Taphonomic attributes of the holotype of the lambeosaurine dinosaur Latirhinus uitstlani from the late Campanian of Mexico: Implications for its phylogenetic systematics

Abstract

Latirhinus uistlani represents one of the most emblematic dinosaurs from Mexico. This hadrosaurid, originally described as a member of the Saurolophinae by Prieto-Márquez and Serrano-Brañas in 2012, was re-evaluated as a lambeosaurine by Ramírez-Velasco et al. (2021). In addition, these authors stated that the description of the 2012 holotype was based on a chimeric skeleton and designated a new holotype (a different concept for the composition of essentially the same individual). The composition of their 2021 holotype was based on the size, association and similar mode of preservation of the bones within the quarry. Notably, no details were provided regarding such mode of preservation. However, the fact that the type locality of L. uitstlani is an attritional bonebed where other similar-sized individuals were also present calls into question the criteria used by Ramírez-Velasco et al. (2021) in the composition of their holotype. We address this shortcoming by describing the taphonomic signature of the skeletal elements in the L. uitstlani holotype of Ramírez-Velasco et al. (2021), as well as that of other bones discussed collected from this species’ type locality and other sites of the late Campanian Cerro del Pueblo Formation. Our observations show different taphonomic attributes among the bones of the 2021 holotype, indicating that it is likely a chimera of different specimens. Such taphonomic attributes support a holotype for L. uitstlani consisting of the original elements listed in Prieto-Márquez and Serrano-Brañas (2012), with exclusion of the IGM 12712 jugal and a right scapula. We concur in that IGM 12712 is actually a fragmentary jugal, which represents an unusually large hadrosaurid specimen. We also tested the referral of L. uitstlani to Lambeosaurinae via a cladistic parsimony analysis that confirmed that this specimen belongs to that major clade of hadrosaurids; however, its relationships with other lambeosaurines remain unresolved. Finally, we re-evaluated the diagnostic utility of the characters used by Ramírez-Velasco et al. (2021) for referring other specimens to different hadrosaurid clades, concluding that several of them can only be referred to Hadrosauridae indeterminate.