CAMBRIAN TRILOBITES

To understand Cambrian trilobites we should compare them with later developments. It appears that there was an "arms race" which resulted in some trilobites adopting an "enrolled" defensive position, more or less automatically, in ages after the Cambrian. Later trilobites can also have fantastic arrays of spikes and horns and barbs. These trilobites are generally found lying flat, with very little decoration.

1. Elrathia kingii is the trilobite everyone has seen. They are found in Utah, and I have specimens with and without the free cheeks. Free cheeks are lost during molting. There is a great animation of the molting process here, halfway down the page:

http://www.trilobites.info/sutures.htm

2. Ogygopsis is the most common species found in the Burgess Shale, in the Canadian Rockies. My Ogygopsis is missing part of its tail, but it is very special because it actually is from the Burgess Shale.

3. Hunanolenus Genaculatus is from Hunan, China. It is embedded on a thick reddish rock. This Hunanolenus genaculatus trilobite fossil (order Redlichidae) hails from the Cambrian in Hunan Province, Peoples Replubic of China, and is one of the most ancient Trilobita. Good preservation quality with genal spines absent or under the shale, as is usually the case for this species.

4. Agnostid trilobites were blind swimmers, found only in the Cambrian. They are sometimes almost as small as fleas, and in some strata occur in very large numbers. I have three examples, two of them "multiples."

5. Olenellus. This early Cambrian trilobite can be recognized by the long spines both on the carapace and about halfway down the body. I have another much larger specimen of Olenellus gilberti in a separate container. Richard Fortey, in "Trilobite!" speculates that this species may have lived near seafloor vents and taken advantage of the sulfur bacteria there.

6. Calcite crystal. Trilobites are unique among higher animals in having compound eyes with calcite lenses, mounted on their heads. There is evidently a kind of starfish with calcite lenses in its "legs" that allow it to see after a fashion.

7. Hyolithids — most likely related to molluscs. These are described in "Wonderful Life" as the favorite snack of the early sea cucumber. Found commonly in Burgess Shale. Also, the similar looking Orthotheca carinatus, from the Spence Shale.

8. Phyllocarid, "leaf shrimp", Early Cambrian, Maotienshan formation, Chengjiang, Yunnan Province, China. Similar fauna to Burgess Shale but older.

9. Gogia, an eocrinoid from the Spence Shale in Idaho. Crinoids are Echinodems, closely related to sea urchins and starfish, and are deuterostomes (like us).