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Geological Magazine; January 2008; v. 145; no. 1; p. 55-71; DOI: 10.1017/S001675680700386X
© 2008 Cambridge University Press (CUP)
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The ontogeny and systematics of the otarionine trilobite Otarionella from the Devonian of the Montagne Noire, France and the Maider, Morocco

RUDY LEROSEY-AUBRIL*, RAIMUND FEIST{dagger},{dagger} and BRIAN D. E. CHATTERTON{ddagger}

* Laboratoire Magmas et Volcans, Université Blaise Pascal, 5 rue Kessler, 63038 Clermont-Ferrand Cedex, France
{dagger} Laboratoire de Paléontologie, Institut des Sciences de l’Evolution, Université Montpellier II, Cc 062, Place E. Bataillon, 34095 Montpellier Cedex 05, France
{ddagger} Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta T6G 2E3, Canada

{dagger} Author for correspondence: rfeist{at}isem.univ-montp2.fr

A new otarionine trilobite Otarionella rastrum sp. nov., from the late Emsian Mont Peyroux Formation (Montagne Noire, France), is described. Silicified remains, recovered from the underlying Bissounel Formation (early to late Emsian), are also attributed to this new species. These isolated silicified sclerites represent metaprotaspid to young holaspid growth stages, which enables the almost complete ontogeny of an otarionine trilobite with a spinose adult morphology to be described for the first time. Comparison with associated larval and juvenile growth stages of Cyphaspis reveal that the pattern of juvenile cranidial spine distribution in Otarionella rastrum sp. nov. differs from all patterns described so far in the Otarioninae, in particular that characterizing the tribe Otarionini. A second species, Otarionella lkomalii sp. nov., known only from a complete articulated specimen discovered in the early Eifelian of southern Morocco, is also described. Like the middle Eifelian Otarionella chamaeleo (Basse, 1997), this new species has only ten thoracic segments, with the fourth and the sixth segments each bearing a long axial spine. In the light of the new elements provided by the ontogenetic sequence of O. rastrum sp. nov. and the adult specimens of this species and O. lkomalii sp. nov., the putative synonymy of Otarionella and Otarion is rejected and a restricted concept of the genus Otarionella is defined.

Key Words: Trilobita • Devonian • ontogeny • systematics • evolution






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