Erratum: Non-marine fishes of the late Santonian Milk River Formation of Alberta, Canada – evidence from vertebrate microfossil localities

n/a

Non-marine fish of the late Santonian Milk River Formation of Alberta, Canada – evidence from vertebrate microfossil localities

The diversity of fishes from the late Santonian Milk River Formation is investigated using a combined taxonomic/morphotype approach. Twenty-one taxa are present, including four elasmobranchs, seven basal actinopterygians, and of ten teleosts. The Milk River fish assemblage is more similar to assemblages from southern Utah than it is to the late Campanian assemblage of Alberta in the presence of the elasmobranch Lonchidion and a member of amiid subfamily Vidalamiinae, the relatively high abundance of the ostariophysan teleost U3/BvD, and the absence of sturgeon, Holostean A, Holostean B, and Coriops. This similarity is hypothesized to be the result of a northern shift in the distribution of these taxa during times of high global temperature, resulting in the presence of a “southern” faunal assemblage in Alberta during the late Santonian. In the relative abundance patterns of major groups of fish, the Milk River Formation assemblage is similar to late Campanian assemblages and different from those of late Maastrichtian in that amiids and lepsisoteids are of relatively low abundance. The abundance of acanthomorph teleosts in the Milk River Formation is similar to that of contemporaneous assemblages from Utah, which supports a pattern of increasing abundance of acanthomorphs from their first occurrence in non-marine vertebrate assemblages of the Western Interior in the Coniacian through to the end of the Cretaceous.

A new tribotherian (Mammalia, Boreosphenida) from the late Santonian to early Campanian upper Milk River Formation, Alberta

A new tribotherian mammal, Tirotherium aptum gen. et sp. nov., is described from the late Santonian to early Campanian upper Milk River Formation of Verdigris Coulee, southern Alberta, Canada. The new mammal is known only from isolated teeth, five upper and three lower molars. The upper molars represent two or possibly three pre-ultimate loci and are marked by reduction and loss of the stylar shelf anteriorly, loss of the stylocone, a paracone that is larger than the metacone, weakly developed conules, a low, small protocone, and specialized postvallum single-rank shear. The lower molars probably represent two pre-ultimate loci and are characterized by an anteriorly positioned paraconid, trenchant paracristid, small, posterolingual metaconid, a distal metacristid, broadly open trigonid angle, and a short, basined talonid in which the hypoconulid is closer to the entoconid than to the hypoconid. The molars of Tirotherium most closely resemble those of Picopsis Fox, 1980, a tribotherian that also occurs in the upper Milk River Formation, but the molars of Tirotherium are significantly larger than those of Picopsis. Nonetheless, Tirotherium aptum is best classified in the Picopsidae, a boreosphenidan family of tiny mammalian faunivores of uncertain relationships to other tribotherians, and displaying a unique mosaic of primitive and derived characters.

A new articulated freshwater fish (Clupeomorpha, Ellimmichthyiformes) from the Horseshoe Canyon Formation, Maastrichtian, of Alberta, CanadaThis article is one of a series of papers published in this Special Issue on the theme Albertosaurus.

Horseshoeichthys armaserratus , gen. et sp. nov., (Clupeomorpha: Ellimmichthyiformes: Sorbinichthyidae) is described from the Horseshoe Canyon Formation (Maastrichtian), Albertosaurus bonebed locality, Alberta, Canada. Horseshoeichthys armaserratus is classified as an ellimmichthyiform based on the following characters: the presence of a sixth infraorbital with a sensory canal that leads to the fifth infraorbital, absence of a supraorbital bone, subrectangular predorsal scutes, parietals in contact with each other at the midline, and two supramaxillae. The specimen is classified in the Sorbinichthyidae Family as it has abdominal ribs articulating in pits on the centra, posterior spines on predorsal scutes, and absence of a median spine on predorsal scutes. A new genus and species is proposed based on the presence of (anteriorly) Y-shaped mesethmoid, supraorbital, subrectangular predorsal scutes with coarse, rounded serrae on the posterior margin and a large anterior projection, scales with serrae on the circuli, and two postcleithra. This specimen represents the first freshwater ellimmichthyiform from the Upper Cretaceous of North America and the highest paleolatitude (59°N) occurrence known for the family. Furthermore, the dentary and centra have distinctive morphologies that are matched by specimens in microvertebrate localities from three underlying formations, including the Milk River Formation (Santonian), which indicates at least a 14 million year history for this lineage.

Diversity and variation of theropod dinosaur teeth from the uppermost Santonian Milk River Formation (Upper Cretaceous), Alberta: a quantitative method supporting identification of the oldest dinosaur tooth assemblage in Canada

The Santonian Deadhorse Coulee Member of the Milk River Formation preserves the oldest dinosaur body fossils found in Alberta. However, vertebrate remains consist almost exclusively of isolated elements and microvertebrate assemblages. Here, 1572 relatively complete shed non-avian theropod teeth from 20 localities in the Deadhorse Coulee Member are measured and analyzed to assess species diversity. Teeth are referred to or similar to Tyrannosaurinae indet., cf. Richardoestesia gilmorei , cf. Richardoestesia isosceles , Dromaeosauridae indet., Dromaeosaurinae indet., Velociraptorinae indet., and cf. Paronychodon lacustris . For the taxa identified, the large sample size allows for the assessment of their range of variation and accurate identification, without the benefit of comparable material of this age. Multivariate statistics, including a principal component analysis and a canonical variate analysis, provide reasonable separation of all taxa, although better results are achieved by separate analyses based on qualitative observations of denticle shape. The best results of the canonical variate analysis identified 96.0% of specimens correctly. This corroborates the qualitative identification of specimens and illustrates a valid way of evaluating diversity in areas and formations from which no described jaw material is known.