This is Mazon Monday post #211. What's your favorite Mazon Creek fossil? Tell us at email:[email protected].
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Mariopteris wilmingtonense is a rare and beautiful variety of Mariopteris found only in Mazon Creek. It was described by George Langford Sr. in 1958 in his first Mazon Creek book "The Wilmington Coal Flora From a Pennsylvanian Deposit in Will County, Illinois".
Langford designates it as a new species on pages 264-265.
1, 2. Mariopteris wilmingtonense. new species.
Fig. 1 is the positive half of the two nodular impressions. It is not flattened, and the pinnae are more or less buried in the matrix in different planes. The rachis of the frond is rather stout and straight, the rachi of the pinnae flexuous. The pinnae are well separated and inclined upward, their pinnules separated, basal attachment broad, pinnules above the base broadly triangular, becoming narrower and closer above, and terminating at the apex in a large pinnule wider than long. The veination is not close, and the larger pinnules have a midvein which sends off veins which fork once or twice, one or more veins appearing to be directly attached to the rachis of the pinna.
A distinctive character is the basal pinnule on the lower side, all of whose veins appear directly attached to the rachis of the frond. This is further illustrated in Figs. 2 and 2a., but as seen in Fig. 2a., the midvein of the pinna sweeps downward, and the veins of the pinnule lead off from it within the rachis, as appears on the negative impression if the preservation is good.
Fig. 3 is added as a possible condition of the pinnae higher up on the frond.
M. wilmingtonense can be found on page 177 of Jack Wittry's "A Comprehensive Guide to the Fossil Flora of Mazon Creek".
Mariopteris wilmingtonense Langford, 1958
1958. Mariopteris wilmingtonense Langford: p. 264, figs. 481-484
1969. Odontopteris aequalis (non Lesquereux); Darrah: pl. 3, fig. 3; non p. 94DESCRIPTION: The penultimate rachis is heavy, unmarked, and straight. The ultimate pinnae are distant, flexuous, and inclined upward. The pinnules near the pinna base are attached by the whole width of their bases and obtuse, while closer to the tip they become more triangular and narrow, terminating at a blunt apex. The venation is distinct in the larger pinnules. The midvein is decurrent. The lateral veins are dense and arched, departing at a steep angle, forking once or twice, and meeting the margin acutely. In the smaller pinnules, all veins enter from the rachis. All of the pinnules display some veins other than the midvein entering from the rachis. The base pinnule on the basiscopic side has a unique characteristic where all veins rise directly from the penultimate rachis. At this point, they arch toward, and then away, from the pinna.
REMARKS: Mariopteris wilmingtonense is rare, but the second most common mariopterid in the Mazon Creek flora. It is unknown elsewhere.
Specimens
From George's Basement
From Witty
