This is Mazon Monday post #60. What's your favorite Mazon Creek fossil? Tell us at email:[email protected].
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This week, we are looking at a species of Annularia. Annularia is actually the foliage of a 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. In life, the plant would have looked something like this, 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.
The description of Annularia inflata appears on page 58 and 59.
Annularia inflata Lesquereux, 1870
1870. Annularia inflata Lesquereux: p. 423, pl. 20, figs. 1, 3; non pl. 20, fig. 2 = Annularia latifolia
1870. Annularia longifolia Brongniart; Lesquereux: p. 423, pl. 20, fig. 4
1879-80. Annularia inflata Lesquereux: p. 47, pl. 2, fig. 2; non pl. 2, fig. 1 ?Annularia radiata
1880. Annularia longifolia White: p. 521, pl. 11, fig. 1; non pl. 11, fig. 2
1925. Annularia stellata Wood; Noé: pl. 3, figs. 1-5
1938. Annularia stellata forma mucronata Bell: p. 85, pl. 89; non pl. 90, fig. 1
1958. Annularia stellata Wood; Abbott: p. 321, pl. 35, fig. 1; pl. 36, figs. 8, 9; pl.41, fig. 58
1958. Annularia stellata Wood; Langford: p. 39, figs. 38, 39
1969. Annularia stellata Wood; Darrah: p. 172, pl. 37, fig. 1
1979. Annularia stellata Janssen: p. 84, fig. 67
1979. Annularia radiata Janssen: p. 85, fig. 68
2017. Annularia inflata Lesquereux; Álvarez-Vázquez and Wagner: p. 26, figs. 4, 5DESCRIPTION: The whorls slightly overlap and lay on the same plane as the axis. The leaves, 20 to 28 per whorl, vary in length, making the whorl appear elliptical rather than round. The widest part is at a right angle to the axis and up to 10 cm wide; the shortest leaves are on the proximal side. The leaves are enrolled at the margins and widest in the upper-third of the leaf. The apex is obtuse, though it appears variable, even on the same whorl due to the amount of compression and enrollment. At the tip of the leaf, there is a short, sharp point (see Fig. 3 inset) referred to as a mucro. This is most often lost in the matrix and not seen. A strong midvein is the only venation, though it is often missing due to poor preservation.
REMARKS: Annularia inflata is common, though only the third most common annularid. The form described here, when found in North America of similar age, had been called Annularia stellata (= Annularia spinulosa) by previous authors. Since their writing, the range of features of A. stellata = A. spinulosa has been better defined and found dissimilar enough to reject its use for the Mazon Creek form. It is replaced by A. inflata in the Mazon Creek flora, a name which was originally erected using Mazon Creek fossils as the type examples.
The book "Keys to Identify Pennsylvanian Fossil Plants of the Mazon Creek Area" provides some nice hints to identify Annularia.
