A Dinichthyid in Middle Devonian of Iowa

• Published in: Journal of paleontology Vol. 43; no. 6; pp. 1423 - 1428
• Main Authors: Straka, Joseph J., Semken, Holmes A.
• Format: Journal Article
• Language: English
• Published: Society of Economic Paleontologists and Mineralogists and the Paleontological Society 01-11-1969
• Subjects: Dams; Fall lines; Lithology; Mathematical cusps; Quarries; Shales; Specimens; Standard deviation; Taxa; Written communication
• ISSN: 0022-3360; 1937-2337

A single, well-preserved left inferognathal of a large Devonian arthrodire (joint-necked fish) referable to the Dinichthyidae was discovered in the rip-rock of the Coralville Dam, Johnson County, Iowa. Engineering records confirmed that all rip-rock for the Coralville Dam was purchased from the nearby Vogel Quarry, Johnson County, Iowa. Matrix associated with this representative of the Dinichthyidae compares favorably with the lithology of the Rapid Member of the Cedar Valley Formation exposed in the Vogel Quarry. Conodonts recovered from the matrix associated with the inferognathal confirm an age between upper Givetian (upper Middle Devonian) and lower Frasnian (lower Upper Devonian). Statistical comparisons of the Vogel specimen with related dinichthyids permit any of the following conclusions: (1) The Vogel representative is specifically distinct from previously reported specimens based on existing interspecific criteria. (2) Dinichthyans may be divided into two groups, larger forms being referable, in part, to Dinichthys and smaller representatives, in part, to Dunkleosteus. (3) Inferognathal ratios may not be specifically diagnostic. (4) The Dinichthyidae samples represent a closely related phyletic group with a coefficient of correlation greater than 0.924 in 21 comparisons. All studied specimens fall within one standard deviation of each regression line. As this regression includes four and possibly five described genera, it would be premature to attach formal nomenclature to this specimen until the taxonomy of the group is revised. Taxonomic revision is not attempted.