CHAPTER TEN
Mikhail B. Burzin, Françoise Debrenne, and Andrey Yu. Zhuravlev
Evolution of Shallow-Water
Level-Bottom Communities
Features of Cambrian level-bottom communities that inhabited carbonate and silici-
clastic substrates are outlined. A high diversity of level-bottom communities with
multiple trophic guilds was established in the Early Cambrian, replacing largely
microbial-dominated Vendian ecosystems. Taxonomic richness of Early Cambrian
communities contrasts with relative impoverishment of their Middle and Late Cam-
brian counterparts. Displacement of communities was common, and entire commu-
nities might migrate into areas with more favorable conditions if their original habi-
tats suffered a crisis.
CAMBRIAN DEPOSITIONAL SYSTEMS can be divided into clastic and carbonate re-
gimes, because substrate type strongly influences community composition. These as-
pects of sedimentation were in general controlled by climate and the size of the area
available for denudation. With few exceptions, environments of carbonate sedimen-
tation were restricted to low latitudes and siliciclastic-dominated settings occurred
mostly in temperate conditions. The Siberian Platform throughout the Cambrian ex-
emplified carbonate-dominated habitats. Baltica, Bohemia, and Avalonia represented
regions where siliciclastic sedimentation prevailed. Laurentia and Australia were char-
acterized by a mosaic of facies.
TROPHIC GUILDS
Although the entire set of trophic guilds existed from the beginning of the period,
Cambrian guilds were different even from their Ordovician successors and probably
had already changed significantly by the end of the Cambrian. Tables 10.1 and 10.2
display the ecospace utilization by Cambrian organisms that are preserved now as
body fossils.
Benthic primary producers were represented chiefly by probable calcified cyano-
bacteria (e.g., Obruchevella) and by carbonaceous algae (e.g., Margaretia) and possible
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218 Mikhail B. Burzin, Franc¸oise Debrenne, and Andrey Yu. Zhuravlev

Table 10.1 Ecospace Utilization by Animals of Level-Bottom
Communities During the Early Cambrian
Epifaunal Infaunal
Trilobites, nontrilobite
arthropods, halkieriids,
low conical helcionelloids,
paragastropods,
orthothecimorphs,
“lobopodians,” polychaetes,
tommotiids
Laterally compressed
helcionelloids,
trilobites, priapulids,
fordillids, polychaetes,
palaeoscolecidans?
Mobile
Sessile
low
tier
(Ͻ10 cm)
Sessile
high
tier
(Ͼ10 cm)
Demosponges, calcareans,
chancelloriids, lingulates,
calciates, anabaritids,
coleolids, hyolithelminths,
tianzhushanellids,
edrioasteroids, pterobranchs,

hyolithomorphs,
orthothecimorphs,
stenothecoids
Plalysolenites,
lingulates
Hexactinellids, heteractinids,
cnidarians, eocrinoids,
helicoplacoids
Table 10.2 Ecospace Utilization by Animals of Level-Bottom
Communities During the Middle and Late Cambrian
Trilobites, nontrilobite
arthropods, tergomyans,
gastropods,

orthothecimorphs,
polychaetes, “lobopodians,”
cephalopods, homoisteleans,
stylophorans
Rostroconchs,
trilobites, priapulids?,
polychaetes?,
palaeoscolecidans?
Demosponges, calcareans,
lingulates, calciates,
edrioasteroids, pterobranchs,
hyolithomorphs,
gastropods
Lingulates
Hexactinellids?,
eocrinoids, crinoids,

graptolites,
branching hyolithelminths
Epifaunal
Infaunal
Mobile
Sessile
low
tier
(Ͻ10 cm)
Sessile
high
tier
(Ͼ10 cm)
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EVOLUTION OF SHALLOW-WATER LEVEL-BOTTOM COMMUNITIES
219
cyanobacteria (e.g., Morania). Noncalcified bacteria grew abundantly in the Cambrian
stromatolites and thrombolites and undoubtedly on most sediment surfaces, as they
do in modern marine environments. It has been suggested that bacteria are the main
producers of micritic carbonates (Riding 1991), which often possess a typical clotted
texture, and of phosphates (Gerasimenko et al. 1996), in the Cambrian. However,
planktic primary producers, including free-living and attached bacteria and phyto-
plankton (acritarchs and prasinophytes, at least), were the main food source for level-
bottom filter and suspension feeders. For instance, acritarchs are abundant in pelleted
carbonates (Zhegallo et al. 1994; Zhuravlev and Wood 1996). Acritarchs were prob-
able endocysts of polyphyletic origin; they possessed a sporopollenin-like wall, simi-
lar to that produced by photosynthetic eukaryotes (Martin 1993; see Moldowan et al.,
this volume, for biomarker data).
Feeding strategies are considered to be diverse among consumers (Debrenne and
Zhuravlev 1997) (figure 10.1).

1. Filtrators consisted of sponges (hexactinellids, heteractinids, demosponges,
and probable calcareans), calciate brachiopods, probably the majority of mollusks—
including helcionelloids, pelecypods, and rostroconchs—and piperock producers (in
this volume, see chapters by Debrenne and Reitner; Kouchinsky; and Ushatinskaya).
2. Suspension feeders were represented by lingulate brachiopods, echinoderms,
chancelloriids, hyolithomorph and some orthothecimorph hyoliths, stenothecoids,
and Late Cambrian trilobites (in thisvolume, see chapters byGuensburg and Sprinkle;
Hughes; Kouchinsky; and Ushatinskaya). Many of the tubicolous taxa (coleolides,
hyolithelminths, anabaritids), as well as brachiopod-like animals (Tianzhushanelli-
dae), were apparently semi-infaunal suspension feeders sensu lato (Bengtson and
Conway Morris 1992; Parkhaev 1998). By analogy with living polychaetes, some of
them could be pure filter feeders consuming bacterioplankton (Sorokin 1992), but
others, such as phosphatic hyolithelminths, with a metabolism probably similar to that
of lingulates, could be true suspension feeders. During the earliest Early Cambrian,
Platysolenites might have been an agglutinated foraminifer (McIlroy et al. 1994), which
belonged to suspension feeders, according to the test morphology (Lipps 1983). Since
the Middle Cambrian, dendroid graptolites joined the group of sessile filter and sus-
pension feeders (Sdzuy 1974) for a short time before planktic forms were developed,
probably in response to the general shift of phytoplankton grazing from the sea floor
to the water column. Flow pattern modeling of sessile conical dendroid graptolites
shows that such colonies were well designed to use ambient currents to reduce the
energetic cost of suspension feeding (Melchin and Doucet 1996). This modeling also
supports the suggestion by Rickards et al. (1990) that different dendroid rhabdosomal
morphologies may have been adapted to different currents. The aperture of even large
graptolite thecae with simple openings rarely exceeded 2 mm, severely restricting the
maximum size for food particles; most graptolites had even smaller apertures, and in
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220 Mikhail B. Burzin, Franc¸oise Debrenne, and Andrey Yu. Zhuravlev
many species these are reduced by lobes, lappets, or spines, even further restricting
the maximum size of particle uptake (Underwood 1993). Pterobranchs were already

present in the Early Cambrian.
3. Predator and scavenger guilds consisted of a variety of cnidarians, trilobites, and
nontrilobite arthropods, “lobopodians,” and giant anomalocaridids, which were large
and mostly mobile carnivores (Fortey and Owens 1999; Nedin 1999; in this volume,
see chapters by Debrenne and Reitner; Hughes; and Budd). Some polychaetes, pria-
pulids, and their close relatives palaeoscolecidans exploited this feeding strategy
Figure 10.1 Approximate average share of dif-
ferent trophic groups among Cambrian bodied
animals and their representatives. Suspension
and filter feeders: 1, crustacean Skara; 2, hel-
cionelloid mollusk Yochelcionella; 3, arthropod
Sarotrocercus; 4, graptolite Archaeolaphoea; 5,
radiocyath Girphanovella; 6, eocrinoid echino-
derm Lepidocystis; 7, hyolithomorph hyolith; 8,
chancelloriid Chancelloria; 9, lingulate brachio-
pod; 10, archaeocyath sponge Coscinocyathus.
Deposit feeders: 11, helcionelloid mollusk Hel-
cionella; 12, arthropod Naraoia. Carnivores and
scavengers: 13, arthropod Sidneyia; 14, trilobite
Olenoides; 15, conodont-chordate; 16, “lobo-
pod” Xenusion; 17, halkieriid Halkieria; 18,
priapulid Ottoia; 19, arthropod Sanctacaris;
20, anomalocaridid Laggania. Browsers: 21,
chitonlike mollusk Matthevia.
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EVOLUTION OF SHALLOW-WATER LEVEL-BOTTOM COMMUNITIES
221
(Conway Morris 1976, 1979; Hou and Bergström 1994). Protoconodonts may have
occupied a demersal predator niche by analogy with extant chaetognaths (Szaniawski
1982), as well as later euconodonts (Purnell 1995). Boreholes in shells and scars of

healed injuries in trilobite carapaces resulted from the action of unknown predators
and scavengers ( Jago 1974; Conway Morris and Bengtson 1994; Pratt 1994).
4. Destructors, which attacked hard mineral and cellular substances, were com-
mon. Cambrian endolithic borings are known in ooids, echinoderm ossicles, brachio-
pod shells, archaeocyath cups, various small shelly fossils, and conodonts (Müller and
Nogami 1972; Kobluk and Kahle 1978; Li 1997). In some cases, tentative interpreta-
tion in favor of cyanobacterial and fungal borings has been provided (Kobluk and
Risk 1977). Saprophytes have been recognized in the Cambrian communities, in-
cluding phycomycetes and actinomycetes (Burzin 1993b).
5. Trace fossil data (Crimes 1992) indicate that the Cambrian biota includes 50%
(Nemakit-Daldynian) to 40% (Atdabanian) deposit feeders (feeding traces). Crimes
(1992) also suggests that grazing traces account for 10% to 20% of the total trace
fossil diversity. But given that these are recorded on soft substrates, in contrast to the
feeding strategy of true grazers, they should instead be considered as deposit feed-
ers, the percentage of which had thus increased to 60%. Chondrites and many other
branching traces exemplify deposit-feeding strategies, some of which were very pecu-
liar and restricted to the Cambrian. For instance, a vermiform Plagiogmus-producer
burrowed within the substrate but fed on surface detritus by means of a siphon (McIl-
roy and Heys 1997). Microburrowings may represent detritivorous meiofauna (Wood
et al. 1993). Body fossils, however, do not allow us to infer the true producers of these
traces. Deposit feeders on silty substrates are recognized among low-spired, widely
expanded helcionelloid mollusks, most orthothecimorph hyoliths, some trilobites,
and nontrilobite arthropods;small paragastropods wereprobable mobile epifaunal de-
posit feeders (in this volume, see chapters by Kouchinsky and by Hughes and Budd).
6. Possible Cambrian algal croppers have been noted by Edhorn (1977) from the
Bonavista Group of Avalon. These “croppers” are sessile orthothecimorph hyoliths
(“Ladatheca” of Landing 1993). However, Kobluk (1985) reported some possible
grazer scratches on calcimicrobes from the Upper Shady Dolomite.
7. Among parasites, pentastomes are established in the Cambrian (Walossek et al.
1994). Some borings and skeletal abnormalities may also be interpreted as parasite

traces (Conway Morris and Bengtson 1994; in this volume, see chapters by Hughes
and by Budd).
CARBONATE-DOMINATED SETTINGS
Evaporite Basins
Evaporite basins, containing carbonates and evaporites, are typified by low clastic in-
put and high evaporation rates. Their coastlines are characterized by chains of islands
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222 Mikhail B. Burzin, Franc¸oise Debrenne, and Andrey Yu. Zhuravlev
that shelter hypersaline lagoons with reduced tidal ranges, where microbial mats are
formed. They produced extensive stromatolite deposits; the best examples occurred
in the Toyonian Angara Formations of the Siberian Platform where stratiform and co-
lumnar stromatolites formed low but very wide buildups, up to several kilometers in
length, peripherally covered by ooidal grainstones (Korolyuk 1968). This stromatolite
community did not change during the Cambrian. However, various mollusks (ros-
troconchs and chitonlike forms) intruded into barrier complexes formed under gen-
erally higher salinities in Australia during the Datsonian (Druce et al. 1982).
On the periphery of evaporite basins, an oligotypic trilobite community occurred
locally (e.g., Olekma Formation, Siberian Platform) from the Atdabanian through the
remainder of the Cambrian. Rare hyoliths and brachiopods also were present (Repina
1977).
Peritidal Carbonate Environments
Peritidal carbonate environments include oolite shoals, carbonate sand shoals and
beaches, and intertidal to subtidal flat settings. Since Atdabanian time, Ophiomorpha-
like trace producers (Aulophycus) occupied shifting lime muds in shoal agitated back-
reef conditions. Ophiomorpha-type burrows represented innovative behavior, in their
ability to produce pellet-lined burrows, which prevent collapse in substrates of rela-
tively low cohesive strength (Crimes and Droser 1992). The Aulophycus community
persisted through the entire Cambrian: Atdabanian Nokhoroy Unit and Kyndyn For-
mation, Botoman upper Kutorgina and Toyonian Keteme formations of the Siberian
Platform, and Botoman Poleta Formation and Shady Dolomite of Laurentia (Balsam

1974; Zhuravleva et al. 1982; Astashkin 1985; Droser and Bottjer 1988).
In restricted nutrient-rich lagoons, cyanobacterial communities, chiefly oscillato-
riaceans, formed phosphatized mats of helically coiled and prostrate filaments (Roza-
nov and Zhegallo 1989; Sergeev and Ogurtsova 1989; Soudry and Southgate 1989).
Such communities were common during the Nemakit-Daldynian–Tommotian (e.g.,
Chulaktau Formation, Kazakhstan; Khesen Formation, Mongolia) but became rare
later in the Cambrian.
Peritidal limestones were deposited in Avalonia under temperate conditions (Bra-
sier and Hewitt 1979; Landing et al. 1989; Landing 1991, 1993). Here peritidal lime-
stones have stromatolitic, mud-cracked caps and include helcionelloid mollusks (Igo-
rella, Oelandiella), phosphatic sclerite-armored animals (Eccentrotheca, Lapworthella),
phosphatic tube dwellers (Torellella), and orthothecimorph hyoliths (Turcutheca, La-
ratheca) that are absent in subtidal shales. In the early Tommotian (Chapel Island For-
mation upper Member 3 through Member 4), the Watsonella crosbyi fauna existed, in-
cluding “Ladatheca” thickets overgrown by stromatolites. Later in the Atdabanian
(e.g., Home Farme Member), these thickets were ecologically displaced by Coleoloides
typicalis thickets of vertically oriented tubes (Brasier and Hewitt 1979). Atdabanian-
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EVOLUTION OF SHALLOW-WATER LEVEL-BOTTOM COMMUNITIES
223
Botoman peritidal limestones of the Weymouth Formation contain an especially rich
fauna, including coleolids, hyolithelminths, “lobopodians,” chancelloriids, halkieri-
ids, tommotiids, hyoliths, helcionelloids, paragastropods, lingulate brachiopods, and
eodiscid and olenelloid trilobites. The faunal enrichment of the shallowest envi-
ronments in Avalonia probably reflects its high latitudinal position and thus a high
thermocline.
Shallow Carbonate Seas
Shallow carbonate seas include several carbonate environments, all of which lay at or
below fair-weather wave base. A high range of communities inhabited this zone, in-
cluding level-bottom, reefal, and hardground communities. The latter two are scruti-

nized elsewhere (Pratt et al. and Rozhnov, both in this volume).
In terms of taxonomic composition and dominant feeding strategies, Early and
early Middle Cambrian level-bottom communities were similar to coeval reefal set-
tings but differed by absence of heavily calcified organisms. In both cases, filter and
suspension feeders dominated in both number and diversity (Zhuravleva et al. 1982,
1986; Wood et al. 1993; Kruse et al. 1995) (figures 10.2.1 and 10.2.2).
The shallow level-bottom community underwent significant changes during the
Cambrian (see tables 10.1 and 10.2). After the demise of the Tommotian Evolutionary
Fauna by the end of the Early Cambrian, communities were dominated by trilobites
and lingulate brachiopods until the Middle Ordovician in Laurentia and Siberia (Sep-
koski and Sheehan 1983; Sukhov and Pegel’ 1986; Varlamov and Pak 1993), as well
as in Australia, China, and Kazakhstan. During the Steptoean–Early Ordovician, com-
munity reorganization proceeded through the addition of new elements, especially
gastropods, rostroconchs, and, from the Datsonian, cephalopods (Chen and Teichert
1983). In the Marjuman, trilobites account for two-thirds of the species present, as-
sociated with inarticulate brachiopods and hyoliths (Westrop et al. 1995). By the
Datsonian–Early Ordovician interval, paleocommunity compositions were split more
or less evenly between trilobites and mollusks. Finally, during the Middle Ordovician,
trilobites were reduced to about one-third of the species composing communities
(Westrop et al. 1995).
The Dysaerobic Community
The dysaerobic community represents an unusual kind of level-bottom community
that usually exists in deep waters but, in case of hypertrophy, can also appear in shal-
low-water conditions.
A typical Early Cambrian example was recognized by Zhuravlev and Wood (1996)
from the Botoman Sinsk Formation of the Siberian Platform (figure 10.2.3). The Sinsk
biota is represented by the calcified cyanobacterium Obruchevella and the abundant
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224 Mikhail B. Burzin, Franc¸oise Debrenne, and Andrey Yu. Zhuravlev
BENTHIC PREDATORS

palaeoscolecidans
polymeroid trilobites?
BENTHIC MACROFAUNA
DS F B
DS FB
D
S
FB
lingulate brachiopods
miomeroid trilobites
polymeroid trilobites
hexactinellids
calcareans
demosponges
gastropods?
BENTHIC
BACTERIA
sulfate-reducing
"NET"
PHYTOPLANKTON
acritarchs
NANNO-
PLANKTON
?
ATTACHED
BACTERIA
?
FREE-LIVING
BACTERIA
?

BENTHIC
CYANOBACTERIA
(
Yuwenia
)
(
Obruchevella
)
BENTHIC
ALGAE
(
Margaretia
)
BENTHIC
DETRITUS
WATER
COLUMN
DETRITUS
DISSOLVED
ORGANIC
MATTER
BENTHIC PREDATORS
BENTHIC MACROFAUNA
SESSILE :
MOBILE :
cnidarians nontrilobite arthropods
polychaetes
trilobites, "lobopodians"
? DEMERSAL
PREDATORS

anomalocaridids
ctenophores
cnidarians
lingulate brachiopods
polychaetes
hexactinellids
demosponges
mollusks
nontrilobite arthropods
trilobites trilobites
nontrilobite arthropods
echinoderms
hemichordate
hyolithomorph hyoliths
chancelloriids
priapulids
BENTHIC
MEIOFAUNA
?
BENTHIC
BACTERIA
"NET"
PHYTOPLANKTON
acritarchs
NANNO-
PLANKTON
?
ATTACHED
BACTERIA
?

FREE-LIVING
BACTERIA
?
BENTHIC
CYANOBACTERIA
(
Obruchevella
)
BENTHIC
ALGAE
?
BENTHIC PREDATORS
protoconodonts (?)
borers halkieriids/sachitids (?)
halkieriids/sachitids (?)
halkieriids/sachitids (?)
helcionelloids
orthothecimorph
hyoliths
tommotiids (?)
tommotiids (?)
burrowers
Aldanotreta
anabaritids
helcionelloids
rostroconchs
orthothecimorph &
hyolithomorph hyoliths
chancelloriids
coleolids

hyolithelminths
archaeocyaths
Cysticyathus
(?)
spiculate sponges
Aldanella
BENTHIC
DETRITUS
WATER
COLUMN
DETRITUS
DISSOLVED
ORGANIC
MATTER
?DEMERSAL
PREDATORS
BENTHIC MACROFAUNA
BENTHIC
MEIOFAUNA
BENTHIC
BACTERIA
"NET"
PHYTOPLANKTON
acritarchs
NANNO-
PLANKTON
?
ATTACHED
BACTERIA
?

FREE-LIVING
BACTERIA
?
BENTHIC
CYANOBACTERIA
(
Renalcis
)?
BENTHIC
DETRITUS
WATER
COLUMN
DETRITUS
DISSOLVED
ORGANIC
MATTER
3
2
1
priapulids
bivalve arthropods
cnidarians
?
?
?
?
?
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EVOLUTION OF SHALLOW-WATER LEVEL-BOTTOM COMMUNITIES
225

Figure 10.2 Trophic webs in the principal
Early Cambrian benthic communities. 1, Reefal
archaeocyath-coralomorph-hyolith commu-
nity; 2, level-bottom open marine priapulid-
nontrilobite arthropod-spicular sponge com-
munity; 3, level-bottom dysaerobic trilobite-
lingulate community (modified after Zhuravlev
and Debrenne 1996). B ϭ browsers and graz-
ers; D ϭ deposit feeders; F ϭ filter feeders;
S ϭ suspension feeders.
Figure 10.3 Distribution of major marine groups composing the Cambrian biota,
relative to water depth. Source: Modified after Debrenne and Zhuravlev 1997.
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226 Mikhail B. Burzin, Franc¸oise Debrenne, and Andrey Yu. Zhuravlev
green fleshy alga Margaretia as primary producers; by spicular sponges as filter feed-
ers; by hyoliths, lingulate brachiopods, and probable cnidarians as suspension feed-
ers, and rare paragastropods as grazers; and by palaeoscolecidans and, possibly, pro-
tolenin trilobites as carnivores. Abundant miomeroid trilobites could feed on minute
organic particles, including algae (Fortey and Owens 1999). The absence of burrows
reveals extreme reduction of deposit-feeders. Polymeroid trilobites with a wide, thin
exoskeleton, a smooth carapace, multiple thoracic segments, and enlarged pleurae
were nektobenthic trilobites adapted to low oxygen tension (Repina and Zharkova
1974; Fortey and Wilmot 1991). In turn, two other common groups, lingulates and
palaeoscolecidans (closely related to priapulids), could survive dysaerobic conditions
because their respiration was maintained by hemerythrin (Runnegar and Curry 1992).
Volumetrically, trilobites and lingulates dominated. The latter might have fed on the
abundant but monotypic acritarch flora. Despite harsh conditions, a multilevel tier-
ing was developed by hexactinellids and demosponges that ranged in height from 4
to 60 cm (Ivantsov et al. 2000). A similar community occurred on the Siberian Plat-
form during the late Early–early Middle Cambrian (Pel’man 1982). Later, agnostids

and olenids replaced eodiscids and protolenins, respectively.
SILICICLASTIC SETTINGS
Deltas
Deltas are major depositional centers that produce thick sedimentary successions.
High nutrient input, high turbidity, and decreased salinity are typical of deltaic areas.
In the prograde delta-front sequence of the Chapel Island Formation of the
Nemakit-Daldynian of Avalonia, the higher-energy environments show a preponder-
ance of vertical burrows (e.g., Arenicolites, Skolithos), simple horizontal burrows (Bu-
thotrephis, Planolites), and few more-complex feeding burrow systems (e.g., Phycodes)
(Crimes and Anderson 1985; Myrow and Hiscott 1993). Trace fossils from the Middle
Cambrian deltaic Oville Sandstones of northern Spain were subdivided into several
associations according to their restriction to tidal channel (Rusophycus, Diplocraterion,
Arenicolites), sand flat (Diplocraterion, Arenicolites), mixed flat (Arenicolites, Planolites,
Rusophycus, Skolithos, Cruziana, Diplocraterion), bar/beach (Skolithos), tidal delta slope
(Planolites, Rusophycus, Phycodes), lower delta slope (Teichichnus, Planolites), or shelf/
pro-delta (Planolites, Teichichnus) facies (Legg 1985). These examples show a diversity
of feeding strategies in the deltaic communities, closely correlated with the energy
conditions and mud content rather than with water depth.
Due to water column stratification, a dysaerobic bottom layer commonly devel-
oped in estuaries. This peculiar environment was deployed by organisms as early as
the middle Vendian (Redkinan). In the estuaries of Baltica, the bushy alga Eoholynia
formed floating mats (Burzin 1996). Their remains accumulated on the pycnocline,
where they were further destroyed by sulfate-reducing bacteria before final deposi-
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EVOLUTION OF SHALLOW-WATER LEVEL-BOTTOM COMMUNITIES
227
tion on the bottom (Burzin 1996). Sabelliditid-like tube-dwelling Saarinidae were the
first animals adapted to such conditions in Baltica (Gnilovskaya 1996). During the
Nemakit-Daldynian and Tommotian, true sabelliditids occupied similar conditions in
this region. Their tubes contain pyrite framboids (Burzin 1993a), which may indicate

sabelliditid symbiotic interactions with sulfate-reducing bacteria.
The early Botoman Chengjiang fauna of China has been regarded as an outer shelf
to slope-basin assemblage (Hou and Sun 1988; Hou et al. 1991). However, close sed-
imentological examination has revealed that this impoverished community inhabited
estuarine conditions (Lindström 1995). Nonetheless, this community contains di-
verse fleshy algae, spicular sponges, arthropods, and “lobopodians,” as well as some
palaeoscolecidans, anomalocaridids, cnidarians, chordates, and brachiopods (Chen
and Zhou 1997). Several tiers are observed in this community, at least among sponges
(Debrenne and Reitner, this volume). A similar community of trilobites, bivalved ar-
thropods, palaeoscolecidans, anomalocaridids, and brachiopods is recognized in the
youngest late Botoman of Australia (Big Gully fauna, Emu Bay Shale) but is inter-
preted as a lagoonal community (Nedin 1995).
Clastic Shoreline Systems
Clastic shoreline systems encompass a variety of environments—such as tidal flats,
low intertidal, beach, shoreface, and barrier islands and very shallow, low-gradient
subtidal and sand-shoal environments—that lie within fair-weather and average sea-
sonal storm wave base or are continuously reworked by tidal and oceanic currents.
J-, U- or Y-shaped burrows were especially abundant and might have been pro-
duced by filter or suspension feeders that were deploying milieu energy (Vogel and
Bretz 1972). Dense assemblages of Skolithos, a simple vertical tube, characterized
shifting sandy substrates and high-energy conditions during the Cambrian (Hallam
and Swett 1966; Droser 1991; Gozalo 1995). Diplocraterion probably dominated in
warm semiarid climates (Middle Cambrian Riley Formation, Laurentia), where it re-
placed Skolithos under similar conditions (Cornish 1986). High-energy tidal channel
sands and associated intertidal sand and mud flats contained only Arenicolites, Astro-
polichnus, Bergaueria, Diplocraterion, Skolithos, and rare Cruziana, Rusophycus, and
Planolites (Crimes et al. 1977). In subtidal to intertidal areas of the Random Forma-
tion, with migrating sand bars and intervening channels, a variety of “deep”-water
types such as Helminthoida crassa, Nereites, Paleodictyon, Protopaleodictyon, and Squa-
modictyon are present in addition to numerous shallow-water traces (Crimes and

Anderson 1985). This anomalous distribution of Nereites ichnofacies may reflect not
only inadequate supplies of food in the deep sea but also the patchy quality of food
in shallow waters (Brasier 1995; Brasier and Lindsay, this volume). On the whole,
these facies were dominated by soft-bodied suspension and filter feeders, with arthro-
pods (e.g., Rusophycus dwellers; Jensen 1990) preying on them.
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228 Mikhail B. Burzin, Franc¸oise Debrenne, and Andrey Yu. Zhuravlev
Shallow Siliciclastic Seas
Shallow siliciclastic seas are below fair-weather wave base but above rare storm wave
base (~10 –200 m). Major influencing factors are rate and type of sediment supply,
type and intensity of the shelf hydraulic regime, sea level fluctuation, climatic and
chemical factors, and organism-sediment interactions.
During the Kotlin interval, a wide, brackish restricted lake-like basin was formed
in Baltica (Pirrus 1986; Burzin 1993a, 1996). Cyanobacterial, mostly oscillatoriacean,
mats covered temporally dry parts of the basin. In more-stable areas, ribbonlike ven-
dotaeniacean algae thrived and oscillatoriacean mats were restricted (Burzin 1993a,
1996). In the absence of animal competition, prokaryotic actinomycetes (Primo-
flagella) and chytrid fungi (Vendomyces) were principal consumers of the rich de-
tritus (Burzin 1993b). Fungi and the Vendotaeniaceae still existed in the Nemakit-
Daldynian, but the latter were replaced soon by Tyrasotaenia.
Since the Early Cambrian, shallow subtidal siliciclastic substrates that are uncon-
solidated and poorly sorted have been the principal habitats of different trace fossil
dwellers. Lower-energy, thinner-bedded sand and mud flats contain abundant ichno-
fauna, including Cruziana, Rusophycus, Monocraterion, Diplichnites, Planolites, and oc-
casional Plagiogmus, Arenicolites, Diplocraterion, Phycodes, Teichichnus, and Skolithos
(Tommotian-Atdabanian Candana Quartzite and Herrerı´a Sandstone, Spain and up-
per Chapel Island Formation, Avalonia) (Crimes et al. 1977; Crimes and Anderson
1985). With reduction in sediment grain size, a sharp drop in the number of sessile
filter feeders (Skolithos-, Diplocraterion-, and Monocraterion-dwellers) is observed; in
contrast, the number of deposit feeders increases (Paczes´na 1996). Cruziana facies

might bear filamentous algae, polymeroid and miomeroid trilobites, and diverse bra-
chiopods (e.g., Middle Cambrian Murero Formation, Spain) (Liñan 1995). By the Late
Cambrian, it was predominantly a Cruziana-Rusophycus community with additional
lingulates (McKerrow 1978). Characteristic organisms therefore included suspension
and deposit feeders, mobile carnivores, and scavengers.
During the Nemakit-Daldynian and Tommotian on Baltica and Laurentia, the Platy-
solenites community characterized muddy substrates (Rozanov 1983; Mount and
Signor 1985). Later, during the Marjuman-Tremadoc, a shallow epicontinental sea
continued to occupy Baltica (Sablinka, Ülgase, Ladoga, and Tosna formations). The
dynamic conditions of this sea (shifting sands, turbidity) extremely limited benthic
diversity. Only epibenthic obolids (lingulate brachiopods) and Skolithos-dwelling ani-
mals were adapted to such conditions (Popov et al. 1989). Branching hyolithelminths
(Torellella) and acrotretid and/or siphonotretid lingulates formed their own commu-
nity in deeper and less turbid parts of the basin on silty-muddy substrates, which were
unfavorable for obolids. Torellella occupied a higher tier, and lingulates exploited the
lower one. Modern analogies in the formation of economic phosphatic shell concen-
trations (Hiller 1993) and the Baltica paleoposition both reveal an influence of up-
welling, bringing phosphate-rich cold waters onto a shallow shelf.
10-C1099 8/10/00 2:10 PM Page 228
EVOLUTION OF SHALLOW-WATER LEVEL-BOTTOM COMMUNITIES
229
Amgan to Marjuman communities of shallow subtidal, rough-water, sandy envi-
ronments of Bohemia ( Jince Formation) consisted mostly of lingulates and polymer-
oid trilobites with few stylophoran echinoderms (Ceratocystis). In calmer, muddier,
and deeper conditions, the diversity of trilobites increased, and agnostids, bradoriids,
calciates, hyoliths, mollusks, and edrioasteroid, eocrinoid, and ctenocystoid echino-
derms were associated with them (Mergl and Slehoferová 1990).
Open Shelves
Open shelves, facing the open ocean, offered shelter to level-bottom communities that
lived in low-energy conditions. The Middle Cambrian Stephen and Wheeler Forma-

tion faunas (Laurentia) as well as Kaili Formation (South China) provide a unique
insight into the structure of a level-bottom community, because of exceptional soft-
part preservation (Conway Morris 1986; Robison 1991; Zhang et al. 1995) (see fig-
ure 10.2.2). A high ecologic complexity is recognized in the Phyllopod Bed (Stephen
Formation) community, with a finer niche partitioning: low levels were occupied
mostly by brachiopods, rare edrioasteroids, and sponges, together with rarer pel-
matozoan echinoderms, which dominated at higher levels. More contrasting is the
role of fleshy algae and cyanobacteria as primary producers and deposit-feeding
arthropods as consumers. Diverse predators are confirmed by the abundance of ef-
fectively soft-bodied carnivores, together with some carnivores with hard parts.
CONCLUSIONS
On the whole, Vendian (pre–Nemakit-Daldynian) benthic communities were domi-
nated by microbial ecosystems. Only in temperate conditions, usually coupled with
active hydrodynamics, were more-complex communities developed. Although the
Ediacara fauna is known from shallow-water onshore and offshore sandstones, deep-
water turbidites, and shallow-water carbonates (Fedonkin 1987), it may be attributed
to a single community of sessile filter and/or suspension feeders and to a few deposit
feeders independently of the systematic interpretation of its members (Lipps et al.
1992).
Cambrian communities evolved by further partitioning ecologic niches and by
replacing older forms by new ones within established trophic guilds. This is espe-
cially noticeable in ecospace utilization, as recognized by developed tiers and diverse
feeding strategies (tables 10.1 and 10.2; see also figures 10.1 and 10.2). In this re-
spect, the Cambrian biota was very different from the Neoproterozoic one, but also
from younger Paleozoic and Meso-Cenozoic biotas (Bambach 1977; Ausich and Bot-
tjer 1982; Bottjer and Ausich 1986). The relatively diverse Early Cambrian benthos
was replaced during the Middle Cambrian by a simpler, trilobite-dominated Cam-
brian sensu stricto Evolutionary Fauna. Taxonomic impoverishment of Cambrian
10-C1099 8/10/00 2:10 PM Page 229
230 Mikhail B. Burzin, Franc¸oise Debrenne, and Andrey Yu. Zhuravlev

Figure 10.4 Distribution of major marine groups composing the Cambrian biota,
relative to salinity. Source: Modified after Debrenne and Zhuravlev 1997.
communities is observed in siliciclastic as well as in carbonate level-bottom commu-
nities. A similar trend is obvious in reefal communities (Zhuravlev 1996). In terms of
taxonomic composition, proximal communities were the most conservative; distal,
deep-water communities grew permanently by addition of new elements (Conway
Morris 1989); and intermediate shallow shelf subtidal communities were the most
changeable.
10-C1099 8/10/00 2:10 PM Page 230
EVOLUTION OF SHALLOW-WATER LEVEL-BOTTOM COMMUNITIES
231
Displacement of communities was common. The earliest deep-water communities
were derived from former shallow-water water elements (Bottjer et al. 1988; Crimes,
this volume). On the other hand, a trilobite-lingulate community, which during the
Middle Cambrian occupied normal marine conditions, at first appeared in dysaero-
bic Early Cambrian basins (see figure 10.2.3).
Although Cambrian organisms occupied various depositional regimes, they were
largely restricted to normal marine and to shallow subtidal conditions (figures 10.3
and 10.4). Possibly, the further spreading into these environments was one of the
sources of higher Ordovician and Mesozoic-Cenozoic radiations.
Acknowledgments. We thank Mary Droser and Peter Crimes for helpful comments and
Françoise Pilard and Henri Lavina for the preparation of figures. This paper is a con-
tribution to IGCP Project 366.
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