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A Pleistocene Ecosystem
by Wesley Gordon
page 18

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Sixty-Eight Fossil in Eight Hours

At the end of their workday on a Wednesday during summer vacation, the boys were delighted to discover that they had collected sixty-eight specimens. The variety was amazing:

Snails
Clams
Spines, fish
Femur, frog
Femur, toad
Plates, turtle
Lower teeth, horse
Upper teeth, horse
Incisor, camel
3
3
6
1
1
6
2
3
2

Upper teeth, camel
Patella, camel
Metatarsal, camel
Wrist bones, camel
Molar, pocket mouse
Lower jaw, pocket gopher
 
(with incisor, 3 molars)
Claws, unknown
Small vertebrae, unknown

   5
   5
   1
   5
   1
   1
 
   9
 10

Note that the list includes invertebrates as well as fish, amphibians, reptiles, and mammals. Of the five classes of vertebrates, only the birds are missing. Although the nine claws had not been identified at the time of this writing, the entire Irvington fossil collection is being restudied at the university by Jean Firby, a graduate student. It is possible that she will identify a small bone to be that of Tetrameryx, a 2-foot-high antilocaprid. This fossil was found by the author at Irvington more than ten years ago. It was studied first by Firby only recently.

Les Kent Jr, one of the original Boy Paleontologists is at site T2 screening for rodent bones.  A new species of mouse (Peromyscus [Haplomylomys] irvingtonensis Savage) was discovered here by this method.  The sedimentary layers (clay alternating with the fine sand) are dipping 20 to 25 degrees toward the northeast.

The boys found most of their fossils by screening very fine sand from a layer only 9 inches thick. For the sifting process they used window screening. Immediately above this layer of fine sand was a 2-foot bed of cobbles and pebbly sand; below was an undetermined thickness of compact, fine sand. The wide difference in the size of the sedimentary particles indicated that then, as now streams sometimes flowed slowly and sometimes swiftly, depending on the weather. (Swift waters mover larger sediments, such as cobbles. Sand and other fine particles are deposited by slowly flowing streams.)

The reasons for the remarkable concentration of fossils listed are not known. It is not surprising to find clams and snails buried with fish, frogs, toads, and turtles. Nor is it odd to find herbivores such as horses, camels, antilocaprids, and rodents buried together. But to find all of these in one 9-inch layer is amazing!

Can you develop two or three hypothesis concerning this matter? How was so many kinds of animals buried together? Were they all buried at the same time, alive? If not, how do we explain this concentration of fossils? Incidentally, none of these small fossils seemed to have been carried very far by water. Even under a 20-power hand magnifier, they showed no rounded or smoothed areas.

If you do attempt to reconstruct a moment in time at Irvington by using only animals on the above list, carnivores cannot be included. This problem was expressed by one of the boys: A food pyramid without carnivore? Not possible! Was he right?

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