Hadrosauridae.nex from Dinosaurs from the Santonian–Campanian Atlantic coastline substantiate phylogenetic signatures of vicariance in Cretaceous North America

During the Cretaceous, diversifications and turnovers affected terrestrial vertebrates experiencing the effects of global geographical change. However, the poor fossil record from the Middle Cretaceous has concealed how dinosaurs and other terrestrial vertebrates responded to these events. I describe two dinosaurs from the Santonian to Early Campanian of the obscure North American paleolandmass Appalachia. A revised look at a large, potentially novel theropod shows that it likely belongs to a new clade of tyrannosauroids solely from Appalachia. Another partial skeleton belongs to an early member of the Hadrosauridae, a highly successful clade of herbivorous dinosaurs. This skeleton is associated with the first perinate dinosaur specimens from the Atlantic Coastal Plain. The tyrannosauroid and hadrosaurid substantiate one of the only Late Santonian dinosaur faunas and help pinpoint the timing of important anatomical innovations in two widespread dinosaur lineages. The phylogenetic positions of the tyrannosauroid and hadrosaurid show Santonian Appalachian dinosaur faunas are surprisingly comparable to coeval Eurasian ones, and the presence of clades formed only by Appalachian dinosaur taxa establishes a degree of endemism in Appalachian dinosaur assemblages attributable to episodes of vicariance.

白垩纪（Cretaceous）时期，全球地理格局变化引发的效应促使陆生脊椎动物发生类群辐射与更替。然而，白垩纪中期（Middle Cretaceous）的化石记录极度匮乏，使得我们难以探明恐龙与其他陆生脊椎动物对上述地质事件的响应模式。本文记述了产自隐没的北美古陆块阿巴拉契亚（Appalachia）桑托阶（Santonian）至坎潘早期（Early Campanian）的两件恐龙化石：对一件体型庞大、疑似新种的兽脚类（theropod）标本的重新研究显示，该标本隶属于一个仅分布于阿巴拉契亚的暴龙超科（tyrannosauroids）新演化支；另一件部分保存的骨骼则属于鸭嘴龙科（Hadrosauridae）的早期类群——该科是一类极为成功的植食性恐龙演化支。该鸭嘴龙类骨骼与大西洋沿岸平原（Atlantic Coastal Plain）出土的首批围产期恐龙标本伴生出土。这两件暴龙超科与鸭嘴龙科标本，确证了目前仅存的晚桑托阶恐龙动物群之一，并助力精准确定两个广布恐龙支系中关键解剖学创新的出现时间。该暴龙超科与鸭嘴龙科的系统发育位置（phylogenetic positions）表明，桑托阶阿巴拉契亚恐龙动物群与同时期的欧亚大陆动物群存在出人意料的相似性；而仅由阿巴拉契亚恐龙分类群构成的演化支的存在，证明阿巴拉契亚恐龙组合存在一定程度的特有性（endemism），该特有性可归因于多轮隔离分化（vicariance）事件。