In Texas, United States
Size:  (not chosen)
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The site is in the bed of the South San Gabriel River. Access is by hiking along the river.
Access to this cache site (if the water is low) is by walking and wading up the river from US 183. Parking at N30 37.160 W097 51.610.
DANGER! DO NOT ATTEMPT THIS EARTHCACHE IF THE WATER IS HIGH! DANGER!
Tools you will need: a camera and a tape measure
Did you know that at one time all of central Texas had an ocean view? Back in the Cretaceous time (about 65 to 145 million years ago), much of central Texas was covered in warm, shallow seas. At the cache site, you will find yourself standing on rock exposed in the bed of the South San Gabriel River. The rocks here belong to the Upper Glen Rose and Walnut Formations, rocks of lower Cretaceous age. The rock is limestone, which is composed of calcium carbonate, along with some clays and sand. As you look around, one of the most striking things you should notice is that there is a distinct trackway of three toed prints visible in the exposed rock. These three toed prints were made by a theropod dinosaur. Perhaps the most famous of the theropods is the well known Tyrannosaurus rex. Another well known theropod is the Velociraptor. The theropods were a numerous group of dinosaurs and include our present day birds. In any case, there is not enough information to determine the species of the theropod that made the tracks that you have in front of you. Still, there are things that we can learn from the trackway.
Studies of theropod skeletons has shown that the height of the hip joint is related to the length of the foot. The hip, for the larger theropods, can be estimated to have a height of 5*(individual print length). The total length of the theropod, head to tail, can be estimated as 10*(individual print length).
So, was our dinosaur walking, trotting, or running? Studies have shown that if you take the stride length and divide it by the hip height, the resulting fraction indicates the type of movement:
Stride length is the distance between two successive foot prints (remember, this is not each step but rather either left-left or right-right), SL.
Hip height, H
If SL/H is less than or equal to 2.0, the dinosaur was probably walking
If SL/H is between 2.0 and 2.9, the dinosaur was probably trotting
If SL/H is greater than 2.9, the dinosaur was probably running.
To log this cache, you will need to do the following:
1) Post a picture of yourself and your GPS at the site
2) Post a picture of your GPS and one of the tracks
Email me the following information:
3) Determine the average length of the stride (see above)
4) Determine the average length of the foot prints
5) What do you calculate the hip height to be?
6) What do you calculate the total length of the theropod to be?
7) Was the dinosaur walking, trotting, or running? Why?
8) We know that the sediment that the rock was formed from was deposited in a shallow sea. What additional information about the depositional environment does the presence of foot prints from a terrestrial dinosaur give us?
(No hints available.)
Last Updated: on 8/10/2014 6:06:35 PM Pacific Daylight Time (1:06 AM GMT)
Coordinates are in the WGS84 datum