Bonapartesaurus

Bonapartesaurus is an extinct genus of herbivorous ornithopod dinosaur that belonged to the Hadrosauridae family. Its name, meaning "Bonaparte's lizard," honors José Bonaparte. This dinosaur inhabited the region of modern-day Argentina during the Campanian and Maastrichtian stages of the Late Cretaceous period.

Discovery and Naming

The remains that would eventually be classified as Bonapartesaurus were first excavated in 1984 by paleontologist Jaime Powell and his collaborators. Initially, Powell described them in 1987 as a possible indeterminate lambeosaurine, noting similarities to Hypacrosaurus and Barsboldia due to the large neural spines. Later, in 2010, a new genus, Willinakaqe salitralensis, was erected from materials found in different locations within the Allen Formation. However, a review in 2016 by Penélope Cruz-Caballero and Rodolfo Coria suggested that the material attributed to Willinakaqe might represent more than one hadrosaurid taxon and that the diagnostic characteristics were not valid, downgrading it to an indeterminate saurolophine and rendering Willinakaqe salitrensis a nomen vanum. In a 2017 study, Cruz-Caballero and Powell reassigned the paratype of W. salitralensis to its own genus and species, Bonapartesaurus rionegrensis, recognizing it as distinct from the previously described materials.

Description and Paleopathology

The holotype specimen of Bonapartesaurus rionegrensis (MPCA-Pv SM2/1-71) includes a partial skeleton comprising dorsal and caudal vertebrae, a sacrum, ribs, fragments of the scapula and humerus, a complete ulna, an ilium, a nearly complete pubis, fragments of ischia, both femurs, tibias, fibulae, an astragalus, a calcaneus, and an articulated left foot, along with tendons. These fossils were recovered from the Salitral Moreno site in Río Negro province, Argentina, from the lower member of the Allen Formation. Unique characteristics of Bonapartesaurus include specific proportions of its vertebral spines, the morphology of its ilium, and features of its tibia and astragalus.

In 2021, CT scans revealed three paleopathologies on the holotype. These included fractures of the spinous processes on two caudal vertebrae, one showing signs of post-traumatic infection. Additionally, a probable malignant bone tumor, such as osteosarcoma, was identified on the left metatarsal II bone. While these conditions likely caused pain and affected the dinosaur's mobility, they are not believed to have been the direct cause of its death.

Phylogeny

Phylogenetic analyses have placed Bonapartesaurus within the Hadrosauridae family. Early analyses followed traditional classifications, placing it within the Hadrosaurinae and the Saurolophini tribe, suggesting it was more derived than Prosaurolophus but more basal than Saurolophus spp.. More recent studies, such as the 2023 description of Gonkoken, have recovered Bonapartesaurus as a member of the Austrokritosauria, a clade of South American saurolophines closely related to kritosaurins.