Temporal range: Late Jurassic
|An artist's illustration of Galeamopus hayi|
Tschopp et al., 2015
| †Galeamopus hayi|
Galeamopus is a genus of herbivorous diplodocid sauropod dinosaurs. It contains two known species: Galeamopus hayi, known from the Late Jurassic lower Morrison Formation (Kimmeridgian age, about 155 million years ago) of Wyoming, United States, and Galeamopus pabsti, known from the Late Jurassic fossils from Wyoming and Colorado. The type species is known from one of the most well preserved diplodocid fossils, a nearly complete skeleton with associated skull.
On the back of the skull, the paroccipital process is curved in side view. The teeth have paired wear facets. The first neck vertebra, the atlas, has a neural spine with processes pointing to the front and the inside, which are separate from the rear wing of the spine. This rear wing shows a continuous transverse width over most of its length. The neural arch of the atlas has on each side of its base a small triangular spur. The second neck vertebra, the axis, has a neural spine with a knob-shaped bump on the front end of the ridge on its front side. With the middle and rear neck vertebrae, the ridge between the rear joint processes, the postzygapophyses, does not extend beyond the rear edge of the neural arch.
The study also determined six autapomorphies of the type species Galeamopus hayi alone. The part of the parietal bone forming the edge between the rear skull and the skull roof is low, with a height less than that of the foramen magnum. The appending basipterygoid processes at the underside of the braincase strongly diverge at an angle of more than 60°. The ulna of the lower arm is long, with a minimum length equalling 76% of the humerus, upper arm bone, length. The surface on the radius contacting the ulna is limited in size and relatively smooth. The joint surface at the underside of the radius is bevelled relative to the shaft, at an angle of about 15°. The outer edge of the top surface of the shinbone forms a pinched process, behind the cnemial crest at the front.
Combined, there are thirteen autapomorphies present in Galeamopus, exactly the minimum the study used as a criterion to distinguish separate genera.