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The depth to which a vertebrate track is indented can provide a wealth of information, being a direct result of the weight, duty factor, and limb kinematics of the animal as well as media (5 substrate or sediment) consistency. In order to recreate the formation of the track and elucidate media consistency at the time of track formation, such factors as animal mass, duty factor, and foot morphology must be taken into consideration. This study uses Finite Element Analysis and physical modeling to demonstrate for the first time that the shape of the foot is an important factor that influences the depth to which the sediment is penetrated. In cohesive sediment, less compact morphology allows more sediment to move vertically upwards at the edges of the foot, dissipating force at the surface, and retarding transmission of load vertically down into the sediment. The reverse of this effect is seen in noncohesive sediment. Foot morphology, therefore, has a direct impact on preservation potential, both of surface tracks and undertracks, that is irrespective of the pressure exerted on the sediment surface by the foot and independent of mass and duty factor. INTRODUCTION
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PALAIOS, 2010, v. 25, p. 356–360
Research Article
DOI: 10.2110/palo.2009.p09-164r
School of Earth, Atmospheric and Environmental Science, University of Manchester, Williamson Building, Oxford Road, Manchester, M13 9PL, UK;
Computing, University of Manchester, Devonshire House, Oxford Road, Manchester, M13 9PL, UK;
Department of Earth and Environmental Science, University of
Pennsylvania, 254-b Hayden Hall, 240 South 33rd Street, Philadelphia, Pennsylvania 19104-6316, USA
e-mail: peter.falkingham
The depth to which a vertebrate track is indented can provide a wealth of
information, being a direct result of the weight, duty factor, and limb
kinematics of the animal as well as media (5 substrate or sediment)
consistency. In order to recreate the formation of the track and elucidate
media consistency at the time of track formation, such factors as animal
mass, duty factor, and foot morphology must be taken into consideration.
This study uses Finite Element Analysis and physical modeling to
demonstrate for the first time that the shape of the foot is an important
factor that influences the depth to which the sediment is penetrated. In
cohesive sediment, less compact morphology allows more sediment to
move vertically upwards at the edges of the foot, dissipating force at the
surface, and retarding transmission of load vertically down into the
sediment. The reverse of this effect is seen in noncohesive sediment. Foot
morphology, therefore, has a direct impact on preservation potential, both
of surface tracks and undertracks, that is irrespective of the pressure
exerted on the sediment surface by the foot and independent of mass and
duty factor.
In this paper, the effect of foot morphology on track depth is
investigated by using Finite Element Analysis (FEA) to indent a series
of abstract foot geometries. As a measure of foot morphology, a metric
derived from circumference, or edge length, has been used, where edge
length can be defined as the boundary between foot and sediment when
seen in plan view. FEA has previously been applied to the study of
track formation to show that interdigital webbing may arise as an effect
of media deformation, rather than as the impression of true webbing
(Falkingham et al., 2009), and to illustrate subsurface deformation and
undertrack formation beneath vertical and heel-toe cycle loads
(Margetts et al., 2005, 2006; Falkingham et al., 2007, 2008).
While vertebrate ichnotaxa may be difficult to constrain to specific
environmental or media (5 substrate) conditions, we are provided with
tracks produced in multiple media with relatively consistent loading
conditions (e.g., pressure, force vectors, pedal morphology, etc),
resulting in track morphologies that may vary to a considerable degree
due entirely to media consistency (Manning, 2004; Mila`n and Bromley,
2006, 2008;
nez et al., 2009). Even if two different animals
that share foot morphology and limb kinematics are separated
temporally and spatially, there may be enough consistency in loading
conditions that differences in the tracks—magnitude of displacement
rims, radial cracks, track depth—can be used to infer media conditions
at the time of track formation in different strata. Much of this
sedimentary variation may be linked to water content (e.g., Platt and
Hasiotis, 2006), which is in turn controlled by environmental factors
(e.g., Hasiotis, 2007). In a cohesive medium, water content directly
determines both the shear strength of the material (through creating
cohesion between particles) and the Poisson ratio (compressibility).
Extremes of moisture content prevent track formation either because
the medium is too loose, or too liquid (Laporte and Behrensmeyer,
1980; Platt and Hasiotis, 2006).
Given that track depth is a function of the force applied through the
sole of the foot over a given medium, there is therefore the potential to
use tracks as paleopenetrometers (Lockley, 1987; Allen, 1989; Nadon
and Issler, 1997; Nadon, 2001), whereby the depth of a track may be
used to gauge the medium consistency at the time of track formation,
and subsequently used to refine paleoenvironmental interpretations
(Lockley, 1986; Nadon and Issler, 1997; Nadon, 2001; Platt and
Hasiotis, 2006). In order to do so with confidence, other confounding
factors influencing the depth of a track must be understood and taken
into account.
Two experiments consisting of FEA simulations were carried out to
investigate the effects of varying pedal complexity on penetration of the
medium. FEA provides a means for investigating stress and strain
within a continuous medium under load, and is now a tried and tested
technique in paleontology. See Rayfield (2007) for a comprehensive
review of the method, and Falkingham et al. (2007, 2008, 2009) and
Margetts et al. (2005, 2006) for details of the method as applied to track
The first experiment involved generating geometrically abstract
shapes to act as indenters, which maintained a consistent surface area,
but differed in complexity. The same pressure was then applied to the
surface of each indenter. By using geometrically abstract shapes,
complete control over shape complexity could be achieved, and FEA
meshes consisting of relatively few elements used, facilitating rapid
analysis (Rayfield, 2007).
These analyses were undertaken using a program written by us using
ParaFEM (, checked March 2010), a freely
available parallel finite element library. The program was validated
using a series of geotechnical engineering test problems, such as the
bearing capacity of a smooth flexible footing (Smith and Griffiths,
2004). Results of these validation examples were compared with
empirical solutions and with analyses carried out using Abaqus/CAE
version 6.8-2 (, checked March 2010).
A second experiment was carried out using physical modeling.
Indenters of equivalent shape as those used in experiment 1 were cut
from wood and used to indent natural media.
Measuring shape.—In order to draw comparisons between indenters
of differing morphology, a metric was required. As a measure of shape,
edge length—the circumference of the indenter—was used as this varies
with shape for a given sized indenter. Using absolute circumference or a
* Corresponding author.
2010, SEPM (Society for Sedimentary Geology) 0883-1351/10/0025-0356/$3.00
ratio of edge length to surface area, however, provides a function that
varies with size; a small square has a higher circumference to surface
area ratio than a larger square. To take account of this, edge length was
normalized using equation 1.
e~ e
A ð1Þ
Where e9 is the normalized edge length, e is edge length, or
circumference, of the indenter, and A is the surface area of the
indenter. A square will always have an e9 value of 1, regardless of size,
whilst less compact morphologies will have a higher value, but one that
will remain constant as size varies.
Experiment 1
An FEA mesh representing a volume of elastic–perfectly plastic soil
was created using 20-node hexahedral elements and given the properties
of a stiff mud (Young’s Modulus 5 100,000 kPa, Poisson Ratio 5 0.4,
Shear Strength 5 100 kN/m
(Leach, 1994)). On the surface of this
mesh, an indenter was created, and given a Young’s Modulus and Shear
Strength sufficiently high as to make the indenter nondeformable
relative to the medium. This is a technique used by FEA users in
geotechnical engineering to model rigid indenters (Potts and Zdravko-
, 1999, 2001). The elements used to define the indenter were arranged
in seven different configurations, forming seven indenters, each with a
surface area of nine square units, but with edge lengths ranging from 12
units (the minimum possible for nine elements) to 20 units (the
maximum possible) (Fig. 1). Corresponding values of e9 ranged from 1
to 2.78. Two variations were created each for edge lengths of 14 and 20
units, one (Figs. 1C, F) more complex than the other (Figs. 1B, G). A
uniform pressure of 10 units per unit area was applied to the surface of
each indenter to provide a vertical load.
A second series of indenters were generated to explore the effects of
indenter size on track depth, and each had a surface area of 16 square
units (using 16 elements), providing a greater range of e9 (1 to 4.52)
(Fig. 2). The same pressure was applied as for the above scenario, and
the soil properties remained constant. The parameters of each indenter
are summarized in Table 1.
There are many more possible indenter shapes that would retain
constant surface area over a range of edge lengths, but it is not feasible
to attempt to model them all here. The indenters used herein represent
most of the extreme forms of complexity and simplicity.
In order to avoid effects of low-resolution meshes, a series of analyses
were run on consecutively higher resolution meshes until the difference
in final result became negligible. Final mesh sizes were on the order of
400,000 elements. Figure 3 shows how meshes were refined.
Experiment 2
For this experiment, indenters matching those used in experiment 1
(Fig. 1) were made from wood. These indenters were used to indent a
soft mud with shear strength of ,5–10 kN/m
as measured in situ with a
penetrometer. A consistent pressure of 3 kN/m
was slowly applied
through each indenter using the penetrometer. Subsequent displace-
ment was then measured. The above procedure was repeated for dry,
fine-grained sand. These experiments were carried out numerous times
and recorded depths were averaged for each indenter.
FIGURE 1—Indenter shapes used in experiment 1 (surface area 5 9 units
) in plan
view. Indenters are subsequently referred to as 1A–G.
FIGURE 2—Indenter shapes with surface area 5 16 units
, viewed in plan view.
Subsequently referred to as indenters 2A–I. See table for details of edge lengths.
TABLE 1—Details of indenter surface area, edge length, edge length to surface area
ratio, and e9.
Surface area
Edge length
Normalized edge
length (e9)
1A 9 12 1.33 1
1B 9 14 1.56 1.36
1C 9 14 1.56 1.36
1D 9 16 1.78 1.78
1E 9 18 2 2.25
1F 9 20 2.22 2.78
1G 9 20 2.22 2.78
2A 16 16 1 1
2B 16 18 1.125 1.26
2C 16 20 1.25 1.56
2D 16 22 1.375 1.89
2E 16 24 1.5 2.25
2F 16 26 1.625 2.64
2G 16 30 1.875 3.52
2H 16 32 2 4
2I 16 34 2.125 4.52
FIGURE 3—Increasing mesh resolution. Left; element size 5 1 unit
, Middle;
elements with dimensions 50% smaller (volume 25% of original), and Right; smallest
elements used (0.25 units
). Each image is shown to the same scale.
Experiment 1
Maximum displacement was plotted against edge length (Fig. 4). The
maximum depth to which the indenters displaced the sediment
decreased as complexity (given by e9) increased. The most complex
shape (Fig. 1F), however, does not follow the pattern, instead indenting
to a greater depth than the simple indenter of edge length 20 (Fig. 1G).
The data show an overall decrease in maximum vertical displacement
corresponding to an increase in e9.
Experiment 2
The values for depth of indentation in the mud and dry sand are
shown in Figure 5. The indenters in mud showed slight reduction in
depth with increasing e9; it can be seen that indenters 1G and 1F (e95
2.78) both indented to a lesser degree than did indenter 1A (e951),
showing an extreme of only 50% of the depth of indenter 1A. The sand
showed the reverse trend seen in the experiments with mud and in the
FEA simulations; an increase in e9 produced a greater depth of
indentation. There is still the dichotomy between indenters 1B and 1C,
and between 1F and 1G.
The results from experiment 1 show a general trend for decreasing
displacement as edge length (e9) increases (Figs. 4, 6). Experiment 2
shows this trend in cohesive media, but that the reverse is true in
noncohesive sand. This is consistent with soil mechanics theory; a
noncohesive sand will displace to the greatest extent at the edges of an
indenter because values of Young’s Modulus vary with confining
pressure (Craig, 2004). Sediment grains are able to move past each
other, and as a result grains located between protrusions of indenters
are not pulled downwards by cohesion, unlike in muds and clays.
Penetration in cohesive media decreased by nearly 20% when
normalized edge length was increased from shortest to longest (most
compact shape to least compact). When displacement is normalized to a
percentage of the depth indented by the most compact form, it can be
seen that size of indenter does not significantly affect the pattern
(Fig. 6).
The larger indenters (surface area 5 16 units
) penetrated to greater
depths than the smaller set of indenters (Fig. 4). Even though pressure
remains constant, indenter size affects penetration depth independently
of shape. This is consistent with geotechnical theory, which shows a
relationship between footing size and bearing capacity of a soil (Zhu et
al., 2001; Kumar and Khatri, 2008).
The implication for vertebrate paleoichnology is that two dissimilar
foot morphologies may indent to very different track depths, even when
the same pressure is applied. A sauropod track may be deeper than a
theropod track, for instance, not due to the weight of the animal, which
when distributed over the surface area of the foot creates an equal
pressure to the smaller animal, but due to the morphology and
geometry of the foot being larger, and more compact in shape.
The mechanism by which normalized edge length affects track depth
can be explained through soil mechanics. As the load is applied, the
FIGURE 4—Graph plotting maximum vertical displacement beneath indenters of
varying edge length, for indenters consisting of 9 or 16 elements, with subsequent
surface area of 9 or 16 units
(diamonds and squares, respectively).
FIGURE 5—Mean depths of indentation for indenters 1A–F in mud (diamonds) and
dry sand (squares). Increasing normalized edge length results in a decrease in depth
indented in cohesive mud, but an increase in noncohesive sand.
FIGURE 6—Data for normalized edge length against maximum displacement
(normalized as a percentage of the most compact indenter) as recorded from FEA
simulations of geometric shapes. Trend lines are shown for both sets of data, and
show a close similarity (diamonds 5 surface area of 9 units
, squares 5 surface area
of 16 units
FIGURE 7—Vectors of displacement beneath the corner of a loading template.
Sediment is forced vertically down beneath the center of the indenter, but moves
outwards and upwards at the edge of the indenter, according to Prandtl theory. A
higher edge length to surface area ratio provides more opportunity for sediment to
move upwards and laterally, reducing energy transmitted down.
medium is displaced. At the surface, beside the indenter, the path of
least resistance allows the sediment to move upwards (Fig. 7). Directly
beneath the indenter, sediment can only move vertically down, creating
a ‘dead zone’ (Allen, 1989, 1997; Manning, 2004). As such, an indenter
with a high edge to surface area ratio provides relatively more
opportunity for sediment to move upwards around the indenter. The
result is that energy is lost at the surface, rather than transmitted
vertically, and shallower tracks are produced. This is in agreement with
Jackson et al. (2009) who noted that it was the widest parts of indenters
that transmitted displacement most deeply.
There are exceptions to this, however, where an increase in edge
length can lead to indentation to a greater degree. For example,
indenter 1F, despite having a normalized edge length of 2.78, indented
further than indenter 1G with equal edge length (Fig. 4), this is because
the medium was unable to move upwards in the small gaps present in
indenter 1F due to cohesion. The stiffness of the medium prevented
easy movement, and instead the areas between protrusions were forced
down, essentially decreasing the effective e9 for indenter 1F. By creating
a more complex shape (with more corners), the effects of a stiff,
cohesive medium mean that effective e9 is reduced. This is exaggerated
in a low-resolution finite element mesh where only a single element is
present between indenting elements (e.g., in indenter 1F) and is unable
to deform to an extent allowing it to pass between the protrusions of the
indenter. Such a scenario highlights the importance of choosing the
correct FEA mesh resolution.
In order to use vertebrate tracks as paleopenetrometers, estimates of
mass and speed must be used in conjunction with observed or implied
pedal morphology and geometry. It is not enough to say that two
tracks, made by animals of similar size with similar-sized feet represent
comparable indenters; pedal morphology must also be constant.
Investigating the effects of pedal morphology also brings insight to
advantageous pedal forms. These experiments indicate that an animal
with a given mass may be provided with an advantage towards reducing
the depth to which its feet sink in soft media, either through an increase of
the surface area of the foot, which subsequently reduces pressure, or by an
increase in the edge length of the foot. Such an advantage may be linked
to the morphology of the feet of wading birds. Many wading birds possess
long, slender toes with no interdigital webbing (Brown et al., 1987;
Paulson, 1992). Such animals traverse soft media regularly. Increasing
surface area of the foot directly would be disadvantageous towards
moving the foot through water. By increasing edge to surface area ratio
and employing the effect described here, however, a low surface area can
be maintained whilst the effect of sinking into soft media may be reduced.
Tracks made by two animals of comparable size (mass and pedal
surface area) in similar media conditions may nevertheless be of
differing depth. The complexity of the foot morphology, as measured
using the normalized edge length e9, is one cause of this variation in
depth. Cohesion of the medium means that areas not directly in contact
with the indenter are still displaced down by neighboring medium,
essentially decreasing effective pressure. The effects of morphology are
reversed in noncohesive media, where increasing relative edge length
results in greater depth of tracks. Neoichnological and laboratory
experiments and observations must, therefore, be used comparatively
only with similar media if meaningful comparisons are to be drawn.
Size also has an independent effect on total displacement; larger
indenters penetrate the medium to a greater extent, when morphology
and pressure are kept constant.
PLF was funded by Natural Environment Research Council (NERC,
award NER/S/A/2006/14033). HPCx project e46 funded through
Engineering and Physical Sciences Research Council (EPSRC, grant
EPF055595-1). We also acknowledge support from Louise Lever
for assisting with the FEA visualization, James Jepson and Karl
Bates for comments on an early draft, and Research Computing
Services at the University of Manchester for providing free access to the
local HPC system Horace. We also thank Stephen T. Hasiotis and two
anonymous reviewers whose comments helped to improve the
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... 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). ...
... 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.
... Early studies have shown strong relationships between locomotor mode and linear morphometric measurements in a wide variety of extant animals (Alexander, 1989;Alexander & Jayes, 1983;Coombs Jr, 1978;Hildebrand & Goslow Jr., 2001). To better understand locomotion in extinct taxa, paleobiologists have made use of many tools to uncover how nonavian dinosaurs were capable of locomoting effectively and efficiently, including finite element analysis (e.g., Falkingham et al., 2010;Goussard et al., 2010 [in Elephas]; Hohn, 2011), beam theory and computational modeling (e.g., Bates et al., 2012;Heinrich et al., 1993;Sellers et al., 2017), as well as linear and geometric morphometric analyses (e.g., Bonnan, 2007;Carrano, 2001;, among many other techniques. Linear and geometric morphometrics have been invaluable tools for better understanding stance, posture, and locomotion in different nonavian dinosaur groups. ...
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Using morphometrics to study nonavian dinosaur fossils is a practice that predates the origin of the word "dinosaur." By the 1970s, linear morphometrics had become established as a valuable tool for analyzing intra- and interspecific variation in nonavian dinosaurs. With the advent of more recent techniques such as geometric morphometrics and more advanced statistical approaches, morphometric analyses of nonavian dinosaurs have proliferated, granting unprecedented insight into many aspects of their biology and evolution. I outline the past, present, and future of morphometrics as applied to the study of nonavian dinosaurs zeroing in on five aspects of nonavian dinosaur paleobiology where morphometrics has been widely utilized to advance our knowledge: systematics, sexual dimorphism, locomotion, macroevolution, and trackways. Morphometric methods are especially susceptible to taphonomic distortion. As such, the impact of taphonomic distortion on original fossil shape is discussed as are current and future methods for quantifying and accounting for distortion with the goal of reducing the taphonomic noise to biological signal ratio. Finally, the future of morphometrics in nonavian dinosaur paleobiology is discussed as paleobiologists move into a "virtual paleobiology" framework, whereby digital renditions of fossils are captured via methods such as photogrammetry and computed tomography. These primary data form the basis for three-dimensional (3D) geometric morphometric analyses along with a slew of other forms of analyses. These 3D specimen data form part of the extended specimen and help to democratize paleobiology, unlocking the specimen from the physical museum and making the specimen available to researchers across the world.
... Specific anatomical adaptations have also evolved to mitigate the energetic cost increase caused by snow, such as relatively longer limbs and larger foot areas. Relatively longer foot edge lengths may also be advantageous, although empirical evidence of this has only been obtained on natural granular media other than snow (Falkingham et al. 2010). Having a "snowshoe" foot is an effective adaptation for moving over unsupportive snow. ...
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Synopsis Substrate supportiveness is linked to the metabolic cost of locomotion, as it influences the depth to which the foot of a moving animal will sink. As track depth increases, animals typically reduce their speed to minimize any potential energetic imbalance. Here, we examine how self-selected speed in the Svalbard rock ptarmigan is affected by snow supportiveness and subsequent footprint depth measured using thin-blade penetrometry and 3D photogrammetry, respectively. Our findings indicate that snow supportiveness and footprint depth are poor predictors of speed (r2 = 0.149) and stride length (r2 = 0.106). The ptarmigan in our study rarely sunk to depths beyond the intertarsal joint, regardless of the speed, suggesting that at this relatively shallow depth any increased cost is manageable. 3D reconstructions also indicate that the ptarmigan may exploit the compressive nature of snow to generate thrust during stance, as a trend toward greater foot rotations in deeper footprints was found. It remains unclear whether the Svalbard ptarmigan are deliberately avoiding unsupportive snowy substrates. However, if they do, these results would be consistent with the idea that animals should choose routes that minimize energy costs of locomotion.
... Thus, it is possible to affirm that these SSD structures develop due to the downward strain exerted by an external agent, probably directly on the surface of the original substrate. During this process, the deformational amplitude decreases downwardly (Fig. 6A-F) due to the radial dissipation of the pressure, with the increase in the distance from the tracking surface (Allen, 1997;Manning, 2004;Milàn and Bromley, 2006;Falkingham et al., 2009Falkingham et al., , 2010. The presence of sandy casts that fills all the studied examples reinforces that these downwardly convex structures were originally depressions on the terrain surface, later passively filled by the sands deposited immediately above. ...
Soft-sediment deformation structures are conspicuous features found in both ancient and modern, shallowly buried, loose, and water-saturated sediments related to diverse depositional environments. Numerous triggering mechanisms can induce their development, including seismicity, glaciotectonics, overload, and bioturbation. The presence of soft-sediment deformation in the Jurassic fluvial-eolian Pirambóia Formation has been known for a long time and was usually associated with seismic-induced triggers. Recently described synsedimentary structures in wet interdune deposits from the lower part of this unit, close to its type area in São Paulo State, southeastern Brazil, are now interpreted as true cross-section tracks produced by large tetrapods based on examples from the literature and morphological analyzes. Based on their age, size, and comparisons with dinosaur tracks described in Jurassic lithostratigraphic units from Paraná Basin in Brazil (Guará Formation) and Waterberg Basin (Etjo Formation), we suggest here, for the first time, that some of those deformational structures were produced by dinosaurs. Furthermore, the cross-section tracks from the Pirambóia Formation in São Paulo State exceed in size the tracks with therapsid affinity described in the Permian-Triassic unit in southern Brazil, hindering their full correlation. This finding may potentially represent the oldest evidence of the presence of dinosaurs in the São Paulo State territory, expanding our knowledge of the poorly known Jurassic tetrapod fauna of Brazil. Additionally, these cross-section tracks reinforce the possible correlation, at least in part, of the Pirambóia Formation in its northern occurrence (near to its type area) with the Jurassic Guará Formation from southern Brazil.
... This is consistent with the aquatic locomotion of the trackmaker, as well as the aquatic adaptations of all temnospondyls known from the Lower Keuper (Fig. 9E). In this regard, the almost absence of displacement or expulsion rims surrounding the ichnites is also indicative of a relatively compact morphology of the limb (Falkingham et al., 2010). Furthermore, the prevalence of manus tracks (see also Section 6.3 below) suggests that the body centre of mass was located anteriorly. ...
Triassic temnospondyl amphibian tracks are relatively rare, in contrast with the body fossil record. Herein we report temnospondyl tracks from the base of the Anthrakonitbank carbonate bed, within the upper Middle Triassic Lower Keuper succession (Erfurt Formation) in the Vellberg Fossil-Lagerstätte of southern Germany. The sedimentary succession comprises restricted marine deposits, and the track-bearing layer includes microbial mats covering thin bone-beds. The ichnological material includes >20 footprints, four of which are arranged in a trackway, and all footprints comprise manus impressions with no pes preserved. The combination of characters, such as tetradactyl clawless manus impressions, relative digit length and angulation, and trackway with low pace angulation, are different from any known tetrapod ichnotaxon. While the scarcity of material precludes a confident ichnotaxonomy, comparison with the autopodia in the body fossil record suggests capitosaur stereospondyls as the most probable trackmakers. Ichnological and sedimentological features indicate that the trackmakers displayed a walking-swimming locomotion, with a sprawling posture, only touching the substrate with the forelimbs, as seen in present-day swimming crocodiles. The Vellberg tetrapod tracks reported here contribute to our knowledge of the Triassic ichnological record, as well as the life style and habitats of temnospondyls.
... The first vertebrate-based ichnozonation scheme of the Stormberg Group, which in addition to the Elliot Formation, encompasses the underlying Molteno and overlying Clarens Formations, was attempted by Ellenberger (1970;1972), and later revised by Olsen and Galton (1984). While the biostratigraphic utility of these vertebrate tracks had been attempted before, their application in palaeoenvironment and palaeoecosystem reconstructions is lagging (Lockley, 1986;Whyte and Romano, 2001;Falkingham et al., 2010), especially in southern Africa. This is despite the wealth of information in ichnite-bearing rocks that pertain to the conditions of the track-bearing sediments at the time of track formation. ...
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The Ha Nohana palaeosurface in southern Lesotho preserves tridactyl and tetradactyl tracks and trackways attributable to Early Jurassic bipedal, theropod-like dinosaurs. Complementary sedimentological and ichnological observations along the palaeosurface and in the strata below and above it allow detailed interpretations of climatically driven changes in this southern Gondwana palaeoecosystem. Sedimentological evidence suggests trackmaking under a semi-arid climate with heavy storms and episodic flash flooding that induced ephemeral, unconfined sheetwashes. The palaeosurface is overlain by rhythmically bedded, organic-matter rich mudstones that formed in a deep, stratified lake indicative of a longer and wetter period in the history of the site. The unique morphological details of the Ha Nohana tracks help refine the properties of the substrate during track making, the ichnotaxonomic affinities of the footprints and the interpretation of the foot movement relative to the substrate. Two footprint morphotypes, ~ 300 m apart, are defined on the palaeosurface. Tracks of morphotype I are tridactyl, shallow, contain digital pad impressions and were impressed on a firm, sand rippled substrate that underwent desiccation. Conversely, tracks of morphotype II are tetradactyl, deep, and have an elongated posterior region. These tracks are preserved on the surface of a massive sandstone and are associated with soft sediment collapse structures related to the animal’s foot sinking into the water-saturated, malleable sediment layer. Morphotype II tracks show that as the animal waded across the substrate, the liquefied sediment lost its cohesive strength and could only partially support the weight of the animal. In so doing, the animal’s foot sunk deep enough into the sediment such that the impression of the metatarsal and digit I (hallux) are now visible. Thus, the palaeosurface was walked on by small-to-medium sized theropods that traversed over ripple marks in firmer moist sand, as well as a larger theropod that tottered through water-logged sand.
... Substrate consistency depends on its rheology and mechanics and varies with the texture (i.e., size, sorting, sphericity, roundness, etc.) of the sand grains, the mineralogical composition of the clasts and the moisture, but other conditions also affect track preservation in an eolian setting, such as the rapid burial of the perturbed sediment, the dip angle of the substrate, and the moisture content at the exact moment of the production of the tracks (McKee, 1944(McKee, , 1947Allen, 1997;Manning, 2004;Milàn, 2006;Milàn & Bromley, 2006;Jackson, Whyte & Romano, 2009;Jackson, Whyte & Romano, 2010;Scott, Renaut & Owen, 2010;Razzolini et al., 2014;Mancuso et al., 2016;Milàn & Falkingham, 2016). Biological (such as the animal's mass, limb dynamics and the geometry of the autopodia) and ecological (such as the trackmaker's speed and direction of the travel) variations are also known to affect the preservation of tetrapod tracks (Thulborn, 1990;Falkingham, Margetts & Manning, 2010;Falkingham et al., 2011;Falkingham, 2014;Falkingham, Hage & Bäker, 2014). ...
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Tetrapod tracks in eolianites are widespread in the fossil record since the late Paleozoic. Among these ichnofaunas, the ichnogenus Chelichnus is the most representative of the Permian tetrapod ichnological record of eolian deposits of Europe, North America and South America, where the Chelichnus Ichnofacies often occurs. In this contribution, we describe five sets of tracks (one of which is preserved in cross-section), representing the first occurrence of Dicynodontipus and Chelichnus in the “Pirambóia Formation” of southern Brazil. This unit represents a humid desert in southwestern Pangea and its lower and upper contacts lead us to consider its age as Lopingian–Induan. The five sets of tracks studied were compared with several ichnotaxa and body fossils with appendicular elements preserved, allowing us to attribute these tracks to dicynodonts and other indeterminate therapsids. Even though the “Pirambóia Formation” track record is sparse and sub-optimally preserved, it is an important key to better understand the occupation of arid environments by tetrapods across the Permo–Triassic boundary.
At Cabo Mondego (western central Portugal), the Upper Jurassic marine to coastal succession contains several stratigraphic levels preserving dinosaur footprints on the surface bedding plane, as well as convolute bedding and soft sediment injection structures interpreted as dinoturbation structures. At least nineteen new three-dimensional structures observed in cross-sections are interpreted as produced by dinosaur trampling. The identification of three-dimensional structures of dinosaur footprints provides an important complement to the information obtained from footprints preserved on single bedding surfaces, such as the substrate consistency, potential trackmaker identification, and the possibility to enhance the distinction of sauropods and tridactyl dinosaurs, and paleoenvironmental interpretations. In the lower part of the Arenitos da Boa Viagem Formation, eight levels of probable lowermost Kimmeridgian age (ca. 157–156 Ma), displaying the above-mentioned deformational structures, were analyzed in detail. They support interpretations concerning the relationship between the footprints and the substrate consistency at the time of their formation. Three distinct cohesiveness patterns, defined by the penetration of the feet from the paleosurface, are the result of different degrees of substrate cohesiveness. Identifying the trackmakers of levels belonging to the middle Oxfordian–lower Kimmeridgian has important implications for Late Jurassic ecosystem reconstructions, as the footprints observed in Cabo Mondego indicate a change in the morphotypes throughout the Upper Jurassic succession.
The origin and preservation of a track are related to many distinct environmental factors, concerning especially the substrate cohesiveness, plasticity, grain size, texture and water content. Then, the environment, through the sedimentation processes, plays a role that enhances the origin and quality of the tracks and their preservation. Three distinct contexts - tidal flats, aeolian, fluvial-lacustrine paleoenvironments, that encompass the majority of fossil footprints occurrences are analyzed. Footprints as biosedimentary structures, due to their close relationships with physical and chemical processes that control their formation, represent an important clue to paleoenvironmental interpretation. The present study is mainly based on the direct examination of ichnosites that allow us to evaluate the aspects of Mesozoic tracks from different regions of the paleocontinent Gondwana, currently correspondent to Argentina, Australia, Bolivia, Brazil, Congo, Iran, India, Madagascar and Morocco as sedimentary structures and their use in paleoenvironmental interpretations.
Three parallel, manus-only sauropod trackways from the Coffee Hollow A-Male tracksite (Glen Rose Formation, Kendall County, Texas) were studied separately by researchers from the Heritage Museum of the Texas Hill Country and the Houston Museum of Natural Sciences. Footprint and trackway measurements generally show good agreement between the two groups’ data sets. Footprints appear to be shallowly impressed true tracks rather than undertracks. One of the Coffee Hollow trackways shows marked asymmetry in the lengths of paces that begin with the left as opposed to the right forefoot, and two of the Coffee Hollow trackways are unusually broad. The Coffee Hollow trackways differ enough from the manus portions of other Glen Rose Formation sauropod trackways to suggest that they were made by a different kind of sauropod. Greater differential pressure exerted on the substrate by the forefeet than the hindfeet probably explains the Coffee Hollow trackways, like other manus-only sauropod trackways, but the possibility that they indicate unusual locomotion cannot at present be ruled out.
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Fossilised footprints and trackways provide palaeontologists with information regarding dinosaur locomotion such as their gait, posture and speed. Current best practice is to interpret trackways as 2D surface features. Using computational geomechanics, this paper demonstrates that subsurface deformation can lead to transmitted or false footprints at different depths, whose size and shape relates to a distorted 3D pressure bulb. The results of parallel 3D finite element simulations are compared with a set of transmitted tracks owned by Amherst College, USA. At Amherst College, palaeontologists have peeled away each layer of solidified sediment to find a footprint in each one. Each of these footprints has a unique geometry, a different length and angle between digits. If each of these was found in isolation, they would be erroneously interpreted as coming from different species of dinosaur. Significantly, palaeontologists use a simple equation relating the length of the foot and the distance between two footprints (stride) to calculate the dinosaur’s speed. As the footprint length changes with depth, so does the apparent stride. The consequence is a different speed for the trackway at each depth: a clear source of misinterpretation. To simulate the transmission of the footprint through the soil layers, an elasto-plastic soil model is used together with a fine resolution 3D mesh. The requirements of such a model have a marked impact on the computational cost and the authors describe how existing parallel libraries were extended to build a scalable footprint simulator.
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Backstripping techniques for basin and stratigraphic analyses assume that the original porosity of the sediments is known within reasonable limits. Erroneous original porosity assumptions lead to serious errors in stratigraphic sections with a significant proportion of fine-grained material. The present algorithms, which assume initial porosities of between 50% and 70% for muds and 40% to 50% for sands, are only applicable to sediments that were never subaerially exposed. Outcrop data from floodplain deposits show that the differential compaction between sandstones and mudstones that should be present if those assumptions were correct does not exist. Modern floodplain silts and clays below the liquid limit, i.e., that behave as plastics, have porosities that vary from 34% to 39%, and sands have 27-35% porosity. Sections decompacted using the marine shale and sandstone porosity values overestimate the original thickness of floodplain strata by as much as 31%. These errors mean that the estimates of total basin subsidence in regions, such as proximal foreland basins, are seriously overestimated. The subtle inflections in burial history curves, sometimes used to infer either eustatic or tectonic sea-level fluctuations in these basins, are noise rather than signal.
Environmental analysis of the Pliocene-Pleistocene Koobi Fora Formation reveals many vertebrate footprints and trackways in fluvial and lake-margin strata. Examination of tracks and game trails in similar modern Kenyan environments, and comparison with those in older sediments, indicate characteristics useful for their recognition elsewhere. Preservation is best in mud and sand interbeds of medium thickness where the animal foot punches out a plug of coherent surface sediment (usually mud) and presses it into underlying units of contrasting lithology (usually sand). Thicker and less coherent muds simply mold the foot. -from Authors
: Continental biota are related to sedi-ment through feeding, dwelling, locomotion, repro-duction, and searching behavior evident as tracks, trails, burrows, nests of animals, and rooting patterns of plants. Such vestiges are preserved in the geologic record as trace fossils. The lateral and vertical distribution of modern trace-making organisms within an environment is controlled by sediment characteristics, soil moisture, water-table levels, eco-logical associations, and more. Trace fossils in the geologic record can be used to interpret the palaeoen-vironmental, palaeoecologic, palaeohydrologic, and palaeoclimatic settings because a well-defined rela-tionship exists between climate, hydrology, soils, environment, and all biodiversity. Trace fossils also relate information about soil formation and develop-ment, the type of biologic activity, topography of the landscape and its relationship to groundwater profile, and duration of time that a body of sediment has been stable at the surface with respect to sedimentation rate. Thus, trace fossils in the continental realm are proxies for: (1) biodiversity in terrestrial and aquatic palaeoenvironments not recorded by body fossils; (2) above-and below-ground palaeoecological associa-tions; (3) palaeosol formation; (4) palaeohydrology and palaeo-groundwater profiles; and (5) seasonal and annual palaeoclimate indicators and climate change.
A recently discovered dinosaur tracksite from the Upper Jurassic Morrison Formation, Bighorn Basin, Wyoming, contains abundant sauropod tracks that exhibit varying degrees of preservation. Most of these tracks appear as indistinct bulges on the bottoms of sandstone beds, but several are well preserved and show foot-pad and skin impressions. Three track morphotypes are recognized: a sauropod pes print, a Brontopodus-like manus print, and a diplodocid manus print. The Brontopodus-like manus print most likely represents the footprint of a brachiosaur. This morphotype also contains evidence of phalangeal nodes—the first reported for a sauropod manus. The diplodocid manus print is unique because it contains impressions of a substantial ungual on digit I and a heel pad. A partial sauropod track cast also contains an impression of interlocking, polygonal scales. This is only the second known North American sauropod footprint that contains skin impressions. The spectrum of preservational quality of the tracks and associated trace fossils is used to infer the relative moisture content of the original substrate. Moisture content of the original substrate is estimated to have been moist to borderline saturated. Observations of the tracks at the study areas also are used to establish a list of features that can be used to distinguish deep vertebrate tracks from load casts resulting from gravity-induced soft-sediment deformation.
A reconnaissance study is outlined showing how an improved understanding of the formation and character of fossil vertebrate tracks in soft sediments is provided by the application of the mechanical engineer's indenter theory, supported by complementary scaled laboratory experiments. Only the footprint at the bottom of the shaft cut by the animal's limbs in general offers the best preservation of the shape of the underside of the foot. The character of the foot is less well preserved in the deformed bedding beneath the footprint and among laminae deposited in the shaft after the passage of the animal. This understanding will help to reduce errors in the use of tracks in taxonomic, biostratigraphic, palaeoecological, behavioural and environmental studies.
This paper presents the results of a research program of strip and circular footings resting on dry dense sand. The scale effect on the bearing capacity and the shape factor Sy of the footings is investigated numerically and experimentally. The footings are analyzed using the method of characteristics. A wedge failure mechanism has been adopted. Triaxial compression tests conducted under confining pressures up to 2,500 kPa show that the friction angle of dense sand decreases with stress level. The stress-dependent friction angle of soil is adopted in the characteristics analysis. The numerical results indicate that the bearing capacity increases exponentially with footing size. With increasing footing size, the bearing capacity factor Ny is reduced, while the shape factor Sy is increased. Centrifuge tests of strip and circular footings with dimensions up to the equivalent of 7 m have been conducted. The experimental work verified the numerical analysis through the consistency of results.
Tracks can potentially offer unique sources of information, providing insight into the environments, gait and posture, locomotion and behaviour. Track preservation can yield important information on substrate consistency and enable the recognition of transmitted subsurface tracks. The ability to recognize transmitted tracks has broad implications for the understanding of palaeoenvironments and interpretation of ichnological assemblages. In order to gain an understanding of how tracks are formed in three dimensions, and of their variability of expression in different substrates, controlled laboratory simulations were undertaken. Experiments were designed to recover subsurface track layers, yielding for the first time detailed information on subsurface morphology that could be related to 'true' surface track features. It was found that subsurface track relief can be correlated with the magnitude and distribution (across a foot) of load acting on the surface sediment. This pressure is transmitted through the sediment, and deforms successive layers at depth, producing an undertrack. The most significant factor controlling track morphology, whether surface or subsurface, was found to be the moisture/density relationship within the substrate at the time of track formation. Variability in the dimensions of simulated tracks, relative to the 'true' surface track, indicates that caution should be exercised when using fossil tracks to calculate hip height, speed, age, and population dynamics. In addition, comparison of experimental tracks with dinosaur tracks from the Yorkshire coast suggests that many morphological differences between vertebrate ichnotaxa reflect sediment rheology and taphonomy rather than taxonomy of the track-maker.