Fossils and Evolution Slides

Steven Dutch, Professor Emeritus, Natural and Applied Sciences, University of Wisconsin - Green Bay

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About Fossils

	Fossils only occur in sedimentary rocks. Well, most of the time. This is a mold of a tree trunk from a lava flow in Hawaii. Now it's no particular news to know there were palm trees in Hawaii a few centuries ago, but a similar mold from a Silurian lava flow would be very significant indeed.
	There are a lot of things that look like fossils but are not. The nodule on the right is a concretion, a structure formed where the cement in the rock was a bit different from its surroundings. Concretions can sometimes form around fossils (you will see an example later), but the concretion itself is not a fossil. On the left, the fern-like patterns are dendrites, formed by crystals of manganese oxide and other minerals, very much the way similar patterns form in frost on a window pane. Structures that superficially resemble fossils are called pseudofossils.
	This structure looks something like a shell, with fine radiating lines, but it's another pseudofossil, actually a variety of dendrite that formed on a fine crack in the rock. In general, if something looks like it might be a fossil, it probably isn't. It's only a fossil if it's obvious beyond doubt.
	This looks like a vaguely erotic sculpture, but actually it's a very large and ornate concretion.
	Having seen there are things that look like fossils but are not, it's a bit easier to understand that some people once seriously questioned whether fossils really were the remains of living things. Some held they were natural but inorganic, others that they were supernatural to test our faith or tempt us. One advocate of the inorganic school was Johannes Beringer, who collected the specimens here, now on display in the museum at Wurzburg, Germany.
	Beringer published this elaborate book to advance his theories. Unfortunately, even a cursory glance at Beringer's specimens shows that they're fakes. Two colleagues, who despised Beringer's pompous behavior, planted abundant fakes at Beringer's real fossil locality. For the full story, see Stephen Jay Gould's "The lying stones of Wurzburg and Marrakech," in the April 1998 issue of Natural History.

Kingdom Protista

	These single-celled organisms are free-swimming and build calcareous shells. The disks, a centimeter in diameter, are the great blue whales of Kingdom Protista. The small spindle-shaped shells make up the limestone of the Pyramids. The Greek traveler Herodotus was told that they were petrified grains of wheat eaten by the workers who built the Pyramids (telling a good yarn for the tourists is an ancient craft!)
	Single-celled plant-like organisms are the algae, seen here in Lake Winnebago (yummy!) Free-swimming forms color the water green while filamentous colonial forms grow from the rocks.
	During the Precambrian, the tidal flats of the world were dominated by colonial algae called stromatolites that built mound-like colonies. The appearance of bottom grazing organisms ended the dominance of the stromatolites, though they are found in a few places today. This fossil is at High Cliff State Park.

Kingdom Animalia

	The simplest organisms with distinctly different types of cells for specialized functions are the sponges and their relatives. A modern sponge is at upper right. Thw two fossils are organisms of uncertain affinity that are thought to be sponge-like. The banded specimen occurs as water-worn pebbles on the Lake Michigan shore, and is sometimes called "Lake Michigan Agate." Its scientific name is stromatoporoid.
	The coelenterates are the simplest organisms that have three distinct cellular layers, typical of all more complex animals. Jellyfish like these are 98% water and are rarely fossilized for obvious reasons.
	The coelenterates called corals are abundant in the geologic record.
	Brachiopods were abundant in the Paleozoic and still exist in a few places. They superficially look like clams but are completely different in their internal organs. Best way to tell them apart: clams have asymmetrical shells but the two mating shells are (usually) identical. Brachiopods have symmetrical shells but the two mating shells are different.
	Mollusks are abundant fossils. During the Paleozoic, cephalopods, relatives of the nautilus, squid and octopus, were abundant. Some had coiled shells like a nautilus, others had long straight conical shells.
	The most abundant organisms in terms of number of species are the arthropods, including insects, spiders, scorpions, and crustaceans. Most of the fossils shown here are trilobites, which were abundant throughout the Paleozoic but then became extinct.
	Echinoderms include starfish, sand dollars and sea urchins. Crinoids are something like starfish on a stalk. They were abundant in the Paleozoic and still live in some deep ocean areas.
	Chordates are organisms with a stiffening rod along one side. They include mammals, birds, reptiles, amphibians, several classes of fish, and several classes of simpler organisms, including things one would scarcely guess at first sight were chordates.
	A few chordate fossils. If you find a piece of rock with a white lump in it, you can be absolutely certain it is not a bone Real fossil bones are dark brown because of mineralization.
	Dinosaur tracks near Denver, Colorado.
	Probably the most dramatic intermediate fossil form. Archaeopteryx ("ancient winged one") has feathers but its skeleton is purely reptilian with four fully-formed paws, a bony vertebrate tail and jaws with teeth.
	Few subjects have been as rich a source of hoaxes as the origins of humans. The photos purportedly show ancient giant fossil footprints but the author made the mistake of putting a real foot in the photograph. Real feet are narrower and the line acoss the toes slants more sharply back than the fakes. In the 19th century, a celebrated fake fossil of a petrified giant human was exhibited in Cardiff, New York and came to be called the "Cardiff Giant." Showman P.T. Barnum tried to buy it for his museum. When the owner refused to sell, Barnum decided a fake is a fake is a fake, had one carved, and put the fake fake on display anyway!

Kingdom Fungi

Fungi differ so fundamentally from other plants that they are now considered a separate kingdom. Since they lack hard parts they are rarely fossilized.

Kingdom Plantae

	Spore-bearing plants include the mosses (shown here) as well as several other groups of plants.
	Club mosses are small spore-bearing plants today but their Paleozoic relatives grew to tree size.
	Horsetails are closely related to club mosses.
	Ferns are the best-known spore-bearing plants.
	During the Paleozoic, ferns grew to tree size. There are still some tree ferns in the world. These, near Kilauea in Hawaii, are six inches thick and 30-40 feet high.
	Fossils of ferns and their allies. The scaly specimen is a piece of bark from a tree rather like a giant horsetail. It dropped branches as it grew, leaving the distinctive scar pattern on the bark
	The simplest true seed plants are the conifers.
	Metasequoia, shown here, was abundant worldwide in the Mesozoic but thought to be extinct until it was discovered growing in a remote region in China. A redwood forest, not a jungle, was the world of the dinosaurs.
	Angiosperms, or broad-leaved plants, are the most complex and abundant plants. This maple tree is an example.
	These fossil leaves from Illinois occur within concretions. The organic matter of the leaf changes the chemistry of the surrounding rock enough to cause the precipitation of a different kind of cement. However, the concretion itself is not a fossil.
	How easy is it to make a fossil? These leaf prints on a sidewalk show that it takes very little time to leave an organic film behind.

References

The true story of the Beringer affair is rather different from the version presented in many textbooks. The most easily accessible reference is:

Stephen Jay Gould, "The lying stones of Wurzburg and Marrakech,"  Natural History, April 1998. Gould bases his account of the Beringer affair on:

Melvin E. Jahn and Daniel J. Woolf, 1963; The Lying Stones of Dr. Beringer, Berkeley, University of California Press, 344p.

And thanks to reader Jason Loxton for pointing out these references.

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Created 16 July 1998, Last Update 13 January 2020