Iani smithi, youngest rhabdodontomorph iguanodont from North America

[VD231991]

https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0286042

Recent phylogenetic analyses by Dieudonné et al. (2021) and Poole (2022) have demonstrated that the basal iguanodonts Muttaburrasaurus, Fostoria, and Tenontosaurus belong to the iguanodont clade Rhabdodontomorpha, which includes the Late Cretaceous rhabdodontids and an unnamed form from the Early Cretaceous of Vegagete, Spain. Because Iani smithi is from the Cenomanian-age Mussentuchit Member of the Cedar Mountain Formation, which is younger than geologic deposits that have yielded Tenontosaurus, it constitutes the youngest member of Rhabdodontomorpha from North America, but given the phylogenetic instability in the composition of Rhabdodontomorpha using the phylogenetic matrices of Dieudonné et al. (2021) and Poole (2022), more work remains to be done to illuminate the evolution of Rhabdodontomorpha in the Hauterivian to Cenomanian interval, given that the recovery of the Vegagete taxon, Muttaburrasaurus, and Fostoria as late-diverging rhabdodontid conflicts with their pre-Turonian age. Therefore, the phylogenetic results for Iani using the data matrix from Poole (2022) likely hold more water, especially as the recovery by Zanno et al. of Atlascoposaurus as a basal rhabdodontomorph using using Poole's matrix suggests a Gondwanan origin for Rhabdodontomorpha despite the Vegagete rhabdodontomorph being of late Barremian to early Aptian age. Since Iani is of the same age as the non-hadrosaurid hadrosauromorphs Eolambia and Protohadros, it is apparent that basal iguanodonts co-existed with non-hadrosaurid hadrosauroids in the Cenomanian of North America.

Dieudonné, P.E., Cruzado-Caballero, P., Godefroit, P., and Tortosa, T., 2021. A new phylogeny of cerapodan dinosaurs. Historical Biology 33(10): 2335–2355.

Poole, K., 2022. Phylogeny of iguanodontian dinosaurs and the evolution of quadrupedality. Palaeontologia Electronica 25(3): 1–65.