Mazon Monday #57: Species Spotlight - Alethopteris serlii #fossil #MazonCreek #MazonMonday #fern #carboniferous

This is Mazon Monday post #57.  What's your favorite Mazon Creek fossil?  Tell us at email:[email protected].

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If you've seen one, you know that Alethopteris serlii can have breathtaking beauty.  Whether from the Mazon River or one of the other more terrestrial localities, like its sister taxa Alethopteris sullivantii, it is generally bold in preservation.  Recall, we looked at A. sullivantii back in Mazon Monday #37.

Alethopteris serlii is common.  It is a seed fern (Pteridospermatophyta).  They first show up in the fossil record during the late Devonian and went extinct during the late Cretaceous Period.  Fossil specimens are typically 3 dimensional.  Seed ferns are thought to be the first plants to develop seeds.

A. serlii appears on pages 182-183 in "A Comprehensive Guide to the Fossil Flora of Mazon Creek".

Alethopteris serlii (Brongniart) Göppert, 1836

1834. Pecopteris serlii Brongniart: p. 292. pl. 85 1879-80. Alethopteris serlii (Brongniart) Goppert; Lesquereux: p. 176, pl. 29, fig. 1, ?figs. 2-5
1925. Alethopteris serlii (Brongniart) Göppert; Noe: pl. 38, figs. 1-4; pl. 39, figs. 2-3, non fig. 4
1958. Alethopteris serli (Brongniart) Göppert; Langford: p. 241, figs. 434-437
1958. Alethopteris lonchitica; Langford: figs. 438, 439, (fig. 438 re-figured here as Fig. 6)
1968. Alethopteris serli (Brongniart) Göppert; Wagner: p. 137. pls. 56-59, figs. 161-169
1979, Alethopteris serli (Brongniart) Göppert; Janssen: p. 142, figs. 126-128

DESCRIPTION: The pinnae are linear and taper sharply to an elongated terminal pinnule at the apex. The rachis is rather thin and striate. The pinnules may be broadly confluent when small, less so when large and distant. The pinnules have convex sides with the greatest width near the middle. The pinnules seldom touch and rise at about a 65° angle from the rachis. The pinnule apex is bluntly acuminate and the bases are strongly decur rent. A contraction occurs on the acroscopic side of the pinnule with only a slight narrowing on the basiscopic side, making the midvein appear to enter the pinnule more toward the acroscopic side. The pinnules may appear long and narrow or short and wide, with a full range of variations in between. The midvein is well marked, thin, and straight. The lateral veins are thin, flexuous, rise obliquely, then quickly arch, fork at least once, sometimes twice at irregular intervals. They meet the margin at nearly a right angle, with a count of 35 veins per centimeter. Some veins will enter the pinnule from the rachis on the basiscopic side only.

REMARKS: Alethopteris serlii is common and the second most common Mazon Creek alethopterid. As seen here, it can be variable in pinnule shape and size. Different authors have had conflicting opinions on this degree of vari ability. Darrah (1969) considered many of the specimens figured by Langford as different taxa to belong to A. serlii. Wagner (1968) believed A. serlii to be less variable and erected a new taxon, Alethopteris lesquereuxii var. les quereuxii, which included many of the specimens Darrah had previously placed in A. serlii. Wagner's opinion is followed here. Darrah's opinion that the long, thin, and distant form (see Fig. 6) of A. serlii is also accepted.

The "keys to Identify Pennsylvanian Fossil Plants of the Mazon Creek Area" also mentions Alethopteris in general and Alethopteris serlii specifically,

ALETHOPTERIS

1. Pinnules directly and broadly attached to rachis, especially on the lower side
2. Pinnules generally robust
3. Midvein sharply defined and straight
4. Veins generally close and deep
5. Some veins enter the base of pinnule directly from the rachis independent of the midvein on one or both sides
6. 6. See "Alethopteris" on page 35, Seed Fern Key

Genus Alethopteris is a seed fern with broadly attached pinnules and systematic branching from a prominent mid-vein. Growth stages of the plant confuse identification. When studying immature pinnules the correct species can be difficult to determine.

Alethopteris serli

This species has a large quadripinnate frond (see "Appendix B. Frond Nomenclature" on page 49). The pinnules are oblong, blunt, united (decurrent) at the base, and are alter nate or sub-opposite on the rachis. The midvein is thick and straight to the bluntly pointed apex. The veins are at nearly right angles to the midvein, close and numerous, simple but sometimes fork once halfway to the margin. The rachial veins arise from the rachis below the midvein.

 

Examples