Abstract
The taxonomy, osteology, phylogenetic position, and historical biogeography of the lambeosaurine hadrosaurid Magnapaulia laticaudus (new combination) are revised. The diagnosis of this species is amended on the basis on two autapomorphies (i.e., longest haemal arches of proximal caudal vertebrae being at least four times longer than the height of their respective centra; base of prezygapophyses in caudal vertebrae merging to form a bowl-shaped surface) and a unique combination of characters (i.e., downturned cranioventral process of the maxilla; tear-shaped external naris with length/width ratio between 1.85 and 2.85; neural spines of dorsal, sacral, and proximal caudal vertebrae being at least four times the height of their respective centra). A maximum parsimony analysis supports a sister taxon relationship between M. laticaudus and Velafrons coahuilensis. Both taxa constitute a clade of southern North American lambeosaurines, which forms a sister relationship with the diverse clade of helmet-crested lambeosaurines from northern North America that includes well-known genera like Corythosaurus, Lambeosaurus, and Hypacrosaurus. According to the results of a Dispersal-Vicariance analysis, southern North American lambeosaurines split from the northern forms via vicariance from a common ancestor that lived in both the northern and southern regions of the continent.
Highlights
Lambeosaurines form a major clade of ‘‘duck-billed’’ (Hadrosauridae) dinosaurs that are remarkable for their bewildering variety of hollow supracranial crests [1,2]
The external naris of V. coahuilensis is approximately 25 cm in length in the type specimen CPC-59, and 27 cm in LACM 17715. This indicates that CPC-59 and LACM 17715 likely represent similar ontogenetic stages, clearly substantially smaller than the larger individuals known for M. laticaudus (e.g., LACM 17712; see Fig. 2)
The autapomorphies of V. coahuilensis [8] occur in cranial elements that are not preserved in M. laticaudus, such as the postorbital, quadrate, and ceratobranchial (Table 4)
Summary
Lambeosaurines form a major clade of ‘‘duck-billed’’ (Hadrosauridae) dinosaurs that are remarkable for their bewildering variety of hollow supracranial crests [1,2]. These crests enclose hypertrophied nasal passages that have apomorphically migrated caudodorsally relative to the ancestral antorbital position [3,4]. Approximately half of the more than 20 species currently recognized have been found in North America, most of them having been recovered from late Campanian to early Maastrichtian strata of the northern sedimentary basins of the continent [6]. No species of hollow crested hadrosaurid has been named in South America, various appendicular and axial hadrosaurid remains from Argentina have been referred to Lambeosaurinae indeterminate [13,14,15]
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