This is Mazon Monday post #231. What's your favorite Mazon Creek fossil? Tell us at email:[email protected].
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Pecopteris strongii is a rare fossil fern known only from the Mazon Creek Fossil Flora. It was named for early Mazon Creek collector Samuel Strong by Leo Lesquereux in 1870. Strong was a prolific collector, who later sold most of his collection to Yale. Some specimens were named Pecopteris resupinata, however they were later identified to be immature Pecopteris strongii. Lesquereux was a swiss-born bryologist and a pioneer of American paleobotany. He is widely credited with naming the Mazon Creek fossil deposit, when he referred to the Mazon River as a creek in his 1870 publication "Report on the Fossil Plants of Illinois". Lesquereux also worked extensively with the Florissant fossil plants.
Lesquereux in 1864
Lesquereux's description can be found on George's Basement.
PECOPTERIS STRONGII, Lesqx., Plate XXXIX, Figs. 14-15a.
Frond bipinnate; pinnae oblong, broader in the middle, gradually lanceolate to the apex; pinnules alternate, in right angle to a narrow rachis, disconnected, even distant in the lower part of the pinnce, somewhat enlarged and rounded to the point of attachment, narrower in the middle, obtusely acuminate; medial nerve distinct in the sterile branches; veins obsolete; fructifications in rows of large round sori, close to each border.
The relation of this fine species was, when first described, somewhat doubtful, on account of the peculiar disposition and form of the pinnules, which give to the pinna the appearance of a simply divided frond. I have seen, later, large specimens representing primary pinnae forty to fifty centimeters long, linear-lanceolate, with secondary divisions alternate or opposite, long, the lowest sixteen centimeters or more. These branches, with a thin smooth, flexuous rachis ascending up parallel to the main stem, or reflexed, and curved in various directions, have their pinnules of the same character as those described and figured upon the plate, variable in length from seven to fourteen millimeters or less according to their place. As in the former species the leaflets become slightly, minutely lobate toward the base of the pinnae, in their transition from pinnules to branches of a second order. In these specimens the rachis more distinctly exposed is smooth, not punctulate, the pinnules have a thick epidermis, but the veins simple or forking once and obliquely inclined to the borders are sometimes discernible. The fructifications have the same disposition upon all the fragments, the medial nerve of the fertile pinnules being always as if erased and the space between the sori flat.
The only relation I find to this fern is Cyatheites (Pecopteris) pulcher, Heer, Fl. foss. Helv., IV, p. 29, Pl. VIII, f. 7. The specimens not figured, on which is remarked above, have the pinnae alternate or opposite, as in the European plant; the rachis however is not articulate or noduse at the joints of the secondary branches as figured by Heer. But this is apparently a mere casual deformation. It is not mentioned by the author in the description. Heer also describes the pinnules as subpetiolate, but says that he has seen traces of a petiole only in a few or in one pair of them. Except this all the characters are alike.
Habitat—Roof shale of the coal of Morris; nodules of Mazon Creek; not seen elsewhere.
Regular readers might remember "Postcards from Mazon Creek", which was Mazon Monday #213. In that post, a couple of photos of fossil ferns from the McLuckie collection were featured in postcards. One of those contained a breathtaking specimen of Pecopteris strongii, which currently resides at the Smithsonian.
The McLuckie postcard
Photo from the Smithsonian collection
P. strongii appears on page 128 of Jack Wittry's "A Comprehensive Guide to the Fossil Flora of Mazon Creek". There are some very nice specimen photos.
Pecopteris strongii Lesquereux, 1870
1870. Pecopteris strongii Lesquereux: p. 399, pl. 13, figs. 7-9
1879-80. Pecopteris strongii Lesquereux: p. 236, pl. 39, figs. 14, 15
1889. Pecopteris resupinata Lesquereux; Lesley: p. 608
1959. Pecopteris potoniei Nemejc; Remy and Remy: p. 237, pl. 189
1963. Pecopteris sp. Langford: p. 209, figs. 815-817
2009. Pecopteris potoniei Nemejc; Bartel: p. 3/53, figs. 106-108DESCRIPTION: The penultimate pinna is widest above the middle and contracts to an acuminate apex. The ultimate pinna is oblique, linear-lanceolate, and terminates in a small, blunt lobe. The rachis is broad, unmarked, or may display a channel down the middle. The pinnules are very distant, alternate, slightly oblique, oblong, up to six times longer than wide, occasionally appear to be slightly constricted in the middle, rounded at the tip, and expanded at the base where they may lightly touch. They are more confluent when small. The midvein is heavy. deeply immersed in the thick lamina, well marked by a groove, and extends to the tip. The lateral veins are dis- tant, oblique, and fork once near the middle. The upper veinlet meets the margin at a 45° angle. Usually, the vena- tion is obscured in the thick lamina. Pecopteris strongii produces a polymorph (see Figs. 6 through 9) described by Lesquereux under Pecopteris resupinata. It represents the immature and poorly developing ultimate pinnae of P. strongii. The sori have an asterothecoid appearance with 4 or 5 sporangia.
REMARKS: Pecopteris strongii is rare. All known examples have come from the Mazon Creek area, though a near identical form was described later by Nemejc (1940) from the lower Permian in Germany under the name Pecopteris potoniei.
Specimens
From Lesquereux. 14, 15, and 15a.
FMNH PP1215
FMNH PP26950
FMNH PP52920
