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Finite-element analysis was used to investigate the extent of bias in the ichnological fossil record attributable to body mass. Virtual tracks were simulated for four dinosaur taxa of different sizes (Struthiomimus, Tyrannosaurus, Brachiosaurus and Edmontosaurus), in a range of substrate conditions. Outlines of autopodia were generated based upon osteology and published soft-tissue reconstructions. Loads were applied vertically to the feet equivalent to the weight of the animal, and distributed accordingly to fore- and hindlimbs where relevant. Ideal, semi-infinite elastic-plastic substrates displayed a 'Goldilocks' quality where only a narrow range of loads could produce tracks, given that small animals failed to indent the substrate, and larger animals would be unable to traverse the area without becoming mired. If a firm subsurface layer is assumed, a more complete assemblage is possible, though there is a strong bias towards larger, heavier animals. The depths of fossil tracks within an assemblage may indicate thicknesses of mechanically distinct substrate layers at the time of track formation, even when the lithified strata appear compositionally homogeneous. This work increases the effectiveness of using vertebrate tracks as palaeoenvironmental indicators in terms of inferring substrate conditions at the time of track formation. Additionally, simulated undertracks are examined, and it is shown that complex deformation beneath the foot may not be indicative of limb kinematics as has been previously interpreted, but instead ridges and undulations at the base of a track may be a function of sediment displacement vectors and pedal morphology.
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The ‘Goldilocks’ effect: preservation
bias in vertebrate track assemblages
P. L. Falkingham1,*, K. T. Bates2, L. Margetts1,3
and P. L. Manning1,4
School of Earth, Atmospheric and Environmental Science, University of Manchester,
Williamson Building, Oxford Road, Manchester M13 9PL, UK
Department of Musculoskeletal Biology, Institute of Aging and Chronic Disease, University
of Liverpool, Sherrington Buildings, Ashton Street, Liverpool L69 3GE, UK
Research Computing, University of Manchester, Devonshire House, Oxford Road,
Manchester M13 9PL, UK
Department of Earth and Environmental Science, University of Pennsylvania,
Philadelphia, PA 19104, USA
Finite-element analysis was used to investigate the extent of bias in the ichnological fossil
record attributable to body mass. Virtual tracks were simulated for four dinosaur taxa of
different sizes (Struthiomimus, Tyrannosaurus, Brachiosaurus and Edmontosaurus), in a
range of substrate conditions. Outlines of autopodia were generated based upon osteology
and published soft-tissue reconstructions. Loads were applied vertically to the feet equivalent
to the weight of the animal, and distributed accordingly to fore- and hindlimbs where rel-
evant. Ideal, semi-infinite elasticplastic substrates displayed a ‘Goldilocks’ quality where
only a narrow range of loads could produce tracks, given that small animals failed to
indent the substrate, and larger animals would be unable to traverse the area without becom-
ing mired. If a firm subsurface layer is assumed, a more complete assemblage is possible,
though there is a strong bias towards larger, heavier animals. The depths of fossil tracks
within an assemblage may indicate thicknesses of mechanically distinct substrate layers at
the time of track formation, even when the lithified strata appear compositionally homogeneous.
This work increases the effectiveness of using vertebrate tracks as palaeoenvironmental indi-
cators in terms of inferring substrate conditions at the time of track formation. Additionally,
simulated undertracks are examined, and it is shown that complex deformation beneath the
foot may not be indicative of limb kinematics as has been previously interpreted, but instead
ridges and undulations at the base of a track may be a function of sediment displacement vectors
and pedal morphology.
Keywords: footprint; finite-element analysis; trackway; computer
modelling; dinosaur
The sample we have of the body fossil record is notor-
iously incomplete [14] and may be fundamentally
biased by environmental and taxon-specific factors
that potentially hamper our interpretation of ecological
and evolutionary dynamics through deep time [58].
Interdependent environmental and taxon-specific
biases are equally likely to affect the ichnological, or
trace fossil, record. The potential for systematic bias
towards ichnofossils produced by larger animals has
previously been recognized in the field of vertebrate
palaeoichnology, and particularly in the dinosaur
track record [9]. Sites preserving only the tracks of
very large saurischian dinosaurs (i.e. track lengths
greater than 0.5 m) are generally recognized as size-
biased assemblages and presumed to represent
sedimentary conditions in which only animals above a
certain threshold of body mass were capable of
producing recognizable tracks [9]. However, beyond
this supposition, the influence of body size on the
recorded diversity of vertebrate ichnofossil assemblages
is poorly understood both qualitatively and quantitat-
ively. It is therefore imperative that the process of
track formation and the variables associated with
environment and animal biology are investigated.
The relationship between the size of an animal and
the load applied to the substrate is not straightforward.
Given that pressure is a measure of force over area, the
resultant pressure exerted on the sediment surface is a
function not only of the animal’s mass (as weight),
but also the geometry of the autopodia. Quadrupedal
animals benefit from more feet in contact with the
ground, further reducing the load on the substrate
*Author for correspondence (
Electronic supplementary material is available at
10.1098/rsif.2010.0634 or via
J. R. Soc. Interface (2011) 8, 1142–1154
Published online 13 January 2011
Received 15 November 2010
Accepted 21 December 2010 1142 This journal is q2011 The Royal Society
beneath any single foot, as compared with a similar-
sized biped. In addition to size, foot morphology also
plays an important role in determining the magnitude
of deformation expressed as the depth of a track. Differ-
ing shapes present different paths for sediment
movement, resulting in variable distributions of force
that affect the extent to which any given foot may
indent a substrate [10,11]. These considerations are
not trivial if data on fossil track occurrences and abun-
dances are to be used in ‘higher level’ [12]
palaeobiological and palaeoecological inferences. Allen
[13] noted over a decade ago that a widespread under-
standing of track formation lagged behind knowledge
of anatomical aspects and distributions of fossil
tracks, and despite a number of rigorous experimental
studies in the intervening years [1420], this still
remains the case.
Among vertebrates, the Dinosauria represent a
useful model system for studying track formation;
their high taxonomic diversity and long evolutionary
history yield an array of disparate foot morphologies
and a huge range in body mass with which to test for
possible biological factors underpinning preservational
bias. The group contains small and large obligate
bipeds, quadrupeds and supposed intermediate loco-
motor strategists (e.g. facultative bipedalism [2123])
that may have exerted different underfoot pressures
according to foot geometry and body shape (i.e. mass
distribution). Coupled with a vast quantity of research
describing dinosaur tracks spanning more than a cen-
tury and a half [24 26], dinosaurs provide the ideal
basis on which to further our understanding of fossil
track formation, and the size-related biases associated
In this paper, information on foot anatomy and mass
distribution from osteological evidence and soft tissue
reconstructions are integrated with geotechnical
theory and computer simulation to explore the poten-
tial for size bias in the vertebrate track record. In
addition, features related to underfoot pressure and
foot morphology were examined in surface and subsur-
face planes (true tracks and undertracks). Previous
work on track formation using computer simulation
has explored independently the effects of substrate con-
sistency [27], foot anatomy [11] and force [28]. This
paper aims to present a combined study in which the
quantifiable variables of track formation are considered
as a whole system, in the hope of elucidating aspects of
preservational bias inherent in the fossil track record.
The following experiments used parallel finite-element
analysis (FEA) software developed by authors
Margetts and Falkingham, using the freely available
ParaFEM libraries ( to model
track formation [11,2729]. A number of dinosaur
tracks were simulated over a range of substrates in
order to explore bias in their formation resulting from
substrate- or taxon-specific factors.
2.1. The virtual foot
Four dinosaurs (Struthiomimus, Edmontosaurus,
Tyrannosaurus and Brachiosaurus) were chosen to
create a varied virtual track assemblage on a cohesive
substrate, representing a range of body masses, and
including obligate bipeds, an obligate quadruped and
a facultative biped (table 1). These particular taxa
were also chosen because they all have published data
on body mass and centre of mass (CM) position
[30,31], and represent a wide range in size, mass
and autopodial morphology. The taxa were not
selected in order to create some geotemporally correct
track assemblage.
A track is formed through the interaction of three
factors; force, foot anatomy and substrate [32,33].
Force applied and foot anatomy are both dependent
upon the track maker. To apply a reasonable force,
the body mass for each dinosaur was taken from the lit-
erature ([30,31]; see table 1). The reader is directed to
Bates et al.[30] for a comprehensive discussion on the
confidence of CM and body mass reconstructions. Ani-
mals spend a very small proportion of their time moving
at anything more than a walking speed, and it would
therefore be expected that most tracks are made by
walking animals. Indeed, this is corroborated by the
numbers of trackways showing walking, rather than
running gaits [34,35]. Stride length is positively cor-
related with speed [36,37], meaning that at low
speeds, the hip joint and CM will move a shorter dis-
tance horizontally from the contact between the foot
Table 1. Mass, weight, foot metrics and pressures used to represent various dinosaur taxa used in this study. Data for
Struthiomimus, Edmontosaurus and Tyrannosaurus from Bates et al.[30], and data for Brachiosaurus from Henderson [31].
trackmaker mass (kg) force (kN) foot length (m) foot surface area (m
) pressure (kN m
Struthiomimus 423 4.15 0.336 0.026 161.21
Edmontosaurus (biped) 813 7.98 0.29 0.052 151.92
Edmontosaurus Quadruped manus 813 2.55 0.12 0.011 241.39
Edmontosaurus Quadruped pes 813 5.42 0.29 0.052 103.31
Tyrannosaurus 7654 75.09 0.72 0.234 320.26
Brachiosaurus manus 25 922 95.11 0.6 0.144 662.29
Brachiosaurus pes 25 922 159.19 0.87 0.401 396.58
813 7.98 n.a. 0.063 126.46
25 922 254.29 n.a. 0.545 466.59
Edmontosaurus and Brachiosaurus are also shown with pressure values from manus and pes combined.
The ‘Goldilocks’ effect P. L. Falkingham et al. 1143
J. R. Soc. Interface (2011)
and the ground, resulting in a smaller angle of ground
reaction force (GRF) [37]. As such, for the purposes of
this paper, a purely vertical component to the applied
force was assumed. Force distributed through feet in
contact with the ground was taken as the weight of
the animal, calculated as mass gravity (9.81 m s
An animal of 100 kg would therefore exert a vertical
force upon the ground of 981 N.
For a biped, maximum force is transmitted through a
single foot when the opposite foot is raised, so the
pressure applied in this case was equal to the weight of
the animal divided by the surface area of a single foot.
This is to approximate the peak force at any one time
during limb support. In the case of quadrupedalism,
CM plays a role in determining how much of the animal’s
weight is distributed to the fore- and hindlimbs, after
which the two sets of limbs can be treated separately
as bipeds [37]. This is a simplification of the loads experi-
enced by the autopodia of a quadruped during
locomotion, but provides reasonable input values for
the purposes of this paper. CM estimates for Edmonto-
saurus and Brachiosaurus were taken from the
literature (see [30]forEdmontosaurus CM and [31]for
Brachiosaurus) and used to apportion force between
fore- and hindlimbs. The amount of the animal’s
weight given to each pair of limbs was equal to the rela-
tive position of the CM between the pelvic and pectoral
girdles, i.e. a CM 60 per cent of the way from the pectoral
girdle to the pelvic girdle would imply a weight distri-
bution of 60 per cent to the hindlimbs, and 40 per cent
to the forelimbs [31](figure 1). Treating the animal as
two linked bipeds with appropriate weights was sufficient
for the purposes of these experiments (see [37]forwalk-
ing models of quadrupeds represented as two bipeds in
tandem). While this may be a very simplified solution
that ignores the effects of complex gaits, walking vel-
ocities and limb kinematics of dinosaurs are unknown
and employing the loading regime outlined above
avoids incorporating additional unfounded assumptions
into the simulations. Consideration is given to the effects
of duty factor and locomotion later in the discussion.
Hadrosauridae have been interpreted as primarily
bipedal with facultative quadrupedalism at either low
[21,23] or high [38] speeds, based on anatomical features
in the forelimbs suggestive of either mode of loco-
motion, and trackway evidence also supporting both
gait reconstructions [35,39,40]. Edmontosaurus tracks
were therefore simulated as being made by both a
bipedal animal and a quadrupedal animal.
The indenters, or ‘virtual feet’, were created by produ-
cing outlines around ventral views of reconstructed
skeletal autopodia (figure 2). Skeletal geometry was
scaled to the same size as the specimens used by Bates
et al.[30] and Henderson [31] so as to remain consistent
with mass estimates. The outlines were then increased
in size to account for soft tissue. The outline of the
Edmontosaurus manus does not follow the osteology as
closely as the other indenters, instead being based on
the exceptionally preserved hadrosaur body fossil MRF
03(thoughscaledtothespecimenusedby[30]), as fig-
ured in Sellers et al.[38, fig. 5], where the manus soft
tissue takes a ‘mitten’-like form over the skeleton. This
is supported by hadrosaur manus tracks illustrated by
Lockley & Wright [39], and those described as ‘crescent
shaped’ by Currie [41]. The indenters representing the
manus and pes of Brachiosaurus were generated as in
Falkingham et al.[28] from reconstructions by Wright
[42]. These outlines defined the nodes and elements
that would be loaded on the FE substrate volume
(figure 2). For each animal, a volume of substrate was cre-
ated for each foot to be indented into. Only one pes
needed to be indented for each bipedal condition, and
only one manus and one pes for the Brachiosaurus and
quadrupedal Edmontosaurus.
100 N
100 N
50 N50 N
100 N
100 N
30 N70 N
CM = 0%
CM = 50%
CM = 70%
0 N
Figure 1. Loads beneath fore- and hindlimbs as determined by
CM position. A CM position of 50% gleno-acetabular position
applies equal load to both fore- and hindlimbs. As the CM is
positioned more anterior or more posterior, more load is
applied to the fore- or hindlimbs, respectively.
Figure 2. Foot outlines used to create indenters. (a)Edmonto-
saurus manus, (b) pes, (c)Brachiosaurus manus, (d) pes
(adapted from [42]), (e)Struthiomimus and ( f)Tyranno-
saurus. Scale bars, 0.1 m. Edmontosaurus pes shows how
foot outline was derived based on osteology.
1144 The ‘Goldilocks’ effect P. L. Falkingham et al.
J. R. Soc. Interface (2011)
2.2. The virtual substrate
An elastic-perfectly plastic von Mises model was applied
in order to model a cohesive clay-like substrate. The
mechanical properties of the substrate were defined by
the undrained shear strength (C
), Young’s modulus
(E) and Poisson’s ratio (v). These parameters relate,
respectively, to
— The strength of the substrate, that is, how much
stress is needed before failure of the sediment ( per-
manent deformation). Essentially a measure of
cohesion between grains, shear strength is most
strongly affected by water content [10,43]. Typical
values of C
in sediments located on the tidal
banks of the Bahia Blanca Estuary, Argentina,
were shown to range between 50 and 150 kN m
in the surface 1 m [44]. Values of C
according to
the British Standards for Geotechnical Engineering
are summarized along with field testing methods
in table 2.
— The stiffness of the substrate—how much defor-
mation is recoverable through elastic behaviour
before (and after) plastic deformation takes place.
The value of Young’s modulus is typically 1000
the value of C
in cohesive substrates [45].
— The compressibility of the substrate. In an entirely
incompressible substrate, v¼0.5. Such a substrate
will not change in volume when deformed, resulting
in expansion equal to compression along an axis per-
pendicular to that of the primary stress [10]. An
incompressible substrate could be considered to be a
fully saturated sediment, in which void space air has
been completely replaced by water (note: though
water is technically compressible to some extent, at
the magnitude of forces dealt with here, it can
safely be considered incompressible). Typical values
for saturated clay or mud would be 0.4–0.5 [46].
Many palaeontological FEA studies concerning
stress within bone use elastic models, in which there is
a linear relationship between stress and strain
(figure 3a), determined by E. The introduction of a fail-
ure criterion (C
), however, produces an elastic-perfectly
plastic model, whereby initial loading deforms the
material in a recoverable elastic manner (line OY0in
figure 3b) until the load is sufficient to plastically
deform the substrate. Further loading equals or exceeds
Table 2. Undrained strength classification of clays according
to BS 8004:1986, along with simple field tests (from [10]).
undrained strength
(kN m
) test
hard .300 can be scratched by
thumb nail
very stiff 150–300 can be indented by
thumb nail
stiff 75 150 can be indented slightly
by thumb
firm 40 75 thumb makes
impression easily
soft 20–40 finger pushed in up to
10 mm
very soft ,20 finger easily pushed in
up to 25 mm
Y¢Y¢¢ P
bearing capacity
first yield
v = 0.49
v = 0.1
Figure 3. (a) Elastic stress– strain relationship, (b) elastic-per-
fectly plastic stress– strain relationship. Initial elastic
deformation occurs along line O–Y0until stress exceeds the
strength of the substrate, at which point failure occurs and
deformation takes place along line Y0–P. If loading is halted
at Y00, and then removed, elastic recovery occurs along line
Y00 U, parallel to initial deformation O– Y0.(c) The effects
of an elastic-perfectly plastic model distributed over a sub-
strate volume, in which parts are in plastic failure, and
others are in the elastic region. (d) The effects of Poisson’s
ratio on the overall form of the stress– strain relationship
within a substrate; dotted line, v¼0.49; solid line, v¼0.3;
dashed line, v¼0.1.
The ‘Goldilocks’ effect P. L. Falkingham et al. 1145
J. R. Soc. Interface (2011)
the bearing capacity and results in failure, where the sub-
strate can no longer support the load (line Y0–P in
figure 3b). When the load is removed, recovery occurs
along a line parallel to the original elastic deformation
(line Y00 –U in figure 3b). On the scale of individual
elements, this relationship is clear and well defined, but
over an entire mesh, where some elements may be in a
plastic state and others in an elastic one, the relationship
becomes less defined, with a curved portion where plastic
deformation occurs (figure 3c).
A soft clay-like substrate was generated in the FEA
simulations using 20-node hexahedral elements. The
20-node element is required in this case because of
the nature of the deformation; indenting into soft
substrate causes a large gradient of deformation from
negative vertical displacement beneath the edge of the
indenter, to positive vertical displacement adjacent to
the indenter. Eight-node elements lack the numerical
flexibility to deal with such a gradient, and so by
increasing the number of nodes defining the element,
a more accurate solution can be found. The volume of
substrate modelled was equal to four times the foot
length in all dimensions in order to avoid boundary
effects [13].
2.3. The process of indenting
While the foot of an animal can move at joints and the
soft tissue is deformable to an extent, as a whole, the
foot can be considered rigid compared with the non-
rigid substrate. In order to create a rigid loaded area,
rigid-body interface elements were generated above
the area on the mesh that would be loaded [47], essen-
tially creating a solid meshed foot on the surface of
the virtual substrate. The weight of the animal was
then applied to the interface elements to generate a uni-
form load over the foot. The ‘foot’ was loaded vertically
as a static analysis (i.e. independent of loading rate),
and then removed vertically in order to allow the sub-
strate to recover the elastic part of the deformation,
as would be the case in the formation of a real track.
The effects of loading rate are considered later in §4.
For each indenter, substrates were generated with a
high C
, and this was incrementally lowered until the
substrate could no longer support the load (i.e. bearing
capacity was exceeded). In all cases, Ewas equal to
, and v¼0.4. Maximum depth of indentation
beneath the virtual foot was recorded in each
experiment, as this value is a fair indication of the
degree to which a track is observable. Additionally,
surface tracks and undertracks were visualized and
qualitatively observed.
If the body mass and total foot surface area of the
models are logged, it can be shown that foot surface
area is proportional to mass
(see electronic
supplementary material, S1). This is close to the
relationship predicted by isometric scaling, where
surface area is proportional to mass
[48,49], and
suggests that as animals increase in size, the pressure
exerted on the substrate (discounting the effects of
locomotion) increases at a proportionally greater rate.
The small sample size used in this study means that
any difference in this relationship between quadrupeds
and bipeds cannot be observed, nor can the effects of
allometric scaling be explored.
In homogeneous substrates, there is a very narrow
range of C
values for any given pressure that allow
the formation of observable surface tracks (figure 4).
If C
is higher than this value, indenters fail to
deform the substrate to an appreciable degree, attaining
maximum track depths of less than a millimetre. Given
that many of the autopodia used were tens of centi-
metres in length, such deformation cannot realistically
be considered to be an observable track. Lower values
of C
than this narrow range cannot support the
applied load, and the substrate fails. The maximum
load a substrate can support beneath an indenter can
be approximated by calculating the bearing capacity
beneath a circular indenter under the specified load
using the following equation [50]:
bearing capacity ¼Cuð2þ
where Sis a shape factor equal to 1 þ0.2 (breadth/
Using this equation, it can be seen that a substrate for
which C
¼100 kN m
will fail when the load on a circu-
lar indenter (S¼1.2) reaches 616.8 kN m
pressure (kN m–2)
pressure (kN m–2)
0 20406080
no tracks
(substrate too soft;
firm subsurface
layer required)
no tracks
(substrate too firm)
shallow tracks
Cu (kN m–2)
Cu (kN m–2)
100 120 140 160 180
Figure 4. (a) Bubble plot of maximum track depth for a given
load on varying substrates. Size of bubbles qualitatively rep-
resent maximum depth of track. Line shown denotes the
predicted minimum C
required to support any given load
applied to a perfectly circular indenter. (b) Diagrammatic of
results. Tracks are only formed to any significant depth at
values approximately equal to those defined by the line, or
to the left of the line only if a firmer underlying layer is pre-
sent. Below and to the right of the line, loads are
insufficient to produce tracks of significant depth.
1146 The ‘Goldilocks’ effect P. L. Falkingham et al.
J. R. Soc. Interface (2011)
approximated failure point for circular indenters at any
given load is plotted as a line in figure 4.Thisprediction
is not the true value of bearing capacity for any specific
track, however, owing to variations in foot morphology.
However, as can be seen from figure 4,thisapproximation
is sufficiently close as to highlight the relationship.
The range of C
in which tracks of significant depth can be
generated is very small regardless of foot morphology or
load (figure 5). This limits tracks made in truly homo-
geneous substrates to an extremely narrow range of
pressures and subsequently producer sizes and foot mor-
phology. Below the minimum value of C
formed providing there is a firmer substrate layer beneath.
If there is no firmer subsurface layer, the substrate cannot
support the load, and the animal in question will be
unable to traverse the area without becoming mired.
A key observation is that in simulating track
formation in a homogeneous semi-infinite elastic-
perfectly plastic substrate, generation of tracks to any
significant depth is difficult to achieve—many tracks
were so shallow that for real tracks of a similar depth,
it would be unreasonable to expect discovery in the
field. This is because the load required to plastically
deform the substrate and the maximum load that the
substrate can support are very close, implying that a
very specific pressure is required to generate a track in a
homogeneous substrate. There is therefore a ‘Goldilocks’
quality to homogeneous substrates regarding possible
track formation. A faunal assemblage represented by
tracks at a given tracksite will be strongly biased towards
0.002 0.004 0.006
maximum depth (m)
Cu (kN m–2)
0 0.002 0.004 0.006 0.008
0 0.002 0.004 0.006
0 0.0005
0.005 0.01 0.015
Cu (kN m–2)Cu (kN m–2)
0.0002 0.0004 0.0006 0.0008
0.005 0.01 0.015
maximum depth (m) maximum depth (m)
Cu (kN m–2)
Figure 5. Graphs showing maximum track depth and substrate C
for each indenter. The horizontal dashed line depicts theor-
etical bearing capacity for a circular indenter applying the same pressure. (a)Struthiomimus,(b)Tyrannosaurus,(c)
Brachiosaurus manus, (d)Brachiosaurus pes, (e)Edmontosaurus manus (quadrupedal loading), ( f)Edmontosaurus pes (quad-
rupedal loading), and (g)Edmontosaurus pes (bipedal loading). Each graph shows there is a very narrow range in which tracks
are generated, but the substrate is still able to support the load.
The ‘Goldilocks’ effect P. L. Falkingham et al. 1147
J. R. Soc. Interface (2011)
the largest animals the substrate can support, resulting in a
very low diversity of recorded body sizes. Taxa exerting
more pressure beneath their feet than the substrate can
support will avoid the area or become mired, while animals
producing less pressure than is required to create a track
will not leave observable impressions.
More commonly, substrates are polyphasic, with het-
erogeneous mechanical properties varying vertically
and laterally. If a substrate is underlain by a firmer
layer (e.g. compacted sediment or rock), then tracks
will be formed if the surface layer fails. If we consider
the scenario of a series of substrate layers becoming pro-
gressively firmer with depth (figure 6), it is observed
that any animal creating sufficient load as to deform
the uppermost substrate will generate a track. Refining
this stratification such that C
increases gradually with
depth results in the intuitive case that heavier animals
generate deeper tracks. It can be seen from figure 4b
that this being the case, there is a much larger range
of possible track-bearing substrates for animals exerting
a greater pressure (i.e. by being larger or moving faster).
Given the shallow nature of the tracks modelled in
homogeneous substrates, it becomes apparent that
most real tracks must therefore be formed in mechani-
cally heterogeneous substrates, or in relatively shallow
homogeneous substrates underlain by rock.
If a substrate is stratified with mechanically distinct
layers, then the depths and surface areas of present
tracks can be used to infer the depth and mechanical
properties of these layers at the time of track formation.
A track-bearing surface on which small and medium
tracks are impressed to a similar depth, yet on which
tracks made by larger animals appear deeper, will indi-
cate a mechanically homogeneous surface layer as deep
as the small and medium tracks (after accounting for
subsequent weathering/erosion). Such consideration of
tracks as palaeo-penetrometers may prove useful in
interpretations of palaeoenvironment, at least in so far
as determining substrate conditions at the time of
track formation.
Examining the biases inherent in track formation as
a consequence of animal size permits discussion of gen-
uine and artificial signals regarding diversity as
interpreted from tracksites. A track site limited to
large producers, e.g. a purely sauropod track assem-
blage, is likely to be a preservational artefact, or
indistinguishable from such. Smaller animals may
have been abundant at such a site, but unable to pro-
duce tracks in the substrate. Allen [51] noted in his
discussion of the Flandrian deposits of the inner Bristol
Channel and Severn Estuary that the fauna represented
by tracks lacked records of smaller mammals such as
foxes and dogs, arguing this was a preservational
rather than an ecological issue. The results presented
here support this hypothesis, and may be applicable
to other fossil tracksites dominated by large fauna
such as Fumanya, Spain [52,53], or the tracksites at
Paluxy River, Glen Rose, TX, USA [54]. In the case
of the Glen Rose tracks, the site is dominated by large
sauropod and medium to large theropod tracks. One
trackway has been interpreted as showing the inter-
action of a theropod and sauropod [55], implying that
the trackways were contemporary. Given the consider-
able depth of both the theropod and sauropod tracks,
and the lack of tracks from smaller animals, the track-
ways appear to be consistent with the Goldilocks
effect. Both the theropod and sauropod exceeded the
bearing capacity of the surface mud, and indented
deep tracks until supported by firmer substrate layers
beneath the surface. However, the depth of the soft sur-
face mud may have been too great for smaller animals to
safely traverse while leaving tracks, resulting in the for-
mation and subsequent preservation only of the largest
animals present. A similar case can be made for the
sauropod trackways at Fumanya, where deep sauropod
tracks dominate. Shallow theropod tracks were pre-
viously reported from the site, but have since been
subjected to weathering and are no longer present
[52]. In this case, only larger animals were able to pro-
duce tracks, resulting in an impoverished track
assemblage, whose low diversity has been exacerbated
further by weathering and the complete removal of
the shallower tracks left by smaller animals.
Given that there is a strong bias towards greater
underfoot pressures, the preservation potential of
track assemblages representing mixed age groups
(herd behaviour) is greatly reduced; there will be a
strong bias towards preserving only the largest mem-
bers of the group. If the adults within a group are
0.05 m
0.05 m
Cu = x
Cu = y
Cu = z
Figure 6. Hypothetical scenario in which three substrate layers
are considered, where C
increases with depth. Animals pro-
ducing loads that cause the surface layer to fail, but not the
subsequent layer (a,load ,b) will create tracks of 0.05 m
maximum depth. Animals producing loads sufficient to
deform layer two, but insufficient to deform layer three (a,
b,load ,c) will generate tracks to 0.1 m depth. Animals
producing loads above the bearing capacity of layer three
(load .c) will be unable to traverse the substrate, while
animals producing less pressure than is required to deform
the surface layer (load ,a) will not generate tracks.
1148 The ‘Goldilocks’ effect P. L. Falkingham et al.
J. R. Soc. Interface (2011)
particularly large, as in the case of sauropods for
instance, the range of substrates traversable by the
group will be constrained by the minimum substrate
strength that can support the largest animals. As
such, tracks from smaller individuals become far less
likely to form and subsequently preserve, because the
substrates over which the animals move may not be
soft enough to record the passage of smaller, juvenile
forms. This reduction in preservation potential of
mixed-age herds is supported by the fossil record;
Myers & Fiorillo [56] noted that of 13 sauropod track-
way associations indicating gregarious behaviour, only
three sites contained tracks from multiple age groups.
The presence on a single track-bearing surface of
both small and large true tracks (rather than trans-
mitted or undertracks), indented to approximately the
same depth (evidently halted by a firmer subsurface
layer), is likely to be more indicative of true diversity
in the area at the time of track formation (providing
effects of time averaging can be removed). Presence of
small, shallow tracks and large, deep tracks may not
be indicative of true diversity, however, if the large
deep tracks are particularly deep. In such a scenario,
it is possible that medium-sized animals produce too
great a pressure underfoot to be supported by the soft
surface layer, but sink too far before reaching a suppor-
tive layer as to be able to traverse the area. This
highlights the importance of considering not just the
tracks present at a tracksite, but their total three-
dimensional morphology, including foot anatomy and
track depth, in order to make interpretations about
faunal diversity.
The Goldilocks effect described in this study is miti-
gated when a substrate is exposed for a period of time
during which the mechanical properties alter, such as
when a substrate is drying out. Changes in mechanical
properties will undoubtedly be the rule, rather than the
exception, but the rate at which these changes occur
will determine the overall applicability of the Goldilocks
effect to the fossilized tracksite. In cases where the sub-
strate dries out over a relatively prolonged period,
the Goldilocks effect will be applicable over short time
spans, but will not be evident over the recording life
of the substrate, or in the preserved track surface. The
presence of sedimentary features such as drying cracks
or displacement rims that are unique to some trackways
and not others may shed some light on the preserva-
tional context, and as to whether the Goldilocks effect
noted here applies to a given track assemblage.
The experiments carried out in this study have used
body mass to apply a force through the autopodia in a
number of taxa. Loading in this way assumes a direct
relationship between body mass and force, and was car-
ried out as a rate-independent (i.e. static) analysis as
the focus of the work was to explore bias relating to
size, not necessarily locomotor mode. This was done
to avoid incorporating unfounded assumptions into
the simulations, given that the habitual gaits of dino-
saurs are unknown. Nevertheless, consideration must
be given to the effects of locomotion, duty factor and
limb kinetics and kinematics. As an animal begins to
move, the GRF gains a horizontal (forward backward)
component in order to move the animal forwards [57].
This force vector may also incorporate a lateral com-
ponent depending on the animal’s gait. As speed
increases, the magnitude of the GRF also increases. In
terms of pressure applied, the pressure beneath an ani-
mal’s foot will increase as speed increases. As an animal
increases in speed, the minimum C
required to support
the load also increases, such that a substrate that pre-
viously would be incapable of recording an animal
standing or moving slowly may fail beneath the foot
of a running animal.
As an animal traverses a substrate, the rate of load-
ing is intrinsically linked to the speed and duty factor of
the animal, with loading rate increasing as duty factor
decreases. An increased loading rate results in more
resistance from the substrate, and the result is that
deformation occurs to a lesser extent (see electronic
supplementary material, S2). However, at higher
speeds, an animal exerts a greater force upon the sub-
strate, as noted above. As such, although the loading
rate increases with speed, the effects on substrate dis-
placement will be mitigated by the increased load
applied by the foot. It is important to note that the ana-
lyses carried out in this study were static, and thus did
not account for the effects of rate-dependent loading
and thixotropy. Exploring this complex interplay
between loading magnitude and loading rate is
beyond the scope of this study, and is impossible with-
out comprehensive locomotor reconstructions of the
animals in question. Instead, the Goldilocks effect can
be considered to be the base mechanic around which
other confounding factors such as limb dynamics, loco-
motion and substrate thixotropy have an effect. To
provide some insight into these complex issues, and
their relationship to the Goldilocks effect, the results
from a series of simple dynamic simulations are pro-
vided and discussed in electronic supplementary
material, S2.
Given the static vertical loading conditions employed
in this study, the relationship between size and track-
forming potential could be predicted to a reasonable
degree with simple mechanics and geotechnical
theory, as evidenced by the close correlation between
equation (3.1) and the results (figure 4a). However,
FEA provides benefits over simple mechanics. Simulat-
ing track formation allows for differing foot
morphologies to be tested, which was shown to be a
potentially important factor by Falkingham et al.[11].
FEA also allows us to explore the full three-dimensional
volume of simulated tracks. The importance of under-
standing the relationship between foot morphology,
three-dimensional deformation and undertrack pro-
duction will be demonstrated by the discussion of
features observed in the models.
The simulations undertaken for this study present an
opportunity to investigate track features at the original
track surface, and in subsurface undertracks. Specific fea-
tures related to autopodia morphology and undertrack
depth are discussed here. In order to generate deeper
The ‘Goldilocks’ effect P. L. Falkingham et al. 1149
J. R. Soc. Interface (2011)
tracks and associated undertracks, failure was allowed to
occur, but was halted when maximum depth reached
0.05 m, approximating a firm subsurface layer.
The values of mass, foot morphology and CM pos-
ition used for the Edmontosaurus produce differing
pressures between manus and pes (151.93 kN m
103.31 kN m
, respectively). These differing pressures
imply that substrates of different C
are required to sup-
port the loads, which in turn creates a range of
substrates (C
¼2040 kN m
), where the manus
causes the substrate to fail, but the pes does not. In
such substrates, if underlain by a firmer layer, only
the manus will generate tracks. This is the same mech-
anism as described in detail by Falkingham et al.[28]
for sauropod manus-only trackways. It is interesting
to note that the resulting pressure beneath the pes
when bipedal locomotion is assumed is less than for
the manus in a quadrupedal mode of locomotion.
Depending on the validity of the mass, CM and foot
outline input parameters used here, this may support
the hypothesis that differing modes of locomotion may
have been used for traversing different substrates. The
values employed in this study would suggest quadru-
pedalism to be potentially more advantageous on
firmer substrates, where the manus will not sink,
while a bipedal mode of locomotion would allow traver-
sal of softer substrates. However, this suggestion is
based only on underfoot pressures, and further factors
such as stability will ultimately determine gait. It
may therefore be unwise to infer otherwise unknown
locomotor styles from trackways in which the substrate
conditions at the time of track formation cannot be con-
strained. The reader is directed to Wilson et al.[58] for
discussion of a trackway in which an ornithopod track-
maker transitions between bipedal and quadrupedal
gaits as substrate changes.
As described above for the Edmontosaurus track
simulations, and as described by Falkingham et al.
[28], there are a range of substrates in which only the
manus, and not the pes, of Brachiosaurus produce
enough pressure to deform the substrate. When the
subsurface undertracks generated by manus and pes
are visualized, important features can be observed.
The bowl-like form of the Brachiosaurus pes
(figure 7) is reminiscent of a number of reported
sauropod tracks (e.g. [59,60]). The simulations here
indicate that such a bowl-like form is potentially
characteristic of undertracks. This is consistent with
the assumption that the plantar surface of the foot
was approximately flat, given that the shape of foot
required to form bowl-like tracks would prove unstable
on firm ground.
When the Brachiosaurus manus track is observed as
a subsurface undertrack at approximately 0.2 m depth,
a ridge running transversely across the track can be seen
(figure 8a,b). This ridge appears superficially similar to
the undulating track surface hypothesized to result
from three-phase movement of the foot [16,61]. How-
ever, with full control of all input variables, it is
known that in this case the loading was carried out in
an entirely vertical manner, evenly distributed through
a flat foot, and so the ridge cannot be a function of limb
kinematics or foot anatomy. Instead, this ridge is
produced through the displacement of sediment accord-
ing to Prandtl theory [10]. As substrate is deformed by a
load, it is pushed down and out from beneath the inden-
ter (figure 8c). The base of the actively deforming zone
of substrate undulates against the rigid, non-moving
zone [13]. A cross section through this area results in
a subsurface track containing a ridge of non-deformed
substrate. This effect is seen in the Brachiosaurus
manus track because of the round shape of the indenter.
This ridge is very subtle, and its absence from the other
simulated tracks implies that its formation is closely
linked with indenter morphology. Dynamic limb
motion consisting of more complex, non-vertical loading
will deform this ridge accordingly (e.g. see theropod
track in [16]); however, fossil track evidence indicates
that, as is the case here, sauropods placed the manus
vertically, at least when traversing soft substrates [62].
Further study is required to fully understand
this phenomenon and to avoid erroneous interpretation
of tracks with undulating bases. Note that some
previously described ridges in sauropod tracks
(e.g. [63]) appear more defined and morphologically
different to those outlined here, and we do not suggest
this mode of ridge formation for those cases.
0.06 m
0.12 m
0.2 m
0.4 m
Figure 7. Series of undertracks as generated by the Brachio-
saurus pes, seen in isometric view. Note the bowl-like form
of successive undertracks, as compared with the flat interior
and distinct outlines of the uppermost tracks. Darker shading
represents deeper parts of the track.
1150 The ‘Goldilocks’ effect P. L. Falkingham et al.
J. R. Soc. Interface (2011)
Both theropod tracks (Struthiomimus and Tyranno-
saurus) indented to a considerably greater degree at the
posterior of the virtual foot (figure 9). The pes of the
Edmontosaurus also exhibited this feature, albeit to a
lesser extent. This effect is a function of the shapes of
the indenters as seen in Falkingham et al. [11]. The
appearance of a deeper posterior track portion under uni-
form loading of a flat indenter has important
consequences for interpretations of limb kinematics from
fossil tracks. Commonly, the morphology of real tridactyl
tracks is deeper beneath the distal areas of the digits as a
result of the increased pressure as the animal kicks off, but
in the simulated case there is no such loading regime. The
development of a deeper track beneath a larger, more
compact part of the foot would mean that the ‘two-
phase’ interaction of the foot (weight bearing and toe
off) described by Thulborn & Wade [61] could poten-
tially produce a track with the appearance of a ‘three-
phase’ foot–substrate interaction (which precedes the
above phases with touch-down), where the heel and
toes are deeper than the centre portion of the track
[16,64]. It has been proposed that the two-phase and
three-phase modes of locomotion represent knee-based
and hip-based retraction of the limb, respectively ([64]
and references therein), and that the associated pressures
across the foot differ accordingly. However, if vertical
loading, as has been used here, produces a deeper ‘heel’ in
tridactyl tracks without a ‘heel-down’ kinematic phase,
then attempting to differentiate between the locomotor
modes of theropod dinosaurs and birds from fossil tracks
may be considerably more difficult than has previously
been assumed without ongoing experimental studies.
The resultant tracks from these simulations are rel-
evant for studies of tracks where interpretations of
locomotion have been made based on the ‘pitch’ of the
track [57,65]. Such interpretations must consider as an
alternative, or at least confounding factor, varying shear
strength (as a function of water content) throughout the
total substrate layer at the time of track formation, result-
ing in track pitch altering systematically along a trackway.
Alternatively, variations in track ‘pitch’ may be influ-
enced by grain size or compositional differences, given
that sand responds in the opposite manner to mud [11],
allowing greater deformation beneath digits.
The simulation of tracks from a series of dinosaur taxa
ranging in size from 400 to 25 000 kg shows a linear
relationship between body mass and substrate shear
strength required to produce observable tracks. The
point of failure for a given track and subsequently the
shear strength of the substrate at the time of track for-
mation can be approximated by calculating the bearing
capacity required for a circular indenter of equal size
and load. Variations around this approximation are
due to the effects of foot shape.
Tracks of significant depth are not possible in homo-
geneous, cohesive substrates without the presence of a
firmer subsurface layer, because failure of the substrate
will result in the animal being unable to traverse the
area. A homogeneous cohesive substrate will only record
tracks from the largest animals that substrate can support
without failing. There is, however, a strong bias towards
tracks made by larger animals if there is a firmer substrate
beneath a softer layer. This Goldilocks effect means that
for a homogeneous substrate, loading conditions (that is,
the animal size, locomotion and foot morphology) must
be ‘just right’ in order for the animal to be able to traverse
the area but still form tracks. This has wide-ranging
implications for interpretations of palaeodiversity and
palaeoecology based on vertebrate track assemblages
preserved in lithified muds and silts.
Figure 8. (a) Isometric and (b) cross-section views of sauropod
manus undertrack at a depth of 0.2 m (track generated in sub-
strate of C
¼110 kN m
and halted when track depth
reached 0.05 m). Note the transverse ridge running medio-later-
ally through the track, appearing similar to the three-phase
track described by Manning ([16,fig.6a]; [64, fig. 12.7]).
Darker shading represents deeper parts of the track. (c)Theor-
etical displacement beneath a strip load in a cohesive substrate.
If a track is exposed in a layer corresponding to that marked,
tracks may appear to contain an internal ridge running across
thewidestpartofthetrack((c) modified from [13]).
Figure 9. (a)Tyrannosaurus and (b)Struthiomimus tracks
viewed in plan and cross-section though digit III. Vertical dis-
palcement is greater at the posterior of the track owing to the
compact nature of the indenter in this area. Darker shading
represents deeper parts of the track.
The ‘Goldilocks’ effect P. L. Falkingham et al. 1151
J. R. Soc. Interface (2011)
Presence of small and large tracks indented to the
same depth on a single track-bearing surface (assuming
time-averaging/transmitted tracks can be accounted
for) offer the highest possibility of presenting a true rep-
resentation of faunal diversity in the area at the time of
track formation. Caution is strongly advised in making
any interpretations of faunal diversity or population
dynamics from track assemblages where all tracks
have been produced by similar-sized producers. Such
assemblages most likely represent a strongly biased
preservation, or an ‘instantaneous’ event. Substrates
which have dried out over relatively long time periods
will provide a fuller record of faunal diversity in the
area, but will be subject to biases and other erroneous
data associated with time-averaging.
Specific features regarding track and undertrack for-
mation have been noted for this range of indenters
based on dinosaur taxa. Bowl-like sauropod pedal
impressions may be indicative of being undertracks,
potentially of significant depth. Internal ridges may
form in tracks due to the vectors of displacement
beneath a uniform load (as in the Brachiosaurus
manus), or as a result of autopodia morphology causing
non-uniform displacement under uniform loading (as in
the tridactyl tracks). That these features can be formed
independent of limb kinematics is of great importance,
and highlights the need for further experimental work
to clarify the specifics of their formation.
The approach used here, of computer simulation using
FEA, has allowed the generation of tracks and associated
undertracks for a range of animal sizes that would be diffi-
cult to replicate using physical modelling. Employing
computational methods has also catered for constancy in
input variables between experiments, and has provided
the ability to easily and systematically manipulate those
variables. We recognize that this study makes a number
of assumptions and simplifications in terms of loading,
and expect subsequent research to build on the methods
used here to produce more complex models. Many of
the conclusions and observations recorded here are related
to the mechanics of substrates under load, and we hope
that this will encourage further research into the effects
of complex limb kinematics and kinetics on track
formation, in light of the confounding geotechnical effects
described here.
P.L.F. and K.T.B. were funded by the Natural Environment
Research Council (NER/S/A/2006/14033 and NER/S/A/
2006/14101, respectively). FEA simulations were run on the
HPCx supercomputing service, using Engineering and
Physical Sciences Research Council grant EP/F055595/1,
awarded to L.M. We would also like to thank James Jepson
for commenting on an early draft of the manuscript, and
also Jeff Wilson and one anonymous reviewer for their
constructive, helpful comments.
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... Manus-only and manus-dominated trackways had been originally associated with sauropods swimming with the forelimb touching the bottom and the hindlimb floating (Bird, 1944;Ishigaki, 1989;Farlow et al., 2019;Demathieu et al., 2022). Nevertheless, some of these trackways have been questioned and explained by the under-tracking hypothesis (e.g., Vila et al., 2005;Ishigaki and Matsumoto, 2009;Falkingham et al., 2011Falkingham et al., , 2012. Other manus-only trackways have been also proposed for swimming ankylosaurids (Riguetti et al., 2021). ...
... The morphology of the tracks results from a set of factors such as the anatomy and behavior of the producer, syn-depositional and post-depositional processes (Peabody, 1955;Falkingham et al., 2010;Avanzini et al., 2012;Belvedere and Farlow, 2016;Marchetti, 2018;Marchetti et al., 2019Marchetti et al., , 2020). An important aspect concerning the morphology is the consistency of the sediments (Laporte and Behrensmeyer, 1980;Lockley, 1991;Nadon, 2001;Gatesy, 2003;Mil an, 2003;Dalman and Weems, 2013;Falkingham and Gatesy, 2014;Belvedere et al., 2017;Gatesy and Falkingham, 2017), and this close relationship with the nature of the substrate allows the paleoenvironmental interpretations (Lockley, 1986;Avanzini, 1998;Gatesy et al., 1999;Mil an et al., 2004;Mil an and Bromley, 2006;Falkingham et al., 2010Falkingham et al., , 2011Platt et al., 2012;Díaz-Martínez et al., 2018;Menezes et al., 2019). There are some requirements concerning the substrate cohesiveness, plasticity, grain size, texture and water content to allow the footprint to register (Lockley et al., 1989;Avanzini et al., 2000;Leonardi and Mietto, 2000;Dalla Vecchia, 2008;Getty et al., 2017;Melchor et al., 2019). ...
The dinosaur tracks in the Rio do Peixe basins (Lower Cretaceous, Rio da Serra-Aratu stages) occur in at least 39 individual tracksites through approximately 98 stratigraphic levels in the western part of the State of Paraíba, Brazil. The Triunfo basin (one of the four Rio do Peixe basins) is a 480 km² asymmetric graben, located in the counties of São João do Rio do Peixe, Uiraúna, Poço, Brejo das Freiras, Triunfo, and Santa Helena, controlled by a NE transcurrent fault system. To date, only four isolated footprints and two incomplete trackways have been identified in the Antenor Navarro Formation. Among the isolated footprints, three probably belong to theropods. One incomplete trackway consists of just two digitigrade, rounded digits, suggesting they were made by a small ornithopod. In this study we describe a new ichnosite, located at Sítio Pereiros, São João do Rio do Peixe county, Paraíba State. The one and a half meter thick succession of fine-grained sandstones, siltstones, mudstones and shales with ripple marks, climbing ripples and mud cracks of the Sousa Formation reveals a bedding plane with three trackways, with a total of 19 tridactyl, mesaxonic footprints. These trackways are interpreted as produced by theropods, two large and one smaller. In these beds there are also ostracods, spinicaudatans (conchostracans), and fragments of microvertebrates (fish scales, teeth and bones). The Sítio Pereiros ichnosite represents a deposition in a floodplain area, with temporary aerial exposure of the superficial sediments in which tracks were impressed. The ichnofauna from this locality increases knowledge of the theropod fauna from the Triunfo basin and the distribution of the dinosaur tracks throughout the interior basins of Northeastern Brazil. Description of these new theropod tracks permits evaluation of the behavior of these three theropods, including inferences about trackmaker speed and the type of gait of the three animals, and also of their possible size. This is the 40th ichnosite in the Rio do Peixe basins, extending analysis of the types of trackmaker associations present at such ichnosites, as well as the dinosaur diversity represented at each of them. New interpretations are presented about the environments, and the relationship between the various groups represented in this region in the Early Cretaceous.
... Otherwise, it will be necessary to develop appropriate analyses to accommodate coarse taxonomic resolution.99 Track assemblages preserve ample evidence of birds and other small creatures, suggesting that size-biased preservation is a less serious issue in the ichnological record than in the skeletal record.Certain substrates may be more likely to capture tracks of larger or smaller animals,100 but tracks of widely different sizes are often preserved on single track surfaces. Other unique modes of preservation bias also exist in track assemblages, however. ...
Hominin footprints have not traditionally played prominent roles in paleoanthropological studies, aside from the famous 3.66 Ma footprints discovered at Laetoli, Tanzania in the late 1970s. This contrasts with the importance of trace fossils (ichnology) in the broader field of paleontology. Lack of attention to hominin footprints can probably be explained by perceptions that these are exceptionally rare and "curiosities" rather than sources of data that yield insights on par with skeletal fossils or artifacts. In recent years, however, discoveries of hominin footprints have surged in frequency, shining important new light on anatomy, locomotion, behaviors, and environments from a wide variety of times and places. Here, we discuss why these data are often overlooked and consider whether they are as "rare" as previously assumed. We review new ways footprint data are being used to address questions about hominin paleobiology, and we outline key opportunities for future research in hominin ichnology.
... This method had suffered some revision from the same author (Alexander 2006) and others. First, some taphonomic processes related with the substrate conditions affect the track and stride lengths measurements, data key for further analyses (e.g., Allen 1997;Gatesy et al. 1999;Nadon 2001;Manning 2004;Milàn and Bromley 2006;Marty et al. 2009;Falkingham et al. 2011). Second, some anatomical aspects were analyzed by Thulborn (1989Thulborn ( , 1990, who points out that the relationship between the height at the hip joint and the footprint length (h/L) varies in systematic fashion among dinosaur taxa, and that this h/L ratio certainly changes during ontogeny, on account of the allometric growth that prevails in terrestrial vertebrates. ...
Forty years ago, L. Branisa and G. Leonardi discovered the first sauropodomorph tracks in South America during expeditions to Toro Toro (Bolivia). Since then, numerous findings, mainly in Argentina, Bolivia, and Brazil, have increased the record. The first research lines mainly covered morphological description, ichnotaxonomic identification, and behavioral analyzes (e.g., gregariousness and speed). Some Cretaceous tracksites allowed the description of three new ichnotaxa: Sauropodichnus giganteus (Calvo in Ameghiniana 28:241–258, 1991), Titanopodus mendozensis (González Riga and Calvo in Palaeontology 52:631–640, 2009), and Calorckosauripus lazari (Meyer et al. in Ann Soc Geol Pol 88:223–241, 2018), the former two corresponding to Argentina, and the latter to Bolivia. A new research line named ‘ichnology and comparative anatomy’ has become relevant in the last years linking the skeletal information to the ichnological record, thus providing an integral interpretation of the set. This kind of approach allowed making more accurate inferences about paleoecological aspects, including limb posture, gauge, gait, speed, and size diversity recorded. In sum, this chapter aims to provide an overview of the South American sauropodomorph ichnotaxonomy, the history of the discoveries, and the results of new research lines in development.
... This method had suffered some revision from the same author (Alexander 2006) and others. First, some taphonomic processes related with the substrate conditions affect the track and stride lengths measurements, data key for further analyses (e.g., Allen 1997;Gatesy et al. 1999;Nadon 2001;Manning 2004;Milàn and Bromley 2006;Marty et al. 2009;Falkingham et al. 2011). Second, some anatomical aspects were analyzed by Thulborn (1989Thulborn ( , 1990, who points out that the relationship between the height at the hip joint and the footprint length (h/L) varies in systematic fashion among dinosaur taxa, and that this h/L ratio certainly changes during ontogeny, on account of the allometric growth that prevails in terrestrial vertebrates. ...
After the extinction of rebbachisaurids during the Cenomanian–Turonian interval, titanosaurs were the only group of sauropods to face the K–Pg event. This same global pattern also holds for the end-Cretaceous (Campanian–Maastrichtian) titanosaur record in South America, where their remains can be found from southern Argentina to Ecuador, with more frequent findings in Argentina and Brazil. In this chapter, we review these fossil findings and the main aspects of the taxonomy, systematics, and paleogeographic implications of this record and briefly discuss the importance of these occurrences for the understanding of titanosaur evolution. The diversity and abundance of end-Cretaceous titanosaur taxa in South America represent about 25% of the known Titanosauria species in the world, which makes them the most common group of large terrestrial herbivores of that time. Cretaceous titanosaurs from South America also vary highly in morphology and size, comprising small to large-sized taxa, for example. Their record mainly consists of appendicular and axial remains, including rare skull material, but also comprises eggs, nests, footprints, and coprolites. In South America, by the end of the Late Cretaceous, titanosaurs were generally represented by more derived titanosaurians that are mainly taxonomically assigned to more derived species within Aeolosaurini and Saltasaurinae.
... On deformable substrates, however, the ground yields with each step. If the substrate deforms plastically (i.e., the deformation is not elastically recovered), a footprint, or track, is made (Allen, 1989;Falkingham et al., 2011;Falkingham, 2014). Previous studies have revealed that with increasing substrate deformability, greater subsurface foot motions occur, and increasingly larger volumes of substrate are impacted (Milàn, 2006;Hatala et al., 2018;Gatesy and Falkingham, 2020;. ...
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The stance phase of walking is when forces are applied to the environment to support, propel, and maneuver the body. Unlike solid surfaces, deformable substrates yield under load, allowing the foot to sink to varying degrees. For bipedal birds and their dinosaurian ancestors, a shared response to walking on these substrates has been identified in the looping path the digits follow underground. Because a volume of substrate preserves a 3-D record of stance phase in the form of footprints or tracks, understanding how the bipedal stride cycle relates to this looping motion is critical for building a track-based framework for the study of walking in extinct taxa. Here we used biplanar X-ray imaging to record and analyze 161 stance phases from 81 trials of three Helmeted Guineafowl (Numida meleagris) walking on radiolucent substrates of different consistency (solid, dry granular, firm to semi-liquid muds). Across all substrates, the feet sank to a range of depths up to 78% of hip height. With increasing substrate hydration, the majority of foot motion shifted from above to below ground. Walking kinematics sampled across all stride cycles revealed six sequential gait-based events originating from both feet, conserved throughout the spectrum of substrate consistencies during normal alternating walking. On all substrates that yielded, five sub-phases of gait were drawn out in space and formed a loop of varying shape. We describe the two-footed coordination and weight distribution that likely contributed to the observed looping patterns of an individual foot. Given such complex subsurface foot motion during normal alternating walking and some atypical walking behaviors, we discuss the definition of “stance phase” on deformable substrates. We also discuss implications of the gait-based origins of subsurface looping on the interpretation of locomotory information preserved in fossil dinosaur tracks.
Heteropody Index (HI) is a tool used to calculate area differences between the manus and pes of fossil trackways. HI uses a simple length × width calculation to estimate area. However, since most foot impressions are rarely close to square in shape, HI using a different area calculation could potentially more accurately reflect differences in manus and pes foot area. In this study, accuracy of length × width (L×W) as an area estimate for basic shapes and animal footprints, was tested against two other area calculations, the area of a circle: πr2, and length × carpal width (L×CW) (the width at the most proximal point of the foot in contact with the ground). In addition, accuracy of HI calculations using these methods was tested against HI calculations using actual area of the corresponding shape or underfoot area. It was discovered that in general L×W is a better estimate for area than πr2, in most animals except ungulates. However, for those animals where L×W was a better estimate than πr2, L×CW was more accurate. This paper additionally proposes that by combining the findings of these tests with those of Strickson et al. (2019), foot area estimates for dinosaurs can be estimated more accurately using L×CW, to return an area close to estimates for soft tissue. Previous HI measurements may have overestimated extreme heteropody in sauropod dinosaurs.
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Evidence of Late Triassic large tetrapods from the UK is rare. Here, we describe a track-bearing surface located on the shoreline near Penarth, south Wales, United Kingdom. The total exposed surface is c. 50 m long and c. 2 m wide, and is split into northern and southern sections by a small fault. We interpret these impressions as tracks, rather than abiogenic sedimentary structures, because of the possession of marked displacement rims and their relationship to each other with regularly spaced impressions forming putative trackways. The impressions are large (up to c. 50 cm in length), but poorly preserved, and retain little information about track-maker anatomy. We discuss alternative, plausible, abiotic mechanisms that might have been responsible for the formation of these features, but reject them in favour of these impressions being tetrapod tracks. We propose that the site is an additional occurrence of the ichnotaxon Eosauropus , representing a sauropodomorph trackmaker, thereby adding a useful new datum to their sparse Late Triassic record in the UK. We also used historical photogrammetry to digitally map the extent of site erosion during 2009–2020. More than 1 m of the surface exposure has been lost over this 11-year period, and the few tracks present in both models show significant smoothing, breakage and loss of detail. These tracks are an important datapoint for Late Triassic palaeontology in the UK, even if they cannot be confidently assigned to a specific trackmaker. The documented loss of the bedding surface highlights the transient and vulnerable nature of our fossil resources, particularly in coastal settings, and the need to gather data as quickly and effectively as possible.
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subdivided into three informal members: A lower member is marked by reddish-brown, trough cross-bedded, coarse-to medium-grained sandstone interbedded with thin beds of varicolored mudstone, reflecting deposition in a braided fluvial system, a middle member is characterized by reddish-white to yellow, planar cross-bedded, medium-grained sandstone with ferruginous siltstone intercalations, interpreted as meandering fluvial deposits, and an upper member consists of repeated coarsening-upward cycles of rippled siltstone to fine-to medium-grained sandstone and planar cross-bedded, yellowish-white sandstone, containing many vertebrate footprints and invertebrate trace fossils, reflecting deposition in a coastal to deltaic environment. Sixteen dinosaur footprints are recorded at the base of the upper member of the Nubian Sandstone, on inclined surfaces of rippled, fine-grained sandstones. Twelve are overlapping each other and belong to distinct individuals of dinosaurs, the other four are distributed on a younger bedding surface. Twelve footprints are from more than one sauropod dinosaur, while three of the isolated footprints belong to a thero-pod dinosaur. The footprints described are semiplantigrade and digitigrade. This discovery is the second record of tetrapod footprints in Egypt and the first record of tetrapod footprints in the Eastern Desert.
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Footprints taken experimentally of a captive Komodo monitor (Varanus komodoensis) were recorded in potter's clay and cast in plaster. These show morphologic features, also seen in fossil footprints of large reptiles, that reflect a particular pattern of stance and gait. Footprint form and kinematics must be analyzed separately for fore- and hindlimbs because a certain amount of mosaic evolution occurs in limb morphology and locomotion. Comparisons of footprint form with still photographs of the animal walking reveal that the distinct, unmuddied prints of the manus result from an effectively parasagittal movement of the forearm and hand, rotating around a horizontally-oriented humerus. This differs from the lateral arc of protraction in the forearm movement of crocodiles, whose manus prints are generally less distinct. The monitor's pes moves parasagittally, somewhat as in crocodiles. Tail marks were not conspicuous. The Komodo monitor tracks are similar in great detail to those of Triassic pseudosuchian thecodonts and (to a lesser extent) Early Jurassic crocodiles. Footprint faunas since the Upper Triassic are completely devoid of similar tracks. The similarities probably reflect retention in all these groups of a primitive reptilian locomotory pattern. Hence, the Komodo monitor tracks underscore the extent to which fossil footprints are classified by grade of organization and locomotion. Lacertilian tracks are uncommon in the fossil record. Similarities of Komodo monitor tracks to fossil footprints of nonlacertilians suggest that analysis of modern lacertilian footprints may provide insight into ontogenetic and functional differences underlying much of the basis of paleoichnologic taxonomy.
The narrow- and wide-gauge trackways attributed to sauropod dinosaurs are hypothesized to be a consequence of the relative positions of their centers of mass. This hypothesis was tested using three-dimensional, trackway-producing computer models of two sauropods and studies of Asian elephants. Centers of mass of sauropod models were computed using density distributions that reflect the high degree of pneumatization of the skeletons and air sacs within the body. A close correspondence was found between the relative areas of hand and foot prints in different trackways and the relative fractions of the body weight borne by the forefeet and hindfeet in the different types of sauropods inferred to have made the trackways. Experimental studies of Asian elephants corroborated the close correspondence between relative areas of the hindfeet and forefeet and body weight distribution. Replicating actual sauropod trackways with the walking models enabled testing of proposed gaits for a sauropod model. Brachiosaurus brancai, with its more centrally positioned center of mass, was stable and possessed a wide safety margin only when replicating a wide trackway. Conversely, Diplodocus carnegii, with a more posteriorly placed center of mass, was most stable when replicating a narrow trackway. A trend for large sauropods (>12 tons), independent of clade, to have more anteriorly positioned centers of mass was identified, and it is proposed that all large sauropods were restricted to producing wide-gauge trackways for stability reasons. The primitive gait state for Sauropodomorpha was determined to be one that produced narrow-gauge tracways.
The study of tracks is often regarded as a fringe subdiscipline outside the scientific mainstream. Papers dealing with footprints traditionally appear either in popular magazines like Natural History (Bird 1939, 1944; Brown 1938), or in very obscure publications (Sarjeant 1974). Usually it is only the spectacular discoveries, which are directly applicable to topical debates, that rouse much scientific interest. For example, the discovery of Pliocene hominid tracks (Leakey and Hay 1979) provided unequivocal evidence for the antiquity of bipedalism (cf., Napier 1967). Similarly the tracks of a running theropod allowed for direct estimates of the speed attained by dinosaurs (Farlow 1981), and the tracks of a herd of running theropods fueled debate about gregariousness and stampede behavior (Thulborn and Wade 1984).
The narrow- and wide-gauge trackways attributed to sauropod dinosaurs are hypothesized to be a consequence of the relative positions of their centers of mass. This hypothesis was tested using three-dimensional, trackway-producing computer models of two sauropods and studies of Asian elephants. Centers of mass of sauropod models were computed using density distributions that reflect the high degree of pneumatization of the skeletons and air sacs within the body. A close correspondence was found between the relative areas of hand and foot prints in different trackways and the relative fractions of the body weight borne by the forefeet and hindfeet in the different types of sauropods inferred to have made the trackways. Experimental studies of Asian elephants corroborated the close correspondence between relative areas of the hindfeet and forefeet and body weight distribution. Replicating actual sauropod trackways with the walking models enabled testing of proposed gaits for a sauropod model. Brachiosaurus brancai, with its more centrally positioned center of mass, was stable and possessed a wide safety margin only when replicating a wide trackway. Conversely, Diplodocus carnegii, with a more posteriorly placed center of mass, was most stable when replicating a narrow trackway. A trend for large sauropods (>12 tons), independent of clade, to have more anteriorly positioned centers of mass was identified, and it is proposed that all large sauropods were restricted to producing wide-gauge trackways for stability reasons. The primitive gait state for Sauropodomorpha was determined to be one that produced narrow-gauge tracways.
The Purbeck Limestone Group (late Jurassic-early Cretaceous) contains a rich vertebrate trace fossil fauna. Research on this fauna has been almost entirely concerned with the dinosaur tracks. By contrast, the feeding traces and coprolites, which are occasionally abundant, have received little attention. The implications of some recent papers, including those where ichnotaxa were assigned, are considered along with the stratigraphic and geographic distribution of reptilian tracks. A plan of the principal footprint horizon at Townsend Road, Swanage, is presented and the more unusual aspects of the site illustrated. An appendix gives a comprehensive listing of published and manuscript accounts dealing with footprints from these strata. Some of the neglected feeding traces and coprolites are described and illustrated for the first time.
Six compilations of fossil tetrapod families, spanning 100 years, each contain a broadly similar diversity patten since the Upper Devonian. Comparison of four recent data bases, one of which is derived from a strict cladistic treatment, reveals widespread taxonomic and stratigraphic inaccuracies in three earlier data bases. Improvement of our intepretation of the tetrapod fossil record will come through continued taxonomic and stratigraphic revision as well as discovery of new fossils. -Authors
This chapter discusses the anatomy, evolution, biogeography, taphonomy, paleoecology, and paleobiology of prosauropaud dinosaurs. Prosauropods have been found on all the major continents, including Antarctica. They were medium- to large-sized, bipedal, facultatively bipedal or quadrupedal sauropodomorphs with long necks and tails. Prosauropods were probably the slowest of the bipedal dinosaurs but better runners than most other quadrupedal dinosaurs. Among prosauropods, Saturnalia and Thecodontosaurus are considered fully bipedal. Riojasaurus and other melanorosaurids were fully quadrupedal and the remaining prosauropods were probably only facultatively bipedal.