Aquilops Temporal range: Early Cretaceous, 107 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Holotype skull seen from the sides (left), above, and below (right)
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Clade:	Dinosauria
Clade:	†Ornithischia
Clade:	†Ceratopsia
Clade:	†Neoceratopsia
Genus:	†Aquilops Farke et al., 2014
Species:	†A. americanus
Binomial name
†Aquilops americanus Farke et al., 2014

Aquilops is an early herbivorous ceratopsian dinosaur dating from the Early Cretaceous of North America, approximately 109 million to 104 million years ago. The type species is A. americanus.

Discovery and naming

In 1997, the paleontologist Scott K. Madsen was volunteering for an expedition with the purpose of finding microfossils, mammals and lower cretaceous rocks along the border of Montana and Wyoming. In the Cloverly Formation of Carbon County, southern Montana, he noticed a grapefruit-sized bit of white on a rock, picked it up and noticed it contained teeth, realizing it was a skull of rare size. He brought it to his camp, where it was already clear the teeth belonged to a plant-eating dinosaur, assumed by researchers to belong to Zephyrosaurus, the only dinosaur known from there of that size. Madsen brought it to Vernal, Utah to prepare it under a microscope, where he discovered it did not match the other animal, but belonged to a little ceratopsian dinosaur.^[1][2]

After preparing the fossil, Madsen turned it over to researchers he was working with at the Sam Noble Oklahoma Museum of Natural History, where it was catalogued as specimen OMNH 34557.^[1][2] In 2014, the specimen was made the holotype of the new genus and species Aquilops americanus by the paleontologists Andrew Farke [wd], W. Desmond Maxwell, Richard L. Cifelli, and Matt J. Wedel. The generic name is derived from the Latin word aquila, meaning "eagle", and the Greek ὤψ, ops, meaning "face", in reference to the dinosaur's hooked beak. The specific name americanus refers to the species being the first unequivocal early neoceratopsian found in North America.^[2]

The holotype specimen consists of a partial skull with associated predentary and partial left dentary of the lower jaws, along with unidentified fragments. The skull is somewhat skewed to the right, along with some compression from side to side and top to bottom, which mainly affects the upper part. The right side of the skull is more complete and better preserved than the left. The specimen was probably a subadult individual. The front end of the rostral nasal bones, the braincase, and most of the palatal bones are missing.^[2]

Farke stated that the age of the specimen could not be determined through sectioning due to the lack of limb bones which are the most reliable way of determining growth stages. While dinosaur features can change as they age, naming new species based on young specimens can be problematic, but Farke noted that even if the skull belonged to a young individual, it was distinct enough in features that would be stable throughout life, so that they would be recognizable in an adult. While only the skull was known, Farke wanted to include the body in the artwork used to publicize the find by the paleoartist Brian Engh, which they based on relatives such as Archaeoceratops and the more distantly related Psittacosaurus.^[3]

Description

The skull is 84.2 mm (3.3 in) long. The holotype is possibly not from a full-grown individual. A comparison with related species indicates it might have been at 60% of its adult length.^[2] Wedel estimated the total body length of Aquilops at 60 cm (23.6 in) and its weight at 1.5 kg (3.3 lb).^[2] Its size has been compared to that of a house cat or a rabbit.^[1]

The authors established some unique traits. The rostral, the bone core of the snout beak, curves downwards and has an arched keel on its top with a bump on the front. In front of the tooth row the upper jaw rim is over its total length concave in side view. The skull opening, the antorbital fenestra, is twice as long as it is tall and has a pointed rear, below the eye socket.^[2]

Classification

3D scans of the holotype cranium (above) and lower jaws (below); click thumbnails to turn the models around

Aquilops was placed in the Neoceratopsia. A cladistic analysis showed that it was positioned rather basal, below Leptoceratops in the evolutionary tree, with only Liaoceratops being more basal. A more derived position, e.g. as a leptoceratopsid or a protoceratopsid, was less likely; it was improbable that it was a ceratopsoid. The fact that the holotype was a subadult might have distorted these results because juvenile individuals often show basal traits. However, after correcting for traits that might change during ontogeny, the resulting tree was basically the same. The ceratopsians more derived than psittacosaurids, called neoceratopsians, evolved in Asia: the presence of a basal neoceratopsian in North America was seen as an indication for a late Early Cretaceous migration event, the ancestors of Aquilops invading from Asia. Two later such events would have occurred in the early Late Cretaceous.^[2]

Paleoenvironment

Aquilops is known from Unit VII also known as the Himes Member of the Cloverly Formation of Montana, which has been dated to about 104–109 million years ago, during the middle to early late Albian of the Early Cretaceous.^[2] At the end of Cloverly times, the shallow sea would expand to cover the entire region and would eventually split North America completely in half, forming the Western Interior Seaway.^[4] Abundant fossil remains of coniferous trees suggest that these plains were covered in forest.^[5] Grasses would not evolve until later in the Cretaceous, so Early Cretaceous dinosaurian herbivores browsed from a variety of conifers and cycads.^[6]

The most abundant herbivorous dinosaur of the time was the large iguanodont Tenontosaurus. The smaller hypsilophodont Zephyrosaurus, the nodosaur Sauropelta, titanosaurs, and a type of ornithomimosaur also lived there. The dromaeosaurid theropod Deinonychus fed upon some of these herbivores, and the sheer number of Deinonychus teeth scattered throughout the formation are a testament to its abundance.^[5][4] Microvenator, a small basal oviraptorosaur, hunted smaller prey,^[5][4] while the apex predators of the Cloverly was the large carcharodontosaurid theropod Acrocanthosaurus.^[7] Lungfish, triconodont mammals, and several species of turtles lived in the Cloverly, while crocodilians prowled the rivers, lakes, and swamps, providing evidence of a year-round warm climate.^[5][4]

See also

• 2014 in paleontology
• Neoceratopsia
• Timeline of ceratopsian research

References

External links

• Aquilops americanus - video about the display at Sam Noble Oklahoma Museum of Natural History
• The Aquilops has his day at the Sam Noble Museum - news report about Aquilops's popularity following Jurassic World: Rebirth