A new species of stem actinopterygian, Helmolepis cyphognatus sp. nov., is reported from the Lower Triassic Sulphur Mountain Formation of western Canada (probably Smithian). This taxon differs from the only other known Early Triassic platysiagid, H. gracilis from the Lower Triassic Wordie Creek Formation of East Greenland (Griesbachian), in counts of branchiostegal rays, shape of the maxilla, shape (and possibly counts) of extrascapulars, and the size ratio of major opercular bones. In spite of their overall unfavorable preservation, the numerous available specimens amend our knowledge of the little known genus Helmolepis considerably: it has become evident that the morphology of Helmolepis cyphognatus sp. nov. comes closest to Platysiagum minus (Middle Triassic Besano Formation of central Europe). This study suggests placement of the two genera in the family Platysiagidae. Investigation of this new species also shows certain features of the cheek and the caudal fin are more primitive than previously believed, whereas the snout region is probably derived but of yet uncertain affinities in Helmolepis.

No abstract

No abstract

Contrary to ideas that Cretaceous fresh waters contained few teleosts, there were several taxa of Esocoidei (pikes and relatives) in North American Cretaceous rivers. Dentaries and palatines of Campanian to Maastrichtian age all have C-shaped tooth bases and other distinctive features of shape and foramina. The fossils include at least three distinct kinds, two of which are described here as new genera and species in the Esocidae: Estesesox foxi n. gen. and sp. and Oldmanesox canadensis n. gen. and sp.These old, diverse, and apparently primitive specimens show that pikes radiated when Eurasia and North America were still joined. Some references in the literature to the Cretaceous fish Platacodon Marsh are based on referred dentaries that are here identified as esocoid fossils. The Esocidae are the first example of a family of Recent North American freshwater teleosts that has been shown to have speciated in Cretaceous fresh waters and survived the terminal Cretaceous extinction.

Newly discovered fossil fish material from the Cretaceous Dinosaur Park Formation of Alberta, Canada, documents the presence of a tropical fish in this northern area about 75 million years ago (Ma). The living relatives of this fossil fish, members of the Characiformes including the piranha and neon tetras, are restricted to tropical and subtropical regions, being limited in their distribution by colder temperatures. Although characiform fossils are known from Cretaceous through to Cenozoic deposits, none has been reported previously from North America. The modern distribution of characiforms in Mexico and southern Texas in the southernmost United States is believed to have been the result of a relatively recent colonization less than 12 Ma. The new Canadian fossils document the presence of these fish in North America in the Late Cretaceous, a time of significantly warmer global temperatures than now. Global cooling after this time apparently extirpated them from the northern areas and these fishes only survived in more southern climes. The lack of early Cenozoic characiform fossils in North America suggests that marine barriers prevented recolonization during warmer times, unlike in Europe where Eocene characiform fossils occur during times of global warmth.