Scolecopteris, the maggot fern: "maggots" fat and lean
deutsche Version
The pinnules of the large fronds of the big tree ferns whose fossil trunks are known as Psaronius * had not been recognized as plant fossils when first discovered in rare chert samples, called maggot stones, found in the Lower Permian Döhlen basin near Dresden, Upper Saxony, in the second half of 18th century. The small curved pinnules with sporangia and fringes pointing downward were mistaken for little arthropods as they are seldom seen nearly as distinctly as in Fig.1. After they had been recognized as plant parts, they got the name Scolecopteris, which literally means maggot fern, with the species name elegans, in 1837 [1]. The amusing and instructive story of repeated misinterpretations of the "maggot stones"  has been told elsewhere [2]. It may serve as an encouragment to question recent interpretations.
Scolecopteris pinnules side view
Fig.1: Scolecopteris pinnules as seen on the surface of a chert fragment smoothed by water transport : The sporangia (partially fused into synangia) seen on the lengthwise section (left) and the fringes seen on the pinnule in side view (right) are liable to be mistaken for arthropod limbs if less well preserved. Width of the drawing 8mm.

The recent recovery of more than a thousand fossiliferous chert samples from the type locality of Scolecopteris elegans, starting with the purposeful search by Gert Müller
and H.Ahlheim in 1985, has revealed a large variety of pinnules, including such ones that look like grubs or nymphs of some insect (Fig.2) still more than those ones did which fooled the 18th century scholars. As one of several indications of diversity, the curvature of the pinnules is distinct in Fig.1 but insignificant in Fig.2.
"Maggot stone" of uncommon aspect

Fig.2: "Maggot stone" of uncommon aspect: Scolecopteris pinnules with rather lean constitution and unevenly developed sporangia. Width of the picture 7mm.

It is not obvious which ones of such examples of variety are due to the variability of the species or to the presence of other species, possibly undescribed ones. Nevertheless, all recent finds in the Döhlen basin have been assigned to the same species [2,4]. Evidence has accumulated which casts severe doubts upon the hypothesis of only one species.  Hence, the recent finds have to be compared with more than two dozen Scolecopteris species hitherto discovered worldwide [5].

As an intriguing fact, fertile and sterile pinnules shaped such that they may be called succulent (Figs.3-6) have been found among those of normal aspect (Fig.7) even in one and the same chert sample, which means they became silicified within the same layer of mud.
Succulent Scolecopteris pinnule Scolecopteris pinnule, succulent formScolecopteris pinnule, succulent form          Scolecopteris pinnules, succulent form

Figs.3-6: Cross-sections of thick pinnules of Scolecopteris found in small numbers among the leaner ones in the sample of Fig.7.  
Fig.3: 2.3mm wide, with sporangia, others sterile, same scale.
Scolecopteris in chert
Fig.7: Cut face of a chert sample of uncommon aspect containing thousands of fertile and sterile Scolecopteris pinnules.
Note the lengthwise section of a pinnule related to a pinna cross-section on the left, also the tiny black dot on one of the fertile pinnule cross-sections indicating the central strand of the pinnule midrib (on the right). Width of the picture 32mm.

The pinnules with bloated midrib (Figs.3-6) were first noticed in one sample of a rare chert variety (Fig.7), where they make up about 1% of the total amount of pinnules. They had been pictured in [4] but their presence among the leaner pinnules has not been adequately discussed or explained hitherto. Hence, the observation deserves further attention.
The sample is an old fragment of a solid and rather homogeneous chert layer, and the fat pinnules are not restricted to a particular position in the layer. This seems to indicate that they grew among the normal foliage. As they are seen in rows of two or three (Fig.6), the abnormal growth is not confined to individual pinnules but affects the pinna or frond part.
Fungus infection is known as a cause of abnormal growth, including hypertrophy of tissue, which can be useful for water storage. Symbiotic fungi seem to have been present even in the first land plants [6]. Hence, fungus activity should always be considered if unexpected phenomena in plants defy
other explanations.

Samples: Old fragments of Lower Permian chert with more or less rounded edges, found among younger fluviatile deposits in Döhlen basin near Dresden, Saxony, Germany.
Fig.1: Pe/3, found in 1994 near Pesterwitz, apparently as the only sample with pinnules ever found there.
Fig.2: Bu8/23.2 , found in 1997 by U. Wagner on the area of Burgk close to the historic "maggot stone" site near Kleinnaundorf. For a wider view of this sample see [7], Bild 67.  (The mirror image is reproduced there, and not in natural size as claimed there but magnified by a factor of 1.7 .) The sample is kept by U. Wagner, Dresden.
Figs.3-7: H2/1+35, found in 1993 at Hänichen.

Fig.7: H2/35.1, Photograph by M. Barthel (1994), detail.
The samples Pe/3 and H2/1+35 are of a rare black/gray/white variety, own finds, stored in the own collection. H2/1 and H2/35 had been found separately, with months in between, and later recognized as fitting together.
* A most remarkable collection of big polished Psaronius sections is on display at the Naturkunde Museum Chemnitz [7].

H.-J. Weiss       2011 

[1]  F.C. Zenker : Scolecopteris elegans, ein neues fossiles Farrngewächs mit Fructification. Linnaea 11(1837), 509-12
[2]  M. Barthel : The maggot stones from Windberg ridge.  in: U. Dernbach, W.D. Tidwell : Secrets of Petrified Plants, D'ORO Publ., 2002. p65-77.
[3]  G. Müller :
[4]  M. Barthel, W. Reichel, H.-J. Weiss : "Madensteine" in Sachsen. Abhandl. Staatl. Mus. Mineral. Geol. Dresden 41(1995), 117-135.
[5]  M.A. Millay : A review of permineralized Euramerican Carboniferous tree ferns.  Rev. Palaeobot. Palyn. 95(1997), 191-209.
[6]  T.N. Taylor, E.L. Taylor, M. Krings :  Paleobotany, Elsevier 2009.
R. RÖßLER: Der versteinerte Wald von Chemnitz, Museum für Naturkunde Chemnitz 2001.
Scolecopteris pinnule cross-section, Sardinia Permian Chert News 1

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