This is Mazon Monday post #246. What's your favorite Mazon Creek fossil? Tell us at email:[email protected].
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Seeds were relatively rare in the Pennsylvanian Period. Most plants, including the true ferns, reproduced via spores. The only plants that bore seeds were the medullosan pteridosperms, or seed ferns. The most common seed found in the Mazon Creek fossil deposit is Stephanospermum konopeonus. George Langford described a few species of seed in his first Mazon Creek book "The Wilmington Coal Flora from a Pennsylvanian Deposit in Will County, Illinois" from 1958. Some of these (Carpolithus konopeonus, Codonospermum olivaeformae, Stephanospermum akeniodes, Lagenospermum sinclairi, and Neuropterocarpus pachytesta) have since been consolidated as Stephanospermum konopeonus. In 1990, Andrew Drinnan, Janai M. Schramke, and Peter R. Crane wrote "Stephanospermum konopeonus (Langford) Comb Nov.: A Medullosan Ovule from the Pennsylvanian Mazon Creek Flora of Northeastern Illinois, U.S.A.", which looked for evidence that this genus of ovules was related to Medullosales.
Abstract
More than 150 permineralized ovules of Carpolithus konopeonus Langford, preserved in sideritic concretions, have been recovered from the Middle Pennsylvanian (Westphalian D) Mazon Creek flora of northeastern Illinois. Ovules were borne apically on slender branching structures. The sarcotesta is bilaterally symmetrical with a pair of distinct lateral wings and, at the apex of the ovule, forms a prominent funnel that leads to the micropyle. The sclerotesta is radially symmetrical with a prominent beak and collar at the apex. The nucellus is free from the integument except at the base and extends into the basal part of the micropylar tube. The apex of the nucellus forms a distinct pollen chamber. Ovule vasculature consists of six or more bundles in the sarcotesta and a continuous sheath of vascular tissue in the nucellus. Pollen preserved in the micropyle and pollen chamber is of the Monoletes-type The Mazon Creek material is assigned to a new species of Stephanospermum Brongniart as S. konopeonus (Langford) comb. nov. and provides further evidence that this genus of ovules was produced by representatives of the Medullosales.
Jack Witty addresses S. konopeonus on page 232 of his 2019 book "A Comprehensive Guide to the Fossil Flora of Mazon Creek".
Stephanospermum konopeonus (Langford) Drinnan, Schramke & Crane, 1990
1958. Carpolithus konopeonus; Langford: p. 340, figs. 654-657
1958. Codonospermum olivaeformae; Langford: p. 328, fig. 629
1958. Stephanospermum akeniodes; Langford: p. 329, figs. 631, 632
1958. Lagenospermum sinclairi; Langford: p. 330, figs. 633-635
1958. Neuropterocarpus pachytesta; Langford: p. 334, fig. 642, non 641, 643
1958. Carpolithus; Langford: p. 339, fig. 652, non 648-651, 653
1979. Samaropsis; Janssen: p. 168, fig. 163
1990. Stephanospermum konopeonus Langford; Drinnan et al.: p. 385-401DESCRIPTION: These seeds are radiospermic and rounded at their bases, with truncated and outwardly extended apices. The nucellus is smooth and ovate. The seed dimensions are 12 to 15 mm long and 5 to 6 mm wide. The nucellus size is 6 to 8 mm long and 3 to 5 mm wide. There are four evenly spaced wings that run down the length of the seed, though they are seldom seen in the fossils.
REMARKS: Stephanospermum konopeonus is common and the most common seed taxon in the Mazon Creek flora. It was originally described based on fossils from this area. Stephanospermum is now broken into two species in the Mazon Creek flora. Using a new technique called X-ray Micro-Tomography (XMT), a virtual 3-D reconstruction of an ovule is possible. From this method, a very similar species was discovered (Spencer et al., 2013) and named Stephanospermum braidwoodensis. Unfortunately, they are so similar that separating the two without using XMT is impossible. This may only be the beginning of discovering new ovule species. S. konopeonus was borne on a branched rachis of an undetermined medullosan pteridosperm.
George Langford's handwitten page about Stephanospermum (from George's Basement)
Specimens
Stephanospermum konopeonus - FMNH PP27766
Stephanospermum konopeonus - FMNH PP9672
Stephanospermum konopeonus - FMNH PP30416 (From Witty)
From George's Basement
ESCONI Member collection
