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The effect of temperature and slope on the morphology of experimental spider and scorpion trackways

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The effect of temperature and slope on the morphology of experimental spider and scorpion trackways
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Azain, Jaime Suzanne
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xi, 31 leaves : illustrations ; 28 cm

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Footprints, Fossil -- Effect of temperature on ( lcsh )
Slopes (Physical geography) ( lcsh )
Scorpions, Fossil ( lcsh )
Spiders, Fossil ( lcsh )
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bibliography ( marcgt )
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non-fiction ( marcgt )

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Includes bibliographical references (leaf 31).
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by Jaime Suzanne Azain.

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Full Text
THE EFFECT OF TEMPERATURE AND SLOPE ON
THE MORPHOLOGY OF EXPERIMENTAL SPIDER AND SCORPION TRACKWAYS by
Jaime Suzanne Azain B.S., Kansas State University, 2001 M.I.S., University of Colorado at Denver, 2006
A thesis submitted to the University of Colorado at Denver in partial fulfillment of the requirements for the degree of Masters of Integrated Science 2006


This thesis for the Masters of Integrated Science degree by
Jaime Suzanne Azain has been approved
Date


Azain, Jaime Suzanne (MIS)
The Effect of Temperature and Slope on the Morphology of Experimental Spider and Scorpion Trackways
Thesis directed by Assistant Professor Joanna Wright
ABSTRACT
Terrestrial trackways of arthropods are common in certain strata, such as the Permian Coconino Sandstone of Arizona, and are often the only evidence of the animals that once traversed the area. Some of the more common ichnogenera of these strata are Paleohelcura and Octopodichnus, attributed to scorpions and spiders respectively. Several studies have attempted to reproduce these trackways in the laboratory but none systematically investigated the effects of temperature and gradient on the locomotion of the trackmakers and the trackways produced.
Experimental trackways were created using a modem African Emperor scorpion, Pandinus imperator, and a modem Pink-Toed tarantula, Avicularia avicularia. The trackmakers were videotaped in order to accurately document their stepping patterns. Speed of the animal, slope, and temperature affected the placement of the feet, which led to differences amongst the trackways. Drag created by the tarantulas legs established direction of travel for both uphill and downhill movements when experiments were created with a 20 angle. At temperatures above 21 C, scorpion tracks tend to remain elongated while tarantula tracks are


more oblong. These experiments show similarities with previous studies such as a wide variety of track morphologies for scorpions with impressions that varied from two to four tracks on each side and that tarantula tracks are consistent with four tracks on each side. However, with experiments in damp or slightly moist sand, tracks were not created with either species because the animals were too light to leave impressions. These experiments support earlier hypotheses that spiders are the possible trail makers for Octopodichnus raymondi. Only at temperatures of 21 C and a slope of approximately 20 do scorpion tracks show similarities to Paleohelcura trackways.
This abstract accurately represents the content of the candidates thesis. I recommend its publication.
Signed
ffLUr/ifh
J Joanna Wright


DEDICATION
I dedicate this thesis to my mother, father, and sister for their undying support and confidence while I was writing this.


ACKNOWLEDGEMENT
My thanks to my advisor, Joanna Wright, for her support and guidance during these past two years.


CONTENTS
Figures.................................................viii
CHAPTER
1. INTRODUCTION...............................................1
Previous Experimental Trackways.........................2
Previous Experiments of Stepping Patterns in Modem Arthropods..............................................5
General Methods.........................................7
Background Information..................................8
Stepping Patterns in Modem Arthropods..................10
Terminology............................................13
Notes on Illustrations.................................13
2. EXPERIMENTAL TARANTULA TRACKWAYS..........................14
Experimental Scorpion Trackways........................18
Comparison of Modem Day Tarantula and Scorpion
Trackways..............................................21
Comparison of Tarantula Trackways to Octopodichnus Trackways..............................................23
Comparison of Scorpion Trackways to Paleohelcura
Trackways..............................................24
3. SUMMARY AND PROSPECTUS....................................29
vii


BIBLIOGRAPHY
31
viii


FIGURES
Figure
1 Trackways found in the Coconino Sandstone...............................2
1.1 Paleohelcura tridactyla.................................................2
1.2 Paleohelcura dunbari....................................................2
1.3 Paleohelcura lyortensis.................................................2
1.4 Triavestigia niningeri..................................................2
1.5 Mesichnium benjamini....................................................2
1.6 Octopodichnus didactylous...............................................2
1.7 Octopodichnus minor.....................................................2
1.8 Octopodichnus raymondi..................................................2
1.9 Sediment tray used for all experiments..................................8
1.10 Common name: African Emperor Scorpion
Scientific name Pandinus imperator.....................................9
1.11 Common name: African Emperor Scorpion
Scientific name: Pandinus imperator....................................9
1.12 Common name: Pink-Toed Tarantula
Scientific name Avicularia avicularia..................................9
1.13 Outline of scorpion and tarantula with legs numbered from front to back of
animal. Illustrated are the differences in leg structure. For numbering purposes the scorpions legs are stretched out...................12
IX


1.14 Stepping pattern of a modem scorpion........................................12
1.15 Stepping pattern of a modem tarantula.......................................12
2.1 Pink-Toed Tarantula, no slope, 27 C, with pedipalps........................15
2.2 Trace of Figure 2.1 without pedipalps.......................................15
2.3 Pink-Toed Tarantula, no slope, 16 C........................................16
2.4 Trace of Figure 2.3, dotted arrow indicates direction of travel.............16
2.5 Tarantula, 20 slope, 21 C, walking down gradient. Scale in cm, arrow
indicates direction of movement.............................................17
2.6 Trace of Figure 2.5, dotted line represents midline of trackway, no pedipalp
imprints....................................................................17
2.7 Tarantula, 20 slope, 21 C, walking up gradient. Scale in cm, arrow indicated
direction of movement.......................................................17
2.8 Trace of Figure 2.7, dotted line represents midline of trackway, no pedipalps
imprints....................................................................17
2.9 Large scorpion, no slope, 27 C.............................................18
2.10 Trace of Figure 2.9. Center feature formed by tail..........................18
2.11 Large scorpion, 20 slope, 21 C, walking down gradient....................20
2.12 Trace of Figure 2.11. Center feature formed by tail.........................20
2.13 Large scorpion, 20 slope, 210 C, walking up gradient.......................20
2.14 Trace of Figure 2.13. Center feature formed by tail.........................20
x


2.15 Trace of Pink-Toed Tarantula, no slope, 27 C. Tracks are numbered 1-4
corresponding legs to imprints. Stride length is represented using imprints from leg 2.........................................................22
2.16 Trace of large African Emperor Scorpion, no slope, 27 C. Imprints are
numbered 1-4 corresponding legs to imprints. Stride length is represented using imprints from leg 3..........................................22
2.17 Octopodichnus raymondi, direction of travel is not known................23
2.18 Trace of tarantula tracks (Figure 2.2), no slope, 21 C, without pedipalp
imprints. Arrow indicates direction of travel...........................23
2.19 Large scorpion, 20 slope, 21 C, walking up gradient...................26
2.20 Large scorpion, 20 slope, 21 C, walking down gradient.................26
2.21 Enlarged section from Figure 2.19 showing similarity between Paleohelcura
tridactyla and modem African Emperor Scorpion tracks....................26
2.22 Enlarged Section from Figure 2.20 showing similarity between Paleohelcura
tridactyla and modem African Emperor Scorpion tracks....................26
2.23 Paleohelcura tridactyl, direction of travel is unknown..................26
2.24 Small African Emperor Scorpion, no slope, 21 C. The scorpion started at
the top right-hand side, made a U-turn and walked up the left hand side of the sediment tray......................................................28
2.25 Triavestigia niningeri, direction of travel is unknown..................28
2.26 Right hand side of Figure 2.24..........................................28
XI


CHAPTER 1 INTRODUCTION
Fossil arthropods are very scarce in the geologic record. These animals have a mineralized exoskeleton that is rarely calcified. Scorpions are first reported from the Silurian, approximately 435 million years ago, while the earliest known spiders are in the Devonian, approximately 400 million years ago (Petrunkevitch, 1960). Fossilized arthropod trackways, however, are very common in certain Permian age sediments such as the Coconino Sandstone of Arizona. However, no scorpions and very few spider body fossils are known from this period. The general body structures of arthropods have changed very little since their arrival on land (Petrunkevitch, 1960). With this in mind, two scorpions and one tarantula were used to create trackways at different temperatures and gradients. These animals were videotaped to determine stepping patterns and foot placement in order to establish which legs formed which imprints. Scorpions and spiders are both eightlegged animals but have different leg structures and thus create trackways with two distinct patterns allowing positive identification of the tracks of each taxon. Scorpions produced small, elongated imprints and their trackways sometimes resemble Paleohelcura. Spiders created rounded imprints in a trackway pattern that resembled those of Octopodichnus rqymondi.
1


Previous Experimental Trackways
Several sets of experiments using scorpions, beetles, and millipedes have been carried out to determine likely track makers for trackways in the Coconino Sandstone (Figure 1-1.8). Certain scorpions created trackways resembling
1.1
.1
1 cm
1.2
1


*




1 cm
i 3

,
*


1 cm
Figures 1-1.8
1) Trackways found in the Coconino Sandstone. 1.1) Paleohelcura tridactyla. 1.2) Paleohelcura dunbari. 1.3) Paleohelcura lyonensis. 1.4) Triavestigia niningeri. 1.5) Mesichnium benjamini. 1.6) Octopodichnus didactylous. 1.7) Octopodichnus minor. 1.8) Octopodichnus raymondi. Figures from Braddy, 1995.
2


Paleohelcura however, none of these animals created trackways resembling those of Octopodichnus (Sadler, 1993). Brady (1947), used several different species of scorpions. He used a modem dune environment for comparison with those of the Permian Dime Formations. With Centruroides exilicauda or Bark Scorpions, commonly found in Arizona, he noted that the scorpion refused to move on wet sand. On slightly moist sand, no tracks were created although the animal moved.
At temperatures of 8 C (45 F), on dry sand, the animal was sluggish and left impressions of all eight feet but no tail drag. At approximately 15 C (60 F), the scorpion created tracks resembling Paleohelcura. At temperatures above 20 C (70F), the tracks became irregular. He also stated that the front pair of walking legs did not impress when a slope of 10 was incorporated into experiments and the temperature was 15 C. The direction of travel was not indicated. He carried out experiments with five different species of scorpions but noted that the Bark Scorpion was the only animal to leave a tail drag. He refers to Pandinus imperator or African Emperor Scorpion only to note that this larger tropical form did not leave a tail drag because they carry their tail arched over their back during normal locomotion. The basal spurs on the scorpions legs were too small to create impressions in these experimental trackways. Experimental scorpion trackways show a wide variety of track morphologies; the number of imprints in each imprint group left on each side of the scorpion varied from two to four (Brady, 1947).
3


Until 1993, no experiments were successful in creating trackways using a spider in sediment. Alf (1968) used spiders with his experiments but used ink and paper instead of sand. The trackways created in ink are very different than tracks created in sediment.
Sadler (1993), performed experiments with a male scorpion (Hadrurus sp.) and a female tarantula (Aphonopelma sp.). She created a runway that measured 4.0 m by 0.5 m using fine, well sorted sand similar to that of the Coconino Sandstone. A dry sand dune with a slope of 25 was placed in the middle of the runway. A level portion of the runway .05 m long was sprayed with water to produce different degrees of moisture in the sediment. In order to obtain different speeds a stream of air was directed at the animals. Her experiments were performed at room temperature at 25 C.
Previous experiments had suggested that small invertebrates failed to make tracks on anything but dry sand and on slopes of no more than 12 (McKee, 1947). But Sadler created identifiable tracks in her experiments on slightly damp sand. Although tracks created in dry sand tended to be bigger and deeper, avalanche structures obscured much imprint detail (Sadler, 1993). Trackways in damp sediment were smaller and sharper. If the sand was too moist the animal did not leave impressions because the sediment was cohesive. The same occurred if the sand was allowed to dry and form a crust on the surface. The slope of 25 was too steep for the scorpion and the tarantula to create clear identifiable tracks.
4


Scorpion and spider tracks show bifurcations, open in the direction of travel (Sadler, 1993). Elongated tic marks formed as the foot was dragged forward between strides. The triangular pattern of individual imprints made by the scorpion greatly resembled the ichnospecies Paleohelcura dunbari (Figure 1.2). The peak of the triangle can face forward or backward, so determining direction of travel of fossil trackways from imprint morphology is probably not possible. Tarantula trackways may closely resemble at least one species of Octopodichnus.
Trace fossils differ from body fossils in that one animal can produce several different trackway morphologies. These can differ sufficiently to be placed in two different ichnotaxa. Fossil trackways rarely show this although, it is quite common in experimental trackways. Sadlers scorpion consistently created several different patterns. This pattern changed from the right to left side of the trackway and even within a few strides with no obvious reason. The obvious reasons include, change in light, moisture content, direction, and speed. The scorpion produced very irregular trackways, sometimes resembling those of Octopodichnus although, most resembled Paleohelcura (Sadler, 1993).
Previous Experiments of Stepping Patterns in Modem Arthropods
Arachnid legs are well fanned out from their bases so they have a mechanical advantage in comparison to animals with fewer pairs of walking legs.
5


They hang from their legs unless the legs are relatively short. The knee in spiders is pointed upwards while scorpions knee when flexed do not project upwards as in spiders, but fold against and over the body so that the dorsal surface of the leg is displaced so that the anterior face is always visible from above. There appears to be a slight twist of the leg so that the anterior face is visible dorsally. Leg movements in each group can be very different from one another in detail although the basic features are the same for each animal.
Arachnids show gait irregularities especially when turning. Legs of a pair normally step in opposite phase, but after turning the grouped footprints on each side of the animal no longer alternate and may be in any position. Manton created a cinematograph with a scorpion, Buthus australis and a spider, Trochosa ruricola. With both of these animals she noted that legs 1, 3,2,4 on the left corresponded to legs 2,4,1,3 on the right (Manton, 1977).
Different arachnids exhibit different stepping patterns (Herreid II and Fourtner, 1981). Scorpions step in a 4, 2, 3, 1 sequence on the left corresponding to 3,1,4, 2 on the right when walking forward. The propulsive phases of the individual legs are temporally offset and staggered. They utilize two alternating waves of diagonally stepping legs, rather than two sets of strictly alternating tetrapods. Forward movement is achieved by the staggered coordination. All legs do not contribute equally in generating forward propulsion (Herreid II and Fourtner, 1981).
6


Tarantulas employ at least six different gaits although some patterns are more common than others. In the three most common, leg 4 moves first followed by a variation of legs 1-3. Left and right sides of the tarantula may be uncoupled to a certain extent so that the two sides can actually step at different rates (Herreid, Fourtner).
General Methods
All experiments were created in a sediment tray that measured 76 cm x 41 cm (Figure 1.9). The sediment used in experiments was Mississippi silt. The grain size of the silt ranged from .05mm-.074mm. The tray had rollers on the bottom so that the sand could be evenly distributed. The tray was shaken after trackways were created to redistribute the sand. The depth of the sediment was approximately 3-4 cm for each experiment and was never compacted down.
Temperatures varied from 16-27 C for all trackways created. In order to raise the temperature of the sand, a heat lamp was enclosed on the tray until the desired temperature was achieved. When the temperature needed to be lowered below room temperature, the sediment was placed outside overnight and the
7


Figure 1.9
Sediment tray used for all experiments.
experiments were performed before the heat of the sun raised the temperature. The temperature readings were taken with a small wall thermometer. The gauge was placed directly on the sand to achieve an accurate reading.
A slope of approximately 20 or no slope was used for all experiments. When the sediment was ready the scorpion or tarantula were placed in the tray, allowed to move around freely, and observed during trackmaking.
Background Information
Two African Emperor scorpions and one Pink-Toed tarantula were used for the following experiments. The smaller scorpion (Figure 1.10) was female approximately 2 years of age and missing leg 4 on the left hand side. The larger scorpion (Figure 1.11) was also female, approximately 5 years of age. Scorpions have four pair of true legs with two basal spurs at the end of each leg, and a pair of
8


pedipalps with pinchers on the end that aid in feeding. The legs of this particular scorpion are very short relative to their body size. The natural environment for
Figure 1.10 Figure 1.11
Common name: African Emperor Scorpion Common name: African Emperor Scorpion Scientific name: Pandinus imperator Scientific name: Pandinus imperator
Figure 1.12
Common name: Pink-Toed Tarantula Scientific name: Avicularia avicularia
these animals is a very warm, humid climate in Africa. As a general rule, scorpions are clumsy animals that tend to move by side stepping or backing up as much as they go forward. The normal temperature range for an African Emperor in captivity
9


is approximately 21 C. In this paper, temperature is manipulated at and below their normal temperature range. When the temperature was lowered below 27 C the movements of the scorpion slow down slightly due to their cold blooded nature. At 16 C the scorpion refused to move. On the other hand, if their surroundings become too warm they will go into distress, lie on their backs, and appear to sting themselves (Rankin, Walls, 1994). For the safety of the animal the temperature never exceeded 21 C.
The tarantula (Figure 1.12) used in this paper is an adult female, around 5 years of age. She has four pairs of true legs with one basal spur at the end of each leg, and a pair of pedipalps that aid in feeding and investigations of her surroundings. Her legs are long compared to her body size and radiate out from the center of the cephalothorax. Her natural habitat is also from a tropical climate. The normal temperature range for this particular tarantula in captivity is maintained at approximately 21 C (Rankin & Walls, 1994). Lowering the temperature below normal range had the same slowing effect on the spider as it did on the scorpion.
Stepping Patterns in Modem Arthropods
The larger scorpion and tarantula were videotaped walking on sediment as described in the general methods section. The digital tape was transferred onto a CD that allowed the speeds at which the animals moved to be slowed down. This in
10


turn gave an idea of the stepping patterns for these modem arthropods. The limbs are numbered from front to back (Figure 1.13). The scorpion had a very regular foot pattern. When walking in a straight line the animal placed limbs in the order 2,4,1,3 on the left corresponding to 1,3,2,4 on the right (Figure 1.14). The only time that this was not observed was when the animal was turning. The scorpions pedipalps came down from time to time making a track-like indent on the sand.
Even though the pinchers imprints were outside the realm of the tracks created by the animals legs, they obscured the trackway with a fifth set of tracks. Also noted was an occasional tail drag. Legs 3 & 4 leave tracks that are very close together; so that sometimes the imprints coalesce into one elongate imprint. Imprints produced by leg 2 were sometimes overstepped by those of leg 4. The videotape allowed assessment of which legs created which tracks. The legs that left tracks closest to the body, when walking in a straight line were left by leg 1, followed by 4 and 2.
Leg 3 left tracks furthest away from the body.
The tarantula on the other hand had a very erratic gait. The most noted pattern was 2,4,3,1 on the left corresponding to 1,3,4,2 on the right (Figure 1.15). This was not the only pattern but no other set pattern could be distinguished. The pedipalps on a tarantula are very large and leave imprints in every spider trackway. Pedipalps imprints are generally in line with the body of the animal and are not put down in any particular pattern as they are used for investigation of the surroundings. Therefore, the trackways show five sets of tracks on each side of the midline of the
11


1
1
Figure 1.13
Outline of scorpion and tarantula with legs numbered from front to back of animal. Illustrated are the differences in leg structure. For numbering purposes the scorpions legs are stretched out.
Figure 1.14 Figure 1.15
Stepping patterns of a modem Stepping patterns of a modem
scorpion tarantula
12


body. The legs that left tracks closest to the center of the tarantulas body, when walking in a straight line were created by leg 4, followed sequentially by 1, 3, and 2.
Terminology
The terms track and imprint are defined as solitary features whereas a trackway is defined as a continuous pattern of tracks. An imprint group represents tracks or imprints created by one complete cycle of limb movement. Stride is defined as the distance between footfalls of the same appendage (Braddy, 1995).
Note on Illustrations
Direction of travel for experimental trackways is indicated by arrow unless otherwise noted in the figure description.
13


CHAPTER 2
EXPERIMENTAL TARANTULA TRACKWAYS With experimental trackways created at 27 0 C on a flat slope, triangular patterns of three appear on both sides of the trackway (Figure 2.1). Legs 3 and 4 create more oblong imprints, showing a slight drag while the imprints of legs 1 and 2 retain a more circular shape. The fourth imprint can be anywhere around the triangle depending on where the 4th leg touches the ground. Tracks created by the pedipalps have been edited out of the traced trackway (Figure 2.2).
Lowering the temperature to 16 C on a flat slope, created a very different trackway pattern (Figure 2.3). In colder temperatures, both the legs, and the pedipalps, spend more time on the ground. The individual imprints left behind are bigger and more circular. They form imprints groups of four (Figure 2.4). These are the only trackways that did not show triangular imprint groups.
Experiments with the tarantula performed at 21 C with a slope of approximately 20, walking down a gradient, created a triangular pattern of three, pointing in the direction of motion on the right-hand side of the trackway (Figure 2.5). The tracks on the left do not show this particular pattern although all four legs did leave imprints (Figure 2.6). The imprints of Leg 1 are elongate parallel to the direction of motion. Legs 2 & 4 on each side created noticeable drag marks in front
14


Figure 2.1
Pink-Toed Tarantula, no slope, 21 C, with pedipalps
Figure 2.2
Trace of Figure 2.1, without pedipalps


Figure 2.3
Pink-Toed Tarantula, no slope, 16C
Figure 2.4
Trace of Figure 2.3, dotted arrow indicates direction of travel
of the foots initial landing whereas tracks created by legs 1 & 3 created a more circular pattern with slight mounds forming behind the imprint. The drag marks are a good indication of the direction of movement. In larger species of spiders, pushbacks or mounds are created in the sediment. If the spider is walking on an incline, the sand forms a mound behind the foot. The opposite occurs for downhill movement (Sadler, 1993). Under the same conditions, when the spider walked up the gradient drag marks were also created by leg 4 on each side (Figure 2.7). The other sets of legs created a more circular pattern with slight mounds forming behind the imprint. The oblong shapes seen with the downhill gradient are not as pronounced in uphill movement. The right side of the trackway showed the triangular pattern of three while the left side showed a more random pattern (Figure 2.8).
16


Figure 2.5
Tarantula, 20 slope, 21 C, walking down gradient. Scale in cm, arrow indicates direction of movement
Figure 2.6
Trace of Figure 2.5, dotted line represents midline of trackway, no pedipalp imprints
Figure 2.7
Tarantula, 20 slope, 21 C, walking up gradient. Scale in cm, arrow indicates direction of movement
Figure 2.8
Trace of Figure 2.7, dotted line represents midline of trackway, no pedipalp imprints
17


Experimental Scorpion Trackways
Experiments with modem scorpions created trackway patterns that were random and erratic under varying environments. Trackways formed on sediment at a temperature of 27 C on a horizontal surface show the most variation in the trackways (Figure 2.9). On the right hand side of the scorpion three sets of imprints are the most common (Figure 2.10). These imprints groups may show the diagonal pattern of three or a triangular pattern of three. Leg 4 on the left hand side of the scorpion created drag marks obscuring the imprints left by leg 2. The tracks left closest to the taildrag were created by leg 1. The left and right side of Figure 8.1 shows the variation in the imprints left by leg 1.
Figure 2.9 Figure 2.10
Large scorpion, no slope, 21 C Trace of Figure 2.9. Center feature formed
by tail.
18


When conditions for the larger scorpion were set at a temperature of 21 C with an approximate slope of 20 groups of imprints vary from two to four on each side of the animal. When walking up the gradient (Figure 2.11), the most notable pattern was sets of three imprints arranged in diagonal lines on the left hand side of the scorpion, although a couple of sets show imprints of two and four tracks. The right hand side shows a pattern of three to four imprints alternating throughout the trackway (Figure 2.12). Leg 1 on each side of the animal did not always create an imprint.
When walking down the gradient (Figure 2.13) the right hand side of the trackways varies from two to three groups of imprints, as does the left side. Three sets of prints are common on the right side while two sets of prints are more dominant on the left (Figure 2.14). Drag marks are seen in front of the imprints left behind by leg 4 on the right hand side while leg 3 created drag marks on the left.
19


0
0



Figure 2.13
Large scorpion, 20 slope, 21 C, walking up gradient
Figure 2.14
Trace of Figure 2.13. Center feature formed by tail
20


Comparison of Modem Day Tarantula
and Scorpion Trackways
There are two main differences between the body plan of a scorpion and a tarantula. The first is the length of their legs relative to their body. Tarantulas have long legs that are stretched away from the body when walking while scorpions have short legs that are bent and held closer to the body while walking. This could be part of the reason for the difference in their trackways even though they are both eight-legged animals. Scorpions can create tracks with or without tail drags. Temperature and slope did not affect when the tail was placed on the sediment.
The tarantula had an erratic gait but created consistent trackways with different temperatures and slope. These experimental trackways show that every leg created imprints on the sediment under all of the varying circumstances. A tarantulas stride length is constant on flat slopes (Figure 2.15) and remains constant under changing environments. Tarantula imprints tend to be rounder and placed further from the trackway midline.
The scorpion had a regular stepping gait but consistently created different trackway patterns under varying conditions. Groups consisted of two to four imprints on either side trackway. Scorpions stride length can change from short to long strides even on flat slopes without a change in the environment (Figure 2.16). The legs created elongated tracks that are close to the trackway midline.
21


Figure 2.15
Trace of Pink-Toed Tarantula, no slope, 270 C. Tracks are numbered 1-4 corresponding legs to imprints. Stride length is represented using imprints from leg 2.
Trace of large African Emperor Scorpion, no slope, 27 C. Imprints are numbered 1-4, corresponding legs to imprints. Stride length is represented using imprints from leg 3.
22


Comparison of Tarantula Trackways to
Octopodichnus Trackways
Octopodichnus raymondi consists of four sets of imprints that are in a V-shaped pattern (Figure 2.17). The peak of the V faces the same direction in the trackway. This ichnotaxon resembles experimental tarantula trackways when the temperature is raised to 21 C on a horizontal surface (Figure 2.18). This pattern is also seen in trackways of a modem day tarantula above temperatures of 21 C or higher in portions of a trackway. Experimental trackways created on slopes still show a pattern of four imprints although it varies with uphill and downhill gradients.
Figure 2.17
Octopodichnus raymondi, direction of travel is not known.
Figure 2.18
Trace of tarantula tracks (Figure 2.2), no slope, 27 C, without pedipalp imprints. Arrow indicates direction of travel.
23


Direction of travel for Octopodichnus raymondi in not known. In experimental trackways the peak of the V can face forward or backward. Thus the direction of travel of the producers of these fossil trackways is a matter of speculation.
Comparison of Scorpion Trackways to Paleohelcura Trackways
The trackways created by modem day scorpions show few similarities to previous experiments performed by other scientists and the fossil record of Paleohelcura. One of the main differences between the fossil tracks those made by this African Emperor scorpion is the size of the tail drag. In experiments, when the tail was dragged for a long period, the drag imprint was dramatically wider in relation to the size of the individual tracks. When the tail was dragged in smaller spurts, the width of the drag was comparable to the size of the imprints. When looking at the tail drag in the fossil record, it is approximately the same width as the tracks.
The common feature that all of the experimental trackways have is the variation of imprint groups of two to four on each side of the midline. The right side of the fossil trackway of Mesichnium benjamini also shows these features (Figure 1.5). This trackway is described as a variation on Paleohelcura (Braddy, 1995). Mesichnium benjamini has a distinct regular medial imprint that is possibly
24


the result of a rounded tail segment or poison sac of the scorpion coming in contact with the ground. This fossil is regarded as a discrete ichnospecies within Paleohelcura (Braddy, 1995). No other fossil trackways show this type of variation but this morphology was quite frequent in experimental trackways.
A similarity between scorpion and Paleohelcura trackways occurred when the conditions for the larger scorpion were set at a temperature of 21 C with an approximate slope of 20 (Figure 2.19 & 2.20). When the animal walked up the gradient an arrangement of imprints occurred that resembled the fossil record. Two sets of tracks on the right hand side of the scorpion show a diagonal shaped pattern of three imprints arranged in a line (Figure 2.21).
When walking down the gradient with the same conditions as the uphill gradient, the same results occur. The right hand side of scorpion created three sets of tracks resembling Paleohelcura tridactyla (Figure 2.22). Paleohelcura tridactyla trackways show a diagonal shaped pattern of three prints arranged in a perfect line with a continuous taildrag throughout the middle of the trackway (Figure 2.23).
With a flat slope and the temperature at 27 C, there were one set of tracks on each side of the animal that showed resemblance to that of Paleohelcura tridactyla.
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Figure 2.19
Large scorpion, 20 slope, 21 C, walking up gradient
Figure 2.21
Enlarged section from Figure 2.19 showing similarity between Paleohelcura tridactyla and modem African Emperor Scorpion tracks.
Figure 2.20
Large scorpion, 20 slope, 21 C, walking down gradient
Figure 2.22
Enlarged section from Figure 2.20 showing similarity between Paleohelcura tridactyla and modem African Emperor Scorpion tracks.
1 cm
Figure 2.23
Paleohelcura tridactyla, direction of travel is unknown
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As stated earlier, on several occasions throughout the video, legs 3 and 4 of the scorpion, on both sides, were placed close to or in the same area of sediment, creating one imprint instead of two separate imprints. This might be a possible explanation for why there are only three sets of tracks on each side of the fossil trackways of Paleohelcura tridactyla.
The last similarity between the fossil record and the smaller African Emperor scorpion occurred during an experiment created on a flat slope at 21 C (Figure 2.24). Triavestigia niningeri is a trackway, divided by a taildrag, showing tracks consisting of one imprint down one side of the trackway and two sets of imprints on the other (Figure 2.25). In 1927, Gilmore examined this trackway and determined that it represented only one half of a large Paleohelcura track. He concluded that one side gradually faded and the other side washed out entirely (Braddy, 1995). An experimental trackway similar to Triavestigia niningeri occurred one time during experiments (Figure 2.26). As stated earlier the smaller African Emperor was missing leg 4 on the left hand side. This picture is not only a great representation of how one test track can contain many different features but also demonstrates that Triavestigia niningeri can be recreated by a scorpion missing an appendage. Each of the African Emperor scorpions created tracks that were very random and erratic, therefore, showing few similarities within a trackway to the fossil record of Paleohelcura.
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Figure 2.24
Small African Emperor Scorpion, no slope, 21 C. The scorpion started at the top right-hand side, made a U-turn and walked up the left hand side of the sediment tray.
Figure 2.25
Triavestigia niningeri, direction of travel unknown.
Figure 2.26
Right hand side of Figure 2.24
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CHAPTER 3
SUMMARY AND PROSPECTUS
Due to the lack of arthropods in the fossil record in sediments of Permian age it is difficult to determine what kinds of creatures were creating the trackways of Paleohelcura and Octopodichnus. By manipulating the environment of controlled experiments and through videotape, modem day scorpions and spiders shed some light on the possible track makers for some of the trackways in the fossil record. Stepping patterns and gaits of modem arthropods show variation within different species. Variation also occurs within the same species causing trackways to be consistently different.
The tarantula created trackways that resembled Octopodichnus raymondi at temperatures above 21 C on flat surfaces and slopes of approximately 20 in portions of the trackway. The peak of the V-shaped pattern can point forward or backward therefore it is a matter of speculation for the direction of travel in the fossil record. Stride length is consistent under varying circumstances making the experimental trackways more consistent on the whole.
All experimental scorpion trackways show a similarity to one side of the fossil trackway of Mesichium benjamini. Variation of two to four sets of imprints are present throughout the trackway. The larger scorpion showed similarities to
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Paleohelcura tridactyla throughout short sections of trackways if conditions were at 21 C and a slope of 20. The smaller scorpion that was missing leg 4 on the left hand side created a trackway resembling Triavestigia niningeri with the temperature at 21 C and a flat slope. Stride length varies from short to long strides even within a short distance with African Emperor scorpions, hence changing the pattern throughout a single trackway.
These experiments are consistent with previous interpretations of spiders being the trackmakers of Octopodichnus. The experimental data from African Emperor Scorpions show more similarities to Mesichnium benjamini (an ichnospecies within Paleohelcura) than to classic Paleohelcura, although under certain conditions some similarities between these experimental trackways and Paleohelcura can be seen.
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BIBLIOGRAPHY
Alf, R.A. (1968). A Spider Trackway from the Coconino Formation, Seligman, Arizona. Bulletin of the Southern Academy of Sciences, 6,125-128.
Braddy, S.J. (1995). The Ichnotaxanomy of the Invertebrate Trackways of the Coconino Sandstone (Lower Permian), Northeastern Arizona. New Mexico Museum of Natural History and Science Bulletin, 6, 219-224
Brady, L.F. (1947). Invertebrate Tracks From the Coconino Sandstone of Northern Arizona. Journal of Paleontology, 21, 466-472.
Fourtner, C.R., & Herreid II, C.F. (1981). Locomotion and Energetics in Arthropods. New York: Plenum Press.
Manton, S.M. (1977). The Arthropoda: Habits, Functional Morphology, and Evolution. Oxford: Clarendon Press.
Mckee, E.D. (1947). Experiments on the Development of Tracks in Fine, Cross-Bedded Sand. Journal of Sedimentary Petrology, 7, 23-28.
Petrunkevitch, A. (1960). Arachnida. Treatise on Invertebrate Paleontology. Geological Society of America and University of Kansas Press, Lawrence, KS. 42-162
Rankin, W. & Walls, J.G. (1994). Tarantula and Scorpions: Their Care in Captivity. New Jersey: T.F.H. Publications.
Sadler, C.J. (1993). Arthropod Trace Fossils From the Permian De Chelly Sandstone, Northeastern Arizona. Journal of Paleontology, 67, 240-249.
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Full Text

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THE EFFECT OF TEMPERATURE AND SLOPE ON THE MORPHOLOGY OF EXPERIMENTAL SPIDER AND SCORPION TRACKWA YS by Jaime Suzanne Azain B.S., Kansas State University, 2001 M.I.S., University of Colorado at Denver, 2006 A thesis submitted to the University of Colorado at Denver in partial fulfillment of the requirements for the degree of Masters of Integrated Science 2006

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This thesis for the Masters of Integrated Science degree by Jaime Suzanne Azain has been approved by Randall Tagg Date

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Azain, Jaime Suzanne (MIS) The Effect of Temperature and Slope on the Morphology of Experimental Spider and Scorpion Trackways Thesis directed by Assistant Professor Joanna Wright ABSTRACT Terrestrial trackways of arthropods are common in certain strata, such as the Permian Coconino Sandstone of Arizona, and are often the only evidence of the animals that once traversed the area. Some of the more common ichnogenera of these strata are and attributed to scorpions and spiders respectively. Several studies have attempted to reproduce these trackways in the laboratory but none systematically investigated the effects of temperature and gradient on the locomotion of the trackmakers and the trackways produced. Experimental track ways were created using a modern African Emperor scorpion, and a modem Pink-Toed tarantula, The trackmakers were videotaped in order to accurately document their stepping patterns. Speed of the animal, slope, and temperature affected the placement of the feet, which led to differences amongst the trackways. Drag created by the tarantula's legs established direction of travel for both uphill and downhill movements when experiments were created with a 20 angle. At temperatures above 210 C, scorpion tracks tend to remain elongated while tarantula tracks are

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more oblong. These experiments show similarities with previous studies such as a wide variety of track morphologies for scorpions with impressions that varied from two to four tracks on each side and that tarantula tracks are consistent with four tracks on each side. However, with experiments in damp or slightly moist sand, tracks were not created with either species because the animals were too light to leave impressions. These experiments support earlier hypotheses that spiders are the possible trail makers for Only at temperatures of21 0 C and a slope of approximately 20 do scorpion tracks show similarities to trackways. This abstract accurately represents the content of the candidate's thesis. recommend its publication. Signed Joanna

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DEDICATION I dedicate this thesis to my mother, father, and sister for their undying support and confidence while I was writing this.

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ACKNOWLEDGEMENT My thanks to my advisor, Joanna Wright, for her support and guidance during these past two years.

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CONTENTS Igures ............................................................................ VUl CHAPTER 1. INTRODUCTION ................................................................ 1 Previous Experimental Trackways ........................................ 2 Previous Experiments of Stepping Patterns in Modem Arthropods ......................................................................... 5 General Methods ................................................................ 7 Background Infonnation ....................................................... 8 Stepping Patterns in Modern Arthropods .................................. 10 Terminology ................................................................... 13 Notes on Illustrations ........................................................ 13 2. EXPERIMENTAL TARANTULA TRACKWAYS ........................ 14 Experimental Scorpion Trackways ........................................ 18 Comparison of Modern Day Tarantula and Scorpion Trackways .................................................................... 21 Comparison of Tarantula Trackways to Trackways ..................................................................... 23 Comparison of Scorpion Trackways to Trackways ....................................................................... 24 3. SUMMARY AND PROSPECTUS .......................................... 29 vii

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. 31 viii

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FIGURES Figure 1 Trackways found in the Coconino Sandstone ................................. ....... .2 ......................................... ................................. 2 ............................................................. 2 ............................................................. 2 .................................................................... 2 .............................................................. .2 1.9 Sediment tray used for all experiments ................................................ 8 1.10 Common name: African Emperor Scorpion Scientific name .............. '" ........................... 9 1.11 Common name: African Emperor Scorpion Scientific name: ................................................ 9 1.12 Common name: Pink-Toed Tarantula Scientific name ............................................. 9 1.13 Outline of scorpion and tarantula legs numbered from front to back of animal. Illustrated are the differences in leg structure. For numbering purposes the scorpion's legs are stretched out. .................................... .12 ix

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1.14 Stepping pattern of a modem scorpion .............................................. 12 1.15 Stepping pattern of a modem tarantula ............................................... 12 2.1 Pink-Toed Tarantula, no slope, 27 C, with pedipalps ............................ 15 2.2 Trace of Figure 2.1 without pedipalps ............................................... 15 2.3 Pink-Toed Tarantula, no slope, 16 C ............................................... .16 2.4 Trace of Figure 2.3, dotted arrow indicates direction oftravel.. ................. 16 2.5 Tarantula, 20 slope, 21 C, walking down gradient. Scale in cm, arrow indicates direction of movement. ..................................................... 17 2.6 Trace of Figure 2.5, dotted line represents midline of trackway, no pedipalp imprints ................................................................................... 17 2.7 Tarantula, 20 slope, 21 C, walking up gradient. Scale in cm, arrow indicated direction of movement ................................................................. 17 2.8 Trace of Figure 2.7, dotted line represents midline of trackway, no pedipalps imprints. ................................................................................ 17 2.9 Large scorpion, no slope, 27 C ....................................................... 18 2.10 Trace of Figure 2.9. Center feature formed by tail.. .............................. 18 2.11 Large scorpion, 20 slope, 21 C, walking down gradient ........................ 20 2.12 Trace of Figure 2.11. Center feature formed by tail.. ............................. 20 2.13 Large scorpion, 20 slope, 21 C, walking up gradient ........................... 20 2.14 Trace of Figure 2.l3. Center feature formed by tail ............................. .20 x

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2.15 Trace of Pink-Toed Tarantula, no slope, 27 C. Tracks are numbered 1-4 corresponding legs to imprints. Stride length is represented using imprints from leg 2 ........................ ........................... .. ........................... 22 2.16 Trace of large African Emperor Scorpion, no slope, 27 C. Imprints are numbered 1-4 corresponding legs to imprints. Stride length is represented using imprints from leg 3 ............................................................... 22 direction of travel is not known ............... ........ .23 2.18 Trace of tarantula tracks (Figure 2.2), no slope, 27 C, without pedipalp imprints. Arrow indicates direction of travel ....................................... 23 2.19 Large scorpion, 20 slope, 21 C, walking up gradient ............................. 26 2.20 Large scorpion, 20 slope, 210 C, walking down gradient ....................... 26 2.21 Enlarged section from Figure 2.19 showing similarity between and modem African Emperor Scorpion tracks ............................ .26 2.22 Enlarged Section from Figure 2.20 showing similarity between and modem African Emperor Scorpion tracks ......................... .26 direction of travel is unknown ........................... 26 2.24 Small African Emperor Scorpion, no slope, 21 C. The scorpion started at the top right-hand side made a U-turn and walked up the left hand side of the sediment tray ............................................................................ 28 direction of travel is unknown .......................... .... 28 2.26 Right hand side of Figure 2.24 ........................................................ 28 Xl

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CHAPTER 1 INTRODUCTION Fossil arthropods are very scarce in the geologic record. These animals have a mineralized exoskeleton that is rarely calcified. Scorpions are first reported from the Silurian, approximately 435 million years ago, while the earliest known spiders are in the Devonian, approximately 400 million years ago (Petrunkevitch, 1960). Fossilized arthropod trackways, however, are very common in certain Permian age sediments such as the Coconino Sandstone of Arizona. However, no scorpions and very few spider body fossils are known from this period. The general body structures of arthropods have changed very little since their arrival on land (Petrunkevitch, 1960). With this mind, two scorpions and one tarantula were used to create trackways at different temperatures and gradients. These animals were videotaped to determine stepping patterns and foot placement in order to establish which legs formed which imprints. Scorpions and spiders are both eight legged animals but have different leg structures and thus create trackways with two distinct patterns allowing positive identification of the tracks of each taxon. Scorpions produced small, elongated imprints and their trackways sometimes resemble Spiders created rounded imprints in a trackway pattern that resembled those of

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Previous Experimental Trackways Several sets of experiments using scorpions, beetles, and millipedes have been carried out to determine likely track makers for trackways in the Coconino Sandstone (Figure 1-1.8). Certain scorpions created trackways resembling 1.1 1.6 Iem Icm .-Iem 1.3 ,e ." ," .. ," lem 1.7 '" Figures 1-1,8 ", Ie .. :. a -: ',.0 .. ,. 0 0 .. 0 0 Ie .. 1.8 "0 1) Trackways found in the Coconino Sandstone. 1.1) 1.2) 1.4) 1.5) 1.6) 1.7) 1.8) Figures Braddy 1995. 2

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however, none of these animals created trackways resembling those of (Sadler, 1993). Brady (1947), used several different species of scorpions. He used a modem dune environment for comparison with those of the Permian Dune Fonnations. With or Bark Scorpions, commonly found in Arizona, he noted that the scorpion refused to move on wet sand. On slightly moist sand, no tracks were created although the animal moved. At temperatures of 8 C (45 F), on dry sand, the animal was sluggish and left impressions of all eight feet but no tail drag. At approximately 15 C (60 F), the scorpion created tracks resembling At temperatures above 20 C (70F), the tracks became irregular. He also stated that the front pair of walking legs did not impress when a slope of 10 was incorporated into experiments and the temperature was 15 C. The direction of travel was not indicated. He carried out experiments with five different species of scorpions but noted that the Bark Scorpion was the only animal to leave a tail drag. He refers to or African Emperor Scorpion only to note that this larger tropical fonn did not leave a tail drag because they carry their tail arched over their back during nonnal locomotion. The basal spurs on the scorpion's legs were too small to create impressions in these experimental trackways. Experimental scorpion trackways show a wide variety of track morphologies; the number of imprints each imprint group left on each side of the scorpion varied from two to four (Brady, 1947) 3

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Until 1993, no experiments were successful in creating trackways using a spider in sediment. Alf (1968) used spiders with his experiments but used ink and paper instead of sand. The trackways created in ink are very different than tracks created in sediment. Sadler (1993), performed experiments with a male scorpion sp.) and a female tarantula sp.). She created a runway that measured 4.0 m by 0.5 m using fine, well sorted sand similar to that of the Coconino Sandstone. A dry sand dune with a slope of 25 was placed in the middle of the runway. A level portion of the runway .05 m long was sprayed with water to produce different degrees of moisture in the sediment. In order to obtain different speeds a stream of air was directed at the animals. Her experiments were performed at room temperature at 25 C. Previous experiments had suggested that small invertebrates failed to make tracks on anything but dry sand and on slopes of no more than 12 (McKee, 1947). But Sadler created identifiable tracks her experiments on slightly damp sand. Although tracks created in sand tended to be bigger and deeper, avalanche structures obscured much imprint detail (Sadler, 1993). Trackways damp sediment were smaller and sharper. If the sand was too moist the animal did not leave impressions because the sediment was cohesive. The same occurred if the sand was allowed to dry and form a crust on the surface. The slope of 25 was too steep for the scorpion and the tarantula to create clear identifiable tracks.

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Scorpion and spider tracks show bifurcations, open in the direction of travel (Sadler, 1993). Elongated "tic" marks formed as the foot was dragged forward between strides. The triangular pattern of individual imprints made by the scorpion greatly resembled the ichnospecies (Figure 1.2). The peak of the triangle can face forward or backward, so determining direction of travel of fossil trackways from imprint morphology is probably not possible. Tarantula trackways may closely resemble at least one species of Trace fossils differ from body fossils in that one animal can produce several different trackway morphologies. These can differ sufficiently to be placed in two different ichnotaxa. Fossil trackways rarely show this although, it is quite common in experimental trackways. Sadler's scorpion consistently created several different patterns. This pattern changed from the right to left side of the trackway and even within a few strides with no obvious reason. The obvious reasons include, change in light, moisture content, direction, and speed. The scorpion produced very irregular trackways, sometimes resembling those of although, most resembled (Sadler, 1993). Previous Experiments of Stepping Patterns Modem Arthropods Arachnid legs are well fanned out from their bases so they have a mechanical advantage in comparison to animals with fewer pairs of walking legs. 5

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They hang from their legs unless the legs are relatively short. The knee in spiders is pointed upwards while scorpions' knee when flexed do not project upwards as in spiders, but fold against and over the body so that the dorsal surface of the leg is displaced so that the anterior face is always visible from above. There appears to be a slight twist of the leg so that the anterior face is visible dorsally. Leg movements in each group can be very different from one another in detail although the basic features are the same for each animal. Arachnids show gait irregularities especially when turning. Legs of a pair normally step in opposite phase, but after turning the grouped footprints on each side of the animal no longer alternate and may in any position. Manton created a cinematograph with a scorpion, and a spider, With both of these animals she noted that legs 3,2,4 on the left corresponded to legs 2, 4, 1, 3 on the right (Manton, 1977). Different arachnids exhibit different stepping patterns (Herreid II and Fourtner,1981). Scorpions step in a 4,2,3, 1 sequence on the left corresponding to 3, 1,4,2 on the right when walking forward. The propulsive phases of the individual legs are temporally offset and staggered. They utilize two alternating waves of diagonally stepping legs, rather than two sets of strictly alternating tetrapods. Forward movement is achieved by the staggered coordination. All legs do not contribute equally in generating forward propulsion (Herreid II and Fourtner, 1981). 6

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Tarantulas employ at least six different gaits although some patterns are more common than others. In the three most common, leg 4 moves first followed by a variation oflegs 1-3. Left and right sides of the tarantula may be uncoupled to a certain extent so that the two sides can actually step at different rates (Herreid, Fourtner). General Methods All experiments were created in a sediment tray that measured 76 cm x 41 cm (Figure 1.9). The sediment used in experiments was Mississippi silt. The grain size of the silt ranged from .05mm-.074mm. The tray had rollers on the bottom so that the sand could be evenly distributed. The tray was shaken after trackways were created to redistribute the sand. The depth of the sediment was approximately 3-4 em for each experiment and was never compacted down. Temperatures varied from 16-27 C for all trackways created. In order to raise the temperature of the sand, a heat lamp was enclosed on the tray until the desired temperature was achieved. When the temperature needed to be lowered below room temperature, the sediment was placed outside overnight and the 7

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Sediment tray used for all experiments. experiments were performed before the heat of the sun raised the temperature. The temperature readings were taken with a small wall thermometer. The gauge was placed directly on the sand to achieve an accurate reading. A slope of approximately 20 or no slope was used for all experiments. When the sediment was ready the scorpion or tarantula were placed in the tray, allowed to move around freely, and observed during trackmaking. Background Information Two African Emperor scorpions and one Pink-Toed tarantula were used for the following experiments. The smaller scorpion (Figure 1.10) was female approximately 2 years of age and missing leg 4 on the left hand side. The larger scorpion (Figure 1.11) was also female, approximately 5 years of age. Scorpions have four pair of true legs with two basal spurs at the end of each leg, and a pair of 8

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pedipalps with pinchers on the end that aid in feeding. The legs of this particular scorpion are very short relative to their body size. The natural environment for Common name : African Emperor Scorpion Scientific name: Common name : African Emperor Scorpion Scientific name: Common name : Pink-Toed Tarantula Scientific name: these animals is a very warm, humid climate in Africa. As a general rule, scorpions are clumsy animals that tend to move by side stepping or backing up as much as they go forward The normal temperature range for an African Emperor in captivity 9

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is approximately 27 C. this paper, temperature is manipulated at and below their normal temperature range. When the temperature was lowered below 27 C the movements of the scorpion slow down slightly due to their cold blooded nature. At 16 C the scorpion refused to move. On the other hand, if their surroundings become too warm they will go into distress, lie on their backs, and appear to sting themselves (Rankin, Walls, 1994). For the safety of the animal the temperature never exceeded 27 C. The tarantula (Figure 1.12) used in this paper is an adult female, around 5 years of age. She has four pairs of true legs with one basal spur at the end of each leg, and a pair ofpedipalps that aid in feeding and investigations of her surroundings. Her legs are long compared to her body size and radiate out from the center of the cephalothorax. Her natural habitat is also from a tropical climate. The normal temperature range for this particular tarantula in captivity is maintained at approximately 27 C (Rankin Walls, 1994). Lowering the temperature below normal range had the same slowing effect on the spider as it did on the scorpion. Stepping Patterns in Modem Arthropods The larger scorpion and tarantula were videotaped walking on sediment as described in the general methods section. The digital tape was transferred onto a CD that allowed the speeds at which the animals moved to be slowed down. This in 10

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turn gave an idea of the stepping patterns for these modem arthropods. The limbs are numbered from front to back (Figure 1.13). The scorpion had a very regular foot pattern. When walking in a straight line the animal placed limbs in the order 2,4,1,3 on the left corresponding to 1,3,2,4 on the right (Figure 1.14). The only time that this was not observed was when the animal was turning. The scorpion's pedipalps came down from time to time making a track-like indent on the sand. Even though the pincher's imprints were outside the realm of the tracks created by the animal's legs, they obscured the trackway with a fifth set of tracks. Also noted was an occasional tail drag. Legs 3 4 leave tracks that are very close together; so that sometimes the imprints coalesce into one elongate imprint. Imprints produced by leg 2 were sometimes overstepped by those of leg 4. The videotape allowed assessment of which legs created which tracks. The legs that left tracks closest to the body, when walking in a straight line were left by leg 1, followed by 4 and 2. Leg 3 left tracks furthest away from the body. The tarantula on the other hand had a very erratic gait. The most noted pattern was 2,4,3,1 on the left corresponding to 1,3,4,2 on the right (Figure 1.15). This was not the only pattern but no other set pattern could be distinguished. The pedipalps on a tarantula are very large and leave imprints in every spider trackway. Pedipalps imprints are generally in line with the body of the animal and are not put down in any particular pattern as they are used for investigation of the surroundings. Therefore, the trackways show five sets of tracks on each side of the midline of the

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3 :a::=::::"", Outline of scorpion and tarantula with legs numbered from front to back of animal. Illustrated are the differences in leg structure. For numbering purposes the scorpion's legs are stretched out. 3 Stepping patterns of a modem scorpion 12 Stepping patterns of a modem tarantula

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body. The legs that left tracks closest to the center of the tarantula's body, when walking in a straight line were created by leg 4, followed sequentially by 1,3, and 2. Terminology The terms "track" and "imprint" are defined as solitary features whereas a "trackway" is defined as a continuous pattern of tracks. An "imprint group" represents tracks or imprints created by one complete cycle oflimb movement. "Stride" is defmed as the distance between footfalls of the same appendage (Braddy, 1995). Note on Il1ustrations Direction of travel for experimental trackways is indicated by arrow unless otherwise noted in the figure description.

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CHAPTER 2 EXPERIMENTAL TARANTULATRACKWAYS With experimental trackways created at 27 0 C on a flat slope, triangular patterns of three appear on both sides of the trackway (Figure 2.1). Legs 3 and 4 create more oblong imprints, showing a slight drag while the imprints of legs 1 and 2 retain a more circular shape. The fourth imprint can be anywhere around the triangle depending on where the 4th leg touches the ground. Tracks created by the pedipalps have been edited out of the traced trackway (Figure 2.2). Lowering the temperature to 160 C on a flat slope, created a very different trackway pattern (Figure 2.3). colder temperatures, both the legs, and the pedipalps, spend more time on the ground. The individual imprints left behind are bigger and more circular. They form imprints groups of four (Figure 2.4). These are the only trackways that did not show triangular imprint groups. Experiments with the tarantula performed at 21 C with a slope of approximately 20, walking down a gradient, created a triangular pattern of three, pointing in the direction of motion on the righthand side of the trackway (Figure 2.5). The tracks on the left do not show this particular pattern although all four legs did leave imprints (Figure 2.6). The imprints of Leg 1 are elongate parallel to the direction of motion. Legs 2 4 on each side created noticeable drag marks in front 14

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PinkToed Tarantula, no slope, 27 C, with pedipalps Trace of Figure 2.1, without pedipalps 15

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Figure 2.3 Pink-Toed Tarantula, no slope, 16C ,. Figure 2.4 Trace of Figure 2.3, dotted arrow indicates direction of travel ofthe foot's initial landing whereas tracks created by legs 1 3 created a more circular pattern with slight mounds forming behind the imprint. The drag marks are a good indication of the direction of movement. In larger species of spiders, pushbacks or mounds are created in the sediment. If the spider is walking on an incline, the sand forms a mound behind the foot. The opposite occurs for downhill movement (Sadler, 1993). Under the same conditions, when the spider walked up the gradient drag marks were also created by leg 4 on each side (Figure 2.7). The other sets of legs created a more circular pattern with slight mounds forming behind the imprint. The oblong shapes seen with the downhill gradient are not as pronounced in uphill movement. The right side of the trackway showed the triangular pattern of three while the left side showed a more random pattern (Figure 2.8). 16

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2.5 Tarantula, 20 slope, 21 C, walking down gradient. Scale in em, arrow indicates direction of movement 2.7 Tarantula, 20 slope, 210 C, walking up gradient. Scale in em, arrow indicates direction of movement W- ... ,,...... 2.6 Trace of Figure 2.5, dotted line represents midline of trackway, no pedipalp imprints .. Figure 2.8 Traee of Figure 2.7, dotted line represents midline of trackway, no pedipalp imprints

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Experimental Scorpion Trackways Experiments with modem scorpions created trackway patterns that were random and erratic under varying environments. Trackways fonned on sediment at a temperature of C on a horizontal surface show the most variation in the trackways (Figure 2.9). On the right hand side of the scorpion three sets of imprints are the most common (Figure 2 10). These imprints groups may show the diagonal pattern of three or a triangular pattern of three. Leg 4 on the left hand side of the scorpion created drag marks obscuring the imprints left by leg 2. The tracks left closest to the taildrag were created by leg 1. The left and right side of Figure 8.1 shows the variation in the imprints left by leg 1 .. Figure 2.9 Large scorpion, no slope, 270 C 18 Figure 2.10 Trace of Figure 2.9. Center feature formed by tail.

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When conditions for the larger scorpion were set at a temperature of 21 C with an approximate slope of 200 groups of imprints vary from two to four on each side of the animal. When walking up the gradient (Figure 2.11), the most notable pattern was sets of three imprints arranged in diagonal lines on the left hand side of the scorpion, although a couple of sets show imprints of two and four tracks. The right hand side shows a pattern of three to four imprints alternating throughout the trackway (Figure 2.12). Leg 1 on each side of the animal did not always create an imprint. When walking down the gradient (Figure 2.13) the right hand side of the trackways varies from two to three groups of imprints, as does the left side. Three sets of prints are common on the right side while two sets of prints are more dominant on the left (Figure 2.14). Drag marks are seen in front of the imprints left behind by leg 4 on the right hand side while leg 3 created drag marks on the left. 19

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Large scorpion, 200 slope, 210 C, walking down gradient. Large scorpion, 20 slope, 21 C, walking up gradient 20 Trace of Figure 2.11. Center feature formed tail Trace of Figure 2.13. Center feature formed tail

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Comparison of Modern Day Tarantula and Scorpion Trackways There are two main differences between the body plan of a scorpion and a tarantula. The first is the length of their legs relative to their body. Tarantulas have long legs that are stretched away from the body when walking while scorpions have short legs that are bent and held closer to the body while walking. This could be part of the reason for the difference in their trackways even though they are both eight-legged animals Scorpions can create tracks with or without tail drags. Temperature and slope did not affect when the tail was placed on the sediment. The tarantula had an erratic gait but created consistent trackways with different temperatures and slope. These experimental trackways show that every leg created imprints on the sediment under all of the varying circumstances A tarantula's stride length is constant on flat slopes (Figure 2.15) and remains constant under changing environments. Tarantula imprints tend to be rounder and placed further from the trackway midline. The scorpion had a regular stepping gait but consistently created different trackway patterns under varying conditions Groups consisted of two to four imprints on either side trackway. Scorpions stride length can change from short to long strides even on flat slopes without a change in the environment (Figure 2.16). The legs created elongated tracks that are close to the trackway midline.

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- "' 4 4 1 1 1 1 3 .2 3 2 3 ., -2 SL ern Figure 2.1S Trace of Pink Toed Tarantula, no slope, 27 C. Tracks are numbered 1-4 corresponding legs to imprints. Stride length is represented using imprints from leg 2 1em SL Figure 2.16 3 Trace of large African Emperor Scorpion no slope 27 C. Imprints are numbered 3 1 -4 corresponding legs to imprints Stride length is represented using imprints from leg 3. 22

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Comparison of Tarantula Trackways to Octopodichnus Trackways consists of four sets of imprints that are in a Vshaped pattern (Figure 2.17). The peak of the V faces the same direction in the trackway. This ichnotaxon resembles experimental tarantula trackways when the temperature is raised to 270 C on a horizontal surface (Figure 2.18). This pattern is also seen in trackways of a modem day tarantula above temperatures of 21 C or higher portions of a trackway. Experimental trackways created on slopes still show a pattern of four imprints although it varies with uphill and downhill gradients. lcm Figure 2.17 direction of travel not known. 23 Figure 2.18 r Trace of tarantula tracks (Figure 2.2), no slope, 27 C, without pedipalp imprints. Arrow indicates direction of travel.

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Direction of travel for in not known. In experimental trackways the peak of the V can face forward or backward. Thus the direction of travel of the producers of these fossil trackways is a matter of speculation. Comparison of Scorpion Trackways to Trackways The trackways created by modern day scorpions show few similarities to previous experiments performed by other scientists and the fossil record of One of the main differences between the fossil tracks those made by this African Emperor scorpion is the size of the tail drag. In experiments, when the tail was dragged for a long period, the drag imprint was dramatically wider in relation to the size of the individual tracks. When the tail was dragged in smaller spurts, the width of the drag was comparable to the size of the imprints. When looking at the tail drag in the fossil record, it is approximately the same width as the tracks. The common feature that all of the experimental trackways have is the variation of imprint groups of two to four on each side of the midline The right side of the fossil trackway of also shows these features (Figure 1.5). This trackway is described as a variation on (Braddy, has a distinct regular medial imprint that is possibly 24

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the result of a rounded tail segment or poison sac of the scorpion coming in contact with the ground. This fossil is regarded as a discrete ichnospecies within (Braddy, 1995). No other fossil trackways show this type of variation but this morphology was quite frequent in experimental trackways. A similarity between scorpion and trackways occurred when the conditions for the larger scorpion were set at a temperature of 21 C with an approximate slope of 20 (Figure 2.19 2.20). When the animal walked up the gradient an arrangement of imprints occurred that resembled the fossil record. Two sets of tracks on the right hand side of the scorpion show a diagonal shaped pattern of three imprints arranged in a line (Figure 2.21). When walking down the gradient with the same conditions as the uphill gradient, the same results occur. The right hand side of scorpion created three sets of tracks resembling (Figure 2.22). trackways show a diagonal shaped pattern of three prints arranged in a perfect line with a continuous taildrag throughout the middle of the trackway (Figure 2.23). With a flat slope and the temperature at 27 C, there were one set of tracks on each side of the animal that showed resemblance to that of 25

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Large scorpion, 20 slope, 21 C, walking up gradient Enlarged section from Figure 2.19 showing similarity between and modern African Emperor Scorpion tracks. Large scorpion, 20 slope, 2 F C, walking down gradient Enlarged section from Figure 2.20 showing similarity between and modern African Emperor Scorpion tracks direction of travel is unknown 26

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As stated earlier, on several occasions throughout the video, legs 3 and 4 of the scorpion, on both sides, were placed close to or in the same area of sediment, creating one imprint instead of two separate imprints. This might be a possible explanation for why there are only three sets of tracks on each side ofthe fossil trackways of The last similarity between the fossil record and the smaller African Emperor scorpion occurred during an experiment created on a flat slope at 21 C (Figure 2.24). is a trackway, divided by a taildrag, showing tracks consisting of one imprint down one side of the trackway and two sets of imprints on the other (Figure 2.25). In 1927, Gilmore examined this trackway and detennined that it represented only one half of a large track. He concluded that one side gradually faded and the other side washed out entirely (Braddy, 1995). experimental trackway similar to occurred one time during experiments (Figure 2.26). As stated earlier the smaller African Emperor was missing leg 4 on the left hand side. This picture is not only a great representation of how one test track can contain many different features but also demonstrates that can be recreated by a scorpion missing an appendage. Each of the African Emperor scorpions created tracks that were very random and erratic, therefore, showing few similarities within a trackway to the fossil record of 27

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, ,:r Small African Emperor Scorpion, no slope, 210 C. The scorpion started at the top right-hand side, made a U-turn and walked up the left hand side of the sediment tray. 1('11 direction of travel unknown. Right hand side of Figure 2.24 28

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CHAPTER 3 SUMMARY AND PROSPECTUS Due to the lack of arthropods in the fossil record in sediments of Permian age it is difficult to determine what kinds of creatures were creating the trackways of and By manipulating the environment of controlled experiments and through videotape, modem day scorpions and spiders shed some light on the possible track makers for some of the trackways in the fossil record. Stepping patterns and gaits of modem arthropods show variation within different species. Variation also occurs within the same species causing trackways to be consistently different. The tarantula created trackways that resembled at temperatures above 210 C on flat surfaces and slopes of approximately 200 in portions of the trackway. The peak of the V-shaped pattern can point forward or backward therefore is a matter of speculation for the direction of travel in the fossil record. Stride length is consistent under varying circumstances making the experimental trackways more consistent on the whole. All experimental scorpion trackways show a similarity to one side of the fossil trackway of Variation of two to four sets of imprints are present throughout the trackway. The larger scorpion showed similarities to 29

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throughout short sections oftrackways if conditions were at 210 C and a slope of 200 The smaller scorpion that was missing leg 4 on the left hand side created a trackway resembling with the temperature at 210 C and a flat slope. Stride length varies from short to long strides even within a short distance with African Emperor scorpions, hence changing the pattern throughout a single trackway. These experiments are consistent with previous interpretations of spiders being the trackmakers of The experimental data from African Emperor Scorpions show more similarities to (an ichnospecies within than to classic although under certain conditions some similarities between these experimental trackways and can be seen. 30

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BIBLIOGRAPHY Alf, R.A. (1968). A Spider Trackway from the Coconino Fonnation, Seligman, Arizona. 6,125-128. Braddy, S.J. (1995). The Ichnotaxanomy of the Invertebrate Trackways of the Coconino Sandstone (Lower Permian), Northeastern Arizona. 6, 219-224 Brady, L.F. (1947). Invertebrate Tracks From the Coconino Sandstone of Northern Arizona. 21, 466-472. Fourtner, C.R., Herreid II, C.F. (1981). Locomotion and Energetics Arthropods. New York: Plenum Press. Manton, S.M. (1977). Oxford: Clarendon Press. Mckee, E.D. (1947). Experiments on the Development of Tracks in Fine, Cross Bedded Sand. 7,23-28. Petrunkevitch, A. (1960). Geological Society of America and University of Kansas Press, Lawrence, KS. 42162 Rankin, W. Walls, J.G. (1994). New Jersey: T.F.H. Publications. Sadler, C.J. (1993). Arthropod Trace Fossils From the Pennian De Chelly Sandstone, Northeastern Arizona. 67,240-249. 31