PBDB Taxon

Basic info	Taxonomic history	Classification	Included Taxa
Morphology	Ecology and taphonomy	External Literature Search	Age range and collections

Acristavus gagslarsoni

Reptilia - Hadrosauridae

Taxonomy

Acristavus gagslarsoni was named by Gates et al. (2011). Its type specimen is MOR 1155, a partial skeleton, and it is a 3D body fossil. Its type locality is MOR TM-281, which is in a Campanian coarse channel fill sandstone in the Two Medicine Formation of Montana.

It was considered a nomen dubium by Dalla Vecchia (2014).

Year	Name and author
2011	Acristavus gagslarsoni Gates et al. p. 799 figs. 2A, 3A-D, G, 4, 7-8, 10-11
2013	Acristavus gagslarsoni Prieto-Marquez
2014	Acristavus gagslarsoni Gates et al. p. 156
2014	Acristavus gagslarsoni Xing et al. p. 1819
2016	Acristavus gagslarsoni Lehman et al. p. 346
2016	Acristavus gagslarsoni Prieto-Márquez et al. p. 6
2017	Acristavus gagslarsoni Cruzado-Caballero and Powell p. 11
2018	Acristavus gagslarsoni Gates et al. p. 20
2019	Acristavus gagslarsoni Takasaki et al. p. 5
2021	Acristavus gagslarsoni McDonald et al. p. 2

Diagnosis

Reference	Diagnosis
T. A. Gates et al. 2011	Acristavus is a hadrosaurine hadrosaurid diagnosed by the following unique features: enlarged posterodorsal brow of postorbital and basioccipital extending posteriorly well beyond the dorsal border of the foramen magnum to a greater extent than in other hadrosaurine species (these two are preserved on the holotype MOR 1155), as well as the following best observed in the referred specimen UMNHVP 16607: deep laterally squared frontonasal suture; swelling of the interdigitate suture between the prefrontal and frontal; deep depression on the lateral surface of the postorbital jugal process. Acristavus also possesses a unique combination of the following features: widely expanded alar process; deeply developed basipterygoid ridge; deep, flattened supratemporal bar; absence of nasal ornamentation; lacrimal wide in posterior view; anterior nasal process terminating posteriorly to anterior margin of external nares; dentary with nearly flat ventral margin. Acristavus also possesses the following differential diagnostic characters: alar processes positioned near vertically in a plane with the basipterygoid processes of the basisphenoid and expanded from near the dorsal surface of the basisphenoid to nearly contact the basisphenoid processes, a characteristic seen exclusively in this taxon, Brachylophosaurus, and Maiasaura; basipterygoid ridge descends to lower level of basipterygoid processes as seen in Brachylophosaurus and to a lesser extent in Maiasaura, but no other hadrosaurid taxa; supratemporal bar deep and flattened as seen in Maiasaura, Gryposaurus notabilis, and G. monumentensis, but not in Brachylophosaurus; absence of nasal ornamentation as seen in most (i.e., not Lophorothon atopus) nonhadrosaurid iguanodontians as well as the hadrosaurine Edmontosaurus spp.; lacrimal wide in posterior view, as seen in Gryposaurus notabilis and G. monumentensis, but not in Brachylophosaurus or Maiasaura; anterior nasal process terminates prior to anterior margin of external nares as seen in nonhadrosaurid iguanodontians, some specimens of Brachylophosaurus, and Maiasaura, and all specimens of Gryposaurus spp., but no other hadrosaurid species; dentary with nearly flat ventral margin as seen in nonhadrosaurid iguanodontians such as Jinzhousaurus but not seen in any other hadrosaurid.

Measurements

No measurements are available

Time interval	Ma	Country or state	Original ID and collection number
Early/Lower Campanian - Middle Campanian	83.6 - 72.2	USA (Utah)	Hadrosaurinae indet. (120364)
Middle Campanian	83.6 - 72.2	USA (Montana)	Acristavus gagslarsoni (type locality: 120363)