RE: Making Tracks

From: Glenn Morton <glennmorton@entouch.net>
Date: Wed Apr 07 2004 - 06:54:54 EDT

-----Original Message-----
From: asa-owner@lists.calvin.edu [mailto:asa-owner@lists.calvin.edu]On Behalf Of Bill Payne
Sent: Monday, April 05, 2004 10:31 PM
To: smsmith@usgs.gov; ksharman@pris.bc.ca

>It didn't happen all at once under your scenario. That doesn't mean it didn't happen all at once.

and

>Since you have access to and are familiar with the Morrison, why don't you take some time and present a reasoned response?
>That might be helpful.

and

>At this point I don't know how many footprints there really are. If there was a raft(s) of vegetation with dinosaurs and
>the dinos got separated as the raft began to break up, and they landed in different areas, then widely separated individuals
>could make tracks that are being interpreted as migratory. Before you blast me, you need to explain where/what they ate.

Bill, you should look at http://home.entouch.net/dmd/termites.htm. Much of that data is from the Morrison formation. There are cicadas, termites, dino tracks. When you say that it didn't happen all at once, how to you explain cicada burrows. You know, cicadas have a life cycle of several years. As to how many tracks, there are billions of tracks throughout the west at multiple layers.

Here is are several descriptions

Jurassic
     "The Entrada is another eolian, sand sea deposit that has traditionally be regarded as devoid of paleontological evidence. Although bones are restricted to one occurrence, recent discoveries reveal the presence of tracks at about thirty sites in eastern Utah. All the tracks known to date re those of medium to large carnivorous dinosaurs.
     "Almost all reported Entrada Sandstone tracksites are associated with the very top of the formation in the vicinity of Arches National park, near Moab, Utah. These sites, however, are not isolated concentrations or patches of tracks in different layers or strata. They are all part of a single vast expanse of tracks covering an area of over 300 square miles (about 1000 square kilometers) and occuring only in the uppermost (youngest) layer of the formation, where it passes up into the overlying strata of the Summerville Formation. Figure 4.35 maps the occurrences of these Entrada sites.
     "Such extensive track﷓bearing layers have been referred to as 'megatracksites.' Megatracksites in general, by definition, are regionally extensive. Significantly, they tend to be associated with the tops of formations, that is, at the boundaries or contacts between formations. In the case of the Moab megatracksite this can lead to some confusion. Were the tracks made during the final stages of Entrada time or at the beginning of Summerville deposition in this area? There is even a third possibility﷓﷓that the tracks were made after the accumulation of Entrada Sandstone but before the beginning of Summerville deposition. In other words, the tracks represent dinosaur activity during a hiatus or break in sediment accumulation.
     "Such breaks in sediment deposition are well known to geologists and are termed *unconformities* (where a deposit rests without conformity or continuity on the deposit below it). Tracks are often associated with such unconformities. This is a paradox, in a way, almost a contradiction: a record of dinosaurs where the rock is missing."
     Regardless of the complexities involved in the geological sequence of formations in this region, we can state that the Moab megatracksite is associated with some type of unconformity or hiatus late in the middle to late Jurassic. We also know that this is the oldest megatracksite currently known and tht, like the Cretaceous examples to be discussed in chapter 5, the track﷓bearing layers represent some type of low﷓lying coastal plain environment, probably close to sea level. In such coastal settings, broad low﷓lying regions are subject to inundation by the sea or to wetting by proximity to coastal lagoons and waterways. Overall, a megatracksite is a sign that extensive areas were good for trackmaking.
     "Estimates suggest that there are literally billions of tracks in the Moab megatracksite. One track per square meter equals one million per square kilometer. In more heavily trampled or dinoturbated areas, ten tracks per square meter equals ten million per square kilometer, and so on. So, in this thousand﷓square﷓kilometer area there are between one billion and ten billion tracks, based on an average density estimate of between one and ten per square meter. Bearing in mind the unconformity phenomenon, such astronomical footprints numbers and trampling are not necessarily attributable to a huge rise in the population of dinosaurs. One must be careful not to jump to a biological conclusion and postulate a population explosion. Instead, the track zone results largely from the long span of time during which the substrate was available for trackmaking, and the simple fact that conditions were suitable for the preservation of this zone. Whatever the cause, the large nu!
mber of tracksites and tracks available for study represents an explosion in available data for paleontologists. Figure 4.36 gives a visual indication of the wealth of tracks available from just one part of the megatracksite, known as the 'Stomping Ground.' here we see about 2,300 tracks in an area of about two acres.
     " Like the majority of Carmel Formation footprints, tracks from the Entrada﷓Summerville boundary sequence are all attributable to three﷓toed dinosaurs, probably theropods....
      "One track﷓bearing bed about five meters below the main Entrada﷓Summerville boundary level contains an assemblage of smaller theropod tracks, with foot lengths of about 15 cm." ~ Martin Lockley and Adrian P. Hunt, Dinosaur Tracks, (New York: Columbia University Press, 1995), p. 152-157
**
Jurassic
     "We now know of four pterosaur tracksites, two in the Summerville-Sundance marine coastal deposits and two, including Stoke's original report, said to be immediately above this level in the lower part of the Morrison Formation (our own investigations at Stokes' original *Pteraichnus* locality in Arizona have revealed tracks in the top of the Summerville, not in the Morrison)." ~ Martin Lockley and Adrian P. Hunt, Dinosaur Tracks, (New York: Columbia University Press, 1995), p. 161
**
Jurassic Morrison
     "One of the most recent and interesting Summerville finds was the discovery, by geologist John Robinson, of several sauropod footprint casts showing skin impressions. (A cast is a preserved infilling of an impression.) The sauropod casts were found near the contact between the Tidwell Member of the Summerville and the overlying Saltwash Member of the Morrison Formation, near bullfrogs, Utah, on the north side of Lake Powell. This find represents the first report of skin impressions from a sauropod footprint anywhere in the world." ~ Martin Lockley and Adrian P. Hunt, Dinosaur Tracks, (New York: Columbia University Press, 1995), p. 163
**
Jurassic
     "Nevertheless, at least thirty fossil footprint sites are known from the Morrison Formation." ~ Martin Lockley and Adrian P. Hunt, Dinosaur Tracks, (New York: Columbia University Press, 1995), p. 164
**
Jurassic
"The Rancho Del Rio dinosaur tracksite in Colorado reveals at least six bedding surfaces in the Morrison Formation that contain tracks, some with extensive dinoturbation." ~ Martin Lockley and Adrian P. Hunt, Dinosaur Tracks, (New York: Columbia University Press, 1995), p. 166 Figure 4.46 This is over a 15 meter interval
**
Jurassic
     "These small sites, though important, are dwarfed by the late Jurassic tracksite in the Purgatoire Valley of southeastern Colorado. The Purgatoire site is now famous as one of the world's largest and most spectacular dinosaur footprint assemblages. it is accessible for viewing by tourists and amateurs, as well as by professionals. Over 1,300 dinosaur tracks have been mapped in a single layer (level 2 in figure 4.49), and tracks occur at three additional levels. The footprints indicate an animal community dominated by sauropods and theropods of different sizes.
     "The huge extent of the Purgatoire site, which is about 400 meters in its longest dimension, has made it particularly useful for reconstructing the ancient environment in which dinosaurs of the Morrison thrived. Along with the tracks can be found fossils of plants, algae, snails, clams, crustaceans, and fish﷓﷓all indicative of a freshwater or slightly alkaline lake." ~ Martin Lockley and Adrian P. Hunt, Dinosaur Tracks, (New York: Columbia University Press, 1995), p. 166-167
**
Jurassic
"Figure 4.54 A trackway that includes clam fossils. Some of the clams appear to have been crushed by brontosaur trampling." ~ Martin Lockley and Adrian P. Hunt, Dinosaur Tracks, (New York: Columbia University Press, 1995), p. 173
**
Jurassic
"It was not just the sediment that was disturbed; at one level clams have been crushed and destroyed by the impact of brontosaur feet and plant stems have been flattened into the limey lakeshore sediments." ~ Martin Lockley and Adrian P. Hunt, Dinosaur Tracks, (New York: Columbia University Press, 1995), p. 173

You must explain why the dinosaur tracks got progressively larger from the Triassic through the Cretaceous.

And they aren't just in the Morrison. Note that this happens on 160 different layers. That says clearly it didn't happen all at once

     "The Jingdong Formation tracks are of particular interest because they occur at as many as 160 distinct horizons throughout 300 m of gray shales and siltstones that comprise the formation. Although multiple trackbearing horizons are known from many formations, few formations reveal the wealth of trackway data yielded by the Jindong succession. To date more than 250 discrete trackways have been recorded and mapped." ~ Seong-Kyu Lim, Seong-Young Yang and Martin G. Lockley, " Large Dinosaur Footprint Assemblages from the Cretaceous Jindong Formation of Southern Korea," in D. D. Gillette and M. G. Lockley(eds.), Dinosaur Tracks and Traces, (Cambridge: Cambridge University Press, pp 333-336, p. 333
Received on Wed Apr 7 06:58:00 2004

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