Trace fossils in the Ediacaran–Cambrian transition: Behavioral diversification, ecological turnover and environmental shift

Abstract

After taxonomic revision, trace fossils show a similarly explosive diversification in the Ediacaran–Cambrian transition as metazoan body fossils. In shallow-marine deposits of Ediacaran age, trace fossils are horizontal, simple and rare, and display feeding strategies related to exploitation of microbial matgrounds. Equally notable is the absence of arthropod tracks and sinusoidal nematode trails. This situation changed in the Early Cambrian, when a dramatic increase in the diversity of distinct ichnotaxa is associated was followed by the onset of vertical bioturbation and the disappearance of a matground-based ecology (‘‘agronomic revolution’’). On deep sea bottoms, animals have been present already in the Ediacaran, but ichnofaunas were poorly diverse and dominated by the horizontal burrows of undermat miners. As shown by the ichnogenus Oldhamia, this life style continued to be predominant into the Early, and to a lesser extent, Middle Cambrian. Nevertheless, there was an explosive radiation of behavioral programs during the Early Cambrian. When exactly the bioturbational revolution arrived in the deep sea is uncertain. In any case, the Nereites ichnofacies was firmly established in the Early Ordovician. The rich ichnofauna in the Early Cambrian Guachos Formation of northwest Argentina probably marks a first step in this ecological onshore–offshore shift.

Full text

Trace fossils in the Ediacaran–Cambrian transition: Behavioral
diversification, ecological turnover and environmental shift
Adolf Seilacher
a
, Luis A. Buatois
b,
*, M. Gabriela Ma´ngano
b
a
Geologisches Institut, Sigwartstasse 10, D 72076 Tu¨bingen, Germany, and Department of Geology, Yale University,
P.O. Box 208109, New Haven, CT 06520, USA
b
Department of Geological Sciences, University of Saskatchewan, 114 Science Place, Saskatoon, Canada SK S7N 5E2
Received 12 November 2004; received in revised form 30 May 2005; accepted 3 June 2005
Abstract
After taxonomic revision, trace fossils show a similarly explosive diversification in the Ediacaran–Cambrian transition as
metazoan body fossils. In shallow-marine deposits of Ediacaran age, trace fossils are horizontal, simple and rare, and display
feeding strategies related to exploitation of microbial matgrounds. Equally notable is the absence of arthropod tracks and
sinusoidal nematode trails. This situation changed in the Early Cambrian, when a dramatic increase in the diversity of distinct
ichnotaxa is associated was followed by the onset of vertical bioturbation and the disappearance of a matground-based ecology
(ddagronomic revolutionTT). On deep sea bottoms, animals have been present already in the Ediacaran, but ichnofaunas were
poorly diverse and dominated by the horizontal burrows of undermat miners. As shown by the ichnogenus Oldhamia, this life
style continued to be predominant into the Early, and to a lesser extent, Middle Cambrian. Nevertheless, there was an explosive
radiation of behavioral programs during the Early Cambrian. When exactly the bioturbational revolution arrived in the deep sea is
uncertain. In any case, the Nereites ichnofacies was firmly established in the Early Ordovician. The rich ichnofauna in the Early
Cambrian Guachos Formation of northwest Argentina probably marks a first step in this ecological onshore–offshore shift.
D2005 Elsevier B.V. All rights reserved.
Keywords: Ediacaran–Cambrian; Ichnology; Microbial mats; Diversification
1. Introduction
Difficulties to analyze the ichnologic record of the
Ediacaran–Cambrian transition result from the tapho-
nomic filter biogenic structures passed through, but
also from taxonomic idiosyncrasies contained in pub-
lished data. The latter bias applies particularly to
Proterozoic trace fossils, whose rarity and antiquity
raise the tendency to describe and name specimens
that would otherwise pass as non-descript or be sim-
ply referred to as Planolites or Palaeophycus-like
structures. In the present paper we critically review
the ichnofauna of the Ediacaran shallow-marine biota
0031-0182/$ - see front matter D2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.palaeo.2005.06.003
* Corresponding author. Tel.: +1 306 966 5730.
E-mail addresses: geodolf@tuebingen.netsurf.de (A. Seilacher),
luis.buatois@usask.ca (L.A. Buatois), gabriela.mangano@usask.ca
(M. Gabriela Ma´ngano).
Palaeogeography, Palaeoclimatology, Palaeoecology 227 (2005) 323 – 356
www.elsevier.com/locate/palaeo

and then discuss the development of deep-water ich-
nocoenoses in the Ediacaran and Early Cambrian,
with new data from North Carolina (USA) and north-
west Argentina. Subsequently, we raise the question
of when the Cambrian agronomic revolution (Seila-
cher and Pflu¨ ger, 1994) reached the deep sea. Finally,
the taxonomy of some Ediacaran–Cambrian trace fos-
sils is addressed in the light of new discoveries and
reanalysis of selected specimens.
2. Ediacaran shallow-marine trace fossils
While an earlier compilation (Crimes, 1994) lists 35
ichnogenera for the Ediacaran period, this number
shrinks considerably in view of recent revisions (Gehl-
ing et al., 2000; Jensen, 2003; Seilacher et al., 2003).
In addition, some members of the Ediacaran ichno-
fauna (Yelovichnus,Palaeopascichnus,Intrites and
Harlaniella) are no longer considered trace fossils.
2.1. Pseudofossils
The ubiquity of biomats on Precambrian sea bot-
toms accounts for certain sedimentary structures that
are rare in later deposits (Seilacher and Pflu¨ ger, 1994;
Seilacher, 1997). Sinusoidal shrinkage cracks
(ddmanchuriophycusTT) and small-scale load casts
(belephant-skin structuresQ), as well as various wrinkle
patterns (e.g., bchloephycusQ,bkinneyiaQ), are now
generally recognized as pseudofossils (Pflu¨ger, 1995;
Hagadorn and Bottjer, 1999; Chakrabarti, 2001). In
Neoproterozoic and Cambrian rocks, some of these
structures have been repeatedly interpreted as trace
fossils. For example, sinusoidal synaeresis cracks
were referred to as Cochlichnus (e.g., Kulkarni and
Borkar, 1996), while elephant skin structures and wrin-
kle marks have been confused with Protopaleodictyon
(e.g., Durand and Acen˜olaza, 1990) and Squamodict-
yon (Durand et al., 1994) (see Chakrabarti, 2001 and
Buatois and Ma´ngano, 2003a, for reinterpretations).
Vertical burrows in shallow-marine Ediacaran
deposits, typically assigned to Skolithos or, less com-
monly, to Arenicolites and Monocraterion, are doubt-
ful (cf. Jensen, 2003). Supposedly vertical burrows
described by Banks (1970) from Finnmark were sub-
sequently reinterpreted as dewatering pillars (Farmer
et al., 1992). Structures from Namibia assigned to
Skolithos by Crimes and Germs (1982) have been
subsequently considered as body fossils (Crimes and
Fedonkin, 1996). Specimens from the Carolina slate
belt, assigned by Gibson (1989) to Monocraterion?
isp. are in all probability inorganic, most likely soft-
sediment deformation structures. The origin of Sko-
lithos declinatus Fedonkin from the White Sea
(Fedonkin, 1985) is still uncertain. In short, no un-
doubted examples of vertical burrows have been
documented from the Ediacaran.
2.2. Xenophyophorean protozoa
Xenophyophorea is a group of giant rhizopods hav-
ing flexible, agglutinated chambers. Today they are
restricted to abyssal depths (Tendal, 1972). It has
been suggested that Ediacaran representatives still
inhabited shallow seas and were embedded in biomats
(Seilacher et al., 2003). This life style highly increased
their fossilization potential. On the other hand, these
structures may be easily mistaken for trace fossils,
because in producing their chamber walls, these
protists actively moved sand grains into the under-
lying mud layer just as a tracemaker would do (Fig.
1). Thus, the tightly packed chambers of Palaeopas-
cichnus delicatus Palij, P. sinuosus Fedonkin and
Yelovichnus gracilis Fedonkin were originally inter-
preted as meandering traces (Glaessner, 1969;
Fedonkin, 1985; Crimes and Fedonkin, 1994),
while chains of globular chambers (Neonereites renar-
ius Fedonkin, N. biserialis Seilacher and Intrites punc-
tatus Fedonkin) have been compared to backstuffed
burrows. More recently, however, they have been
regarded as body fossils (Haines, 2000; Gehling et
al., 2000; Seilacher et al., 2003; Jensen, 2003), because
both kinds do branch, which would be impossible in
trace fossils of seemingly similar morphologies. Re-
examination of some of the supposedly meandering
trails (e.g., Palaeopascichnus) also fails to reveal the
presence of actual meanders.
In the same vein, Jensen (2003) questioned the trace
fossil interpretation of Harlaniella podolica Sokolov
(see also Palij, 1976). Harlaniella confusa Signor
described by Signor (1994) is most likely also a
body fossil. A third morphotype of Ediacaran xeno-
phyophoreans consists of an agglomerate of chambers,
from which agglutinated tubules radiate into the sur-
rounding sediment. Forms corresponding to this group
A. Seilacher et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 227 (2005) 323–356324

Fig. 1. Xenophyophoreans on modern deep-sea bottoms and their Ediacaran shallow-marine counterparts. Palaeopascichnus, previously
regarded as a meandering trace fossil, is now regarded as a protist body fossil. In the same vein, chains of globular chambers currently ascribed
to Neonereites in Ediacaran rocks, are also considered protist body fossils (after Seilacher et al., 2003).
A. Seilacher et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 227 (2005) 323–356 325

(Eoporpita, Hiemalora) have been described as chon-
drophore colonies; so their re-interpretation does not
affect the number of Ediacaran trace fossils.
2.3. Poorly defined ichnotaxa
As trace fossils are more variable and poorer in
distinctive characters than most body fossils, their tax-
onomy is also more subjective. Names appearing in the
literature should therefore be properly checked before
they can be treated as reliable data. In many cases, it
turns out that identification was based on superficial
similarities that fall into the preservational and behav-
ioral variability of a few general ichnogenera.
Ecologically Ediacaran ichnofaunas are dominated
by poorly specialized grazing trails that tend to devel-
op indistinct patterns, such as Gordia,Helminthoi-
dichnites and Helminthopsis. As noted by Jensen
(2003), all these ichnotaxa represent horizontal move-
ment through the sediment in search for food and
there are no convincing examples of true branching.
Simple grazing trails that are occasionally parallel to
each other have been mistaken for the bilobate trace
Didymaulichnus (Bordonaro et al., 1992).
A slab from the Flinders Ranges (Seilacher et al.,
2003,Fig. 4) shows various grooves that may be
referred to as Helminthoidichnites. Although they
fail to show a distinct behavioral program, they nev-
ertheless contain relevant ecological information. As
indicated by an associated trilobozoan body fossil
(Tribrachidium), the trails are preserved on a sole
face that probably corresponds to a matground.
Being preserved as hypichnial grooves, they must
either result from undermat mining (below the level
of Tribrachidium) or have been produced after depo-
sition of the overlying sand (probably a thin storm
bed) by an animal that avoided the sponge-like Tri-
brachidium. As turns may be relatively sharp, one
may also conclude that the tracemaker was either a
very flexible worm or a shorter animal with a small
turning radius. Yet, none of this information would be
contained in the ichnogenus name and may be over-
looked in an analysis based solely on trace fossil lists.
2.4. Nenoxites and Torrowangea
These ichnogenera show distinctive features in
addition to their winding course. Nenoxites curvus
Fedonkin (Fig. 2) is based on a single specimen
from the Winter Coast of the White Sea (Fedonkin,
1985). In schematic drawings (Crimes, 1987), it is
commonly depicted as a segmented angular meander.
Fig. 2. Nenoxites curvus. Segmentation reflects a wall lining made of elongate fecal pellets oriented perpendicularly to the burrow axis.
Ediacaran, White Sea, Russia.
A. Seilacher et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 227 (2005) 323–356326

Re-study of the original specimen suggests, however,
that the turns are not as sharp and that the segmenta-
tion reflects a wall lining made of elongate fecal
pellets oriented perpendicularly to the burrow axis
(Fig. 2) (see also Fedonkin, 1985).
A somewhat similar form is Torrowangea rosei
Webby described by Webby (1970) from New South
Wales and subsequently documented from other Edia-
caran to Early Cambrian shallow-to deep-marine suc-
cessions (Hofmann, 1981; Narbonne and Aitken,
1990; Paczes
´na, 1986). This ichnotaxon consists of
horizontal, sinuous to irregularly meandering traces
characterized by distinct, but irregularly spaced con-
strictions. It is most likely a feeding trace of deposit
feeding annelids that burrowed peristaltically (Nar-
bonne and Aitken, 1990).
2.5. Bilobate trails
Bilobate trails have been commonly recorded
from Lower Cambrian strata, but very rarely from
the Ediacaran (Seilacher, 1956; Palij et al., 1979;
Fedonkin, 1985; Crimes, 1987; Paczes
´na, 1996; Jen-
sen et al., 2002). Those displaying a regularly to
irregularly meandering or spiral course and preserved
as positive epireliefs have been variously referred to
as Aulichnites,Taphrhelminthopsis,Taphrhel-
minthoida,Scolicia and, more rarely, Sellaulichnus,
Jinningichnus and Multilaqueichnus (Crimes et al.,
1977; Fedonkin, 1985; Crimes and Jiang, 1986;
Crimes, 1987; Hofmann and Patel, 1989; Jenkins,
1995; Zhu, 1997; Li et al., 1997; Hagadorn et al.,
2000; Acen˜olaza and Alonso, 2001). Zhu (1997)
reanalyzed the type specimens of Sellaulichnus
meishucunensis Jiang in Jiang et al. and noted that
the burrows show branching and that the bilobed
morphology may have resulted from collapse. Fur-
ther study is necessary to evaluate if true branching
occurs in this ichnotaxon. Re-examination of the
type specimen of Aulichnites parkerensis Fenton
and Fenton indicates that this ichnogenus is a junior
synonym of Psammichnites (D’Alessandro and
Bromley, 1987; Ma´ ngano et al., 2002). An alterna-
tive name for some of these bilobate traces (which
are much simpler than the younger Psammichnites)
is Archaeonassa (Jensen, 2003). Archaeonassa is a
monospecific ichnogenus that includes straight to
sinuous or gently meandering traces having a median
groove flanked by rounded ridges (Fenton and Fen-
ton, 1937; Yochelson and Fedonkin, 1997). Howev-
er, the ichnotaxonomic status of Archaeonassa is still
uncertain (Ma´ngano and Buatois, 2003). These trails
were probably made by a mollusk-like bilateral an-
imal that bulldozed along bedding planes or buried
biomats by displacing sediment along the sides of its
body from the front into a terminal backfill. Sell-
aulichnus and Multilaqueichnus show similarities to
what is usually called Taphrhelminthopsis.Taphrhel-
minthoida and Taphrhelminthopsis have been recur-
rently mentioned in Lower Cambrian rocks. In
particular, the ichnospecies Taphrhelminthopsis cir-
cularis Crimes et al. and Taphrhelminthoida dailyi
Hofmann and Patel seem to be typical of Lower
Cambrian strata (Crimes et al., 1977; Crimes,
1987; Hofmann and Patel, 1989). However, Seila-
cher (1986) and Uchman (1995) demonstrated that
the type specimens of Taphrhelminthopsis and
Taphrhelminthoida are preservational variants of
Scolicia, which is produced by spatangoid echinoids.
Spatangoid traces are complex endichnial structures
characterized by a meniscate backfill, a double ven-
tral fecal string or drain, and mucus-lined vertical
shafts (Bromley and Asgaard, 1975; Plaziat and
Mahmoudi, 1988; Bromley, 1996). Scolicia occurs
in Mesozoic and Cenozoic strata, while Paleozoic
recordings should be transferred to other ichnogenera
(Smith and Crimes, 1983; Uchman, 1995; Seilacher-
Drexler and Seilacher, 1999; Ma´ngano et al., 2002).
Additionally, it should be noted that post-Paleozoic
Taphrhelminthopsis and Taphrhelminthoida are pre-
served as positive hyporeliefs (not positive epireliefs;
see Schlirf, 2002, for discussion), recording a search
strategy that is similar to that of Psammichnites
rather than Scolicia.
Ediacaran trails consisting of two parallel furrows
preserved as negative epireliefs have been described
as Bilinichnus simplex Fedonkin and Palij (Palij et al.,
1979). As noted by Keighley and Pickerill (1996) and
Buatois et al. (1998a), this is a problematic form. Its
mode of formation is difficult to explain, assuming
that no metazoans bearing hard parts (i.e. arthropods)
were available (Keighley and Pickerill, 1996). Bili-
nichnus was also regarded as a gastropod trail pro-
duced by peristaltic crawling (Fedonkin, 1985).
Although it has been tentatively synonymized with
Diplopodichnus (Buatois et al., 1998a), a mode of
A. Seilacher et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 227 (2005) 323–356 327

origin similar to that of Diplopodichnus from conti-
nental settings is hard to envisage. Furthermore, speci-
mens illustrated as Bilinichnus simplex by Fedonkin
(1994) closely resemble Archaeonassa.
Though common in the Cambrian, bilobate traces
preserved as hypichnial ridges are very rare, if present
at all, in Ediacaran strata. Bilobate hyporeliefs have
been commonly referred to as Didymaulichnus,
among other names. Didymaulichnus includes smooth
bilobate hypichnial ridges. Its presence in Ediacaran
strata is dubious; in fact one of its ichnospecies, D.
miettensis Young, has been regarded as indicative of
the Early Cambrian (Young, 1972; Crimes, 1987;
Walter et al., 1989).
2.6. Mawsonites
Mawsonites is a problematic Ediacaran taxon that
was originally described as a jellyfish (M. spriggi)by
Glaessner and Wade (1966). The jellyfish interpreta-
tion was maintained in a subsequent study in which an
additional species, M. randellensis, was proposed
based on three fragmentary specimens (Sun, 1986).
More specifically, Runnegar (1992a) regarded Maw-
sonites as a partly decayed medusa. An alternative
interpretation was proposed by Seilacher (1989), who
considered Mawsonites as a trace fossil consisting of a
relatively large system of actively backfilled probings,
and a vertical shaft with lateral seleniform backfill.
Most probably, however, Mawsonites is a pseudofos-
sil like ddAstropolithonTT, i.e. a sand-volcano interact-
ing with biomats (Fig. 3). Alignment of the ddprobesTT
along radial cracks is the main argument for this
interpretation, which also allows for the lateral back
fill.
2.7. Aulozoon
bAulozoonQis an informal name for large fossils
that look like flattened sand-filled sausages about 2
Fig. 3. Drawing of Mawsonites, which is reinterpreted as a sand-volcano interacting with biomats.
A. Seilacher et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 227 (2005) 323–356328

cm wide and only 1–2 mm thick. They were originally
referred to as large sinuous trails (Glaessner, 1969,
Fig. 5E). As such flattening could hardly be compac-
tional, Seilacher et al. (2003) assumed that they are
trace fossils of a large flatworm. In this interpretation,
the structures were first lined with mucus and then
backfilled with the sand removed in front of the
animal and transported along the body by ciliary
waves as on a conveyor belt. Living cnidarians and
platyhelminths have been suggested as modern analo-
gues of Neoproterozoic tracemakers (Collins et al.,
2000).
This view is supported by a large slab (Fig. 4)
(see also Runnegar, 1992b, Fig. 3.10). Elephant-
skin structures suggest that we deal with the sole
of a sandy biomat. Uniformly sized vendobionts
(Phyllozoon) were living below the mat and are
therefore perfectly preserved in their original
bhuggingQpositions. Dickinsonia, in contrast, lived
solitarily on top, where it could use its limited
mobility (Fedonkin, 1992) to digest new areas of
the living mat. Accordingly, Dickinsonia specimens
are preserved only as vague phantoms pressed
through the mat by compaction (Gehling, personal
communication 2003).
In the trace fossil interpretation (Seilacher et al.,
2003), while bulldozing along the base of the
biomat, the Aulozoon producer reacts upon colli-
sion with an undermat Phyllozoon in specific ways.
If approaching it at a low angle, the animal con-
tours the vendobiont and turns away, while colli-
sions at larger angles are avoided by passing either
above or below the Pyllozoon. In contrast, Aulo-
zoon does not react to the Dickinsonia phantoms.
However, Aulozoon departs from the typical style
of Ediacaran trace fossils being a conspicuous
structure, significantly larger than unquestionable
trails. For the moment, Aulozoon should be treated
as a problematic form. The study of additional
slabs may eventually point to an alternative inter-
pretation as a body fossil (Gehling, written com-
munication 2004).
Fig. 4. Drawing of a basal surface with Phyllozoon (death masks), Dickinsonia (phantom preservation) and Aulozoon (sand-filled ribbons).
Ediacaran, Flinders Ranges, Australia (after Seilacher et al., 2003,Fig. 5).
A. Seilacher et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 227 (2005) 323–356 329

2.8. Dickinsoniid resting trails
Resting and locomotion traces of Dickinsonia and
the related genus Yorgia have been recorded in Edia-
caran shallow-marine deposits of the White Sea
(Ivantsov and Malakhovskaya, 2003;Fedonkin,
2003) and Australia (Gehling, unpublished). In the
White Sea, the presence of body fossils in direct
association with the trace fossils allows identification
of the producers, namely Yorgia waggoneri Ivantsov
and Dickinsonia tenuis Glaessner and Wade (Ivantsov
and Malakhovskaya, 2003). In addition, similarities in
shape and size between the resting trace and the body
fossil allow linking a third type of trace with Dick-
insonia costata Sprigg, although the two have not
been found in direct connection. In contrast to dick-
insoniid body fossils, which are preserved as negative
hyporeliefs, trace fossils are preserved as positive
hyporeliefs. As noted by Fedonkin (2003), the produ-
cers glided over the sea bottom during short pulses of
locomotion that alternated with long resting phases
associated with intense mucus production. These find-
ings are remarkable because they documentat for the
first time trace fossils produced by vendobionts.
2.9. Radulichnus
This is one of the few Ediacaran trace fossils that
was made from above the sediment surface. Originally
considered as scratch marks of trilobite legs (Mono-
morphichnus;Jenkins, 1995), these are clearly
scratches rasped by paired radular teeth (Gehling et
al., unpublished). More exactly, their producer was the
bsoft limpetQKimberella (see Fedonkin and Wagg-
oner, 1997), whose ventral death masks are commonly
associated (Fig. 5) and have occasionally been found
in flagranti in the White Sea area (Fedonkin, 2003).
In contrast to later radula traces, the paired scratches
of the Ediacaran form are arranged not in meanders,
but in fans whose tips are always missing. As Gehling
concluded (personal communication 2001), Kimber-
ella did not move-on while it was browsing, but used
a long proboscis that swung out more widely the
further it extended away from the stationary body.
Equally unusual is the preservation of the radular
scratches. In the Mesozoic and Cenozoic, Radulich-
nus is preserved only on hard surfaces, such as mol-
lusk shells, while scratches made on soft substrates
became wiped-out as the producer bulldozed over
them. Only when the surface was indurated by
tough biomats could they escape such fate. This was
certainly the case of Ediacaran sea bottoms and of
very shallow Cambrian deposits in Saudi Arabia (Sei-
lacher, 1977) and China (Dornbos et al., 2004). This
also explains why only the raspings of adult Kimber-
ella are preserved: the radulae of smaller individuals
did not penetrate deep enough to appear as under-
traces at the base of the mat. Nor did Kimberella leave
a trail when it moved from one station to the next.
2.10. Treptichnus and supposed Chondrites
Treptichnus is typically Phanerozoic, with the first
appearance of Treptichnus pedum (Seilacher)
regarded as index of the Precambrian–Cambrian
boundary (Brasier et al., 1994; Narbonne et al.,
1987). However, in South Australia (Jensen et al.,
1998), Namibia (Jensen et al., 2000) and Newfound-
land (Gehling et al., 2001), Treptichnus may occur in
strata that still contain Ediacaran body fossils and it
certainly persisted into the Ordovician (Fig. 6). In
any case, branched, three-dimensional burrow sys-
tems indicating shallow-tier bioturbation, were al-
ready present by the end of the Neoproterozoic.
Chondrites has also been mentioned in Ediacaran
strata (e.g., Jenkins, 1995). However, these structures
are preserved as furrows that lack the characteristic
burrow fill. They have been reinterpreted as poorly
preserved specimens of the body fossil Hiemalora
(Narbonne, personal communication 2002).
2.11. Plug-shaped burrows
Plug-shaped burrows, preserved as positive hypor-
eliefs, are regarded as resting or dwelling traces of
cerianthid or actinarian anemones (Pemberton et al.,
1988). Although Ediacaran examples, commonly in-
cluded in Bergaueria, have been recorded in a few
localities (e.g., Crimes and Germs, 1982; Fedonkin,
1985), distinction from body fossils, such as Intrites ,
Beltanellifomis and Beltanelloides, is problematic
(Crimes, 1992; Crimes and Fedonkin, 1996; Jensen,
2003). However, specimens from Canada described
by Narbonne and Hofmann (1987) and Seilacher et
al. (2003) display the typical morphology of plug-
shaped burrows and includes a series of overlapping
A. Seilacher et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 227 (2005) 323–356330

discs. Therefore, these structures, included in Ber-
gaueria sucta, reveal the lateral displacement of an
anemone-like animal. Plug-shaped burrows, howev-
er, are much more abundant since the Cambrian
(Crimes and Anderson, 1985; Crimes and Fedonkin,
1996).
2.12. Final remarks on shallow-marine Ediacaran
ichnodiversity
In conclusion, Ediacaran trace fossils have a much
lower numerical diversity than it appears from the
literature. They are also less common than in younger
rocks. Behavioral complexity is limited as well: ex-
cept for the burrow systems of Treptichnus and the
scratches of Radulichnus, there are no systematic
search patterns. Equally notable is the absence of
tracks or trails of larger arthropods, or of sinusoidal
nematode trails, which could well be preserved and
easily recognized. Even small benthic arthropods ap-
pear to have been absent, because they would likely
have destroyed the biomats and produced a flocculent
surface layer (Waloszek, 2003).
This situation changes dramatically in the Early
Cambrian, when not only the number of recogniz-
able taxa, but also their behavioral and tiering com-
plexity reaches much higher levels. Since shallow-
marine ichnocoenoses from the Lower Cambrian
have been well described (e.g., Jensen, 1997), we
focus here on another problem: the conquest of deep
sea bottoms.
3. Trace fossils from Ediacaran and lowermost
Cambrian deep sea deposits
Deep-sea deposits are characterized by thick se-
quences of laminated mudstones and coarser-grained
Fig. 5. The primitive mollusk Kimberella as the tracemaker of the radular scratches Radulichnus. Originally considered as scratch marks
of trilobite appendages, these are regarded here as scratches rasped by paired radular teeth. Note that the scratches of smaller individuals
did not penetrate deep enough to produce undertraces at the base of the biomats. Ediacaran, White Sea, Russia (after Seilacher et al.,
2003).
A. Seilacher et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 227 (2005) 323–356 331

turbidites and the absence of wave-induced struc-
tures (e.g., oscillation ripples; hummocky cross strat-
ification). For the present study two areas have been
chosen, where thick deep-marine turbiditic succes-
sions are exposed: the Albemarle Group of the
Carolina slate belt in eastern United States and the
Fig. 6. Stratigraphic distribution of Treptichnus pedum in Ediacaran to Ordovician rocks.
A. Seilacher et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 227 (2005) 323–356332

Puncoviscana Formation, northwest Argentina. Be-
cause of intense tectonic deformation, lithologic uni-
formity, and scarcity of guide fossils, these
successions are difficult to subdivide. Nevertheless,
a Neoproterozoic age is established for the Albe-
marle Group by a handful of Ediacaran body fossils
(Pteridinium carolinense Gibson et al. (Gibson et
al., 1984). The Puncoviscana Formation is regarded
as Ediacaran to Early Cambrian. This age is based
on stratigraphic relations with the overlying upper
Lower to Middle Cambrian Meson Group, trace
fossils and radiometric dates (see Ma´ngano and
Buatois, 2004a; Buatois and Ma´ngano, 2005). The
ichnofossiliferous strata are considered Nemakit–
Daldynian in age (Buatois and Ma´ngano, 2003a).
3.1. Ediacaran deep-marine ichnofaunas
The ichnology of the Albemarle Group was first
analyzed by Gibson (1989). Re-study of this ich-
nofauna suggests a number of taxonomic reassess-
ments. In particular, the Floyd Church Member of
the McManus Formation contains a poorly diverse
assemblage consisting of Circulichnis montanus
Vyalov (=?Gordia arcuata Ksia˛ykiewicz of Gibson,
1989), Helminthoidichnites tenuis Fitch [=Planolites
beverleyensis (Billings) and Planolites montanus
Richter of Gibson, 1989], ?Helminthopsis isp., Old-
hamia recta isp. n. (=Syringomorpha nilssoni?of
Gibson, 1989) and Treptichnus? isp. (=?Neonereites
isp. of Gibson, 1989). Other forms described from
this unit are here considered as dubious. The ich-
nofauna is dominated by nondiagnostic and poorly
specialized grazing trails (Helminthopsis ichnoguild
of Buatois and Ma´ngano, 2003b), that also occur
in shallow-marine environments of the same age.
Oldhamia recta (see taxonomic Appendix) made by
a small undermat miner and preserved in positive as
well as negative hyporeliefs, is so far the only dis-
tinctive ichnospecies. These early pioneers had no
obvious ancestry in shallow-marine realms.
Ediacaran deep-marine ichnofaunas have also been
recorded from the Mackenzie Mountains in Canada
(Narbonne and Aitken, 1990; MacNaughton et al.,
2000) and central Spain (Vidal et al., 1994). Nonspe-
cialized grazing trails similar to those from the McMa-
nus Formation were recorded in both cases. Structures
indicative of microbial mats were noted by Mac-
Naughton et al. (2000). As shown by these trace
fossils, deep-sea bottoms were colonized by benthic
animals already in Ediacaran times. However, behav-
ioral diversity, as well as the disparity of life styles,
remained very low. Colonization of deep sea bottoms
during the terminal Proterozoic is also supported by
the body fossil record (Narbonne, 1998, 2005; Nar-
bonne and Gehling, 2003; Clapham et al., 2003;
Grazhdankin, 2004).
3.2. Early Cambrian deep-marine ichnofaunas
The Puncoviscana Formation of northwest Argen-
tina provides a glimpse into the ecology of early
Phanerozoic deep-marine ecosystems. Puncoviscana
trace fossils were first described in the seventies
(Acen˜olaza and Durand, 1973) and have since been
the focus of a series of studies (e.g., Durand and
Acen˜olaza, 1990; Acen˜olaza et al., 1999a). More
recently, the composition and paleoenvironmental sig-
nificance of this ichnofauna and its importance for the
ecology of deep sea infaunal communities in the Early
Cambrian has been stressed (Buatois and Ma´ngano,
2003a,b, 2004). Deep-marine trace fossil assemblages
of the Puncoviscana Formation are present in the San
Antonio de los Cobres/Cuesta de Mun˜ano area (Salta
Province) and, further south, in the Sierra de la Ove-
jerı´a region of the Catamarca Province. This associa-
tion is dominated by the ichnogenus Oldhamia (O.
antiqua Forbes, O. flabellata Acen˜ olaza and Durand,
and O. radiata Forbes; see taxonomic Appendix and
Fig. 7), and grazing trails, such as Helminthoidich-
nites tenuis and Helminthopsis tenuis Ksia˛ ykiewicz.
Other components are Palaeophycus tubularis Hall,
Cochlichnus anguineus Hitchcock and Diplichnites
isp. (Fig. 8A) (Buatois and Ma´ngano, 2003b). Appar-
ently branching specimens of sinusoidal traces
(Cochlichnus-type) were also found (Fig. 8B). Most
of these trace fossils were emplaced in the uppermost
millimeters of a relatively firm substrate. Wrinkled
surfaces, ripple patches and palimpsest ripples sug-
gest the presence of microbial mats (Figs. 8A–B,
9A–B). Benthic communities developed in direct
association with these organically bound surfaces.
Their strategies included mat grazing and undermat
mining (Buatois and Ma´ngano, 2003b).
Similar Early to, more rarely, Middle Cambrian
deep-marine ichnofaunas (Oldhamia association) are
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known from folded rocks in Ireland, Belgium,
Alaska, Canada, United States and Morocco (For-
bes, 1849; Malaise, 1883; Sollas, 1900; Churkin
and Brabb, 1965; Crimes and Crossley, 1968; Dho-
nau and Holland, 1974; Hofmann and Cecile, 1981;
El Hassani and Willefert, 1990; Lindholm and
Casey, 1990; Sweet and Narbonne, 1993; Hofmann
et al., 1994; Holland, 2001). Contemporaneously
with shallower habitats, deep-sea ichnocoenoses expe-
rienced a burst in behavioral diversity. During the first
stage, however, this radiation was restricted to the
ichnogenus Oldhamia. It reached its climax by the
Early Cambrian, when various behavioral modifica-
tions are represented by distinct ichnospecies (Buatois
and Ma´ngano, 2003b). Oldhamia has rarely been re-
corded in shallow-marine facies (Crimes et al., 1977;
Kowalski, 1987; Goldring and Jensen, 1996; Buatois
and Ma´ngano, 2004). In deep-marine environments,
Fig. 8. Trace fossils associated with Oldhamia in the San Antonio
de los Cobres ichnofauna, Puncoviscana Formation, northwest
Argentina. A. Poorly preserved arthropod trackway. B. Branching
Cochlichnus. Field photos.
Fig. 7. Ichnospecies of Oldhamia made by unknown undermat miners. Note the explosive radiation of behavioral programs in the Early
Cambrian.
A. Seilacher et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 227 (2005) 323–356334

however, Oldhamia is always the dominant ich-
notaxon and occurs in relatively low-diversity assem-
blages, in contrast to shallow-marine settings where it
is only an accessory element of otherwise diverse
ichnocoenoses (Buatois and Ma´ngano, 2003b, 2004).
Within the Puncoviscana Formation, the Oldha-
mia-dominated association is in sharp contrast with
the ichnofaunas of the Guachos Formation in the
Sierra de Mojotoro area of Salta Province. This
facies, which can be conveniently studied in the
Los Guachos quarry or on sidewalks in the city of
Salta, displays a higher diversity of trace fossils and
more varied ethologic patterns (see Appendix and
Fig. 10). The Guachos facies consists of centimetric
flagstones of very fine-grained siltstone, which are
massive or laminated and continue laterally over
large distances. Their sharp erosional bases, graded
bedding, and rhythmic interbedding with mudstone
layers suggest sedimentation from distal turbidity cur-
rents. However, some of these beds contain com-
bined-flow ripples and ripple cross-lamination,
Fig. 9. Biomat structures from the Puncoviscana Formation, San
Antonio de los Cobres, Argentina. A. Chloeophycus. B. cf. Kin-
neyia. Field photos.
Fig. 10. The Guachos ichnofauna, Guachos Formation, northwest Argentina.
A. Seilacher et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 227 (2005) 323–356 335

suggesting deposition near to the slope break, rather
than in deep basinal settings (see also Omarini et al.,
1999).
3.3. Concluding remarks on Ediacaran and Early
Cambrian deep-marine ichnodiversity
On deep sea bottoms, benthic faunas were present
since the Ediacaran (Narbonne and Aitken, 1990;
MacNaughton et al., 2000; Crimes, 2001; Orr,
2001). In Ediacaran times, ichnofaunas were as yet
very simple. Cambrian deep sea ichnocoenoses are
richer, but they still differ from their younger equiva-
lents by being less diverse, lacking the typical ele-
ments of the Nereites ichnofacies, and containing
instead shallow-marine elements, such as arthropod
trackways (Orr, 2001). Ecologically, undermat miners
continue to dominate ichnocoenoses into the Early
Cambrian, with Oldhamia experiencing a remarkable
behavioral diversification. Regardless the taxonomic
relationships of their makers, Oldhamia ichnospecies
represent an ecologic guild that became rare after the
Cambrian agronomic revolution, particularly in shal-
low-marine environments (Seilacher and Pflu¨ ger,
1994). In this sense, the Oldhamia assemblage repre-
sents a Proterozoic bhangoverQin the deep sea (Buatois
and Ma´ngano, 2003b).
There is little doubt that the Oldhamia ichnospe-
cies stand for animals that differed at least at the
species level. Behavioral programs are too distinct
to be environmentally induced. Furthermore, different
ichnospecies are only very rarely associated on the
same bedding plane. In the Blow Me Down Brook
Formation of western Newfoundland, different Old-
hamia ichnospecies occur at different stratigraphic
levels (Lindholm and Casey, 1990). They can poten-
tially be used for biostratigraphic zonation.
4. Arrival of the Cambrian explosion at the deep
sea bottom
ddCambrian explosionTT means many things: (1) the
sudden radiation of metazoan phyla, following the
extinction (Vendobionts) or the retreat to the deep
sea environment (Xenophyophoreans) of the giant
protozoans that had been dominating shallow-marine
benthic biota in Ediacaran times (Seilacher et al.,
2003); (2) the emergence of mineralized skeletons in
unrelated animal phylla, and thereby (3) the beginning
of the ecological arm’s race and the increasing com-
plexity of trophic chains.
For the ichnologist, however, the most relevant
change was the bioturbational destruction of resistant
microbial mats that affected all benthic ecosystems
except the most hostile environments. Responsible
for this turnover (bagronomic revolutionQof Seila-
cher and Pflu¨ger, 1994;bCambrian substrate
revolutionQof Bottjer et al., 2000) were the many
kinds of infaunal animals that penetrated deeper into
the sediment and left distinctive trace fossils within
the sediment or along lithologic interfaces. Equally,
or even more important, was the activity of inters-
titial animals. While being too small (Waloszek,
2003) to leave behind recognizable trace fossils,
they transformed the uppermost millimeters of the
sediment from a resistant biomat into a soft and
fluffy mixed layer. While being no more suitable
for the attachment of sessile organisms, such sub-
strates facilitated diffusional exchanges between pore
and sea water.
The fact that the evolutionary burst affected trace
fossils as much as body fossils puts an end to the
notion that the Cambrian explosion only results from
the higher fossilization potential of mineralized ske-
letons. On the other hand, trace fossils can also be
used to track the proliferation of this event into deep-
sea environments, where mineralized skeletons are
less likely to be preserved.
While the agronomic revolution transformed shal-
low-marine environments already in the Tommotian–
Atdabanian, the precise timing of this event in the
deep sea is still uncertain. As previously discussed,
the Oldhamia ichnoguild was still rampant in the
deep sea during the Early Cambrian. It also seems to
have persisted into the Middle Cambrian, as sug-
gested by its presence in the uppermost strata of
the Grand Land Formation of arctic Canada (Hof-
mann et al., 1994) and in the Kerrn Nesrani Forma-
tion of Morocco (El Hassani and Willefert, 1990).
More importantly, Crimes (1976) documented ichno-
faunas from the Lower to Middle Cambrian Bray
Group of Ireland, where shallow-marine strata that
already contain abundant vertical burrows (Skolithos ,
Arenicolites) are followed by deep-marine deposits
with Oldhamia.
A. Seilacher et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 227 (2005) 323–356336

Available data suggest that increasing predator
pressure and competition for ecospace and/or
resources in shallow-marine ecosystems triggered
emigrations into deeper settings by the end of the
Cambrian (Crimes, 2001; Orr, 2001). The main
lineages of deep-marine trace fossils were established
in the deep sea by the Early Ordovician (Seilacher,
1963). In particular, Crimes et al. (1992) documented
a moderately diverse ichnofauna in Arenigian turbi-
dites of the Ribband Group in southeastern Ireland. It
includes graphoglyptid networks, radial traces, mean-
dering trails and back-filled structures. More recently,
a deep-marine ichnofauna of Late Tremadocian age
has been recorded in the Puna area of Argentina
(Benedetto et al., 2002; Ma´ngano and Buatois, 2003).
This suggests that a deep-marine ecosystem of mod-
ern aspect (Nereites ichnofacies) existed at least since
the Early Ordovician (Orr, 2001; Ma´ngano and Droser,
2004). Intensified bioturbation at all scales put not only
an end to an ecology based on microbial matgrounds. It
also led to the closure of the so-called bdeep-water
slope-basin taphonomic windowQthrough destruction
of non-biomineralized tissues, which had been com-
monly preserved in Cambrian deep-marine lagersta¨t-
ten (Orr et al., 2003). Intense bioturbation by a mobile
infauna resulted in a series of changes, most notably
enhanced microbial degradation, chemosymbiosis, in-
creased substrate permeability, and the disruption of
geochemical gradients conducive to mineral authigen-
esis (McIlroy and Logan, 1999; Orr et al., 2003).
Further search in Upper Cambrian turbidites will be
necessary to exactly date the advent of the agronomic
revolution on deep sea bottoms.
5. Conclusions
1. Ediacaran ichnodiversity is much lower than it
appears from the literature. Also, trace fossils are
less common in Ediacaran strata than in younger
rocks and behavioral complexity is still very limited.
Furthermore, arthropod tracks or trails and sinusoi-
dal nematode trails are conspicuously absent. This
situation changed dramatically in the Early Cambri-
an, where not only the number of recognizable
ichnotaxa, but also their complexity reached much
higher levels, particularly in shallow-marine envir-
onments. In other words, the shallow-marine trace
fossil record shows a similarly explosive diversifi-
cation as skeletal body fossils. Thus, the bCambrian
explosionQis not a preservational artifact.
2. On deep sea bottoms, benthic biotas were already
present in the Ediacaran, but Ediacaran deep-ma-
rine ichnofaunas were as yet extremely simple. As
exemplified by the behavioral diversification of
Oldhamia, they also diversified in the Early Cam-
brian, although the dominant life style (undermat
mining) was more reminiscent of Ediacaran times
(Seilacher, 1999). This means that the Cambrian
explosion and the agronomic revolution did not
coincide (Ma´ngano and Buatois, 2004b).
3. While the agronomic revolution transformed the
ecology of shallow-marine environments by the
Early Cambrian, it is still uncertain when exactly
this event arrived in the deep sea. By Early Ordovi-
cian times, the main lineages of deep-marine trace
fossils were already present (Nereites ichnofacies).
Accordingly, the ichnofauna of the Guachos Forma-
tion may represent a first step in this onshore/off-
shore expansion.
Acknowledgments
We thank Jim Gehling, Richard Jenkins, So¨ ren
Jensen and Guy Narbonne for valuable discussions.
Palaeo-3 reviewers Alfred Uchman and So¨ ren Jensen
and editor Finn Surlyk provided useful comments.
Ricardo Alonso and Cristina Moya showed the
authors outcrops near the city of Salta. Ignacio
Sabino helped Buatois during fieldwork in Quebrada
del Toro. We also thank Cope MacClintock for his
assistance at the Yale Peabody Museum, New
Haven, Connecticut, USA and Florencio Acen˜ olaza,
who provided access to the collections at the Miguel
Lillo Institute, San Miguel de Tucuma
´n, Argentina.
Financial support was provided by the Antorchas
Foundation (Buatois) and the Research Council of
the University of Tucuman (Ma´ngano). During the
last phase of the study, financial support was pro-
vided by the University of Saskatchewan Start-up
funds (Buatois) and a Natural Sciences and Engi-
neering Research Council (NSERC) Discovery Grant
311726-05 awarded to Buatois. as well as by a
NSERC Discovery Grant 311727-05 awarded to
Ma´ngano.
A. Seilacher et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 227 (2005) 323–356 337

Appendix A. Taxonomic
In this Section we provide descriptions and inter-
pretations of selected trace fossils from the Albemarle
Group of North Carolina, the Grand Pitch Formation
of Maine, the Besonderheid Formation of South
Africa and the Puncoviscana Formation of northwest
Argentina, including its coeval units, the Suncho For-
mation of Catamarca Province and the Guachos For-
mation outcropping near the city of Salta. Trace
fossils are listed alphabetically. Figs. 11–23
?Curvolithus isp.
(Fig. 11A)
Unit: Guachos Formation.
Localities: Los Guachos quarry (Salta Province,
Argentina).
Remarks: The name Curvolithus stands for continu-
ous burrows that have a flatly elliptical cross section
and appear trilobed in upper surface views (Buatois et
al., 1998b). They were probably made by flatworms
that burrowed by removing sediment in front of the
head and conveying it backwards along the body
(Seilacher, 1990). This is a technique used by various
kinds of infaunal bulldozers. In Curvolithus, however,
there is not only a terminal backfill formed behind the
body; in addition, sediment was redeposited laterally
along the right and left margins of the animal; i.e. in
front of the terminal backfill (Heinberg, 1973). The
combination of the two backfill structures makes the
trace fossil appear trilobed. Specimens from Los Gua-
chos (Fig. 11A) are not as well preserved as the ones
from younger shallow-marine sandstones and their
three-dimensional morphology is uncertain. Accord-
ingly, they are assigned to Curvolithus with doubts.
This ichnogenus is also known in Lower Cambrian
shallow-marine deposits of Canada (Narbonne et al.,
1987; Narbonne and Myrow, 1988). Curvolithus has
also been mentioned in possibly Ediacaran rocks of
Australia (Webby, 1970).
cf. Heliochone isp. Seilacher and Hemleben (1966)
(Fig. 11B)
Unit: Guachos Formation.
Localities: Los Guachos quarry, now on Salta city
sidewalk (Salta Province, Argentina).
Remarks: This large trace fossil consists of a continu-
ous ring that is surrounded at some distance by a
concentric ring of round dots. It can only be under-
stood by comparison with a still larger trace fossil from
the Lower Devonian Hunsru¨ck Shales of Germany
(Seilacher and Hemleben, 1966). In the latter case,
serial sectioning revealed that the basic structure was
a ring-shaped tunnel with equidistant vertical outlets.
As the inhabitant widened and lowered this tunnel
system, it produced a conical backfill with radial
Fig. 11. Trace fossils from the Guachos Formation, northwest Argentina. Salta sidewalks. A. ?Curvolithus isp. B. cf. Helichone isp. C. cf.
Treptichnus pedum.
A. Seilacher et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 227 (2005) 323–356338

walls left by the outlets. The radial backfills are not
seen in the Puncoviscana specimen. Accordingly, this
specimen is only compared with Heliochone.
Oldhamia alata isp. n.
(Figs. 12A, 13)
2004 Oldhamia n. isp. Buatois and Ma´ngano, Fig. 2G
Holotype: MPEF IC-424 (Paleontological Museum
Egidio Feruglio, Argentina), El Mollar (Quebrada
del Toro) (Salta Province, Argentina), Punoviscana
Formation.
Unit: Puncoviscana Formation.
Localities: Rio Capillas and El Mollar (Quebrada del
Toro) (Salta Province, Argentina).
Diagnosis: Relatively complex Oldhamia with thin,
unbranched probes which contour previous ones as in
aLophoctenium-like spreite. Alternating wings are
usually centrifugal and only occasionally centripetal,
but successive probes always proceed to the convex
side. Lobation within wings is common.
Description: Complex systems oriented parallel to
the bedding plane formed by closely spaced prob-
ings resembling a small Lophoctenium structure.
Probings always proceed to the convex side com-
monly starting at the center and protruding outward.
However, a centripetal pattern has been detected in
the construction of some wings (Fig. 7). Opposite,
1808symmetrical wings are occasionally observed,
Fig. 12. Ichnospecies of Oldhamia.A.Oldhamia alata. Upper specimen is the holotype. MPEF IC-424 (Paleontological Museum Egidio
Feruglio, Argentina). Puncoviscana Formation, northwest Argentina. B. Oldhamia antiqua. Grand Pitch Formation, Maine. C. Oldhamia
flabellata. Puncoviscana Formation, northwest Argentina. D. Oldhamia geniculata. Holotype. Field photo. Puncoviscana Formation, northwest
Argentina.
A. Seilacher et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 227 (2005) 323–356 339

but more complex asymmetrical systems in which
successive wings alternate along an imaginary axis
are more common (Fig. 13). Successive wings do
not cross each other. Some specimens consist of up
to eight asymmetric wings forming complex cumu-
lative structures. Lobation within wings reflected by
abrupt changes in the length of probes is another
well developed feature, with two to four lobes in
each wing.
Remarks: This ichnospecies was informally referred to
as ba new ichnospecies of OldhamiaQby Buatois and
Ma´ngano (2004). As in all ichnospecies of Oldhamia,
the probings end blindly. However, in O. alata they not
only bend back on previous ones, but follow them so
closely that the whole structure looks like the spreite of
a minute Lophoctenium. This probably means that the
backfill is not terminal, but that processed sediment
was continuously pushed to one side (i.e. towards the
previous probing) as the animal ate its way from the
center to the periphery. The probings are usually pro-
truding outward in a centrifugal fashion from a central
point or imaginary axis. The second wing in the spec-
imen illustrated in Fig. 7, however, protruded towards
the center and direction changed by 1808in the last
wing. This means that the direction of strip mining was
determined by the curvature of the first probe rather
than a fixed program. In all cases the spreite grew on the
convex side. As in many feeding burrows, the devel-
opment of subsequent wings was also constrained by a
taboo against overcrossing previous structures.
Lobation within the wings reflects yet another
fabricational constraint. Normally the probes end in
harmony with the previous ones, so that the tips
form a smoothly curved margin. However, from
time to time the length of the probes exceeded a
certain limit that was possibly related to the length of
the worm-like tracemaker. The response to this di-
lemma was always the same: start a new lobe with
shorter probes, but without loosing contact with the
previous ones. Contact was only given up when the
available mat area had been filled. Therefore, the
animal had to produce a new exploratory probe
followed by the construction of a new wing-shaped
spreite further ahead on the opposite side.
Oldhamia alata records a highly specialized Old-
hamia that efficiently explored the microbial mat. The
fact that there is no unexplored sediment between
successive probes reflects an improved feeding pro-
gram compared to other Oldhamia ichnospecies. Old-
hamia alata somewhat resembles some of the
Fig. 13. Variations of Oldhamia alata. Puncoviscana Formation, northwest Argentina. Based on specimens housed at the Paleontological
Museum Egidio Feruglio (Trelew, Argentina).
A. Seilacher et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 227 (2005) 323–356340

asymmetrical morphotypes of O. curvata. However,
in O. alata probes stay in closer contact with previous
ones and the wings are far more complex and com-
monly alternate. Lobation within wings records an
additional fabricational constrain that is typical for
O. alata.
Oldhamia antiqua Kinahan, 1858
(Figs. 12B, 14, 15)
*1858 Oldhamia antiqua Kinahan, p. 69
1895 Oldhamia (Murchisonites) occidens Walcott,
pp. 314–315, Fig. 1.
1904 Oldhamia (Murchisonites) occidens Dale (1904),
p. 13, Fig. 1
1929 Oldhamia occidens Ruedemann, pp. 47–55,
Figs. 28–29
1942 Oldhamia occidens Ruedemann, p. 7, Figs. 1.5,
2.1, 2.2 and 3.4
1942 Oldhamia smithi Ruedemann, p. 10, Fig. 3.5
1962 Oldhamia smithi Neuman, Fig. 2
1990 Oldhamia kernnesraniensis El Hassani and
Willefert, pp. 234–235, Figs. 1.1–1.4 and 1.7–1.8.
1990 Oldhamia flabellata El Hassani and Willefert,
pp. 234, Figs. 1.5–1.6
1994 Oldhamia cf. antiqua Buggisch et al., pp. 22,
Fig. 20b
Unit: Puncoviscana Formation (Argentina) and Grand
Pitch Formation (Maine).
Localities: San Antonio de los Cobres and Quebrada de
San Rafael (Cordo´n de Cobres) (Salta Province, Argen-
tina), and Grand Pitch Falls (Maine, United States).
Emended Diagnosis:Oldhamia in which diverging
curved to straight probings display a palm leaf ar-
rangement or resemble rays of fireworks. Successive
probings are separated by narrow strips of unexplored
sediment.
Remarks:Oldhamia antiqua is the type ichnospecies of
Oldhamia. In the Puncoviscana Formation it was docu-
mented for the first time by Acen˜olaza and Durand
(1982) and has been reanalyzed by Buatois and Ma´n-
Fig. 14. Variations of Oldhamia antiqua. Antarctic specimens collected by Buggisch. Maine specimens housed at the Geological and
Paleontological Institute of the University of Tubingen (Germany).
A. Seilacher et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 227 (2005) 323–356 341

gano (2003b). In addition to its occurrence in Argentina
and in its type area in Ireland (Forbes, 1849; Kinahan,
1858, 1859; Murchison, 1859; Sollas, 1900; Dhonau
and Holland, 1974; Crimes and Crossley, 1968;
Crimes, 1976; Holland, 2001), it has been recorded
from Lower Cambrian to, very rarely, lower Middle
Cambrian strata in Poland (Kowalski, 1987), Belgium
(Malaise, 1883; Verniers et al., 2001), Canada (Lind-
holm and Casey, 1990; Hofmann et al., 1994), United
States (Walcott, 1895; Ruedemann, 1929, 1942; Neu-
man, 1962), Morocco (El Hassani and Willefert,
1990), and Antarctica (Buggisch et al., 1994). With
the exception of the Moroccan and Polish occur-
rences, it is present in folded and otherwise non-
fossiliferous deep-marine successions. Oldhamia
(Murchisonites) occidens Walcott is a junior synonym
of O. antiqua (Lindholm and Casey, 1990). Oldhamia
kernnesraniensis El Hassani and Willefert and Old-
hamia smithi Ruedemann are also regarded as junior
synonyms of O. antiqua.
Oldhamia antiqua consists of straight to curved
probings in a fan-like arrangement. Tunnels radiate
from a short stem and curve slightly back at the sides
like the leaves of a palm tree or the rays of fireworks.
The zigzag arrangement of fans and the axial connect-
ing stem, observed in the type material, are not diag-
nostic elements of O. antiqua. In fact, they are
relatively uncommon in other described occurrences
of this ichnospecies.
Oldhamia antiqua reflects a search behavior found
in many kinds of feeding traces (e.g., Chondrites,
Arthrophycus, Phycodes) that approach the nutritious
layer from above or below at an oblique angle, but in
Oldhamia probings are all in a single bedding plane.
If the makers of Oldhamia were undermat miners, we
may assume that the stem part opened to the surface
and the probings spread below the active biomats,
where older mat zones were degraded enough to be
readily digestible (Seilacher, 1999).
In the construction of each leaf-like structure, prob-
ings presumably started from the axis with new ones
added on the sides. Some specimens display serial
arrangements of such fans (Fig. 7); the same individ-
ual could make many such patterns in succession.
Other specimens show two stemless fans pointing in
opposite directions, indicating a vertical shaft in the
center.
Oldhamia curvata Lindholm and Casey, 1990
(Fig. 16)
1965 Oldhamia sp. Churkin and Brabb, Fig. 4
1972 Oldhamia sp. Mirre´ and Acen
˜olaza (1972),
pp. 75–76, Fig. ac
1973 Oldhamia radiata Acen˜ olaza and Durand,
Figs. 1B, E
1978 Oldhamia radiata Acen˜ olaza (1978), p. 28,
Fig. 13
1981 Oldhamia radiata Acen˜ olaza and Toselli (1981),
p. 51, Figs. 2, 3
1982 Oldhamia antiqua Acen˜ olaza and Durand,
p. 709, Fig. 8
1984 Oldhamia antiqua Acen˜ olaza and Durand
(1984),Figs. 1D, 2D
1986 Oldhamia Acen˜olaza and Durand (1986),
Fig. 3J
1987 Oldhamia antiqua Acen˜ olaza and Durand
(1987), pl. 1, Fig. F
1989 Oldhamia antiqua Lindholm and Casey (1989),
p. 6, Fig. 3C, D
Fig. 15. Large slab containing several specimens of Oldhamia
antiqua. Several of these specimens are illustrated in Fig. 14.
Grand Pitch Formation, Maine (USA). Cast of Tubingen specimen
housed at Yale Peabody Museum (United States), YPM 204587.
A. Seilacher et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 227 (2005) 323–356342

*1990 Oldhamia curvata Lindholm and Casey,
pp. 1276–1278, Fig. 8D–G
1990 Oldhamia antiqua Durand and Acen˜ olaza, p. 94,
Figs. 3.43.5
1993 Oldhamia smithi Sweet and Narbonne, p. 71,
Fig. 3a
1993 Oldhamia antigua (lapsus calami)Durand
(1993) , pl. 1, Fig. H
1996 Oldhamia antiqua Durand (1996), pl. 1, Fig. D
1999a Oldhamia antiqua Acen˜ olaza et al., Fig. 9C
1999b Oldhamia radiata Acen¨ olaza et al. (1999b),
pl. 2, Fig. 6
Unit: Suncho Formation.
Localities: Sierra de la Ovejerı´a (Catamarca Province,
Argentina) (see Acen˜olaza and Durand, 1982, for
locality details).
Emended Diagnosis:Oldhamia with thin, uniformly
curved, unbranched probings, commonly forming al-
most symmetrical fan structures and leaving a gap in
the center. Probings commonly regularly spaced,
maintaining the curvature along their trajectory.
Asymmetric forms rare.
Remarks: This ichnospecies has been defined by
Lindholm and Casey (1990) based on specimens
from the Early Cambrian of Newfoundland. Subse-
quently, Sweet and Narbonne (1993) and Hofmann et
al. (1994) documented the same ichnospecies from
Que´bec and Arctic Canada, respectively. In addition,
Hofmann et al. (1994) noted that some of the speci-
mens referred to as O. radiata and O. antiqua from
the Puncoviscana Formation in previous studies (Ace-
n˜ olaza and Durand, 1973, 1982) should be included in
O. curvata (see also Buatois and Ma´ngano, 2003a)
and that Oldhamia isp. described from Alaska by
Churkin and Brabb (1965) should also be placed in
O. curvata.Oldhamia curvata is characterized by its
thin and uniformly curved rays, commonly displaying
regular spacing (Lindholm and Casey, 1990). The
central gap and the curvature suggest that the probings
were made in a centripetal succession.
Fig. 16. Variations of Oldhamia curvata. Based on specimens illustrated by Lindholm and Casey (1990),Sweet and Narbonne (1993), and
Hofmann et al. (1994).
A. Seilacher et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 227 (2005) 323–356 343

Oldhamia flabellata Acen˜ olaza and Durand, 1973
(Figs. 12C, 17)
?1859 Oldhamia antiqua Kinahan, partim, Fig. 4, 9.
*1973 Oldhamia flabellata Acen˜ olaza and Durand,
p. 49, pl. 1, Figs. C, D, F
1981 Oldhamia radiata Hofmann and Cecile,
Fig. 40.3F
1981 Oldhamia? sp. Hofmann and Cecile, p. 281,
Fig. 40.3C
Unit: Puncoviscana Formation.
Localities: San Antonio de los Cobres (Salta Prov-
ince, Argentina).
Emended Diagnosis:Oldhamia with irregular, sinu-
ous, occasionally discontinuous probings closely
packed to form a leaf-line structure. Probings
were made in a centrifugal succession to both sides.
Remarks:Oldhamia flabellata was originally de-
scribed from northwest Argentina by Acen˜olaza and
Durand (1973) and is also known from Canada (Lind-
holm and Casey, 1990; Hofmann et al., 1994). Speci-
mens from Morocco included in O. flabellata (El
Hassani and Willefert, 1990) more likely belong to
O. antiqua.
Oldhamia flabellata comprises irregular, rectilinear,
irregular and somewhat discontinuous tunnels. Com-
monly, the point of origin of the tunnel system is not
apparent. While being one-sided like O. antiqua, this
ichnospecies differs by the more irregular course of its
probings and their tendency to hug previous ones. By
adding new probings on either side of the midline, the
patterns become leaf-shaped and cover efficiently a
given surface, being optimal in feeding strategy. Serial
and opposite arrangements may also occur.
Oldhamia geniculata isp. n.
(Figs. 12D, 18)
1997 Oldhamia recurvata Seilacher, p. 29 (nomen
nullum)
1998 Oldhamia Almond, cover photo and Figs. un-
numbered
Holotype: MPEF-IC 431 (Paleontological Museum
Egidio Feruglio, Argentina), Los Chorrillos (Queb-
Fig. 17. Variations of Olhamia flabellata. Puncoviscana Formation, northwest Argentina. Based mostly on specimens housed at the Miguel Lillo
Institute (San Miguel de Tucuma´ n, Argentina).
A. Seilacher et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 227 (2005) 323–356344

rada del Toro) (Salta Province, Argentina), Punovis-
cana Formation.
Units: Puncoviscana Formation (Argentina) and
Besonderheid Formation (South Africa).
Localities: Los Chorrillos (Quebrada del Toro) (Salta
Province, Argentina) and Western and Northern Cape
Provinces (South Africa) (see Almond, 1998, for
South African locality details).
Diagnosis: Relatively large ichnospecies of Oldha-
mia, in which probings radiate in a centrifugal se-
quence and turn the tips back 1808on the free side to
fill the sectors in between, forming a hook-like struc-
ture. Instead of a fixed point of central branching,
there is a curved spreite-like structure in the center.
Description: Relatively large systems oriented parallel
to the bedding plane, in which branches radiate in a
centrifugal sequence and turn the tips back 1808on the
free side. A curved spreite-like structure in the center
occurs rather than a fixed point of branching.
Remarks: This new ichnospecies was informally in-
troduced in a drawing as Oldhamia recurvata (Seila-
cher, 1997) and is formally defined herein as
Oldhamia geniculata in order to avoid confusion
with O. curvata.Oldhamia geniculata , so far only
known from South Africa (Almond, 1998) and north-
west Argentina, met the requirement of filling radial
sectors without branching: a certain distance from the
main shaft, each probe turns by 1808on the free side
and stops at about 1 / 2 to 1/ 3 of the way back.
Strangely, the hook is always made in foresight on
the advancing side of the probe series, rather than
backwards, where guidance would have been provid-
ed by the previous probe. The direction of the swing
can be derived from the kinks in loops 5 and 6 of Fig.
18; they show that there was a near-collision with the
hook of the previous probe.
Another striking feature, namely the segmentation
of individual branches, is a tectonic artifact. It occurs
only in probes running at approximately right angles
to a faint schistosity. The segmentation is therefore a
product of tectonic stress that deformed the rock
together with the trace fossils and broke up the tube
fillings at regular intervals. Their higher competence
may have been due to an original mucus content or
Fig. 18. Variations of Oldhamia geniculata. Puncoviscana Formation, northwest Argentina. Based on the holotype (Fig. 18b, MPEF-IC 431)
housed at the Paleontological Museum Egidio Feruglio (Trelew, Argentina) and field specimens.
A. Seilacher et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 227 (2005) 323–356 345

early diagenetic cementation. In any case it proves
that the tunnels were actively backfilled and therefore
behaved unlike the matrix. Recognition of the stress
direction also allows to retrodeform the feeding pat-
terns to their original shapes (Fig. 18).
Oldhamia radiata Kinahan, 1858
Unit: Puncoviscana and Suncho Formations.
Localities: San Antonio de los Cobres and Cuesta
Mun
˜ano (Salta Province, Argentina) and Sierra de la
Ovejerı´a (Catamarca Province, Argentina).
Emended Diagnosis:Oldhamia with probings that
branch and radiate to all sides from a central point
in a Chondrites-like fashion, but except from
the central area they all remain in a single bedding
plane.
Remarks: In the Puncoviscana Formation, Oldhamia
radiata was documented for the first time by Ace-
n
˜olaza and Durand (1973) and has been recently re-
analyzed by Buatois and Ma´ngano (2003b). In addi-
tion to its occurrence in Argentina and in its type
area in Ireland (Forbes, 1849; Kinahan, 1858, 1859;
Sollas, 1900; Dhonau and Holland, 1974; Crimes
and Crossley, 1968; Crimes, 1976; Holland, 2001),
Oldhamia radiata is also known from Spain (Crimes
et al., 1977), Canada (Lindholm and Casey, 1990;
Hofmann et al., 1994), Mongolia (Goldring and
Jensen, 1996) and Antarctica (Buggisch et al.,
1994). With the exception of the occurrences from
Mongolia and Spain, it is invariably present in deep-
marine deposits.
Oldhamia radiata consists of rectilinear to slightly
curved rays forming a radial pattern from a central
area of origin. This ichnospecies reaches even cover-
age by means of making probes radiate to all sides of
a vertical shaft and filling the sectors between them by
branching. This principle is also used by plant roots
and the trace fossil Chondrites. Yet the present ich-
nospecies should better be affiliated with Oldhamia
because it spreads in one plane and is similar in fine
morphology, size and preservation. On the other hand,
branching required a change of burrowing behavior:
probes could not be entirely backfilled with processed
or introduced sediment until all branches had been
finished.
Oldhamia recta isp. n.
(Figs. 19, 20)
1989 Syringomorpha sp. Gibson, p. 5, Figs. 4.3–4.4
1992 Oldhamia cf. flabellata Seilacher and Pflu¨ger,
Fig. 1
1997 Oldhamia recta Seilacher, p. 29.
1999 Oldhamia simplex Omarini et al., p. 89 (nomen
nullum)
Holotype: YPM.204453 (Yale Peabody Museum),
Saint Martin quarry, Carolina Slate Belt (North Car-
olina, United States), Floyd Church Member, McMa-
nus Formation (Albermarle Group).
Unit: Floyd Church Member of the McManus Forma-
tion (Albermarle Group).
Localities: various localities in the Carolina Slate Belt
(North Carolina, United States) (see Gibson, 1989, for
locality details).
Fig. 19. Oldhamia recta. Holotype. YPM.204453 (Yale Peabody
Museum). Floyd Church Member, McManus Formation (Albermarle
Group), Saint Martin quarry, Carolina Slate Belt (North Carolina,
United States).
A. Seilacher et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 227 (2005) 323–356346

Diagnosis:Oldhamia with straight backfilled tun-
nels parallel to the bedding plane that are arranged in
non-intercutting and seemingly unconnected bundles.
Description: Bundles of straight, subparallel, un-
branched and closely spaced tunnels oriented parallel
to the bedding plane. Tunnels are a few centimeters
long and up to 1.5 mm in diameter. Preserved as
positive as well as negative reliefs on the same bed-
ding plane.
Remarks: These tunnel systems were formerly
assigned to Syringomorpha by Gibson (1989). How-
ever, they were subsequently placed in Oldhamia by
Seilacher and Pflu¨ger (1992) based on the fact that the
tunnels were confined to the bedding plane instead of
being vertical as in Syringomorpha (see also Jensen,
1997).
The tunnels must have been actively backfilled,
because they are preserved either as positive or as
negative hyporeliefs. Therefore these structures made
by worm-like undermat miners can be affiliated with
the ichnogenus Oldhamia, which evolved much more
sophisticated search behaviors in the lowermost Cam-
brian (Fig. 7). The pattern shows that the tracemaker
had a well developed central nervous system that
allowed it to sense the proximity of previous prob-
ings.
Psammichnites saltensis (Acen˜ olaza and Durand,
1973)
(Figs. 21, 22A, B, D)
*1973 Nereites saltensis Acen˜olaza and Durand,
p. 49–50, Fig. 2A
1974 Nereites Seilacher, Fig. 2 (Cambrian example)
1977 Nereites Seilacher, Fig. 4 (Cambrian example)
1978 Nereites saltensis Acen˜olaza (1978), p. 28.
Fig. 12
1986 Nereites saltensis Acen˜olaza and Durand
(1986),Fig. 3.F
1987 Nereites saltensis Acen˜olaza and Durand
(1987), pl. 1, Fig. B
1990 Nereites saltensis Durand and Acen˜ olaza,
p. 92–92, Fig. 3.1
Fig. 20. Variations of Oldhamia recta. Floyd Church Member, McManus Formation (Albermarle Group), North Carolina, United States. Based
on specimens housed at the Yale Peabody Museum (United States).
A. Seilacher et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 227 (2005) 323–356 347

1993 Nereites saltenis (lapsus calami)Durand (1993),
pl. 1, Fig. F
1994 Helminthorhaphe isp. Hofmann et al., p. 773,
Fig. 3A, C
1994 Nereites saltensis Durand (1994), pl. 1, Fig. F
1996 Nereites saltensis Durand (1996), pl. 1, Fig. H
1999a Nereites saltensis Acen˜olaza et al., p. 103, Fig.
2F, I
1999b Nereites saltensis Acen˜olaza et al., pl. 2, Fig. 2
2001 Nereites saltensis Acen˜ olaza and Alonso, Fig. 3.2
2004 Guided meandering trace fossil Buatois and
Ma´ngano, Fig. 2D
Unit: Guachos and Puncoviscana Formation.
Localities: Los Guachos quarry, Cachi, Rancagua,
Rı´o Capillas, and Campo Quijano, (Salta Province,
Argentina).
Remarks: Because of its bilobed profile and regular
meandering, this Puncoviscana trace fossil has orig-
inally been affiliated with Nereites (Acen˜ olaza and
Durand, 1973; Seilacher, 1974). It was only through
the specimen shown in Figs. 21 and 22D that this
assignment could be corrected. This unique slab is
interesting in various respects: (1) there is an arthro-
pod trackway with oblique series of appendage
imprints (Diplichnites); (2) the impressions are not
blurred, so they were not made on a biomat; (3)
because the appendage imprints stick out as ridges,
we deal with a sole face; and (4) in crossing a large
meandering trail, the trackway contours its negative
profile, but is neither obliterated, nor does it change
its course. This is surprising, because arthropod
trackways, even if preserved as undertracks, belong
to a shallower tier and were therefore made earlier
than the meandering traces. The contradiction
resolves if one takes the soft margins of the trace
in Fig. 21 into account: this bedding plane was not
touched by the meandering Psammichnites animal,
but simply lifted up, as the hydrostatic creature
wedged itself along at a deeper level. This is why
the pre-existing arthropod trackway did not become
wiped out. However, the Psammichnites overtrace
would have collapsed again, had the tunnel not
Fig. 21. Variations of Psammichnites saltensis. Note size differences. Guachos Formation, northwest Argentina. Based on material studied in
the field.
A. Seilacher et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 227 (2005) 323–356348

Fig. 22. Grazing traces and arthropod trackways from the Guachos Formation, northwest Argentina. A. Psammichnites saltensis. Enhanced
with chalk on Salta sidewalk. B. Psammichnites saltensis. Cast at the Geological and Paleontological Institute of the University of Tubingen.
C. Psammichnites cf. gigas. Field photograph. Preserved as hyporelief. D. Psammichnites saltensis deforming Diplichnites isp. Field
photograph. E. Tasmanadia cachii. Field photograph.
A. Seilacher et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 227 (2005) 323–356 349

been backfilled with extra sediment probably intro-
duced from the surface (Seilacher-Drexler and Sei-
lacher, 1999). As the backfill of Nereites consists
always of sediment scraped away in front of the
head, it is concluded that the present trace should
better be affiliated with Psammichnites. Meandering
is not uncommon in Psammichnites. Examples are
known from Lower Cambrian and Carboniferous
shallow-marine facies (Ma´ngano et al., 2002). How-
ever, none of them has the kink in each loop, by
which the maker of P. saltensis appears to have
assured itself that it was close to the previous turn.
Because the kink also triggered the next turn, it was
performed even if the contact with the previous turn
had failed (Seilacher, 1986). This behavioral program
remained the same through all growth stages (Fig.
21), but as it avoided overcrossing, it was more
efficient than the looping behaviour of the contem-
poraneous P. gigas (Torell).
Psammichnites cf. gigas (Torell, 1868)
(Fig. 22C)
2001 Nereites saltensis Acen˜olaza and Alonso,
Fig. 2.3
Unit: Guachos Formation.
Localities: Los Guachos quarry (Salta Province,
Argentina).
Remarks: One of the most impressive Lower Cambri-
an trace fossils is the lasso trail Psammichnites gigas .
It is known from lowermost Cambrian shallow-marine
sandstones in Sweden (Torell, 1868, 1870), Canada
(Hofmann and Patel, 1989), Australia (Walter et al.,
1989), Greenland (Pickerill and Peel, 1990), Spain
(Seilacher and Ga´mez-Vintaned, 1995, 1996), Zhu
(1997), France (A
´lvaro and Vizcaı¨no, 1999), United
States (Jensen et al., 2002), Iran (Seilacher, unpub-
lished data), and Sardinia (Fro¨hler, 1994). Consider-
ing the kind of backfill, the transversal sculpture on
the ventral, and a conspicuous sinusoidal line on the
Fig. 23. Variations of Tasmania cachii. Guachos Formation, northwest Argentina. Specimens studied in the field.
A. Seilacher et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 227 (2005) 323–356350

dorsal side, P. gigas has been interpreted as the work
of a slug-like animal that bulldozed inside the sedi-
ment and collected food from the surface with a
pendulating siphon (Seilacher-Drexler and Seilacher,
1999). None of these details can be observed in the
Guachos specimen (Fig. 22C). Yet, the lasso-like
loops and relatively large size leave little doubt that
we deal with a similar behavioral program as per-
formed by the P. gigas organism.
Tasmanadia cachii Durand and Acen˜olaza, 1990
(Figs. 22E, 23)
Unit: Guachos and Puncoviscana Formation.
Localities: Los Guachos quarry and Cachi (Salta
Province, Argentina).
Remarks: In addition to ordinary arthropod under-
tracks (Diplichnites), the Guachos facies contains
abundant trackways that are difficult to interpret in
terms of arthropod locomotion. In trilobite trackways,
one can distinguish series of appendage impressions
that become more obvious if the animal moved at a
slight angle to its body axis. Each of these series
corresponds to one wave of activation passing along
the body from the rear to the front legs. These meta-
chronal series must overlap, because each wave dis-
places the body only by a fraction of its length. In
Tasmanadia cachii, subsequent series of imprints do
not overlap. Instead, they form individualized pat-
terns, whose bracket shapes probably correspond to
the general outline of the tracemaker. This means that
the animal was not continuously supported; rather it
must have moved in jumps, driven by the simulta-
neous action of all appendages. In agreement with this
model, subsequent patterns may be out of line, be-
cause the animal was displaced during the jump by a
lateral current (Fig. 23).
But what kind of an animal produced these tracks?
It got about 7 cm long, had an oval outline and 10
pairs of appendages. Not all of these must have left an
impression, because smaller legs near the front or rear
ends, which cannot readily be distinguished, because
there are no pushback heaps, may not have penetrated
to the interface, on which the undertrack is preserved.
So some kind of arthropods would be a possibility.
True legs, however, touch and scratch the substrate
with their tips, while each appendage imprint of T.
cachii consists of 56 small bifid impressions in a
radiating row. Another possibility is a polychaete
worm, similar to modern Aphrodite, that had setate
parapodia on each body segment. Or could there be an
arthropod in Burgess-type biota that fits our ichnolo-
gical profile?
cf. Treptichnus pedum (Seilacher, 1955)
(Fig. 11C)
Unit: Guachos Formation.
Localities: Los Guachos quarry (Salta Province,
Argentina).
Remarks: This structure, consisting of two series of
knobs, might at the first sight be mistaken for an
arthropod trackway. More likely we deal with outlets
emerging from a horizontal tunnel in an alternating
fashion. Similar, but smaller, burrow systems are
known from shallow-marine Middle Cambrian sand-
stones of the Grand Canyon (Bicavichnites Lane et al.,
2003). Like the latter, the Guachos specimen is here
tentatively considered an epichnial expression of
Treptichnus pedum.
The multiple exits require a special explanation,
because in an open tunnel system, active ventilation
would have been easier in a U-shaped structure with
only two openings to the surface. Most likely, the
multiple exits served for passive ventilation and/or
for trapping organic particles that drifted along the
sediment surface. Alternatively, they could have be-
come actively backfilled upon completion of the next
exit. Treptichnus pedum was more three-dimensional
than the burrows of typical undermat miners. Never-
theless, it could have exploited the same niche.
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