Abstract
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.
Highlights
Fishes are an important component of Late Cretaceous non-marine paleocommunities and understanding their diversity and distribution is important for a full understanding of the taxonomic composition of these paleocommunities and changes in their organization over time
To help get a more accurate understanding of teleosts in the Late Campanian of Alberta, Brinkman and Neuman (2002) and Neuman and Brinkman (2005) adopted a combined included in a formal taxonomic framework and distinctive elements that could not be identified below the level of Teleostei were given alpha-numeric designations. These were evaluated as to whether or not they represented distinct taxonomic groups, and when it was concluded that this was most likely the case, they were treated as taxonomically distinct indeterminate teleosts. This approach allowed all available elements to be included in the analysis of diversity and distribution, which increases the likelihood that paleoecologically significant patterns of faunal changes through the Late Cretaceous can be recognized
Horseshoeichthys was reported by Newbrey et al (2010) on the basis of vertebral centra and jaw elements that matched those of the type specimen, one of the few articulated non-marine teleost specimens known from the Late Cretaceous of the Western Interior Basin
Summary
Fishes are an important component of Late Cretaceous non-marine paleocommunities and understanding their diversity and distribution is important for a full understanding of the taxonomic composition of these paleocommunities and changes in their organization over time. These were evaluated as to whether or not they represented distinct taxonomic groups, and when it was concluded that this was most likely the case, they were treated as taxonomically distinct indeterminate teleosts This approach allowed all available elements to be included in the analysis of diversity and distribution, which increases the likelihood that paleoecologically significant patterns of faunal changes through the Late Cretaceous can be recognized. In subsequent papers, this combined taxonomic/morphotype approach was used to document non-marine teleost fishes from vertebrate microfossil localities of Utah and Montana ranging in age from the Cenomanian to the. The Milk River Formation is laterally equivalent to the marine Lea Park Formation, to the south-east, it is equivalent to the Deadhorse Coulee Member of the Eagle
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
