Lepidodendron: A Form Genus EarthCache
Lepidodendron: A Form Genus
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Lepidodendron: A Form Genus
When you arrive at ground zero you will be in a parking lot between two buildings of geological significance. During normal school hours beware of parking in areas that you may get ticketed. If you are lucky enough to get one, there are seven or eight 30 minute parking spots in this lot. You will need a tape measure or some means of measuring the girth of an object to complete this EarthCache.
The building to the east of you is Walter B. Jones Hall and houses the Geological Survey of Alabama and the Alabama State Oil and Gas Board – state agencies not directly affiliated with the University of Alabama, but which have historically been located on the campus since they were formed – 1848 for the GSA and 1945 for the OGB. Walter B. Jones served as the State Geologist of Alabama and Director of the Alabama Museum of Natural History from 1927 to 1961.
The building to the west is Eugene Allen Smith Hall. It is the location of the Alabama Museum of Natural History which until 1961 was a division of the Geological Survey. Eugene Allen Smith served as the second State Geologist of Alabama and served from 1873 to 1927.
Lepidodendron stump
At the posted coordinates, you will find the fossil Lepidodendron stump pictured above along with a small plaque. This stump, as with the other two you will see, is an example of cast fossilization – that is – after death, the original tree became hollow and filled with sediment. Then after the tree completely decomposed, it left a cast of what the inside of the hollowed-out tree looked like.
Question 1: From the plaque, in sediments of what geologic period was this fossil found?
Question 2: Do you find fossilized features of the Lepidodendron tree on the top of the fossil, or the sides, or both? Why?
OK. Now go to the west side of Smith Hall (N33 12.713 W087 32.649). You will be at the front side of the Museum of Natural History. You will see two large stumps similar to the one at the first location on either side of the entrance.
The stump on the north side of the entrance (your left when facing the building) is also labeled as a Lepidodendron.
Question 3: According to the plaque, how many years ago was this stump placed in front of Smith Hall.
Question 4: If we assume a circumference to height ratio of 1:12 for the Lepidodendron tree, what would have been the approximate height of this tree? Take your circumference measurement near the base of the fossil stump.
The stump on the south side of the entrance is labeled as Sigillaria. Both Lepidodendron and Sigillaria are names for now extinct, coal-age tree-sized plants referred to as “scale trees”. These trees were not related to the tree-sized plants that we think of today: angiosperms (such as oak, maple, or birch) or gymnosperms (such as pine, fir, or cedar). They are most closely related to the low-growing plants known as club mosses. These trees were very significant plants during the coal age – the geologic Mississippian and Pennsylvanian periods. Coal balls (a very interesting subject for another time) from Walker County, Alabama, show that over 80 percent of the coalified plant material in the New Castle seam was of scale-tree origin – Lepidodendron, Sigillaria, and/or Lepidophloios.
Question 5: What was the geologic formation that this stump came from?
All that being said, the fact is, the three fossil stumps are technically not Lepidodendron or Sigillaria. Though, the fossil tree is known as the Lepidodendron tree, the fossil that the term Lepidodendron actually refers to is the outer bark of the tree. This is the fossil that looks like snake skin. The scale appearance is caused by the strap-like leaves falling off the bark leaving behind leaf base scars. Sigillaria is another bark pattern attributed to scale trees.
Lepidodendron bark pattern (left) -- Sigillaria bark pattern (right)
This is what is known as a “form” genus. A form genus describes a fossil when the actual affinity of the fossil in unknown. When a tree dies and begins to decompose, the tree falls apart into different pieces. As each of these pieces are discovered in the fossil record, they are given a form genus name to describe them. We now know what the Lepidodendron tree looks like due to the hard work by paleobotanists and a whole lot of luck. The only way to prove that one part of a plant belongs to another is to find a fossil that has both parts in organic connection. For example finding a spore in a cone, a cone or a leaf attached to a stem, or a stem or root attached to a trunk, etc. These kinds of fossils are very rare.
Question 6: From information gathered from the internet, match the form genera names with the anatomical part of the Lepidodendron tree. In some cases this may be difficult -- just do your best.
Anatomical parts:
A. leaves
B. roots/underground stems
C. female cone
D. male cone
E. fertile cone leaf
F. exfoliated trunk
G. spores
Form genera:
1. Lepidostrobus
2. Lycospora
3. Lepidostrobophyllum
4. Lepidocarpon
5. Knorria
6. Lepidophyloides
7. Stigmaria
Question 7: The three fossil trunks that you have examined are actually examples of the exfoliated trunk (trunk of tree with bark removed) of the scale tree. What form genus do these fossils actually belong to?
To log a find on this EarthCache, you must email me the answers to the 7 questions asked above. Please place “Lepidodendron: A Form Genus – GC2BRN7” as the first line in your email. Logs without accompanying email will be deleted. A photo of you near this site is not required, but it would be appreciated – but please, no spoilers in the pics.
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