The fossil record for neoceratopsian (horned) dinosaurs in the Lower Cretaceous of North America primarily comprises isolated teeth and postcrania of limited taxonomic resolution, hampering previous efforts to reconstruct the early evolution of this group in North America. An associated cranium and lower jaw from the Cloverly Formation (?middle–late Albian, between 104 and 109 million years old) of southern Montana is designated as the holotype for Aquilops americanus gen. et sp. nov. Aquilops americanus is distinguished by several autapomorphies, including a strongly hooked rostral bone with a midline boss and an elongate and sharply pointed antorbital fossa. The skull in the only known specimen is comparatively small, measuring 84 mm between the tips of the rostral and jugal. The taxon is interpreted as a basal neoceratopsian closely related to Early Cretaceous Asian taxa, such as Liaoceratops and Auroraceratops. Biogeographically, A. americanus probably originated via a dispersal from Asia into North America; the exact route of this dispersal is ambiguous, although a Beringian rather than European route seems more likely in light of the absence of ceratopsians in the Early Cretaceous of Europe. Other amniote clades show similar biogeographic patterns, supporting an intercontinental migratory event between Asia and North America during the late Early Cretaceous. The temporal and geographic distribution of Upper Cretaceous neoceratopsians (leptoceratopsids and ceratopsoids) suggests at least intermittent connections between North America and Asia through the early Late Cretaceous, likely followed by an interval of isolation and finally reconnection during the latest Cretaceous.
Six compilations of fossil tetrapod families, spanning 100 years, each contain a broadly similar diversity pattern since the Upper Devonian. Comparison of four recent data bases, one of which is derived from a strict cladistic treatment, reveals widespread taxonomic and stratigraphic inaccuracies in three earlier data bases. Improvement of our interpretation of the tetrapod fossil record will come through continued taxonomic and stratigraphic revision as well as discovery of new fossils.
ABSTRACT The discovery of a nearly complete skeleton of Tenontosaurus tilletti and closely associated multiple shed teeth of the dromaeosaur Deinonychus antirrhopus provides evidence that may support the often repeated suggestion that Deinonychus was a pack-hunting predator. The taphonomy of the specimen adds weight to the additional conclusion that Tenontosaurus was the specific food preference of the Deinonychus predator population. Among theropods, the only other specific animals that have been found as unmistakable food objects are Bavarisaurus in Compsognathus and Coelophysis in Coelophysis. These two could have been examples of opportunistic incidental predation or scavenging, but it appears that Deinonychus actively preyed on a deliberate food choice, Tenontosaurus.
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