A new gyracanthid from the Mississippian of Delta, Iowa, U.S.A.

ABSTRACT

A new gyracanthid, Gyracanthus? jasperi, is described based on partially articulated and isolated elements from the Lower Carboniferous (Mississippian) lower Waugh Member of the Ste Genevieve Formation, at the early tetrapod site near Delta, Iowa, U.S.A. Pectoral fin spines of the new gyracanthid are characterized by the insertion on the fin spine being a half to one-third the length of the spine and maximum length:depth ratio 10:1. Ornament ridges on the pectoral fin spine converge at ≥90° along a low leading edge ridge, and ridge tubercles are oriented oblique to the ridge; the distal end of one pectoral is described using micro-computed tomography. The scapulocoracoids have an anteriorly curving bulbous apex, and a base length that is 35–40% of pectoral spine length. The procoracoid is associated with an unornamented ventral plate. A possible isolated dorsal fin spine is more symmetrical and less worn than the pectoral fin spines. Pelvic spines are dorsoventrally flattened, with oblique ridges meeting at approximately 100° proximally and 80° distally, along a smooth leading edge ridge. Scales, found on the partial articulated specimen and as isolated remains, are polyodontode with a flat base. Adults of the new taxon are estimated to have been about one meter long. Deposition was in debris flows, within a sinkhole lake most likely removed from the edge of the ocean. Other Carboniferous gyracanthids from North America are reviewed.

http://zoobank.org/urn:lsid:zoobank.org:pub:5C26F98A-E630-4FD6-99A5-F08B5CBB1549

DISCLOSURE STATEMENT

No potential conflict of interest was reported by the author(s).

ACKNOWLEDGMENTS

This paper is dedicated to the memory of Donald ‘Don’ Baird (1926–2011), who did so much to further gyracanth studies in North America. We acknowledge the help of the late John Bolt (Chicago), A. A. Warren (Melbourne), J. Anderson and J. Pardo (University of Calgary), as well as W. Simpson, A. Stroup, and C. Van Beek (FMNH), and MacKenzie Shepard (Duke University). CJB and ST thank the Queensland Museum (Geosciences) for provision of basic facilities. DS was supported by a gift from the estate of the late Ruth Shadle.

AUTHOR CONTRIBUTIONS

The project began as a part of the dissertation work for DS, supervised by J. Bolt and others. ST (in 1990s) and CJB also contributed primary observations. X-ray and computer tomographic data were collected and analyzed by DS. All authors contributed equally to writing the manuscript; CJB drafted Figs. 2, 4B, and 6B, DS drafted Fig. 1C, D, and CJB and DS compiled the figures.

SUPPLEMENTARY FILE

Supplementary File 1.mpg: movie compiled from CT scan data of the distal end of FMNH 15270.

DATA AVAILABILITY STATEMENT

The scan data that support the findings of this study are openly available in Morphosource at: http://morphobank.org/permalink/?P5206.

Correction Statement

This article has been corrected with minor changes. These changes do not impact the academic content of the article.