Early jurassic spiriferid brachiopodsfrom Alaska and their paleogeographic significance

Abstract

Spiriferid brachiopods are described in detail for the first time from the Jurassic of North America. The specimens are referred to the genera Liospiriferina and Callospiriferina, both originally described from the Early Jurassic of Morocco and Spain by Rousselle (1977). The species identified herein, Liospiriferina rostrata and Callospiriferina tumida, are known from Europe, South America, and northern Africa, with L. rostrata also recorded from Indonesia. The new occurrences in Alaska indicate a lower-latitude placement during the Early Jurassic, at least temperate latitudes, for the Farewell (probably during the Sinemurian) and Peninsular (Sinemurian-basal Toarcian) terranes. Liospiriferina and Callospiriferina range through much of the Early Jurassic. These new occurrences are significant because they indicate further parallels between the composition of Mesozoic brachiopod faunas of Europe, where faunas were initially monographed in the nineteenth century, and those of North America and South America. The spiriferids therefore show evidence of survival in North America beyond end-Triassic extinctions, underscoring the global nature of the continuity of the Spiriferida into the Jurassic before their demise by the end of the Early Jurassic. In terms of the composition of Mesozoic brachiopod faunas spiriferids have been identified as preferring deeper-water shelf environments. It has not been determined if this was the case for these Jurassic spiriferids: the collections studied herein show Liospiriferina to be associated with sandy lithologies while Callospiriferina was collected from a black shale. Based on external morphology Liospiriferina is closely homeomorphic with the cosmopolitan Triassic athyrid brachiopod Oxycolpella. However, on closer examination and preparation of serial sections of internal structures the Alaskan specimens showed the presence of dental lamellae, a large, persistent median septum, a spiralium (spiral brachidium), and punctate shell, indicating affinities to the Spiriferida. The material had originally been tentatively identified as terebratulids.