'Glishades ericksoni', an indeterminate juvenile hadrosaurid from the Two Medicine Formation of Montana: implications for hadrosauroid diversity in the latest Cretaceous (Campanian-Maastrichtian) of western North America
'Glishades ericksoni', an indeterminate juvenile hadrosaurid from the Two Medicine Formation of Montana: implications for hadrosauroid diversity in the latest Cretaceous (Campanian-Maastrichtian) of western North America
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DOI：
10.1007/s12549-012-0097-1
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发表时间：
2013-03-01
影响因子：
1.4
通讯作者：
Evans, David C.
中科院分区：
文献类型：
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作者：
Campione, Nicolas E.;Brink, Kirstin S.;Evans, David C.
Glishades ericksoni是根据在美国蒙大拿州晚坎帕尼亚双药组收集到的部分成对前颌骨命名的，被描述为一种非鸭嘴龙。这种对G. ericksoni的解释对鸭嘴龙的多样性和分布具有重要意义，因为它代表了北美晚坎帕纪首次出现非鸭嘴龙鸭嘴龙，因此表明这些形式与鸭嘴龙之间有很长一段时间的同生关系，或者与亚洲的生物交换。鉴于它的小尺寸，因此潜在的幼鱼状态，这里重新评估了G. ericksoni的分类身份。与两个医学组（原龙、鹰头龙和母龙）中大小相近、分类确定的和同时期的鸭嘴龙标本的比较表明，用于区分G. ericksoni为非鸭嘴龙的特征组合在鸭嘴龙中分布更广泛或单独可变，或者可以解释为个体发生变异的结果。特别是，在原龙、鹰头龙和母龙的幼年个体中也发现了用于诊断埃里克森氏杆菌的独特特征组合。在原始的系统发育分析中，将这些分类群的幼体包括在内，根据可比的解剖结构进行评分，恢复了鸭嘴龙科以外的幼年鸭嘴龙标本。因此，不能自信地将G. ericksoni与在双药组上部和中部常见的幼年saurolophine区分出来，因此被认为是一种普通的dubi。考虑到它们在样本丰富的晚坎帕纪和马斯特里希特沉积中缺失，在北美西部的晚坎帕纪，非鸭蛋龙似乎已经完全被鸭蛋龙所取代。
Glishades ericksoni was named on the basis of partial paired premaxillae collected from the Late Campanian Two Medicine Formation of Montana, and was described as a non-hadrosaurid hadrosauroid. This interpretation of G. ericksoni has significant implications for hadrosauroid diversity and distribution because it represents the first occurrence of a non-hadrosaurid hadrosauroid in the Late Campanian of North America, and therefore implies either a prolonged period of sympatry between these forms and hadrosaurids or a biotic interchange with Asia. Given its small size, and therefore potential juvenile status, the taxonomic identity of G. ericksoni is re-evaluated here. Comparison with similarly-sized, taxonomically determinate, and coeval hadrosaurid specimens from the Two Medicine Formation (Prosaurolophus, Gryposaurus, and Maiasaura) suggest that the combination of characters used to distinguish G. ericksoni as a non-hadrosaurid hadrosauroid are more widely distributed or individually variable in hadrosaurids, or can be explained as the result of ontogenetic variation. In particular, the unique combination of characters used to diagnose G. ericksoni is also found in juvenile individuals of Prosaurolophus, Gryposaurus, and Maiasaura. Inclusion of juveniles of these taxa, scored on the basis of comparable anatomy, in the original phylogenetic analysis recovers the juvenile hadrosaurid specimens outside Hadrosauridae. Consequently, G. ericksoni cannot be confidently differentiated from a juvenile saurolophine, which are common in the upper and middle sections of the Two Medicine Formation, and is thus considered a nomen dubium. Given their absence in well-sampled Late Campanian and Maastrichtian deposits, non-hadrosaurid hadrosauroids appear to have been completely replaced by hadrosaurids in western North America by the Late Campanian.