Description of a New Upper Triassic Fossil Lungfish (Sarcopterygii:dipnoi) Locality From the Garita Creek Formation, East-Central New Mexico, With a Reevaluation of Late Triassic Lungfish Diversity in the American Southwest

Mesozoic lungfish fossils ordinarily consist of isolated tooth plates. Many tooth plates, typically assigned to Arganodus, are known from the Upper Triassic of the American Southwest. The new Homestead Site at Garita Creek is the most ex-tensive vertebrate assemblage described from the Garita Creek Formation in east-central New Mexico. It has yielded enough new lungfish fossils (18 nearly complete-complete and 43 fragmentary tooth plates) to qualify as the second-richest Upper Triassic lungfish site in North America. We measured the tooth plates of Homestead and several others from the Chinle, identifying multiple tooth plate morphotypes, including ones with only 4–5 ridges that fall outside the diagnosis of Arganodus, suggesting that the Homestead assemblage preserves at least two taxa. Reevaluating 32 previously published PEFO tooth plates further supports the presence of two morphologies: a more common morph we assign to Arganodus sp., and a second morph that we assign to cf. Ptychoceratodus. Ptychoceratodus has a limited presence in North American strata but is known from the Late Triassic of Greenland. A ptychoceratodontid in the Upper Triassic of western North America greatly increases their geographic range during the Triassic and shows that they coexisted with Arganodus on at least three modern continents.