ArticlePDF Available

A late ordovician planktic assemblage with exceptionally preserved soft-bodied problematica from the Martinsburg Formation, Pennsylvania


Abstract and Figures

Here we report a locality containing exceptionally preserved (soft-bodied) fossils of mid-Late Ordovician age from the geologically complex Martinsburg Formation in central Pennsylvania. The fossils, which resemble specimens from Burgess Shale-type deposits, include enigmatic specimens (problematica) and phyllocarid arthropods (with preserved appendages) which are associated with graptolites. The locality is notable for preservation of a low diversity community of soft-bodied planktic animals, likely captured and rapidly buried by a turbidity current. The problematica lack sufficient anatomical detail for confident systematic placement; however, they can be superficially compared to a number of possible metazoans including: nominally/non- shelled mollusks (including veligers), cnidarians, lophophorates, or possibly aberrant tube-dwelling priapulids or polychaetes. Overall, the problematica may belong to one (or several) extinct clades or some unknown clade of animal life. The complex geologic history of the region has reduced the resolution of the problematica’s original exceptional preservation, yet the fossils retain many key features. Hence, this locality has implications for our understanding of exceptional preservation, its alteration over geological history, and the planktic communities of ‘‘The Great Ordovician Biodiversification Event’’ (GOBE) in the planktic realm.
Content may be subject to copyright.
PALAIOS, 2018, v. 33, 36–46
Research Article
Geophysical Laboratory, Carnegie Institution of Science, 5251 Broad Branch Rd. NW, Washington, District of Columbia 20015, USA
Consulting Geologist, 749 Burlwood Drive, Southern Pines, North Carolina 28387, USA
Department of Geosciences, State University of New York, Geneseo, New York 14454, USA
Department of Geology, University of Leicester, Leicester, UK
GeoZentrum Nordbayern, Fachgruppe Pal¨
aoUmwelt, Friedrich-Alexander-Universit¨
at Erlangen-N¨
urnberg, Erlangen, Germany
ABSTRACT: Here we report a locality containing exceptionally preserved (soft-bodied) fossils of mid-Late Ordovician
age from the geologically complex Martinsburg Formation in central Pennsylvania. The fossils, which resemble
specimens from Burgess Shale-type deposits, include enigmatic specimens (problematica) and phyllocarid arthropods
(with preserved appendages) which are associated with graptolites. The locality is notable for preservation of a low
diversity community of soft-bodied planktic animals, likely captured and rapidly buried by a turbidity current. The
problematica lack sufficient anatomical detail for confident systematic placement; however, they can be superficially
compared to a number of possible metazoans including: nominally/non- shelled mollusks (including veligers),
cnidarians, lophophorates, or possibly aberrant tube-dwelling priapulids or polychaetes. Overall, the problematica
may belong to one (or several) extinct clades or some unknown clade of animal life. The complex geologic history of
the region has reduced the resolution of the problematica’s original exceptional preservation, yet the fossils retain
many key features. Hence, this locality has implications for our understanding of exceptional preservation, its
alteration over geological history, and the planktic communities of ‘‘The Great Ordovician Biodiversification Event’’
(GOBE) in the planktic realm.
The Great Ordovician Biodiversification Event’’ (GOBE) is a time of
rising biodiversity which resulted in an increase in the ecological
prominence of benthos suspension feeders and the proliferation of the
planktic realm (Webby 2004; Harper et al. 2015; Algeo et al. 2016; Servais
et al. 2016). Causes of the GOBE are mainly credited to an Early to Middle
Ordovician greenhouse climate that promoted a rise in sea level and the
development of ecospace partitioning in the form of planktic predators,
including graptolites and radiolarians, followed by a terminal Late
Ordovician glaciation (Bambach 1983; Servais et al. 2010) and sea level
The increased availability of food, such as plankton, in the water column
has been suggested as a driver for this radiation (Servais et al. 2009, 2016).
Proposed agents also include increased orogenic activity (Miller and Mao
1995), the appearance of new substrates (Rozhnov 2001), the large-scale
diversification of phytoplankton (Servais et al. 2010), asteroid impacts
(Schmitz et al. 2008), and cooling of the oceans (Trotter et al. 2008). The
GOBE is a multifaceted event with very pronounced taxonomic,
geographic and temporal dimensions, making it difficult to determine
what trigger(s) set in motion this complex event in the early Paleozoic.
Additionally, our understanding of the GOBE chiefly derives from the
shelly fossil record (Servais et al. 2010, 2016) because few exceptionally
preserved fossil assemblages (Konservat-Lagerst¨atten) had been reported
from the Ordovician until recently (Schiffbauer and Laflamme 2012; Van
Roy et al. 2015; Muscente et al. 2017). With the exception of the Fezouata
Biota most of these faunas generally represent marginal or otherwise
unusual environments and atypical, low-diversity communities. Most have
limited usefulness in understanding evolution of the planktic realm during
the GOBE.
Exceptionally preserved fossils, those that preserve non- or weakly
biomineralized organisms (Allison and Briggs 1993; Schiffbauer et al.
2014), provide key insights into ancient biodiversity (Muscente et al.
2017); especially because they include species with low preservation
potentials that drive up measures of taxonomic and ecological richness and
extend the ranges of known species (Farrell et al. 2009; Van Roy et al.
2010; Briggs 2014). Notable examples of exceptionally preserved fossil
localities in the Ordovician include: the Fezouata and Tafi lalt Biota of
Morocco (Van Roy et al. 2010, 2015), Beecher’s Trilobite Bed and similar
sites in New York State (Farrell et al. 2009), the Soom Shale of South
Africa (Gabbott et al. 2017), and the Llanfallteg and Afon Gam biotas of
Wales, UK (Botting et al. 2015; Hearing et al. 2016). Many of these fossils
occur as ‘Burgess Shale-type’ (BST) assemblages (Butterfield and
Nicholas 1996; Meyer et al. 2012; Schiffbauer and Laflamme 2012) of
soft-bodied (non-biomineralized) organisms, however other preservational
modes (Cai et al. 2012) are also present such as pyritization (Beecher’s)
and Ediacaran-type (Tafilalt). Conditions leading to BST preservation were
more common in marine environments in the Ediacaran and especially the
early-middle Cambrian, with the possibility of the late Cambrian; see
Lerosey-Aubril et al. (2017), but are less common post-Cambrian (Meyer
et al. 2012; Schiffbauer and Laflamme 2012; Muscente et al. 2017).
This paper describes a new locality from a geologically complex area in
central Pennsylvania, where mid-Late Ordovician marine clastic rocks of
the Martinsburg Formation contain exceptionally preserved fossils. These
fossils include enigmatic spindle- or conotubular-shaped animals (prob-
lematica) and phyllocarid arthropods, found with graptolites. The
Published Online: January 2018
Copyright Ó2018, SEPM (Society for Sedimentary Geology) 0883-1351/18/033-036/$03.00
problematica are compared to nominally/non-shelled mollusks, cnidarians,
lophophorates, or possibly aberrant tube-dwelling priapulids or poly-
chaetes, though they may belong to an extinct clade.
The faunal suite of graptolites, problematica, and phyllocarids
(fragments and a single whole specimen) are from the Martinsburg
Formation near Hummelstown, east of Harrisburg, PA, USA (40.296443
N, -76.726004 W). The regional geology (Fig. 1) is structurally
complicated (Ganis and Wise 2008; Wise and Ganis 2009) and the rocks
are generally anchizone rank, defined by illite crystallinity and Conodont
Alteration Indexes (CAI). Conodonts from the Martinsburg Formation in
the general vicinity have a CAI of 4.5, indicating a thermal exposure
between approximately 275–3008C, which agrees with the illite crystal-
linity data (John Repetski, USGS, personal communication). Physio-
graphically, the site lies within the Great Valley Section of the Piedmont
Province in the Appalachians. The Martinsburg Formation has been
tectonically affected by Taconic (Late Ordovician) and Allegenian (middle
to late Paleozoic) orogenies, which left the rocks highly sheared, folded
and faulted (Wise and Ganis 2009). Large-scale overthrusting regionally
positioned the low greenschist Cocalico terrane over the Martinsburg in
this area of the Great Valley (Wise and Ganis 2009).
The road-cut section (see Fig. 1B) is primarily gray-black shale with
penetrative multi-oriented cleavage, but the fossil-bearing strata (~10 cm
in thickness) are more thickly bedded siltstones, with nominal bedding-
parallel cleavage (macro-scale observation). Graptolites collected from the
siltstones show little damage from cleavage generation. However, the
orientations of some specimens of problematica show evidence of partial
damage by incipient cleavage acute to the bedding, which is not otherwise
apparent in slab samples. Collecting at this site has been light, and
additional excavation is warranted.
Graptolites of the Diplograptus foliaceus Zone (þ/- Climacograptus
bicornis Zone, see Fig. 2B) were recovered indicating a position in the
lower Martinsburg Formation, Late Ordovician, Sandbian age. The
interpreted depositional environment here, and for the Martinsburg
Formation in general, is a deep-marine turbidite system, infilling the
Taconic foreland basin (McBride 1962; Ganis et al. 2001; Ganis and Wise
2008). The Martinsburg foreland fill consists almost exclusively of
siliciclastics of deep-water origin. Graptolites are common in black shales
deposited under dysoxic to anoxic bottom water conditions, and are
generally absent in gray-green oxic facies. Graptolites accumulated in the
sediment via deadfall or were captured within the water column from
turbidity currents (where they can be found in coarser sediment). Overall,
the Hummelstown site is a thick (at least tens of meters thick) section of
mostly shale and lesser siltstones, compatible with typical Martinsburg
All figured specimens are reposited in the collections of the National
Museum of Natural History (Smithsonian Institution). Reflected light
photographs were made with a Canon PowerShot SX20 IS, Panasonic
(Lumix) DMC-FZ300, and an Olympus DP-25 attached to a binocular
microscope. Digital photographs were processed in Adobe Photoshop CS5,
and composite images (Figs. 2–6) were stitched together using the
‘Photomerge’ option in Adobe Photoshop CS5.
Electron microscopic analyses (Figs. 2, 3) were conducted using an FEI
Nova NanoSEM 600 field emission environmental scanning electron
microscope (ESEM) in high vacuum mode using secondary (topographic)
and backscattered (atomic number contrast) electron detectors. Energy-
dispersive X-ray spectroscopic (EDS) point spectra and elemental maps (of
fossils on unpolished bedding surfaces) were generated using an integrated
ThermoFisher energy-dispersive X-ray detector and a Gatan cathodolumi-
nescence detection system. Identical operating conditions were maintained
for all EDS analyses: 20 keV accelerating voltage, 5.0 spot size (a unitless
measure of beam current and probe diameter), 11.5 mm working distance,
and X-ray signal count-rates between 25–35 kcps. All elemental maps were
acquired for 600 seconds live-time, and individual point spectra were
collected for 100 seconds live-time. Elemental peaks from point spectra
were identified and quantified (with zaf and Au-Pd coating corrections
applied) using ThermoFisher Pathfinder software. Specimens were
uncoated and unpolished on the hand sample surfaces (polishing would
have likely destroyed the specimens).
Elemental maps were generated (Figs. 2C–2E, 3) for all elements found
at .1% (normalized weight percentage; nwp) in point analysis. While
topography of unpolished specimens can significantly affect EDS analysis
and elemental mapping, it is clear from our analyses here that elemental
signal trends observed in the elemental maps generally do not match
specimen topography from secondary electron imaging, suggesting that
observed elemental distributions are due to chemical, not topographic
differences. In addition, EDS point analyses of unpolished specimens on
bedding surfaces were carefully placed in locally flat surfaces of the
specimens to minimize topographic irregularities that may obscure X-ray
Fossils collected from the Hummelstown locality (Fig. 1A) are
graptolites (Figs. 2B, 2D, 3D–3E), phyllocarid arthropods (Fig. 2C), and
enigmatic ‘problematica’ specimens; collectively referred to as the
‘Hummelstown problematica’ or HTP, here forward (Figs. 2–6). Most
HTP specimens (n ¼~50) are fragmentary or poorly exposed; the best 26
problematica fossils are exhibited (Fig. 6) for quick comparisons between
specimens. The graptolites are preserved as collapsed tubaria with some
residual relief. They generally possess fair to good anatomical definition
typical of carbonaceous compressions of graptolites with completely
sclerotized (hardened) tissue. In addition to fragments, we collected a
single complete specimen of a phyllocarid arthropod (Fig. 2C). Although
its appendages are not well preserved and the systematics of the specimen
have not been evaluated, it possesses a distinctive cuticular carapace,
abdomen with 5–7 segments, and pointed telson.
A typical HTP fossil has two main morphological features; a cone-
shaped posterior body and an anterior external body mass which appears to
protrude beyond the aperture-like structure (the specimen in Fig. 4 is
considered a model example). The boundary between the cone-shaped
body and the external mass is seen as a discontinuity across the cone’s axis
(Figs. 4, 5J, 5K), except where the exterior body is absent (or possibly has
been retracted within the cone-shaped posterior body). Most of the fossils
are smooth-sided and straight, but some show a slight curvature (Figs. 2A,
2D, 5F–5H). Overall, they are approximately 3–10 mm long and 1–3 mm
wide at the aperture-like structure. The external body mass ranges in size
from relatively small (,1 mm) to a length similar to the posterior cone-
shaped body (Fig. 5J). There are two very general morphological groups of
cone fauna, one, which is long and narrow, and the other, which is shorter
and wider (Fig. 6). Often, the narrowing apex terminates in a spindle-like
shape as a rod (Figs. 5F–5H).
We found no evidence of branching, holdfasts, or connection points at
the apex of any specimen (Figs. 3B, 6). Likewise, we found no discernable
internal anatomical features within cone-shaped posterior bodies, and the
external mass consistently exhibits an amorphous appearance save for the
small spikes or flaps seen on some specimens. Although, this condition
may simply reflect marginal preservation, it may be considered that this is
the outline expression of an anatomically simple, pliable body (proposed
taxonomic affinity is discussed below). None of the cone-shaped posterior
bodies possess any unambiguous evidence of biomineralization (Fig. 3B),
but we cannot rule out the possibility that the fossil represents an originally
biomineralized skeletal element, which underwent taphonomic demineral-
ization during diagenesis or weathering (Muscente and Xiao 2015).
Currently, there is no evidence for moldic impressions of the HTP fossils.
The HTP fossils are preserved as carbonaceous compressions, which
can be seen in the dark-black appearance (low atomic mass, or Z) in
backscattered electron (BSE) imagery, the large carbon signal from EDS
point analysis, and their black color in hand sample (Figs. 2F, 3A–3C).
FIG. 1.—Geological map of fossil locality. A) Simplified geological map showing the major geologic units and tectonic features around Hummelstown, PA (scale bar ¼2
km). Inset shows the location of the state of Pennsylvania on eastern coast of the United States (with the star showing the location of Washington DC). Modifi ed from
Blackmer and Ganis (2015). B) Panorama looking west at the outcrop, person for scale. C) A close-up of the bedding at the outcrop, rock hammer for scale. D) Image of
fossil-bearing slab freshly collected. Weathering has lightened the black shales; pencil for scale.
Under magnification in reflected light microscopy, the fossil specimens
have a golden-colored sheen in reflected light due to the abundance of
pyrite framboids (now Fe-oxide pseudomorphs with no sulphur present;
see Fig. 2E) and many fossils are surrounded by pyritic envelopes (Fig. 3).
Elemental EDS analysis also show that some of the HTP fossils also
contain relatively higher concentrations of Si than their surrounding
matrixes (Fig. 2F). The Si likely occurs within thin Fe-rich clay veneers on
the fossils, which we observed in BSE images (Fig. 3B). We did not detect
FIG. 2.—Reflected light, BSE, and EDS imagery of fossil specimens. A) Reflected light image of hand sample containing HTP and graptolite fossils (black arrows). Red
arrow points to apex of HTP specimen pictured in Figure 3B. (hand sample 700852 pictured). B) Reflected light image of Diplograptus?foliaceous (Murchison 1839)
graptolite fossil found in association with the HTP fossils. C) Phyllocarid fossil with a well-defined carapace and segmented abdomen (700849). D) Numerous fossils in
association, including i) Amplexograptus cf. A. maxwelli,ii) problematica, and iii) an unknown fossil (700826). White arrow points to transition from narrower to wider cone-
shaped body on problematica specimen. Blue arrow points to possible aperture location. Yellow arrow points to overlap of unknown fossil by problematica specimen (and
corroborated by counterpart, not pictured). E) BSE/SEM hybrid image of Fe-oxides, formerly pyrite framboids (hand sample 700852 pictured). F) EDS maps of the cone-
shaped posterior body area of fossil (700830). Fossil body is between white dashed lines. Scale bars: A, B ¼2 mm, C, D ¼1 mm, and E, F ¼100 um.
the Si signal of these veneers in all specimens (Fig. 3B, 3C), but this may
represent a consequence of their thinness and the low surface-sensitivity of
EDS analysis (Orr et al. 2009; Muscente and Xiao 2015). Tectonic
cleavage can contain high Si levels, and although it cuts through the HTP
fossils, it is not expressed in the graptolites or phyllocarids in a similar
manner. While this cleavage breaks up the fossils and degrades the
resolution of minute features, overall, fossil morphology remains intact.
Paleoecological Considerations
The graptolites, phyllocarids, and HTP specimens occur in dense mixed
assemblages at the Hummelstown locality. The close association of these
fossils suggests the HTP represent organisms with planktic habits and
possible ecological relationships with the other fauna. However, due to the
enigmatic taxonomic affinities of the HTP, their ecology is unknown.
Among the mixed specimens of graptolites and problematica, one pair of
specimens (Fig. 3D, 3E) appears to show physical attachment between
organisms of the two groups, but this example may represent an accident of
fossil placement. Additional specimens of this type would be required to
indicate ecological interaction.
No unusual sedimentological conditions are apparent at the Hummels-
town site that might explain the special conditions necessary for
preservation of soft-bodied organisms, although that topic deserves further
study. However, the role of the post-burial alteration (either geochemically
or physically), also needs to be better understood (see below).
Evidence for Burgess Shale-Type Preservation
The HTP specimens collected from the Hummelstown locality resemble
BST fossils in terms of their overall preservation. In general, BST fossils
FIG. 3.—EDS maps and reflected light images of HTP and graptolite theca. A) BSE/SEM hybrid image and EDS map composites of graptolite theca (700850). B,C) BSE/
SEM hybrid images and EDS maps of HTP (700824). Inset shows location on magnified specimen photo (in same position as in B and C). View B is apex tip. View C is
possible external body mass. D,E)Cryptograptus insectiformis partially covered by HTP (700851). View D is original image. View E is highlighted image, graptolite (blue)
and HTP (green). Scale bars: A–C ¼100 lm, D, E ¼2 mm.
represent non-biomineralized tissues (Butterfield 2003) often preserved via
pyritization or clay minerals (Schiffbauer et al. 2014). Fossils of
phyllocarid carapaces often signify non-biomineralized elements (Caron
and Jackson 2008; Gabbott et al. 2008) and there is evidence the HTP
fossils may represent labile tissue (Figs. 4–6). The EDS spectra of the HTP
contain prominent carbon signals, consistent with the preservation of
organic matter, but we cannot rule out that the HTP fossils (with the
possible exception of the external body mass) were originally biominer-
alized skeletal elements, which were taphonomically demineralized during
diagenesis and/or weathering, leaving behind carbonaceous residuals of the
shells’ organic matrices (Muscente and Xiao 2015).
The occurrence of the fossils in a black shale suggests preservation
occurred in a deep water, organic-rich, anoxic setting, which is very
favorable to conservation of organic matter and formation of diagenetic
pyrite. An absence of bioturbation suggests that the fossils experienced
rapid burial in a benthic environment that contained effectively no benthic
mobile animals (or at least at the level at which the fossils were buried).
Pyrite framboids found with the HTP fossils are similar to those found in
association with Wiwaxia sclerites of the Burgess Shale (Butterfield 2003;
Butterfield and Harvey 2012) and trilobites of Beecher’s Trilobite Bed
(Farrell et al. 2009); in addition to fossils at various other localities (Cai et
al. 2012; Schiffbauer et al. 2014; Muscente et al. 2017). Higher
concentrations of Fe-oxides around the Hummelstown fossils provide
FIG. 4.—Hummelstown Problematica Fossil. A) Typical specimen with two-part
body plan and clear aperture and external body-mass exhibited; raw image of
specimen (700823). This specimen also displays a ‘spindle’ shape where the cone-
shaped posterior body widens and narrows closer to the aperture. B) Same specimen
as in A, annotated. Black bars indicate extent of external body-mass. Blue ar row
denotes intersection of the cone-shaped posterior body and the external body mass.
White arrows show pointed features. Dotted white line shows narrowing of the
‘spindle’ shape and the flared terminus of the cone-shaped body. Scale bar ¼3 mm.
FIG. 5.—Basic Hummelstown Problematica fossil forms. Each row contains (from
left to right) a model of the Hummelstown Problematica body construction and
preservation next to example fossil specimens. AD) Specimens with only the cone-
shaped posterior body (pb) preserved; the external body mass may be missing or
retracted (B ¼700830; C ¼700842; D ¼700829). EH) Specimens with some
external body mass (xbm) present (possibly partially retracted) (F ¼700839; G ¼
700825; H ¼700840). IK) Specimens with relatively large amounts of external
body mass present (J ¼700843; K ¼700845). Blue arrows denote intersection of pb
and xbm. Black arrows point to distinctive narrowing of the body near the posterior
apex. White arrows show pointed features. Black brackets indicate extent of external
body mass on fossil specimen. Scale bars ¼1 mm.
further evidence for microbial cycling of sulfur (Fig. 3C). In reflected light
(Fig. 2A), the HTP differ from the associated graptolites (which have less
of a sheen), perhaps due to different body integument types and the
volatility of those tissues (Gabbott et al. 2004). Elemental analysis of the
HTP specimens supports a much lighter (or absent) taphonomic
mineralization. Whereas some of the sclerotized graptolites are heavily
pyritized, the HTP are primarily non-mineralized carbonaceous material.
Since pyritization results from the degradation of organic matter and the
precipitation of sulfide by sulfur-reducing bacteria, the differing amounts
in the two fossils suggests that the problematica had much less organic
matter in their bodies than the graptolites.
The relationship between clay minerals and exceptional preservation is
still under study (Meyer et al. 2012; Schiffbauer et al. 2014). Various
studies of authigenic (Harvey and Butterfield 2017) and detrital clay
materials (Orr et al. 1998, 2002; Liu et al. 2016) in fossils have argued that
they play a role in soft tissue conservation by inhibiting autolytic decay
(Meyer et al. 2012; McMahon et al. 2016) Nonetheless, evidence indicates
the metamorphism also plays a role in creating and/or altering clays within
fossils (Butterfield 2003; Orr et al. 2003; Butterfield et al. 2007; Muscente
and Xiao 2015). The origin of the clays in the HTP fossils is undetermined,
thus, their role in preservation is speculative. Although the overall
morphology of the HTP fossils is intact, the paucity of fi nely preserved
features or internal details might be a consequence of the illite crystallinity
associated with the anchizone rank of the rock. However, the fossiliferous
rocks of the Burgess Shale are greenschist rank (see Powell 2003) so
anchizone rank does not preclude the preservation of fine features. Post-
formational metamorphic effects on exceptionally preserved fossils have
received little discussion in the literature, as most authors focus on the
formational processes. Hence, the taphonomic history of the Hummels-
town locality provides a potential resource for studying the effects of
matrix alteration/degradation on the processes of exceptional preservation.
Taxonomic Affinity
While assigning a taxonomic affinity of the problematica is challenging,
the fossil’s deep marine depositional environment (anoxic black shale),
association with pelagic graptolites (Sheets et al. 2016), soft-bodied
taphonomy, and the absence of co-occuring benthic faunal, infers a
planktic habitat. Ordovician rocks contain few examples of non-
biomineralized pelagic organisms, particularly those of small size, because
they have a low preservational potential and high susceptiblity to
taphonomic degradation. Hence, there are a limited number of represen-
tative small, pelagic, cone-shaped organisms from the fossil record of this
interval. Most cone-shaped fossils are larger than the HTP, even during
their early ontogenetic stages, such as with nautiloids, although their early
record is still under investigation (Kr¨oger and Mapes 2007; Kr¨oger et al.
2009, 2011; De Baets et al. 2012; Landing and Kr¨oger 2012).
The tentaculitoids are unlikely to be possible candidate organisms
(Wood et al. 2004; Farsan 2005; Filipiak and Jarzynka 2009; Wittmer and
Miller 2011). The long and narrow HTP superficially resemble
tentaculitoids, but the latter are more heavily mineralized and have a
lower degree of aperatural expansion (Farsan 2005) than the HTP.
Tentaculitoids have a bulbous initial chamber and many have longitudinal
and transverse ornamentation (which are still recognizable in decalcified
specimens; see Filipiak and Jarzynka 2009). Major forms of planktic
tentaculitoids like dacryoconarids fi rst appeared in the Devonian
´et al. 2009; Wittmer and Miller 2011). Similar bulbs can also
be seen in externally shelled cephalopods preserved as ‘‘ ghosts’’ or fi lms
(De Baets et al. 2013).
Conulariids are excluded due to their much larger size and heavily
biomineralized external structure (Babcock 1991; Ford et al. 2016). We
found no evidence of holdfasts in any of the ~50 specimens examined, so
while their absence may be taphonomic, this is unlikely and supports the
interpretation that the HTP inhabited pelagic environments, unlike
conulariids. Sphenothallus has been variously described to have similar
affinity to annelids (Mason and Yochelson 1985) or cnidarians (van Iten et
al. 1992; Muscente and Xiao 2015; Vinn and Kirsimae 2015). Regardless,
Sphenothallus represents a phosphatic or organophosphatic tubular or
conotubular shell presenting as two peripheral longitudinal thickenings
FIG. 6.—Specimens of Hummelstown problematica, grouped by morphotypes: A
P) Long and narrow (white background); QZ) Short and wide (gray background).
Specimen identification numbers are: A ¼700823, B ¼700824, C ¼700825, D ¼
700826, E ¼700827, F ¼700828, G ¼700829, H ¼700830, I ¼700831, J ¼700832,
K¼700833, L ¼700834, M ¼700836, N ¼700837, O ¼700838, P ¼700835, Q ¼
700839, R ¼700840, S ¼700841, T ¼700842, U ¼700843, V ¼700844, W ¼
700845, X ¼700846, Y ¼700848, Z ¼700847. Scale bars ¼2 mm.
(when flattened) separated by relatively thinner walls; the shell attached to
the seafloor via a conical holdfast, which is not always preserved. Although
Sphenothallus is often found preserved as carbonaceous fossils, the
absence of the other features precludes placement of the HTP with that
taxon (possible cnidarians affinities other than Sphenothallus are discussed
Hyolithids, commonly grouped with the lophophorates (Moysiuk et al.
2017), have a similar short and wide morphology as have the HTP and are
often found in great numbers on a bedding plane while occasionally being
preserved as organic fossils (Babcock and Robison 1988; Mart´ı Mus 2014,
2016; Kimmig and Pratt 2015). However, hyolithid affinities can be
excluded due to numerous factors, including: surface structures, ornamen-
tation, and general morphology (Mart´ı Mus and Bergstr ¨om 2005).
Although the absence of these features may reflect the poor preservation
of the HTP, such features are present even in hyolithids preserved as
carbonaceous compression (Mart´ı Mus 2014, 2016; Moysiuk et al. 2017).
Hyolithid shells rarely show bending or curvature and are often (but not
always) found with their biomineralized parts (the helens and operculum)
nearby: features which we did not observe at the Hummelstown locality.
Certain corynoidid graptolites are degenerative forms consisting of a
single large sicula and one or two smaller thecae in parallel growth. Yet,
they clearly exhibit characteristics common to graptoloid sicular growth
(fusellar rings and cortical bandage) with prosicular and metasicular stages,
as well as the presence of a prominent virgella and nema (Maletz and
Zhang 2016). Although the large corynoidid sicula is cone shaped, as is the
HTP cone, the latter lacks all other characteristics associated with
graptolite morphology; other graptolites from this location do have well
preserved morphology.
Cone-shaped algae, which superficially resemble the HTP specimens,
are often preserved as organic compressions, such as Winnipegia cuneata
(Fry 1983). Nonetheless, these algae have clear holdfasts at their apex and
differ in size from the HTP specimens. Some Ediacaran algae or organic
forms (i.e., Vendotaenia) are preserved in a similar manner (Meyer et al.
2016) while other early algae display branching that could be broken up
into smaller cone-shaped fragments (Du et al. 2017; Nowak et al. 2017).
However it is unlikely that the HTP fossils represent broken stipes. The
regular morphology of the HTP fossils, which fall within a relatively
narrow size range, does not exemplify any Paleozoic algae (LoDuca et al.
2017). Thus, we also exclude algal affinities.
The known cone-shaped fossil organisms that occurred in comparable
habitats to the HTP fossils, which can be excluded for various reasons,
were discussed above. A further list of animals with the potential for
affinity are discussed below, which includes nominally/non-shelled
mollusks (including veligers), cnidarians, lophophorates, and aberrant
tube-dwelling priapulid or polychaete worms. It should be noted that the
cone section of the problematica could be either tubicolous or visceral, but
it is putatively non-biomineralized. It is tempting, and perhaps prudent, to
consider all the HTP fossils as belonging to a single animal category.
However, there is at least a possibility that the population represents a
mixed community of different taxa that all share the same gross outward
morphology and, at a minimum, two different morphotypes are present (see
Fig. 6) based on length versus width ratios.
The cnidarian fossil that most closely resembles the HTP is the
enigmatic Cambrorhytium from the middle Cambrian Marjum Formation,
which has been classified as a tubicolous cnidarian (Conway Morris and
Robison 1988). The exceptionally preserved biotas from the middle
Cambrian of Utah all represent BST preservation deposits (Conway Morris
and Robison 1988). The overall simple cone-shape of Cambrorhytium is
similar to the HTP fossils, including a slight bend near the apex, and two
‘species’ based on length versus width ratios (C. major is long and narrow
while C. fragilis is short and wide).
There may be evidence for an external body mass in Cambrorhytium
(see Conway Morris and Robison 1988, fig. 12, 3b). By analogy, the HTP
cone would be a tubicolous structure and the external mass in the HTP
would be the body (with mangled and matted tentacles?). Despite these
similarities, the Cambrorhytium are much larger than any of the collected
HTP specimens and the presence of prominent annulations in Cambro-
rhytium may exclude it as a comparable organisms (sensu stricto). Overall,
the broad range of morphological variety and life modes within Cnidaria
(and those fossils sometimes grouped with cnidarian affinity) might
possibly accommodate the HTP fossils.
A molluscan affinity may be possible, as the problematic fossils
superficially resemble two extant molluscan forms: pelagic thecosoma-
tous pteropods and gastropod planktotrophic veligers (possibly as a
retention of juvenile characteristics by an adult form, also known
paedomorphy). Both of these taxa have two-part body plans, and in some
cases a retractable foot (possibly analogous to the external body mass of
the HTP). Some of the earliest gastropod fossils display apical larval
shells, indicating that early gastropods employed planktic larvae as early
as the late Cambrian (Bandel 1997; Peterson 2005; Fr ´
yda 2012; Nielsen
2013), and the development of planktotrophy and the expansion into
pelagic niches by gastropods in the Ordovician (N¨
utzel et al. 2006,
2007a, 2007b). Specifically, Peterson (2005) determined that gastropod
veligers (planktotrophic or feeding larvae) most likely appeared in the
Early to Middle Ordovician.
During this time the appearance of actively feeding larvae coincided
with the emergence of multi-tiered suspension feeders and a restructuring
of the planktic ecosystem (Peterson 2005; Servais et al. 2009, 2010).
Therefore, it could have been more beneficial for veligers to become
holoplanktic, like extant pteropods, and remain in the planktic ecosystem
for their entire life cycle (N ¨
utzel and Fr´
yda 2003; N¨
utzel et al. 2006,
2007b; Servais et al. 2009; Nielsen 2013). The HTP can be morpholog-
ically compared to lightly biomineralized (now dissolved), nominally to
non-shelled veligers, or adult mollusks with a pteropod-like life style
(based on superficial morphology); thus, that type of organism is a
candidate for the HTP identity. However, true pteropods are only
documented from the latest Mesozoic (Cuvier 1817; Janssen and
Peijnenburg 2014; Janssen and Goedert 2016) which eliminates affinity
to extant or fossil pteropods. Therefore, an adult molluscan form with a
similar form and life-style would imply homoplasy within the Late
Ordovician molluscan clade.
Other Lophophorates
Of the major groups of Lophophorates, Brachiopoda, and Bryozoa,
can be dismissed as not comparable to the HTP fossils, leaving Hyolitha
and Phoronida for discussion. Hyolitha is discussed above as a non-viable
candidate. The Phoronida are worm-like sessile dwellers, which build
chitinous tubes, thus having a simple body plan like the HTP fossils. The
actinotroch larvae of the group are free-swimming. The fossil record of
Phoronida is sparse due to their lack of mineralized hard parts and limited
preservational potential. May (1993) identified the presence of phoronids
based on phoronid-like borings, Talpina from the Devonian, but provided
no evidence of soft-bodied fossils themselves. Without better exclusion-
ary criteria revealed by taxonomic detail, the potential accommodation of
the HTP fossils within the Phoronida, as an aberrant pelagic form, can be
held open wherein the external mass is interpreted as a lophophoric
Aberrant Tube-Dwelling Priapulids or Polychaetes
The lack of annulation or segmentation in the HTP fossils is not
necessarily indicative of a preferred placement into either priapulids or
polychaetes (Liu et al. 2014; Wilson and Butterfield 2014; Parry et al.
2016; Hou et al. 2017a; Slater et al. 2017). As previously mentioned, the
overall marginal resolution of the HTP fossils as organic films generally
obscures anatomical details, which would be further masked if the cone is
tubicolous. However, the regular morphology of the HTP fossils may be
evidence against tubes, which may be irregular in shape depending on
position and integument type (see Meyer et al. 2012 for discussion on tube
preservation). Typically benthic priapulids have a ringed body often circled
with spines and proboscis ornamented with longitudinal ridges (Liu et al.
2014; Hou et al. 2017b; Hu et al. 2017). We did not observe any of these
features in the HTP fossils. Polychaetes are segmented worms, which often
build biomineralized living tubes and have mineralized teeth, identified as
scolecodonts (Rouse and Pleijel 2001; Hou et al. 2017b). Scolecodonts are
common and found at some BST localities (Slater et al. 2017), but have not
yet been found at the Hummelstown locality. HTP association with either
of these groups would seem to require aberrant forms residing in tubicolius
cone-like structures and living in the pelagic realm.
Discovery of exceptionally preserved enigmatic fossils provides a rare
glimpse into the character of the Late Ordovician planktic community
during the GOBE. The problematica occur as part of a low-diversity
assemblage that also includes graptolites and phyllocarids. The fossils
appear to have been rapidly buried below the benthic surface after capture
in a turbidity event. The flattened graptolites have a fair to good
preservation, and the phyllocarid appendages are clearly visible, but
without fine detail. The problematica are organic films, generally
marginally preserved. The taphonomy of these fossils, especially the
presence of framboidal pyrite in association with soft-bodied organic
compressions, indicates a Burgess shale-type preservation pathway. The
paucity of finely preserved features or internal details may reflect the
regional low anchizone metamorphic history of the Martinsburg
Formation, which is highly sheared and geologically complex at the
collection locality near Hummelstown, Pennsylvania. The phylogenetic
identity of the problematica, which consists of a cone-shaped body and
external mass, is uncertain (which might include an extinct clade) with
suggestions including nominally to non-shelled mollusks, cnidarians,
lophophorates, and aberrant priapulid or polychaete worms. The
taphonomic factors responsible for the preservation of these fossils merit
further study, as we find no evidence of unusual sedimentological
conditions at the Hummelstown site. The effects of post-burial (physical
and geochemical) metamorphic processes, as they pertain to the Hummels-
town locality and BST deposits in general, also merit further consideration.
Lastly, it seems significant that the HTP fossils appear unfamiliar given
their placement in a time of intense diversification (notwithstanding
preservation issues) and unveils a possible association between graptolites
and soft-bodied planktic organisms during the GOBE.
The authors would like to thank the reviewers of previous versions of this
manuscript for their insight and suggestions. We would also like to thank the
Department of Mineral Sciences at the Smithsonian National Museum of
Natural History in Washington, DC for use of their ESEM and facilities that
made the analyses in this study possible. Thanks go out to Emma Bullock and
Timothy Rose for their help in gaining access, and use, of the analytical
equipment at the Smithsonian. Thank you to Arie Janssen and John Repetski for
their comments on early drafts of this manuscript. We would also like to thank
Gale Blackmer of the Pennsylvania Geological Survey and Elizabeth Graybill
for their assistance in the preliminary work on this fossil locale, which was
discovered during mapping under grant G09AC00181 from the USGS National
Cooperative Geologic Mapping Program. M.B. Meyer and G.R. Ganis carried
out field work, J.M. Wittmer (and others) contributed to the interpretation of the
fossils. MBM, GRG, and JMW wrote the paper with input from the other
ALGEO, T.J., MARENCO, P.J., AND SALTZMAN, M.R., 2016, Co-evolution of oceans, climate,
and the biosphere during the ‘Ordovician Revolution’: a review: Palaeogeography,
Palaeoclimatology, Palaeoecology, v. 458, p. 1–11.
ALLISON, P.A. AND BRIGGS, D.E.G., 1993, Exceptional fossils record: distribution of soft-
tissue preservation through the Phanerozoic: Geology, v. 21, p. 527–530.
BABCOCK, L., 1991, The Enigma of Conulariid Affinities: The Early Evolution of Metazoa
and the Significance of Problematic Taxa: Cambridge University Press, Cambridge, p.
BABCOCK, L.E. AND ROBISON, R.A., 1988, Taxonomy and paleobiology of some middle
Cambrian Scenella (Cnidaria) and Hyolithids (Mollusca) from western Nor th America:
The University of Kansas Paleontological Contributions, v. 121, p. 22.
BAMBACH, R.K., 1983, Ecospace utilization and guilds in marine communities through the
Phanerozoic, in M.J.S. Tevesz and P.L. McCall (eds.), Biotic Interactions in Recent and
Fossil Benthic Communities: Plenum Press, New York, p. 719–746.
BANDEL, K., 1997, Higher classification and pattern of evolution of the Gastropoda: A
synthesis of biological and paleontological data: Courier Forschungsinstitut Sencken-
berg, v. 201, p. 57–81.
´, S., FR´
S, P., 2009, Unsucces sful predation on middle Paleozoic
plankton: shell injury and anomalies in Devonian dacryoconarid Tentaculites: Acta
Palaeontologica Polonica, v. 52, p. 407–412.
BLACKMER, G.C. AND GANIS, G.R., 2015, Graptolites, conodonts, stratigraphy, and structure:
mapping the Taconic foreland in the Great Valley of Pennsylvania: Geological Society of
America Abstracts and Programs, v. 47.
BOTTING, J.P., MUIR, L.A., JORDAN,N.,AND UPTON, C., 2015, An Ordovician variation on
Burgess Shale-type biotas: Scientific Reports, v. 5, p. 9947.
BRIGGS, D.E.G., 2014, Paleontology: a New Burgess Shale Fauna: Current Biology, v. 24,
p. R398–R400.
BUTTERFIELD, N.J., 2003, Exceptional fossil preservation and the Cambrian Explosion:
Integrative and Comparative Biology, v. 43, p. 166–177.
BUTTERFIELD, N.J., BALTHASAR,U.,AND WILSON, L.A., 2007, Fossil diagenesis in the Burgess
Shale: Palaeontology, v. 50, p. 537–543.
BUTTERFIELD, N.J. AND HARVEY, T.H.P., 2012, Small carbonaceous fossils (SCFs): a new
measure of early Paleozoic paleobiology: Geology, v. 40, p. 71–74.
BUTTERFIELD, N.J. AND NICHOLAS, C.J., 1996, Burgess Shale-type preservation of both non-
mineralizing and ‘‘ shelly’’ Cambrian organisms from the MacKenzie Montains,
northwestern Canada: Journal of Paleontology, v. 70, p. 893–899.
CAI, Y., SCHIFFBAUER, J.D., HUA, H., AND XIAO, S., 2012, Preservational modes in the
Ediacaran Gaojiashan Lagerst¨atte: pyritization, aluminosilicifi cation, and carbonaceous
compression: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 326-328, p. 109–
CARON, J.-B. AND JACKSON, D.A., 2008, Paleoecology of the Greater Phyllopod Bed
community, Burgess Shale: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 258,
p. 222–256.
CONWAY MORRIS,S.AND ROBISON, R.A., 1988, More soft-bodied animals and algae from the
middle Cambrian of Utah and British Columbia: The University of Kansas
Paleontological Contributions, v. 122, p. 23–84.
CUVIER, G., 1817, M´emoires pour servir `a l’histoire et `a l’anatomie des mollusques:
Deterville, Paris.
Ammonoidea and the age of the Hunsr¨
uck Slate (Rhenish Mountains, Western
Germany): Palaeontographica Abteilung A, v. 299, p. 1–113.
DEBAETS, K., KLUG, C., KORN,D.,AND LANDMAN, N.H., 2012, Early evolutionary trends in
ammonoid embryonic development: Evolution, v. 66, p. 1788–1806.
DU, W., LIAN WANG, X., KOMIYA, T., ZHAO, R., AND WANG, Y., 2017, Dendroid multicellular
thallophytes preserved in a Neoproterozoic black phosphorite in southern China:
Alcheringa: An Australasian Journal of Palaeontology, v. 41, p. 1–11.
Beyond Beecher’s Trilobite Bed: widespread pyritization of soft tissues in the Late
Ordovician Taconic foreland basin: Geology, v. 37, p. 907–910.
FARSAN, N.M., 2005, Description of the early ontogenic part of the Tentaculitids, with
implications for classification: Lethaia, v. 38, p. 255–270.
FILIPIAK,P.AND JARZYNKA, A., 2009, Organic remains of tentaculitids: new evidence from
Upper Devonian of Poland: Acta Palaeontologica Polonica, v. 54, p. 111–116.
FORD, R.C., VAN ITEN, H., AND CLARK, G.R., 2016, Microstructure and composition of the
periderm of conulariids: Journal of Paleontology, v. 90, p. 389–399.
FRY, W.L., 1983, An algal flora from the upper ordovician of the Lake Winnipeg region,
Manitoba, Canada: Review of Palaeobotany and Palynology, v. 39, p. 313–341.
YDA, J., 2012, Phylogeny of Palaeozoic Gastropods Inferred from Their Ontogeny, in J.A.
Talent (ed.), Earth and Life: Global Biodiversity, Extinction Intervals and Biogeographic
Perturbations Through Time: Springer Netherlands, Dordrecht, p. 395–435.
GABBOTT, S.E., BROWNING, C., THERON, J.N., AND WHITTLE, R.J., 2017, The late Ordovician
Soom Shale Lagerst¨atte: an extraordinary post-glacial fossil and sedimentary record:
Journal of the Geological Society, v. 174, p. 1–9.
GABBOTT, S.E., HOU, X.G., NORRY, M.J., AND SIVETER, D.J., 2004, Preservation of early
Cambrian animals of the Chengjiang biota: Geology, v. 32, p. 901–904.
GABBOTT, S.E., ZALASIEWICZ,J.,AND COLLINS, D., 2008, Sedimentation of the Phyllopod Bed
within the Cambrian Burgess Shale Formation of British Columbia: Journal of the
Geological Society, London, v. 165, p. 307–318.
GANIS, G.R., WILLIAMS, S.H., AND REPETSKI, J.E., 2001, New biostratigraphic information
from the western part of the Hamburg klippe, Pennsylvania, and its signifi cance for
interpreting the depositional and tectonic history of the klippe: Geological Society of
America Bulletin, v. 113, p. 109–128.
GANIS, G.R. AND WISE, D.U., 2008, Taconic events in Pennsylvania: datable phases of a ~
20 m.y. orogeny: American Journal of Science, v. 308, p. 167–183.
HARPER, D.A.T., ZHAN, R.-B., AND JIN, J., 2015, The Great Ordovician Biodiversification
Event: reviewing two decades of research on diversity’s big bang illustrated by mainly
brachiopod data: Palaeoworld, v. 24, p. 75–85.
HARVEY, T.H.P. AND BUTTERFIELD, N.J., 2017, Exceptionally preserved Cambrian loriciferans
and the early animal invasion of the meiobenthos: Nature Ecology and Evolution, v. 1, p.
TAYLOR, A.C., AND BRASIER, M.D., 2016, Survival of Burgess Shale-type animals in a
Middle Ordovician deep-water setting: Journal of the Geological Society, v. 173, p. 628–
Y., PURNELL, M.A., AND WILLIAMS, M., 2017a, The Paleoecology of the Chengjiang Biota,
The Cambrian Fossils of Chengjiang, China: John Wiley and Sons, Ltd, Chichester, UK,
p. 30–34.
Y., PURNELL, M.A., AND WILLIAMS, M., 2017b, Priapulida and Relatives, The Cambrian
Fossils of Chengjiang, China: John Wiley and Sons, Ltd, Chichester, UK, p. 114–137.
HU, S.-X., ZHU, M.-Y., ZHAO, F.-C., AND STEINER, M., 2017, A crown group priapulid from
the early Cambrian Guanshan Lagerst¨atte: Geological Magazine, v. 154, issue 6, p. 1–5.
JANSSEN, A.W. AND GOEDERT, J.L., 2016, Notes on the systematics, morphology and
biostratigraphy of fossil holoplanktonic Mollusca, 24, first observation of a really
Mesozoic thecosomatous pteropod: Basteria, v. 80, p. 59–63.
JANSSEN, A.W. AND PEIJNENBURG, K.T.C.A., 2014, Holoplanktonic Mollusca: Development
in the Mediterranean Basin during the last 30 million years and their future, in S.
Goffredo and Z. Dubinsky (eds.), The Mediterranean Sea: Its History and Present
Challenges: Springer Netherlands, Dordrecht, p. 341–362.
KIMMIG,J.AND PRATT, B.R., 2015, Soft-bodied biota from the middle Cambrian (Drumian)
Rockslide Formation, Mackenzie Mountains, northwestern Canada: Journal of
Paleontology, v. 89, p. 51–71.
OGER,B.AND MAPES, R.H., 2007, On the origin of bactritoids (Cephalopoda):
Pal¨aontologische Zeitschrift, v. 81, p. 316.
OGER, B., SERVAIS,T.,AND ZHANG, Y., 2009, The origin and initial rise of pelagic
cephalopods in the Ordovician: PLoS One, v. 4, p. e7262.
OGER, B., VINTHER,J.,AND FUCHS, D., 2011, Cephalopod origin and evolution: a
congruent picture emerging from fossils, development and molecules: Bioessays, v. 33,
p. 602–613.
OGER, B., 2012, Cephalopod ancestry and ecology of the hyolith
‘‘Allatheca’’ degeeri s.l. in the Cambrian Evolutionary Radiation: Palaeogeography,
Palaeoclimatology, Palaeoecology, v. 353–355, p. 21–30.
ally-preserved late Cambrian fossils from the McKay Group (British Columbia, Canada)
and the evolution of tagmosis in aglaspidid arthropods: Gondwana Research, v. 42, p.
2016, Tracing Earth’s O2 evolution using Zn/Fe ratios in marine carbonates:
Geochemical Perspectives Letters, v. 2, p. 24–34.
LIU, Y., XIAO, S., SHAO, T., BROCE,J.,AND ZHANG, H., 2014, The oldest known priapulid-like
scalidophoran animal and its implications for the early evolution of cycloneuralians and
ecdysozoans: Evolution and Development, v. 16, p. 155–165.
LODUCA, S.T., BYKOVA, N., WU, M., XIAO, S., AND ZHAO, Y., 2017, Seaweed morphology
and ecology during the great animal diversification events of the early Paleozoic: a tale of
two floras: Geobiology, v. 15, p. 588–616.
MALETZ,J.AND ZHANG, Y., 2016, Treatise Online no. 79: Part V, Second Revision, Chapter
21: Suborder Glossograptina: Introduction, Morphology, and Systematic Descriptions:
Treatise Online,
IMUS, M., 2014, Interpreting ‘shelly’ fossils preserved as organic films: the case of
hyolithids: Lethaia, v. 47, p. 397–404.
IMUS, M., 2016, A hyolithid with preserved soft parts from the Ordovician Fezouata
Konservat-Lagerst¨atte of Morocco: Palaeogeography, Palaeoclimatology, Palaeoecology,
v. 460, p. 122–129.
OM, J.A.N., 2005, The morphology of Hyolithids and its
functional implications: Palaeontology, v. 48, p. 1139–1167.
MASON,C.AND YOCHELSON, E.L., 1985, Some tubular fossils (Sphenothallus: ‘‘Vermes’’)
from the middle and late Paleozoic of the United States: Journal of Paleontology, v. 59, p.
MAY, A., 1993, Zur Fossilf¨
uhrung des Ohler Schiefers (Devon: Eifelium) im West-
Sauerland (Rheinisches Schiefergebirge): Dortmunder Beitr ¨age zur Landeskunde, v. 27,
p. 109–122.
MCBRIDE, E.F., 1962, Flysch and associated beds of th e Martinsburg Formati on
(Ordovician), central Appalachians: Journal of Sedimentary Research, v. 32, p. 39–91.
MCMAHON, S., ANDERSON, R.P., SAUPE, E.E., AND BRIGGS, D.E.G., 2016, Experimental
evidence that clay inhibits bacterial decomposers: implications for preservation of
organic fossils: Geology, v. 44, p. 867–870.
MEYER, M., SCHIFFBAUER, J.D., XIAO, S., CAI,Y.,AND HUA , H., 2012, Taphonomy of the
upper Ediacaran enigmatic ribbonlike fossil Shaanxilithes: PALAIOS, v. 27, p. 354–372.
MEYER, M.B., BROCE, J., SELLY,T.,AND SCHIFFBAUER, J.D., 2016, Insights into Vendotaenid
taphonomy and structure: new data on an old fossil: Geological Society of America
Abstracts and Programs, v. 48.
MILLER, A.I. AND MAO, S., 1995, Association of orogenic activity with the Ordovician
radiation of marine life: Geology, v. 23, p. 305–308.
MOYSIUK, J., SMITH, M.R., AND CARON, J.-B., 2017, Hyoliths are Palaeozoic lophophorates:
Nature, v. 541, p. 394–397.
MURCHISON, R.I., 1839, The Silurian System, Founded on Geological Researches in the
Counties of Salop, Hereford, Radnor, Montgomery, Camermarthen, Brecon, Pembroke,
Monmouth, Gloucester, Worcester, and Stafford; with Descriptions of the Coal-fi elds and
Overlying Formations: John Murray, London, 768 p.
JR, G.D., HINMAN, N.W., HOFMANN, M.H., AND XIAO, S., 2017, Exceptionally preserved
fossil assemblages through geologic time and space: Gondwana Research, v. 48, p. 164–
MUSCENTE, A.D. AND XIAO, S., 2015, New occurrences of Sphenothallus in the lower
Cambrian of South China: implications for its affinities and taphonomic demineralization
of shelly fossils: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 437, p. 141–
MUSCENTE, A.D. AND XIAO, S., 2015, Resolving three-dimensional and subsurficial features
of carbonaceous compressions and shelly fossils using backscattered electron scanning
electron microscopy (BSE-SEM): PALAIOS, v. 30, p. 462–481.
NIELSEN, C., 2013, Life cycle evolution: was the eumetazoan ancestor a holopelagic,
planktotrophic gastraea?: BMC Evolutionary Biology, v. 13, p. 1–18.
SERVAIS, T., 2017, Filamentous eukaryotic algae with a possible cladophoralean affinity
from the Middle Ordovician Winneshiek Lagerst¨atte in Iowa, USA: Geobios, v. 50, p.
YDA, J., 2003, Paleozoic plankton revolution: evidence from early
gastropod ontogeny: Geology, v. 31., p. 829–831.
´YDA, J., YANCEY, T.E., AND ANDERSON, J.R., 2007a, Larval shells of late
Palaeozoic naticopsid gastropods (Neritopsoidea: Neritimorpha) with a discussion of the
early neritimorph evolution: Pal¨aontologische Zeitschrift, v. 81, p. 213.
YDA, J., 2007b, Origin of planktotrophy—evidence from
early molluscs: a response to Freeman and Lundelius: Evolution and Development, v. 9,
p. 313–318.
I., 2006, Origin of planktotrophy—evidence from
early molluscs: Evolution and Development, v. 8, p. 325–330.
ORR, P., KEARNS, S.L., AND BRIGGS, D.E.G., 2002, Backscattered electron imaging of fossils
exceptionally-preserved as organic compressions: PALAIOS, v. 17, p. 110–117.
ORR, P.J., BENTON, M.J., AND BRIGGS, D.E.G., 2003, Post-Cambrian closure of the deep-
water slope-basin taphonomic window: Geology, v. 31, p. 769–772.
ORR, P.J., BRIGGS, D.E.G., AND KEARNS, S.L., 1998, Cambrian Burgess Shale animals
replicated in clay minerals: Science, v. 281, p. 1173–1175.
ORR, P.J., KEARNS, S.L., AND BRIGGS, D.E.G., 2009, Elemental mapping of exceptionally
preserved ‘carbonaceous compression’ fossils: Palaeogeography, Palaeoclimatology,
Palaeoecology, v. 277, p. 1–8.
PARRY, L.A., LEGG, D.A., AND SUTTON, M.D., 2016, Enalikter is not an annelid: homology,
autapomorphies and the interpretation of problematic fossils: Lethaia, v. 50, p. 222–226.
PETERSON, K.J., 2005, Macroevolutionary interplay between planktic larvae and benthic
predators: Geology, v. 33, p. 929–932.
POWELL, W., 2003, Greenschist-facies metamorphism of the Burgess Shale and its
implications for models of fossil formation and preservation: Canadian Journal of Earth
Sciences, v. 40, p. 13–25.
ROUSE, G.W. AND PLEIJEL, F., 2001, Polychaetes: Oxford University Press, Oxford, 354 p.
ROZHNOV, S.V., 2001, Evolution of the hardground community, in A. Yu. Zhuravlev and R.
Riding (eds.), The Ecology of Cambrian Radiation: Columbia University Press, New
York, p. 238–253.
SCHIFFBAUER, J.D. AND LAFLAMME, M., 2012, Lagerst¨atten through time: a collection of
exceptional preservational pathways from the terminal Neoproterozoic through today:
PALAIOS, v. 27, p. 275–278.
AND KAUFMAN, A.J., 2014, A unifying model for Neoproterozoic–Palaeozoic exceptional
fossil preservation through pyritization and carbonaceous compression: Nature
Communications, v. 5, article 5754.
breakup linked to the Great Ordovician Biodiversification Event: Nature Geosciences, v.
1, p. 49–53.
Understanding the Great Ordovician Biodiversification Event (GOBE): influences of
paleogeography, paleoclimate, or paleoecology?: GSA Today, v. 19, p. 4–10.
OGER,B.,AND MUNNECK E, A., 2010, The Great
Ordovician Biodiversification Event (GOBE): the palaeoecological dimension: Palaeo-
geography, Palaeoclimatology, Palaeoecology, v. 294, p. 99–119.
onset of the ‘Ordovician Plankton Revolution’ in the late Cambrian: Palaeogeography,
Palaeoclimatology, Palaeoecology, v. 458, p. 12–28.
HAWKINS, A.D., 2016, Graptolite community responses to global climate change and the
Late Ordovician mass extinction: Proceedings of the National Academy of Sciences, v.
113, p. 8380–8385.
SLATER, B.J., HARVEY, T.H.P., GUILBAUD, R., AND BUTTERFIELD, N.J., 2017, A cryptic record
of Burgess Shale-type diversity from the early Cambrian of Baltica: Palaeontology, v. 60,
p. 117–140.
ECUYER, C., AND NICOLL, R.S., 2008, Did
Cooling Oceans Trigger Ordovician Biodiversification? Evidence from Conodont
Thermometry: Science, v. 321, p. 550–554.
VAN ITEN, H., COX, R.S., AND MAPES, R.H., 1992, New data on the morphology of
Sphenothallus Hall: implications for its affinities: Lethaia, v. 25, p. 135–144.
VAN ROY, P., BRIGGS, D.E.G., AND GAINES, R.R., 2015, The Fezouata fossils of Morocco; an
extraordinary record of marine life in the Early Ordovician: Journal of the Geological
Society, v. 172, p. 541–549.
AND BRIGGS, D.E.G., 2010, Ordovician faunas of Burgess Shale type: Nature, v. 465, p.
VINN,O.AND KIRSIMAE, K., 2015, Alleged cnidarian Sphenothallus in the Late Ordovician
of Baltica, its mineral composition and microstructure: Acta Palaeontologica Polonica, v.
60, p. 1001–1008.
WEBBY, B.D., 2004, The Great Ordovician Biodiversification Event: Columbia University
Press, New York, 484 p.
WILSON, L.A. AND BUTTERFIELD, N.J., 2014, Sediment effects on the preservation of Burgess
Shale–type compression fossils: PALAIOS, v. 29, p. 145–154.
WISE, D.U. AND GANIS, G.R., 2009, Taconic Orogeny in Pennsylvania: a ~15–20 m.y.
Apennine-style Ordovician event viewed from its Martic hinterland: Journal of Structural
Geology, v. 31, p. 887–899.
WITTMER, J.M. AND MILLER, A.I., 2011, Dissecting the global diversity trajectory of an
enigmatic group: the paleogeographic history of tentaculitoids: Palaeogeography,
Palaeoclimatology, Palaeoecology, v. 312, p. 54–65.
WOOD, G.D., MILLER, M.A., AND BERGSTROM, S.M., 2004, Late Devonian (Frasnian)
tentaculite organic remains in palynological preparations, RadomLublin region, Poland:
Memoirs of the Association of Australian Palaeontologists, v. 29, p. 253–258.
Received 27 April 2017; accepted 25 November 2017.
... Another well-known marine shelf Lagerstätte, the Walcott Rust Quarry in New York, shows soft-tissue preservation largely confined to trilobite appendages (Brett et al., 1999). Finally, a few other examples of soft-tissue preservation in deep basinal environments demonstrate potential for further discoveries, but presently sampling has yielded only a low diversity of problematica (Macgabhann and Murray, 2010;Meyer et al., 2018;Peel et al., 2019). Thus, while all these sites provide critical insights, their biotas are not easily comparable to those of Cambrian Lagerstätten from open marine shelf environments. ...
... Another well-known marine shelf Lagerstätte, the Walcott Rust Quarry in New York, shows soft-tissue preservation largely confined to trilobite appendages (Brett et al., 1999). Finally, a few other examples of soft-tissue preservation in deep basinal environments demonstrate potential for further discoveries, but presently sampling has yielded only a low diversity of problematica (Macgabhann and Murray, 2010;Meyer et al., 2018;Peel et al., 2019). Thus, while all these sites provide critical insights, their biotas are not easily comparable to those of Cambrian Lagerstätten from open marine shelf environments. ...
Ordovician open marine Lagerstätten are relatively rare and widely dispersed, producing a patchy picture of the diversity and biogeography of nonmineralized marine organisms and challenging our understanding of the fate of Cambrian groups. Here, for the first time, we report soft-bodied fossils, including a well-preserved marrellomorph arthropod, fragmentary carapaces, and macroalgae, from the Late Ordovician (Katian) Upper Member of the Kirkfield Formation near Brechin, Ontario. The unmineralized elements and associated exceptionally preserved shelly biota were entombed rapidly in storm deposits that smothered the shallow, carbonate-dominated shelf. The marrellomorph, Tomlinsonus dimitrii n. gen. n. sp., is remarkable for its ornate, curving cephalic spines and pair of hypertrophied appendages, suggesting a slow-moving, benthic lifestyle. Reevaluation of marrellomorph phylogeny using new data favors an arachnomorph affinity, although internal relationships are robust to differing outgroup selection. Clades Marrellida and Acercostraca are recovered, but the monophyly of Marrellomorpha is uncertain. The new taxon is recovered as sister to the Devonian Mimetaster and, as the second-youngest known marrellid, bridges an important gap in the evolution of this clade. More generally, the Brechin biota represents a rare window into Ordovician open marine shelf environments in Laurentia, representing an important point of comparison with contemporaneous Lagerstätten from other paleocontinents, with great potential for further discoveries. UUID:
... et al. 2018) and Llanfallteg Formation in Wales (Hearing et al. 2016); and the Upper Ordovician Beecher's Trilobite Bed of New York ( Briggs et al. 1991), Big Hill Formation of Michigan ( Lamsdell et al. 2017), Martinsburg Formation of Pennsylvania ( Meyer et al. 2018), BUpper Ordovician Lagerstätten^ from Manitoba, Canada ( Young et al. 2007Young et al. , 2012, Bardahessiagh Formation of Ireland ( MacGabhann and Murray 2010), and Soom Shale of South Africa ( Aldridge et al. 1994;Gabbott 1998). The information preserved in these Ordovician exceptional deposits has greatly improved knowledge on the expansion of biodiversity during the Great Ordovician Biodiversification Event (GOBE) ( Webby et al. 2004;Servais and Harper 2018). ...
Full-text available
Soft-bodied preservation is common in the Cambrian but comparatively rare in the Ordovician. Here, a new deposit preserving soft-bodied fossils is reported from the Middle Ordovician (Dapingian-Darriwilian) upper Valongo Formation of northern Portugal. The deposit contains the first known occurrences of soft-bodied fossils from the Middle Ordovician (Dapingian-Darriwilian) of Portugal and is the first Ordovician example of soft-tissue preservation involving carbonaceous films from the Iberian Peninsula. It also represents the lone deposit of soft-bodied fossils from the Middle Ordovician of northern Gondwana. Thus temporally, it lies between the exceptional deposits of the Lower Ordovician of Fezouata (Morocco) and the Upper Ordovician of the Soom Shale (South Africa); it also serves as a biogeographic link between these and the various Ordovician soft-bodied deposits in Laurentia. The soft-bodied fossils come from the deep-water slates of the upper part of the Valongo Formation and include a discoidal fossil questionably referable to Patanacta, wiwaxiid sclerites, and a possible pseudoarctolepid arthropod.
... Famous examples from the Palaeozoic include the Cambrian Burgess Shale in Canada (Briggs et al., 1995) and the Maotianshan Shales in Chengjiang, China (Zhang et al., 2008), as well as the Devonian Hunsrück Slate in Germany (Bartels et al., 2009). Ordovician Konservat-Lagerstätten are mainly known from siliciclastic deposits of the Lower Ordovician of Morocco (shale; Van Roy et al., 2010, 2015Lefebvre et al., 2016;Martin et al., 2016) and Wales (mudstone; Botting et al., 2015), the Middle Ordovician of Iowa, USA (shale; Nowak et al., 2018;Briggs et al., 2018) and Wales (mudstone; Hearing et al., 2016), and the Upper Ordovician of Scotland (shale; Stewart and Owen, 2008), Wales (mudstone; Botting et al., 2011), Morocco (sandstone;Gutiérrez-Marco and García-Bellido, 2015), New York, USA (shale; Briggs et al., 1991;Farrell et al., 2009), Pennsylvania, USA (shale; Meyer et al., 2018) and South Africa (shale; Gabbott et al., 2017). In contrast, exceptional preservation of soft-bodied biota from Palaeozoic carbonates is rarely known and includes the Fossil-Lagerstätte of Manitoba, Canada (Young et al., 2007(Young et al., , 2012. ...
A diverse benthic fauna containing exceptionally preserved soft-bodied organisms is described from the new Vauréal Konservat-Lagerstätte from the Upper Ordovician Vauréal Formation (Katian) of Anticosti Island, Canada. These fossils occur as pyritic (or goethitic, if weathered), calcitic aggregates or sediment-filled voids on micritic bedding planes of a marlstone-limestone alternation originated on a shallow tropical carbonate ramp. Many organisms are preserved in association with their traces (e.g. burrows, trails), whose changing shapes indicate increasing cohesiveness of the substrate. Rapid burial (obrution) under dysoxic bottom conditions must have favoured exceptional preservation. Although anatomical details of the organisms are often lacking due to recrystallization, members of different groups of organisms could be interpreted based on their shape and other characteristic features, including those of which represent their oldest fossil record (i.e. Acoelomorpha, Turbellaria, Nemertea, Nematoda), beside Polychaeta, Sipuncula, Ostracoda and other Arthropoda. In parallel with molecular data, which recently have changed the phylogenetic status of some clades, this soft-bodied fauna and their traces not only record their appearance but add to the understanding of their body plan and behaviour. The new Konservat-Lagerstätte provides important information about a diverse benthic community in the Late Ordovician after the Great Ordovician Biodiversification Event (GOBE), and represents a calibration point for comparison across the Late Ordovician mass extinction. Moreover, comparable Fossil-Lagerstätten are probably more common in shallow-marine carbonates than currently known but might have been simply overlooked.
... Research over the last few decades paints a picture of animal origins that began on the ocean floor. While millimeter-scale acritarchs and phytoplankton drifted across the open oceans, the fossil record suggests multicellular life proliferated on the seabed, where simple forms competed to colonize, crawl, and chew their way through thick microbial mats (Droser et al. 2017; but see Meyer et al. [2018] for a discussion of possible preservational biases). At some point animals left their benthic competitors behind, leveraging muscle-powered swimming to take to the open ocean. ...
Molecular and fossil data place the initial diversification of animals in the Neoproterozoic, though there remains too much enough uncertainty to produce an exact chronology. This is unfortunate, as the Neoproterozoic represents a period of intense climate change, including multiple global glaciation events as well changes to ocean chemistry and oxygen content. Several authors have suggested that the coevolution of animals and their environment was tightly coupled, but such hypotheses rest on the presence of swimming (pelagic) species. In this paper, I review the evidence for pelagic animals during the Neoproterozoic. I conclude that there are very few groups of planktotrophic swimming animals that were likely to have existed at this time, with the possible exception of medusozoan cnidarians (jellyfish). Ultimately, hypotheses connecting Earth and animal evolution in the Neoproterozoic need to be tested with more geochemical work, fossil discoveries, and refinement of molecular clocks targeted on the relevant groups.
Full-text available
Among marine invertebrates, mollusks preserve size and morphology throughout ontogeny in their skeleton, which allows to document their body size evolution as well as morphological disparity in relation to environmental changes and extinctions. However, not only abiotic, but also biotic factors like symbiotic interactions or parasitism can influence their growth and evolution. The influence of parasitism is more difficult to assess, as soft-bodied parasites have been understudied and have a patchy fossil record. Nevertheless, their evolutionary origin can be constrained with the aid of molecular clocks. Furthermore, characteristic pathologies caused in their hosts can be traced more continuously through time and are crucial to disentangling changes in biotic interactions in deep time. In all these cases, unraveling the influence of mode of life, mineralogy, and physiology on preservation is an important prerequisite to interpret the rarity of particular invertebrate taxa or anatomical features to constrain their evolution and functional morphology. In some cases, heavily infested and abnormally coiled ammonoids survive until adulthood; suggesting streamlining was not that important in these forms. These compiled works highlight the importance of integrating first-hand observations on ontogenetic and discrete characters as well as body size and mineralogy into evolutionary and paleobiological studies. The origin and evolution of soft-bodied organisms can be more accurately and less circularly constrained by combining the geological and molecular records in molecular clock approaches. However, the evolution of biotic interactions and biomineralization can be more accurately constrained across geologically rapid environmental changes by using host skeletons. Furthermore, experimental taphonomy and computed tomography can be valuable methods in interpreting the evolutionary significance of rare taxa or anatomical features. In summary, we can exploit much more information from fossils than only their adult morphology and diversity, highlighting the need for reinvestigation of museum material and new field research in addition to literature studies.
Full-text available
A well-preserved fossil priapulid worm, Xiaoheiqingella sp., is reported from the early Cambrian Guanshan Lagerstätte (Cambrian Series II, Stage 4) near Kunming City, Yunnan Province, SW China. The body of the animal consists of four sections: a swollen introvert, a constricted neck, a finely annulated trunk and a caudal appendage. The body configuration exhibits a close resemblance to that of the crown group priapulid Xiaoheiqingella peculiaris from the early Cambrian Chengjiang Lagerstätte. The new discovery provides another striking example of crown group priapulids, representing the third occurrence of crown group fossil priapulids after the Chengjiang Lagerstätte (Cambrian Series II, Stage 3) and the Mazon Creek Lagerstätte (late Moscovian Stage, Pennsylvanian). The discovery also sheds new light on the early diversity and evolution of priapulid worms.
Full-text available
Microscopic animals that live among and between sediment grains (meiobenthic metazoans) are key constituents of modern aquatic ecosystems, but are effectively absent from the fossil record. We describe an assemblage of microscopic fossil loriciferans (Ecdysozoa, Loricifera) from the late Cambrian Deadwood Formation of western Canada. The fossils share a characteristic head structure and minute adult body size (~300 μm) with modern loriciferans, indicating the early evolution and subsequent conservation of an obligate, permanently meiobenthic lifestyle. The unsuspected fossilization potential of such small animals in marine mudstones offers a new search image for the earliest ecdysozoans and other animals, although the anatomical complexity of loriciferans points to their evolutionary miniaturization from a larger-bodied ancestor. The invasion of animals into ecospace that was previously monopolized by protists will have contributed considerably to the revolutionary geobiological feedbacks of the Proterozoic/Phanerozoic transition.
Full-text available
Exceptionally preserved ‘Burgess Shale-type’ fossil assemblages from the Cambrian of Laurentia, South China and Australia record a diverse array of non-biomineralizing organisms. During this time, the palaeocontinent Baltica was geographically isolated from these regions, and is conspicuously lacking in terms of comparable accessible early Cambrian Lagerstätten. Here we report a diverse assemblage of small carbonaceous fossils (SCFs) from the early Cambrian (Stage 4) File Haidar Formation of southeast Sweden and surrounding areas of the Baltoscandian Basin, including exceptionally preserved remains of Burgess Shale-type metazoans and other organisms. Recovered SCFs include taxonomically resolvable ecdysozoan elements (priapulid and palaeoscolecid worms), lophotrochozoan elements (annelid chaetae and wiwaxiid sclerites), as well as ‘protoconodonts’, denticulate feeding structures, and a background of filamentous and spheroidal microbes. The annelids, wiwaxiids and priapulids are the first recorded from the Cambrian of Baltica. The File Haidar SCF assemblage is broadly comparable to those recovered from Cambrian basins in Laurentia and South China, though differences at lower taxonomic levels point to possible environmental or palaeogeographical controls on taxon ranges. These data reveal a fundamentally expanded picture of early Cambrian diversity on Baltica, and provide key insights into high-latitude Cambrian faunas and patterns of SCF preservation. We establish three new taxa based on large populations of distinctive SCFs: Baltiscalida njorda gen. et sp. nov. (a priapulid), Baltichaeta jormunganda gen. et sp. nov. (an annelid) and Baltinema rana gen. et sp. nov. (a filamentous problematicum). © 2016 The Authors. Palaeontology published by John Wiley & Sons Ltd on behalf of The Palaeontological Association.
Full-text available
Documentation of non- or weakly biomineralizing animals that lived during the Furongian is essential for a comprehensive understanding of the diversification dynamics of metazoans during the early Palaeozoic. However, the fossil record of ‘soft’-bodied metazoans is particularly scarce for this critical time interval, consisting of rare fossils found at a dozen or so localities worldwide. Here we report new occurrences of exceptional preservation in Furongian (Jiangshanian) strata of the McKay Group near Cranbrook, British Columbia, Canada. This locality had already yielded trilobites with phosphatised guts, with all specimens representing the same species and occurring within a 10-m-thick interval. Two stratigraphically higher horizons with soft-tissue preservation are reported herein; one has yielded a ctenophore and an aglaspidid arthropod, the other a trilobite with a phosphatised gut belonging to a different species than the previously described specimens. The ctenophore represents the first Furongian record of the phylum and the first reported occurrence of Burgess Shale-type preservation in the upper Cambrian of Laurentia. The aglaspidid belongs to a new species of Glypharthrus, and is atypical in having twelve trunk tergites and an anteriorly narrow ‘tailspine’. These features suggest that the tailspine of aglaspidids evolved from the fusion of a twelfth trunk segment with the telson. They also confirm the vicissicaudatan affinities of these extinct arthropods. Compositional analyses suggest that aglaspidid cuticle was essentially organic with a thin biomineralised (apatite) outer layer. The trilobite reveals previously unknown gut features, such as medial fusion of digestive glands, possibly related to enhanced capabilities for digestion, storage, or the assimilation of food. The new fossils demonstrate that conditions conducive to soft-tissue preservation repeatedly developed in the outer shelf environment represented by the Furongian strata near Cranbrook. Future exploration of the c. 600-m-thick, mudstone-dominated upper part of the section may result in more abundant discoveries of exceptional fossils.
Previous studies on the Darriwilian (Middle Ordovician) Konservat-Lagerstätte of the Winneshiek Shale in Iowa (USA) have reported various animal and trace fossils. A search for “small carbonaceous fossils” (SCFs) in palynological samples from the Winneshiek Shale has now led to the discovery of several different kinds of organic-walled microfossils. Here we report on a particular group of filamentous microfossils that occur abundantly throughout the exposed and subsurface successions of the Winneshiek Shale. The fossils are characterised by large, elongated cells (220-600 μm in length, 60-240 μm in diameter) with thin and delicate walls and occasional branching. The cells often contain dark internal bodies, most likely condensed protoplasmic remains. Together, these features identify these fossils as eukaryotic rather than cyanobacterial in origin. More specifically, the cell size, cross-walls and branching pattern are shared with forms of benthic ulvophycean green algae, a group with a long but sporadic fossil record that is otherwise restricted to Proterozoic Lagerstätten. The new specimens therefore expand the known diversity of local primary producers in the palaeoenvironment of the Winneshiek Shale, and suggest that the apparent dearth of delicate filamentous green algae in the Phanerozoic record may be, in part, an artefact of low preservation potential combined with destructive processing techniques.
Non-calcified marine macroalgae ("seaweeds") play a variety of key roles in the modern Earth system, and it is likely that they were also important players in the geological past, particularly during critical transitions such as the Cambrian Explosion (CE) and the Great Ordovician Biodiversification Event (GOBE). To investigate the morphology and ecology of seaweeds spanning the time frame from the CE through the GOBE, a carefully vetted database was constructed that includes taxonomic and morphometric information for non-calcified macroalgae from 69 fossil deposits. Analysis of the database shows a pattern of seaweed history that can be explained in terms of two floras: the Cambrian Flora and the Ordovician Flora. The Cambrian Flora was dominated by rather simple morphogroups, whereas the Ordovician Flora, which replaced the Cambrian Flora in the Ordovician and extended through the Silurian, mainly comprised comparatively complex morphogroups. In addition to morphogroup representation, the two floras show marked differences in taxonomic composition, morphospace occupation, functional-form group representation, and life habit, thereby pointing to significant morphological and ecological changes for seaweeds roughly concomitant with the GOBE and the transition from the Cambrian to Paleozoic Evolutionary Faunas. Macroalgal changes of a similar nature and magnitude, however, are not evident in concert with the CE, as the Cambrian Flora consists largely of forms established during the Ediacaran. The cause of such a lag in macroalgal morphological diversification remains unclear, but an intriguing possibility is that it signals a previously unknown difference between the CE and GOBE with regard to the introduction of novel grazing pressures. The consequences of the establishment of the Ordovician Flora for shallow marine ecosystems and Earth system dynamics remain to be explored in detail but could have been multifaceted and potentially include impacts on the global carbon cycle.
Geologic deposits containing fossils with remains of non-biomineralized tissues (i.e. Konservat-Lagerstätten) provide key insights into ancient organisms and ecosystems. Such deposits are not evenly distributed through geologic time or space, suggesting that global phenomena play a key role in exceptional fossil preservation. Nonetheless, establishing the influence of global phenomena requires documenting temporal and spatial trends in occurrences of exceptionally preserved fossil assemblages. To this end, we compiled and analyzed a dataset of 694 globally distributed exceptional fossil assemblages spanning the history of complex eukaryotic life (~ 610 to 3 Ma). Our analyses demonstrate that assemblages with similar ages and depositional settings commonly occur in clusters, each signifying an ancient geographic region (up to hundreds of kilometers in scale), which repeatedly developed conditions conducive to soft tissue preservation. Using a novel hierarchical clustering approach, we show that these clusters decrease in number and shift from open marine to transitional and non-marine settings across the Cambrian-Ordovician interval. Conditions conducive to exceptional preservation declined worldwide during the early Paleozoic in response to transformations of near-surface environments that promoted degradation of tissues and curbed authigenic mineralization potential. We propose a holistic explanation relating these environmental transitions to ocean oxygenation and bioturbation, which affected virtually all taphonomic pathways, in addition to changes in seawater chemistry that disproportionately affected processes of soft tissue conservation. After these transitions, exceptional preservation rarely occurred in open marine settings, excepting times of widespread oceanic anoxia, when low oxygen levels set the stage. With these patterns, non-marine cluster count is correlated with non-marine rock quantity, and generally decreases with age. This result suggests that geologic processes, which progressively destroy terrestrial rocks over time, limit sampling of non-marine deposits on a global scale. Future efforts should aim to assess the impacts of such phenomena on evolutionary and ecological patterns in the fossil record.
Full text available free online at Hyoliths are abundant and globally distributed ‘shelly’ fossils that appear early in the Cambrian period and can be found throughout the 280 million year span of Palaeozoic strata. The ecological and evolutionary importance of this group has remained unresolved, largely because of their poorly constrained soft anatomy and idiosyncratic scleritome, which comprises an operculum, a conical shell and, in some taxa, a pair of lateral spines (helens). Since their first description over 175 years ago, hyoliths have most often been regarded as incertae sedis, related to molluscs or assigned to their own phylum. Here we examine over 1,500 specimens of the mid-Cambrian hyolith Haplophrentis from the Burgess Shale and Spence Shale Lagerstätten. We reconstruct Haplophrentis as a semi-sessile, epibenthic suspension feeder that could use its helens to elevate its tubular body above the sea floor. Exceptionally preserved soft tissues include an extendable, gullwing-shaped, tentacle-bearing organ surrounding a central mouth, which we interpret as a lophophore, and a U-shaped digestive tract ending in a dorsolateral anus. Together with opposing bilateral sclerites and a deep ventral visceral cavity, these features indicate an affinity with the lophophorates (brachiopods, phoronids and tommotiids), substantially increasing the morphological disparity of this prominent group.
A megacheiran arthropod, Enalikter aphson, was recently described by Siveter et al. (2014) from the mid-Silurian (late Wenlock) of Herefordshire. Previously, megacheirans had only been recognized from the Cambrian. Struck et al. (2015) considered the body plan of Enalikter to be incompatible with this affinity, arguing that many of the arthropod features were either not present or misinterpreted. Instead, they compared Enalikter to polychaete annelids, identifying characters from numerous polychaete lineages which they considered to be present in Enalikter. A reply to this critique by Siveter et al. (2015) reaffirmed arthropod affinities for Enalikter by presenting additional evidence for key arthropod features, such as arthropodized appendages. Here, we augment Siveter et al. by critically addressing the putative annelid characters of Enalikter presented by Struck et al. and additionally explore the morphological and phylogenetic implications of their hypothesis. We conclude that similarities between Enalikter and polychaetes are superficial and that character combinations proposed by Struck et al. are not present in any annelid, living or extinct. This taxon highlights the importance of using a phylogenetic framework for interpreting fossils that present unusual morphologies, such that proposed shared characters are hypotheses of homology rather than merely phenotypic similarities. Crucially, we argue that autapomorphic characters of subgroups of large taxa (like families or classes within phyla) should not be used to diagnose problematic fossils.