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Ankylosaurus origins

The rareness of Ankylosaurus was probably due to its preference for well inland habitat; AMNH 5895 and even the Scollard specimens may have been washed in from the uplands. This is unusual considering the ubiquity of Euoplocephalus and may support Starkov's scenario of Tyrannosaurus arising well inland in response to Alamosaurus. Perhaps there were different species of Euoplocephalus in the lowland and inland environments. The latter may have been long exposed to the ancestors of T. rex-something akin to Daspletosaurus or T. bataar-which appear excluded from the lowlands in the early Maastrichtian. It is possible that only the inland Euoplocephalus had time to adapt, giving rise to Ankylosaurus, and the virtual absence of ankylosaurids in the Lancian lowlands reflects the habitat preference of the surviving lineage and the vulnerability of E. tutus or whatever species was present in the upper Horseshoe Canyon.

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