The Dakota Group:

The Dakota Group consists of rocks that formed along the western shore of the Western Interior Seaway, a shallow oceanic strait that in Cretaceous time connected the Gulf of Mexico with the Arctic Ocean. These rocks were laid down in lakes, rivers, and river deltas, as well as the ocean. Dakota Group strata extend from central New Mexico more or less northward through Colorado to southern Wyoming (east of the present-day Rocky Mountains and extending westward into the Front Range of Colorado). From northern Colorado to central New Mexico, the upper layers of the Dakota Group (dating to the Albian-Cenomanian) are rich in dinosaur tracks and trackways. These tracks are given added importance by the fact that no dinosaur bones have been found in this part of the Dakota Group; the tracks are the only evidence that dinosaurs once lived in the region. Dinosaur Ridge (See Earthcache: GCMQGG - Dinosaur Ridge EarthCache) , just west of Denver, Colorado, and Clayton Lake State park (See Earthcache: GC2AP6C - Clayton Dinosaur Trackway), in the NE corner of New Mexico, are some well-known and publicly accessible tracksites in the Dakota Group.

Mosquero Creek:

The large dinosaur trackway at Mosquero Creek was discovered by local cowboys. Here there are 55 parallel north-trending trackways of small quadrupedal Ornithopods. This site also contains ten trackways of larger, bipedal ornithopods that were heading in the opposite direction. This evidence is reminiscent of shoreline trackway patterns, in which animals often travel in two opposing directions. The evidence also indicates that small and large animals (presumably representing different age groups of the same species because the tracks are identical except for size) often traveled in separate groups. Overall the Mosquero Creek site is exceptional because it reveals such a large number of parallel trackways. Although it is a relatively small area, there is mapping of the largest concentration of parallel trackways of large ornithopods ever recorded from a single surface. Moreover, the pattern of the outcrop of track-bearing surfaces suggest that there were many adjacent areas where additional trackway eroded away. Thus the total of 55 recorded, parallel trackways is clearly a minimum estimate. Not all the trackways are perfectly parallel, but most conform to two slightly divergent trends. This suggests that there may have been two waves, or groups, of trackmakers that went by at slightly different times. Consistent measurement of the depths of the footprints in all the trackways would suggest that the animals had all passed at more or less the same time (that is, when the substrate had the same consistency).

Basic Terms and Definitions:

Fossilized dinosaur tracks are forms of trace fossils, also known as ichnites or ichnofossils. Unlike body fossils, which are the remains of dead bodies, trace fossils record the active movements and behaviors of ancient organisms. Besides footprints, trace fossils include fossilized burrows, dens, feeding tunnels, eggs, nests, stomach contents, coprolites (excrement), tooth and claw marks, and any other product or trace formed while an ancient organism was still alive. The study of trace fossils is known as ichnology. Some scientists restrict the term to mean the study of fossil traces. Others include both modern and ancient traces, using the term paleoichnology to specify the study of ancient traces. At any rate, the study of modern traces often helps in interpreting ancient traces.

The terms track, print, footprint and footmark are often used interchangeably, although the first two include footprints as well as marks from other body parts, such as a tail, snout, or belly. A series of two or more consecutive tracks by the same animal is known as a trackway or trail.

In 1986 the First International Symposium on Dinosaur Tracks and Traces was held in Albuquerque, New Mexico, bringing together dinosaur trackers from all over the globe. The papers presented at the symposium were subsequently published in a book entitled Dinosaur Tracks and Traces (Lockley and Gillette, Ed. 1989). Subsequently two other books devoted to dinosaur tracks were published: Dinosaur Tracks, by Tony Thulborn (1990), and Tracking Dinosaurs, by Martin Lockley (1991). Each has a slightly different focus, but combined they provide a good review of modern dinosaur tracking.

Information from Dinosaur Tracks:

Some of the most direct information available from dinosaur tracks concerns locomotion. Trackways can indicate whether a dinosaur was walking, trotting, running, or wading. They also show whether the animal was traveling in a bipedal (two-legged) or quadrupedal (four-legged) manner, or altering its gait between these modes. One can also calculate approximately how fast the trackmaker was moving. Additionally, tracks tells us how a trackmaker carried its tail, whether it walked with a narrow or sprawling gait, and in some cases, what posture the animal assumed while resting.

Inspection of individual prints provides data on the size and shape of the trackmaker's feet, and the number the toes. Clear prints can even reveal details of the soft anatomy of the foot, including the pattern of pads and muscles on the feet, and the flexibility of the digits. These track features, combined with trackway patterns, reveal important clues about the identity of the trackmaker.

Tracks also provide clues about the social behaviors of dinosaurs, and the environment in which they lived. Some sites contain dozens of parallel trails heading in the same direction, indicating a herding or migratory behavior. Often such trails seem to indicate the position of an ancient shoreline. Other sites indicate several herbivores clustered around apparent tree impressions, suggesting a feeding group. One interesting site has been interpreted by some as recording an ancient chase scene. Another site appears to record a dinosaur "stampede" (Thulborn, 1990).

Tracks also complement body fossils in providing information about geographic distributions of dinosaur groups, as well as their chronologic ranges. Knowledge of ancient ecology and population biology can also be expanded by studying dinosaur tracks. For example, researchers may tabulate the ratio of carnivore to herbivore tracks in a region, or the proportions of large to small trackmakers.

How to Observe and Record Tracks and Trackways:

Tracks vary considerably in size and shape, and trackways vary in the number and distribution of prints. A systematic approach for describing and recording them is essential.

The first step in measuring vertebrate tracks and trackways is to record the size and shape of individual hind and fore footprints and the distances and angles between the steps. The hind foot is also known as the pes and the fore foot as the manus. Measurements of individual footprints tell us how big the trackmaker was, how many weight-bearing digits it had on its feet, and whether it had larger hind feet than fore feet, as in most dinosaurs, or larger front feet than hind feet as in many mammals. Using your own hands and feet as a model, we can count toes or fingers one to five (I-V), following the convention that the thumb and big toe are I and the little toe and finger are V.

Animals whose limbs end in five digits, and tracks with five-digit impressions, are referred to as pentadactyl. Humans, bears, and some lizards - and the tracks they make - are prominent examples today. Tetradactyl trackmakers have four functional digits on each limb, as in hippos, cats, and dogs. Tridactyl trackmakers, such as tapirs and some birds, are three-toed. A two-digit or functionally didcatyl condition is common today in cud-chewing mammals such as sheep, cattle, and deer. A single-toed condition is called monodactyl and is found in horses.

Counting the number of toes in a fossil print is the first step in its identification. There are many fossil examples of tracks with different numbers of toe impressions. Is is these fundamental differences in shape and size of tracks, as well as the configuration of the trackways, that ultimately allow us to identify the trackmakers. We must exercise caution, however, in noting that not all of an animal's toes may touch the ground. For example, four-toed birds often leave tracks with three-digit impressions.

In any discovery of footprints it is important to record the trackway configuration, which includes step and stride length, trackway width, and the degree to which feet are placed at an angle to the general direction of travel. This information will help determine, first, if the animal was two footed (bipedal) or four footed (quadrupedal). Did it have long legs and a short body, like a camel, or short legs and a long body like a hippo> With four-footed animals we can reconstruct the trunk length by using the trackway to estimate the positions of the hip and shoulder sockets. Trackway data also reveal whether an animal was an erect walker, with a narrow trackway, or a sprawler, with a wide trackway. We will also learn if the trackmaker's feet rotated in (pigeon-toed) or out (duck-footed). Finally, we can determine if the animal was walking, running, hopping, or moving in some other fashion.

Fossil tracksites generally reveal footprints of more than one animal and often several different species or types. At sites with dozens - even hundreds - of trackways, you can make a map of the whole site and count the different individuals that made the tracks and from this derive the relative abundance of each species or type.

FURTHER READING

• Lockley, M. G. 1991. Tracking Dinosaurs. Cambridge University Press. Cambridge, England.
• Gillette, D.D. and M. G. Lockley, editors. 1989. Dinosaur Tracks and traces. Cambridge Uni versity Press, Cambridge, England.
• Lockley, M. G. and Hunt, A. P. 1995. Dinosaur tracks and other fossil footprints of the western United States. New York, Columbia University Press, 338 pp.
• Lucas, S. G. 1993.Dinosaurs of New Mexico. Albuquerque, New Mexico Academy of Science, 130 pp.
• Thulborn, T. 1990. Dinosaur Tracks. Chapman and Hall, London.

Everything you need to log this cache is available outside the museum. But as long as you are here you might take advantage and visit. The New Mexico Museum of Natural History and Science is open from 9:00 AM to 5:00 PM every day except Thanksgiving, Christmas, and New Years Day. Entry fees can be found on their Hours and Admissions page.

Thanks to the New Mexico Museum of Natural History and Science for assistance in the creation and allowing placement of this EarthCache!