Bio geography and morphological conservatism of tropidoleptus brachiopoda orthida during the devonian

Isaacson, P.E.; Perry, D.G.

Journal of Paleontology 51(6): 1108-1122


ISSN/ISBN: 0022-3360
Accession: 004829232

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Very few articulate brachiopods exhibit imperceptible morphologic change through as long a span of time approaching that of a geologic period. Tropidoleptus occurs in Gedinnian through Frasnian age beds in the circum-Atlantic region, with early forms exhibiting many of the same features and morphological variances (e.g., angle of divergence of the tooth sockets, length of the median septum, number and nature of the costae) which are found in later forms. Considering that the Early Devonian was marked by high faunal provincialism (presumably due to thermal barriers to faunal migration and restriction of seaways during mid-Early Devonian regression), it appears that Tropidoleptus was an eurythermal organism, and occurred with endemic brachiopod faunas in the Rhenish-Bohemian Region of the Old World Realm, and in the Malvinokaffric Realm. The genus also persisted into Middle and Late Devonian times of relative faunal cosmopolitanism. Starting in Nova Scotia [Canada] in Gedinnian age (earliest Devonian) beds, Tropidoleptus occurrences apparently made a clockwise migration around the Atlantic (or Proto-Atlantic) Ocean, with Siegenian occurrences in central Europe, Emsian-Eifelian occurrences in North Africa and most of South America, and Middle and Late Devonian occurrences in the Appalachian Basin. The genus remained in North Africa in beds ranging through Frasnian in age. Coincident with the Taghanic onlap of the North American craton is the appearance of Tropidoleptus in New Mexico [USA] in Frasnian beds.