[Palaeontology, Vol. 54, Part 6, 2011, pp. 1223–1242]
PROBLEMATIC MEGAFOSSILS IN CAMBRIAN
PALAEOSOLS OF SOUTH AUSTRALIA
by GREGORY J. RETALLACK
Department of Geological Sciences, University of Oregon, Eugene, OR 97403, USA; e-mail: [email protected]
Typescript received 13 February 2009; accepted in revised form 20 August 2009
Other axial structures (Prasinema nodosum and P. adunatum
gen. et spp. nov.) are larger and show distinctive surface
irregularities (short protuberances and irregular striations,
respectively). The size and form of these filaments are most
like rhizines of soil-crust lichens. Other evidence of life on
land includes quilted spheroids (Erytholus globosus gen. et sp.
nov.) and thallose impressions (Farghera sp. indet.), which
may have been slime moulds and lichens, respectively. These
distinctive fossils in Cambrian palaeosols represent communities comparable with modern biological soil crusts.
Abstract: Red calcareous Middle Cambrian palaeosols from
the upper Moodlatana Formation in the eastern Flinders
Ranges of South Australia formed in well-drained subhumid
floodplains and include a variety of problematic fossils. The
fossils are preserved like trace fossil endichnia but do not
appear to be traces of burrows or other animal movement.
They are here regarded as remains of sessile organisms, comparable with fungi or plants living in place, and are formally
named as palaeobotanical form genera under provisions of
the International Code of Botanical Nomenclature. Most
common are slender (0.5–2 mm) branching filaments flanked
by green-grey reduction haloes within the red matrix of palaeosol surface horizons (Prasinema gracile gen. et sp. nov.).
Key words: Cambrian, South Australia, palaeosol, fungus,
slime mould, lichen.
B iol ogical soil crusts in the distant geological past
have long been suspected because of dispersed spores
(Gray 1981; Strother 2000), abundance of pedogenic clay
(Kennedy et al. 2006), unusually deeply weathered composition of Cambrian sandstones (Dott 2003), carbon isotopic composition of palaeosols (Watanabe et al. 2000)
and microbially textured bedding planes (Prave 2002).
Middle Cambrian microbial filaments (Southgate 1986)
and lichen-like fossils (Fleming and Rigby 1972; Müller
and Hinz 1992; Retallack 1994) from phosphorites of
western Queensland are in sedimentary facies with evidence of exposure within tidal flats and rock platforms
(Southgate 1986), but such marine-influenced communities are not directly comparable with biological soil crusts
of modern deserts. Unlike grey marine cherts and phosphorites with permineralized fossils or grey shales with
carbonaceous compressions, Silurian to Quaternary red
oxidized palaeosols seldom preserve cellular detail of carbonaceous fossils, so efficient is recycling in well-drained
soils (Retallack 1998). Nevertheless, post-Silurian oxidized
palaeosols commonly preserve impressions of leaves,
stems and roots, often with drab mottling from biochemical reduction of buried organic matter (Retallack 1997c).
Problematic megafossil traces of life on dry land now
come from numerous green-red-mottled palaeosols in the
Middle Cambrian, Moodlatana Formation of the Flinders
Ranges, South Australia (Text-figs 1–3). The Cambrian
palaeosols described here predate the evolution of land
plants but nevertheless contain three distinct kinds of
enigmatic megafossils: (1) drab-haloed filament traces
(Prasinema gen. nov.), (2) quilted spheroids (Erytholus
gen. nov) and (3) thalloid impressions (Farghera sp. indet.). Although the biological affinities of these fossils
remain uncertain, they provide new guides to the appearance of Cambrian life on land.
Formal naming of fossils aids future investigation and
wide recognition, as demonstrated by other problematic
fossils. For example, Vendobionta were informally noted
by Mawson (1938, p. 259) as ‘fossil impressions resembling brachiopod or bivalve form’, but formal description
of five species by Sprigg (1947) was needed before their
global distribution and importance as Ediacaran fossils
could be appreciated (Fedonkin et al. 2007). The various
fossils in Cambrian palaeosols formally named here are
preserved as bedding disruptions comparable with some
kinds of trace fossil (endichnia of Martinsson 1970) but
lack backfills, sequential prints or shapes recording movement or behaviour of motile organisms. Each of the different fossil genera described here is preserved in a
different way, but all appear to have been remains of
sessile organisms such as fungi, lichens, algae or plants in
place of growth. Thus, the nomenclatural system
ª The Palaeontological Association
doi: 10.1111/j.1475-4983.2011.01099.x
1223
1224
PALAEONTOLOGY, VOLUME 54
T E X T - F I G . 1 . Geological map and
fossil locality on Ten Mile Creek, South
Australia.
appropriate to these fossils is not that of ichnofossils in
the International Code of Zoological Nomenclature
(Häntzschel 1975; Ride et al. 1999) but rather of palaeobotanical form genera in the International Code of Botanical Nomenclature (McNeill et al. 2006). Form genera
such as Thallites (Walton 1923) and Algites (Seward
1894), for example, are used for fossils with the distinctive
dichotomizing form of algal, liverwort or lichen thalli, but
whose exact systematic affinities are uncertain, because
histological and reproductive structures are not preserved.
strom
atolitic
GEOLOGICAL SETTING
All fossils reported here were collected from a large exposure of the upper Moodlatana and lower Balcoracana Formation, within a prominent anticline, north of the big
bend in Ten Mile Creek, six miles west of the road to
Martins Wells, on Wirrealpa Station, South Australia
(3125¢N, 13894¢E). These palaeosols are early Middle
Cambrian in age, immediately above upper Moodlatana
Formation grey shales with the trilobite Onaraspis rubra
limes
tone
Mindi palaeosol
Natala palaeosol
Viparri palaeosol
A
hammer
B
T E X T - F I G . 2 . Selected fossiliferous palaeosols (A) and distinctive features (B) of the fossil locality in the uppermost Moodlatana
Formation in cliffs flanking Ten Mile Creek, South Australia. The stromatolitic limestone marker here is the base of the Balcoracana
Formation. For other palaeosols, see Retallack (2008).
RETALLACK: CAMBRIAN PALAEOSOL FOSSILS
1225
T E X T - F I G . 3 . Field sketch of three successive palaeosols, including those yielding fossils described here (upper two only), Middle
Cambrian, uppermost Moodlatana Formation, Ten Mile Creek, South Australia. The palaeosols are at 3602 m in Ten Mile Creek
section and measured palaeochannels from 3557 and 3561 m, in the next outcrop to the south and west.
(Jago et al. 2006), equivalent to the Oryctocephalus indicus
zone (Gradstein et al. 2004). At 3602 m in the composite
section in Ten Mile Creek, these palaeosols are 508.8 Ma
old in the age model of Retallack (2008).
Unlike thin marine dolomites and shales of the Moodlatana and overlying Balcoracana Formations (Moore 1990),
the fossiliferous palaeosols represent dry land in terms of
both soil drainage and palaeoclimate (Table 1). Pervasive
cracking, haematite, loess-like grain-size distribution and
low FeO content of red parts of the palaeosols (Table 2)
are evidence of well-drained soils of floodplains and supratidal flats. Crack orientation orthogonal to fluvial palaeochannels (Text-fig. 3) is characteristic of gilgai microrelief
of Vertisols (Paton 1974). Nodules of gypsum and micritic, low magnesium calcite at shallow depths within the palaeosols are evidence of semiarid to subhumid Middle
Cambrian palaeoclimate. Different kinds of palaeosols
(pedotypes) have been interpreted to represent different
local conditions (Retallack 2008), ranging from intertidal
to fluvial (Table 1). The Irkili pedotype for example has
much relict bedding, including flaser and linsen bedding,
and prominent calcite geodes after gypsum crystals, as in
soils of supratidal flats. The Natala and Viparri pedotypes
in contrast have extensively disrupted bedding and subsurface caliche nodules (Text-fig. 3) of floodplain soils. The
Mindi pedotype is intermediate between these extremes,
with small subsurface gypsum crystals and some persistent
bedding, and is interpreted as a high supratidal palaeosol
(by Retallack 2008). All the fossils described here are from
only three (Mindi, Natala and Viparri) of seven pedotypes
known in the upper Moodlatana Formation (Table 1).
Both Natala and Viparri pedotypes have a calcic horizon
deeper than usual for the Moodlatana Formation and represent a time of subhumid, rather than semi-arid climate,
immediately before marine transgression of the basal Balcoracana Formation (Retallack 2008).
The fossils described here are surprisingly large and
plentiful for what would be expected in Cambrian palaeosols (Retallack 2008), and the question may be raised
whether they represent biological activity after the Cambrian. They do not appear to be products of modern
weathering, Cenozoic lateritization or Permian glacial
landscapes because found in deep boreholes: Prasinema is
common at 1493–1504 feet, Farghera at 1498–1500 feet in
Lake Frome no. 2 core and Prasinema at 2089–2090 feet in
Lake Frome no. 3 cores archived in the Primary Industries
Not relevant
Thick
Viparri
Red clay
Big
Natala
Warru
Net
Mindi
Wandara Sand
Salt
Irkili
Thin green mottles (A)
in red shale
Green mottles (A) over red shale
with chalcedony geodes (By)
Grey-red-mottled siltstone (A)
Ash
Imba
Time for formation
Palaeotopography
Former biota
Palaeoclimate
Pedotype Adnamatna Diagnosis
name
meaning
Palaeosol pedotypes in the Middle Cambrian, Moodlatana Formation, Ten Mile Creek, South Australia.
TABLE 1.
Fluvial microbial mat,
Supratidal-alluvial
5–10 years
with Prasinema gracilis,
mud flat
Arid (100–300 MAP),
Intertidal microbial mat,
Supratidal and alluvial 10–200 years
high evapotranspiration
with Prasinema gracilis,
mud flat
Not relevant
Polsterland, with Prasinema gracilis, Supratidal mud flat
5–10 years
Erytholus rotundus and
Farghera sp. indet.
Red siltstone (A) over deep (>50 cm)
Subhumid (500–800 mm MAP) Polsterland, with Prasinema gracilis, Low alluvial terrace
500–2000 years
calcareous nodules (Bk)
P. nodulosa, P. fascicularis
and floodplain
Red siltstone (A) with pseudo-anticlinal Subhumid (500–800 mm MAP), Polsterland, with
Low alluvial terrace
500–2000 years
sandy layers over deep (>50 cm)
with marked dry season
Farghera sp. indet.
and floodplain
calcareous nodules (Bk)
Ferruginized sandstone (A)
Not relevant
Polsterland, with
Alluvial levee and
5–10 years
Prasinema gracilis,
point bar
Red clayey siltstone (A) over shallow
Not relevant
Polsterland, with Prasinema gracilis, Supratidal sand flat
500–1000 years
(<50 cm) calcareous nodules (Bk)
PALAEONTOLOGY, VOLUME 54
1226
and Resources South Australia (PIRSA) core library at
Glenside, a suburb of Adelaide. In outcrop, these fossils
can be found more than a metre back from the surface
within rock that has organic matter reflectance and claymineral illitization of lower greenschist facies of regional
metamorphism (Retallack 2008). All the fossils are in
strata-concordant, dipping layers, traceable laterally for
about 50 m and at an angle to modern soils and landscapes. The red palaeosols with fossils are also interbedded
with unweathered black shales and stromatolitic limestones (Text-fig. 2). These fossils are an integral part of
Cambrian soil structures and horizons (Retallack 2008).
MATERIALS AND METHODS
Fieldwork in South Australia in 2003, 2006 and 2007
included measurement of stratigraphic sections, azimuths
from trough cross-beds and palaeosol crack orientations
using a Brunton compass, spacing of fossils using a
milliners tape and dimensions of fossils using a digital
callipers. Samples were thin-sectioned for petrographic
observations and analysed for major element composition
and iron valence state using XRF and potassium dichromate titration (respectively), by ALS Chemex of Vancouver (Canada), against Canada granodioritic stream gravel
standard SDMS-2. Fossil specimens are housed in collections of the South Australian Museum, Adelaide.
SYSTEMATIC PALAEONTOLOGY
Kingdom INCERTAE SEDIS
Form genus PRASINEMA gen. nov.
Text-figures 4D–F, 5B, C, 6A–D, 8B–F
Type species. Prasinema gracile sp. nov.
Derivation of name. Elided from Greek prasinos (green) and
nema (neuter, thread).
Diagnosis. Network of fine (<2 mm diameter) filamentous green-grey, sediment-filled, irregular tubes, radiating
and decreasing in abundance downward from a sedimentary surface, clear grey-green reduction haloes around
the filaments contrast with red sedimentary matrix;
unbranched or branching at irregular intervals and angles,
without distinct orders of branch thickness.
Taphonomy. Networks of drab-haloed filaments are common at
the surface of both Mindi and Natala pedotype palaeosols (Textfigs 2A, 3), which were probably Aquepts and Calcids, respectively (Retallack 2008) in the US soil taxonomy (Soil Survey
RETALLACK: CAMBRIAN PALAEOSOL FOSSILS
TABLE 2.
1227
XRF chemical analyses of red and green samples (weight per cent).
Pedotype Hue
Hoz Spem SiO2
Al2O3 Fe2O3 FeO CaO
Natala
Natala
Mindi
Mindi
A
Bw
A
C
12.97
12.78
12.26
10.25
0.825
Green
Red
Green
Red
R3315
R3316
R3333
R3334
Error
54.12
52.37
48.51
41.19
2.705
3.57
3.68
2.87
2.41
0.395
MgO Na2O K2O
1.60 4.64 5.6
1.67 5.19 6.06
1.73 6.94 7.33
1.47 10.51 8.91
n.d. 0.22 0.175
1.16
1.05
0.85
0.75
0.105
4.07
4.06
3.9
3.27
0.125
TiO2 MnO P2O5 SrO BaO LOI
Total
0.68
0.68
0.56
0.48
0.06
98.8
98.91
99.16
98.1
0.06
0.06
0.07
0.09
0.025
0.16
0.14
0.12
0.11
0.035
0.01
0.01
0.01
0.01
n.d.
0.05
0.05
0.05
0.04
n.d.
10.1
11.1
13.95
18.6
0.353
Error is from 10 analyses in same laboratory (ALS-Chemex, Vancouver, BC, Canada) and standard (BC Canada granodioritic stream
gravel SDMS-2).
Staff 2000). These palaeosols also include green-grey horizons
and planar features coating soil structure (Text-fig. 5B), but
Prasinema is only applied to tubular, ellipsoidal or elongate
structures of irregular form (Text-figs 4D, 6A). Drab-haloed filament traces are especially clear in horizons between the entirely
drab surface and red subsurface horizons. These structures grew
through the soil, dilating and disrupting primary bedding under
low (not deep burial) confining pressures (Text-fig. 6C). A central filament <2 mm in diameter is filled with yellow-green claystone with sharp contacts to green-grey matrix extending
outwards to a diffuse contact with red matrix (Text-figs 4C, 5B,
6A–D). Both green-grey halo and red matrix have the same silty
petrographic texture, but the filament fill is slightly more silty
(Text-fig. 6A–D). Furthermore, the green-grey claystone is not
much different in total iron content than the red claystone,
though richer in ferrous iron (Table 2), unlike comparable redoximorphic features in Mesoproterozoic (Driese et al. 1995)
and Cenozoic gleyed palaeosols (Retallack 1983; Retallack et al.
2000). The green-grey matrix is thus a chemically reduced alteration halo, produced largely during closed-system diagenesis,
rather than during open-system gleization in a waterlogged soil,
or during introduction of contrasting material before burial
(Retallack 2001a). Alteration during burial also is supported by
correlation of central filament diameter with halo diameter, generally similar to that known from drab-haloed root traces of
trees in Devonian and younger palaeosols (Table 3; Retallack
1997a). Filament traces are more like fine root traces than large
woody large root traces in scaling closer to surface area (2pr in
two dimensions of cross sections measured) than to volume (pr2
also in cross section: Text-fig. 7).
Cambrian drab haloes are very similar to Devonian and younger root traces, referable to the form species Radicites erraticus
(Arafiev and Naugolnykh 1998), and thought to have formed
through gleization of iron oxides and hydroxides by dysaerobic
microbes consuming remnant soil organic matter shortly after
burial (Retallack et al. 2000). The drab-haloed filaments have
top-down gleization like that of surface-water gley, rather than
bottom-up gleization of groundwater gley (Retallack 2001a).
Surface-water gley is unlikely because grain-size distributions of
Cambrian palaeosols failed to detect any fine-grained or cemented impermeable horizon (Retallack 2008) that would perch
water table. The most likely explanation is formation of gleyed
haloes during microbial consumption of organic matter immediately after burial of the palaeosol and relative rise of water table
in a subsiding floodplain. By this view, drab-haloed filaments
represent the last crop of the palaeosol before burial, but red fil-
amentous structures of comparable size (Text-fig. 4D) represent
organisms that died and decayed within the oxidizing environment of the original soil.
Comparisons. The palaeobotanical form genus Radicites (Potonie
1893) includes root traces of tracheophytes (Arafiev and Naugolnykh 1998; Yakimenko et al. 2004) and differs from Prasinema
in larger size and branches of distinct orders of thickness.
Drab-haloed root traces such as Radicites erraticus (Text-fig. 7)
are much more widespread than indicated by Arafiev and
Naugolnykh (1998) and Yakimenko et al. (2004) and have a continuous fossil record in Silurian and younger palaeosols (Table 3).
Radiculites (Lignier 1906) is a fossil root with permineralized
xylem and Rhadix (Fritsch 1908) a dubiofossil (Arafiev and
Naugolnykh 1998), both much stouter than Prasinema.
Also generally similar to Prasinema are drab filaments from
palaeosols of the 1.8 Ga Lochness Formation, near Mt Isa,
Queensland (Driese et al. 1995), which differ in having much
less total iron in the drab than red palaeosol matrix, and haloes
of local iron enrichment. Comparable Cenozoic drab-haloed pedotubles with iron–manganese bands have been interpreted as
root traces of plants adapted to seasonally waterlogged palaeosols, which lost ferrous iron to groundwater (Retallack 1983).
Unnamed tubular Precambrian fossils with green-grey haloes in
red quartzites from the 2.0 Ga Medicine Peak Quartzite of Wyoming are described as stouter and more bluntly ending than
Prasinema (by Kauffman and Steidtmann 1981).
Biological affinities. Prasinema was a large organism for Cambrian palaeosols, with filaments extending as much as 30 cm
down into palaeosols and interconnected into larger networks.
Thin sections (Text-fig. 6) betray no evidence for biomineralization in Prasinema. The taphonomic model for these and other
drab-haloed tubular structures (Retallack et al. 2000) proposes
that the filaments were made of organic carbon compounds,
later consumed as fuel for biological reducing power to create
the drab haloes. Furthermore, the log-normal (negatively
skewed) size distribution of both Prasinema and Radicites diameters is evidence of indeterminate growth, as has been argued for
other fossils comparable with colonial animals, plants and fungi
(Peterson et al. 2003).
Biological soil crusts contain a variety of unskeletonized
organisms comparable in size, structure and growth with Prasinema: adventitious roots of grasses and other herbaceous
tracheophytes, rhizoids of liverworts or mosses, bundles of filamentous cyanobacteria (Microcoleus), fungal hyphal bundles or
PALAEONTOLOGY, VOLUME 54
1228
A
B
C
F
E
D
G
H
J
I
T E X T - F I G . 4 . Interpretative sketches of problematic fossils from palaeosols of the Middle Cambrian upper Moodlatana Formation,
Ten Mile Creek, South Australia.
RETALLACK: CAMBRIAN PALAEOSOL FOSSILS
red
1229
green
A horizon
green
1 cm
C horizon
red
A
1 cm
C
D
1 cm
E
green
yellow
B
red
1 cm
F
1 cm
A, Problematic megafossils from a Mindi palaeosol (see also Text-fig. 2A). B, Prasinema gracile gen. et sp. nov.,
holotype, South Australian Museum, specimen number P42257. C, Prasinema nodosum gen et sp. nov., South Australian Museum,
specimen number P42340a. D–F. Erytholus globosus gen. et sp. nov. South Australian Museum, in slab (D, specimen number P42255),
exposed exterior (E, specimen number P42256) and naturally broken open (F, specimen number P42255).
TEXT-FIG. 5.
lichen rhizines (Belnap and Lange 2003). Roots or rhizoids are
unlikely because longer and shorter, respectively, and also forming a sharper boundary with soil matrix than apparent in thin
section (Text-fig. 6A–D). Incorporation of soil matrix within the
central tubular hole within the drab halo is more like bundles of
cyanobacteria and fungal hyphae. A hyphal origin is most likely
considering the deep reach (30 cm) of these structures within
the palaeosols, well beyond the surficial zone of light penetration, because taphonomic evidence for burial gleization discussed above is an indication that drab-haloed Prasinema is the
current crop of organic structures, as in comparable drab-haloed
root traces (Retallack et al. 2001). Very similar structures to
Prasinema are hyphal bundles of non-lichenized fungi, such as
the bootstrap fungus (Armillaria mellea: Mihail and Bruhn 2005)
and rhizines of Ascolichens and Basidolichens, especially placoid
forms (Vogel 1955; Poelt and Baumgärtner 1964). These two
alternatives cannot be distinguished on morphological grounds,
although primary productivity of Cambrian palaeosols lacking
embryophytic plants would be unlikely to support such abundant hyphae of non-lichenized fungi.
Prasinema gracile sp. nov.
Text-figures 4D, 5B, 6A, B, 8D, E
Holotype. Near-vertical specimen, concertina-shaped from burial
compaction in the centre of the saw slab (P42257; left-hand side;
Text-fig. 4D; right-hand side; Text-fig. 5B), from the type Mindi
1230
A
C
E
PALAEONTOLOGY, VOLUME 54
0.5 mm
0.5 mm
0.5 mm
B
D
F
0.5 mm
0.5 mm
0.5 mm
T E X T - F I G . 6 . Petrographic thin sections all cut vertical to bedding. A, B, Prasinema gracile gen. et sp. nov. from type Mindi
palaeosol. C, D, P. nodosum sp. nov. from type Mindi palaeosol. E, Farghera sp. indet. from the type Natala palaeosol. F, Erytholus
globosus gen. et sp. nov. from the type Mindi palaeosol.
palaeosol, upper Moodlatana Formation, at the big bend in Ten
Mile Creek, South Australia (3125¢N, 13894¢E).
Other localities. This is the most abundant fossil in Cambrian palaeosols of South Australia and is found in almost all outcrops and
drillcore of the Parachilna, Billy Creek, Moodlatana and Balcoracana Formations, and in some outcrops of the Pantapinna and
Grindstone Range Sandstones. Prasinema gracile thus ranges in
geological age from earliest Cambrian perhaps to Early Ordovician
in the Flinders Ranges of South Australia (Retallack 2008).
RETALLACK: CAMBRIAN PALAEOSOL FOSSILS
TABLE 3.
1231
Additional occurrences of Radicites erraticus (drab-haloed root traces).
Location
Formation
Age
Ma
References
Dominion Range, Antarctica
Khaur, Pakistan
Khaur, Pakistan
Nyakach, Kenya
Khaur, Pakistan
Majiwa, Kenya
Khaur, Pakistan
Rusinga Island, Kenya
Puente Centenario, Panama
Rusinga Island, Kenya
Songhor, Kenya
Koru, Kenya
Painted Hills, OR, USA
Badlands NP, SD, USA
Clarno, OR, USA
Clarno, OR, USA
Landslide Butte, MT, USA
Russell, Kansas, USA
Kanapolis, KS, USA
Dinosaur, CO, USA
Petrified Forest NP, AZ, USA
Long Reef, NSW, Australia
Mt Rosenwald, Antarctica
Mt Boyd, Antarctica
Bethulie, South Africa
Lootsberg Pass, South Africa
Bethulie, South Africa
Lootsberg Pass, South Africa
Tekloof Pass, South Africa
Kiama, NSW, Australia
Loyal, OK, USA
Beaufort West, South Africa
Purcell, OK, USA
Seymour, TX, USA
Manitou, OK, USA
Lake Kemp, TX, USA
Kadane Corners, TX, USA
Byars, OK, USA
Nocona, TX, USA
Manhatten, KS, USA
Archer City, TX, USA
Gateway, CO, USA
Marietta, OH, USA
Drake, MO, USA
Unadilla, NY, USA
Mt Crean, Antarctica
Caldey Island, Wales, UK
Palmerton, PA, USA
Danville, PA, USA
Meyer Desert Formation
Dhok Pathan Formation
Chinji Formation
Nyakach Formation
Kamlial Formation
Maboko Formation
Murree Formation
Hiwegi Formation
Cucharacha Formation
Kiahera Formation
Kapurtay Agglomerate
Koru Formation
John Day Formation
Chadron Formation
John Day Formation
Clarno Formation
Two Medicine Formation
Dakota Formation
Dakota Formation
Morrison Formation
Petrified Forest Formation
Bald Hill Claystone
Fremouw Formation
Fremouw Formation
Katberg Formation
Katberg Formation
Balfour Formation
Balfour Formation
Tekloof Formation
Gerringong Volcanics
Flowerpot Shale
Abrahamskraal Formation
Hennessey Formation
Clear Fork Group
Garber Formation
Waggoner Ranch Format.
Petrolia Formation
Stillwater Formation
Nocona Formation
Blue Rapids Shale
Archer City Formation
Cutler Formation
Marietta Sandstone
Cheltenham Formation
Oneonta Formation
Azrtec Silstone
Moor Cliffs Formation
Bloomsburg Formation
Bloomsburg Formation
Pliocene
Late Miocene
Late Miocene
Middle Miocene
Early Miocene
Middle Miocene
Early Miocene
Early Miocene
Early Miocene
Early Miocene
Early Miocene
Early Miocene
Early Oligocene
Late Eocene
Late Eocene
Late Eocene
Late Cretaceous
Late Cretaceous
Late Cretaceous
Late Jurassic
Late Triassic
Early Triassic
Early Triassic
Early Triassic
Early Triassic
Early Triassic
Late Permian
Late Permian
Late Permian
Middle Permian
Middle Permian
Middle Permian
Middle Permian
Early Permian
Early Permian
Early Permian
Early Permian
Early Permian
Early Permian
Early Permian
Early Permian
Early Permian
Early Permian
Pennsylvanian
Late Devonian
Middle Devonian
Early Devonian
Late Silurian
Late Silurian
3.5
8
12
14
15
15
17
18
18
19
20
20
33
35
43
45
72
94
96
150
216
245
246
246
251
251
253
253
254
261
264
266
268
277
280
282
285
290
291
296
296
297
298
308
376
387
414
419
421
Retallack et al. (2001)
Retallack (1991)
Retallack (1991)
Wynn and Retallack (2001)
Retallack (1991, 1997b)
Retallack et al. (2002)
Retallack (1991)
Retallack et al. (1995)
Retallack and Kirby (2007)
Bestland and Retallack (1993)
Retallack (1991)
Retallack (1991)
Retallack et al. (2000)
Retallack (1983)
Retallack et al. (2000)
Retallack et al. (2000)
Retallack (1997d)
Retallack and Dilcher (1981)
Retallack (1997c)
Retallack (1997d)
Retallack (1997d)
Retallack (1997a)
Retallack and Krull (1999)
Retallack and Krull (1999)
Retallack et al. (2003)
Retallack et al. (2003)
Retallack et al. (2003)
Retallack et al. (2003)
Retallack (2005)
Retallack (1999)
Retallack (2005)
Retallack (2005)
Retallack (2005)
Retallack (2005)
Retallack (2005)
Retallack (2005)
Retallack (2005)
Retallack (2005)
Retallack (2005)
Retallack (1997a)
Retallack (2005)
Retallack (1997a)
Retallack (1997a)
Retallack and Germán-Heins (1994)
Retallack (1997a)
Retallack (1997a)
Retallack (1997a)
Retallack (1992)
Retallack (1992)
Derivation of name. Latin gracilis meaning slender.
Diagnosis. Prasinema with fine (<1 mm) filaments,
flanked by a drab halo extending a comparable thickness
outward into reddish matrix; slender, striated and flexu-
ously bent; branching irregularly and sparsely, without
orders of branching; permeating rock matrix and destroying primary sedimentary structures with no clear preferred orientation.
1232
PALAEONTOLOGY, VOLUME 54
A
C
B
D
E
G
I
F
H
J
Dimensions. Mean diameters (±standard deviation, range) of
237 filaments from the Mindi palaeosol were 0.56 (±0.29, 0.03–
1.58) mm, and their haloes were 1.73 (±0.78, 0.43–5.80) mm
(Text-fig. 7). Comparable diameters of 430 filaments in the Natala palaeosol were 0.50 (±0.25, 0.12–2.13) mm, and their haloes
were 1.46 (±0.69, 0.47–7.12) mm.
Comparisons. These conspicuously drab-haloed tubular features
are relatively nondescript compared with other species of Prasinema with stouter (>2 mm) and less flexuous filaments (P. adunatum) and lateral thickenings (P. nodusum). Sparse and
irregular branching of Prasinema gracile, ramifying in all
directions through the rock, obscures primary sedimentary structures, which are prominent in beds abruptly overlying the palaeosol, and also lower in the palaeosol where Prasinema is sparse
(Text-fig. 5A).
Prasinema nodosum sp. nov.
T E X T - F I G . 7 . Size distributions and
scaling relationships in Prasinema gracilis
gen. et sp. nov. in Cambrian palaeosols,
Moodlatana Formation, South Australia
(A–D, K–O), compared with postCambrian drab-haloed root traces (E–J).
Halo widths are larger than filament or
root widths at their centre but show
close relationship. Size distributions are
skewed from normal (dashed lines
calculated for same mean and standard
deviation as the measurements). A–D,
drab-haloed filament traces in Cambrian
Mindi and Natala paleosols. E, F, drabhaloed root traces in Devonian, Bucktail
palaeosol in Oneonta Formation, near
Unadilla, New York, USA (Retallack
1997a). G, H, drab-haloed root traces in
Triassic, Long Reef palaeosol in Bald
Hill Claystone, Long Reef, New South
Wales (Retallack 1997a, c). I, J, drabhaloed root traces in Luca palaeosol,
Eocene, John Day Formation, Clarno,
Oregon, USA (Retallack et al. 2000).
Diagnosis. Prasinema with fine (<1 mm) filaments densely invested with outwardly directed emergences, varying
from globose to spinose in shape, and narrow green-grey
halo into red matrix; unbranched and straight; subvertical
preferred orientation.
Description. These fossils are rare, and their relationship with
the slender filaments is unclear. The spacing of emergences
ranges from tightly clustered (Text-fig. 4F) to well spaced (Textfig. 6D), so that it is conceivable that these are fertile or specialized segments of Prasinema gracile. Unlike P. gracile, which runs
in all directions in the rock, P. nodosum was only found near
vertical to bedding planes defining the tops and bottoms of
enclosing palaeosols. In thin section, they include drab-coloured
matrix comparable in texture with the red matrix, and so these
are interpreted as organisms in place of growth within the soil,
rather than parts of organisms protruding from and then onlapped by upbuilding soil.
Text-figures 4F, 5C, 6C–D, 8B, F
Holotype. Left-hand example illustrated (Text-figs 4F, 8B) in
specimen P42310 from Natala palaeosol in Ten Mile Creek.
Derivation of name. Latin nodosus meaning knotty.
Dimensions. Mean (±standard deviation, range, number of
measurements) include central filament diameter of 0.95 mm
(±0.05, 0.91–0.99, 2), external diameter of 2.51 mm (±0.56,
2.11–2.90, 2) mm and external thickening diameter of 0.72 mm
(±0.08, 0.61–0.91, 11) mm.
RETALLACK: CAMBRIAN PALAEOSOL FOSSILS
Comparisons. Middle Cambrian unnamed phosphatized tubes
with sharp lateral extensions from the Beetle Creek Formation at
Mt Murray, Queensland (Fleming and Rigby 1972), differ in
mode of preservation, are hollow with crushing indicative of
horizontal preservation and about twice the size of P. nodosum.
Nevertheless, both fossils have a striated or filamentous construction and lateral spines, which may reflect comparable biological affinities.
Less similar to Prasinema nodosum are other congeneric species, which either lack the outer thickenings (P. gracile) or are
much thicker (P. adunatum). Prasinema nodosum has a superficial resemblance to a spinose plant, such as the fossil moss Muscites guelescini (Anderson and Anderson 1985), the zosterophyll
Sawdonia ornata (Gensel 1991), or the putative alga Margaretia
dorus (Gunther and Gunther 1981), but unlike these does not
appear to have a finished cellular epidermis or cuticle. This same
objection also distinguishes Prasinema from problematica that
have been regarded as mosses or lycopsids, such as the Cambrian ‘Aldanophyton’ (probably junior synonym of Margaretia
according to Rozanov and Zhuravlev 1992), and Ordovician Akdalophyton (Snigirevskaya et al. 1992) and Boiophyton (Obhrel
1959). Like Prasinema, Mesoproterozoic Horodyskia moniliformis
is also found as grey-green markings within purple-red siltstones
(Fedonkin and Yochelson 2002; Martin 2004; Fedonkin et al.
2007, p. 33) but has the appearance of beads loosely strung on a
thread, rather than the clustered thickenings of Prasinema nodosum.
Prasinema adunatum sp. nov.
Text-figures 4E, 8C
Holotype. Single thick axis on specimen P42313 (Text-fig. 8C);
from the type Natala palaeosol in Ten Mile Creek.
Derivation of name. Latin adunatus meaning united.
Diagnosis. Prasinema of stout (2 mm) filaments, with a
striated appearance and irregular swellings and thinnings;
unbranched and subhorizontal in orientation.
Description. This axis runs oblique to relict bedding planes but
is closer to horizontal than vertical within the bounding surfaces
of the type Natala palaeosol. Branching of the axis was not seen,
nor is there any clear connection with closely associated filaments of Prasinema gracile. Like P. gracile, P. adunatum has a
similar sedimentary texture in both drab-coloured material and
surrounding red matrix.
Dimensions. The single specimen found ranged from 2.10 to
2.45 mm wide (mean 2.32 mm, standard deviation 0.18 mm).
Comparisons. Middle Cambrian phosphatized tubes (unnamed)
from the Beetle Creek Formation at Mt Murray, Queensland
(Fleming and Rigby 1972), are similar to P. adunatum in size,
longitudinal striation and sub-horizontal preservation but differ
in their prominent lateral spines. Prasinema adunatum differs
from both P. gracile and P. nodusm in larger diameter, which
1233
appears to be the result of numerous subparallel filaments of
comparable form. Cambrian marine algae such as Yuknessia simplex (Gunther and Gunther 1981) differ in showing dichotomous branching, cellular margins and preservation as organic
compression within bedding planes.
Form genus ERYTHOLUS gen. nov.
Text-figures 4G–I, 5D–F, 6F
Type species. Erytholus globosus sp. nov.
Derivation of name. Elided from Greek erythros (red) and tholos
(masculine, dome).
Diagnosis. Spheroidal sandy and silty structures, with
median vertical column and glide symmetry of 4–12 subhorizontal internal partitions; a thin axial thread within
the central column extends vertically above and below the
spheroid.
Taphonomy. These distinctive quilted spheroids within the type
Mindi palaeosol are comparable with trace fossil endichnia (of
Martinsson 1970), yet there is no evidence of animal movement.
They are entirely oxidized. Although surrounded and penetrated
by drab-haloed filaments of Prasinema gracile, there is no thickening, curvature or other accommodation of drab filaments suggestive of relationship between P. gracile and Erytholus globosus.
An axial thread seen in many specimens of E. globosus is always
red (Text-fig. 4G–J), never grey-green like Prasinema. Erytholus
can be observed in outcrop on vertical faces, and by cracking
open rock. Most specimens shatter through the middle to reveal
subhorizontal chambers (Text-figs 4G, I, 5F); very few expose
the strongly curved, thick walled, outer surface (Text-figs 4J,
5E). Internal quilting was not a bedded cavity fill or internal
mould (colloform illuviation argillan, of Retallack et al. 2000,
fig. 88), burrow backfill (Retallack 2001b) or internal chambering or backfill of a sediment-ingesting organism (Seilacher 1992;
Savazzi 2007), because it cannot have been moved within the
whole structure, as revealed by the following observations. In
one vertical face, two Erytholus were exposed by breaking open
the rock vertically and recording former orientation (Textfig. 5F). The upper smaller Erytholus has a more sandy upper
than lower zone, and the lower large one has a more clayey central zone, with sandy upper and lower portions. These lithological differences are seen also as beds in the immediately flanking
surrounding matrix. Thus, the internal organic quilt grew within
the sediment or was a hollow structure filled with sediment
increments, without moving sediment far from original layering,
as has been suggested for some Ediacaran fossils (Grazhdankin
and Seilacher 2002; Grazhdankin 2005). The taphonomic mode
of Erytholus can be interpreted in two distinct ways: (1) internal
mould or (2) sand skeleton. By the sand skeleton interpretation,
the organism grew within the sediment, but by the internal
mould interpretation, the chambered organism lived (and died?)
at the surface and was later infiltrated by increments of local
sediment.
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PALAEONTOLOGY, VOLUME 54
Comparison. When first discovered, Erytholus specimens were
suspected to be enrolled trilobites or aglaspids. However, thin
sections and sawn slabs (Text-figs 5D, 6F) revealed no exoskeletal remains, doublure, axial fold or limb impressions. The axial
column runs vertically through the middle of the structure and
is not curved around the periphery, as in an enrolled trilobite.
Other similar ovoid structures in red beds are Ediacaran fossils
with comparable gliding plane symmetry and quilting (Tojo
et al. 2007), such as Ernietta, Pambikalbae and Ventogyrus. Ernietta is hollow, rather than a three-dimensional internally layered
structure, with internal column and threads, and this hollow is
filled with white quartz sandstone distinct from the red siltstone
matrix (Dzik 1999). Pambikalbae has a central column and lateral chambers but is much larger (>29 cm long) and more elongate than Erytholus (Jenkins and Nedin 2007). Like Erytholus,
Pambikalbae is preserved in three dimensions within red sandstones. Ventogyrus is ovoid, with a central column and thread,
lateral threads and thick wall, but differs from Erytholus in its
distinct trigonal vertical divisions and is also larger (up to 6 cm
diameter and 12 cm long; Fedonkin and Ivantsov 2007).
However, Ventogyrus is preserved with central thread and column
vertical to bedding in red-mottled fine sandstones (Fedonkin
et al. 2007, pp. 142–145; D. Grazhdankin, pers. comm. 2008),
comparable with Erytholus in the Mindi palaeosol. These similarities of preservation and internal structure suggest that Erytholus
may be grouped with Pambikalbae and Ventogyrus within the
problematic group Vendobionta (Seilacher 1992, 2007).
Biological affinities. Fedonkin and Ivantsov (2007) regarded the
comparable vendobiont Ventogyrus as a siphonophore cnidarian
(comparable with the ‘bluebottle’, Physalia physalis), and Dzik
(2003) compares Ventogyrus with ctenophore cnidarians (‘comb
jellies’, such as Cestum veneris). Ctenophores are known as flattened impressions back at least as old as Early Cambrian, in the
Natala palaeosol
1 cm
A horizon
Bw horizon
B
red
green
C
D
1 cm
Bk horizon
surface cracks
Viparri palaeosol
E
G
A horizon
1 cm
1 cm
F
1 cm
I
1 cm
Bk horizon
A
hammer
H
1 cm
A, problematic megafossils from Natala and Viparri palaeosols. B, Prasinema nodosum gen. et sp. nov., holotype;
South Australian Museum, specimen number P42310. C, P. adunatum gen et sp. nov., holotype; South Australian Museum, specimen
number P42313. D, E, P. gracile sp. nov. from a Natala palaeosol; South Australian Museum, specimen numbers P42311 (D) and
P42312 (E). F, Prasinema nodosum gen. et sp. nov.; South Australian Museum, specimen number P42317. G–I, Farghera sp. indet.
from a Viparri palaeosol; South Australian Museum, specimen numbers 42315 (G), P42314 (H) and P42315 (I).
TEXT-FIG. 8.
RETALLACK: CAMBRIAN PALAEOSOL FOSSILS
Chengjiang fauna of China (Hou et al. 2004), so their fossil
record does not rest entirely on interpretation of controversial
vendobionts. Neither of these groups of hollow, flimsy, marine
organisms is a suitable explanation for fully inflated and littledeformed specimens of Erytholus in a palaeosol, filled with sediment preserving exterior bedding.
In contrast, Seilacher (2007; Seilacher et al. 2005) regards
vendobionts such as Dickinsonia and Palaeopascichnus as xenophyophores, comparable with the giant (up to 25 cm) Stannophyllum zonarium of deep marine sediments. An appealing aspect
of this interpretation is the included sediment (xenophyae), faeces (stercomare) and exudates (barite) within xenophyophores
(Levin 1994), comparable with observations of Erytholus in thin
section (Text-fig. 6F). However, xenophyophores have irregular
or meandrine chambers and lack internal organization of central
thread within a vertical column, and flanking chambers seen in
Erytholus. No xenophyophores are known in soil or nonmarine
settings. The fossil record of xenophyophores, other than controversial Vendobionta, is equally controversial: trace fossils
(Palaeodictyon and other graphoglyphid traces) no older than
Early Cambrian, and calcareous skeletonized forms (so called
‘phylloid algae’) no older than Carboniferous (Levin 1994).
Other plausible biological models for the whorled filamentous
construction of Erytholus are green algae, particularly Charales
known back to Early Devonian (Feist and Feist 1997), or Dasycladales such as Chaetocladus known back to Middle Ordovician
(Kenrick and Vinther 2006). Such algae are aquatic and not
known from palaeosols but could conceivably have been a part
of the aquatic parent material of the Mindi palaeosol, as in an
enigmatic calcite-filled axis from Ordovician red beds of the Juniata Formation in Pennsylvania (Retallack 2001b). This enigmatic fossil from Pennsylvania, like Charales and Dasycadales,
was a system of dichotomously branching tubes arranged in
whorls. In contrast, Erytholus is not constructed as a whorled
scaffolding but quilted from planar to filamentous partitions
without true whorling, and a glide symmetry of offset laterals.
Another possible biological model for Erytholus is a truffle,
meant here in the general sense of underground fungus, rather
than implying the commercial extant species Tuber melanosporum (Pezizales, Ascomycota). Truffle growth form evolved independently in several fungal lineages: Zygomycotina (pea truffles),
Ascomycota (true truffles), Basidiomycota (false truffles) and
Deuteromycota (anamorphous fungi: Bruns et al. 1989; Pegler
et al. 1993). Truffles have internal chambers in a variety of
patterns: radial, alveolar and spongy. Radial–bilateral chambers
most like Erytholus are known from Elaphomyces muricatus
(Elaphomycetales, Ascomycota: Pegler et al. 1993), but this lacks
a central column or thread. There is a possible Precambrian
fossil record of Ascomycota (Retallack 1994, 2007), ‘higher
fungi’ (Ascomycota + Basidiomycota: Butterfield 2005) and
Glomeromycota (Yuan et al. 2005), so that these Cambrian fossils would not be unusually old fungi. Nevertheless, all truffles
exclude sediment from their interior, and although it could infiltrate chambers of decayed examples, the abundant included sediment continuous with exterior grain-size variation makes truffles
an unlikely explanation for Erytholus.
A final possibility for Erytholus is a sporangium of a slime
mould (Myxomycota), traditionally regarded as related to fungi
1235
(as ‘myxomycetes’), but now regarded as more closely allied to
Amoebozoa (of Baldauf 2003). These creatures are generally dispersed in the soil as flagellated or amoeboid cells or as an irregularly shaped multinucleate plasmodium (Stephenson and Stempen
1994), but the stalked sporangia have a variety of internal structures similar to Erytholus. A reproductive rather than vegetative
organ is suggested by the near-normal distribution of sizes (Textfig. 9), unlike the skewed distribution of Prasinema (Text-fig. 7)
and other fossils of indeterminate growth (Peterson et al. 2003).
In the slime mould Physarum crateriforme, for example, the stalk
of the sporangium continues up within the spheroidal mass of
sporangia as a columella, which gives off a network of lateral filaments (capillitium) defining crude chambers within an outer thick
wall (peridium: Martin et al. 1983). Such structures release spores
into the air above the ground and, for Erytholus, would imply
growth from the soil surface, with later covering and infiltration
by increments of aeolian or waterlain silt. Such a gap in time for
decay of organic matter is compatible with the lack of drab haloes
around Erytholus, in contrast to the taphonomy of what are here
interpreted as freshly buried Prasinema. Putative slime mould
compression microfossils have been reported from the 1.025 Ga
Lakhanda Group of Siberia (Hermann and Podkovryov 2006),
and problematic trails of about the same age from the Chorhat
Sandstone of India may have been created by slime moulds (Conway Morris 2000), so neither Erytholus nor comparable Ediacaran
Ernietta, Ventogyrus, or Pambikalbae would be the oldest fossil
record of such organisms. Differences between Erytholus and slime
mould sporangia include an order of magnitude larger size and
continuation of the axial thread out the top of the structure.
Erytholus globosus sp. nov.
Text-figures 4G–I, 5D–F, 6F
Holotype. Large lower example of specimen P42255 (Textfig. 5D, F); from the type Mindi palaeosol in Ten Mile Creek
(top of specimen was marked by a black circle coplanar with the
ancient land surface).
Derivation of name. Latin globosus meaning spherical.
Diagnosis. Erytholus 5–20 mm in diameter, with 4–12
stacked internal layers divided by a wide (4–6 mm) vertical column.
Description. Erytholus spheroids are smooth or sparsely ridged
when cracked out of the rock in exterior view, but, in cross section, show an irregular system of subhorizontal chambers filled
with red claystone and white sandstone. The chambers have the
general appearance of bilateral symmetry around a central column but, in detail, are not entirely symmetrical, with horizontal
quilting at slightly different levels and chamber margins turning
either up or down at the margins (Text-fig. 4). The chambers
are also ill-defined by ferruginized claystone (Text-fig. 6F). The
chamber floors are deflected where they meet the central column, but a narrow tubular structure within that extends both
above and below the structure for an undetermined distance.
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PALAEONTOLOGY, VOLUME 54
The size distribution of Erytholus, and the number and size of
its chambers are near normal (Text-fig. 9A–D). Burial compaction has rendered them slightly oblate, on average, so that width
is generally greater than height (Text-fig. 9E). Chamber thickness
does not vary with overall width except in the smallest specimens,
but this relationship does not have the statistical significance
expected of growth relationships of metazoans (Text-fig. 9F).
The distribution of Erytholus within the type Mindi palaeosol
is highly variable, from barely a centimetre apart (Text-fig. 5F)
to more than a metre. Average spacing of 78 specimens seen in
outcrop along 62 m strike length of the Mindi palaeosol was
1.19 ⁄ m. All were in the upper 20 cm of the palaeosol, which has
relict bedding indicative of a cumulic A horizon (Retallack
2008), and thus supportive of a taphonomic model of a surface
hollow structure filled by increments of sediment.
Dimensions. Mean (±standard deviation, range) of 145 specimens of Erytholus globosus include horizontal diameter (coplanar
with bedding) of 13.09 mm (±4.82, 3.36–34.77), vertical dia
meter 10.25 mm (±3.65, 2.85–24.18), chamber height 1.53 mm
(±0.43, 0.46–2.57) and number of chambers 7.45 (±1.10, 5–12).
Localities. Most of the fossils of Erytholus globosus were found in
the type Mindi palaeosol in the uppermost Moodlatana Formation at 3602 m in the composite section in both Ten Mile
(3125¢S, 13894¢E) and Balcoracana Creeks (3118¢S, 13890¢E),
but others were seen at the Ten Mile Creek locality in the Irkili
palaeosol of the lower Balcoracana Formation at 3611 m.
Comparisons. Only one species of Erytholus is currently recognized.
Form genus FARGHERA Retallack, 2009
Farghera sp. indet.
Text-figures 4A–C, 6E, 8G–I
Description. Viparri palaeosols have disrupted surficial sandy
layers and deep cracks oriented orthogonal to palaeochannel
direction (Text-fig. 3) like those of modern swelling clay soils, or
Vertisols (Soil Survey Staff 2000). These light-coloured sandstone
stringers give good contrast between thin structures filled with
red clay and with regular dichotomous branches radiating from a
centre, spreading upward at low angles to relict bedding (Textfigs 4A–C, 6E, 8G–I). These specimens were examined under an
environmental scanning electron microscope (FEI QANTA capable of forming an image without coating), and only clay was seen,
with no histological details. Thin section examination confirms
that these are impressions filled with clayey sediment and have
shelf-like or tubular extensions (Text-fig. 6E).
Dimensions. Mean width (±standard deviation, range) of 500
specimens of Farghera sp. indet. is 1.78 mm (±0.58, 0.53–3.68,
see Text-fig. 10).
Taphonomy. The preservational style of these dichotomizing
fossils is identical with plant impressions preserved in red
palaeosols in growth position, such as leaves of Evolsonia from
the Permian of Texas (Mamay 1989) and Sanmiguelia from the
Triassic of Colorado (Tidwell et al. 1977). Lack of histological
details rules out the taphonomic model of Spicer (1977) in
which a replica of the leaf surface is made by predepositional
ferric oxide coatings fuelled by microbial decay. This latter
T E X T - F I G . 9 . Measurements of Erytholus globosus gen. et sp. nov. in a Mindi palaeosol, showing width in plane of bedding (A),
thickness vertical to bedding (B), chamber thickness vertical to bedding (C), number of chambers in vertical stack (D), isometric
growth in width to thickness relationship (E), and indeterminate growth relationship of chamber addition (F).
RETALLACK: CAMBRIAN PALAEOSOL FOSSILS
1237
irregular branching (Retallack 2009). The only species of Farghera
known so far is F. robusta, which has rounded thallus terminations about half the width of these specimens from the Viparri
palaeosol. Viparri specimens are more fragmented and also represent a larger thallus of more wrinkled form. The broad thallus
may be an indication of a more mesophytic form than F. robusta
known from sandy Entisol palaeosols (Upi pedotype associated
with Adla and Matarra Aridosols) of drier climate than Vertisols
(Viparri of Retallack 2008). This material is a different species
than Farghera robusta, but detailed characterization will have to
wait discovery of more complete and informative material.
T E X T - F I G . 1 0 . Width measurements of 500 Farghera sp.
indet. in a Viparri palaeosol. The dashed line is a computed
normal curve with the same mean and standard deviation as the
measurements: the data are normally distributed.
model applies best to Cretaceous Araliaephyllum leaves from
swales of seasonally waterlogged palaeosols in sandy levees in the
Dakota Formation of Kansas (Retallack and Dilcher 1981). Viparri palaeosols in contrast show cracking patterns and orientations suggestive of well-drained soils (Text-fig. 3).
Comparisons. Impressions and compressions of dichotomously
branching thalli are commonly assigned to the form genera Thallites (Walton, 1923) and Algites (Seward, 1894), but Farghera differs from both form genera in its rhizine-like structures scattered
along the margins of the thallus, and occasional monopodial and
Biological affinities. Comparable dichotomizing thalli are found
in liverworts such as Marchantia (Smith 1990) and algae such as
Fucus and Dictyota (Graham and Wilcox 2000), but these lack
the rhizine-like extensions characteristic of Farghera (Retallack
2009). The Viparri thalli are comparable with foliose lichens
such as Xanthoparmelia reptans and Physcia caesia (Textfig. 11B). Small lichens of ground-hugging rosette growth habit
are common in biological soil crusts of modern deserts (Belknap
and Lange 2003). Farghera would not be the oldest known
lichen, because putative permineralized lichens are known from
the 0.6 Ga Doushantuo Formation of China (Paramecia among
others, as interpreted by Retallack 1994; unnamed crustose form
of Yuan et al. 2005) and also the 2.6 Ga Carbon Leader of the
Witwatersrand Group of South Africa (Thucomyces of Hallbauer
and Van Warmelo 1974; Hallbauer et al. 1977). Other fossil
lichens include Devonian crustose (Taylor et al. 2004) and foli-
1 cm
A
0.5 mm
B
hammer
C
1 mm
D
1 mm
E
T E X T - F I G . 1 1 . Modern organisms comparable with problematic Cambrian palaeosol megafossils: A, exterior and cutaway view of
the internally chambered sporangium of a slime mould (Myxomycota), Physarum crateriforme, Iowa, USA. B, crustose-thallose lichen
(Ascomycota) Physcia caesia, Painted Hills, Oregon, USA. C, placoid lichen with rhizomorphs (Ascomycota) Toninia sedifolia from the
Austrian alps. D, placoid lichen with rhizines (Basidiomycota) Endocarpon sp. indet., from the Namibian desert. E, biological soil
crust, 2 km west of fossil site in Billy Creek, South Australia. A is after Martin et al. (1983); C is after Poelt and Baumgärtner (1964);
D is after Vogel (1955): others original.
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PALAEONTOLOGY, VOLUME 54
T E X T - F I G . 1 2 . Reconstructed soil
biota and coastal-fluvial landscapes of
the Moodlatana Formation.
ose forms (Jurina and Krassilov 2002), Eocene microscopic
epiphyllous forms (Sherwood-Pike 1985) and Oligocene fragments in amber (Poinar 1992).
CONCLUSIONS
Biological soil crust is a term introduced by Belnap and
Lange (2003) because such desert vegetation includes
microbes (cyanobacteria and algae), microbial fruiting
bodies (mushrooms and slime moulds), vascular
cryptogams (lycopsids and ferns) and nonvascular plants
(mosses and liverworts). Such wide definition of biologi-
cal soil crusts thus includes (1) microbial earths, recognized by stromatolitic and other microbial textures, (2)
polsterlands, recognized by discrete megascopic nonvascular forms, and (3) brakelands, recognized by megascopic
herbaceous vascular plants other than grasses (Retallack
1992). Cambrian polsterlands are thus indicated by this
paper, which reports three problematic kinds of megascopic remains comparable with those of lichen thalli and
rhizines, and slime mould fruiting bodies from Cambrian
palaeosols (Text-fig. 11). Weathering, carbon sequestration and landscape stabilization under modern polsterlands are modest compared with those under vascular
RETALLACK: CAMBRIAN PALAEOSOL FOSSILS
land plants, but far from negligible (Retallack 1992), as
indicated also by petrographic and geochemical study of
Cambrian palaeosols (Retallack 2008).
Lack of water, heat and essential nutrients is an important limit to productivity of modern biological soil crusts
in deserts, but they thrive also in warm-wet regions until
outcompeted by other plant communities (Belnap and
Lange 2003), such as brakelands dating only back to Early
Silurian and woodlands dating back to Middle Devonian
(Retallack 1992). An important limit to life on land on the
early Earth was ultraviolet light, especially before about
2 Ga when oxygen levels were less than 0.1 times modern
level, too low to create a significant ozone layer (Kasting
1987). Drab-haloed filament traces in red oxidized soils
comparable with those reported here have been described
(though not interpreted as biological soil crusts) from the
1.8 Ga Lochness Formation of western Queensland (Driese
et al. 1995). Even with significant ultraviolet radiation, life
could survive within soil at levels where hard radiation was
filtered by overlying transparent grains (Sagan and Pollack
1974), so that the antiquity of drab-haloed root traces or
other evidence of life in palaeosols may not be a reliable
guide to past variation in Earth-surface ultraviolet radiation.
In summary, a long suspected fossil record of polsterlands in pre-Devonian rocks now includes a variety of
megafossils in surface horizons of moderately developed
Cambrian palaeosols representing stable land surfaces
of floodplains and supratidal flats (Text-fig. 12). These
megafossils include drab haloes around filamentous structures, chambered spheroids and thalloid impressions.
Comparable structures may be widely overlooked in preDevonian red beds, and this account provides search
images, a taxonomic framework and an introduction to
their interpretation.
Acknowledgements. Pauline Coulthard offered advice on aboriginal sacred sites, and Barbara and Warren Fargher graciously gave
permissions for fieldwork on Wirrealpa Station. Research was
funded by the Petroleum Research Fund of the American Chemical Society, and fieldwork aided by Christine Metzger.
Editor. Lyall Anderson
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