[1] The holotype of Iguanacolossus, UMNH VP 20205, was discovered by Donald D. DeBlieux in 2005, unearthed from the Yellow Cat Member of the Cedar Mountain Formation, Utah; dating from the Valanginian stage in the Early Cretaceous, it wasn't named and described until 2010 by Andrew T. McDonald, James I. Kirkland, Donald D. DeBlieux, Scott K. Madsen, Jennifer Cavin, Andrew R. C. Milner, and Lukas Panzarin, along with the genus Hippodraco, also from the Cedar Mountain Formation.

UMNH VP 20205 is assigned to a single individual, including skull elements: fragmented predentary, partial right maxilla, right squamosal, teeth, right and left quadrates.

Body remains compromise: vertebrae (cervical, dorsal and caudal), chevrons, ribs, right scapula, right ilium, right pubis, right metatarsals and left fibula.

The generic name, Iguanacolossus, is a combination of the reptile genus "Iguana", and the Latin word "colossus" (meaning colossal and/or giant) in relation to the iconic Iguana-like teeth of iguanodontians and the notorious large body size of the specimen.

[4] The other paleofauna is from the Upper Yellow Cat, which includes such dinosaur genera as the sauropods Cedarosaurus and Moabosaurus, the fellow iguanodontians Cedrorestes and Hippodraco, the theropods Martharaptor and Utahraptor (as well as the avian ichnogenus Aquatilavipes), and the nodosaurid Gastonia.