Describer

Prieto-Márquez, Chiappe & Joshi  2012

Time

Cretaceous Late Campanian

Classification

Ornithischia Ornithopoda Hadrosauridae Lambeosaurinae

Diet

Herbivore

Fossilsite

El Gallo Formation, Estado de Baja, California Norte, Mexico

Info

Magnapaulia laticaudus  (Prieto-Márquez, Chiappe & Joshi, 2012) > Lambeosaurus laticaudus (Morris, 1981)

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.

Isolated skull and postcranial elements.

Holotype

LACM 17715, consisting of left premaxilla, left maxilla, left jugal, partial atlas, three partial and two nearly complete cranial to middle cervical vertebrae, one nearly complete caudal cervical vertebra, two cervical postzygapophyseal processes, two nearly complete cranial-most dorsal vertebrae, two cranial dorsal neural arches, two partial cranial dorsal vertebrae, three cranial dorsal centra, one fragment of cranial neural arch, two fragments of middle to caudal dorsal vertebrae, two caudal dorsal neural arches, one caudal dorsal centrum, partial sacrum composed of four co-ossified vertebrae (three neural arches with neural spines and one centrum), two pairs of co-ossified sacral centra, one caudal sacral vertebra lacking the centrum, one sacral centrum, one sacral neural spine, six fragmentary sacral ribs, two caudal neural arches, partial right sternum, left coracoid, right scapula, right humerus, left ischium, complete left femur and fragmentary femur, proximal end of left tibia, and a nearly complete left metatarsal III (Fig. 2). Measurements of LACM 17715 are given in Tables 1–3.

Referred specimens

LACM 17698 (cervical vertebra), 17699 (tooth), 17700 (tooth), 17702 (cervical and dorsal rib fragments, one proximal and one distal caudal vertebrae, centrum and neural arch of a proximal caudal vertebra, and eight caudal neural spine fragments), 17703 (left ischium), 17704 (tibia and femoral fragment), 17705 (articulated series of 11 proximal caudal vertebrae), 17706 (left tibia), 17707 (partial right humerus), 17708 (ischium), 17709 (dorsal vertebra), 17710 (proximal region of dorsal rib), 17711 (left tibia), 17712 (dorsal vertebra and numerous integumentary impressions), 17713 (dentary fragment), 17716 (right humerus and humeral fragment), 17717 (partial left fibula), 20873 (articulated series of 21 proximal to middle caudal vertebrae), 20874 (partial left dentary, nearly complete dorsal vertebra, three caudal dorsal centra, twelve fragments of dorsal neural spines, one caudal centrum, nearly complete right ilium, proximal region and shaft fragment of left ischium, left pubis, distal processes of left and right ischia), 20875 (distal processes of left and right ischia), 20876 (left tibia), 20883 (numerous associated vertebral fragments), 20884 (dentary and pubic fragments), and 20885 (partial left fibula). Measurements of selected specimens are given in Tables 1–3. The referral to Magnapaulia laticaudus of theabove specimens is based on 1) presence of lambeosaurine characters (see description below) in the appendicular elements (e.g., humeri, ischia, pubes) that are also found in the type specimen, in combination with 2) the specimens were found associated with the type specimen within locality LACM 7253.

These two reasons together suggest that the most parsimonious interpretation is that these lambeosaurine remains belong to the same taxon. The alternative choice would be to name two distinct taxa from the same locality, because the type LACM 17715 is diagnostic on its own, and so is LACM 17705. However, Prieto-Márquez et al think that the first choice of considering a single taxon is the most conservative, simpler explanation given the anatomical data athand.

Etymology

Magna, the Latin for ‘‘large’’, refers to the unusually large size reached by at least some specimens of this lambeosaurine; paulia honors Mr. Paul Haaga for his outstanding support to the research and public programs of the Natural History Museum of Los Angeles County and its Dinosaur Institute.

Diagnosis

Lambeosaurine hadrosaurid possessing the following autapomorphies: longest haemal arches of proximal caudal vertebrae being at least four times longer than the depth of their respective centra, and the base of prezygapophyses in caudal vertebrae merging to form a bowl-shaped surface, which, in the proximal-most caudals, is continuous dorsally with a deep sulcus on the cranial surface of the neural spine. In addition, Magnapaulia laticaudus is characterized by the following unique combination of characters: downturned rostroventral process of the maxilla (convergent in Tsintaosaurus spinorhinus, Angulomastacator daviesi, and Olorotitan arharensis), the ventral margin of which forms a 18-degree angle with the alveolar margin of the element at its mid-length; tear-shaped external naris with length/width ratio between 1.85 and 2.85, being rostrocaudally longer than in Hypacrosaurus altispinus but shorter than in Lambeosaurus spp., Corythosaurus spp., and H. stebingeri, and mediolaterally wider than in Parasaurolophus walkeri (condition shared with Velafrons coahuilensis and convergent in Olorotitan arharensis); and greatly elongated neural spines (at least four times the depth of their respective centra) of dorsal, sacral, and proximal caudal vertebrae (convergent in Hypacrosaurus spp. for the dorsal neural spines and Barsboldia sicinskii for the sacral and proximal caudal neural spines).

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