Ankylosaurian dinosaur palaeoenvironmental associations were influenced by extirpation, sea-level fluctuation, and geodispersal

Abstract

More species of nodosaurid ankylosaurians than ankylosaurid ankylosaurians have been found in marine sediments, and some previous quantitative studies of global dinosaur occurrences provide support for an association between nodosaurids and marine depositional environments. We compiled a dataset of global ankylosaurian occurrences and found that the geographic distribution of marine ankylosaurian occurrences is regionally biased with 54% of records stemming from western North America in the Cretaceous—a time of regional highstands in sea level and epicontinental flooding, coupled with differential extirpation of ankylosaurian subclades inhabiting the Western Interior Basin (WIB). Within the Western Interior Basin, we found little statistical support for an association between ankylosaurian subclades and palaeoenvironment in a chronological context. Only the Albian–Cenomanian transgressive–regressive cycle had statistical support for an overabundance of nodosaurids in marine environments compared to ankylosaurids. The apparent overabundance of nodosaurids relative to ankylosaurids in marine sediments in the Western Interior Basin overall cannot be decoupled from the extirpation of North American ankylosaurids during the Cenomanian and the subsequent absence of ankylosaurids in North America during the Turonian to early Campanian prior to the immigration of Asian ankylosaurine ankylosaurids. The North American ankylosaurian record highlights the difficulty in interpreting habitat preferences in the context of a shifting seaway, regional extinctions, and intercontinental dispersals.