This is Mazon Monday post #103. What's your favorite Mazon Creek fossil? Tell us at email:[email protected].
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By Falconaumanni - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=56797814
Today, we look at another part of the plant Calamites. Recall that paleobotany uses form genera as a strategy to identify plant parts. If you aren't familiar with the concept, there is a good explanation in the "Keys to Identify Pennsylvanian Fossil Plants of the Mazon Creek Area".
THE CONCEPT OF FORM-GENERA IN IDENTIFYING FOSSIL PLANTS
Biologists and paleobiologists who study and classify organisms often find biological structures that cannot be confidently assigned to any known organismic species. Such structures -- mostly parts, life-stages, or sedimentary traces of organisms contain considerable biological information and provide insights into the morphology, life-style, and behavior of past (and present) species. For example, for many present-day fungi, both the asexual and sexual stages of the life-cycle is known, but each stage cannot be causally linked to the other. These stages may have separate, taxonomic names, yet belong to the same species. Similarly, trace fossils distinctively-shaped impressions and burrows indicating particular behavioral habits are given separate taxonomic names, and are not assuredly linked to any known fossil species.
And so it is with fossil plants, in which particular organs are preserved in isolation from other organs belonging to the same plant species. Thus plant leaves, roots, stems, fruits, seeds, and even pollen or spores, have separate taxonomic names. These names are termed "form genera". Several form-genera, each designating a specific part of the plant, can refer to a single fossil plant species, but it is often impossible to know which leaf-genus is associated with which seed-genus or pollen-genus, and so on.
Furthermore, in some cases it is clear that structures assigned to one form were actually produced by two or more different kinds of plants, e.g., Lepidophylloides produced by both Sigillaria and Lepidodendron. Therefore, even when we can demonstrate, or hypothesize, that two or more form-genera are actually part of a single plant species, we cannot be certain that all fragmentary specimens of the genera are correctly treated in this way. For these reasons, form-genera are an indispensable, if slightly confusing, tool in identifying fossil plants.
For more information of the parts of Calamites, have a look at some of our previous Mazon Monday posts. In Mazon Monday #94, we highlighted Calamites cisti, which is the stem of the Calamites plant. For Mazon Monday #99, we looked at Calamostachys, which is the reproductive cone structure. And, way back in Mazon Monday #60, we had Annularia inflata in the spotlight. Annularia is a foliage part of the plant. An additional foliage part is Asterophyllites and Asterophyllites equisetiformis is the subject of this post.
Asterophyllites equisetiformis was described in 1829 by Alexandre Brongniart, a French chemist, mineralogist, geologist, paleontologist, and zoologist. He described many of the species of Mazon Creek from specimens found in France in the early 1800's. He is probably most known for his work that classified reptiles into four different groups, one of which eventually became Amphibia. Later he collaborated with Georges Cuvier to study the geology of the region around Paris, France.
The "Keys to Identify Pennyslvanian Fossil Plants of the Mazon Creek Area", mentions A. equisetiformis. along with the excellent drawings of Don Auler, Past President of ESCONI.
ASTEROPHYLLITES
Like Annularia, this genus is a series of whorls of linear leaves encircling the nodes of Calamites stems. However, the leaves are narrower, more sharply pointed, and the whorls are usually seen side view, not flattened as in Annularia.
Asterophyllites equisetiformis
Leaf length is equal to or slightly greater than the distance between the nodes.
In "A Comprehensive Guide to the Fossil Flora of Mazon Creek" by Wittry, A. equisetiformis appears on page 65.
Asterophyllites equisetiformis Brongniart, 1829
1829. Asterophyllites equisetiformis Brongniart: p. 159, 176
1879-80. Asterophyllites equisetiformis Brongniart; Lesquereux: p. 35, pl. 2, fig. 3
1899. Asterophyllites equisetiformis (Schlotheim) Brongniart; White: p. 146, pl. 59, fig. 1c
1925. Calamocladus equisetiformis; Noé: pl. 4, fig. 1
1958. Asterophyllites equisetiformis Schlotheim; Langford: p. 43, figs. 49, 50 3
1969. Asterophyllites equisetiformis Schlotheim; Crookall: p. 695, pl. 142, fig.
1969. Asterophyllites equisetiformis Brongniart; Darrah: p. 173, pl. 40, figs. 3, 4
1979. Asterophyllites equisetiformis Brongniart; Janssen: p. 88, fig. 71DESCRIPTION: The number of leaves per whorl ranges from 10 to 20, but they can rarely be counted. The leaves of a whorl are of equal length, and generally as long as or slightly longer than the internode length. They are linear, widest in the middle, pointed at the tip, and all arch upward toward the branch apex. The venation consists of a single, thick midvein.
REMARKS: Asterophyllites equisetiformis is common, and the most common of the Asterophyllites species. Darrah (1969) stated that there is a large range of features seen in fossils of this taxon. The variation in leaf length, number per whorl, and arching make it likely that more than one biological species have been placed in this taxon. This does not seem to be the case in the Mazon Creek flora where this taxon appears to have a consistent set of characteristics.
Specimens
Field Museum via "A Comprehensive Guide to the Fossil Fauna of Mazon Creek".
From an ESCONI member
