[1] The original specimen that would form the basis for Galleonosaurus was discovered at the Flat Rocks locality of the Wonthaggi Formation in 2008 by palaeontologist Gerry Kool.

The specific name dorisae was given in recognition of Doris Seegets-Villiers for her geological, palynological, and taphonomic work on the Flat Rocks fossil vertebrate locality.

The latter possesses an elongate form and a larger number of tooth positions (alveoli), and was therefore tentatively considered likely to belong to Galleonosaurus; however, without overlapping material it is impossible to confirm.

Additionally, specimens resembling both Galleonosaurus maxillae and VOD3 dentaries are known from the Eric The Red West (ETRW) fossil site of the Eumeralla Formation, also hailing from Victoria but dating to several million years later.

Three distinct postcranial morphotypes are also known from Eumerella, including the holotype of Diluvicursor; it is considered very likely one of the three represents Galleonosaurus, but without overlapping remains it is unknown which.

It is characterized by five potential autapomorphies: ascending ramus of the maxilla has two slot-like foramina on the anterior (front) margin that communicate with the neurovascular tract; neurovascular tract bifurcates internally to exit at two anteroventral (front, on the bottom) maxillary foramina; lingual (inner) margin of maxillary tooth roots in midregion of tooth row form an S-bend at their bases; posterior third of maxilla on some, but not all, specimens deflects posterolaterally (backwards, to the side) at an abrupt kink; and lateral end of palatine lateral ramus forms a hatchet-shaped flange.

Some specimens including the holotype have fifteen alveoli, or tooth positions, whereas others have thirteen or fourteen, though show indications of small or developing ones.

However, due to the fragmentary nature of the Victorian taxa of interest, they extensively revised the dataset so as to have heightened chances of good resolution in the results.

[3] The cladogram below shows results from the analysis by Herne et al., 2019:[1] Heterodontosauridae Eocursor Thyreophora Lesothosaurus Agilisaurus Hexinlusaurus Yandusaurus Nanosaurus Jeholosauridae Thescelosauridae Marginocephalia Parksosaurus Talenkauen Macrogryphosaurus Gasparinisaura Galleonosaurus Leaellynasaura Anabisetia Diluvicursor Hypsilophodon Iguanodontia Inferences have been made about the evolution of Victorian ornithopods, including Galleonosaurus.

A maxilla specimen from the Wonthaggi Group, designated as VOM4, shows a mixture of traits known from Atlascopcosaurus and Galleonosaurus; though considered somewhat more similar to the former and tentatively assigned to it, it may indicate the lineages of both genera had only very recently diverged from a common ancestor in the Late Barremian.

During the Early Cretaceous period, the area of Victoria these units hail from would have been part of a rift valley between the continents of Australia and Antarctica, and would have been a much higher latitude, within the Antarctic Circle.

Local ornithopods such as Galleonosaurus appear to have been able to survive these large changes in their ecosystem, as they remain speciose and conservative in morphology across a vast span of time.

[1][3] Other taxa include the giant temnospondyl Koolasuchus, an aquatic predator and the last member of a lineage that had long since gone extinct elsewhere in the world, the possible ankylosaur Serendipaceratops, and several species of primitive mammal.