A new Late Cretaceous (Turonian) basal euteleostean fish from Lac des Bois of the Northwest Territories of Canada

Abstract

A new genus and species of Late Cretaceous euteleost, Avitosmerus canadensis, is described from an assemblage of fossil fishes found in a Late Cretaceous (Turonian) unnamed member (unit E) of the Great Bear Basin from Lac des Bois, Northwest Territories, Canada. It is a small fusiform fish characterized by a long slender supraorbital, the presence of a small suprapreopercle, branches of the preopercular sensory canal that reach the edge of the preopercle, and an anterior supraneural that is twice as large as those posterior to it. Additionally, elements of its caudal fin show a high degree of fusion. Avitosmerus is one of ten described Cretaceous basal euteleosts that are found worldwide (Avitosmerus, Barcarenichthys, Erichalcis, Gaudryella, Gharbouria, Humbertia, Kermichthys, Manchurichthys, Paravinciguerria, and Stompooria). Avitosmerus and Erichalcis are the only two basal euteleosts that have been described from the Cretaceous of North America. Placement of Avitosmerus into the Euteleostei is based on the presence of a free stegural, and the large first supraneural. Both of these characters are somewhat controversial and are in need of reexamination. Avitosmerus shares a number of characters with the other Cretaceous basal euteleosts, as well as Recent basal euteleosts, including a separate rostrodermethmoid and mesethmoid (Gaudryella, Erichalcis, Gharbouria, the Osmeridae, and the Coregonidae), lobate condyles of the hyomandibula (Avitosmerus, Gaudryella, and Gharbouria), leaf-shaped neural spine on the first preural centrum (Kermichthys), and the fusion of the parhypural, first, and second hypurals (Gaudryella).

New information on two Late Cretaceous (Turonian) fishes from Lac des Bois, Northwest Territories, Canada

“…The premaxillary teeth are larger, fewer and spaced farther apart than those of the maxilla. The maxilla is less deep than previously described (Fielitz 2002: fig. 7), broadly arched with a narrow edentate head and has a fringe of small closely spaced teeth along the rest of the bone.…”

“…The new material includes individuals ranging from the smallest specimen, CMN 56504, with a head length of 18 mm, to the largest specimen (UALVP 55704) having a head length of 39 mm. Most of the 2010 specimens are smaller than the holotype and figured specimens from the 1969 collection (Fielitz 2002), suggesting smaller individuals are better preserved in the shales compared to the nodules. Several isolated elements that can be confidently attributed to A. canadensis were also collected, allowing the anatomy of these elements (hyomandibula, dentary, premaxilla, preopercle, and pelvic girdle) to be better known.…”

“…EUTELEOSTEI sensu Arratia, 1997 EUTELEOSTEI incertae sedis Avitosmerus canadensis Fielitz, 2002 Figures 3 plete fish in part and counterpart.…”

“…Fielitz (2002) described this new taxon based on a nearly complete specimen (the holotype, CMN 17456) and 16 other specimens varying from mostly complete to isolated heads and caudal fins. The material from the 2010 collections also consists of many more isolated heads than complete specimens.…”

“…The fossils collected by Bardack and his team were almost exclusively recovered from calcareous concretions, collected in situ and where tumbled down along the base of a kilometre-long shale outcrop. From this collection, several fishes were named including Avitosmerus canadensis Fielitz, 2002, a small euteleost, Aquilopiscis wilsoni Cumbaa and Murray, 2008, a pachyrhizodontid, and Ornatipholis sahtu Cumbaa and Murray, 2008, an enchodontoid. Other fishes reported from the locality are an unidentified caturid amiiform, Ichthyodectes ctenodon (Ichthyodectiformes), Osmeroides sp.…”