This is Mazon Monday post #117. What's your favorite Mazon Creek fossil? Tell us at email:[email protected].
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Crenulopteris mazoniana is a somewhat uncommon extinct species of fern from the Mazon Creek fossil flora. It was first named by Leo Lesquereux in 1870 as Alethopteris mazoniana. As seen from its fertile form shown in a specimen below, it was a spore fern unlike the seed fern Alethopteris.
The names of some of these common fern species have tortured pasts, which only makes them harder to classify. In Jack Wittry's first book, "The Mazon Creek Fossil Flora", it was referred to as Pecopteris mazoniana and to add to the confusion Pecopteris miltoni in the ESCONI "Keys to Identify Pennsylvanian Fossil Plants of the Mazon Creek Area". P. miltoni is a British species, which was named by Edmund Tyrell Artis in 1825 as Filicites miltoni.
From George Langford
Asterotheca miltoni. Artis; GL handwritten text.
From the ESCONI Keys.
Pecopteris miltoni
This species was formerly named Asterotheca miltoni. The frond is large and quadripinnate. The pinnules are alternate on, and perpendicular or nearly perpendicular to, the rachis. On the lower portion of the pinna, they are separate. Near the apex of the pinna, the pinnules become united in varying degrees. At the apex of the pinna, the pinnules become merely the crenulate margin of the elongate primary pinnule. The ventral (upper) surface is villous. (hairy).
The venation is thin and indistinct, and often obscured by a covering of fine hairs. The midvein is straight, at a right angle to the rachis, and extends nearly to the apex where it forks.
The lateral veins arise at a 45 degree angle, are straight, fork once near the base, sometimes forking a second time. In larger pinnules, the lower veinlet is commonly unforked while the upper veinlet is forked. The smaller, more terminal pinnules commonly show single forking, with the smallest, united pinnules having unforked veins. In such pinnules the midvein is usually slightly curved.
The fertile pinnules are similar in shape and venation to the infertile. The dorsal surface has Asterotheca-type synangia that are roughly shaped like a star or cross, having four or five arms of unequal length.
This most common of the Mazon Creek Pecopterid fronds, named "miltoni," after a British species by earlier paleobotanists, can be quite variable in size and appearance. A recent restudying of Mazon Creek specimens demonstrates enough consistent differences between the British paratype and those from Illinois, to prompt some workers into advocating naming the species "mazoniana" as did Lesquereux more than a century ago.
Wittry recategorizes P. mazoniana as Crenulopteris mazoniana in "A Comprehensive Guide to the Fossil Flora of Mazon Creek".
Crenulopteris mazoniana (Lesquereux) Wittry, comb. nov.
1870. Alethopteris mazoniana Lesquereux: p. 391, pl. 9, figs. 1-8; pl. 13, figs. 5, 6
1879-80. Pseudopecopteris mazoniana Lesquereux: p. 190, pl. 32, figs. 1-7a, (fig. 2 re-figured here as Fig. 1)
1903. Mariopteris mazoniana (Lesquereux) White
1940. Mariopteris mazoniana (Lesquereux) White; Janssen: p. 58. pl. 14, figs. 1-3, 7
1963. Pecopteris mazoniana (Lesquereux) Langford: p. 206, figs. 809-811, (fig. 809 re-figured here as Fig. 4)
1969. Mariopteris mazoniana (Lesquereux) White; Darrah: p. 122Basionym; Alethopteris mazoniana Lesquereux, 1870. Ill. Geol. Surv., Vol. 4, Report on the Fossil Plants of Illinois. p. 391 pl. 9, figs. 1-8; pl. 13 figs. 5, 6
DESCRIPTION: The pinnae are linear and gradually contract to a blunt apex. The rachis is marked by fine, irregular, longitudinal striations, and is channeled and winged when the upper surface of the pinna can be seen (see Fig. 8). The lower surface of the rachis is narrowed by decurrent pinnules that may overlap at the their bases (see Fig. 5). The mature pinnules on the ultimate pinna (see Fig. 1) are close, oblong, obtuse, joined at the base, slightly oblique to the rachis, and crenate. The margins of the pinnules are generally reflexed. The pinnules are variable in length along the pinna. The venation is very thin and is often totally obscured in the lamina. The midvein is well marked by a groove and is slightly decurrent, becoming thinner near the tip. The lateral veins are distant, rise at a 30° angle, and meet the margins obliquely. They fork once near the base with the lower veinlet becoming straight and meeting the margin at an acute angle. The upper veinlet will remain simple or fork once or twice more. The sori touch each other as they closely follow the edge of the margin, and have an asterothecoid appearance with 4 or 5 sporangia. The isolated spores are correlated with Punctatosporites/Laevigatosporites minutus.
REMARKS: Crenulopteris mazoniana is uncommon. The features of C. mazoniana necessitate its removal from Alethopteris, Pecopteris, and Mariopteris. The spores are monolete and thus quite different from the trilete spores of Pecopteris sensu stricto; the sori most resemble those of the marattialean ferns. The well-documented Palaeozoic marattialean ferns, with mostly crenate or lobed mature pinnae and "lobatopterid" venation, are now accommodated in Crenulopteris.
Specimens
From Langford
Wittry
Keith Robitschek - fertile form
Mazon River
