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Sigournea multidentata, a new stem tetrapod from the Upper Mississippian of Iowa, USA

Published online by Cambridge University Press:  11 August 2017

John R. Bolt  and
R. Eric Lombard
John R. Bolt
Affiliation:
Department of Geology, Field Museum of Natural History, 1400 S. Lake Shore Drive, Chicago, Illinois 60605,
R. Eric Lombard
Affiliation:
Department of Organismal Biology and Anatomy, University of Chicago, 1027 E. 57th Street, Illinois 60637,
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Abstract

Sigournea multidentata n. gen. and sp., an early tetrapod, is described from the Late Mississippian Delta locality of southern Iowa, USA. The holotype and only known specimen, a right mandible, is unique in the structure of the symphysial region, and in addition has a unique combination of characters that are shared with other tetrapods. The free ventral border of the single exomeckelian fenestra is formed by infradentary bones. Its visible portion shows several arch bases, separated by notched or straight intervals. This morphology is interpreted as indicating that the arch bases and intervals between them reflected a series of Meckelian fenestrae that were partly exo- and partly endoskeletal, due to the fact that the exoskeletal arch bases continued dorsally in Meckelian cartilage. We suggest that this may exemplify a stage in the evolution of exomeckelian fenestrae, in at least some lineages of early tetrapods. The relations of Sigournea are indeterminate. That it is a tetrapod is indicated by the presence of pit and ridge ornamentation, an open lateral line sulcus, a dorsally directed glenoid, a single elongate exomeckelian fenestra, absence of intercoronoid fossae, absence of coronoid fangs, a single row of marginal teeth on the dentary, and an absence of dentition on the prearticular. It is at present impossible to determine its relationship with other early tetrapods, and we conclude that Sigournea is best considered as an early tetrapod incertae sedis.

Type
Research Article
Information
Journal of Paleontology , Volume 80 , Issue 4 , July 2006 , pp. 717 - 725
Copyright
Copyright © The Paleontological Society 

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