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Converting meters per second to kilometers per hour:

Step 4. = (2.1 m/s) x (3600 s/h) x (1 km/1000 m) Step 5. = 7.6 km/h

To put this speed in perspective, the Olympic record for the men's 20-km race-walk (as of the writing of this book) is a mean speed of 15.5 km/h, which is more than twice as fast as our theropod and was sustained over a 20-km distance. This example demonstrates a slowly-moving theropod. Indeed, most measurements of dinosaur trackways reflect that they behaved just like most animals during the majority of their lifetimes: they walked, but not briskly. If we treat these calculated speeds as hypotheses, they can be cross-checked with the qualitative data mentioned before, such as pressure-release structures and other evidence of considerable stresses to a substrate that might have been imparted by a running versus a walking animal. Running animals also tend to become more digitigrade. This means that only the distal ends of the phalanges make impressions in the sediment, although such prints also could be undertracks.

The fastest known speeds indicated by dinosaur trackways, using the preceding methodology, were about 40 km/h. This speed seemingly was restricted to small-and medium-sized theropods (Chapter 9). However, this situation may be a result of biased sampling, because large theropod trackways are relatively rare. So far, the trackways made by quadrupedal dinosaurs, such as sauropods (Chapter 10), ornithopods (Chapter 11), and ceratopsians (Chapter 13), with the exception of one ankylosaur trackway mentioned earlier (Chapter 12), only show relatively slow walking speeds. If these animals were capable of running at speeds approaching those of some theropods, trackway evidence has not yet revealed such abilities.

Dinosaur Group Behaviors Indicated by Tracks

When dinosaur tracks are found as multiple trackways on the same horizons, hypotheses can be made about how dinosaurs related to one another, intraspecifically or interspecifically. Track maps are especially useful for formulating these types of interpretations. In combination with other qualitative and quantitative information, track maps can be used to either verify or dispute dramatic scenarios of multiple dinosaurs in close association with one another.

Intraspecific behavior related to gregariousness is best supported by track evidence. For example, did dinoaurs prefer to travel with many individuals of their own species or were they "lone dinosaurs"? If many herbivorous dinosaurs of the same species lived together as a group and traveled together, they were said to have behaved as a herd. In contrast, a grouping of carnivorous dinosaurs similar to a herd is termed a pack. These are conceptually analogous to modern mammals, such as caribou and wolves, respectively, that show the same behaviors. Birds of the same species displaying group behavior are flocks, regardless of their eating habits, and the same term has been applied to dinosaur groups in recognition of some of their behavioral similarities to modern birds (Chapter 15).

Some dinosaur trackways do indeed suggest either herding or pack-hunting behavior (Chapters 9 to 13). Track maps clearly show a preferred directionality by different individual dinosaurs of the same or different species, which may reflect herds migrating or predator-prey relations. However, these track data should be examined critically for the possibility that a geographic or ecological barrier, such as a cliff or water body, could have caused a preferred path for these dinosaurs. The latter interpretation is supported by parallel trackways that show 180° orientations to one another with regard to direction of movement.

Quantitative methods help to determine whether unidirectional trackways represent group behavior by:

1 calculating their speeds, keeping in mind that animals moving together will H^f typically do so at the same speed; and

2 measuring the spacing between each trackway and their degree of parallelism.

Modern animals of the same species moving together will space themselves at nearly equal intervals to avoid "invading each other's space," and accordingly will move in formation. Indeed, a bedding plane exposure of the Late Jurassic Morrison Formation in southern Colorado shows five sauropod trackways that are parallel and equally spaced, all apparently moving at the same speed and even turning in harmony with one another (Chapter 10). Similarly, multiple parallel theropod trackways in a Cretaceous stratum in Mongolia argue for a group movement of these animals.

One of the most interesting interpretations of group behavior in dinosaurs of different species is a "stampede" recorded in an Early Cretaceous bedding plane in Queensland, Australia. At this site, a large number of small theropod and ornithopod trackways show unidirectional movement away from the trackway of a single large theropod. Some of the speeds, calculated from footprint and stride lengths, indicate that most of the smaller dinosaurs were running in the opposite direction to the large theropod. The interpretation is that a group of small theropods, perhaps of the same species (based on similarities of footprint size and morphology), was startled by the approach of a large theropod and ran away from it in a panic. Nevertheless, the exact timing of the larger dinosaur arriving on the scene relative to all of the smaller ones is uncertain; some of the smaller theropod tracks register within the larger one's tracks and thus post-date the latter.

Such examples may seem exciting and dynamic, but scientists have to critically examine the track evidence for what is actually preserved, rather than what is presumably preserved. This caution is especially warranted with reference to more dramatic interpretations of group behavior. Knowing that tracksites may represent the cumulative actions of animals traversing an area over the course of a few days or months diminishes the probability that any given set of tracks actually relates to one another through cause and effect. Yet another "reality check" is that the preservation requirements of dinosaur tracks allow for the probability of undertracks. This means that a bedding plane containing dinosaur tracks may have specimens impressed into it by animals that lived much later (perhaps by years) than the other animals that made tracks on the same surface (Fig. 14.8).

However, once these possibilities are accounted for, the usefulness of dinosaur tracks far outweighs their problems. Understanding the fundamental concepts of tracking and how they relate to dinosaur tracks provides a better basis for critically examining the case examples covered in other chapters. In many of these cases, dinosaur tracks have supplemented other dinosaur fossil data or have been the sole piece of evidence for dinosaurs, data that relate directly to the evolution, paleo-biogeography, and paleobiology of major groups of dinosaurs (Chapters 10 to 15). 14

Dinosaur Behaviors Not Indicated by Tracks

Dinosaur tracks are valuable as sources of doubt or outright falsification of either new or long-held hypotheses of dinosaur behavior based only on skeletal data. Incorrect interpretations of dinosaur tracks also can lead to problems with

Theropod track

Hopping mammal tracks Crayfish burrow

Dung TPJil beetle

Feces (future coprolite)

Theropod track

Hopping mammal tracks Crayfish burrow

Dung TPJil beetle

Old track

Worm burrows

Even older track

FIGURE 14.8 How varying depths of tracks and preservational modes can result in a track assemblage on a bedding plane where the tracks are not contemporaneous.

Old track

Worm burrows

Even older track

FIGURE 14.8 How varying depths of tracks and preservational modes can result in a track assemblage on a bedding plane where the tracks are not contemporaneous.

evaluating dinosaur behavior. Regardless of whether the hypotheses emanate from dinosaur body fossils or tracks, careful examinations of dinosaur tracks have helped to demonstrate that the following dinosaur behaviors were either rare or have not been clearly demonstrated.

Habitual Tail Dragging

Although often seen in older, popular depictions of dinosaurs, tail dragging seldom happened. Only a few rare instances have been found of a dinosaur's tail impressed on the same substrate as its feet, which in these cases showed that a dinosaur temporarily had a "tripod" stance or stooped to a low profile. In the past 20 years or so, the revelation that dinosaurs did not drag their tails has finally had an influence on dinosaur art. Well-informed artists now show dinosaurs of all sizes and shapes with their tails held straight behind them in nearly horizontal planes parallel to the rest of a dinosaur's axial skeleton. Skeletal data have also corroborated that dinosaur tails were horizontal and held off the ground. For example, some theropods and ornithopods had ossified tendons that stiffened the tail to assume such a posture. Before this revelation, some museum preparators in the early part of the twentieth century actually broke the caudal vertebrae of mounted dinosaur skeletons to make the vertebrae lie on the ground behind the main skeleton. Because dinosaurs were once considered as large reptiles, the prevalent view held was that dinosaurs must have been "tail-draggers" as well, but a closer look at their tracks would have revealed otherwise.

Swimming or Immersion in Water

Original interpretations of some dinosaurs, especially huge sauropods (Chapter 10) but also a few hadrosaurids (Chapter 11), held that these animals were adapted for an aquatic lifestyle. For sauropods, the reasoning was that an animal of such tonnage could not support its own weight on land, so it needed the buoyancy of water to cope. Track data were, in some cases, fitted to this hypothesis. For example, Roland Bird (Chapter 4) described a sauropod trackway where only manus impressions were preserved. Bird proposed that the rear feet were involved with swimming above a seafloor and only the front feet touched down. However, re-examination of this trackway showed that the pattern was attributable to partial preservation (under-tracks), and that the pes impressions did not sufficiently impart enough stress to be preserved equally with the manus impressions. Other sauropod tracks, as well as those of every other dinosaur, do not show conclusive evidence of swimming or an otherwise aquatic habit. This is not to say that all dinosaurs did not occasionally venture into water bodies or that they did not swim. In fact, more "swimming theropod" trackways have been interpreted in recent years with more convincing evidence of such behavior for those dinosaurs. Nevertheless, the paucity of trackway evidence for swimming in most dinosaurs encourages healthy skepticism of such interpretations.

Obligate Quadrupeds Rearing up on Their Hind Legs

Although some male quadrupedal dinosaurs probably were capable of temporarily rearing up on to their hind legs to assume a mating position behind a female (Chapter 8), no trackway evidence has shown that they actually did this. For example, anatomical reconstructions of sauropods (Chapter 12) and stegosaurs (Chapter 14) provide evidence that the center of gravity for some species may have been far enough toward the rear of their bodies that a temporarily bipedal posture was possible. This behavior was advanced as a hypothetical adaptation for herbivorous animals to reach the tops of tall-standing vegetation, or for making the animal appear larger to a threatening predator. Some illustrations and one mounted skeleton even show these dinosaurs, some of them an estimated 20 or more tonnes, in near-vertical postures. However, just because a dinosaur could have done a certain behavior does not mean that it actually did, and there is no known evidence of this behavior in sauropod or stegosaur tracks. If obligate quadrupedal dinosaurs did assume "vertical" positions, the rear feet should have doubled the foot stresses transmitted to the underlying substrate. As a result, tracks made by this behavior should be immediately obvious to a trained observer.

Intraspecific Competition or Interspecific Confrontation

So far, no dinosaur trackways provide conclusive evidence of dinosaurs of the same species competing with one another or predators pursuing and attacking a prey species. A disproportionate amount of attention has been paid to predator-prey relationships between dinosaurs, relative to the possibility of certain dinosaurs competing within their own species. The latter subject is now receiving more study (Chapters 9 to 13), but track evidence has not yet shed light on speculations about how males of a certain dinosaur species competed with one another for females. Examples include the much-publicized hypothesis that pachycephalosaurs charged one another at high speed and butted heads like modern rams (Chapter 13). Such behavior would be supported by two trackways composed of nearly equal-sized tracks with vectors heading toward one another on a 180° plane. The trackways also would show mathematically defined running speeds for both tracemakers, followed by abrupt ending of the trackways as they meet.

As noted previously, a few trackways strongly suggest that some theropods deliberately followed sauropods. However, only one trackway has been presented as recording a possible attack by a large theropod on a sauropod, which is in the Lower Cretaceous Glen Rose Formation of Texas (Chapter 9). In this interpretation, originally made by Roland Bird, the theropod's trackway ends when it converges with the sauropod trackway at one point, which Bird explained was where the theropod leaped on to the left side of the sauropod. However, the ending of the theropod trackway can also be explained as a lack of preservation of subsequent tracks. Bird's hypothesis would be supported by "push-off" marks (pressure-release structures) in the final tracks of the theropod that were formed as it leaped. The sauropod also should have shown a change in its weight distribution or another dramatic change in its behavior. After all, if it had a hungry carnivore hanging on to its flank, the sauropod should have responded to such a stimulus. Consequently, its tracks potentially should reflect such responses, but they do not.

Incredible Stride Lengths

Coal mines in Late Cretaceous strata of North America have been the source of numerous hadrosaurid trackway discoveries (Chapter 11), but an overzealous interpretation by Barnum Brown (Chapter 4) of one particular trackway caused a small paleontological controversy. Brown promoted the bipedal trackway as evidence for an enormous stride length in the tracemaker; he measured the distance between the tracks as nearly 5 meters apart. These data implied that the dinosaur was either the largest bipedal dinosaur ever discovered or that it was traveling at a very high speed. Subsequent analyses of the trackway showed that Brown had overlooked the possibility of missing tracks in the sequence, and, sure enough, one was found in between the originally measured tracks. This oversight meant that Brown measured stride length as pace length, effectively doubling the former parameter. Consequently, the trackway indicated an average-sized hadrosaurid that walked at a normal speed. One way Brown could have avoided the misinterpretation would have been to look for pressure-release structures that indicated the direction of movement for each individual footprint. This procedure would have quickly determined whether he was measuring from a left footprint to a right footprint (pace) or a left footprint to a left footprint (stride). In some case, such mistakes are understandable, as the outlines of some ornithopod and theropod tracks are nearly bilaterally symmetrical, which makes discrimination of right and left footprints more difficult.

Hopping, Galloping, or Walking Backward

Modern animals show a wide variety of behaviors in their locomotion that depend on their anatomical adaptations for movement or responses to environmental stimuli. For example, horses change from walking to trotting to cantering to galloping in what appears to be one smooth, continuous sequence. Such a continuum has not yet been recognized in a dinosaur trackway. Neither have other aberrant modes of locomotion, such as hopping, galloping, or reversing direction, been found. Typical track patterns observed in modern mammals, in addition to qualitative data (pressure-release features) associated with individual tracks, can be used for comparison with dinosaur tracks to test hypotheses of dinosaur behavior.

Paleoecological Information Gained from Dinosaur Tracks

Dinosaurs of all sizes generated stresses on substrates through their locomotion, and certain parameters of these substrates are discernible by examining their tracks. Substrate conditions that have already been mentioned are water content and sediment cohesiveness; however, sufficiently repeated stresses can change those conditions. Sediment disturbance by organisms is called bioturbation, an extremely common process produced by invertebrates and vertebrates in nearly every sedimentary environment on the Earth's surface. The products of bioturbation, if preserved in the geologic record, are bioturbate textures. The term ichnofabric is synonymous with bioturbate texture if it occurs in sediment, but also refers to the products of bioerosion, which occurs in solid substrates (e.g., rock, wood, and bone). The movement of animals in and on a substrate produces a large variety of

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