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Eramosa Lagerstätte---Exceptionally preserved soft-bodied biotas with shallow-marine shelly and bioturbating organisms (Silurian, Ontario, Canada)

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  • Royal Ontario Museum & University of Toronto

Abstract and Figures

The middle Silurian Eramosa Lagerstätte of Ontario, Canada, preserves taxonomically and taphonomically diverse biotas including articulated conodont skeletons and heterostracan fish, annelids and arthropods with soft body parts, and a diverse marine flora. Soft tissues are preserved as calcium phosphate and carbon films, the latter possibly stabilized by early diagenetic sulfurization. It is significant that the biotas also include a decalcified, autochthonous shelly marine fauna, and trace fossils. This association of exceptionally preserved and more typical fossils distinguishes the Eramosa from other Silurian shallow-marine Lagerstätten, such as the Waukesha Lagerstätte, and suggests that the Eramosa is not the product of exceptional preservation in an atypical environment, a bias claimed for many post-Cambrian Lagerstätten. The Eramosa Lagerstätte may provide a more reliable, balanced measure of what has been lost from the Silurian fossil record.
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GEOLOGY, October 2007 879
Geology, October 2007; v. 35; no. 10; p. 879–882; doi: 10.1130/G23894A.1; 2 fi gures; 1 table.
© 2007 The Geological Society of America. For permission to copy, contact Copyright Permissions, GSA, or editing@geosociety.org.
INTRODUCTION
Konservat Lagerstätten preserve fossil skel-
etons and soft tissue remains that normally
disarticulate and decay. Consequently, they are
of fundamental importance in (1) providing a
record of the diversity of organisms of which
we would otherwise be ignorant (e.g., >86%
of genera in the Phyllopod Bed of the Burgess
Shale; Conway Morris, 1986); (2) providing
our only direct means of assessing the degree to
which the fossil record of bio diversity is biased
by the loss of nonbiomineralized organisms and
tissues (Briggs, 2003); and (3) revealing the
existence of organisms with unique character
combinations, without which our understanding
of the origins and evolution of major metazoan
groups would remain signifi cantly limited.
Exceptionally preserved biotas of Cambrian
age have received particular attention, partly
because of their signifi cance in understand-
ing the Cambrian explosion, but also because
they are statistically overabundant (Allison and
Briggs, 1993). Most Cambrian Lager stätten
preserve soft-bodied organisms as fl attened
carbon fi lms (Burgess Shale–type preservation;
Butterfi eld, 1995), with more labile tissues
repli cated by authigenic minerals (Orr et al.,
1998; Gabbott et al., 2004), and their reduced
post-Cambrian frequency has been attributed
to an increase in the amount and depth of bio-
turbation, leading to changes in sediment prop-
erties and increased rates of decay (Plotnick,
1986; Orr et al., 2003).
Very few exceptionally preserved biotas of
Silurian age were previously known (Allison
and Briggs, 1993), but they are being increas-
ingly reported (e.g., Briggs et al., 1996), espe-
cially from North America (Kluessendorf, 1994;
Kluessendorf et al., 1999). The North American
reports led Mikulic and Kluessendorf (2001) to
characterize post-Cambrian Konservat Lager-
stätten as forming in atypical marine environ-
ments, with Silurian deposits in North America
containing few shelly taxa and lacking evidence
of bioturbation.
The nature and atypical biotic composition
of previously described shallow-marine Silurian
Lagerstätten emphasize a major concern with
using Konservat Lagerstätten to understand bias
in the fossil record of biodiversity: if exceptional
preservation requires exceptional conditions, to
what degree do Konservat-Lagerstätten preserve
contemporaneous biodiversity (Conway Morris,
1985)? Using them to understand the degree to
which shelly faunas are unrepresentative could
simply substitute one type of bias (taphonomic)
for another (ecological).
We report a 425-m.y.-old Silurian Konservat-
Lagerstätte from the Bruce Peninsula, Ontario,
Canada (
Fig. 1), that contains exceptionally
preserved marine vertebrates, invertebrates, and
plants associated with shelly biotas, and evi-
dence of bioturbation.
ERAMOSA LAGERSTÄTTE
The Eramosa Lagerstätte occurs in a 16 km
outcrop belt of the upper Eramosa Formation
(Brett et al., 1995), an ~15-m-thick middle
Silurian (Wenlock) formation (Stott et al.,
2001) interpreted by Armstrong (1993) as the
lagoonal marine facies of the more massive,
reefal Guelph Formation. Exceptional preser-
vation is confi ned to an ~7–9-m-thick alternat-
ing dolostone, limestone, and bituminous shale
sequence, the Interbedded Unit of Armstrong
and Meadows (1988), recognized only on the
Bruce Peninsula. The Lagerstätte, fi rst identifi ed
and investigated by Tetreault (2001a), contains
three biotas (
Table 1) from different but laterally
intergrading environments.
Biota 1
A complete articulated skeleton of a tolypele pid
heterostracan preserves the fi rst recorded traces
of heterostracan soft-tissue remains as carbona-
ceous fi lms associated with the calcium phos-
phate of the skeletal plates (
Fig. 2A); previously,
articulated Silurian heterostracans were known
only from a single locality (Soehn and Wilson,
1990). Corvaspid heterostracan dermal elements
are common; those of tolypelepids are rare.
All fi sh remains fl uoresce yellow-green under
ultraviolet light. Scolecodonts and eurypterid
molts occur as carbonaceous remains, leperditiid
ostracodes as compressed valves of calcium
carbonate, and beyrichiid ostracodes as three-
dimensional internal calcite molds (Table 1).
Biota 1 occurs only at locality A (Fig. 1),
in thin- to medium-bedded, shaly-weathering,
gray microcrystalline limestone. Stenohaline
organisms and evidence of bioturbation are
absent. The organisms present are known to be
tolerant of a broad range of salinities, occur-
ring in nonmarine and transitional marine-
terrestrial settings, and we interpret Biota 1 to
have occupied the shallowest, most restricted of
the Eramosa environments. The absence of indi-
cators of hypersalinity suggests a stable, hypo-
saline body of standing water, such as a lake or a
brackish nearshore marine environment.
Evidence of early authigenic mineralization
of organic soft tissues is lacking. Energy disper-
sive X-ray analysis (EDX) of the exceptionally
*E-mails: peterv@rom.on.ca; mark.purnell@
leicester.ac.uk; deniskt@uwindsor.ca; castott@uwo.ca.
Eramosa Lagerstätte—Exceptionally preserved soft-bodied biotas
with shallow-marine shelly and bioturbating organisms
(Silurian, Ontario, Canada)
Peter H. von Bitter* Department of Natural History, Royal Ontario Museum and Department of Geology, University of Toronto,
Toronto, Ontario M5S 2C6, Canada
Mark A. Purnell Department of Geology, University of Leicester, Leicester LE1 7RH, UK
Denis K. Tetreault Department of Earth and Environmental Sciences, University of Windsor, Windsor, Ontario N9B 3P4, Canada
Christopher A. Stott Department of Earth Sciences, University of Western Ontario, London, Ontario N6A 5B7, Canada
ABSTRACT
The middle Silurian Eramosa Lagerstätte of Ontario, Canada, preserves taxonomi-
cally and taphonomically diverse biotas including articulated conodont skeletons and
hetero stracan sh, annelids and arthropods with soft body parts, and a diverse marine
ora. Soft tissues are preserved as calcium phosphate and carbon fi lms, the latter possibly
stabilized by early diagenetic sulfurization. It is signifi cant that the biotas also include a
decalcifi ed, autochthonous shelly marine fauna, and trace fossils. This association of excep-
tionally preserved and more typical fossils distinguishes the Eramosa from other Silurian
shallow-marine Lagerstätten, such as the Waukesha Lagerstätte, and suggests that the
Eramosa is not the product of exceptional preservation in an atypical environment, a bias
claimed for many post-Cambrian Lagerstätten. The Eramosa Lagerstätte may provide a
more reliable, balanced measure of what has been lost from the Silurian fossil record.
Keywords: Eramosa Lagerstätte, soft-bodied preservation, conodont and heterostracan vertebrates,
shelly marine fauna, trace fossils, middle Silurian, Ontario, Canada.
880 GEOLOGY, October 2007
preserved heterostracan organic traces and the
eurypterid remains reveals that they are com-
posed primarily of carbon and sulfur. Recent
work suggests that such preservation was prob-
ably by in situ polymerization (e.g., Gupta
et al., 2006), in this case possibly enhanced by
diagenetic sulfurization. The latter taphonomic
process, by which relatively labile organic mol-
ecules are preserved over geological time scales,
may be more widespread than previously real-
ized (e.g., McNamara et al., 2006).
Biota 2
Biota 2 (Table 1) is dominated by jawless ver-
tebrates in the form of articulated conodont skel-
etons (von Bitter and Purnell, 2005) (Figs. 2B,
2C), many preserving remains of conodont eyes
(Figs. 2C, 2D). The several hundred skeletons
recovered, comprising at least seven taxa, are the
most abundant and diverse assemblage of articu-
lated conodont skeletons known, quadrupling
the number known from the Silurian. Conodonts
preserving remains of soft tissues were previ-
ously limited to three genera from three localities
(Briggs et al., 1983; Mikulic et al., 1985a, 1985b;
Aldridge et al., 1993; Aldridge and Theron,
1993; Gabbott et al., 1995). The Eramosa Lager-
stätte adds two additional genera, with poten-
tial for more. Conodont soft tissue reported by
Zhuravlev et al. (2006) cannot be verifi ed, and the
association of dispersed conodont elements and
wrinkled “integument-like material” illustrated
by Liu et al. (2006, p. 971; their Figs. 2D and 3)
are most likely fecal remains.
Biota 2 occurs at localities B and C (Fig. 1) in
laminated, brown, organic-rich calcareous shale,
and in the nodular, dolomitized, micritic limestone
with which it alternates (von Bitter and Purnell,
2005). An ~1-cm-thick, heavily bioturbated bed of
Chondrites burrows is present immediately above
that containing the conodont skeletons at locality
B. The composition of the fauna and the presence
of articulated remains suggest that Biota 2 lived
in a protected, quiet water, marine environment.
The relative abundances of Ozarkodina excavata
and Ctenognathodus cf. murchisoni at localities B
and C, respectively, suggests more open marine
conditions at locality B, with shallower, pos-
sibly slightly more restricted marine conditions
at locality C (Fig. 1) (Aldridge and Jeppsson,
1999). The changes in biota indicate an environ-
mental gradient between localities A–C.
As in Biota 1, evidence for early authigenic
mineralization of soft tissue is lacking. Organic
tissue of conodonts, graptolites, algae, and
eurypterids is preserved as carbonaceous fi lms.
EDX analysis of conodont eye traces reveals the
presence of carbon and sulfur (Figs. 2C, 2D),
suggesting that preservation may have involved
early diagenetic sulfurization, possibly of mela-
nins, the complex biopolymer composition of
which may have rendered them resistant to bac-
terial degradation.
Biota 3
Biota 3 (Table 1) contains a remarkable soft-
bodied marine fauna on dolostone bedding
planes at locality D (Tetreault, 2001a). It includes
lobopodians preserving possible color band-
ing (Figs. 2E, 2F), phosphatized polychaetes
(Fig. 2G), possible annelids of Myoscolex-like
form (Figs. 2H, 2I), branchiopod or remipede-
like arthropods (Fig. 2J), and a uniquely diverse
marine fl ora (Tetreault and LoDuca, 2005).
Preservationally and taxonomically, this is the
most diverse of the three biotas; it includes origi-
nal phosphatic tissue (conodont skeletons, pos-
sible fi sh remains, Sphenothallus, conularids, and
inarticulate brachiopods), early authigenic phos-
phate mineralization (soft tissues of phyllocarids,
xiphosurans, enigmatic polychaetes [some with
phosphatized muscle fi bers, and yellow-green
uorescing setae], and lobopodians), and car-
bonaceous fi lms (lightly sclerotized cuticle and
apparently refractory soft tissues of eurypterids,
scorpions, conodonts, scolecodonts, and algae).
An autochthonous shelly marine fauna (Table 1),
including articulated brachiopods, trilobites,
ophiuroids, crinoids, and echinoids (whole and in
life position; Tetreault, 2001b), occurs on many of
the same bedding planes as the excep tionally pre-
served biota. The shelly fauna, originally mostly
calcareous, has undergone decalcifi cation; sig-
nifi cant silicifi cation, possibly following decal-
cifi cation, particularly affected rhynchonellid
brachiopods and crinoid remains. The siliceous
spicules of articulated choiid demosponges are
now desilicifi ed. The sequence contains many
bioturbated and burrowed horizons.
The mixture of preservational styles in Biota
3 indicates a complex taphonomic history. In the
lower Interbedded Unit, phosphatized soft tissues
retain a degree of three dimensionality, indicating
that some decay-induced collapse, but not com-
plete fl attening of the organisms, had occurred
at the time of mineralization. Other instances,
such as the preservation of conodont eye traces,
indicate that most of the body had decayed away
Figure 1. Location of biotas in the Eramosa
Lagerstätte in town of South Bruce Penin-
sula (Bruce County, Ontario, Canada). A:
Locality A (Park Head)—Biota 1. B, C: Locali-
ties B and C (Hepworth and 2.6 km west of
Hepworth, respectively)—Biota 2. D: Local-
ity D (Wiarton)—Biota 3.
TABLE 1. BIOTAS 1–3 OF THE ERAMOSA LAGERSTÄTTE
Biota Composition
1 Vertebrates: tolypelepid heterostracans, disarticulated dermal elements and complete articulated
skeleton rare; corvaspids, disarticulated dermal elements and element concentrations common.
Arthropods: erettopterid eurypterids, molts common; leperditiid and beyrichiid ostracodes. Annelids:
articulated and disarticulated eunicid polychaete jaws.
2 Vertebrates: conodonts, complete skeletons, often with eye traces, common; isolated elements; at
locality B, Ozarkodina excavata common, O. confl uens, a new genus and species (Ozarkodina? sp.
nov. of Aldridge, 1985), Ctenognathodus cf. murchisoni, Pseudooneotodus boreensis, and Panderodus
sp. rare; at locality C, Ct. cf. murchisoni, Ozarkodina? sp. nov. and Panderodus sp.; Arthropods:
hughmilleriid eurypterids rare; leperditiid ostracodes, articulated, compressed calcareous valves
common. Graptolites: monograptids rare. Sparse, shelly recrystallized fauna of meristellid brachiopods,
orthocone cephalopods, low-spired gastropods, and tabulate corals. Algae: thallophytes, carbonaceous
lms rare; prasinophytes common. Trace fossils: Chondrites burrows.
3U Annelids: articulated and disarticulated eunicid polychaete jaws common. Algae: thallophytes and
dasyclads common.
3M Arthropods: eurypterids and scorpions (Waddington and Jeram, 1997).
3L Vertebrates: Conodonts: exceptionally preserved, articulated skeletons of Ozarkodina excavata, often
with eye traces, rare; ?Fish, concentration of blue-weathering, ?vertebrate phosphate (ROMV
56598 a&b) rare. Arthropods: phyllocarid and ostracode crustaceans, xiphosuran chelicerates,
lobopodians, arthropods of uncertain affi nities (cf. branchiopods or remipedes of Mikulic et al., 1985a,
1985b). Annelids: Myoscolex-like forms, polychaetes (including possible aphroditid-like forms with
phosphatized muscle tissue), spirorbiform tubes and annulated worms of uncertain affi nity. Associated
shelly fauna of decalcifi ed, silicifi ed, articulated rhynchonellid brachiopods, lepidocentrid echinoids
(in life position; Tetreault, 2001b), ophiuroids with intact arms and rare complete crinoids; desilicifi ed
choiid demosponges; trilobites, conularid cnidarians, Sphenothallus, articulate and inarticulate
brachiopods, bivalves, gastropods, and cephalopods. Trace fossils: Planolites-type and phyllocarid
burrows common. Algal mats.
L, M, and U are Lower, Middle, and Upper Interbedded Unit.
GEOLOGY, October 2007 881
before stabilization of the remaining soft tissues,
possibly through sulfurization. In the middle and
upper Interbedded Unit, only originally sclero-
tized tissues, such as cuticle, scolecodonts, and
algae, are preserved as carbonaceous remains,
indicating much higher levels of decay.
SIGNIFICANCE OF THE ERAMOSA
LAGERSTÄTTE
The Eramosa Lagerstätte contains exception-
ally and diversely preserved Silurian organisms
in a unit that transects several intergrading
environments: lacustrine to marginally marine
environments in the south (locality A), to fully
marine conditions in the north (locality D). It is
most similar to the slightly older (Llandovery)
Waukesha Lagerstätte (Mikulic et al., 1985a,
1985b), with which it shares exceptionally
preserved arthropods, including branchiopod
Figure 2. A: Tolypelepid heterostracan; articulated skeleton of original calcium phosphate. Soft-tissue traces are preserved as carbon
and sulfur (evident as dark patches within outlines of skeleton). Biota 1, locality A, ROMV 56092. B, C: Articulated conodont skeletons of
Ozarkodina excavata preserved as original calcium phosphate. Biota 2, locality B, ROMP 57892 and 57890. Conodont elements are labeled
(in B); black circular conodont eye traces are shown (in C). D: Backscattered electron micrograph (bs) and energy dispersive X-ray analysis
maps (carbon, sulfur, calcium, and phosphorus) of eye traces (shown in C), indicating the preservation of soft-tissue remains in carbon and
sulfur. E, F: Lobopodian; phosphatized, with possible original color banding (ROMP 57893). G: Aphroditid-like polychaete with phosphatized
muscle tissue (ROMP 57894). H, I: Possible annelid of Myoscolex-like form (ROMP 57980). J: Branchiopod or remipede-like arthropod with
large, grasping, anterior appendages; phosphatized (ROMP 57891). E–J are Biota 3, locality D. Scale bars: B and C = 1 mm; A, D–J = 10 mm.
A, C, E, G, and H are imaged with cross-polarized incident light: A is under water, others are under glycerol; B, scanning electron micro-
graph; F and I, low-angle incident light.
882 GEOLOGY, October 2007
or remipede-like forms (Fig. 2J), xiphosurans
(Moore et al., 2005), phyllocarid crustaceans,
and lobopodians (Wilson et al., 2004). It dif-
fers, however, in possessing articulated hetero-
stracans (Fig. 2A) and abundant and diverse
conodont skeletons (Figs. 2B, 2C), with soft
parts preserved as carbonaceous fi lms, a variety
of polychaete worms, eurypterids, marine
scorpions, and a well-preserved marine fl ora
( Tetreault and LoDuca, 2005).The Eramosa
Lagerstätte also contains an autochthonous
shelly marine fauna, as well as evidence of
bioturba tion. It is this mixture of diverse and
exceptionally preserved organisms with a more
typical marine fauna that distinguishes the
Eramosa from other shallow-marine Silurian
Lagerstätten, and suggests that the Eramosa
Lagerstätte is not simply the product of an atypi-
cal environment. Biota 3, in particular, may
provide a more reliable, less biased view of
what has been lost from the post-Cambrian, and
specifi cally from the Silurian, fossil record.
ACKNOWLEDGMENTS
We thank Peter Fenton, Sarah Gabbott, Alf Lenz,
Steven LoDuca, David Rudkin, Kevin Seymour,
Susan Turner, Janet Waddington, and Rob Wilson for
sharing their expertise, Stuart Milliken and Arnim
Walter for donating key specimens, Sarina Finlay
for drafting assistance, Derek Armstrong, Todd
Ebel, and John Kroezen for locality information
and samples, Patrick Boyd, Marie Boyd, Bradley
Grimoldby, William Jones, Mike Morton, Lynda
O’Halloran, Harold Stobbe, and Dianna Trask for
access to localities and assistance, and Derek Briggs,
Mark Sutton, and an anonymous reviewer for helpful
comments. von Bitter and Purnell thank the Royal
Ontario Museum Foundation and the Natural Envi-
ronment Research Council (GT59804ES and NER/J/
S/2002/00673), respectively, for fi nancial support.
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Manuscript received 15 March 2007
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Manuscript accepted 16 May 2007
Printed in USA
... Jeppsson had determined through controlled experiments that many conodont elements were damaged or destroyed using the acetic acid processing method and that this was especially apparent in processing dolostone versus limestone samples. This, in part, is why there is generally poor conodont biostratigraphic control of the predominantly dolomitized Silurian carbonate succession in Ontario and the midcontinent region of North America (see discussion and data in Kleffner 1989;Kleffner et al. 2009;Barrick et al. 2010), with some exceptions for the Eramosa Formation (Stott et al. 2001;von Bitter and Purnell 2005;von Bitter et al. 2007;Jones, Purnell and von Bitter 2009). ...
... This work verifies the regional continuity and lithologic variability, and temporal significance of this rock unit. Therefore, this paper refers to those facies assigned to the Eramosa interval by Williams (1915aWilliams ( , 1915bWilliams ( , 1919, Shaw (1937), Bolton (1953Bolton ( , 1957, Sanford (1969a), Telford (1978), Armstrong and Meadows (1988), Armstrong and Dubord (1992), Smith (1990aSmith ( , 1990b, Tetreault (2001) andvon Bitter et al. (2007) as the Eramosa Formation Brunton and Brintnell 2011;Brunton et al. 2012; see Figure 14). Shaw (1937) and Brett et al. (1995). ...
... The lower Vinemount member of the formation also acts as a local to regional aquitard from the Niagara Peninsula through City of Guelph area Brunton et al. 2012). The Reformatory Quarry Member possesses exceptionally preserved soft-bodied biota (fauna and flora) at sites between the City of Guelph and the Bruce Peninsula (see Williams 1915b;Copeland and Bolton 1985;Hewitt and Birker 1986;Tetreault 2001;von Bitter and Purnell 2005;von Bitter et al. 2007;Collette and Rudkin 2010;Härling 2012;Waddington, Rudkin and Dunlop 2015); such sites of exceptional fossil preservation are referred to as Lagerstätten. Figure 19. ...
... While few examples of soft-tissue preservation have been collected to date, the lateral extent and repetitive nature of obrution events in the upper Kirkfield Formation offers a tantalizing hint that further exploration may yield more insights into the origin, biogeography, and longevity of distinctive softbodied fauna. This will provide an important complement to Silurian Lagerstätten of Ontario, which have already yielded rare elements of the Cambrian fauna, such as naraoiids and lobopodians, alongside more typical Paleozoic taxa (Caron et al., 2004;von Bitter et al., 2007). More broadly, our findings illustrate the potential for discovering cryptic cases of soft-tissue preservation among well-studied "shelly" biotas of the mid-Paleozoic. ...
... While few examples of soft-tissue preservation have been collected to date, the lateral extent and repetitive nature of obrution events in the upper Kirkfield Formation offers a tantalizing hint that further exploration may yield more insights into the origin, biogeography, and longevity of distinctive softbodied fauna. This will provide an important complement to Silurian Lagerstätten of Ontario, which have already yielded rare elements of the Cambrian fauna, such as naraoiids and lobopodians, alongside more typical Paleozoic taxa (Caron et al., 2004;von Bitter et al., 2007). More broadly, our findings illustrate the potential for discovering cryptic cases of soft-tissue preservation among well-studied "shelly" biotas of the mid-Paleozoic. ...
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... Abundant microvertebrate faunas have been described from arctic Canadian localities, particularly of thelodont assemblages (e.g., Märss et al. 2007), with rarer descriptions of late Silurian to Early Devonian acanthodians (Spjeldnaes 1967;Vieth 1980;Burrow 2013). From eastern Canada, tolypelepid and corvaspid heterostracans have been reported from the middle Silurian Eramosa Lagerstätte, Ontario (von Bitter et al. 2007). From the late Silurian, Turner (1986) redescribed the only known articulated material of the thelodont type genus Thelodus and identified a Paralogania, as well as an acanthodian, from the Cunningham Creek Formation of southern New Brunswick; and Burrow (2011) described the latter as a new acanthodian Nerepisacanthus denisoni from the nodule horizon. ...
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... A surprisingly large number of non-calcified macroalgae ("thallophytic algae" or "seaweeds") have been recovered from early to middle Palaeozoic strata across the presentday Northern Hemisphere, despite the fact that these algae lack hard parts and thus are unlikely to fossilize (e.g., Whitfield 1894;LoDuca 1997;Yang et al. 2003;Kenrick & Vinther 2006;von Bitter et al. 2007;LoDuca & Behringer 2009;Tinn et al. 2009Tinn et al. , 2015Eriksson & von Bitter 2015;LoDuca et al. 2017). Therefore, when present in the rock record, non-calcified macroalgae generally occur in a special type of Konservat Lagerstätte referred to as "thallophytic-alga-dominated biotas", or simply as "algal-Lagerstätten" (Seilacher et al. 1985;LoDuca 1995LoDuca , 1997. ...
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This paper examines some of the taphonomic variables that may bias the arthropod fossil record. The short-term preservation potential of the modern carid shrimp, Pandalus danae, was studied in a variety of laboratory and field settings. Destruction by scavengers (crabs?) was the probably primary cause of carcass destruction in the field. Further breakdown was caused by bacterial decomposition and disturbance by burrowing infauna. Shrimp remains were placed in a series of glass jars in the laboratory. Decomposition destroyed nearly all soft tissues within a period of two weeks. The cuticle became extremely soft, resulting in loss of physical integrity of the remains. Differences between oxic and anoxic decomposition were minor. These results suggest that disturbance by scavengers or burrowing infauna is a major factor in the destruction of buried arthropod remains. The absence or inhibition of bioturbation may be a necessary condition for arthropod preservation. The preservation potential of arthropods, and of other soft-bodied forms, may have declined since the Paleozoic.-from Author
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A new biota including lightly sclerotized and soft-bodied organisms occurs in finely laminated argillaceous dolomites of late Llandoverian age in Waukesha County, Wisconsin. This discovery fills a gap between well known Cambrian and Devonian Konservat Lagerstatten. The biota is dominated by arthropods. A dalmanitid is the most numerous of 13 genera of trilobites; the crustaceans include phyllocarids and ostracods; the chelicerates are represented by the earliest well preserved xiphosure and the fauna includes a possible marine uniramian. The earliest representative of the enigmatic class Thylacocephala, and at least three arthropods of uncertain affinity are also present. There are at least four worm taxa including a possible leech and a papillate annelid. The locality has also yielded a conodont animal, Panderodus. Graptolites and conulariids are common, but echinoderms, brachiopods, bryozoans, corals and molluscs are extremely rare or absent. The unusual composition and exceptional preservation of this assemblage indicates that the biota lived and died in environments rarely represented in the Silurian fossil record.
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Preservation of soft-bodied fossil biotas (Konservat-Lagerstäten) that preserve traces of volatile nonmineralized tissues (readily degraded by bacteria) are not evenly spaced through geologic time. When compared to outcrop area, exceptional faunas appear to be over-represented in the Cambrian and Jurassic. These concentrations in time correspond to particular environments, indicating that controls on the distribution of exceptional faunas may have operated on a global scale. The reduction in the number of exceptional faunas after the Cambrian may reflect the evolution and diversification of deep bio- turbators. Specific conditions favoring stagnation and episodic burial were required to ensure preservation in younger rocks.
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Graptolites are important fossils in Early Palaeozoic assemblages. Preserved graptolite periderm consists dominantly of an aliphatic polymer, immune to base hydrolysis. It contains no protein even though its structure, and chemical analyses of the periderm of the living relative Rhabdopleura, indicate that it was originally collagen. This anomaly was previously interpreted as the result of replacement by macromolecular material from the surrounding sediment. New analyses suggest that the aliphatic composition of graptolite periderm reflects direct incorporation of lipids from the organism itself by in situ polymerization. A similar process may account for the preservation of most organic fossils.
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A newly-discovered Konservat-Lagerstutte in the Upper Ordovician of South Africa has yielded giant conodont apparatuses, some of which are associated with preserved soft tissues of the conodont animals. Lobate structures located to the anterior of the conodont apparatus in several specimens are interpreted as sclerotic cartilages surrounding the eyes, comparing closely with those of the Silurian agnathan Jarnoytius. One specimen also displays a possible trunk trace.