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SIGNIFICANCE OF ASSEMBLAGE ARRANGEMENTS IN SCOTTOGNATHUS 



The natural assemblage genus Scot togna thus was described by F. H. T. 

 Rhodes (1952) from material that he collected from this outcrop and from 

 earlier collections by E. P. DuBois (1941, 1943). The genus was diagnosed 

 as "consisting of paired conodonts of the 'form genera' Id iogna thodus or 

 Streptognathodus , Ozarkodina , Hindeodella , and Synprioniodina" (Rhodes, 1952, 

 p. 890) in a 2:2:8:2 ratio. The original figures (Rhodes, 1952, plate 126, 

 fig. 11, text-fig. 2, p. 891) illustrate a linear, bilaterally symmetrical 

 arrangement of the component elements (fig. 10A) , which holds up remarkably 

 well in light of new data from our recent collections. In fact, Rhodes' 

 model requires only two revisions to be compatible with the new observations: 

 (1) Present data (fig. 10B) indicate that the hindeodellid elements occur as 

 lateral pairs with two pairs on either side of the assemblage. (2) Synprion- 

 iodinid elements occur farther from the mid-line of the assemblage than shown 

 by Rhodes. 



Despite the foregoing observations, an examination of collections 

 from Bailey Falls shows that preservation of linear arrangements is rela- 

 tively rare but that several patterns of element arrangement reoccur repeat- 

 edly and, by reason of this repetition, are of importance for reconstructing 

 the details of discrete element arrangement in the conodont-bearing animal. 

 We have categorized the patterns as: (1) simple scatter (fig. IOC); (2) 

 simple contraction (fig. 10D) ; (3) simple rotation (fig. 10E) ; and (4) con- 

 traction-rotation combinations (figs. 10F and 10G) . 



Simple Scatter 



Simple scattering of the elements is generally the result of water- 

 current action and of compaction effects. Both tend to destroy the biolog- 

 ical arrangement of the elements during and after decomposition of the 

 animal. If scatter is not great, the assemblage is relatively easy to 

 restore. 



Simple Contraction 



Contraction results from an uncomplicated anterior translation of 

 elements relative to each other ("anterior" as used here relates to the 

 nomenclature of discrete elements). In extreme cases, translation results 

 in juxtaposition of hindeodellid-synprioniodinid and ozarkodinid elements 

 to platform elements. 



Simple Rotation 



Rotation, as encountered here, is parallel to bedding and is the 

 result of a 90-degree rotation of elements with respect to their original 

 alignment. The platforms, the ozarkodinids, and the hindeodellid-synprion- 

 iodinid elements generally have been moved as independent units. Such 

 rotation results in arrangements wherein components are oriented in the 

 same general direction. 



