Skull Anatomy of the Bizarre Crocodylian Mourasuchus nativus (Alligatoridae, Caimaninae)

Abstract

Mourasuchus is a Miocene alligatorid endemic to South America, and is represented by four species. Together with the closely related Purussaurus, it is a peculiar crocodylian taxon of neogene Caimaninae and one of the most bizarre forms among eusuchian crocodiles. The phylogenetic relationships between Mourasuchus species have not been explored, and detailed skull descriptions are scarce. The goal of this study is to provide new data on skull morphology and cranial recesses in Mourasuchus nativus, including a new tomography analysis (3D modeling). We observed that several diagnostic characters of Purussaurus, such as lack of contact between the nasal and lacrimal, separation of the nasal and frontal by the prefrontals, and the posterior dorsal margin of the skull table, are shared with Mourasuchus. M. nativus is characterized by the presence of solid transverse squamosal eminences, large posttemporal fenestrae, and a quadrate laterocaudal bridge separating V 2 -V 3 trigeminal openings. Compared with other crocodylians, the endocast of M. nativus is similar in shape but quite sigmoid in lateral view, the canal of the supraorbital ramus of V 2 is more vertically oriented, the thick tympanic branch canal opens in a large foramen aligned with trigeminal foramen, and the canal of the vagal (X) tympanic ramus is also very wide. Contrary to extant alligatorids, the median pharyngeal recess remains paired throughout its course and only connects its opposite fellow near the external ventral opening. The knowledge of the internal skull anatomy of Mourasuchus contributes to the understanding of the general morphology of alligatorids, Caimaninae, and their variation. Anat Rec,

Crocodylian diversity peak and extinction in the late Cenozoic of the northern Neotropics

“…4). Especially AMU-CURS-212 preserves enough of the diagnostic features (that is, small crest in midline of parietal; entire posterior part of skull table raised; squamosals particularly high and strongly developed forming transverse ridge) for species recognition 14,15 . Previously recognized from the Ituzaingó fauna in Argentina, and Acre in Brazil 1,15,16 , the palaeogeographic occurrence of the species was thus spanning 44000 km from the Buenos Aires region in the South to the Caribbean Sea in the North, which is more than any of the living crocodylians does in South America today.…”

The late Miocene caimanine fauna (Crocodylia: Alligatoroidea) of the Urumaco Formation, Venezuela

“…Although published earlier, the description of M. arendsi from Venezuela was not noted or referenced in the description of M. nativus (Gasparini, 1985). The most detailed anatomical study of M. nativus cranial material to date, including the holotype MLP 73-IV-15-8, was given by Bona et al (2013a). Scheyer et al (2013) Gismondi, 2015) and the late Miocene Yecua Formation in Bolivia (Tineo et al, 2015).…”

Reptiles Extintos - Volumen en Homenaje a Zulma Gasparini

“…This record corresponds mainly to cranial and postcranial fragmentary elements of different taxa, which have been studied by numerous authors since the mid-nineteenth century (Bravard, 1858;Burmeister, 1883;Ambrosetti, 1887;Scalabrini, 1887;Rovereto, 1912;Rusconi, , 1935Patterson, 1936;Langston, 1965;Gasparini, 1968Gasparini, , 1973Langston and Gasparini, 1997). Contrary to modern day ecosystems, in which overall alligatorid diversity is declining and no more than two species occur sympatrically (Scheyer et al, 2013), the "Conglomerado Osífero" could have housed at least six species of caimanines Bona et al, 2012Bona et al, , 2013a. Finally, during the Pliocene-Pleistocene, Argentinean alligatorids were represented by a well-preserved specimen from Salta Province (Barrios, 2013) and some fragmentary materials from the Pleistocene of Salta and Entre Ríos (Patterson, 1936;Noriega et al, 2004).…”

“…This species is characterized by the extremely wide, compressed, and long rostrum with a straight lateral border without festooning, a skull with a relative small skull table but with prominent squamosal eminences (protuberances) in adult stages, and a slender U-shaped mandibles with numerous small conical teeth (Price, 1964;Langston, 1965;Bocquentin and SouzaFilho, 1990;Bona et al, 2012; for the Synonymic List and a detailed history of this taxon see Bona et al, 2013a). The genus Mourasuchus is endemic to South America (Langston and Gasparini, 1997).…”

“…This species was originally named by as Charandaisuchus nativus based on two posterior fragments of skull table. Later, Boquentin and Souza-Filho (1990) described more cranial material of this taxon and considered Charandaisuchus a junior synonym of Mourasuchus, and recently, Bona et al (2012Bona et al ( , 2013a) provided a detailed study of the cranial anatomy of M. nativus and morphological features that clarify the phylogenetic relationships of the species. This species inhabited the Amazonian basin during the Late Miocene, from Venezuela (Urumaco Formation) to northeast Argentina ("Conglomerado Osífero") (Bona et al, 2013a,b;Scheyer et al, 2013).…”