Review of the taxonomic affinities of Latirhinus uitstlani, an emblematic Mexican hadrosaurid

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Highlights

  • Latirhinus uitstlani as originally conceived represents a chimera, composed of five individuals of different size and taxa.

  • Latirhinus uitstlani retained as valid species, composed of caudal vertebrae, forelimb, hindlimb, the pectoral and pelvic girdle.

  • Latirhinus uitstlani was reclassified as lambeosaurine and its diagnosis was amended.

  • The other original holotype components of Latirhinus were reclassified as saurolophine, and lambeosaurine indet.

Abstract

This work presents a detailed study of the bones from the holotype of Latirhinus uitstlani. A Mexican hadrosaurid species known informally as “Isauria”, discovered by Don Ramón López, from the Upper Cretaceous Cerro del Pueblo Formation of Coahuila. The results indicate that this Campanian species from the Ejido Presa San Antonio is a chimera or Frankenstein. Its holotype originally includes bones that were individually misinterpreted, belonging to individuals of different sizes, identifiable to saurolophines and lambeosaurines, even, one bone coming from a different locality. Therefore, after classifying the components of the holotype, we rediagnosed L. uitstlani from its pectoral appendicular bones and pelvic bones, confirming their validity as a species. It was also reclassified as a member of the Lambeosaurine subfamily rather than to Saurolophine, and with an estimated body length of 8.72 m. In addition, we identified a large saurolophine, represented by three specimens, and a small lambeosaurine from the same locality of L. uitstlani, along with a small saurolophine from the Cerro de los Dinosaurios area, originally including in the holotype.

Introduction

The hadrosaurs or duck-billed dinosaurs constitute a derived monophyletic ornithopod clade characterized by the development of a complex dental battery and a conspicuous cranial crest (Stubbs et al., 2019). Abundant fossil remains of this clade have been collected in Mexico since the early XX century (Haarmann, 1913; Taliaferro, 1933). However, few specimens preserve enough diagnostic characters that allow their accurate identification. In 1987, the UNAM paleontologists led by R. Hernández Rivera, L. Espinosa Arrubarrena, and S.P. Applegate, in collaboration with the Antares Group (now the SEPC), launched the project “The first Mexican dinosaur, armed, collected and prepared by Mexicans” with the aim to recover dinosaur remains from the Presa San Antonio, Parras de la Fuente Municipality, Coahuila (Espinosa Arrubarrena et al., 1989; Hernández, 1994). As a result of this project, several hadrosaur bones were recovered and deposited into the paleontological collection of UNAM (Fig. 1). Among these, Kirkland et al. (2006, fig. 11), identified and described a rostrum of an indeterminate specimen of Kritosaurus Brown, 1910, which later Prieto-Márquez (2013) identified as part of the type species K. navajovious. Also, other isolated bones were collected and identified as an indeterminate lambeosaurine (Hernández, 1994; Serrano-Brañas, 2006). The most remarkable specimen from the Presa San Antonio is a partial skeleton preliminarily identified as Edmontosaurus Lambe, 1917, and later as Kritosaurus sp., recovered in the SPA-88-9 quarry (Espinosa Arrubarrena et al., 1989; Hernández, 1994). Such specimen nicknamed “Isauria” was prepared, assembled, and completed with other associated bones from the same quarry to be exhibited in the Museo de Geología of Mexico City (Fig. 2). The morphological and taxonomical study of “Isauria” has been on the charge of Serrano-Brañas (2006), who first suggested that this is an indeterminate specimen of Gryposaurus Lambe, 1914, based on the shape of the nasal bone. Subsequently, almost six years later, “Isauria” was identified as a new saurolophine hadrosaur named Latirhinus uitstlani Prieto-Márquez and Serrano-Brañas, 2012, diagnosed by three characters: 1) the high hook-shaped nasal bone; 2) the wide bony nasal aperture; 3) the deltoid process of the scapula is curved dorsally, which is a condition shared with lambeosaurines.

Ramírez-Velasco et al. (2014) and Ramírez-Velasco and Hernández-Rivera (2015) suggested that the partial skeleton that conforms most of Latirhinus uitstlani is rather a lambeosaurin hadrosaur, which could be the complement with some of those unidentified lambeosaurine bones also collected in the SPA-88-9 quarry. Additionally, these authors noted that part of “Isauria” and other isolated bones from the same quarry represents an indeterminate number of lambeosaurines individuals of different sizes. More recently, Prieto-Márquez et al. (2019) claimed that Aquilarhinus palimentus Prieto-Márquez et al. (2019), and Latirhinus uitstlani form a monophyletic clade of primitive hadrosaurids, supported by the presence of a nasal bone high and hook-shaped, suggesting that these taxa are closely related.

As noted above, the holotype of Latirhinus uitstlani is a chimeric or “Frankenstein” specimen that involves a partial skeleton of a lambeosaurine specimen plus isolated bones of individuals of different sizes that could have lambeosaurine or saurolophine affinities (Fig. 2). Therefore, the present paper aims to recognize the taxonomical identity, size, and the number of individuals that form part of the holotype of Latirhinus uitstlani.

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Section snippets

Material and methods

Anatomical nomenclature and abbreviations. Anatomical details are based on the nomenclature used in similar descriptive studies (i.e. Horner et al., 2004), modifying it, when necessary, according to the guidelines of the standardized terminology employed in the Nomina Anatomica Avium (Baumel et al., 1993), following Harris (2004).

Institutional abbreviations. AMNH, American Museum of Natural History, New York City, New York, USA. CIC, Colección Paleontológica del Centro del Instituto Nacional de

Systematic paleontology

Dinosauria Owen, 1842.

Ornithischia Seeley, 1888.

Hadrosauridae Cope, 1869.

Lambeosaurinae Parks, 1923.

Latirhinus Prieto-Márquez and Serrano-Brañas, 2012

Latirhinus uitstlani Prieto-Márquez and Serrano-Brañas, 2012

Holotype. IGM 6583, Note: Part of those bones assigned to this catalog number by Prieto-Márquez and Serrano-Brañas (2012) belong to different taxa and individuals. Therefore, such bones receive new catalog numbers (Fig. 2). The new IGM 6583 specimen consists of bones associated, collected

Discussion

The preparation and assembly of “Isauria” marked the end of the CONACyT-UNAM project, which was the first large-scale project launched by a Mexican research institution to recover and study the dinosaurs of this country (Espinosa Arrubarrena et al., 1989). An outstanding achievement of this project was the discovery of the fossil deposits of the Ejido Presa San Antonio that today represents an emblematic site of the Mexican Paleontology. The museum goal of this project was achieved fully; since

Conclusion

Against the conclusion of Prieto-Márquez and Serrano-Brañas (2012), Latirhinus uitstlani is identified and re-diagnosed here as a new Cerro del Pueblo Formation lambeosaurine species that is represented only by a part of the bones originally referred to as part of a single individual known. The bones retained here as IGM 6538 and holotype of this species includes 14 caudal vertebrae, both scapulae, humeri, and ulnare, left coracoid, right fused metacarpals III and IV, left manual ungual II,

Credit author statement

Angel Alejandro Ramírez Velasco: Conceptualization, Formal analysis, Investigation, Writing – original draft, Writing – review & editing, Visualization. Luis Espinosa Arrubarrena: Resources, Writing – review & editing. Jesús Alvarado Ortega: Resources, Writing – review & editing, Project administration, Funding acquisition.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

The manuscript is result of the PhD project of the first author, registered into the Programa de Posgrado en Ciencias Biológicas (Sistemática), UNAM. Authors are in debt with the leaders and collaborators of the ISAURIA project, mainly to Shelly (S.P. Applegate) and R. Hernández-Rivera, the López family and people of the Ejido Presa San Antonio (Ramón, José, Antonio, Epitacio, Gonzálo, and Pablo), and the Antares Group (M.C. Aguillón-Martínez, L. Sumiko, C.R. Delgado de Jesús, R. Gómez, and I.

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  • Cited by (3)

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

      2022, Journal of South American Earth Sciences
      Citation Excerpt :

      It is important to highlight that part of the most fragmentary bones that were originally collected within the SPA-88-9 quarry still need to be prepared (Ramírez-Velasco et al., 2021), so this material was not included in our analysis. If one follows the conclusions of Ramírez-Velasco et al. (2021), there is a minimum of seven individuals in this quarry (IGM 6583, IGM 12712, IGM 12713, IGM 12714, Coah 14-1/2, Coah 14-1/4 and Coah 14-1/5). However, our present study considers IGM 6583, IGM 12713 and IGM 12714 as part of the same individual, resulting in a minimum number of individuals represented by these specimens of only five.

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