2025/04/25 by Paul M. Barrett, Susannah C. R. Maidment · 1 voice · 2 citations
Earth and Planetary Sciences · Environmental Science · #Paleontology and Evolutionary Biology #Ichthyology and Marine Biology #Evolution and Paleontology Studies
paper · doi:10.3374/014.066.0102
A variety of small ornithischian dinosaur specimens collected from the Upper Jurassic Morrison Formation of Colorado and Wyoming were described by O.C. Marsh in the late 19th century. These include Nanosaurus agilis, N. rex, Laosaurus celer, L. gracilis, and L. consors. Another taxon from Wyoming, Drinker nisti, was added to this list more recently. The taxonomy of these species has undergone numerous revisions, with differing opinions regarding their validity and potential synonymies and in terms of the specimens referred to each of them. Their systematics have also been debated, with some taxa regarded as ornithopods and others as earlier diverging ornithischians. Here, we provide a critical reappraisal of these species based on first-hand examination of their type specimens. None of the relevant holotypes or syntype series exhibit either autapomorphies or unique character combinations that could be used to support their validity, and we regard all of these taxa as nomina dubia. Most of these specimens can be identified only as indeterminate neornithischians, but some include juvenile iguanodontian remains. “Drinker” possesses some dental and skull features that are known only in pachycephalosaurs, raising the possibility that this material represents an early diverging member of this clade. Other specimens formerly referred to these taxa should be regarded as indeterminate until they have been restudied in detail in order to establish their affinities rigorously and determine the true species richness of the Morrison Formation ornithischian fauna.