This is Mazon Monday post #201. What's your favorite Mazon Creek fossil? Tell us at email:[email protected].
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Annularia latifolia is one of the rarer forms of Annularia. It was named in 1862 by John William Dawson (1820-1899), a Canadian geologist. He was a professor of Geology at McGill University in Montreal. He described fossil plants from the Silurian, Devonian, and Carboniferous. He is considered one of the founders of the science of paleobotany.
From Wikipedia:
From 1855 to 1893 he was professor of geology and principal of McGill University in Montreal, an institution which under his influence attained a high reputation. In 1859 he published a seminal paper describing the first fossil plant found in rocks of Devonian origin. Although his discovery did not have the impact that might have been expected at the time,[3] he is now considered one of the founders of the science of palaeobotany. He later described the fossil plants of the Silurian, Devonian and Carboniferous rocks of Canada for the Geological Survey of Canada (1871–1873). He was elected FRS (Fellow of the Royal Society) in 1862. When the Royal Society of Canada was created he was the first to occupy the presidential chair, and he also acted as president of the British Association at its meeting at Birmingham in 1886, president of the American Association for the Advancement of Science in 1882,[4][5] and president of the Geological Society of America in 1893.[6]
Annularia is the foliage of the plant called Calamites. Calamites is classified as a Sphenopsid, which is a primitive vascular plant characterized by jointed ribbed stems and small leaves usually in whorls at distinct stem nodes. Its closest living relative are the horsetails. The full plant would have had a form like the image below, with some individual plants reaching tens of meters tall.
The following text is from "A Comprehensive Guide to the Fossil Flora of Mazon Creek" by Jack Wittry
SPHENOPSIDA: RELATIVES OF THE HORSETAILS
Modern horsetails all belong to the genus Equisetum and are the distant relatives of the ancient tree-like Calamites and the vine-like Sphenophyllum. They are closely related to and even considered by some researchers to be members of the fern family. Calamites grew to about 30 feet tall, and like today's horsetails, preferred moist lake or river shorelines where they formed dense monospecific stands. Sphenophyllum was a relatively small plant that made up a small part of the forest under story. Both reproduced by spores that were shed from cones hanging from branch tips. Cones are assigned to six genera: Calamostachys, Palaeostachya, the less common Mazostachys, Bowmanites, Macrostachya, and the very rare Tetraphyllostrobus. The foliage of Calamites is placed into two genera: Annularia and Asterophyllites. As with the description of Lepidodendron, the name for the trunk and stems is shared with the plant name Calamites.
In Sphenophyllum, there are only two identified species found in the Mazon Creek flora. All other names found in the literature could not be confirmed and were often placed on small, poorly preserved, or partially buried specimens of what otherwise may have been recognized as one of the common forms.
The stem fossils of calamites have often been referred to as pith casts made by the in-filling of their hollow pith cavity. This has now been shown not to be the case (DiMichele et al., 2012). It was demonstrated that most are really casts of the exterior of the stem, and that the outside of the stem of calamites appears nearly identical to casts made of the pith cavity. In either case, the name remains the same and the descriptions for both preservational aspects are the same. It is possible to distinguish between the two if vascular canal scars are present on the ribs near the nodes. Only the pith casts will display them.
Annularia latifolia is covered on page 60 of "A Comprehensive Guide to the Fossil Flora of Mazon Creek".
Annularia latifolia (Dawson) Kidston 1886
1862. Asterophyllites latifolia Dawson: p. 311, pl. 13, fig. 17
1870. Annularia inflata Lesquereux: pl. 20, fig. 2
1914. Annularia sphenophylloides non Zenker; Stopes: p. 21, pl. 5, fig. 7
1914. Annularia latifolia non Zenker; Stopes: p. 23, pl. 6, fig. 10, 12; pl. 7, fig. 13; non pl. 6, fig. 11
1958. Annularia latifolia (Dawson) Kidston; Abbott: p. 313, pl. 35, fig. 3; pl. 37, fig. 21
2006. Annularia stellata Wood; Wittry: p. 92, fig. 2
2017. Annularia latifolia (Dawson) Kidston; Alvarez-Vazquez and Wagner: p. 30, figs. 6, 7DESCRIPTION: The whorls occur on a branched axis. There are 18 to 24 leaves per whorl. The leaves touch or slightly overlap at the edges of the whorls. To a varying amount, the lateral leaves are generally longer and the lowermost leaves are shorter. The leaves are widest in the upper third and gradually taper to an obtuse apex with a mucro at the tip. The center vein is wide, poorly marked, and often obscure.
REMARKS: Annularia latifolia is very rare. A. latifolia is difficult to separate from smaller examples of Annularia inflata. They share similarly shaped whorls, leaf shape, and leaf count per whorl. Both have a mucro at the leaf apex. Only the axis architecture is different enough to confidently separate these smaller whorl forms to a species. A. latifolia is the only one of the two where the axis branches at the leaf nodes.
Specimens
From Wittry's "A Comprehensive Guide to the Fossil Flora of Mazon Creek".
From the University of California Museum of Paleontology
