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Proc. R. Soc. B
doi:10.1098/rspb.2011.1986
Published online
Skimming the surface with Burgess Shale
arthropod locomotion
Nicholas J. Minter1,*, M. Gabriela Mángano1
and Jean-Bernard Caron2,3
1
Department of Geological Sciences, University of Saskatchewan, 114 Science Place, Saskatoon,
Saskatchewan, Canada S7N 5E2
2
Department of Natural History (Palaeobiology section), Royal Ontario Museum, 100 Queen’s Park,
Toronto, Ontario, Canada M5S 2C6
3
Department of Ecology and Evolutionary Biology, University of Toronto, 25 Willcocks Street,
Toronto, Ontario, Canada M5S 3B2
The first arthropod trackways are described from the Middle Cambrian Burgess Shale Formation of
Canada. Trace fossils, including trackways, provide a rich source of biological and ecological information,
including direct evidence of behaviour not commonly available from body fossils alone. The discovery of
large arthropod trackways is unique for Burgess Shale-type deposits. Trackway dimensions and the requisite number of limbs are matched with the body plan of a tegopeltid arthropod. Tegopelte, one of the rarest
Burgess Shale animals, is over twice the size of all other benthic arthropods known from this locality, and
only its sister taxon, Saperion, from the Lower Cambrian Chengjiang biota of China, approaches a similar
size. Biomechanical trackway analysis demonstrates that tegopeltids were capable of rapidly skimming
across the seafloor and, in conjunction with the identification of gut diverticulae in Tegopelte, supports previous hypotheses on the locomotory capabilities and carnivorous mode of life of such arthropods. The
trackways occur in the oldest part (Kicking Horse Shale Member) of the Burgess Shale Formation,
which is also known for its scarce assemblage of soft-bodied organisms, and indicate at least intermittent
oxygenated bottom waters and low sedimentation rates.
Keywords: Burgess Shale; Cambrian; ichnology; locomotion; trackway; palaeoecology
1. INTRODUCTION
Discovered over 100 years ago, the world-famous Burgess
Shale continues to yield important new insights into the evolution and ecology of animals during the Cambrian explosion
[1–5]. The exceptional preservation of soft tissues in the
Burgess Shale permits functional morphological inferences
on the modes of life and palaeoecology of early metazoans
[6,7]. Trace fossils, including trackways and burrows,
provide direct evidence for animal behaviour in the fossil
record, and can add further crucial insights for unravelling
the palaeoecology of their producers and placing temporal and palaeoenvironmental constraints on the origin of
functional novelties. Here, we report and discuss the significance of the first arthropod trackways discovered from the
Burgess Shale Formation.
Functional morphological studies of the benthic
Burgess Shale arthropods Olenoides [8,9], Naraoia [10],
Sidneyia [11], Molaria [12] and Tegopelte [13] postulated
that they employed slow, low-geared, stable gaits with
many propulsive limbs in contact with the substrate
when walking, and could launch themselves off the substrate to swim or drift. Limb morphology, with spinose
coxae and podomeres, also led to the suggestion that
Olenoides, Naraoia, Sidneyia and Molaria were predators
or scavengers [6,8– 12]. The coxae are not known in
Tegopelte, but it is also inferred to have been a benthic
predator or scavenger [6,13]. The aims of this paper are
to (i) describe the first known arthropod trackways from
the Burgess Shale Formation; (ii) identify their potential
producers; (iii) integrate trackway and body fossil data
to derive the locomotory techniques employed in producing the trackways; and (iv) test previous hypotheses
on their locomotory capabilities and mode of life.
2. GEOLOGICAL SETTING
The Middle Cambrian (Series 3) Burgess Shale Formation
in Yoho National Park (British Columbia, Canada) is a
basinal succession of mudstone and carbonate that has
yielded several fossil assemblages of soft-bodied animals
[14,15]. The trackways were collected from two separate
localities on Mount Stephen and Mount Field (electronic
supplementary material, figure S1) within the Kicking
Horse Shale Member of the Burgess Shale Formation
[14,15]. The Kicking Horse Shale Member comprises
thinly bedded, calcareous muddy siltstone and thin slaty
limestone [14,15]. With the exception of the Sanctacaris
locality on Mount Stephen [16], the Kicking Horse
Shale Member generally contains a low diversity assemblage of soft-bodied animals [14,15]. The Kicking Horse
Shale Member is the oldest unit (Glossopleura Zone) of
the Burgess Shale Formation [14,15].
The exceptional preservation of animals within the
younger (Bathyuriscus Zone) Phyllopod Bed in the Walcott
Quarry Shale Member [14,15] has been attributed to
*Author for correspondence ([email protected]).
Electronic supplementary material is available at http://dx.doi.org/
10.1098/rspb.2011.1986 or via http://rspb.royalsocietypublishing.org.
Received 22 September 2011
Accepted 19 October 2011
1
This journal is q 2011 The Royal Society
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2 N. J. Minter et al. Burgess Shale trackways
(a)
(b)
(c)
(d)
os
im
is
Figure 1. Burgess Shale arthropod trackways. (a) Detail of the beginning of ROM 61454 (see electronic supplementary
material, figures S3 –S5 for full trackway) from the Kicking Horse Shale Member on Mount Field. (b) Line drawing of the
beginning of ROM 61454. (c) ROM 61455, from the Kicking Horse Shale Member on Mount Stephen, showing a gradual
turn and intermittent paired medial imprints, im. (d) ROM 61456, from the Kicking Horse Shale Member on Mount
Stephen, showing a sharp turn with outer splaying of tracks, os, and short inner spurs of tracks, is. All specimens preserved
in negative epirelief. Scale bars, 100 mm.
rapid burial by mud-rich slurry flows [17]. This indicates
that the animals were transported, although recent taphonomic analysis suggests transport and decay were
negligible, and most benthic animals were probably buried
within their habitats [18]. Geochemical analysis of Burgess
Shale-type deposits indicates exaerobic conditions, with the
anoxic–oxic boundary occurring at the sediment–water
interface, rather than anoxic bottom water [19]. Trace fossils are preserved in situ and therefore represent reliable
indicators of local environmental conditions. Simple burrows and trails within the Burgess Shale Formation
[14,18,20] and other Burgess Shale-type deposits of the
USA [21] demonstrate at least intermittent oxygenation
and in situ colonization of the sediment. Diminutive trace
fossil assemblages are also found in association with carapaces of soft-bodied animals in the Stephen Formation of
Canada [22,23] and Chengjiang [24] and Kaili biotas of
China [25,26]. Such occurrences in Burgess Shale-type
deposits have been attributed to increased benthic oxygen
Proc. R. Soc. B
levels following soft-tissue stabilization under anoxic conditions [21]. High rates of sedimentation have also been
invoked to explain the near absence of burrows in parts of
the Burgess Shale Formation [17], although the emplacement of simple trails only requires short colonization
windows [27]. The diminutive nature and shallow
penetration depth of the trace fossils in the Stephen Formation are indicative of oxygen-deficient conditions, and
suggest that oxygen rather then sedimentation rate is the
primary control on their occurrence in Burgess Shale-type
deposits [23].
3. TRACKWAY DESCRIPTION
The five known trackway specimens are reposited at
the Royal Ontario Museum, Toronto, Canada (ROM).
The longest trackway (ROM 61454) is preserved for
over 3 m (figure 1a,b; electronic supplementary material,
figures S2 – S5). The trackway comprises overlapping
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Burgess Shale trackways N. J. Minter et al.
series of up to 25 tracks. It is slightly dimorphic in form.
The tracks on one side are elliptical to curvilinear in shape
and orientated obliquely to the midline of the trackway,
while those on the other are more elongate and orientated
perpendicularly to the midline. The sets of tracks are also
all offset and orientated obliquely relative to the long-axis
of the trackway and the direction of travel. The external
width is 100 –120 mm. Tracks are 2– 27 mm long and
spaced 7– 28 mm apart. The stride is 200 –230 mm.
ROM 61455 preserves a trackway making a gradual
turn (figure 1c). The external width is 120–135 mm.
The trackway splays on the outside of the turn, making
the series more apparent. Highly overlapping series of
up to 25 tracks are observed and the stride is 90–95 mm
on the outside of the turn, decreasing to 60–85 mm on
straighter sections. Tracks are circular to comma-shaped,
2–15 mm long and spaced 5–21 mm apart. Intermittent paired medial imprints are present. ROM 61456
preserves a trackway making a tight U-turn (figure 1d).
The series splay strongly on the outside of the turn,
although a high degree of overprinting obscures the precise
number of tracks per series. Short spurs of tracks are present on the inside of the turn. Tracks range from elliptical
to curvilinear in shape and at least 20 are present within
each series. The external width is approximately 70 mm,
and tracks are 5–18 mm long and spaced 8–22 mm apart.
Several smaller trackways with differing orientations are
preserved in ROM 61457 (electronic supplementary
material, figure S6) with external widths of 58–70 mm
and overlapping series of up to 22 elliptical to curvilinear
tracks. Tracks are 3–10 mm long and spaced 7–22 mm
apart. The stride is 145–150 mm. ROM 61458 is a small
slab that preserves a partial trackway similar to those of
ROM 61457. All trackways can be ascribed to the ichnogenus Diplichnites (electronic supplementary material).
Helminthoidichnites-like trails are also associated with the
trackways (electronic supplementary material, figure S7).
4. PRODUCER IDENTIFICATION
Trace fossil morphology is influenced by the anatomy of
the producer, its behaviour and the substrate conditions.
Compared with other types of trace fossils, trackways are
more strongly influenced by, and therefore more reflective
of, the anatomy of the producer [28]. Fortey & Seilacher
[29] established a set of criteria for assigning a particular
trace fossil taxon to a specific producer: (i) close association in the field; (ii) concurrent stratigraphic range;
(iii) minimal choice of available candidates; (iv) consistent
size range; and (v) consistent biogeographic range. These
ideas can be built upon to create criteria for assigning individual trackways or assemblages of trackways to producers
with varying levels of confidence and corresponding
approximate biotaxonomic rank. In increasing order,
these assignment levels are: (i) general correlation of trackway features with the body plan of an animal group (class
or higher equivalent taxonomic rank at the stem or crowngroup levels); (ii) correlation of features with coeval body
fossils (class–order); (iii) correlation of features with
coeval body fossils from the same palaeobiogeographic
region and environment (order–family); (iv) correlation
of features with body fossils from the same formation
(order–genus); and (v) producer at the end or in close
association with the trackway (species).
Proc. R. Soc. B
3
The majority of Cambrian trackways are broadly
attributed to trilobites [30,31] on the basis of a correlation between trackway features and the general
trilobite body plan (assignment level i), or more specific
groups [32] on the basis of correlation with coeval body
fossils from the same palaeobiogeographic region and
environment (assignment level iii). Trackways from the
shallow marine Bright Angel Shale of Arizona have been
correlated with a producer similar to the coeval (but
deeper-water) Burgess Shale arthropod Habelia [33]
(assignment level ii). A second trace fossil from the
same formation was identified as a trackway, potentially
related to a lobopodian animal resembling Aysheaia
[34], although this particular trace fossil may instead be
an unusual expression of a serially and alternating
branched burrow system [34,35].
The Burgess Shale trackways described herein are
unique in their large size and occurrence in Cambrian Burgess Shale-type deposits. The trackways are of different
sizes (58–135 mm wide) and probably come from different stratigraphic levels within the Kicking Horse Shale
Member, and were thus produced by different individuals.
However, they all share the same characteristics of relative
dimensions and numbers of tracks, and were therefore all
made by the same type of animal. Comparison of key
trackway characters (including size and number of tracks)
with potential producers from the Burgess Shale is facilitated by the exceptional preservation of soft tissues in
census and time-averaged communities [18]. This provides
the potential opportunity to correlate the trackways with
body fossils from the same formation (assignment level iv).
The producers of the Burgess Shale trackways were large
(up to 300 mm long and 135 mm wide) and possessed at
least 25 pairs of walking limbs. Among known Burgess
Shale and other Lower–Middle Cambrian arthropods
with walking limbs (electronic supplementary material,
table S1), only Tegopelte [13] (figure 2) fits these criteria,
reaching 280 mm in length, 140 mm in width and possessing 33 pairs of walking limbs. The posteriormost limbs are
reduced and are unlikely to have been used in locomotion
[13]. Fragmentary remains of Sidneyia from the Middle
Cambrian of Utah are estimated to approach the appropriate size [36], although Sidneyia only has nine pairs of
walking limbs [11]. All other known Burgess Shale arthropods with walking limbs are too small to have made all but
the smallest trackways, but still possess insufficient numbers of appendages (electronic supplementary material,
table S1). Saperion, from the Lower Cambrian Chengjiang
fauna of China, reaches 151 mm in length and possesses
approximately 25 pairs of walking limbs [37].
Tegopelte is the largest benthic arthropod from the
Burgess Shale (figure 2; electronic supplementary material,
figure S8) and is at least twice the size of any other known
benthic Burgess Shale bilaterian. It is also one of the rarest,
with the only two known specimens occurring from the
Walcott Quarry Shale Member [13]. Tegopelte was originally described as a ‘soft-bodied trilobite’ with a thin
unmineralized divided exoskeleton [13]. Subsequent
analysis has determined that the divisions are folds, arising
from compaction during preservation, in an undivided
dorsal shield [37]. Tegopelte is often regarded as belonging
to the lamellipedians [38], a group that includes trilobites;
however, the position of this group is largely unconstrained
[39]. Phylogenetic analysis has resolved a sister relationship
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4 N. J. Minter et al. Burgess Shale trackways
(a)
La
n
Ra
(b)
(d)
La?
Le
Ra
H
Re
H
al
gd
(c)
n
Figure 2. Tegopelte gigas from the Walcott Quarry Shale Member at the Walcott Quarry. (a) Holotype (USNM 189201) showing
the hypostome, H, left antennae, La, right antennae, Ra, notches, n, at the anterior and posterior end and the alimentary
canal, al. (b) Counterpart of the holotype showing the gut diverticulae, gd. (c) Detail of gut diverticulae. (d) Paratype
(USNM 189200) showing the additional presence of a left eye, Le, and right eye, Re. Eyes are tear-shaped and probably ventral
in position. Scale bars: (a,b,d ) 30 mm; (c) 10 mm.
of Tegopelte with Saperion and position in the Order
Helmetiida/Conciliterga [40,41]. Body fossils of Tegopelte
are not known from the Kicking Horse Shale Member,
but the trackways can be attributed to Tegopelte (or, at the
very least, a tegopeltid) on the basis of correlation with
body fossils from the same formation (assignment level iv).
5. LOCOMOTION
Animal locomotion can be defined by three parameters:
the gait ratio (p : r), which is the proportion of the step
cycle that a limb spends in the forward, recovery, protraction period (p) to that spent in the backward, propulsive,
retraction period (r); the successive phase difference (suc),
which is the proportion of the step cycle that a limb moves
before the limb in front; and the opposite phase difference
(opp), which is the proportion of the step cycle that a limb
on one side of the body moves after the paired limb on the
opposing side of the body [42,43]. These parameters can
be derived from trackways and a reconstruction of the
producer (electronic supplementary material), and have
been used to reconstruct the locomotion of numerous
extinct animals [44 –46].
The Burgess Shale trackways reveal that their producers
were capable of performing fast, high-geared walking gaits
and also able to ‘skim’ across the substrate with few limbs
in contact with the substrate at any one point in time. Trackway analysis (electronic supplementary material) yields gait
ratios of 9.3 : 0.7 and 9.4 : 0.6, indicating that limbs only
spent 7 and 6 per cent of the step cycle in the propulsive
backstroke phase, for ROM 61454 (figure 1a,b and electronic supplementary material, figures S3–S5) and ROM
61457 (electronic supplementary material, figure S6),
respectively. Successive limbs on one side of the body
Proc. R. Soc. B
would have moved in advance of the limb in front by
88 per cent of the step cycle. The trackways have opposite
symmetry and so paired limbs on either side of the body
moved synchronously. These parameters indicate that
only one to two pairs of limbs were in contact with the substrate at any one point in time and that metachronal waves
of eight limbs appeared to travel backwards along the
body with short gaps between the placement of proceeding limbs (figure 3; electronic supplementary material,
figures S9a and S10, and animation S1).
ROM 61455 demonstrates a slower but still high-geared
gait. Analysis of the straighter section yields a gait ratio of
7.6 : 2.4, where limbs spent 24 per cent of the step cycle
in the propulsive backstroke phase and successive limbs
moved in advance of the limb in front by 69 per cent of
the step cycle. The trackway has opposite symmetry and
so paired limbs on either side of the body moved synchronously. These parameters indicate that six pairs of limbs
were in contact with the substrate at any one point in
time, and metachronal waves of three limbs appear to
have travelled backwards along the body with short gaps
between the placement of proceeding limbs (electronic
supplementary material, figure S9b).
ROM 61456 indicates the producer was capable of
performing tight turns (figure 1d); however, unlike trilobites, Tegopelte has an unarticulated dorsal shield rather
than an articulated dorsal exoskeleton. Detailed examination of Tegopelte and the trackway demonstrates how
the execution of a tight turn can be ameliorated with an
arthropod with an unarticulated dorsal exoskeleton. In
Tegopelte, the compression of gill filaments on the surface
of the cuticle suggests that its dorsal shield was thin and
would have had some flexibility. In the trackway, the
track series on the outside of the turn are splayed, but
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Burgess Shale trackways N. J. Minter et al.
(a)
time
(b)
r
suc
p
t0 t1 t2 t3 t4 t5 t6 t7 t8 t9
t0
33
18 17
25
1
9
t1
33
18
t2
33
1
10
19 18
25
33
2
33
25
4
5
t6
33
4
12
13
limb
22
6
33
5
5
1
6
14
23 22
25
4
1
13
22 21
21
t5
3
1
12
20
t4
3
11
21 20
25
2
1
11
19
t3
2
10
20 19
25
1
3
9
14
1
6
7
15
25 24 23
23
15
7
1
t7
33
16
25 24
7
24
8
16
8
1
t8
33
9
17
25
8
25
17
9
33
25
25
18
18
1
1
9
1
t9
5
2 1
10
10
1
Figure 3. Locomotion and trackway production of a tegopeltid animal, based on ROM 61454 using a gait ratio of 9.3 : 0.7 and
successive phase difference (suc) of 0.88. (a) Manton gait diagram. Horizontal axis represents progression through time. The
phase relationships of the anterior 10 limbs on one side of the body are depicted. Each complete step cycle of a limb is represented by a couplet of a thick downward sloping line, corresponding to the relative duration of the propulsive, backward,
retraction phase (r) when the limb is in contact with the substrate; and a thin upward sloping line corresponding to the relative
duration of the recovery, forward, protraction phase (p) when the limb is lifted above the substrate. The successive phase difference is the proportion of the step cycle that a limb n þ 1 moves in advance of the limb n in front. Vertical time lines (t0 2 t9)
capture snapshots of the positions of the limbs that are depicted in (b). (b) Time-lapse trackway production. ‘Gait still’ snapshots represent the positions of the limbs and development of the trackway between the placement of limbs n and n þ 1 in the
proceeding step cycle. Light-coloured limbs indicate those in contact with the substrate. The en-echelon arrangement of the
series of tracks has been exaggerated to show the individual tracks.
only with a low degree of curvature, and short spurs of
tracks are present on the inside of the turn (figure 1d ).
Such a tight turn could therefore be achieved by a
tegopeltid through a combination of limited lateral flexure
and side-stepping.
The reconstructed method of trackway production
shows that the anterior tracks of each series are produced
by the posterior limbs (figures 3 and 4). In ROM 61454,
the anterior tracks of each series are situated more
medially to the midline of the trackway (figure 1a,b; electronic supplementary material, figures S3 –S5), which is
consistent with the method of production and the posteriormost limbs being shorter in Tegopelte. The en-echelon
arrangement of tracks in this trackway and ROM 61457
results from the body of the producer being offset obliquely relative to the long axis of the trackway and
direction of travel. This is caused by the animal being
partly buoyed up while producing the trackway and
could be related to a current or the producer being less
able to control the yaw of its body while employing a
high-geared gait ratio. There are no tool marks or
scours preserved with the trackways to indicate the
action of a current. These may not be observed if
the trackways are undertracks [47]; however, undertracks
are unlikely to be produced by an animal that was buoyed
up. Also, in ROM 61457, several trackways have differing orientations (electronic supplementary material,
figure S6), but were all produced by high-geared gaits,
and this is inconsistent with the producers all being
Proc. R. Soc. B
subject to a unidirectional current. The alternative is
that the producers were less able to control the yaw of
their body at these higher-geared gaits, owing to fewer
limbs being in contact with the substrate at any one
point in time, compared with more normal trackways produced by lower-geared walking gaits (figure 1c).
6. DISCUSSION
The discovery of trackways in the Burgess Shale permits
direct insights into animal behaviour and environmental
conditions during the Cambrian. The trackways can be
attributed to the Burgess Shale arthropod Tegopelte,
or at least a tegopeltid (figure 4). No other types of
trackways have been found so far in the Burgess Shale
Formation. On the basis of functional morphology,
Tegopelte was hypothesized as employing a walking gait
that was slow and low-geared (p : r ¼ 3.75 : 6.25,
suc ¼ 0.125), with many propulsive limbs in contact
with the substrate at any one point in time, but could
also perform higher-geared gaits to launch from the substrate and drift or swim [13]. The trackways provide
direct evidence to largely support this hypothesis,
showing that such animals could indeed employ fast,
high-geared gaits akin to ‘skimming’ across the substrate.
The trackways also demonstrate that they were capable of
a slower and lower-geared walking gait that is similar to
those calculated for subaqueously walking myriapods
[45]. This walking gait is higher-geared than that
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6 N. J. Minter et al. Burgess Shale trackways
Figure 4. Reconstruction of Tegopelte gigas producing a trackway. Copyright q 2011 Marianne Collins.
previously proposed for Tegopelte, although it falls within
the hypothesized locomotory end-members [13].
On the basis of functional morphology, Tegopelte is
considered to have been much like the large Sidneyia
and smaller Olenoides, Naraoia and Molaria in being a
benthic predator or scavenger [6]. The trackway evidence
supports the hypothesis of a predatory or scavenging
mode of life, demonstrating that they could employ fast,
high-geared gaits and were also capable of performing
tight turns. Fast, high-geared gaits could potentially be
associated with predator avoidance, although the producers of these trackways would have been twice the size
of any other benthic Burgess Shale arthropod and over
half the estimated size of the largest Anomalocaris [48].
In addition, our re-examination of Tegopelte identified the
presence of gut diverticulae (figure 2b,c). This provides
strong evidence of a predatory or scavenging mode of life
[49,50]. The presence of eyes in Tegopelte [13] was considered to be uncertain [40], but they are confirmed
herein and are probably ventral in position (figure 2d and
electronic supplementary material, figure S8a).
The presence of trackways, along with interface trails,
in the Kicking Horse Shale Member of the Burgess
Shale Formation also permits inferences on environmental conditions. Burrows have been observed in other
members of the Burgess Shale Formation and indicate
at least intermittent oxygenation of the sediment [20],
while the diminutive and shallow nature of burrows and
trails in the adjacent Stephen Formation suggests that
oxygen was a major control on their occurrence [23].
The trackways described herein are the first to be discovered from the Burgess Shale Formation and they are
unique for Burgess Shale-type deposits in their large
size. They provide evidence of arthropods living within
the environment, extending the stratigraphic range of
tegopeltids, and indicate that the bottom waters must
have been sufficiently oxygenated, at least intermittently,
to sustain large benthic animals during deposition of the
oldest member of the Burgess Shale Formation. The preservation of such trackways would also have required that
the substrate was dewatered and stiff owing to breaks in,
or slow rates of, sedimentation. Contrary to younger
Proc. R. Soc. B
Burgess Shale localities [14], the fossil-bearing layers of
the Kicking Horse Shale Member do not lie directly at
the base of the Cathedral Escarpment, and are of low
diversity and abundance. This might suggest that the
Kicking Horse Shale Member represented an environment generally unfavourable for a rich community to
thrive. The presence of large trackways also suggests
that the general scarcity of soft-tissue preservation
may be taphonomic, with a greater prevalence of oxygen
and/or low sedimentation rates throughout deposition
of the Kicking Horse Shale Member.
The Burgess Shale biota provides key insights into the
evolution and ecology of body plans during the Cambrian
explosion. The discovery of arthropod trackways from the
Kicking Horse Shale Member highlights their application
as indicators of environmental conditions. The results
also provide insights into the locomotory capabilities of
extinct animals that can be used to test functional morphological hypotheses on modes of life. Integrated trace
and body fossil evidence provides an innovative and
dynamic picture of arthropods such as Tegopelte as active
carnivores. Early marine communities were therefore
occupied not just by large nektonic predators such as
Anomalocaris, but also by large benthic predators, emphasizing the importance of such lifestyles in shaping early
complex marine communities and evolution during the
Cambrian explosion.
We thank Parks Canada for collecting permits (to ROM—
Desmond Collins and J.-B.C.), and Doug Erwin, Mark
Florence and John Pojeta (Smithsonian Institution) for
access to the Tegopelte specimens and technical assistance.
N.J.M.’s research is supported through a Government
of Canada Post-doctoral Research Fellowship under the
Canadian
Commonwealth
Scholarship
Programme.
M.G.M.’s research is supported by Natural Sciences and
Engineering Research Council (NSERC) Discovery Grant
311727 and University of Saskatchewan StartUp fund
411435. J.-B.C.’s research is supported by NSERC
Discovery Grant 341944 and ROM research and fieldwork
grants. Marianne Collins produced figures 3b and 4,
and electronic supplementary material, figure S10 and
animation S1. This is Royal Ontario Museum Burgess
Shale project number 34. The manuscript benefitted from
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Burgess Shale trackways N. J. Minter et al.
the comments of Greg Edgecombe as the Associate Editor,
and two anonymous reviewers.
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