Translator Disclaimer
1 September 2007 Trigonoceratid nautilids from the Early Carboniferous Imo Formation of Arkansas, Midcontinent North America
Author Affiliations +
Abstract

Four species of trigonoceratid nautilids from the late Chesterian (Early Carboniferous) strata in the Imo Formation of Arkansas, Midcontinent North America are described. A specimen of Aphelaeceras arkansanum Gordon, 1964 reveals the external juvenile whorl morphology. Based on the discontinuous points of its surface lirae, we suggest the possibility that the hatching shell of A. arkansanum is cyrtoconic with two septa and a length of approximately 4.9 mm. Species previously described or assigned to Aphelaeceras are reexamined. Epistroboceras lesliense sp. nov. differs from E. caneyense Niko and Mapes, 2004 and E. pitkinense Niko and Mapes, 2005 in its lower ratios of umbilical zone height per whorl height and lower siphuncular position ratios. Epistroboceras? sp. indet. is also identified in this fauna. A new genus, Imonautilus, is erected on the basis of I. meeki sp. nov. The most characteristic features of this genus are the Stroboceras-like juvenile whorl, the obsolescence of the adoral ventrolateral grooves at or near maturity, and the roundly inflated adoral venter. Based on early ontogenetic similarities, a close evolutionary relationship between Aphelaeceras and Imonautilus is suggested.

SHUJI NIKO and ROYAL H. MAPES "Trigonoceratid nautilids from the Early Carboniferous Imo Formation of Arkansas, Midcontinent North America," Paleontological Research 11(3), 293-303, (1 September 2007). https://doi.org/10.2517/1342-8144(2007)11[293:TNFTEC]2.0.CO;2
Received: 5 December 2006; Accepted: 1 March 2007; Published: 1 September 2007
JOURNAL ARTICLE
11 PAGES


SHARE
ARTICLE IMPACT
RIGHTS & PERMISSIONS
Get copyright permission
Back to Top