The Ecology of the Cambrian Radiation - Andrey Zhuravlev - Chapter 13 doc

During the late Vendian there was an in- crease in megascopic biota in shallow water, with both soft-bodied fossils and trace fossils becoming relatively abundant.. There was also a slig

Megascopic life evolved in the Archean with the buildup of stromatolitic mounds in shallow-water environments By the Proterozoic, stromatolites had already extended down to well below fair-weather wave base During the late Vendian there was an in- crease in megascopic biota in shallow water, with both soft-bodied fossils and trace fossils becoming relatively abundant Some of the soft-bodied forms, such as Pteri- dinium, were large and preserved three-dimensionally, with remarkable detail, in high-energy medium-to-coarse-grained sandstones This style of preservation re- sembles that of trace fossils, which were produced within similar sequences during the Phanerozoic, and may suggest that some of these early life-forms grew through already deposited sediment as a unicellular protoplasmic mass Some Ediacaran body fossils (e.g., Charniodiscus, Ediacaria, Pteridinium) may have survived into the Cambrian by migrating into deeper water, where many of the reported body fossils were exceptionally preserved soft-bodied forms There was also a slight increase in trace fossil diversity in deep water during the Cambrian, and this too may reflect the activity of a dominantly soft-bodied fauna There was a major progressive coloniza- tion by hard-bodied forms of the outer shelf by the Early Ordovician, and of the slope toward the end of the Middle Ordovician In contrast, there is a significant increase

in trace fossil abundance and diversity in deep-water flysch sequences as early as the Early Ordovician It appears that soft-bodied animals, including those which produced trace fossils, were involved first in the onshore-offshore migration and were generally well established in deeper-water niches before the arrival of faunas rich in skeletal forms.

of Precambrian and Cambrian megascopic body and trace fossils occur in sedimentsconsidered to have been deposited in shallow water, mostly above storm wave base.There are, however, several abiological factors that might emphasize this apparentdistribution First, deep-water sediments, by the nature of their tectonic setting, aremore prone to deformation and metamorphism, and these processes will eliminatesome forms and make recovery of others difficult Second, shallow-water shelf seaswere dominant late in the Precambrian and early in the Cambrian Consequently, theexposed area of shallow-water strata representing the period when life was evolvingrapidly far exceeds that of deep water, and third, it is easier to find definitive sedi-mentological evidence for shallow-water environments than for deep-water ones.Nevertheless, it is generally accepted that many animals evolved in shallow waterduring the late Precambrian and early Cambrian and then gradually spread into thedeep oceans (Crimes 1974; Sepkoski and Miller 1985; Sepkoski 1990) Indeed, it hasbeen claimed that there is something unique about shallow-water environments thatpromotes the origin of evolutionary novelties or the assembly of novel communitytypes (Sepkoski and Miller 1985) The most distinctive ecological features of shallow-water environments are the frequent disturbances and the high-energy, stressful, am-bient conditions, and these factors may be conducive to the evolution of novel taxa andcommunities (Steele-Petrovic 1979; Jablonski and Bottjer 1983; Sepkoski and Shee-han 1983; Valentine and Jablonski 1983).

The evolution of a deep-water fauna requires adaptation to certain extreme tions, such as permanent darkness, high pressure, and low temperature (except in thecase of hydrotherms) In addition, deep seas show low fertility In the absence of ter-restrial plant debris influencing community structure, early deep benthos wouldprobably suffer from very limited food (Bambach 1977)

condi-The late Precambrian and Cambrian circumstance of high diversity in shallowwater and decreasing diversity in progressively deeper water is in marked contrast tothat in modern oceans, where unusually high diversity has been found in deep water(Hessler and Sanders 1967) For example, the diversity of polychaetes and bivalvesincreases with depth below the continental shelf and, at bathyal depths, reaches levelsequivalent to those in tropical soft-bottomed communities at subtidal depths (Sanders1968) Similarly, when considered for a single type of substrate, the diversity of gas-tropods and several other groups increases from the shelf to bathyal depths (Rex 1973,

Recent investigations (e.g., Narbonne and Aitken 1990), however, suggest that

even during the Precambrian, animals were penetrating at least into intermediatewater depths, and by the Cambrian there was a limited colonization of even bathyaldepths (e.g., Crimes et al 1992; Hofmann et al 1994).

The purpose of this chapter is to review the progressive colonization of the deepsea from the Precambrian to the Ordovician, that is, through the period of Cambrianradiation

THE ENVIRONMENTAL SET TING OF THE EARLIEST LIFE

It has become fashionable to regard hydrothermal systems as likely sites for organicsynthesis and the origin of life (see Chang 1994 and references therein) Indeed, it hasbeen claimed that present-day microorganisms with the oldest lineages based onmolecular phylogenies are anaerobic, thermophilic, sulfur-dependent chemolitho-autotrophic archaebacteria (Woese 1987) It has been suggested that deep marinecommunities had formed around black smokers and white smokers already in thePrecambrian (Kuznetsov et al 1994) Fossil examples of such communities have beenreported in Silurian, Devonian, and Carboniferous sulphur-rich, hydrothermal strata

in the ophiolitic suites of the Urals and northeastern Russia, where they are panied by vestimentiferans (Pogonophora) and calyptogenid pelecypods similar to theinhabitants of present-day smokers (Kuznetsov 1989; Kuznetsov et al 1994) Recog-nition of such sites in early Proterozoic sequences is, however, likely to prove diffi-cult, and although it might be argued that they were more common during earlyEarth history, they must nevertheless have occupied a small percentage of availableecospace Therefore, unless they were almost uniquely favorable locations, it is sta-tistically unlikely that they would be the “chosen” sites

accom-The earliest well-documented signs of life come from ~3 –3.5 Ga, in early Archeanstrata in the Swaziland Supergroup of South Africa and the Pilbara Supergroup inwestern Australia (Schopf 1994) These units contain stromatolites and microfossils,and it is considered that the former, at least, grew in narrow, shallow-water zonesalong shorelines of volcanic platforms subject to periodic agitation by waves or cur-rents (Groves et al 1981; Byerly et al 1986) The similarity between these stromato-lites and much more recent ones suggests strongly that they exhibited bacterial orcyanobacterial photosynthesis (Schopf 1994) and were therefore restricted to shallowwater

The first sediments considered to have been deposited on a stable carbonate form occur in the Middle Archean Nsuze Group, which includes stromatolitic dolo-mites in a tidally influenced environment (Walter 1983; Grotzinger 1994) By the LateArchean, stromatolite-bearing carbonates were being deposited in cratonic and non-cratonic settings (Grotzinger 1994), but the growth of large cratonic masses of conti-nental lithosphere during the Archean-Proterozoic transition (Veizer and Compston

plat-1976) gave rise to a dramatic increase in carbonate platforms (Grotzinger 1994), andthis provided ecospace for a significant increase in abundance and diversity of stro-matolites (figure 13.1A), which peaked in the Middle Proterozoic (Awramik 1971;Walter and Heys 1985) This increase was accompanied by the occupation of more-varied niches extending down to well below fair-weather wave base but still presum-ably within the photic zone (Grotzinger 1990; Walter 1994: figure 4) The coloniza-tion of “deeper” water seems to have already commenced.

The decline of stromatolites is commonly ascribed to the advent of soft-bodiedMetazoa, as evidenced by the Ediacara fauna and its associated trace fossils (Garrett1970; Awramik 1971) Some of these forms may have been able to destroy stromato-lites by grazing and burrowing, but there has been no significant documentation ofstromatolites affected in this way Competitive exclusion by higher algae may alsohave contributed to the decline (Hofmann 1985; Butterfield et al 1988; and see Droserand Li, Pratt et al., Riding, this volume) Many later organisms may have responded

to competitive pressures by migrating into deep water (Crimes 1974; Sepkoski 1990),but stromatolites, being limited to the photic zone, had probably occupied much ofthe available ecospace by the late Proterozoic and, consequently having “nowhere to

go and nowhere to hide,” might have suffered badly from increased competition with

an expanding trophic web

One of the earliest records of probable metazoan life is Bergaueria-like trace

fos-sils (see Crimes 1994 : 114) from the 800 –1100 Ma Little Dal Group of the zie Mountains, Canada (Hofmann and Aitken 1979) These occur in a carbonate-dominated sequence of varied lithology, considered to be of basinal aspect and de-posited in water several tens to 200 m deep (Hofmann and Aitken 1979 : 153) Thesefossils may therefore also mark an early colonization of slightly deeper water

Macken-THE COLONIZATION OF DEEPER WATER DURING Macken-THE VENDIAN

The Vendian era, extending from ~610 –545 Ma (Grotzinger et al 1995), commenceswith the Varanger tillites and their equivalents and is the first to yield relatively com-mon and diverse undisputed body fossils and trace fossils

The oldest Vendian biota, consisting of Nimbia, Vendella?, and Irridinitus?, was

found in the intertillite Twitya Formation of the Mackenzie Mountains, Canada mann et al 1990) This sequence comprises siliclastic turbidites associated with ma-jor channel-fill conglomerates and is considered to be relatively deep-water (Hofmann

(Hof-et al 1990)

The majority of post-tillite Vendian biotas have been found in shallow-water quences, apparently deposited above fair-weather wave base, and in some regions(e.g., Australia, Namibia, Russia, Ukraine), remarkably abundant, diverse, and well-preserved faunas have been found (see reviews in Glaessner 1984; Sokolov and Iwa-nowski 1985; Fedonkin 1992; Jenkins 1992) Indeed, in some sequences deposited

se-Figure 13.1 “Snapshots” of the ocean floor faunas for Middle Proterozoic, Vendian, and

Cambrian, showing the progressive colonization of deeper water based on body fossils

under varied depths of water, fossils occur only in the shallower-water lithologies.For example, in the Tanafjorden area of Norway, the Vendian Innerelv Member con-sists of two shallowing-upward sequences, each representing a transition from off-shore marine (quiet basin, below wave base) to wave-influenced, shallow, subtidal and

intertidal deposition (Banks 1973), but a biota consisting of Cyclomedusa, Ediacaria?, Beltanella, Hiemalora, and Nimbia? occurs only in sediments interpreted as represent-

ing a current-swept, wave-influenced environment (Farmer et al 1992)

There are, however, a few well-documented examples in which body and /or tracefossils do occur in deeper-water deposits (figures 13.1B and 13.2A) In the case ofbody fossils, it might be possible to claim that they have been transported from shal-low water, but such an argument cannot be applied to trace fossils, which reflect lifeactivity at the precise location where they are now found

In the Wernecke Mountains, Canada, Narbonne and Hofmann (1987) record afairly extensive Ediacara fauna, most of which comes from Siltstone Units 1 and 2, de-

posited under shallow-water conditions This includes the body fossils Beltanella, Beltanelliformis, Charniodiscus, Cyclomedusa, Kullingia?, Medusinites, Nadalia, Spriggia, and Tirasiana, as well as the trace fossils Gordia, Neonereites?, and Planolites However, Charniodiscus was also recorded from the Goz Siltstone, which includes slump and

load structures and was deposited on a slope in a deeper-water setting

A more extensive deeper-water biota has been described by Narbonne and Aitken(1990) from the Sekwi Brook area of northwestern Canada, where the Sheepbed andBlueflower formations include turbidity current – deposited sandstones and commonslump deposits and are interpreted as representing a deep-water basin slope setting,

below storm wave base The biota includes the body fossils Beltanella, Charniodiscus?, Cyclomedusa, Ediacaria, Eoporpita, Inkrylovia, Kullingia, Pteridinium, and Sekwia and the trace fossils Aulichnites, Helminthoida, Helminthoidichnites, Helminthopsis, Lockeia, Neo- nereites, Palaeophycus, Planolites, and Torrowangea More recently, Hiemalora and Win- dermeria have been reported from the same sequence (Narbonne 1994).

Pteridinium has also been recorded from the South Carolina Slate Belt in

deep-water, thinly bedded to finely laminated pelites and siltstones of the AlbermarleGroup, which may have been deposited between 586 and 550 Ma (Gibson et al

1984) This sequence has also yielded the trace fossils Gordia, Neonereites, Planolites, and Syringomorpha (Gibson 1989).

Surfaces covered with numerous predominantly frondlike and bushlike Ediacaran

body fossils, including Charnia and Charniodiscus, occur within volcaniclastic

turbi-dite sequences interpreted as deep-water submarine fan and slope deposits (Myrow1995) within the Conception Group on the Avalon Peninsula, Newfoundland, Can-ada (see Anderson and Misra 1968; Misra 1969; Anderson and Conway Morris 1982;Conway Morris 1989a; Jenkins 1992) Taphonomic and sedimentological data indi-cate that this is an in situ life assemblage that suffered rapid burial by volcanic ash at

Figure 13.2 “Snapshots” of the ocean floor faunas for Vendian, Cambrian, and Ordovician,

showing the progressive colonization of deeper water based on ichnofossils.

some horizons ( Jenkins 1992; Seilacher 1992; Myrow 1995) The turbidites may nothave formed at truly oceanic depths but perhaps on a continental terrace (Benus 1988;Jenkins 1992) A broadly similar setting has been postulated for the occurrence of

Charnia, Charniodiscus, and Pseudovendia within a Vendian sequence at Charnwood

Forest, Leicestershire, England, where Jenkins (1992) suggests that the frequency ofslumps, together with some current rippling and an absence of oscillation ripples,implies deposition on a slope environment below storm wave base Boynton and Ford

(1995) record three new genera from this sequence (Ivesia, Shepshedia, and brookia), but conclude that, despite the presence of graded bedding and absence of

Black-shallow-water indicators, water depth may be little more than wave base

The classic sequence at Ediacara, Australia, which has yielded an abundant and verse nonskeletal fauna, has been interpreted by Gehling (1991) as deposited in anouter shelf setting below fair-weather wave base, with burial of the organisms by stormsurge sands Seilacher (in Jenkins 1992 : 152) considers that the common occurrence

di-of wave oscillation and interference ripples suggests deposition on the shoreface, beit perhaps by storm events, and a shallow-water tidal environment also seems in-dicated by the large polygonal desiccation cracks in the highly fossiliferous parts ofthe section ( Jenkins 1992 : 153)

Evidence of life at truly bathyal depths is largely absent during the Vendian,

al-though records of the trace fossil Planolites within the deep-sea turbidite sequence of

the South Stack Formation of the Mona Complex on Anglesey, Wales, by Greenly(1919) have been substantiated during recent fieldwork The age of these rocks isdebatable, but radiometric dates on intrusive granites suggest that it is greater than

600 Ma (Shackleton 1969)

The conclusion appears to be that while most Ediacarian body and trace fossils fromthe prolific localities in Australia, Namibia, Russia, and Ukraine occurred in shallow-water environments at or above wave base, other localities, including CharnwoodForest, Newfoundland, Sekwi Brook, and Wernecke Mountains, show features sug-gestive of a slightly deeper-water environment below storm wave base, mostly on thecontinental slope There is not, however, any evidence of significant colonization oftruly oceanic depths during the Vendian

Such colonization as took place in intermediate water depths was dominated by

sessile body fossils (e.g., Cyclomedusa, Ediacaria) and detritus-feeding animals that produced traces either on muddy substrates (e.g., Helminthoida, Helminthopsis) or at very shallow depths (e.g., Paleodictyon) Significant bioturbation did not occur until

the Early Cambrian (Crimes and Droser 1992) In present-day oceans, faunas iting muddy substrates are more abundant and diverse than those of sandy areas(Menzies et al 1973), whereas in these ancient seas, the absence of algae and the scar-city of large animals increased the survival possibilities of the detritivorous trophicgroup (Sanders and Hessler 1969; Sokolova 1989)

inhab-BIOTIC CHANGES ACROSS THE PRECAMBRIAN-CAMBRIAN BOUNDARY

Diversity curves of metazoan genera show a fall at the Vendian-Tommotian boundary(Sepkoski 1992: figure 11.4.2) This data set includes genera from all depositional en-vironments, and the fall has been interpreted as reflecting a mass extinction Seilacher(1984) suggested that Vendian biota mark not simply a nonskeletal start to metazoanevolution but a distinct episode to the history of life, terminated by a major extinc-tion He later suggested that they were quilted constructions that represented an evo-lutionary experiment that failed with the incoming of macrophagous predators (Sei-lacher 1989)

There is, however, also a remarkable change in the style of preservation of many ofthe body fossils in passing across the Precambrian-Cambrian boundary (cf Seilacher1984) The Vendian shallow-water sequences are dominated by relatively large forms,commonly exceedingly well preserved in three dimensions and found within fine-to-coarse-grained, well-washed, matrix-poor sandstones (figure 13.3) Such three-dimensional preservation is almost unknown in the Phanerozoic (cf Seilacher 1984,1989) By that time, these high-energy sandstones commonly lack body fossils andare dominated by trace fossils, many of which are produced within or between beds.Explanations for the three-dimensional preservation of Vendian body fossils includeearly mineral precipitation within the matrix ( Jenkins 1992), low rates of microbialdecomposition (Runnegar 1992), absence of scavengers (Conway Morris 1993), andthe supposed existence of mineral crusts formed by cyanobacterial mats (Gehling1991)

The parallels between the three-dimensional preservation of these body fossils in

the Vendian and the trace fossils produced within similar sandstones in the

Phanero-zoic is remarkable but is consistent with the conclusions of Crimes and Fedonkin(1996) that many of these three-dimensionally preserved Vendian body fossils ac-tually formed by growth within the sediment by a process of plasmic permeation.Such animals would then undoubtedly suffer from the incoming of macrophagouspredators in the Phanerozoic as envisaged by Seilacher (1989) They seem to have re-sponded by onshore-offshore migration, and a few appear in deeper-water environ-ments during the Cambrian (Conway Morris 1993; Crimes and Fedonkin 1996).Crimes (1994) has argued that Vendian trace fossils also include many unusual andshort-ranging forms The trace fossil diversity data (Crimes 1992: figure 2; Crimes1994: figure 4.1) do not, however, support a mass extinction, nor indeed is this indi-cated by the body fossil data set of Sepkoski (1992: figure 11.4.1) when considered interms of families, orders, or classes Evidence for such an event is perhaps best shownwhen the fauna is divided into “Ediacaran, “Tommotian,” and “Cambrian sensu stricto”(Sepkoski 1992: figure 11.4.2) There is, however, increasing evidence that some,

or perhaps many, elements of the Ediacara fauna continue through the Daldynian (see Brasier 1989) and into later Cambrian strata (Conway Morris 1992;

Nemakit-Figure 13.3 Three-dimensional nature of Pteridinium from the Kliphoek Member of the

Neopro-terozoic Nama Group (South Namibia) A, Field photograph at Plateau Farm, near Aus; B –F,

speci-mens lodged in a small museum at Aar Farm, by permission of Mr H Erni All scale bars 2 cm.

Crimes et al 1995; Crimes and Fedonkin 1996) Additionally, the data are imprecisebecause of correlation problems at this level

Although an overall reduction in diversity cannot be discounted, the picture is farfrom clear, and, interestingly, Jablonski (1995) places the first of his “Big Five” massextinctions at the end of the Ordovician One might also anticipate that any extinctionevent could have greater consequences in shallow water than in the more constantslope environments considered here In contrast, the dramatic increase in diversity ofboth body and trace fossils in the earliest Cambrian strata is obvious (Sepkoski 1992;

Crimes 1994) and has led to the concept of “explosive evolution.” There are a nificant number of short-ranging forms in the late Precambrian, but the Cambrian isdominated by much longer-ranging forms of Phanerozoic type, and this has promptedCrimes (1994) to suggest that the major change is a biological one in which a period

sig-of early evolutionary failure, as represented by a high proportion sig-of short-rangingforms, is replaced by evolutionary success

CHANGES IN DEEP-WATER BIOTA DURING THE CAMBRIAN

There was a considerable increase in body and trace fossil abundance and diversityfrom the Late Vendian through the Early Cambrian (see figures 13.1c and 13.2b)(Crimes 1974, 1992, 1994; Sepkoski and Miller 1985; Signor 1990; Sepkoski 1991,1992; Crimes and Fedonkin 1994) Most of these developments took place in shal-low water, but this must have resulted in a dramatic increase in dispersal pressures.The first great evolutionary fauna (Sepkoski and Miller 1985) evolved during theCambrian in shelf seas, with many of the first appearances probably in subtidal envi-ronments, below fair-weather wave base (Mount and Signor 1985) This fauna wasdominated by trilobites but with associated hyoliths, eocrinoids, helcionelloid mol-lusks, lingulate brachiopods, and a variety of lightly sclerotized arthropods Maxi-mum diversity was achieved in the late Middle to early Late Cambrian, according toSepkoski (1992; but see Zhuravlev, this volume: figure 8.1a)

By the Tommotian, all the main Phanerozoic trace fossil lineages were well lished in shallow water, and they achieved a high degree of behavioral perfection bythe end of the Atdabanian (Crimes 1992) These lineages include forms that later were

estab-to invade the deep oceans and retreat from shallow-water seas (Crimes 1994)

Ex-amples include the network structure Paleodictyon, which made an initial appearance

in the Vendian (as Catellichnus in Bekker and Kishka 1989: plates 1– 6) and quently appeared with better behavioral programming as Paleodictyon and Squamo- dictyon in the Early Cambrian (Crimes and Anderson 1985; Paczes´na 1985), and me- andering forms such as Helminthoida, Parahelminthoida, and Taphrhelminthoida, which

subse-appear in the Vendian (Narbonne and Aitken 1990; Gehling 1991) and are well veloped by the Early Cambrian (Crimes and Anderson 1985; Hofmann and Patel1989; Goldring and Jensen 1996)

de-Nevertheless, it has long been recognized that this evolutionary burst, and the persal pressures that it must have created, did not immediately lead to dramatic col-onization of the deep sea (Crimes 1974, 1994; Sepkoski and Miller 1985) For ex-ample, numerous investigations over the last 150 years have revealed few records ofbody fossils within the deep-water turbidite sequences of the classic Cambrian out-crops in Wales In northern Gwynedd, a strong cleavage has hampered collecting, but

dis-in the Harlech Dome to the south and, more particularly, on St Tudwal’s Pendis-insula

to the west, deformation is much less The only significant records are small restrictedfaunas of Lower Cambrian trilobites from the Hell’s Mouth Grits of St Tudwal’s Pen-

insula (Bassett and Walton 1960) and Green Slates of northern Gwynedd (Wood1969) There may also be doubt as to whether even these meager faunas are in situ.

The earliest well-documented subthermocline fauna is the Botoman Elliptocephala phoides fauna from the Taconics of New York and Vermont, which has some affinities

asa-with typical Laurentian faunas (Theokritoff 1985)

Several fossil assemblages have been recognized in alternating flaggy limestones,argillaceous limestones, marlstones, and mudstones, deposited in outer slope andopen-marine facies that occurred distally in the Yudoma-Olenek Basin of the SiberianPlatform during the late Middle Cambrian (Fedorov et al 1986) Pterobranchs, ses-sile graptolites, trilobites, lingulate brachiopods, hyoliths, echinoderms, and possible

Brooksella have been described here from the Zelenotsvet, Dzhakhtar, and Siligir

for-mations (Lazarenko and Nikiforov 1972; Astashkin et al 1991; Pel’man et al 1992;Durham and Sennikov 1993)

Sessile dendroid graptolites were ubiquitous elements of muddy substrates Theyhave been reported in the Middle Cambrian Amgan Oville Formation in northernSpain and the Late Cambrian Idamean (Steptoean) of Tasmania (Sdzuy 1974; Rick-ards et al 1990) The graptolites are accompanied mostly by hexactinellid sponges,lingulates, and trilobites, such as solenopleuropsids in the Middle Cambrian and ag-nostids, olenids, and ceratopygids in the Late Cambrian

There was, however, also some colonization of the deep sea by trace fossils ure 13.2B), presumably representing mainly a soft-bodied fauna

(fig-In southeastern Ireland, the Lower to Middle Cambrian Cahore Group is a deep-sea

proximal turbidite sequence that has yielded Arenicolites, Helminthopsis, Helminthoida, Monocraterion, Oldhamia, Palaeophycus, Planolites, and Protopaleodictyon (Crimes and

Crossley 1968; Crimes et al 1992) In North Wales, proximal turbidites of the late

Early Cambrian Hell’s Mouth Grits on St Tudwal’s Peninsula contain Palaeophycus, Phycodes, and Planolites (Crimes 1970; Crimes et al 1992), whereas the Middle Cam- brian Cilan Grits have Bergaueria, Cruziana, Planolites and Protopaleodictyon (Crimes

et al 1992) Deep-water turbidites yielding Oldhamia, and of known or inferred Early

to Middle Cambrian age, occur in many localities, including Belgium, the UnitedStates, and various parts of Canada (see Dhonau and Holland 1974; Hofmann et al

1994 and references therein) In Quebec, Canada, Sweet and Narbonne (1993)

re-corded Oldhamia from a deep-water channel-fan environment that is directly overlain

by strata containing the Early Cambrian brachiopod Botsfordia pretiosa In the Yukon and Alaska, Oldhamia is accompanied by Bergaueria, Cochlichnus, Helminthoidichnites, Helminthorhaphe, Monomorphichnus, Planolites, and Protopaleodictyon in deep-sea sedi-

ments (Hofmann et al 1994) The most diverse collection of Lower to Middle brian deep-water trace fossils occurs in the Puncoviscana and Suncho formations innorthwest Argentina, where Aceñolaza and Durand (1973), Aceñolaza (1978), and

Cam-Aceñolaza and Toselli (1981) have described Cochlichnus, Dimorphichnus, Diplichnites, Glockerichnus, Gordia, Helminthopsis, Nereites, Oldhamia, Planolites, Protichnites, Proto-