This is Mazon Monday post #238. What's your favorite Mazon Creek fossil? Tell us at email:[email protected].
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Alethopteris lesquereuxii was originally named Callipteridium mansfieldi by Leo Lesquereux in 1879. C. mansfieldi was named for the Hon. Ira Franklin Mansfield, who was a politician and an extensive owner of coal mining interest in the middle to late 1800s in the area of Beaver County, Pennsylvania. Mansfield assembled a significant collection of euryperids from the Darlington coal bed. In the 1880s, his his collection was donated to Penn State. He was elected to the American Philosophical Society in 1878.
C. mansfieldi was reclassified as Alethopteris lesquereuxii in 1968 by Richard H. Wagner along with Alethopteris gibsoni.
George Langford Sr. referred to it as Alethopteris grandini.
Alethopteris lesquereuxii can be found on page 179 and 180 in Jack Wittry's "A Comprehesive Guide to the Fossil Flora of Mazon Creek".
Alethopteris lesquereuxii var. lesquereuxii Wagner, 1968
1879-80. Callipteridium mansfieldi Lesquereux: p. 166, pl. 27, fig. 2
1938. Alethopteris friedeli (non Bertrand); Bell: p. 68 in part, pl. 62, fig. 2; non fig. 3, 4 = Alethopteris gibsonii; ?pl. 63
1958 Alethopteris grandini (non Brongniart); Langford: p. 247, fig. 444
1968 Alethopteris lesquereuxi var. lesquereuxi Wagner: p. 89, pls. 30-35, figs. 85-100DESCRIPTION: The ultimate pinnae are linear-lanceolate with pinnules becoming fused and oblique toward their apices. The rachis is heavy and marked by longitudinal striae. The pinnules rise at nearly a right angle or are slightly oblique. They are distant and narrowly confluent at their bases, where they may appear to be slightly constricted. The pinnules are nearly triangular near the pinna apex and more linear or convex toward the pinna base, where they gradually taper into an obtuse apex and have a typical aspect ratio of 3.5 times longer than wide. The pinnules appear inflated due to their thick lamina. The venation consists of a straight, non-decurrent midvein, which is centered in the pinnule; it may appear rather broad, though more commonly somewhat narrow and buried in the thick lamina. The lateral veins are well marked, oblique, straight, fork once generally near the midvein, and occasionally, a second time. Lateral veins on the basiscopic side rise from the midvein at a slightly more oblique angle than those on the acroscopic side (see Fig. 4). Typically, there are about 30 veins per centimeter at the margin. The pinnules have less-densely packed lateral veins at the pinna apex than near the base.
REMARKS: Alethopteris lesquereuxii is uncommon. This taxon is easily mistaken for Alethopteris gibsonii. The pinnules of A. gibsonii are narrower and have a broader midvein than A. lesquereuxii. The lateral veins are all clearly perpendicular in A. gibsonii, in contrast with the oblique and asymmetric veins of A. lesquereuxii.
Specimens
Field Museum specimens from Wittry's "A Comprehesive Guide to the Fossil Flora of Mazon Creek"
From the 2019 ESCONI show
ESCONI member
From McDonald's Farm in Naperville