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Paleoecology of the oldest known animal communities: Ediacaran assemblages at Mistaken Point, Newfoundland

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Ediacaran fossils at Mistaken Point, southeastern Newfoundland (terminal Neoproter-ozoic; 565–575 Ma) represent the oldest known animal communities. In contrast to most Phaner-ozoic fossil assemblages, in which postmortem transportation, bioturbation, and the accumulation of hardparts obscure community relationships, all fossils in the Mistaken Point assemblages were sessile, soft-bodied organisms that show no evidence of mobility in life or transportation after death. Mistaken Point assemblages are spectacularly preserved on large bedding planes as in situ census populations of hundreds to thousands of fossils, recording the living soft-bodied benthic community at the moment it was smothered by volcanic ash. This unique preservation style allows ecological tests routinely conducted in modern communities (e.g., species richness, abundance, ''biomass,'' diversity, and evenness, as well as statistical tests of nearest-neighbor interactions) to be applied to the fossil communities. Observed patterns of community variability are consistent with the theory that Mistaken Point fossil surfaces are ''snapshots'' recording different stages of ecological succession, progressing from communities of low-level feeders (e.g., pectinates and spin-dles) to frond-dominated communities with complex tiering and spatial structure. The presence of diverse slope communities at Mistaken Point suggests that the deep sea was colonized rapidly dur-ing the evolution of complex organisms. Species richness, abundance, and diversity values, as well as levels of intraspecific interaction, all fall within the typical range observed in modern slope com-munities. These structural similarities imply that ecological processes present in Ediacaran com-munities at Mistaken Point were strikingly similar to the processes that operate in modern deep-sea animal communities.
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2003 The Paleontological Society. All rights reserved. 0094-8373/00/2904-0007/$1.00
Paleobiology, 29(4), 2003, pp. 527–544
Paleoecology of the oldest known animal communities:
Ediacaran assemblages at Mistaken Point, Newfoundland
Matthew E. Clapham, Guy M. Narbonne, and James G. Gehling
Abstract.—Ediacaran fossils at Mistaken Point, southeastern Newfoundland (terminal Neoproter-
ozoic; 565–575 Ma) represent the oldest known animal communities. In contrast to most Phaner-
ozoic fossil assemblages, in which postmortem transportation, bioturbation, and the accumulation
of hardparts obscure community relationships, all fossils in the Mistaken Point assemblages were
sessile, soft-bodied organisms that show no evidence of mobility in life or transportation after
death. Mistaken Point assemblages are spectacularly preserved on large bedding planes as in situ
census populations of hundreds to thousands of fossils, recording the living soft-bodied benthic
community at the moment it was smothered by volcanic ash. This unique preservation style allows
ecological tests routinely conducted in modern communities (e.g., species richness, abundance,
‘‘biomass,’’ diversity, and evenness, as well as statistical tests of nearest-neighbor interactions) to
be applied to the fossil communities. Observed patterns of community variability are consistent
with the theory that Mistaken Point fossil surfaces are ‘‘snapshots’’ recording different stages of
ecological succession, progressing from communities of low-level feeders (e.g., pectinates and spin-
dles) to frond-dominated communities with complex tiering and spatial structure. The presence of
diverse slope communities at Mistaken Point suggests that the deep sea was colonizedrapidlydur-
ing the evolution of complex organisms. Species richness, abundance, and diversity values, as well
as levels of intraspecific interaction, all fall within the typical range observed in modern slope com-
munities. These structural similarities imply that ecological processes present in Ediacaran com-
munities at Mistaken Point were strikingly similar to the processes that operate in modern deep-
sea animal communities.
Matthew E. Clapham,* Guy M. Narbonne, and James G. Gehling.
Department of Geological Sciences and
Geological Engineering, Queen’s University, Kingston, Ontario K7L 3N6, Canada.
E-mail: narbonne@geol.queensu.ca
*Present address: Department of Earth Sciences, University of Southern California, Los Angeles 90089-0740.
E-mail: clapham@usc.edu
Present address: South Australian Museum, Division of Natural Science, North Terrace, Adelaide, South
Australia 5000, Australia
Accepted: 11 March 2003
Introduction
The Ediacara biota is a distinctive fossil as-
semblage of sessile, soft-bodied organisms
known from late Neoproterozoic rocks (ca.
575–543 Ma) worldwide (Glaessner 1984; Fe-
donkin 1992; Jenkins 1992; Narbonne 1998;
Martin et al. 2000; Narbonne and Gehling
2003). Ediacaran fossils document a critical in-
terval in Earth history, the transition between
the predominantly microbial ecosystems of the
Precambrian and the animal ecosystems of the
Phanerozoic. Despite their pivotal position in
the evolution of life, relatively little is known
about the ecology of the Ediacara biota. Eco-
logical interactions between individuals and
between species are thought to be limited in
Ediacaran communities, although there are
very few empirical data to support or contra-
dict this hypothesis. Macropredation appears
absent (Glaessner 1984; McMenamin 1986; Sei-
lacher 1992) and other interactions, such as epi-
biosis, interspecific competition, or mutualism,
also were apparently reduced or not present
(Waggoner 1998). Different authors have sug-
gested that the Ediacara organisms were het-
erotrophic suspension feeders (Jenkins and
Gehling 1978; Gehling and Rigby 1996; Cla-
pham and Narbonne 2002), chemosynthetic/
chemosymbiotic (Seilacher 1992), or photosyn-
thetic/photosymbiotic (McMenamin 1986), al-
though the occurrence of Ediacaran fossils in
subphotic deep-water settings implies that
those taxa could not be photoautotrophic (Sei-
lacher 1992; Dalrymple and Narbonne 1996;
MacNaughton et al. 2000). Study of the Edi-
acara biota is critical to the understanding of
the early evolution of animals and the devel-
opment of modern-style ecosystems, yet, ex-
528 MATTHEW E. CLAPHAM ET AL.
F
IGURE
1. A, Location map showing location of study
area in the Avalon Zone (dark gray) of southeastern
Newfoundland. B, Map of the Mistaken Point area.
Studied fossil surfaces are indicated by stars. C, Strati-
graphic section of upper Conception Group and lower
St. John’s Group. Approximate position of surfaces are
marked and dated ash beds are indicated by arrows.
cept for a few local studies, almost nothing is
known about the community ecology of these
oldest complex ecosystems.
The Mistaken Point area of southeastern
Newfoundland (Fig. 1) is a nearly ideal place
to study the ecology of the earliest animal
communities. The Neoproterozoic succession
is thick, richly fossiliferous, and exposed in
long, continuous coastal sections. The sections
are punctuated by volcanic ash beds, which
weather to expose dkm-scale bedding plane
surfaces on the tops of mudstone beds. Many
of these surfaces contain assemblages of hun-
dreds to thousands of well-preserved Edi-
acaran fossils, recording a snapshot of the liv-
ing benthic community at the moment of buri-
al. This lack of taphonomic bias allows out-
standing questions of Ediacaran community
ecology to be resolved by using techniques
routinely applied to modern ecosystems, in-
cluding parameters of species richness, organ-
ism abundance and biomass, and diversity
and evenness coefficients (e.g., Mayer and Pie-
penburg 1996; Gutt et al. 1999). In addition,
Ediacaran ecological processes and organism
interactions can be accurately assessed with
statistical tests describing the spatial pattern
of nearest-neighbor distribution (Thrush 1991;
Anderson 1992; Campbell 1992; Bellingham
1998; Coomes et al. 1999; Haase 2001). Appli-
cation of these techniques from modern ecol-
ogy to the best surfaces through nearly 2.5 km
of stratigraphy permits characterization of
Ediacaran communities and community pro-
cesses at Mistaken Point, and evaluation of
ecosystem development, through comparison
with modern deep-water communities, dur-
ing the earliest stages of animal evolution.
Mistaken Point Fossils
Soft-bodied Ediacaran fossils were first de-
scribed from the Mistaken Point area of the
southeastern Avalon Peninsula, Newfound-
land (Fig. 1), more than 30 years ago (Ander-
son and Misra 1968; Misra 1969). Subsequent
work has documented an abundant and di-
verse biota occurring on more than 100 bed-
ding planes through nearly 2.5 km of strati-
graphic thickness (Anderson and Conway
Morris 1982; Narbonne et al. 2001). The abun-
dance of features typical of deep-water turbi-
529EDIACARAN COMMUNITY ECOLOGY
F
IGURE
2. Census composition and areal coverage val-
ues for Mistaken Point fossil surfaces. Only fossils con-
stituting
.
1% of the census or areal coverage are shown.
dites, coupled with the complete absence of
features implying wave influence or emer-
gence, has led previous workers to conclude
that the Mistaken Point assemblage lived on a
deep-water slope below both wave base and
the photic zone (Misra 1971, 1981; Myrow
1995; Narbonne et al. 2001; Wood et al. in
press). Radiometric dating of a volcanic ash
horizon covering the best-known fossil sur-
face at Mistaken Point yielded a date of 565
6
3 Ma (Benus 1988) and frondose fossils from
the Drook Formation 1500 m lower in the sec-
tion are probably 10 Myr older (Narbonne and
Gehling 2003), suggesting that the Mistaken
Point biota is the oldest record of complex,
megascopic organisms yet discovered and
predates well-known Ediacaran assemblages
from Australia, Russia, and Namibia (Nar-
bonne 1998).
The Mistaken Point biota is reported to con-
tain as many as 30 taxa (Anderson and Con-
way Morris 1982), but in practice only a dozen
forms are common (Narbonne et al. 2001). Our
detailed study of the seven most diverse fossil
surfaces has recorded eighteen taxa (the 14
most abundant are depicted in Fig. 2). With
the exception of the discoidal fossil Aspidella
(Billings 1872; Gehling et al. 2000) and the
frondose Charnia wardi (Narbonne and Gehl-
ing 2003), taxa of the Mistaken Point biota
have only been described in general terms,
and many have not yet been formally named.
Detailed taxonomic studies are in progress,
but in the interim this paper follows other
studies in utilizing a mixture of formal names
of taxa that have been named elsewhere (e.g.,
Charnia,Charniodiscus,Bradgatia) along with
informal but widely and consistently applied
names for endemic taxa (e.g., ‘‘spindles,’’
‘‘pectinates,’’ ‘‘dusters’’) (see also Waggoner
1999; Narbonne et al. 2001).
Mistaken Point Surfaces
Coastal sections in the Mistaken Point area
are punctuated by literally hundreds of large
bedding plane exposures (1–200 m
2
in size)
formed by the preferential erosion of weaker
volcanic ash horizons. These large surfaces
commonly preserve Ediacaran fossils, record-
ing a snapshot of the living benthic commu-
nity at the instant it was smothered by the ash-
fall. Seven diverse and well-preservedMistak-
en Point assemblages, spanning four succes-
sive formations and a stratigraphic distance of
nearly 2.5 km, were selected for detailed study
(Table 1, Fig. 1). Each contains more than 100
fossils and thus provides a census for statis-
530 MATTHEW E. CLAPHAM ET AL.
T
ABLE
1. Summary description of stratigraphic position (below the top of the Trepassey Formation), area studied,
smallest feature preserved, number of fossils, and dominant taxa for the studied fossil surfaces. The smallest feature
preserved is a taphonomic variable quantifying the finest detail visible on each surface.
Surface
Stratigraphic
position
Area
studied
Smallest
feature
preserved
No. of
fossils Dominant taxa
SH
G
E
D
LMP
BC
PC
2
10 m
2
350 m
2
365 m
2
368 m
2
600 m
2
950 m
2
2200 m
47.0 m
2
7.05 m
2
104.75 m
2
63.4 m
2
14.0 m
2
0.71 m
2
16.7 m
2
3.0 mm
1.2 mm
0.5 mm
1.8 mm
2.0 mm
0.3 mm
2.0 mm
370
162
4188
1488
304
106
239
Pectinate
Bradgatia, Charniodiscus
Spindle, Charniodiscus
Spindle
Charnia A
Spindle, Charnia B
Triangle, Ivesia
tical testing and accurate characterization of
community attributes.
The studied surfaces were subdivided with
a meter-square grid to facilitate data collec-
tion. Every fossil was identified and its posi-
tion recorded within the grid system; each of
these records also contains measurements of
fossil dimensions and orientation(s). In addi-
tion, taphonomic information (e.g., bending,
folding, incompleteness, partial preservation
due to fracturing or ash cover) was recorded
where applicable. Superpositional relation-
ships were also noted, indicating which fossil
was preserved underneath in an overlapping
pair.
The resulting database contains detailed re-
cords for hundreds to thousands of fossils on
each surface. However, the Mistaken Point
area has been subjected to pervasive tectonic
deformation and every bedding plane has un-
dergone significant shortening, altering ab-
solute fossil positions as well as both dimen-
sion and orientation values (Seilacher 1999).
Deformed positions, dimensions, and orien-
tations were restored to their original values
by mathematically removing the apparent
bed-parallel shortening in a process called re-
trodeformation (see Wood et al. in press for a
mathematical description of the methodolo-
gy). All ecological tests were conducted on the
retrodeformed database.
How Good Are the Data?
All Mistaken Point taxa represent soft-bod-
ied, sessile organisms. There is little evidence
of postmortem transport and no evidence of
any infauna (Narbonne et al. 2001), so com-
plicating taphonomic effects, such as spatial
mixing of separate populations and time-av-
eraging of living with recently dead material,
which are common in Phanerozoic shelly fos-
sil assemblages (Miller 1986; Fu¨ rsich and
Aberhan 1990; Kidwell 1993; Powell et al.
2002), would not have affected the communi-
ties at Mistaken Point. Preservation of the Mis-
taken Point fossil assemblages as census pop-
ulations of in situ, entirely soft-bodied,epifau-
nal organisms, with no evidence of spatial or
temporal taphonomic mixing, provides a
nearly ideal situation to recreate benthic com-
munity paleoecology. Nektonic and plankton-
ic animals would have had a low preservation
potential so their abundance (or even pres-
ence) in the Mistaken Point biota is uncertain;
however, pelagic organisms are typically not
included in studies of modern slope benthos
either (e.g., Grassle et al. 1975; Smith and
Hamilton 1983; Mayer and Piepenburg 1996;
Gutt et al. 1999).
Observed differences between communities
are indicative of significant biotic patterns
only if the variation within a single commu-
nity is less than that between fossil surfaces.
Our qualitative observations of surfaces that
crop out in several localities along the sea
coast suggested that, although even strati-
graphically closely spaced surfaces can differ
dramatically in fossil content, lateral variabil-
ity in the fossil composition of any surface is
minimal (Narbonne et al. 2001). The amount
and effects of within-surface variation can be
quantified by comparing the classic E ‘‘Yale
surface’’ at Mistaken Point (used for the de-
tailed paleocommunity studies presented be-
low) with a small sample of the E ‘‘Queens
surface,’’ also at Mistaken Point but separated
531EDIACARAN COMMUNITY ECOLOGY
T
ABLE
2. Summary attributes of Mistaken Point fossil
communities.
Surface
Species
richness
Fossil
density
(ind/m
2
)
Areal
cover-
age
Shannon
diversity
Shannon
evenness
SH
G
E
D
LMP
BC
PC
6
6
12
8
11
4
3
7.9
23.0
39.7
23.5
21.7
149.3
14.3
3.4%
6.2%
12.4%
11.2%
7.2%
6.3%
10.7%
0.46
1.54
1.52
0.70
1.31
0.67
0.87
0.26
0.86
0.61
0.33
0.55
0.48
0.80
from the Yale surface by a 10-m-wide expo-
sure gap, and with the same stratigraphic sur-
face more than 1 km away at Watern Cove. The
samples encompassed a range of preservation
quality, from uniformly good preservation at
E (Queen’s) to poorer preservation under thick
ash cover at E (Watern Cove). E (Yale) included
both high-quality areas and fractured and
abraded areas. The effects of preservation
quality, which may influence community pa-
rameters such as species richness, organism
density, and diversity values to varying de-
grees, will be superimposed upon original
compositional differences within the com-
munity. Most community parameters were es-
sentially unchanged between differing taph-
onomic regimes: species richness (10–12 spe-
cies), diversity (H
95
1.52–1.68), and evenness
(E
5
0.61–0.70) are fairly consistent between
the three expressions of the E surface. Organ-
ism density values showed significant differ-
ences that can be directly correlated with
quality of preservation, from 31.9 ind/m
2
at E
(Watern Cove) to 39.7 ind/m
2
on E (Yale) and
56.5 ind/m
2
on E (Queen’s). Lower density on
poorly preserved surfaces reflects thick ash
cover or abrasion, both of which obscure small
specimens. However, areal coverage (a proxy
for biomass) was not greatly affected by ta-
phonomy (observed values ca. 10–15%) be-
cause preservation quality affects the abun-
dance of small fossils only, which are typically
a minor component of community biomass.
These results suggest that organism density is
strongly correlated with preservation quality
in the Mistaken Point assemblages but that
other community parameters are not signifi-
cantly affected by taphonomy and should cor-
respond to meaningful environmental or eco-
logical variables.
Mistaken Point Community Attributes
Mistaken Point communities represent cen-
sus populations of sessile, surface-dwelling
organisms and thus are ideally suited for ap-
plication of ecological techniques derived
from studies of modern communities. Meth-
ods used in this study include simple mea-
sures of community structure, such as species
richness, fossil density, and fossil areal cov-
erage (used as a proxy for biomass), as well as
more complex community descriptors such as
Shannon diversity and evenness coefficients.
Sophisticated statistical tests of nearest-neigh-
bor relationships, for both single populations
and the whole community, were used to quan-
tify organism interactions. Descriptions of
each of these tests, including a detailed expla-
nation of the methodology of each (where ap-
plicable), are presented sequentially in the fol-
lowing sections.
Species Richness
Species richness ranges from 3 to 12 taxa
per locality (Table 2). Because the area sur-
veyed for each surface varied between 0.7 and
105 m
2
, and because these variations in sam-
pled area size may strongly influence the ob-
served species richness, we constructed spe-
cies-area curves (Grassle and Maciolek 1992)
by recording the species richness of several (3–
8) randomly placed subsamples (1–25 m
2
in
size) to investigate the minimum area re-
quired to accurately estimate the total species
richness of each community (Fig. 3). Species-
area curves suggest that the measured species
richness for the BC and LMP communities is
not an accurate estimate of true species rich-
ness but that all other surfaces wereadequate-
ly sampled.
Fossil Density
Organism density results are difficult to
link to ecological or environmental processes
because of the potential taphonomic bias
against small individuals. Measured organ-
ism density in Mistaken Point communities is
typically 21–23 ind/m
2
on the LMP, D, and G
surfaces, with most other values slightly high-
532 MATTHEW E. CLAPHAM ET AL.
F
IGURE
3. Species-area relations for Mistaken Point communities. Species-area curves for each surface were gen-
erated by measuring the species richness of randomly placed subsamples.
er (39.7 ind/m
2
on the E surface) or lower (7.9
and 14.3 ind/m
2
at SH and PC, respectively).
BC is the only surface displaying significantly
anomalous density values (149.3 ind/m
2
), re-
sulting from the abundance of small fossils.
‘‘Biomass’’
Biomass, as measured in modern ecosys-
tems, cannot be directly calculated from Mis-
taken Point communities because of uncer-
tainties as to the three-dimensional shapes
and material properties of the Ediacaran or-
ganisms. Instead, two-dimensional area oc-
cupied by the fossils was adopted as a proxy
for biomass, allowing approximate compari-
son of total community areal coverage be-
tween Mistaken Point surfaces. Although this
is not ideal, it is a far more realistic estimate
of biomass than census counts of individuals
(irrespective of size) could provide. Fossil ar-
eal coverage, expressed as a percentage of to-
tal surface area, ranges from 3.4% (SH) to
12.4% (E). Three communities (G, BC, LMP)
have relatively low areal coverage, at 6.2%,
6.3%, and 7.2% respectively, whereas the re-
maining three communities (PC, D, E) have
higher areal coverage (10.7%, 11.2%, and
12.4% respectively).
Diversity and Evenness
Lowest diversity is observed on the SH sur-
face, which has a Shannon diversity value of
0.46. The most diverse communities are E and
G, with Shannon coefficients of 1.52 and 1.54,
respectively. Intermediate diversity values are
0.67 (BC), 0.70 (D), 0.87 (PC), and 1.31 (LMP).
Shannon evenness values from Mistaken Point
communities span nearly the entire possible
range of equitability, from 0.26 (SH) to 0.86
(Gautam et al. 2000:). The seven communities
are distributed over the entire equitability
range, rather than clustering in discrete
groups. Other Shannon evenness values are
0.33 (D), 0.48 (BC), 0.55 (LMP), 0.61 (E), and
0.80 (PC).
Single-Species Spatial Pattern
Methodology. Many nearest-neighbor tech-
niques for the analysis of spatial pattern exist,
although most are derived for sample areas
with simple polygonal boundaries (Clark and
Evans 1954; Campbell 1992, 1996). Because all
six communities (soft-sediment deformation
at SH did not permit the original positions of
the organisms to be measured accurately) ex-
amined at Mistaken Point had irregular
boundaries imposed by the edge of preserved
outcrop, more-sophisticated statistical tests of
spatial pattern are required. Monte Carlo sim-
ulation methods are able to compensate for ir-
regular outcrop areas by comparing the ob-
served community spatial pattern to the sim-
ulated random spatial patterns of populations
with identical boundaries (Coomes et al.
1999). Complete spatial randomness is simu-
lated by a two-dimensional Poisson process,
and the cumulative distribution of nearest-
neighbor distances from that random popu-
lation is compared with the observed distri-
bution of distances from the actual population
(Coomes et al. 1999).
We modified this procedure slightly for the
533EDIACARAN COMMUNITY ECOLOGY
F
IGURE
4. A, Cumulative probability distribution for
finding a nearest neighbor within specified distance
(thick line) for LMP Charnia Type A. The 95% error lim-
its for random spatial distribution are indicated by
shaded area. Observed distribution (dark line) passes
outside of the upper error bound, indicating an aggre-
gated spatial pattern. B, Cumulative probability distri-
bution for finding a nearest neighbor within specified
distance (thick line) for G surface Bradgatia. The 95% er-
ror limits for random spatial distribution are indicated
by shaded area. Observed distribution (dark line) passes
outside of the lower error bound, indicatinga regular
spatial pattern.
E surface, which contains a large area readily
recognized in the field as exhibiting lower-
quality preservation. The difference in appar-
ent fossil density was incorporated into the
model, resulting in a simulated two-density
population. This variable-intensity Poisson
process provided a more accurate represen-
tation of true spatial pattern by reducing the
impact of taphonomic effects on the model.
We compared the spatial pattern for each tax-
on by simulating random populations with
the same population size in an area with the
same boundary shape. On surfaces containing
both Charniodiscus and dusters, two frondose
taxa with indistinguishable discoid bases, the
two taxa were combined so that frond bases
could be included in the analysis.
Error bounds (95% uncertainty) were esti-
mated by simulating 1000 random popula-
tions. Populations with fewer than 20–25 in-
dividuals could not be simulated because er-
ror bounds on the cumulative distribution of
expected nearest-neighbor distances were too
great. If the cumulative distribution of ob-
served nearest-neighbor distances passes
above the upper boundary of the error enve-
lope, there are significantly more nearest
neighbors within a given distance than ex-
pected from a random population and the or-
ganism has an aggregated spatial pattern (Fig.
4A). Likewise, if the observed distribution
passes outside the lower bound of the error
envelope there are significantly fewer nearest
neighbors than in a random population and
the organism has a regular spatial pattern
(Fig. 4B).
Results. Mistaken Point organisms display
relatively complex single-species spatial pat-
terns: of 20 taxa examined, 9 were distributed
randomly, 8 displayed an aggregated spatial
pattern, and 3 had a regular distribution (Ta-
ble 3). Ivesia displayed consistent spatial pat-
terning in different communities (randomly
distributed on PC and E), as did Charnia Type
B (aggregated on BC and LMP). However,
most other organisms were aggregated or reg-
ular on some surfaces but random on others.
Bradgatia and the frondose group (Charniodis-
cus and dusters) displayed both aggregated
and regular patterns.
Although organisms did not display consis-
tent patterns between surfaces, individual
communities tended to have distinctive con-
stituent spatial patterns. For example, the ma-
jority (4/7) of species on the E surface are ag-
gregated. Only Charnia and the enigmatic lo-
bate forms Ivesia and the Lobate Discs are ran-
domly distributed and Charnia displayed
strong nonsignificant deviation toward aggre-
gation (p
5
0.10). In contrast, all three organ-
isms examined from the G surface displayed
regularity, two significantly and the holdfast
fronds at p
5
0.09. The D surface is unusual in
having both aggregated and regularly spaced
taxa.
Multispecies Spatial Pattern
Methodology. Many methods have been de-
rived to model two-species nearest-neighbor
interactions in square sample areas (Anderson
534 MATTHEW E. CLAPHAM ET AL.
T
ABLE
3. Single-species spatial patterns. Significance levels of aggregation (AGG), regularity (REG), and randomness (Rand) derived from Monte Carlo simulation of
spatial pattern. The ‘‘Frondose’’ label refers to the grouping of Charniodiscus and dusters. The minimum population size for the testing was approximately 20 fossils;
taxa with a smaller population are labeled NS (for ‘‘not sufficient’’). NP stands for ‘‘not present.’’
PC BC LMP D E G
Bradgatia
Charnia A
Charnia B
Frondose
Holdfast stem
Ivesia
NP
NS
NP
NP
NP
Rand (p
5
0.21)
NS
NP
AGG ( p
5
0.005)
NP
NP
NS
NP
AGG ( p
,
0.001)
AGG ( p
5
0.018)
NS
NS
NS
REG (p
5
0.016)
NS
NP
NS
NP
NS
AGG ( p
,
0.001)
Rand (p
5
0.10)
NP
AGG ( p
,
0.001)
NP
Rand (p
5
0.17)
REG (p
5
0.04)
NS
NP
REG (p
5
0.05)
Rand (p
5
0.094)
NS
Lobate disc
Ostrich feather
Pectinate
Spindle
Triangle
NP
NP
NP
NP
Rand (p
5
0.051)
NP
NP
NP
Rand (p
5
0.14)
NP
NP
Rand (p
5
0.14)
NP
NS
NP
NP
NP
Rand (p
5
0.076)
AGG ( p
,
0.001)
NP
Rand (p
5
0.28)
NP
NP
AGG ( p
,
0.001)
AGG ( p
5
0.037)
NP
NP
NP
NP
NP
1992; Dixon 1994; Zou and Wu 1995). Monte
Carlo methods, similar to those used by Coo-
mes et al. (1999), allow simulation of multi-
species interactions in irregular sample areas.
Multispecies Monte Carlo simulation used the
same procedure as single-species simulation,
but extended to simulate a community with
the same number of species and the same-
sized populations as the comparison fossil
community. For each species, we recorded the
identity of each nearest neighbor and tabulat-
ed the probability of having a given species as
nearest neighbor. Error bounds (95% uncer-
tainty) were derived from 1000 simulated
runs. If a species occurs more frequently as a
nearest neighbor than expected from two co-
existing random distributions then the two
species are associated, whereas they are seg-
regated if there are fewer nearest neighbors
than expected.
Results. Only 4 of 64 pairwise nearest-
neighbor interactions simulated displayed
significant deviation from randomness, both
toward segregation. Charnia Type A and os-
trich feathers both have a segregated distri-
bution in the LMP community. The segrega-
tion was two-sided: fewer Charnia Type A
were neighbors of ostrich feathers than ex-
pected, and fewer ostrich feathers were near-
est neighbors to Charnia Type A. Frondose
taxa (Charniodiscus and dusters) and spindles
also displayed two-sided segregation in the E
surface community.
Between-Community Variation
We examined variation in community com-
position by using cluster analysis (log-trans-
formed data, Bray-Curtis similarity, complete
linkage) to classify all Mistaken Point com-
munities, with the three E surface replicates
included as separate samples to assess within-
community variation. Other clustering meth-
ods (e.g., WPGMA, UPGMA) gave similar
dendrograms but tended to group the PC and
SH surfaces by abundance of Ivesia and were
not utilized for the final analysis. The result-
ing cluster dendrogram (Fig. 5) shows that
within-community variations for the Esurface
are much smaller than any between-commu-
nity differences. This strong similarity further
underscores the limited effect of taphonomic
535EDIACARAN COMMUNITY ECOLOGY
F
IGURE
5. Q-mode and R-mode cluster analyses of Mistaken Point communities (complete linkage, Bray-Curtis
similarity coefficient).
alteration on community composition. Small
within-community variation also suggests
that observed between-surface differences are
not simply reections of variability within a
single community type. In addition, the uni-
formity within and between all E surface sam-
ples implies that spatial heterogeneity was
minimal in Ediacaran communities at Mistak-
en Point, even at kilometer-scale, in contrast to
well-developed patchiness in many modern
slope communities (Grassle et al. 1975; Smith
and Hamilton 1983; Vetter and Dayton 1999).
Minimal within-surface variation suggests
that observed compositional differences be-
tween Mistaken Point communities are signif-
icant and reflect the ecological or environmen-
tal processes that structured those communi-
ties. Q- and R-mode cluster analysis (Fig. 5)
reveals a fundamental division between two
major groupings of communities: frond-dom-
inated communities (G, E, LMP, and to some
extent PC) and frond-poor (typically spindle-
or pectinate-dominated) communities (BC, D,
and SH). Cluster analysis clearly shows
groupings of similar communities but does
not display environmentally or ecologically
mediated gradients in community composi-
tion. Such trends are better displayed by or-
dination techniques that map the relationship
between communities in two- or three-dimen-
sional space (Clarke 1993). We chose nonmet-
ric multidimensional scaling (MDS) to com-
pare community similarity because it is a mul-
tivariate ordination technique that does notre-
quire the data to be normally distributed,
making it especially suited to analysis of com-
munity abundance data (Field et al. 1982;
Clarke 1993). MDS ordination was performed
with the PC-ORD software package (McCune
and Mefford 1999) and the results are dis-
played in Figure 6. Although MDS does not
rigidly structure variability along the major
ordination axes (as in PCA, for example), com-
munity trends in ordination space may still be
linked to environmental or ecological vari-
ables through regression analysis (Clarke
536 MATTHEW E. CLAPHAM ET AL.
F
IGURE
6. Nonmetric multidimensional scaling (MDS) ordination plot for Mistaken Point communities. Stress
,
0.01 for three-dimensional solution. Regression lines for preservation quality (A), stratigraphic position (B), and
proposed ecological succession model (C) are shown. Length of regression line is proportional to the strength of
correlation. Shaded ellipses correspond to frond-poor (light gray) and frond-rich (dark gray) groupingsf rom cluster
analysis (Fig. 5).
1993). Observed species composition may be
controlled by a combination of evolutionary,
environmental, and/or ecological factors, al-
though taphonomic effects on species com-
position must also be considered.
Taphonomic Controls
Before environmental or ecological controls
can be assessed as a cause of variation in com-
munity composition, the effect of differences
in preservation quality must be examined.
Taphonomic factors did not significantly af-
fect most community attributes (e.g., richness,
diversity) and had a negligible effect on com-
munity composition within a single surface.
We quantified preservation quality further by
measuring the smallest morphological detail
typically visible on each surface, which ranges
from 0.3–0.5 mm (BC, E) to 3.0 mm (SH). Lin-
ear regression of this preservation quality
measure for each surface onto the MDS ordi-
nation results confirms that taphonomy is
only weakly correlated with community var-
iability (regression line A, Fig. 6), suggesting
that environmental and/or ecological vari-
ables, not preservation quality, are the funda-
mental controls on community composition.
Evolutionary Controls
Long-term trends in ecosystemcomposition
and structure, resulting from local appear-
ance and disappearance of taxa, may be su-
perimposed on environmental and ecological
influences. Local fossil range zones showstep-
wise appearances and disappearances of taxa,
suggesting a possible influence on community
structure. Although the Mistaken Point biota
spans a stratigraphic thickness of nearly 2.5
km, the grouping of communities in the clus-
ter dendrogram suggests that community
composition is only weakly linked to age (Fig.
5). Both clusters contain communities from
throughout the stratigraphic succession, im-
plying that local biostratigraphic changes in
the biota were not the fundamental control on
community composition. However, regression
of stratigraphic position (meters below top of
the Trepassey Formation) on the MDS ordi-
nation plot (Fig. 6) suggests that evolutionary
changes did have some influence on commu-
nity composition. Regression line B shows a
moderate correlation with stratigraphic posi-
tion, with older communities (PC, BC, LMP)
occurring near one end of the axis and youn-
ger communities (D, E, G, SH) near the other
537EDIACARAN COMMUNITY ECOLOGY
(Fig. 6). Some community parameters, espe-
cially richness and diversity, may also have
been influenced by stratigraphic position in
the oldest communities, where the regional
species pool was smaller (Caley and Schluter
1997; Lukaszewski et al. 1999). It should also
be noted that, although there is some corre-
lation between stratigraphic position and
community similarity, biostratigraphic chang-
es may not be the proximate cause of variation
if stratigraphic position is instead linked to a
different environmental or ecological factor.
However, the results of cluster analysis and
MDS ordination suggest that other environ-
mental or ecological variables were more im-
portant in determining overall community
structure and composition.
Environmental Controls
Taxa that inhabit modern slope communi-
ties often display marked substrate preference
(Mayer and Piepenburg 1996; Gutt et al. 1999).
However, all seven studied communities were
living on silty bottom sediments that are in-
distinguishable in thin sections, suggesting
that differences in community composition
did not result from variability in substrate tex-
ture and/or composition. Similarly, major dif-
ferences between the seven diverse Mistaken
Point communities do not appear related to
resource levels. Four communities (BC, LMP,
G, SH) have low areal coverage (‘‘biomass’’)
values (Table 2), implying that resource levels
were low. In addition, the G surface is domi-
nated by regular spatial patterns, suggesting
that competition, likely for food, was intense.
However, these low-‘‘biomass’’ communities
do not show strong similarity on the cluster
dendrogram (Fig. 5), nor does areal coverage
appear as a significant regression trend on the
MDS ordination plot. Correlations between
areal coverage and species richness or diver-
sity, both of which should vary predictably
with resource levels (Wright 1983; Menge et al.
1985; Cosson-Sarradin et al. 1998), are also
weak. Some low-‘‘biomass’’ communities have
low to moderate species richness (BC, G, SH;
four to six species), but the LMP community
has high species richness (11 species). Like-
wise, some of these communities have low di-
versity (H
95
0.46 at SH, 0.67 at BC) whereas
others are more diverse (H
95
1.31 at LMP,
1.54 at G).
Ecological Succession
Important ecological factors in modern
communities include predation (Menge et al.
1985; Seitz and Lipicus 2001), competition
(Drobner et al. 1998; Menge 2000), and ecolog-
ical succession (Connell 1978; Visser 1995).
Predation can be eliminated as an important
structuring mechanism for Mistaken Point
communities because there is no evidence for
macropredators in any Ediacaran ecosystems
(Narbonne 1998). Evidence for intra- or inter-
specific competition is also limited: regular
spatial patterns are rare, as are nonrandom
pairwise patterns. In addition, interspecific
competition, as an isolated factor, may not be
able to influence such disparate community
aspects as composition, species richness, di-
versity, evenness, tiering structure, and spatial
pattern.
Ecological succession produces orderly
changes in community composition, diversity,
spatial pattern, and tiering. Ecological succes-
sion is abundantly evident in modern ecosys-
tems (Helm and Allen 1995; Visser 1995; Lich-
ter 1998) and has been inferred from progres-
sive upward changes in Phanerozoic shelly
fossil assemblages (Nicol 1962; Walker and Al-
berstadt 1975; Copper 1988). However, time-
averaging in Phanerozoic shelly assemblages
may have reduced temporal resolution so that
ecological succession may not be resolvable in
these records; cases of ‘‘succession’’ may in-
stead have been longer-term community re-
placement mediated by environmental change
(Miller 1986). Preservation of Mistaken Point
assemblages as census populations of the ben-
thic communities has the disadvantage of pre-
senting them as ‘‘snapshots’’ of the living
community rather than as a continuous record
of the accumulation of hardparts, but the ab-
sence of time averaging in these entirely soft-
bodied communities provides suitable tem-
poral resolution to recognize ecological suc-
cession, if present. The Ediacaran organisms
at Mistaken Point inhabited a tectonically ac-
tive basin, suggesting that the communities
may have been affected by occasional distur-
bances. These disturbances, such as turbidity
538 MATTHEW E. CLAPHAM ET AL.
currents, volcanic ashfalls, and anoxia and/or
reduced food supply resulting from slowing
or cessation of the contour current (Wood et
al. in press), would have resulted in mass mor-
tality of the local biota at random intervals
during community development.
If Mistaken Point communities preserve dif-
ferent stages of ecological succession they
should also display predictable changes in
composition, diversity, spatial pattern, and ti-
ering structure as the conditions become op-
timized for the growth of different organisms
(Walker and Alberstadt 1975; Whittaker 1993).
Species composition should change from the
pioneer community, characterized by low di-
versity and evenness, limited tiering, and ran-
dom spatial patterns (Walker and Alberstadt
1975), through a mixed mid-successional
stage, characterized by highest diversity and
evenness (Walker and Alberstadt 1975), in-
creasing tiering complexity (Helm and Allen
1995; Lichter 1998), and more nonrandom spa-
tial patterns from competitive exclusion and
preferential colonization of emptyspaces (Bel-
lingham 1998), to the climax community,char-
acterized by high or slightly decreased diver-
sity (Walker and Alberstadt 1975; Clebsch and
Busing 1989), lower evenness values from en-
hanced competitive exclusion (Death 1996;
Drobner et al. 1998), and the greatest tiering
and spatial pattern complexity (Helm and Al-
len 1995; Bellingham 1998; Lichter 1998). The
following section will investigate whether the
‘‘snapshots’’ represented by the Mistaken
Point fossil surfaces might reflect different
stages in this idealized succession model.
Early Succession. Early successional (‘‘pio-
neer’’) stages typically display low diversity
and highly uneven species abundances, with
minimal tiering and spatial pattern complex-
ity. Community parameters measured from
BC, D, and SH communities are most similar
to the values expected from early stages in
ecological succession. Diversity is low (H
95
0.46–0.70), as is evenness (E
5
0.26–0.48). Both
BC and D have random multispecies spatial
patterns (spatial patterning at SH could not be
studied) and tiering is present only in the D
surface community. The extremely low diver-
sity and evenness at SH suggest it could rep-
resent an earlier, pioneer community with BC
and D recording slightly later stages in suc-
cession. The grouping of BC, D, and SH com-
munities as potential pioneer stages is sup-
ported by the cluster dendrogram, which, de-
spite their occurrence at different stratigraph-
ic levels, groups those communities together
as one of two fundamental clusters (Fig. 5).
Middle Succession. Mid-succession com-
munities typically have the highest diversity
and evenness, as well as displaying increas-
ingly complex tiering and spatial pattern. The
G surface community has high diversity and
evenness values, with complex tiering and
random multispecies spatial patterns, and is
most consistent with mid-successional posi-
tion. The E surface community is similar to the
G community in terms of diversity and tier-
ing, but it has lower evenness and contains
nonrandom multispecies spatial interactions,
possibly indicating greater similarity to a later
successional position. The PC community is
difficult to place in the succession, owing to its
low stratigraphic position and corresponding
depauperate fauna. The diversity value of 0.87
is more similar to an early successional stage
but the high evenness value (0.80) is more con-
sistent with a mid-successional position, sim-
ilar to the G surface community.
Late Succession. The LMP community is the
most consistent with a late succession stage,
having both lower diversity and evenness
than the potential mid-succession communi-
ties (E, G), and nonrandom multispecies pat-
terns. The community has a unique species
composition, with a much greater proportion
of frondose taxa, distinguishing it from the
less frond-rich E and G communities. The
LMP community also contains unique meter-
tall organisms not found on any other surfaces
in the study area (Clapham and Narbonne
2002).
Proposed Ecological Succession Model. The
fundamental division between the probable
mid- to late-succession PC, LMP, E, and G
communities and the pioneer-like BC, D, and
SH communities is well supported by cluster
analysis (Fig. 5). The proposed succession pat-
tern (earliest SH to early BC/D to middle PC/
E/G to late LMP) was examined by coding
each stage with an integer value (1 through 4)
and performing regression analysis in MDS
539EDIACARAN COMMUNITY ECOLOGY
F
IGURE
7. Approximate trends in species composition between different Mistaken Point communities. Position of
communities along horizontal scale is based on community parameters, cluster analysis, and MDS ordination and
parallels the proposed ecological succession model.
ordination space. The correlation between a
priori successional stage (1 through 4) and
community variability is strong (regression
line C, Fig. 6).
The trends in community species composi-
tion are consistent with the proposed ecolog-
ical succession model (Figs. 7, 8). The general
trend through succession appears to have
been the replacement of flat-lying organisms
with upright, frondose organisms, possibly as
sediment became increasingly stabilized by
microbial mat. Early successional stages (SH,
BC, D) may have been dominated by pecti-
nates and/or spindles, whereas intermediate
stages (E, G) were characterized by abundant
Charniodiscus, dusters, and Bradgatia. The pro-
posed mid-succession PC community did not
contain these organisms because it predated
their first appearances; however, it is domi-
nated by the triangle form, which was typical
of other mid-succession assemblages (E sur-
face). The potential late-stage community
(LMP) was completely dominated by frondose
organisms: small fronds such as Charnia Type
A and ostrich feathers largely replaced spin-
dles and Bradgatia in the lower tiers, and the
uppermost tier was occupied by rare meter-
tall forms such as the whip stem and Xmas
tree (Clapham and Narbonne 2002).
If the communities reflected different suc-
cessional stages, trends in species composi-
tion (Fig. 7) should result in predictable
changes in multispecies interactions (where
present) as early species were replaced bynew
colonizers (Bellingham 1998). If succession
was based on a tolerance model, in which the
community changed through progressive dis-
placement by species adapted to lower re-
source levels (Miller 1986), later colonizers
should have preferentially settled in locations
where preexisting species were less densely
packed. Observed nonrandom multispecies
spatial patterns are consistent with a tolerance
model of succession. Ostrich feathers (inter-
preted late-stage colonizers of the lower tier)
in the LMP community tend to be segregated
from Charnia Type A, which occurs at every
stage of succession. On the E surface, mid-suc-
cession frondose forms (Charniodiscus and
540 MATTHEW E. CLAPHAM ET AL.
F
IGURE
8. Diorama illustrating idealized progression of communities during ecological succession. A, Charnia
Type B. B, Pectinate. C, Charnia Type A. D, Spindle. E, Bradgatia. F, Duster. G, Charniodiscus. H, Triangle. I, Ostrich
feather. J, Xmas tree.
dusters) are segregated from early-succession
spindles.
Although the preservation of the Mistaken
Point communities as census populations
makes it impossible to prove conclusively that
between-community differences result from
ecological succession, the succession model is
internally consistent and agrees with ob-
served variation in community structure. The
proposed succession model is well supported
by cluster analysis and MDS ordination, and
corresponds well to changes in diversity,
evenness, spatial pattern complexity, and ti-
ering structure. Species composition trends
and interspecific interactions also vary pre-
dictably in correspondence with the proposed
model.
Comparison with Modern Communities
Mistaken Point fossil assemblages provide
the opportunity to study the relationships be-
tween the early evolution of animals and the
evolution of animal ecosystems. Because com-
munities at Mistaken Point preserve census
populations of the benthic megafauna living
in a slope community, they can be compared
directly with modern bathyal megafaunal
communities. Comparisons with Phanerozoic
shelly fossil assemblages are less secure be-
cause of time-averaging and the taphonomic
bias against soft-bodied organisms inherent
in those assemblages. If complex community
structure is an inherent property of assem-
blages of complex animals, the structure (rich-
ness, diversity, spatial patterning) of Mistaken
Point communities should be similar to that of
equivalent modern communities. If, however,
complex communities are a feature that
evolved gradually during early animal evo-
lution, then Mistaken Point may show lower
species richness, lower diversity, or less de-
veloped spatial patterns than modern coun-
terparts.
Species richness, Shannon diversity indices,
and spatial patterning from Mistaken Point
communities were compared with values
from modern bathyal megafaunal communi-
ties. In the comparison studies of modern
slopes, megafauna refers to organisms visible
on photographic transects and generally in-
541EDIACARAN COMMUNITY ECOLOGY
F
IGURE
9. Comparison of species richness, average fossil density, and diversity values from Mistaken Point com-
munities (stars) with typical (filled rectangle) and extreme (solid line) range from modern slope communities of
epibenthic megafauna.
cludes all epifaunal organisms larger than
0.5–3 cm, depending on photographic reso-
lution, a size limit that is comparable with the
taphonomically controlled minimum visible
size at Mistaken Point. Only photographic
studies were used for comparison purposes
because trawl samples typically include infau-
na, which are far more abundant than epifau-
na in modern settings (Grassle et al. 1975),
and which were absent from Ediacaran com-
munities at Mistaken Point.
Species richness varies greatly on the mod-
ern slopes, with typical values between 10 and
30 species, for areas of ca. 10–100 m
2
,anda
maximum range of 2 to 40 species (Grassle et
al. 1975; Smith and Hamilton 1983; Mayer and
Piepenburg 1996; Gutt et al. 1999). Mistaken
Point communities fall within the typical
range of modern communities (Fig. 9), al-
though in general they are moderately spe-
cies-poor with a maximum of 12 species per
community. Mistaken Point communities also
fit well within the observed range of Shannon
diversity coefficients from modern commu-
nities (Fig. 9). Shannon diversity can be as low
as 0.05 (Grassle et al. 1975; Smith and Ham-
ilton 1983) or as high as 3.7 (Mayer and Pie-
penburg 1996) but typically ranges between
0.8 and 2.0 (Gutt et al. 1999), comparing well
with Mistaken Point communities (H
95
0.5–
1.5). Although fossil density measures at Mis-
taken Point are strongly confounded by taph-
onomic bias, density seems to be equal to or
greater than density values observed on mod-
ern slopes. Values as high as 70 ind/m
2
have
been reported from modern settings (Gutt et
al. 1999), but typical values range from 15 to
40 ind/m
2
(Smith and Hamilton 1983; Mayer
and Piepenburg 1996). Observed values in
Mistaken Point communities are as low as 8
ind/m
2
and as high as 148 ind/m
2
(Fig. 9), al-
though evidence from the E surface suggests
that typical density values for Mistaken Point
communities may have been 50–150 ind/m
2
,
much greater than the animal density found
on modern slopes.
Spatial patterns, especially multispecies
distributions, are thought to indicate higher-
level community structuring including intra-
and interspecies interactions. Random single-
species patterns are most common in some
slope communities (Grassle et al. 1975),
whereas aggregation or regularity predomi-
nate in others (Smith and Hamilton 1983). Of
211 single-species distributions examined by
Mayer and Piepenburg (1996), 81 showed sig-
nificant aggregation and the other 130 were
random. Mistaken Point communities also
displayed significant levels of spatial pattern-
ing: more than one-half of single-species dis-
tributions deviate from randomness, with ag-
gregation more common than regularity. Mul-
tispecies spatial patterns are rare at Mistaken
Point, with 60 of 64 pairwise interactions con-
forming to a random distribution, but the fre-
quency of multispecies patterning in the mod-
ern deep sea is poorly understood, making it
difficult to determine if Mistaken Point com-
munities are in fact less complexly structured.
Mistaken Point communities fall within the
typical range of species richness and diversity
for modern marine epibenthic communities
and displayed similar levels of single-species
spatial patterning. Fossil density is consis-
tently higher than in modern slope commu-
nities but interspecies interactions may have
been less common. These results imply that
the structural organization of the oldest ani-
542 MATTHEW E. CLAPHAM ET AL.
mal communities at Mistaken Point was sim-
ilar to community structure of modern slope
communities.
Conclusions
Mistaken Point communities display signif-
icant between-community variation, likely re-
sulting from ecological processes with super-
imposed evolutionary and environmental ef-
fects. Modern communities are influenced by
a myriad of interrelated factors, including nu-
trient levels, disturbance frequency, environ-
mental heterogeneity, competition, predation,
and ecological succession, to name a few.
Some of these controls, such as predation,
were absent from Ediacaran communities at
Mistaken Point. In addition, the homogeneous
nature of the E surface community, even at lo-
calities over 1 km apart, suggests that envi-
ronmental heterogeneity was negligible. Mod-
ern communities display extreme variability
over small and intermediate scales (Grassle et
al. 1975; Mayer and Piepenburg 1996), in con-
trast to the spatially uniform community
structure observed at Mistaken Point. Major
community variability is consistent with con-
trol by ecological succession, and there is also
evidence for intraspecific competition, and
possibly limited interspecific segregation, in
several communities. The presence of these
complex controls implies that Mistaken Point
communities were largely structured by the
same set of parameters that are active in mod-
ern communities.
Although this study does not constrain the
affinities of component organisms, it does al-
low speculation on their environmental toler-
ances and reproductive strategies. For exam-
ple, the abundance of random and regular
spatial distributions in Mistaken Point com-
munities implies that the constituent organ-
isms had a dispersal phase in their life cycle.
The global distribution of Charniodiscus,Char-
nia,andHiemalora further suggests that at
least some Edicaran taxa may have possessed
a teleplanic larva.
The census populations at Mistaken Point
preserve diverse communities that inhabited
the deep slope during the Neoproterozoic.
The presence of a diverse slope biota at Mis-
taken Point suggests that the deep sea was col-
onized rapidly at an early stage of animal evo-
lution. Mistaken Point communities are sig-
nificantly richer than the deep-water biota
from northwestern Canada (Narbonne and
Aitken 1990) and England (Ford 1999), and
similar studies of these localities are necessary
to fully elucidate the paleoecology of Ediacar-
an slope environments. Similarly, shallow-wa-
ter Ediacaran assemblages such as those in
Australia, the White Sea, and Namibia are
markedly different in composition from those
at Mistaken Point, and quantitative studies are
needed to determine how these differences af-
fected their ecological structure.
As a final conclusion of this study, it is in-
teresting to note that the earliest complex
communities in the fossil record have struc-
tural attributes strikingly similar to those of
modern counterparts. Species richness, organ-
ism abundance, and diversity values, as well
as levels of spatial patterning, all fall within
the norms of modern epibenthic slope com-
munities. Only interspecies interactions ap-
pear less common. These community similar-
ities suggest that, although the taxonomic af-
finities of Ediacaran organisms are unknown,
they had many of the same ecological respons-
es as present-day animals.
Acknowledgments
We thank R. Sala and M. Laflamme for help-
ful assistance during fieldwork. Fieldwork in
the Mistaken Point Ecological Reserve was
carried out under Scientific Research Permits
granted by the Parks and Natural Areas Di-
vision, Department of Tourism, Culture, and
Recreation, Government of Newfoundland
and Labrador. Comments by L. Aarssen and
N. James and reviews by A. Miller and B. Wag-
goner greatly improved the manuscript. This
research was supported by a Natural Sciences
and Engineering Research Council of Canada
(NSERC) grant (to Narbonne) and by an
NSERC postgraduate scholarship (to Cla-
pham).
Literature Cited
Anderson, M. 1992. Spatial analysis oftwo-species interactions.
Oecologia 91:134–140.
Ander son, M. M., and S. Conway Morris. 1982. A review, with
descriptions of four unusual forms, of the soft-bodied fauna
of the Conception and St. John’s groups (late-Precambrian),
543EDIACARAN COMMUNITY ECOLOGY
Avalon Peninsula, Newfoundland. Pp.1–8 in B. Ma met and M.
J. Copeland, eds. Proceedings of the Third North American
Paleontological Convention. Universite´ de Montreal, Montre-
al, and Geological Survey of Canada, Ottawa.
Anderson, M. M., andS. B. Misra. 1968. Fossils found in thePre-
Cambrian Conception Group of south-eastern Newfound-
land. Nature 220:680–681.
Bellingham, P. J. 1998. Shrub succession and invasibility in a
New Zealand montane grassland. Australian Journal of Ecol-
ogy 23:562–573.
Benus, A. P. 1988. Sedimentological context of a deep-water Edi-
acaran fauna (Mistaken Point, Avalon Zone, eastern New-
foundland). Pp. 8–9 in E. Landing, G. M. Narbonne, and P. M.
Myrow, eds. Trace fossils, small shelly fossils and the Precam-
brian-Cambrian Boundary. New York State Museumand Geo-
logical Survey Bulletin 463.
Billings, E. 1872. Fossils in Huronian rocks. CanadianNaturalist
and Quarterly Journal of Science 6:478.
Caley, M. J., and D. Schluter. 1997. The relationship between lo-
cal and regional diversity. Ecology 78:70–80.
Campbell, D. J. 1992. Nearest-neighbour graphical analysis of
spatial pattern and a test for competition in populations of
singing crickets (Teleogryllus commodus). Oecologia 92:548–
551.
———. 1996. Aggregation and regularity: an inclusive one-
tailed nearest-neighbour analysis of small spatially patchy
populations. Oecologia 106:206–211.
Clapham, M. E., and G. M.Narbonne. 2002. Ediacaran epifaunal
tiering. Geology 30:627–630.
Clark, P. J., and F. C. Evans. 1954. Distance to nearest neighbor
as a measure of spatial relationships in a population. Ecology
35:445–453.
Clarke, K. R. 1993. Non-parametric multivariate analyses of
changes in community structure. Australian Journal of Ecol-
ogy 18:117–143.
Clebsch, E. E. C., and R. T. Busing. 1989. Secondary succession,
gap dynamics, and community structure in a southern Ap-
palachian cove forest. Ecology 70:728–735.
Connell, J. H. 1978. Diversity in tropical rain forests and coral
reefs. Science 199:1302–1310.
Coomes, D. A., M. Rees, and L. Turnbull. 1999. Identifying ag-
gregation and association in fully mapped spatial data. Ecol-
ogy 800:554–565.
Copper, P. 1988. Ecological succession in Phanerozoic reef eco-
systems: is it real? Palaios 3:136–152.
Cosson-Sarradin, N., M. Sibuet, G. L. J. Paterson, and A. Van-
griesheim. 1998. Polychaete diversity at tropical Atlantic
deep-sea sites: environmental effects. Marine Ecology Pro-
gress Series 165:173–185.
Dalrymple, R. W., and G. M. Narbonne. 1996. Continental slope
sedimentation in the Sheepbed Formation (Neoproterozoic,
Windermere Supergroup), Mackenzie Mountains, N.W.T. Ca-
nadian Journal of Earth Sciences 33:848–862.
Death, R. G. 1996. The effect of habitat stability on benthic in-
vertebrate communities: the utility of species abundance dis-
tributions. Hydrobiologia 317:97–107.
Dixon, P. 1994. Testing spatial segregation using a nearest-
neighbor contingency table. Ecology 75:1940–1948.
Drobner, U., J. Bibby, B. Smith, and J. B. Wilson. 1998. The re-
lation between community biomass and evenness: what does
community theory predict, and can these predictions be test-
ed? Oikos 82:295–302.
Fedonkin, M. A. 1992. Vendian faunas and the early evolution
of Metazoa. Pp. 87–129 in J. H. Lipps and P. W. Signor, eds.
Origin and early evolution of the Metazoa.Plenum, NewYork.
Field, J. G., K. R. Clarke, and R. M. Warwick. 1982. A practical
strategy for analysing multispecies distribution patterns.Ma-
rine Ecology Progress Series 8:37–52.
Ford, T. D. 1999. The Precambrian fossils of Charnwood Forest.
Geology Today 14:230–234.
Fu¨ rsich, F. T., and M. Aberhan. 1990. Significance of time-aver-
aging for paleocommunity analysis. Lethaia 23:143–152.
Gehling, J. G., and J. K. Rigby. 1996. Long expected sponges
from the Neoproterozoic Ediacara fauna of South Australia.
Journal of Paleontology 70:185–195.
Gehling, J. G., G. M. Narbonne, and M. M. Anderson. 2000. The
first named Ediacaran body fossil, Aspidella terranovica.Pa-
laeontology 43:427–256.
Glaessner, M. F. 1984. The dawn of animal life: a biohistorical
study. Cambridge University Press, Cambridge.
Grassle, J. F.,a ndN. J. Maciolek. 1992. Deep-sea species richness:
regional and local diversity estimates from quantitative bot-
tom samples. American Naturalist 139:313–341.
Grassle, J. F., H. L. Sanders, R. R. Hessler, G. T. Rowe, and T.
McLellan. 1975. Pattern and zonation: a study of the bathyal
megafauna using the research submersible Alvin. Deep-Sea
Research 22:457–481.
Gutt, J., E. Helsen, W. Arntz, and A. Buschmann. 1999. Biodi-
versity and community structure of the mega-epibenthos in
the Magellan region (South America). Scientia Marina
63(Suppl. 1):155–170.
Haase, P. 2001. Can isotropy vs. anisotropy in the spatial asso-
ciation of plant species reveal physical vs. biotic facilitation?
Journal of Vegetation Science 12:127–136.
Helm, D. J., and E. B. Allen. 1995. Vegetation chronosequence
near Exit Glacier, Kenai Fjords National Park, Alaska, U.S.A.
Arctic and Alpine Research 27:246–257.
Jenkins, R. J. F. 1992. Functional and ecological aspects of Edi-
acaran assemblages. Pp. 131–176 in J. H. Jipps and P. W. Si-
gnor, eds. Origin and early evolution of the Metazoa.Plenum,
New York.
Jenkins, R. J. F., and J. G. Gehling. 1978. A review of the frond-
like fossils of the Ediacara assemblage. South Australian Mu-
seum Records 17:347–359.
Kidwell, S. M. 1993. Patterns of time-averaging in the shallow
marine fossil record. In S. M. Kidwell and A. K. Behrensmey-
er, eds. Taphonomic approaches to time resolution in fossil
assemblages. Short Courses in Paleontology 9:275–300.
Lichter, J. 1998. Primary succession and forest development on
coastal Lake Michigan sand dunes. Ecological Monographs
68:487–510.
Lukaszewski, Y., S. E. Arnott, and T. M. Frost. 1999. Regional
versus local processes in determining zooplankton commu-
nity composition of Little Rock Lake, Wisconsin,USA. Journal
of Plankton Research 21:991–1003.
MacNaughton, R. B., G. M. Narbonne, and R. W. Dalrymple.
2000. Neoproterozoic slope deposits, Mackenzie Mountains,
northwestern Canada: implications for passive-margin de-
velopment and Ediacaran faunal ecology. Canadian Journalof
Earth Sciences 37:997–1020.
Martin, M. W., D. V. Grazhdankin, S. A. Bowring, D.A. D. Evans,
M. A. Fedonkin, and J. L. Kirschvink. 2000. Age of Neopro-
terozoic bilaterian body and trace fossils, White Sea, Russia:
implications for metazoan evolution. Science 288:841–845.
Mayer, M., and D. Piepenburg. 1996. Epibenthic community
patterns on the continental slope off East Greenland at 75
8
N.
Marine Ecology Progress Series 143:151–164.
McCune, B., and M. J. Mefford. 1999. PC-ORD. Multivariate
Analysis of Ecological Data, Version 4.0. MjM Software De-
sign, Gleneden Beach, Ore.
McMenamin, M. A. S. 1986. The Garden of Ediacara. Palaios 1:
178–182.
Menge, B. A. 2000. Recruitment vs. postrecruitment processes
as determinants of barnacle population abundance. Ecologi-
cal Monographs 70:265–288.
Menge, B. A., J. Lubchenco, and L. R. Ashkenas. 1985. Diversity,
544 MATTHEW E. CLAPHAM ET AL.
heterogeneity and consumer pressure in a tropical rocky in-
tertidal community. Oecologia 65:394–405.
Miller, W. 1986. Paleoecology of benthic community replace-
ment. Lethaia 19:225–231.
Misra, S. B. 1969. Late Precambrian (?)fossils from southeastern
Newfoundland. Geological Society of America Bulletin 80:
2133–2140.
———. 1971. Stratigraphy and depositional history of late Pre-
cambrian coelenterate-bearing rocks, southeastern New-
foundland. Geological Society of America Bulletin 82:979–
988.
———. 1981. Depositional environment of the late Precambrian
fossil-bearing rocks of southeastern Newfoundland, Canada.
Journal of the Geological Society of India 22:375–382.
Myrow, P. M. 1995. Neoproterozoic rocks of the Newfoundland
Avalon Zone. Precambrian Research 73:123–136.
Narbonne, G. M. 1998. The Ediacara biota: a terminal Neopro-
terozoic experiment in the evolution of life. GSA Today 8(2):
1–6.
Narbonne, G. M., and J. D. Aitken. 1990. Ediacaran fossils from
the Sekwi Brook area, Mackenzie Mountains, northwestern
Canada. Palaeontology 33:945–980.
Narbonne, G. M., and J. G. Gehling. 2003. Life after Snowball:
the oldest complex Ediacaran fossils. Geology 31:27–30.
Narbonne, G. M., R. W. Dalrymple, and J. G. Gehling. 2001. Neo-
proterozoic fossils and environments of the Avalon Peninsula,
Newfoundland. Guidebook, Trip B5, Geological Association
of Canada/Mineralogical Association of Canada Annual
Meeting, St. John’s, Newfoundland.
Nicol, D. 1962. The biotic development of some Niagaran reefs:
an example of an ecologic al succession or sere. Journal of Pa-
leontology 36:172–176.
Powell, E. N., K. M. Parsons-Hubbard, W. R. Callender, G. M.
Staff, G. T. Rowe, C. E. Brett, S. E. Walker, A. Raymond, D. D.
Carlson, S. White, and E. A. Heise. 2002. Taphonomy on the
continental shelf and slope: two-year trends, Gulf of Mexico
and Bahamas. Palaeogeography, Palaeoclimatology, Palaeoe-
cology 184:1–35.
Seilacher, A. 1992. Vendobionta and Psammocorallia: lost con-
structions of Precambrian evolution. Journalof the Geological
Society, London 149:607–613.
———. 1999. Biomat-related lifestyles in the Precambrian. Pa-
laios 14:86–93.
Seitz, R. D., and R. N. Lipicus. 2001. Variation in top-down and
bottom-up control of marine bivalves at differing spatial
scales. ICES Journal of Marine Science 58:689–699.
Smith, C. R., and S. C. Hamilton. 1983. Epibenthic megafauna
of a bathyal basin off southern California: patterns of abun-
dance, biomass, and dispersion. Deep-Sea R esearch 30:907–
928.
Thrush, S. F. 1991. Spatial patterns in soft-bottomcommunities.
Trends in Ecology and Evolution 6:75–79.
Vetter, E. W., and P. K. Dayton. 1999. Organic enrichment by
macrophyte detritus, and abundance patterns of megafaunal
populations in submarine canyons. Marine Ecology Progress
Series 186:137–148.
Visser, S. 1995. Ectomycorrhizal fungal succession in jack pine
stands following wildfire. New Phytologist 129:389–401.
Waggoner, B. M. 1998. Interpreting the earliest Metazoan fos-
sils: what can we learn? American Zoologist 38:975–982.
———. 1999. Biogeographic analyses of the Ediacara biota: a
conflict with paleotectonic reconstructions. Paleobiology 24:
440–458.
Walker, K. R., and L. P. Alberstadt. 1975. Ecological succession
as an aspect of structure in fossil communities. Paleobiology
1:238–257.
Whittaker, R. J. 1993. Plant population patterns in a glacier fore-
land succession: pioneer herbs and later-colonizing shrubs.
Ecography 16:117–136.
Wood, D. A., R. W. Dalrymple, G. M. Narbonne, J. G. Gehling,
and M. E. Clapham. In press. Paleoenvironmental analysis of
the Late Neoproterozoic Mistaken Point and Trepassey For-
mations, southeastern Newfoundland. Canadian Journal of
Earth Sciences 40.
Wright, D. H. 1983. Species-energy theory: an extention of spe-
cies-area theory. Oikos 41:496–506.
Zou, G., and H.-I. Wu. 1995. Nearest-neighbor distribution of
interacting biological entities. Journal of Theoretical Biology
172:347–353.
... limited palaeoenvironmental influence on its composition and taxa interactions [11][12][13][14]. The White Sea assemblage (558 to 550 Ma) shows a large increase in morphological diversity, including putative bilaterians [5], in tandem with a greater ecological diversity that includes the appearance of grazing, herbivory, and widespread motility [15,16]. ...
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... The Avalonian metacommunity displays a structure of "nested clumped species loss," whereby taxa-poor communities form nested subsets of increasingly taxa-rich communities, with predictable patterns of taxa loss associated with variation in taxa characteristics [30]. Differences in Avalonian community composition have been suggested to represent different stages of community succession, based on community parameters, cluster analyses and MDS (Multidimensional Scaling)AU : PleasedefineMDSatitsfirstmentioninthesentenceDifferencesinAvalonian ordination [13]. Where multiple different stages of a community succession are analysed using EMS, the succession would result in the observed pattern of clumped taxa loss with early and late succession communities forming less diverse nested subsets of maximally diverse mid-succession communities. ...
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... As some of the earliest examples of the Ediacaran macrofossil biotas, the Newfoundland successions are some of the most important in the world, particularly as there are many extensive fossilized seafloors that preserve assemblages of fossils that have widely been considered to be census populations (e.g., Clapham & Narbonne 2002;Clapham et al., 2003;Mitchell et al., 2015;Mitchell & Butterfield 2018;Mitchell & Kenchington 2018). These assemblages are found in rocks that were deposited in deep marine waters off the continental shelf of a volcanic arc in the Avalon Terrane, which is best known from England, Wales and eastern Canada including Newfoundland (McIlroy & Horák 2006;Liu et al., 2015a). ...
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... These hydrodynamic phenomena and their benefits in context of feeding in aggregated benthic populations have been described for modern marine taxa (see, e.g., Smits and Wood 1985;Butman et al. 1994). Therefore, our results suggest that populations of Pteridinium, similar to Ernietta, represent an ancient example of ecological facilitation, reinforcing the point that -even though there is little evidence to unambiguously link erniettomorphs with animalstheir community structure and ecological interactions show at least some similarities to those formed by metazoans (see also Clapham et al. 2003;Gibson et al. 2019Gibson et al. , 2021a. ...
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Pteridinium simplex is an iconic erniettomorph taxon best known from late Ediacaran successions in South Australia, Russia, and Namibia. Despite nearly 100 years of study, there remain fundamental questions surrounding the paleobiology and paleoecology of this organism, including its life position relative to the sediment–water interface, and how it fed and functioned within benthic communities. Here, we combine a redescription of specimens housed at the Senckenberg Forschungsinstitut und Naturmuseum Frankfurt with field observations of fossiliferous surfaces, to constrain the life habit of Pteridinium and gain insights into the character of benthic ecosystems shortly before the beginning of the Cambrian. We present paleontological and sedimentological evidence suggesting that Pteridinium was semi-infaunal and lived gregariously in aggregated communities, preferentially adopting an orientation with the long axis perpendicular to the prevailing current direction. Using computational fluid dynamics simulations, we demonstrate that this life habit could plausibly have led to suspended food particles settling within the organism's central cavity. This supports interpretation of Pteridinium as a macroscopic suspension feeder that functioned similarly to the coeval erniettomorph Ernietta , emblematic of a broader paleoecological shift toward benthic suspension-feeding strategies over the course of the latest Ediacaran. Finally, we discuss how this new reconstruction of Pteridinium provides information concerning its potential relationships with extant animal groups and state a case for reconstructing Pteridinium as a colonial metazoan.
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... The middle White Sea Assemblage has the greatest morphological and species diversity (Shen et al., 2008), while the youngest Nama Assemblage preserves communities dominated by erniettomorphs, and which are characterized by relatively low species richness and community structures suggestive of limited levels of competition and/or ecological stress (Muscente et al., 2019;Darroch et al., 2015;2018a,b; although see Vaziri et al., 2021). Previous analyses that have investigated the role of size in in-situ Ediacaran populations have typically focused on Avalon-aged (∼571-558 Ma) rangeomorph communities from Mistaken Point, Newfoundland (Clapham and Narbonne, 2002;Clapham et al., 2003;Darroch et al., 2013;Mitchell et al., 2015;Boddy et al., 2021). Building off these, more recent numerical studies have focused on how the spatial arrangement of individual organisms within communities may reflect paleoecological and -biological aspects of individual taxa, including potential reproductive modes, dispersal distances, and interspecific interactions (Hall et al., 2015;Mitchell et al., 2015Mitchell and Butterfield, 2018;. ...
... The middle White Sea Assemblage has the greatest morphological and species diversity (Shen et al., 2008), while the youngest Nama Assemblage preserves communities dominated by erniettomorphs, and which are characterized by relatively low species richness and community structures suggestive of limited levels of competition and/or ecological stress (Muscente et al., 2019;Darroch et al., 2015;2018a,b; although see Vaziri et al., 2021). Previous analyses that have investigated the role of size in in-situ Ediacaran populations have typically focused on Avalon-aged (∼571-558 Ma) rangeomorph communities from Mistaken Point, Newfoundland (Clapham and Narbonne, 2002;Clapham et al., 2003;Darroch et al., 2013;Mitchell et al., 2015;Boddy et al., 2021). Building off these, more recent numerical studies have focused on how the spatial arrangement of individual organisms within communities may reflect paleoecological and -biological aspects of individual taxa, including potential reproductive modes, dispersal distances, and interspecific interactions (Hall et al., 2015;Mitchell et al., 2015Mitchell and Butterfield, 2018;. ...
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Ernietta plateauensis is a semi-infaunal macroscopic eukaryote of unknown affinities common in latest Ediacaran (∼548–539 Ma) shallow marine settings in Namibia. The discovery of in-situ assemblages of Ernietta has demonstrated that these organisms lived in aggregated populations, while studies employing computational fluid dynamics (CFD) modeling have supported the hypothesis that these organisms were likely behaving as gregarious suspension feeders, analogous to many extant invertebrate phyla in present-day marine environments. Careful census and measurement of individuals within these in-situ populations offers an opportunity to examine how their size and location within a larger population affect nutrient delivery dynamics. In this study, we build on previous work by simulating fluid flow over aggregations of Ernietta comprising individuals of disparate sizes, and additionally reconstruct a population of Ernietta preserved in-situ from Farm Hansburg, Namibia. We use a combination of stationary and time-dependent CFD to reconstruct nutrient carrying flow paths, and compare the efficiency with which nutrients are partitioned between individuals of different shapes and sizes. Our results demonstrate that smaller Ernietta experience limited recirculation within their cavities compared to larger individuals. Furthermore, in spatially-accurate distributions, reduced recirculation is limited to isolated individuals of any size, while smaller individuals found downstream of larger ones receive enhanced cavity mixing. These reconstructed flow patterns illustrate that the disadvantage associated with small size is apparently mediated by location within the overall aggregation, suggesting a complex interplay of controls on feeding efficiency. This in turn suggests that aggregations of adult Ernietta would likely have performed a ‘nursery’ function, creating localized conditions ideal for the settlement and growth of younger individuals.
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Chapter
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The first animals appear during the late Ediacaran (572 – 541 Ma); an initial diversity increase was followed by a drop, interpreted as catastrophic mass extinction. We investigate the processes underlying these changes using the “Elements of Metacommunity Structure” framework. The oldest metacommunity was characterized by taxa with wide environmental tolerances, and limited specialisation and inter-taxa interactions. Structuring increased in the middle metacommunity, with groups of taxa sharing synchronous responses to environmental gradients, aggregating into distinct communities. This pattern strengthened in the youngest metacommunity, with communities showing strong environmental segregation and depth structure. Thus, metacommunity structure increased in complexity, with increased specialisation and resulting competitive exclusion, not a catastrophic environmental disaster, leading to diversity loss in the terminal Ediacaran, revealing that the complex eco-evolutionary dynamics associated with Cambrian diversification were established in the Ediacaran.
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Thin bedded cherts and siliceous argillites of the Drook and Fresh Water Point Formations of the Conception Group were deposited above the wave base in most parts, as evident from the nature of bedding, large-scale ripple marks, penecontemporaneous deformation and calcareous nodules. The overlying Cape Cove Formation of the same group is characterized by graded greywackes presumably deposited by turbidity currents. The animals that lived in the Conception sea during deposition of the Cape Cove Formation include pelagic as well as bottom dwellers. The presence of large-scale slump structures in the St. John's Formation (new group) indicates a gently sloping surface of the depositional basin. The depositinal environment of the St. John's Formation had become shallower than that of the underlying Conception Group.-Author
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The youngest formations of the Neoproterozoic Windermere Supergroup in northwestern Canada (Gametrail, Blueflower, and Risky formations) record the transition from slope to shelf deposition on a prograding passive margin. Eleven facies associations are recognized, representing environments ranging from carbonate- and siliciclastic-dominated continental slope to open carbonate shelf and siliciclastic shoreface. Seven simple sequences are recognized, which can be grouped into three composite sequences. Combination of the data presented here with previous work on underlying and overlying formations indicates that the sequence-stratigraphic record is least detailed in the deepest-water facies and most detailed in shelf facies, reflecting the relative inability of high-frequency relative sea-level oscillations to affect deposition in deep-water settings. Falling-stage deposits are especially common in the upper slope region. Several major sequence boundaries (unconformities) are clustered in the interval a short distance below the Precambrian-Cambrian boundary. The most significant of these occurs high in the Blueflower Formation, not at the top of the Risky Formation as commonly inferred. This interval containing several surfaces may reflect thermal uplift related to the rifting recorded in rocks of this age in the southern Canadian Cordillera. Renewed subsidence (thermal relaxation) commenced just prior to the Neoproterozoic-Cambrian boundary, giving rise to a thick succession of shelf to nonmarine basal-Cambrian deposits. Ediacaran body fossils previously reported from the studied units occur in a range of slope to shoreface environments, including some facies that were deposited below the photic zone. The most common taxa occur across a spectrum of facies and were apparently ecological generalists.
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Until recently, paleontological data were almost completely ignored by zoologists studying the origin of major groups of invertebrates and the early phylogeny of the Metazoa, chiefly because Charles Lyell had long ago emphasized the incompleteness of the geological and paleontological record. Charles Darwin adopted the same view and discussed the absence of ancestors of the Cambrian fauna. Only in the last few decades has paleontological information become available that bears on this problem, yet it, too, has been ignored in favor of new methods in the studies of living systems, in particular, from such fields as histology, genetics, biochemistry, and molecular biology. Along with the classical approaches, i.e., comparative anatomy and embryology, neontology dominated the study, not only of the systematics of Recent organisms, but also of the origin and phylogeny of Metazoa.
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Reference to fossil imprints of soft-bodied Ediacaran metazoans made by Hill and Bonney (1877, p. 757) recorded two of “those curious arrangements of concentric rings which have been supposed to be organisms” present on one of the bedding faces of the North Quarry, Woodhouse Eaves in Charnwood, Forest, Leicestershire, England (see Ford, 1958, 1963); the markings were dismissed as being “accidental ... (and) inorganic.” Early this century, P. Range and H. Schneiderhöhn collected fossil remains of equivalent age at Kuibis Farm in South West Africa (Namibia), and the organic nature of this material was confirmed by Gürich (1929, 1933). The history of discovery of such fossils during the mid part of the century (Sprigg, 1947, 1949; Ford, 1958, 1963, 1968, 1979a,b, 1981; Anderson and Misra, 1968) and the subsequent finding of similar materials widely sited about the globe are well known (e.g., Glaessner, 1984; Hofmann, 1987).
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The Ediacara biota is a distinctive assemblage of large, soft-bodied organisms that characterizes terminal Neoproterozoic (latest Precambrian) strata worldwide. Some Ediacaran organisms apparently were the root-stock for the Phanerozoic evolution of animals; other bizarre forms may represent a failed experiment in Precambrian evolution. The Ediacara biota and its nonactualistic preservation and ecosystem characterized the final 20 m.y. of the Proterozoic, and disappeared near the beginning of the Cambrian "explosion" of shelly and burrowing animals.
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Succession involves changes in a community through time, whether internally or externally controlled. As succession progresses, niche specialization, species diversity (variety and equitability), complexity of food chains, and pattern diversity increase; net production and species growth rate decrease. We apply the succession concept to three types of ancient community sequences: 1) fossil reefs (Ordovician—Cretaceous in age), 2) short-term successions occurring through thin stratigraphic intervals, and 3) long-term successions occurring through thicker stratigraphic intervals. Ancient reefs show four vertical zones: (1) a basal stabilization zone (autogenic), 2) the overlying colonization zone (autogenic, pioneer stage), 3) the diversification zone, the bulk of most reefs (diversification culminating in climax), and 4) the uppermost domination zone. The first three zones represent autogenic succession but the final stage may involve allogenic succession. Short-term succession usually occurs where periodic allogenic catastrophes wipe out the community which is rebuilt through autogenic succession. Opportunistic pioneer species are important and in our examples (Ordovician, Silurian, and Cretaceous) are species which pave soft substrata. Paleozoic strophomenid brachiopods filled this role, and inoceramid pelecypods served the function in the Mesozoic. The succession which begins with opportunists progresses to a climax community of equilibrists. Repetition of catastrophe-succession couplets produces a cyclic stratigraphic record. Long-term successions are recorded in thicker stratigraphic sequences, and are of two types: 1) autogenic succession in unchanging physical environments and 2) allogenic succession in changing physical environments. Our examples of these are from the Devonian Haragan-Bois D'Arc formations of Oklahoma and the Lime Creek Formation of Iowa. This type of succession represents a temporal-spatial mosaic. The Haragan data (unchanging environments) indicate characteristic, intergrading, and ubiquitous species in the brachiopod communities. Most ubiquitous species in the pioneer community were eurytopic opportunists. The Lime Creek data allows testing of the prediction that environmental changes cause regression to an earlier succession stage. The brachiopod communities after environmental changes have more ubiquitous and intergrading eurytopic species. These represent an earlier stage in the succession.