A new, Late Cretaceous gonorynchiform fish in the genus †Notogoneus from drill core of crater-lake deposits in a kimberlite maar, Northwest Territories, Canada

Abstract

The Gonorynchiformes are a group of mostly marine fishes that are the sister group to the Otophysi (e.g., carps, tetras, catfishes). They include milkfishes (family Chanidae) and beaked sandfishes (family Gonorynchidae) among extant taxa. The only freshwater genus is the strictly fossil †Notogoneus, which until now contained eight species of Late Cretaceous to early Miocene age. A ninth species, †Notogoneus maarvelis, sp. nov., is described here from a single, small specimen found in a diamond-exploration drill core into strata deposited in a kimberlite maar lake in northern Canada. The maar crater was formed by the explosive emplacement of the “Wombat” kimberlite pipe, one of many in the nearby region. The new species is the oldest known member of the genus †Notogoneus and is dated by U–Pb geochronology on associated tephras as early Campanian or about 82 Ma. Although very small, the type and only specimen is very similar in morphology, meristics, and body proportions to the type species †N. osculus. The most important difference is that the origin of the pelvic fin in the new species is beneath vertebral centrum 26, whereas the origin of the dorsal fin is above vertebral centrum 20. In †N. osculus, in contrast, the two fins both originate opposite centrum 22 or 23. The new species is the only one known among those of †Notogoneus or the extant Gonorynchus in which the pelvic fin origin is well behind that of the dorsal fin. The new species agrees with †N. osculus and other congenerics in key attributes of the genus †Notogoneus, including subopercular clefts and, in the caudal skeleton, autogenous parhypural plus hypurals 1 and 2. The bones of the new species ossified at a much smaller size than did those of young individuals of †N. osculus, suggesting that the new species likely attained a much smaller adult size as well. This small, new species, as well as other unidentified fish fragments, was discovered in a core into maar-lake deposits within otherwise fossil-poor areas of the North American craton. Such discoveries highlight the potential importance of maar lakes and similar crater-lake settings for revealing more about fish diversity in the Late Cretaceous than has been previously known.