Thursday, December 11, 2014

[Paleontology • 2014] Aquilops americanus • A Ceratopsian Dinosaur from the Lower Cretaceous of Western North America, and the Biogeography of Neoceratopsia

Aquilops americanus Farke, Maxwell, Cifelli & Wedel, 2014
doi: 10.1371/journal.pone.0112055.g006
Life restoration by Brian Engh | 

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.

Skull and lower jaw of Aquilops
The only known fossil skull of Aquilops puts the dinosaur's small size in perspective; it was about the size of a rabbit.
photo: Andrew A. Farke |
Life restoration of Aquilops americanus in right lateral view.
The rendering is based on OMNH 34557 (holotype), with missing details patterned after Liaoceratops yanzigouensis and Archaeoceratops oshimai.
Life restoration by Brian Engh. doi: 10.1371/journal.pone.0112055.g006

Systematic Paleontology

Dinosauria Owen 1842  | Ornithischia Seeley 1887
Ceratopsia Marsh 1890  | Neoceratopsia Sereno 1986

Aquilops gen. nov.
Aquilops americanus sp. nov.

Holotype: OMNH 34557, a partial skull, with associated predentary, partial left dentary, and additional associated but unidentifiable fragments (Figs. 3–9; three-dimensional digital scans are contained in Files S7–S12).

Etymology: The genus name is derived from the Latin aquila, meaning “eagle,” and the Greek ops, meaning “face,” referring to the hooked beak on the skull of the animal. The species name, meaning “American” (Latin), reflects the species' status as the earliest unequivocal neoceratopsian in North America.

Locality and horizon: OMNH locality V1057, 45°N 109°W, Carbon County, Montana, United States of America (Figure 2); basal (?middle–late Albian) part of Unit VII (as defined by [20]), Cloverly Formation. Precise locality data are on file at OMNH and are available to qualified investigators upon request.

Figure 10. Hypothesis of phylogeny and biogeography for Neoceratopsia.
Some terminal taxa have been combined for space considerations, and the range bars for each taxon indicate uncertainty rather than known geological ranges. Continent icons indicate the ancestral areas reconstructed by DEC modeling. Silhouettes depict representative members of major clades and grades (Psittacosaurus by J. Headden, Zuniceratops by N. Tamura and modified by T. M. Keesey; Triceratops by R. Amos; all others by A. Farke; all images are CC-BY and provided via Full results are presented in File S1. doi: 10.1371/journal.pone.0112055.g006

Life restoration by Brian Engh |

Andrew A. Farke, W. Desmond Maxwell, Richard L. Cifelli and Mathew J. Wedel. 2014. A Ceratopsian Dinosaur from the Lower Cretaceous of Western North America, and the Biogeography of Neoceratopsia. PLoS ONE. DOI: 10.1371/journal.pone.0112055

Aquilops, the little dinosaur that could
Introducing Aquilops americanus
Bunny-Sized Dinosaur Was First of Its Kind in America via @NatGeo