Aquilops

Chapter • Meet the dinosaur

Overview

Aquilops americanus was one of the smallest horned dinosaurs ever found. The whole animal was about the size of a crow or a rabbit – roughly 60 centimetres from snout to tail tip and weighing perhaps a kilogram and a half. The skull of the holotype measures only about 84 millimetres. At the front sat a parrot-like beak bone, the rostral, which in Aquilops was unusually tall and curved down into a sharp hook – it is this eagle-like beak that gave the dinosaur its name. In front of the eye socket was a distinct pocket in the upper jaw, a feature that helps palaeontologists tell Aquilops apart from other early ceratopsians. Unlike its famous later relatives Triceratops and Styracosaurus, Aquilops had neither horns nor a neck frill, just a small bony shelf at the back of the skull. Aquilops walked on two legs. Its hind limbs were long and slender relative to the body, and the tail acted as a counterweight when the animal ran – held horizontally, never dragged along the ground. At such a small size it was prey for almost everything bigger in the ecosystem, from crocodile relatives to predatory dinosaurs such as Deinonychus, which lived in the same landscape. It probably relied on alertness, short bursts of speed and dense undergrowth to survive. No feathers or bristles are preserved in Aquilops, but since related marginocephalians such as Psittacosaurus had long quills on the tail, similar structures cannot be ruled out. Its diet was plant matter. The powerful beak sheared off tough stems and leaves, and the teeth further back in the jaw ground the food down. In the Early Cretaceous, around 108 million years ago, there were no grasslands yet; instead Aquilops browsed on ferns, cycads, conifers and the first flowering plants, which had only recently begun to spread. Its low body height means it must have fed close to the ground. The fossil was found in 1997 by preparator Scott Madsen during an Oklahoma Museum of Natural History expedition to Carbon County, Montana, in the middle unit of the Cloverly Formation. The small skull, catalogued as OMNH 34557, sat in the collections for years before Andrew Farke and colleagues described it scientifically in 2014 in the journal PLOS ONE. The name means roughly "American eagle face". The find mattered because Aquilops is the oldest securely identified neoceratopsian from North America, showing that the group arrived from Asia rather than originating locally.

Chapter • Where it lived

Habitat

Aquilops lived roughly 109–104 million years ago, during the Albian stage of the Early Cretaceous. All known material comes from the middle unit of the Cloverly Formation in Carbon County, southern Montana, USA. The setting was a humid floodplain east of the rising mountains to the west, crossed by rivers and dotted with stands of conifers, ferns and early flowering plants. Dinosaurs from the same beds include Deinonychus, Tenontosaurus, Sauropelta and Acrocanthosaurus.

Chapter • Wild behavior

Behavior & Ecology

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Chapter • Scientific place

Taxonomy