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ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 492 



indicate systematic differences. The development shown in text figure 

 10, C to D, seems to indicate a simpler pattern of the pinna trace 

 development than that shown in text figure 10, E to F. From coal balls 

 two sequences of pinna trace formation have been described (Stipitopteris 

 and Stewartiopteris) . As Stipitopteris and Stewartiopteris have been 

 shown by Stidd (1971) to occur within the same rachis, even this distinc- 

 tion does not indicate a systematic difference. 



Size, shape, and relative positions of leaf scars are another 

 set of supposedly specific characteristics. However, in living species 

 of tree ferns, extreme variations of these characteristics have been 

 observed (see text fig. 11). Most living tree ferns belong to the 

 Cyatheaceae, which are taxonomically and phylogenetically quite distant 

 from the Marattiaceae. However, the two groups are structurally quite 

 similar, and therefore comparisons of morphological characteristics are 

 valid. Differences in size and shape of leaf scars can occur in living 

 Cyatheaceae on different stems of the same species or even on different 

 parts of the same stem owing to ecological changes (oral communication, 

 Professor Rolla Tryon and Dr. Alice F. Tryon, 1973). In the Pennsylvanian, 

 arrangements of leaf scars in Caulopteris vary from densely packed to 

 widely separated (text fig. 12). If we assume that the fossil forms grew 



P I 



10 

 cm 



Iaaa/vaa/wvxaxJ 



Text fig. 11 - Trunks of Cyathea arborea 

 showing extreme variety of leaf scar 

 size and arrangement within one species 

 of living tree ferns (after Maxon, 

 1912, pi. 3). 



Text fig. 12 - Some types of arrangement 

 of leaf scars occurring in Caulopteris 

 (A after C. saportae from Hirmer, 1927; 

 B after C. varians from Andrews and 

 Doubinger, 1970; C to F possible 

 stages) . 



