This is Mazon Monday post #37. What's your favorite Mazon Creek fossil? Tell us at email:[email protected].
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Today, we look at one of my favorite Mazon Creek plants... Alethopteris sullivantii. A. sullivantii is a seed fern (Pteridospermatophyta), which is a group of plants that went extinct during the late Cretaceous Period. They first show up in the fossil record during the late Devonian. Specimens are usually 3 dimensional and can be quite striking.... see the examples at the end.
A. sullivantii is a fairly common and was included in "The Keys To Identify Pennsylvanian Fossil Plants of the Mazon Creek Area".
Here the art work is by Don Auler, who was President of ESCONI in the 1980s.
The text from "The Mazon Creek Fossil Flora" by Jack Wittry gives a complete history of its name and useful information to help with identification.
Alethopteris sullivantii (Lesquereux) Shimper, 1869
- 1866. CallipterissullivantiLesquereux.p. 440, pl. 38, fig. 1
- 1869. Alethopteris sullivanti (Lesquereux) Shimper. p. 561
- 1870. Callipteris sullivanti Lesquereux. p. 468
- 1880. Callipteridium sullivanti Lesquereux. p. 164
- 1899. Callipteridium sulivanti (lLesquereux) Weiss. White, p. 123, pl. 39, figs. 1-3; pl. 41, figs. 1-3
- 1925. Callipteridium sulivanti (Lesquereux) Weiss. Noé, p. 15, pl. 41, figs. 1-4
- 1958. Alethopteris sullivanti Lesquereux. Langford, p. 241, pls. 440-443
- 1968. Alethopteris sullivanti (Lesquereux) Shimper. Wagner, p. 147, pl. 60, figs. 17o, 171
- 1970. Alethopteris sullivanti (Lesquereux) Shimper. Darrah, p. 114, pl. 4, figs. 1, 3
- 1979. Alethopteris sullivanti Lesquereux. Janssen, p. 146, fig. 134
DESCRIPTION: The pinnae are large, linear-lanceolate, slightly narrowed at their bases and terminate in an oval pinnule. The rachis appears strong and irregularly striate. The pinnules are robust, oblique and often inflated. They are widest two thirds of the way up towards the broadly rounded apex and are generally confluent at the bases, becoming less so near the pinna base where they become constricted (see circled portion of Fig. 2). The venation consists ofa strong, mostly straight and sometimes slightly decurrent midvein, that often appears to enter the pinnule towards the acroscopic side. The midvein varies in appearance. It sometimes rapidly terminates about half-way up the pinnule, dissolving into repeatedly branching veinlets (see Fig. 5); in other cases it extends to nearly the pinnule apex where it branches into oblique lateral veins as in Fig. 3. The lateral veins are thin, oblique, widely spaced and usually fork twice, often three times, then reach the margin at angles between 60° and 80 at a count of about 25 veins per centimeter.
REMARKS: Alethopteris sullivantii is common. This taxon has two forms, shown here as Fig. 1 and Fig.3. The Fig. 1 form is commonly found in the Mazon Creek flora, while the Fig. 3 form is rare. What separates them, is that the common form has a midvein that terminates abruptly near the middle of the pinnule (this agrees with Lesquereux's original description) and pinnules that are inflated, compared with the rarer form, which has a mid- vein extending to near the tip and rather flat pinnules. White commented on these discrepancies, but chose to retain both forms under A. sullivantii His reasons for retaining both forms under A. sullivantii were that they both have midveins that enter the pinnule toward the acroscopic side and basal pinnules that are very constricted at their bases. Some authors still believe that Callipteridium is the correct genus for this form.
This post wouldn't be complete with out a few photos of specimens.
You can find out more in the new ESCONI plant book A Comprehensive Guide to the Fossil Flora of Mazon Creek, Jack Wittry 2020.
