A Ceratopsian Dinosaur from the Lower Cretaceous of Western North America, and the Biogeography of Neoceratopsia.

Andrew A Farke,W Desmond Maxwell,Richard L Cifelli,Mathew J Wedel,Peter Wilf

doi:10.1371/journal.pone.0112055

Andrew A Farke, W Desmond Maxwell + Show 3 more

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https://doi.org/10.1371/journal.pone.0112055

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Abstract

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.

Highlights

Neoceratopsia constitute one of the most taxonomically diverse and morphologically disparate clades of ornithischian dinosaurs during the Cretaceous, and are known for their highly derived cranial anatomy (Figure 1; [1,2,3])
A. americanus probably originated via a dispersal from Asia into North America; the exact route of this dispersal is ambiguous, a Beringian rather than European route seems more likely in light of the absence of ceratopsians in the Early Cretaceous of Europe
Other Early–early Late Cretaceous probable neoceratopsians from North America are represented by teeth from the Arundel Clay of Maryland [10], believed to be early Albian (,113–110 Ma; [83]); teeth from the uppermost Cedar Mountain Formation of Utah [10], of earliest Cenomanian age (,98 Ma; [9]) and a partial postcranial skeleton from the middle to upper Albian Wayan Formation of Idaho (,110–101 Ma; [11])

Summary

Introduction

Neoceratopsia constitute one of the most taxonomically diverse and morphologically disparate clades of ornithischian dinosaurs during the Cretaceous, and are known for their highly derived cranial anatomy (Figure 1; [1,2,3]). The timing and phylogenetic affinities of the clade’s first dispersal into North America have remained unclear, due to a dearth of fossilized material that, until now, has consisted of relatively uninformative isolated teeth and postcranial elements [9,10,11,12]. These specimens indicate the presence of Neoceratopsia in the Early Cretaceous of North America, but cannot be further identified. There is uncertainty on whether the dispersal was directly between North America and Asia (trans-Beringia) or via Europe [12,13,18], the absence of important Asian clades in Europe somewhat favors a trans-Beringian dispersal hypothesis [13,18]

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