Faculty of Biosphere-Geosphere Science, Okayama University of Science, Ridaicho, Kita-ku, Okayama city, Okayama, Japan.
Perot Museum of Nature and Science, Dallas, Texas, United States of America.
PLoS One. 2020 May 6;15(5):e0232410. doi: 10.1371/journal.pone.0232410. eCollection 2020.
Hadrosaurid fossils from the Liscomb Bonebed (Prince Creek Formation, North Slope, Alaska) were the first dinosaur bones discovered from the Arctic. While the Prince Creek Formation hadrosaurids were long identified as Edmontosaurus, a member of the sub-clade Hadrosaurinae, they were recently assigned to a newly-erected taxon, Ugrunaaluk kuukpikensis. However, taxonomic status of the new taxon is ambiguous largely due to the immature nature of the specimens upon which it was based. Here we reexamine cranial elements of the Prince Creek Formation hadrosaurine in order to solve its taxonomic uncertainties. The Prince Creek Formation hadrosaurine possesses a short dorsolateral process of the laterosphenoid, one of the diagnostic characters of Edmontosaurus. The Prince Creek Formation hadrosaurine also shows affinity to Edmontosaurus regalis in the presence of a horizontal shelf of the jugal. Our morphological comparisons with other North American Edmontosaurus specimens and our phylogenetic analyses demonstrate that the Prince Creek Formation hadrosaurine should be re-assigned to Edmontosaurus. Because the Prince Creek Formation Edmontosaurus shows differences with lower latitude Edmontosaurus in a dorsoventrally short maxilla, presence of a secondary ridge on the dentary teeth, and the absence of the transverse ridge between basipterygoid processes of the basisphenoid, we consider that the Prince Creek Formation Edmontosaurus should be regarded as Edmontosaurus sp. until further discoveries of mature hadrosaurines from the Prince Creek Formation Bonebed and/or equivalently juvenile Edmontosaurus specimens from the lower latitudes allow direct comparisons. The retention of the Prince Creek Formation hadrosaurine as Edmontosaurus re-establishes a significant latitudinal distribution for this taxon. Despite the large latitudinal distribution of the taxon, the morphological disparity of Edmontosaurus is small within Hadrosaurinae. The small morphological disparity may be related to the relatively low latitudinal temperature gradient during the latest Cretaceous compared to present day, a gradient which might not have imposed significant pressure for much morphological adaptations across a broad latitudinal range.
从利斯考姆骨床（北坡，阿拉斯加）发现的鸭嘴龙化石是在北极发现的第一批恐龙骨骼。虽然普林斯克里克组鸭嘴龙长期以来被认为是埃德蒙顿龙，是鸭嘴龙亚科的一个分支，但它们最近被归为一个新建立的分类群，Ugrunaaluk kuukpikensis。然而，由于基于其建立的标本的不成熟性质，新分类群的分类地位仍然存在模糊性。在这里，我们重新检查普林斯克里克组鸭嘴龙的头骨元素，以解决其分类不确定性。普林斯克里克组鸭嘴龙具有短的后外侧蝶骨侧突，这是埃德蒙顿龙的一个诊断特征。普林斯克里克组鸭嘴龙也在颧骨存在水平架子的情况下与埃德蒙顿龙 regalis 有亲缘关系。我们与其他北美埃德蒙顿龙标本的形态比较以及我们的系统发育分析表明，普林斯克里克组鸭嘴龙应重新归类为埃德蒙顿龙。由于普林斯克里克组的埃德蒙顿龙在垂直方向上的上颌骨较短、下颌骨齿上存在二次脊以及基蝶骨的基翼突之间没有横脊等方面与低纬度的埃德蒙顿龙存在差异，我们认为普林斯克里克组的埃德蒙顿龙应该被视为埃德蒙顿龙 sp.，直到在普林斯克里克组骨床中发现更多成熟的鸭嘴龙或从低纬度地区发现同等的幼年埃德蒙顿龙标本进行直接比较。将普林斯克里克组鸭嘴龙保留为埃德蒙顿龙，重新建立了该分类群的重要纬度分布。尽管该分类群的纬度分布范围很广，但在鸭嘴龙亚科内部，埃德蒙顿龙的形态差异很小。形态差异较小可能与白垩纪晚期相对较低的纬度温度梯度有关，与现代相比，该梯度不会在广泛的纬度范围内对形态适应施加显著压力。
