How to translate text using browser tools
29 March 2024 The Neogondolella constricta (Mosher and Clark, 1965) group in the Middle Triassic of North America: speciation and distribution
Michael J. Orchard, Martyn L. Golding
Author Affiliations +

Conodont microfossils extracted from limestone at “Fossil Hill” in central Nevada about 60 years ago were the first of Middle Triassic age (ca. 243 My) discovered in North America. These canoe-shaped elements were named Neogondolella constricta, a species that subsequently has been reported worldwide. However, the scope of this species has remained uncertain because it was based on comparatively small early growth stages characterized by features lost during growth. Abundant specimens of the N. constricta group recovered from the original type locality form the basis for documenting changes in morphology during their accretionary growth and provide better definition of the species. This facilitates discrimination of similar species, 10 of which are distinguished in Nevada, including four new taxa; most of these are also identified in British Columbia. Successive associations through the Fossil Hill strata include elements with similar platform shapes but different relative lengths, the younger species being longer. This succession is calibrated with established ammonoid fossil zones and contributes to a parallel conodont biozonation. Eurasian occurrences of the Neogondolella constricta group are assessed and their correlation with the Nevadan scheme summarized.

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.

Michael J. Orchard and Martyn L. Golding "The Neogondolella constricta (Mosher and Clark, 1965) group in the Middle Triassic of North America: speciation and distribution," Journal of Paleontology 97(6), 1161-1191, (29 March 2024).
Accepted: 2 August 2023; Published: 29 March 2024
Get copyright permission
Back to Top