The Neogondolella constricta (Mosher and Clark, 1965) group in the Middle Triassic of North America: speciation and distribution

Abstract

Neogondolella constricta (Mosher and Clark, 1965) from the Prida Formation at Fossil Hill in central Nevada was the first conodont described from Middle Triassic strata in North America. The species has since been widely reported from elsewhere despite uncertainties about its taxonomic scope and that of similar related taxa. Poor definition of these taxa has spawned a diverse nomenclature and inhibited use of the group in biozonation. Starting with a growth series of topotype N. constricta, we reassess allied contemporaneous taxa from North America. In Nevada, 11 conodont taxa are identified: N. constricta, N. aldae Kozur, Krainer, and Mostler, 1994b, N. cornuta Budurov and Stefanov, 1972, N. ex gr. mesotriassica (Kozur and Mostler, 1982), N. postcornuta (Kovács, 1994), N. posterolonga Kozur, Krainer, and Mostler, 1994b, N. quasiconstricta n. sp., N. quasicornuta n. sp., and three subspecies of N. excentrica Budurov and Stefanov, 1972. Successive associations of taxa display symmetry transition in posterior platform configuration. Subdivision of the upper Anisian–lower Ladinian is provided by dominant N. constricta plus relatively uncommon N. quasiconstricta n. sp. and N. excentrica primitiva n. subsp. in the Rotelliformis ammonoid zone. This is followed in the Meeki through the Subasperum zones by dominant N. cornuta, associated N. posterolonga, plus relatively uncommon N. quasicornuta n. sp., and a variety of asymmetric elements: the Meeki Zone includes N. aff. N. cornuta; the Occidentalis Zone adds N. e. excentrica; and finally, N. e. sigmoidalis n. subsp. appears in the Subasperum Zone. In British Columbia, the three subspecies of N. excentrica are recognized in, respectively, the Deleeni, Chischa, and Matutinum (and younger) ammonoid zones. UUID: http://zoobank.org/7d58c8c8-cd68-498f-bb84-5d43de47f779