedding planes remains to be studied. If intermittent, gentle winds followed, the stirring water would have 

formed many cycles of graded bedding. At a final, extremely 

quiet stage, the finest clay-sized particles would have settled 

out to form a plane of weakness, before another storm ensued. 

"Clay" as used herein indicates size and not mineralogical 

composition. The clay material on the bedding planes and elsewhere in the Belt is sericite (D. Winston, pers. comm., 1996). It 

may have been derived from a smectite-bearing illite (Maxwell 

and Hower, 1967) by low-grade metamorphism. Most fossils 

abound at and just above or just below the bedding planes, on 
NUMBER 94 15 

naturally separated surfaces (Figures 6b, la). Evidence of sediment starvation and low energy conditions of bottom water 

would seem to exclude catastrophic burial of organisms, but 

that is a function of scale. Even a slight increase in sedimentation rate could have smothered the organisms, for the beads 

stood only millimeters above the substrate (Figure 1 lc). 

Few strings were found within medial portions of the slabs, 

although many slabs were split in the field. Put in other terms, 

the silt layers were closely packed angular grains and were essentially uncompacted. We recognize a unit of clay-sized arenite compacts much less than the same original thickness composed of clay minerals, and we guess that bedding planes, 

before compaction, represent a few millimeters of clay-sized 

arenite particles. 

Thin sections of the Appekunny were examined by T.A. 

Ivanovskaya, a specialist on glauconite, to search particularly 

for that mineral; it was not identified. Glauconite indicates marine deposition and/or low sedimentation rates (Gary et al., 

1972:40) (a more recent glossary (Jackson, 1997:272) defined 

the mineral but noted that "mode of origin is not a criterion"). 

Grey and Williams (1990:309) mentioned glauconite in the 

Middle Proterozoic Manganese Subgroup, Western Australia. 

Their account suggests a geologic setting in water shallower 

than in the Appekunny. 

Winston and Link (1993:516) presented a diagram depicting 

the older Belt rocks as deposited within a giant lake. The model 

of a modern playa is helpful, but the Appekunny Formation 

was not formed in a fully enclosed body of water, for it interfingers westward with the Pritchard Formation. We are satisfied that the evidence for "lake-like" deposition of the Appekunny Formation is compelling. A plausible setting is lagoonal 

or estuarine, where relatively quiet water might prevail for long 

periods. In such an environment salinity might also have varied 

and affected settling rates of fine particles. 

Although we reject a strict modern lake model, there is merit 

in comparisons. In contrast to eutrophic lakes, a playa may be 

an oligotrophic basin with low input of nutrients and low primary bioproductivity. The Appekunny basin may have been 

oligotrophic partly because of weak ventilation of the bottom 

by currents. Another consideration is the relatively low concentration of free oxygen in the Middle Proterozoic atmosphere so 

that the water column would not have contained as much oxygen as in present-day aquatic conditions. There are many gradations between freshwater lakes and normal marine waters, 

but there are too few constraints to be more specific. Zavarzin 

(1993) discussed some implications of atypical alkaline water 

bodies in the development of life. 

PRESERVATION 

Specimens of Horodyskia moniliformis are on both upper 

bedding plane and sole surfaces. The bulk of the material is 

loose slabs, but a few pieces are from outcrop with top and bottom marked; these confirm our orientation of fossiliferous surfaces. For illustrated specimens where there is uncertainty, we 

have deliberately omitted any comment on orientation from the 

figure caption. 

Specimens on both surfaces show a variety of taphonomic 

effects. Slabs are nearly flat, and, commonly, beads are nearly 

flat. Most strings, by far, are on sole surfaces where beads differ in color from matrix and are readily collected. 

Upper bedding-surface specimens are commonly preserved 

as low hemispheres in positive relief. Unless light is strongly 

oblique, they are more difficult to see. Impressions of specimens—negative relief—are quite rare on upper bedding planes. 

Tiny specimens are on bedding-plane surfaces where a thin 

layer of clay-sized particles is preserved. 

TAPHONOMY OF UPPER BEDDING-PLANE SURFACES.—On 

upper bedding surfaces, strings of hemispheres (Figure la) are 

common on both red and green colored rocks, with those on tan 

to gray rocks being less common. Red hemispheres are more 

prominent to the eye than those in other colors of matrix. The 

hemispheres show less size distribution of the individual beads 

than do beads on sole surfaces, and beads tend toward a larger 

size. This is a collecting artifact, as smaller specimens are obscure, except under ideal lighting conditions. 

The hemispheres show no internal details in thin, polished, 

and fractured sections (Figure \0a~c). The hemispherical surfaces show occasional black flecks with right angles; these may 

have originally been pyrite crystals formed during decay of the 

integument. Another source of a central dark spot is exfoliation 

(Figures 10b, \3b). In detail, beads may be rounded (Figure lb) 

or flattened (Figure 10a), which we attribute to compaction. 

Some flattened beads have rays extending outward, which are 

variable in length, number, and position around the bead. We 

interpret the rays as compaction structures and have not bothered to illustrate them. 

Allen (1982:173-205) discussed in detail the formation of 

"obstacle marks" resulting from water movement. One slab 

shows lineation, referred to as "current shadows" (Figure 

12a). Some strings show "current crescents" of coarser grains 

commonly around one-fourth to one-half of bead circumference; this is particularly striking when coarser material is a 

different color than the matrix (Figures lie, 126). Other beads 

show a faint depression on one side, although it may be a 

modern phenomenon of weathering away of coarser grains 

rather than scour. A few strings show a scour-remnant ridge 

surrounding beads (Figure lib). We interpret the beads as resistant structures standing a short distance, a few millimeters 

or less, above the substrate and therefore affecting a directional current. 

Furthermore, based on these observations, it is likely that the 

cone-shaped beads decayed slowly, for the hemispheres approximate the negative impressions of the sole surface. The upper part of a cone was more likely to have been cemented earlier than parts further within the sediment. Partially compressed 

and decayed beads were resistant enough to form a "buried 

hill" topography. 

The few examples of bedding-plane negative relief are a series of quite shallow pits, showing little detail of the form 
16 SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY 

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FIGURE 10.—a, Slightly oblique view of a flat-topped, nearly circular bead on 

an upper bedding-plane surface. USNM 508116 (scale=l mm); "Apikuni 

Mountain." b, Slightly oblique view of an elongated bead on an upper beddingplane surface; the central depression may result from exfoliation. This bead is 

on the same string and is next to the one shown in a. USNM 508116 (scale=l 

mm), c. Fracture surface through a bead preserved in positive relief on an 

upper bedding-plane surface. An exceedingly thin layer marks the surface of 

the bead. USNM 508117 (scale=l mm); Apikuni Mountain. 

plucked from the hole. Negative relief results from replacement 

of body volume by sediment from above during the process of 

decomposition and subsequent loss of the differentially cemented filling. 

TAPHONOMY OF SOLE SURFACES.—Characteristically, 

strings on sole surfaces at Apikuni Mountain are easy to see because they are white beads in matrix of a different color. The 

hemispherical shape on bedding planes is reflected in the slight 

inward curvature ofbeads. On some strings, nearly all the bead 

is eroded, but the depression retains a thin white residue sufficient to reflect light (Figure 136). 

The material now forming the beads is silica, which is apparently amorphous. We attribute this to replacement of the original bead surface. Presumably, organisms died in situ, were 

smothered by sediment, and became partially compressed, but 

the covering matrix was porous enough to allow penetration of 

silica-rich waters; in Phanerozoic rocks, organic matter may assist the replacement process (Fedonkin, 1987). It is less likely 

that decay products might have locally hardened the sediment 

and silica filled a void. 

Thin sections across these silica plates confirm they are limited to the sole surface and are less than 1 mm thick. Indeed, 

when a section is cut through these structures, they cannot be 

identified without prior knowledge of where a bead was located (Figure 9a). 

Occasional beads show a central dot or two of silt matrix, 

which are prominent because of color difference. When the 

compressed lower surface is present, no matrix is seen, but 

when the lower "layer" is absent, one observes the inner surface of the hemisphere or a break in it. A central spot of matrix 

is seen in beads of varying sizes. Its random presence among 

the beads of a string is probably a taphonomic effect. 

We suggest that at early growth stages a hemispherical upper 

surface was present on a bead. We cannot rule out that at maturity this area might have became slightly invaginated. If so, as 

the organisms were killed by sediment influx, this depression 

collected a few larger grains. 

A different interpretation of this silt speck is that it marks an 

opening at the top of the hemisphere. In that scenario, when the 

cone-like tube was overwhelmed by sediment influx, several 

grains entered a central opening and survived silicification. We 

cannot prove either interpretation, nor can we rule out any others, but we are convinced that a central spot is secondary and 

not an opening in the living organism. 

Examined in detail, the silica plates provide little more data. 

The rock does not split around the fossils but cuts across them 

(Figure 14c). As a result, bead size is not only related to 

growth, but it is also a function of where the parting plane intersects them. Smaller beads tend to be closer spaced than 

larger ones, yet we have examples of seemingly small beads 

widely spaced; these are readily interpreted as the consequence 

of the parting plane cutting relatively high across the hemisphere of larger beads. 

In about one-third of the strings, a brown aureole occurs 

around beads; when present, most or all beads in a string show 

this feature. Commonly, the aureole is wider on one side (Figure 146). There may be a correlation between oval shape and 

aureole width, but too few samples show both features to draw 
NUMBER 94 17 

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FIGURE 11.—a. Chevron-like impression of three strings ofbeads. The inclination of the smaller set of grooves below the right is opposite that of the 

slightly larger grooves above. A short, even smaller set is to the right of the 

larger grooves. This specimen was previous figured by Fedonkin et al. (1994, 

fig. 22). USNM 468250; Apikuni Mountain, b, Individual beads on a dark 

brown, upper bedding-plane surface preserved in negative relief. The asymmetrically expressed depressions adjacent to the beads are scour marks, a 

form of current crescents. The upper left bead is affected by slight spalling of 

the surface; the middle bead shows a slight central protuberance. As a result 

of the extremely low angle of the light, the crescent on one bead appears as a 

moat and on another as a ridge. USNM 508118 (x4); Apikuni Mountain, c, A 

string ofbeads in negative relief on a green sole surface. Each bead is surrounded by an infilled scour mark of coarser material that stands in relief. 

The infilled scour marks rise at least 3 mm and suggest a minimum height of 

the bead of more than 1 cm. USNM 508119; "Apikuni Mountain." d, Chevron-like impressions of a string on a dark green sole surface. They are consistently inclined, being deeper toward the left. These are interpreted as the 

impression of individual beads, and the depth gives an indication of their relative height. The sediment retains some impression, which indicates the stiff 

character of the individual beads. USNM 508120; Apikuni Mountain. 
SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY 

1 cm 

FIGURE 12.—a, A dark gray sole surface showing elongate current shadows running the length of the slab, 

plus current crescents associated with beads. USNM 508121; "Apikuni Mountain." b, A short string ofbeads 

on a light tan sole surface. The apparent halo around the beads is a slightly raised current crescent infilled with 

lighter colored grains. The irregular shape of the various beads may have resulted from deformation by compaction. USNM 508122; Apikuni Mountain, c, A string of quite small beads in positive relief on a grayish 

green upper bedding-plane surface. Several beads show ridges, presumably caused by compaction, USNM 

508123; Apikuni Mountain, d, A long string of closely spaced tiny beads on a gray upper bedding-plane surface is shown to the left, below an irregular lichen patch. This colony, at an early growth stage, shows the fine 

thread, or stolon, connecting the beads. The string is mainly a trough parallel to the edge of a hummock, but at 

the "kink" it trends up the slope of the hummock. A shorter string is to the right above a place where matrix 

has spalled away. USNM 508124; Apikuni Mountain. 
NUMBER 94 19 

FIGURE 13.—a, Part of a string of black beads on a dark gray sole surface. The different orientation of the axes 

of the ovals may indicate inclination of the individuals as a post-mortem effect, but there is no deformation of 

shape to support this interpretation. There are no halos around the beads. USNM 508130 (x4); Rising Wolf 

Mountain, b, A number of tiny beads preserved as flat patches of white silica on a reddish brown matrix. Some 

beads have a dark central spot resulting from flaking away of part of the thin silica layer. USNM 508131 (x4); 

Apikuni Mountain. 
20 SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY 

FIGURE 14.—a. Two strings of different curvature, one across the sole surface 

of a dark gray slab and one on the right edge. The black, flattened beads are 

surrounded by lighter colored halos that vary widely in size. On the string to 

the upper right, the halos are narrower and less prominent. USNM 468248; 

Rising Wolf Mountain. The specimen was illustrated by Fedonkin et al. 

(1994, fig. 21). b, Several strings of large beads on a light gray slab; this may 

be a sole surface. The large beads have extensive halos of iron oxide, and 

those in the slightly smaller string to the upper left have slightly smaller 

halos. USNM 508127; Apikuni Mountain, c, A string on a gray sole surface 

showing an apparent slight size gradient, with larger beads to the right. The 

false gradient is the result of the sole surface not being completely flat, as a 

thin layer was spalled away on the left side. The beads to the right are in very 

slight positive relief, and several show a central dark spot; beads to the left 

are in slight negative relief. The different cross sections vary from nearly circular through elliptical to nearly triangular; this may be a taphonomic effect. 

Several smaller strings are on the lower part of the slab, which is not illustrated. USNM 508128; Apikuni Mountain, d, The only known specimen from 

Otokomi Mountain. The beads are preserved in slight negative relief on the 

dark green sole surface. One string ofbeads trends horizontal near the upper 

edge of the small slab. A second string is broken by the upper edge of the 

slab, and a third is to the upper left and is in the shape of an irregular oval. 

USNM 508129; Otokomi Mountain. 
NUMBER 94 21 

a firm conclusion. Likely, the color is an oxidation product 

from pyrite, which, in turn, may be related to decay of integument and inner cells. A logical interpretation is fast burial and 

decomposition under low permeability, preventing aeration and 

escape of degradation products. 

Strings that show sediment piled on one side of a bead or 

other evidence of current activity are far less common than 

those showing an aureole, although they are better developed 

on the sole surface than on the upper bedding planes. These 

two forms of taphonomic change, scour and aureole, appear to 

be mutually exclusive because they reflect different conditions 

of aeration of the sediment. 

Some strings on the sole surface are preserved in negative relief. In general, these depressions are in the form of acute triangles (Figure 11a,d). In both positive and negative relief the 

cross section does not show any internal structures preserved, 

for the whole volume of the body was replaced. 

Beads from Rising Wolf Mountain are black rather than 

white (Frontispiece, Figure 14a). We have not investigated the 

nature of the color because of the small number of specimens 

available, but we suspect there originally was a higher carbon 

content in the rock, along with deposition of manganese. 

Hypotheses 

PALEOENVIRONMENTAL CONSIDERATIONS 

Experience with Phanerozoic paleoecology demonstrates 

the effectiveness of an actualistic approach by analysis and 

comparison to present-day biota. For example, the presence of 

echinoderms indicates salinity was that of a normal marine 

environment, and a fossil coral reef suggests growing conditions similar to those of modern reef communities. It is a plausible approach to interpreting Proterozoic procaryotic ecosystems of cyanobacterial communities. Unfortunately, this 

approach is not always obvious or even helpful in considering 

Proterozoic eucaryotic organisms. The uncertain systematic 

position of many older eucaryotic organisms of both microscopic and megascopic size does not permit interpretation of 

the environment as in Phanerozoic paleoecologic study. When 

some of the unfamiliar morphologies of Late Proterozoic 

(Vendian) fossils are taken into account, the situation may be 

more dramatic, and strange morphologies might actually correlate with unfamiliar or extinct physiologies. In the still older 

Middle Proterozoic there may well be peculiar relations between organisms and their environment that have no recent 

counterparts. 

Deposition of banded iron provides support for this notion. 

Early in earth history, conditions were appropriate for development of that rock and other "extinct deposits" (Fedonkin, 

1996a). Conditions later changed and such material was no 

longer deposited. One cannot be certain of the systematic 

placement of Horodyskia because no obvious similarities indicate either homology or analogy, and one cannot be confident 

FIGURE 15.—a, A string of tiny beads on an upper bedding-plane surface, 

trending diagonally upward from the lower left and turning toward the right. 

The ridge of uniform width between the beads is interpreted as a stolon. USNM 

508125 (scale=l mm); Apikuni Mountain, b, Enlargement of three of the 

beads illustrated in a. The beads are connected by a stolon. The rays and projections from the beads are judged to be a result of compression. USNM 

508125 (scale=100 urn), c, Oblique view of a curved stolon on an upper bedding-plane surface. Several swellings occur on the lower limb of the U-shaped 

structure. USNM 508126 (scale=l mm); Apikuni Mountain. 

of its environment. Like any rule, actualism should be treated 

with caution. Horodyskia may have lived in an environment 
22 SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY 

FIGURE 16.—a, Enlargement of a bead, not shown on Figure 13a but directly below the one to the lower right. 

The oblique markings across the bead are clear. USNM 508130 (x20). b, The same specimen taken with different 

lighting. Curved marking may be seen on the surface of the bead (x20). 

more like that of the Phanerozoic than like that of the Archean, 

but details cannot be stated. 

Timofeev et al. (1988) suggested that during the earlier 

part of earth history, the hypsometric contrast between 

shelves and ocean basins was less pronounced, the rate of 

sedimentation was lower, and the lateral differentiation of 

clastic sediments was less significant, relative to conditions 

in the Phanerozoic. 

MODE OF LIFE 

Three theoretical modes of life should be considered for Horodyskia: pelagic, infaunal, or epifaunal. Although the last two 

terms imply animal, they are used in an ecological sense only. 

Grey and Williams (1990:322-323) compared their strings to 

various pelagic algae, particularly the brown alga Hormosira 

(Endlicher) Meneghini. One might then view individual beads 
NUMBER 94 23 

FIGURE 17.—a, Enlargement of a bead on the far right of Figure 13a. Elongate markings may be seen. USNM 508130 (xlO). b. The same bead further 

enlarged and with different lighting. Lines in the lower part of the bead area 

are at an angle to those above them (x20). c, A bead from a string on the 

same slab that bears the holotype; it is indicated on the frontispiece by an 

arrow. Markings across the bead at two different angles may be seen. USNM 

508100(x20). 

as air bladders, allowing the string to float. This interpretation 

has merit and cannot be ignored. 

The strings show a variety of shapes. If they settled from the 

water column under extremely quiet water conditions, as deduced from the sediment laminations, one might expect some 

uniformity in shape. We have no strings that are tangled, or any 

instances in which one specimen lies directly across another of 

the same growth size, phenomena to be expected with strings 

falling to the bottom. Dead pelagic organisms lying on the bottom surface might produce drag marks on the bedding plane, 

but such marks have not been observed. As noted, delicate sedimentary structures of obstacle marks, or "current shadows," 

and scour do occur. In Hormoseria, the connection between 

true spheres is horizontal, yet no impressions linking beads beyond the earliest stages have been observed. We find little to 

support the comparison and, equally, for an interpretation of a 

pelagic life mode. 

A modification of pelagic life would be if a string were anchored at one end. We presume that if the beads acted as floats, 

they would show a size gradient. The stem might be imprinted 

on the sediment along with the beads. Neither has been observed, and we rule out this interpretation. 

At an early life stage, it is far easier for a tube of microscopic 

cross section to grow on the sediment surface than within sediment, an argument against continuous covering. None of the 

sawn cross sections, polished sections, or thin sections show 

any significant change in the delicate graded bedding. On virtually all slabs, specimens are limited to bedding-plane and sole 

surfaces. We cannot exclude the possibility of a small, shallowly buried tube-like organ occasionally giving rise to beads 

or short vertical tubes that thrust up through the sediment, although we judge this to be most unlikely. There is no evidence 

of disturbance of laminae. 

Current crescents and scour around beads indicate they stood 

above the bottom during life or were partially uncovered by 

water movement before being smothered by sediment. This 

vertical component of growth seems a powerful argument for 

life extending upward from the bottom. Morphology of the 

strings also supports a benthic mode of life. Unbroken strings 

are six or more beads long. Both very small beads of millimeter 

size and strings of large beads are often preserved on the same 

bedding plane. No evidence of size sorting or dominant orientation has been found. 

We interpret life position as benthonic, and it was a combination of extremely shallow infaunal and epifaunal position as the 

organism grew upward to avoid being buried. The vast majority of these organisms were buried in situ by a sediment influx 

deeper than that through which the organism could grow; 

therefore, the number of strings reflects an extremely high population density. Mode and time of reproduction, details of substrate and microenvironment favorable for settling, and growth 

and subsequent preservation of organisms are among the major 

elements controlling the local mass occurrence of Horodyskia, 

but we are unable to quantify any of these factors. An artistic 

rendering of our interpretation is shown in Figure 18. 

GROWTH 

At least three theoretical models of growth are possible: uniform (coherent) growth of stolon length and bead size; growth 

of some beads and inhibition of others in the process of maturation; and growth of some larger beads and regressive development of other smaller ones. 
24 SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY 

FIGURE 18.—Reconstruction of several strings of Horodyskia of different growth stages living on a fine-grain 

arenite bottom. The specimens are partially covered by sediment so that the "string ofbeads" effect is obvious. 

Current shadows and infillings associated with the beads are in the lee of the current direction. These features are 

more apparent for the larger and older string than for the smaller beads. 

The first model may imply the stolons grew to their full 

length and then gave rise to beads of different size. If upward 

extensions appeared as a stolon elongated, beads would be of 

varying lengths. Either case would not produce proportional 

bead spacing; therefore, we reject this model. 

There is little obvious difference between the second and 

third models. The former implies passivity and therefore more 

opportunity for irregularity. We prefer the third model, in which 

loss of intermediate beads is an active, regulated process. To facilitate discussion, beads continuing to grow are termed "acceptors" and those ceasing growth are termed "donors." 

Although the sedimentation rate was slow, the organism had 

to grow fast enough to either keep the upper portion of beads 

above the bottom or keep them from being buried too deeply. If 

the colony were episodically thinly covered by sediment, donor 

cells would provide nutrients for further upward growth of adjacent acceptors. As bizarre as this speculation may be, it is the 

only one we have been able to envision for the proportionality 

of spacing in Horodyskia. We know of no close modern analogues, although colonial hydrozoans show redistribution of 

cellular material through a colony. 

We presume Horodyskia began growth from one cell settling 

to the bottom. Initial stolon growth may have been unidirectional rather than in both directions from a center, but there is 

no evidence for either possibility. We have reconstructed a life 

cycle partly based on taphonomic interpretations to conclude 

that Horodyskia was sessile and benthonic. It is presented as a 

series of stages, and for ease of understanding, we have eliminated repetition of earlier points, as well as appropriate cautionary comments. An artistic summary has been prepared 

(Figure 19). 

Stage 1. A thin thread grows to some length, but both length 

and orientation seems to be random (Figure 15c). We are now 

convinced that at least some of the tiny trails described by Fedonkin et al. (1994:216-218, figs. 28, 29) may be the first 

growth stage of Horodyskia. Probably a slightly thicker claysized sediment film was preferred for this stage, but intermixing of sizes suggests larval settlement may have been nearly 

continuous. 

Stage 2. The thread expands regularly, developing tiny 

bead-like swellings close to one another (Figure 15a, b). In one 

specimen, swellings appear ellipsoidal rather than spherical, 

but this may be a result of compaction modifying the shape. 

Stage 3. Alternate swellings disappear, and those remaining 

develop to slightly larger and more widely spaced spheres. 

Stage 4. Spherical shape changes to slightly elongated tapering tubes, the upper surface of which is hemispherical (Figure 

7c). Alternate beads, the early donors, decrease in size, but the 

uniformly spaced acceptors enlarge. The donor/acceptor switch 
NUMBER 94 25 

may be triggered by a thin cover of sediment one or two grains 

in thickness. 

Stage 5. More alternate beads cease growth and become donors; acceptors, still proportionally spaced, become wider and 

longer, in part by transfer of donor material and in part from 

their own metabolism. Estimating from the number of smallest 

beads on a string to the largest, suppression of donors may occur at least three to five times, or more. 

Stage 6. An invagination of the upper surface may occur, or, 

far less likely, a small opening may develop in the hemisphere 

at the top of the cone. We have not observed any feature leading to either interpretation on beads smaller than about 3 mm. 

Stage 7. Upward growth is at a decreasing rate and eventually stops. 

A general rule among fossil collections, regardless of the 

group, is that large individuals are rare. For sessile organisms 

where sedimentation events are a matter of life or death, relationship of size to abundance is obvious. Judging from the fine 

laminations, episodes of graded bedded lasted for long intervals. 

Nevertheless, transfer of material must have had limitations, 

particularly for a relatively simple organism. Eventually the 

metabolic cost of this transfer would have become too large, 

thereby putting an upper limit on the size of the beads. The 

largest diameter beads suggest a maximum cone length of 

about 1 cm, but it may have been less. The bead diameter approximated its height above the initial stolon and below the 

curvature of the upper surface. 

In this interpretation of life shape, the ratio of volume within 

the cone to surface area of the hemispherical top is nearly constant. By measuring the length of strings and the total surface 

area of the number of beads in the string, we estimate that surface area remained nearly constant and may actually have increased slightly as the number ofbeads decreased. 

SINGLE ORGANISM VERSUS COLONIAL ORGANISM 

The most remarkable peculiarity of growth in Horodyskia is 

the proportionality of bead size and spacing. As beads grow 

larger, the spacing between beads becomes wider; proportions 

remain nearly constant within the limits to be expected in biologic variation. Because of the interrelationship among beads of 

one string, we judge Horodyskia was a colonial organism. That 

term is used several ways in the literature, but it need not mean 

that many different kinds of cells were present in the colony. 

For a modern analogy, we consider the organism more comparable to a simple hydroid colony than to a complex sea pen. 

INTEGUMENT 

Horodyski (1981; 1993, appendix 10) reported microfossils, 

carbonaceous sphaeromorphs that measured 17-82 u.m (mkm) 

across, from the Appekunny Formation. The very low degree 

of metamorphism in the formation allowed those fossils to survive. Inasmuch as these microrganisms are preserved, their 

walls might have been a cellulose-like compound resistant to 

FIGURE 19.—Schematic representation to show the growth of Horodyskia 

moniliformis Yokelson and Fedonkin. A stolon (1) on the bottom develops tiny, 

closely spaced beads (2) before being covered by sediment (3). As a result of the 

cover, alternating "donor" beads transfer material to "acceptors," which then 

grow upward through the thin sediment cover (4) before being lightly covered 

again (5). Alternating donor beads again contribute to acceptors, permitting 

more upward growth (6) before yet another thin covering of sediment covers the 

string (7). With the loss of another set of alternating donor beads, upward 

growth continues and a conical shape of individual beads develops (8). 

rapid oxidation and biochemical degradation. Accordingly, 

larger organisms of similar organic composition had a chance 

of being preserved. Proterozoic Chuaria Walcott and Grypania 

Walter, Oehler, and Oehler, locally common in other areas, are 

now carbonaceous films. Similar preservation is typical for 

Late Proterozoic algae, such as Tawuia Hofmann (1992b) and 

Vendotaenia Gnilovskaya (1992). The absence of any fragments of organic films within the Appekunny may mean that 

Horodyskia was not formed of a cellulose-like compound. 

Beads from Rising Wolf Mountain are black, similar in color 

to the Proterozoic algal(?) taxa mentioned above, but there is a 

greater thickness to the flattened beads than to carbonaceous 
26 SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY 

films. A few beads show another feature, that of low ridges 

closely spaced on the inner surface. The concept of compression of an upper and lower surface is reinforced by several 

beads that show ridges trending one direction on the interior of 

an upper layer and trending in another direction on a layer below. On one bead, curved traces occur. Large Chuaria of comparable size from the Grand Canyon are strongly wrinkled, 

much like a raisin, whereas beads do not show such irregularities. Close, regular spacing of ridges within the few beads that 

preserve them is further indication of a stiff integument less affected by compaction than a sphere. We suggest that these may 

have been primary structures for strengthening the wall of the 

cone. Some liniations may be the result of tectonism, but these 

are limited to the diameter of the bead, and several show these 

features with different orientations (Figures 16a-c, 17a-c). 

These observations hint that cellulose material was not 

present in the beads; admittedly it is far from any proof. If 

nothing else, the presence of the delicate ridges supports replacement of an integument by silica rather than void infilling. 

Cellulose is more stable than protein in the face of agents such 

as oxidation, biochemical degradation, and heating. Paradoxically, fast decomposition of protein may facilitate fossilization 

of buried soft-bodied organisms, for it leads to a geochemical 

shift of the local microenvironment towards temporary anoxia 

and early sediment diagenesis around a decaying organism (Fedonkin, 1987). Halos around beads imply low permeability and 

fast decomposition. Possibly proteinaceous matter rather than 

cellulose-like material was also significant in decay. 

FEEDING AND POSSIBLE FOOD SUPPLY 

We judge the presence of a central hole on the top of a cone 

as quite unlikely. Assuming reconstruction of the environment 

is reasonably accurate, it carries the concept of nutrient-poor 

water, which, in turn, translates to few microorganisms as a 

food source and less of a prospect for direct feeding. Were a 

central opening present, sediment might drift into the interior, 

unless one postulates a ciliated exterior of the tube actively 

beating to move away small particles, an activity counterproductive for an organism feeding through a mouth. 

If the upper surface of the cone was closed, the organism 

could not have been a suspension feeder. From the standpoint 

of geometry, a hemispherical shape provides a large surface 

area. As noted, although the number of beads in a string decreases through time, the surface area of each remaining bead 

becomes larger. At a late growth stage, minor invagination 

would yield more surface area. 

Photosynthesis as a food source cannot be ruled out and may 

be more plausible than any other suggestion. It presupposes 

such environmental parameters as well-oxygenated bottom water and reasonably clear water for sunlight penetration. An episodic rain of fine arenite particles might inhibit photosynthesis, 

as would low oxygen levels in the water column. 

As an alternative, chemosynthesis should be considered. The 

concept has been well known to generations of bacteriologists, 

although it is only coming into prominence with the discovery 

of deep-sea vent faunas. In general, chemosynthesis is exploited by bacteria, and these in turn are exploited by more 

complex organisms. 

Chemosynthesis requires a redox gradient. Some beds are 

variegated, and many are green; incipient reducing conditions 

may have been present early. We do not know whether the iron 

and manganese coating of arenite grains might be a result of 

bacterial activity, but it is within the realm of possibility that 

the hematite coating could have served as an ultimate energy 

source. It has also been suggested that bacteria play a role in 

binding the individual grains forming the delicate laminae. 

Discussion 

In preceding sections we have attempted to present a reasoned case that Horodyskia moniliformis is an organism that 

should be formally named. Our hope is that this action will lead 

to more paleontological study of siliclastic units. This study 

has also led us to notions that are not rigorously supported, but 

they provide a framework of larger implications concerning 

this fossil. To insure that speculations do not weaken the primary focus of this work, they are discussed below rather than 

in the main body of the text. 

To recapitulate the occurrence of Horodyskia, Winston (in 

litt., 1997) noted that the lower part of the Appekunny Formation has three novel aspects: the extremely well-sorted nature 

of the sediment; the subaqueous depositional environment; and 

the hematite coating on the arenite grains. Thus, the Appekunny is the only fine-grained, subaqueous red unit in the entire Belt Supergroup. 

Study of ecological aspects of the emergence of eucaryotes 

(Rozanov and Fedonkin, 1994) has led to a conclusion that 

those more complex life forms should have occupied a limited 

space in the early Proterozoic biosphere. For much of the early 

history of life, environments were dominated by prokaryotic 

organisms. During the Proterozoic, cyanobacterial communities formed relatively stable ecosystems of stromatolites and 

mats on a global scale. A bacterial community derives two important advantages from stromatolitic structures, a large surface area to be populated plus substrate stability, and these provide stability for any colonizing population. 

Stromatolites are specialized developments of the general 

ecological group of cyanobacteria. Much of the thickness of 

carbonates deposited in the Newland, Altyn, Helena, and Shepard formations of the Belt Supergroup is devoid of stromatolites. Cyanobacterial mats in these units were concentrated at 

nearshore environments where waves broke along the shores 

and flats (Winston, in litt., 1997). A point of significance is that 

mats were not confined to carbonates. Schieber (1986) emphasized the importance of mat formation on Middle Proterozoic 

carbonaceous shales. 
NUMBER 94 27 

One consequence of Proterozoic bacterial activity may have 

been that shallow-water benthic habitats, which for that early 

time were well oxidized and well illuminated by sunlight, 

were, in a sense, a "prohibited zone" for eucaryotic organisms. 

Mat growth might not have allowed space for competitors, 

partly by using available nutrients and partly by producing byproducts harmful to other organisms. A mat would have increased substrate stability and simultaneously isolated subsurface sediment, which in turn would have limited sediment aeration. Under conditions of low sedimentation rate, substrate 

stability, and absence of bioturbators, bacterial mats could have 

negatively affected larger benthonic organisms. 

Modern analogues of these ecosystems, cyanobacterial mats 

of hypersaline lagoons, marshes, and sabkhas, should be considered as relics of the archaic Precambrian world (Awramik, 

1984; Knoll, 1985; Zavarzin, 1993). (Some stromatolites in 

Shark Bay are draped with sea weed, but it is not certain these 

are growing with the mounds.) The mat ecosystems today do 

not leave much ecological space for eucaryotic organisms. We 

would expect the same for the Proterozoic world with the understanding that similar communities controlled far wider areas 

of the shallow-water habitats. Thus, in moving back retrospectively through time, the biotopes or habitats of benthic eucaryotes would have shrunk, and the chance to find their fossil remains decreased accordingly. 

Whereas this point has general applicability, its antithesis 

may be more significant. The Appekunny Formation might 

have been deposited where cyanobacterial communities could 

not dominate the environment. Within member 1, bacterial 

mats are present but are quite rare. Their paucity might be a 

factor that allowed Horodyskia to thrive. Notwithstanding that 

view, one of us (M AF) suggests that the delicate lamination of 

the formation was formed in part under the stabilizing control 

of benthonic bacterial communities. Contrarily, one of us 

(ELY) is impressed with how rare the evidence of mats is 

among the numerous slabs collected. 

To consider occurrence from another aspect, one ecological 

model for the origin and early evolution of Metazoa (Fedonkin, 

1995, 1996b) claims that the habitats of the first metazoans 

may have been limited to cold-water basins, well beyond the 

carbonate belt. During most of the Proterozoic, the carbonate 

belt might have been wide as a result of both relatively high 

temperature and carbonate saturation of sea water (Lowe, 

1994). Relatively cold-water basins could have occurred in 

temperate zones or even in polar regions, as these were ice free 

during most of the Proterozoic. 

In temperate or cool-water basins, loose sediment and a flat 

sandy bottom inhibit upward growth of bacterial communities, 

but inhibition by sand would apply equally well to warmer waters. The presence of hematite in the Appekunny, however, 

tends to tip the balance of interpretation toward warmer rather 

than cooler conditions. 

Moving from ecology to evolution, it is our opinion that diversity within a major taxon or clade is secondary in importance to the distinctiveness of one major taxon from another. 

We think, with many exceptions, that from about the middle 

Paleozoic to the Holocene, distinctiveness decreased and diversity increased. From about the middle to early Paleozoic backward in time, diversity decreased in the fossil record, but distinctiveness increased. If the generalization has any validity, 

still greater disparity of grades of organization and even less diversity would be expected within the Proterozoic. The age and 

morphology of Horodyskia fit this theoretical model. 

Animal body fossils and trace fossils are well known in the 

Vendian Period, about 600 Ma old. Their phylogenetic roots 

must go back much further in the Proterozoic as confirmed by 

the high degree of faunal differentiation at the beginning of the 

Vendian. Various retrospective paleontological models of metazoan evolution (Durham, 1970; Sepkoski, 1992; Valentine, 

1991, 1994) provide a variety of suggested dates for the origin 

of animals. Data from molecular phylogenetics give other dates 

(Wray et al., 1996; Vermeij, 1996). Assumption of constancy 

for a molecular clock is a potential weakness because although 

numbers derived from molecular studies are helpful, in our 

view that method may supplement, but never supplant, discovery of authentic fossils. The fact is that Horodyskia appeared 

about 1.5 billion years ago. The speculations that may be derived from this one fact are many and varied. 

To leave evolutionary concepts and consider specimens, it is 

obvious that soft-part morphology and metabolism of fossils almost never leave any clues, and speculation may be unbounded. 

Even though a Holocene cell may be larger than a grape, the 

length of strings and number ofbeads strongly imply Horodyskia was multicellular. Details of tissues are unknown except 

that the exterior was a stiff integument; a surmise is that several 

kinds of internal tissues were present to aid respiration and to 

transport nutrients. We state only that Horodyskia was an early 

organism, "different" from any younger form. In our view, 

terms such as "primitive" and "advanced" carry too much intellectual baggage. 

In a sense, ideas of primitive and advanced are also involved 

with food chains. With exceptions, the longer the food chain, 

the more complex—advanced—the organism. In whatever way 

Horodyskia may have lived, there is no evidence of a long food 

chain. If the highly speculative concept of chemosynthesis as a 

life style can be confirmed, Horodyskia may represent a major 

evolutionary group that is neither plant nor animal. It is far 

more likely that somehow it ingested bacteria involved in 

chemosynthetic activity. 

Rather than phrasing the systematic position of Horodyskia 

as a purely taxonomic question, it may be more helpful to consider it in terms of autotrophic versus heterotrophic lifestyle. 

The former allows us to better integrate paleoenvironmental 

data with morphologic criteria. This study has led us to the 

conclusion that Horodyskia was an early autotroph, which developed megascopic size. The large size in turn led to multicellularity and to tissue-grade anatomy. Whether this organism 

was an environmental "dead end" or a precursor of later forms 

remains a question for the future. 
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