Brachiopods Appear and Disappear

What is a fact?

"Facts and theories are different things, not rungs in a heirarchy of increasing certainty. Facts are the world's data. Theories are structures of ideas that explain and interpret facts. Facts don't go away when scientists debate rival theories to explain them.

"Moreover, 'fact' doesn't mean 'absolute certainty'; there ain't such an in animal in an exciting and complex world ... In science, 'fact' can only mean 'confirmed to such a degree that it would be perverse to withhold provisional consent."

Stephen J. Gould "Evolution as Fact and Theory", in discover, May, 1981.

Facts on Brachiopods

For paleontologists, facts are the collected observations of thousands of scientists, recorded in the scientific literature. If we had a complete listing of all articles on a certain animal, we would be able to determine where and in what strata the animal had been found.

Fortunately, there is such a list for brachiopods. The Smithsonian Institution has compiled a bibliography of 24,400 articles published on brachiopods from 1607 through 1995 and indexed them by period, location, and genus.

If we look at all of the references for each genus of brachiopod we have found we will have a picture of how these animals are distributed through the geologic column.

What I want you to do is develop a chart showing in which periods each genus of brachiopods has been found. The final product should look like this (with fossils from Davidson County on top and fossils from Decatur County on the bottom.

Genus	Cambrian	Ordovician	Silurian	Devonian	Carboniferous	Permian	Triassic	Jurassic	Cretaceous	Tertiary	Quaternary
Hebertella	-	-	-	-	-	-	-	-	-	-	-
Lepidocyclus	-	-	-	-	-	-	-	-	-	-	-
Platystrophia	-	-	-	-	-	-	-	-	-	-	-
Rafinesquina	-	-	-	-	-	-	-	-	-	-	-
Resserella	-	-	-	-	-	-	-	-	-	-	-
Rhynchotrema	-	-	-	-	-	-	-	-	-	-	-
Zygospsira	-	-	-	-	-	-	-	-	-	-	-
Discomyorthis	-	-	-	-	-	-	-	-	-	-	-
Gypidula	-	-	-	-	-	-	-	-	-	-	-
Leptaena	-	-	-	-	-	-	-	-	-	-	-
Levenea	-	-	-	-	-	-	-	-	-	-	-
Meristella	-	-	-	-	-	-	-	-	-	-	-
Pseudoatrypa	-	-	-	-	-	-	-	-	-	-	-
Schuchertella	-	-	-	-	-	-	-	-	-	-	-
Sphaerirhynchia	-	-	-	-	-	-	-	-	-	-	-
Uncinulus	-	-	-	-	-	-	-	-	-	-	-

What would you expect this distribution to look like? It all depends on what hypothesis you support.

Hypothesis 1: Most sedimentary rocks were deposited in the flood. Since brachiopods are all bottom dwelling animals, they were all buried at the bottom.
Hypothesis 2: Most sedimentary rocks were deposited in the flood. Some brachiopods are attached to the bottom, and these were likely buried at the bottom. However, a few, like Leptaena and Rafinesquina were not attached and could have been swept up in currents and have settled later.
Hypothesis 3: Most sedimentary rocks were deposited in the flood. The turbulence of the flood would have been so great that most brachiopods would have been swept from their original sites. Their distribution is primarily random.
Hypothesis 4: Most sedimentary rocks were deposited in the flood. The turbulence of the flood would have been so great that most brachiopods would have been swept from their original sites. The fossils are distributed by differential settling, i.e. the heavier ones settled first.
Hypothesis 5a:. Fossils have been deposited over a very long time period. Brachiopods have emerged at different times, lived for a while, and then mostly become extinct.
Hypothesis 5b: Same as above, with the addition that Site 1 and Site 2 were deposited at different times.
Hypothesis 6: Can you come up with another one?

When looking at a large collection of data, it is useful to make written predictions about what your results will look like before . Consider the hypotheses listed above and try to predict what strata the fossils will be found in.

Now let's look at the facts.

Building Databases

For this exercise, I am using data on the brachiopods which are in your collection.

Your students can access the data in the Brachiopod Database in three ways:

The easiest way: They can use the simplified summaries of the data which I have constructed.

Genus	Simplified Spreadsheet
Hebertella	data
Lepidoculus	data
Platystrophia	data
Rafinesquina	data
Resserella	data
Rhynchotrema	data
Zygospira	data
Discomyorthis	data
Gypidula	data
Leptaena	data
Levenea	data
Meristella	data
Pseudoatrypa	data
Schuchertella	data
Sphaerirhynchia	data
Uncinulus	data

Somewhat more challenging: They can use the complete bibliographies, extracted from the website.

Genus	Simplified Spreadsheet
Hebertella	data
Lepidoculus	data
Platystrophia	data
Rafinesquina	data
Platystrophia	data
Resserella	data
Rhynchotrema	data
Zygospira	data
Discomyorthis	data
Gypidula	data
Leptaena	data
Levenea	data
Meristella	data
Pseudoatrypa	data
Schuchertella	data
Sphaerirhynchia	data
Uncinulus	data

Most challenging: Work from the Smithsonian Brachiopod Database. itself.

My description I how I have worked with the data, will give you help in analyzing it.

Once you have completed your chart, consider

What evidence there is to support each of the hypotheses you are considering?
Which hypothesis explains the data best?

I assume that high school students can build this chart by themselves. If you have trouble, or if you don't have time to complete it yourself, I have posted the completed chart in my Extinction exercise (under mass extinctions)

Return to main exercise