Galeamopus pabsti was discovered in 1995 by Austrian paleontologist Ben Pabst, who also reconstructed the skull and prepared and mounted the skeleton for display at the Sauriermuseum Aathal in Switzerland. It was described in 2017 by Octávio Mateus and Emanuel Tschopp.
The holotype was found in the Howe-Scott Quarry, a few hundred metres Southwest of another plentiful fossil locality, the Howe Quarry, both North of the town of Shell in Wyoming, USA. A paratype consisting of a second skull was found in Felch Quarry 1 near the town of Garden Park in Colorado, USA.
Galeamopus pabsti is a diplodocine sauropod from the Kimmeridgian age of the Late Jurassic. Diplodocids are large sauropods, though not quite as large as titanosaurs. Diplodocids are long and slender, with short legs, and having rear legs higher than the front legs.
The holotype consists of a nearly complete skull, 21 vertebrae, ribs, a partial sacrum, both scapulae, both humeri, the left front leg (consisting of ulna, radium, and manus), right ilium, right pubis, and left rear leg (consisting of a femur, tibia, fibula, and foot bones). The paratype consists of a partial skull, which was previously thought to be a diplodocus specimen, and was used as the model for the skull to Diplodocus carnegii in 1981.
The other species in the Galeamopus genus, Galeamopus hayi was previously described as Diplodocus hayi in 1924, but was re-classified in 2015 as a genus separate from Diplodocus. The paleontologists involved found 13 automorphies that made Galeamopus distinct from Diplodocus, including a more triangular shape of the neck near the skull, a higher neck in general, and more massive legs.
The holotype of Galeamopus pabsti had been set up as a display after its discovery in 1995, but only when it was studied closely afterwards by Emanuel Tschopp and Octávio Mateus was it discovered to be a new species after they renamed Galeamopus hayi in 2015.
Galeamopus pabsti was found to be a separate species from Galeamopus hayi by 14 automorphies, some of which are not present in the sister species. These includes things such as a fifth toe longer than the third and fourth, and the neck vertebrae being taller than wide.
Galeamopus is herbivorous, as evidenced by its peg-like teeth, the fact that its skull is very similar to other diplodocids (which are also herbivorous sauropods), and its ribs, limbs, vertebrae, and pelvis all showing signs of a large herbivore.
Galeamopus is Latin for "want helmet". The discoverer and describer of the original Galeamopus hayi, known as Diplodocus hayi at the time, both had a first name of William. In 2015, when Swiss paleontologists re-described Diplodocus hayi as a new species, they wanted to honour the original two Williams, and "want helm" can be translated into German as Wil-helm, the German form of William. Additionally, the name also refers to the fact that the braincase appears to be delicate compared to other sauropods. Pabsti refers to the discoverer of the holotype, Austrian paleontologist Ben Pabst.