This is Mazon Monday post #129. What's your favorite Mazon Creek fossil? Tell us at email:[email protected].
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Pecopteris fontainei is a fern belonging to the clade Pteridophyta. They are vascular plants that reproduce by dispersing spores. It was classified by Leo Lesquereux in 1889. This is the sterile form. The fertile form is known as Crossotheca sagittata.
It appears on page 154 of "A Comprehensive Guide to the Fossil Flora of Mazon Creek" by Jack Wittry.
Pecopteris fontainei Lesquereux, 1889: sterile
Crossotheca sagittata (Lesquereux) Sellards, 1902: fertile1870. Staphylopteris sagittatus Lesquereux: p. 407, pl. 14, figs. 3-5
1879-80. Sorocladus sagittatus Lesquereux: p. 329, pl. 48, figs. 10, 10a, 10b
1879-80. Pecopteris abbreviata? Brongniart; Lesquereux: p. 248, pl. 46, figs. 4-6
1889. Pecopteris fontainei Lesquereux; Lesley: p. 606
1940. Crossotheca sagittata Lesquereux; Janssen: p. 66, pl. 17, fig. 2 fig. 495
1958. Renaultia chaerophylloides (non Brongniart); Langford: p. 271,
1958. Crossotheca sagittata Lesquereux; Langford: p. 185, fig. 323
1969. Crossotheca sagittata Lesquereux; Darrah: p. 162, pl. 18, figs. 1-4
1969. Pecopteris fontainei Lesquereux; Darrah: p. 162, pl. 16, fig. 3
1979. Renaultia chaerophylloides (non Brongniart); Janssen: p. 116, fig. 96
1979. Crossotheca sagittata Lesquereux; Janssen: p. 140, figs. 117m, 124, 125DESCRIPTION: These fronds were large and highly variable. The sterile and fertile pinnules and pinnae are rarely found together and are distinctly different. The penultimate pinnae (see Fig. 2) are lanceolate with a strong, straight, cylindrical, and smooth rachis which tapers as it nears the tip. The sterile pinnules/ultimate pinnae are oblique, decurrent, lobed, and undulate near the pinna base, becoming obtuse and connected near the apex. The venation consists of a weak midvein with lateral veins that arch toward the margins and fork once or twice. They often appear irregularly inflated, some for their whole length, but others just at their bases or tips. Occasionally at the pinnule margins, the lateral veins display expanded tips known as hydathodes. This feature can be mistaken for synangia. The fertile pinnules (see Figs. 3, 5, 6) are ovate when small, and arrowhead-shaped when large. They are opposite and attached by a short, thick petiole to a heavy and flexuous rachis. The upper surface is smooth except for a distinct median line. On the lower surface, sporangia occur in a single row and rim the pinnule margin. The margins curve inward and partially cover the sporangia, even when they are fully descended.
REMARKS: These taxa are common when both fertile and sterile forms are considered as one. Both taxa are good examples of the difficulty in naming forms from small nodular fossils. In 1880, Lesquereux described both Pecopteris abbreviata?, a sterile form, and Sorocladus sagittatus, a fertile form, unaware that they were actually from the same plant. Later, he realized his P. abbreviata? form was unlike P. abbreviata as originally erected by Brongniart and changed the name to Pecopteris fontainei. Though this still left the fertile and sterile forms separate, it was a step in the right direction. Fortunately, specimens such as Fig. 6, which display both fertile and sterile pinnules on the same pinna, have clarified the relationship. It is generally agreed that Crossotheca sagittata is a pollen-producing organ (Taylor et al., 2009) which makes this plant a member of the seed ferns.
Specimens
ESCONI member Marie Angkuw
ESCONI member Andrew Young
ESCONI member Rich Holm - Fertile form
Field Museum
