Tyrannosauroid ages.csv 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.

白垩纪时期，全球地理变迁引发的效应影响了陆生脊椎动物的演化辐射与类群更替。然而，中白垩世的化石记录极为匮乏，使得学界难以厘清恐龙与其他陆生脊椎动物如何响应上述地质事件。本文记述了产自鲜为人知的北美古陆块阿巴拉契亚地区桑托期至早坎潘期的两类恐龙：对一件体型庞大、可能属于新物种的兽脚类标本的重新研究表明，该类群大概率隶属于一个仅发现于阿巴拉契亚的暴龙超科新演化支；另一具部分骨架则属于鸭嘴龙科（Hadrosauridae）的早期类群——该类群是一类极为成功的植食性恐龙演化支。该骨架与大西洋沿岸平原出土的首批围产期恐龙标本伴生。这两件暴龙超科与鸭嘴龙科标本，证实了目前仅存的晚桑托期恐龙动物群之一，并帮助精准确定了两类广泛分布的恐龙演化支系重要解剖学革新的出现时间。对该暴龙超科与鸭嘴龙科标本的系统发育位置分析显示，桑托期阿巴拉契亚恐龙动物群竟与同时期欧亚大陆的恐龙动物群具有高度相似性；而仅由阿巴拉契亚恐龙分类群构成的演化支的存在，证明了阿巴拉契亚恐龙组合存在一定程度的特有性，这一现象可归因于多轮地理隔离事件。