Alligatoroidea: Caimaninae) from the Late Miocene of Venezuela and Their Palaeobiological Implications

Historical Biology An International Journal of Paleobiology ISSN: (Print) (Online) Journal homepage: https://www.tandfonline.com/loi/ghbi20 New cranial and postcranial elements of Mourasuchus (Alligatoroidea: Caimaninae) from the late Miocene of Venezuela and their palaeobiological implications Giovanne M. Cidade , Ascanio D. Rincón & Andrés Solórzano To cite this article: Giovanne M. Cidade , Ascanio D. Rincón & Andrés Solórzano (2020): New cranial and postcranial elements of Mourasuchus (Alligatoroidea: Caimaninae) from the late Miocene of Venezuela and their palaeobiological implications, Historical Biology, DOI: 10.1080/08912963.2020.1795844 To link to this article: https://doi.org/10.1080/08912963.2020.1795844 View supplementary material Published online: 29 Jul 2020. Submit your article to this journal View related articles View Crossmark data Full Terms & Conditions of access and use can be found at https://www.tandfonline.com/action/journalInformation?journalCode=ghbi20 HISTORICAL BIOLOGY https://doi.org/10.1080/08912963.2020.1795844 ARTICLE New cranial and postcranial elements of Mourasuchus (Alligatoroidea: Caimaninae) from the late Miocene of Venezuela and their palaeobiological implications Giovanne M. Cidade a,b, Ascanio D. Rincón c and Andrés Solórzano d aLaboratório De Estudos Paleobiológicos, Departamento De Biologia, Universidade Federal De São Carlos, Sorocaba, Brazil; bLaboratório De Paleontologia, Departamento De Biologia, Faculdade De Filosofia, Ciências E Letras De Ribeirão Preto, Universidade De São Paulo, Ribeirão Preto, Brazil; cLaboratorio De Paleontología, Centro De Ecología, Instituto Venezolano De Investigaciones Científicas (IVIC), Miranda, Venezuela; dPrograma De Doctorado En Ciencias Geológicas, Facultad De Ciencias Químicas, Universidad De Concepción; Víctor Lamas, Concepción, Chile ABSTRACT ARTICLE HISTORY A partial skeleton of Mourasuchus, one of the most peculiar crocodylians of all time, that includes cranial and Received 29 March 2020 postcranial elements recovered from the late Miocene bone-beds of the Urumaco Formation (northwestern Accepted 12 July 2020 Venezuela) is herein described. Based on the presence of tall squamosal eminences, we assigned it to KEYWORDS Mourasuchus arendsi. To provide an empirical assessment of the palaeobiological affinities of Mourasuchus, Mourasuchus; Mourasuchus we performed estimations of the body mass and body length based on several Mourasuchus skull measure arendsi; ‘death roll’; Urumaco ments, and an analysis of death roll capability. Our results indicate that Mourasuchus was indeed a large Formation; palaeobiology; crocodylian, with a body length bigger than 9 m and weighed more than 4 tons. We find that Mourasuchus palaeoecology arendsi was incapable of executing the ‘death roll’ as a feeding behaviour and as such was unable to predate giant mammals, which are relatively common in the Urumaco Formation. Finally, the specimen includes a slender humerus, which may indicate that Mourasuchus had weak forelimbs and would spend more time in the water. Introduction Formation, Peru (Salas-Gismondi et al. 2015), Socorro Formation The Venezuelan Neogene geological units contain a significant of Venezuela (Scheyer et al. 2013), the late Miocene Yecua diversity of crocodyliforms (Aguilera 2004; Sánchez-Villagra and Formation, Bolivia (Tineo et al. 2014), Solimões Formation, Brazil Aguilera 2006; Riff et al. 2010; Scheyer et al. 2013; Solórzano et al. (Souza et al. 2016; Cidade et al. 2019a) and Urumaco Formation, 2018, 2019). This is especially true for the Urumaco Formation Venezuela (Scheyer and Delfino 2016). This reflects how biogeo (northwestern Venezuela), which exhibits a unique and unusual graphically widespread Mourasuchus was in South America, espe diversity peak of sympatric crocodylians with distinctive skull mor cially during the middle and the late Miocene. photypes (Scheyer et al. 2013; Scheyer and Delfino 2016). In recent years, intensive palaeontological fieldwork has been A remarkable example of an uncommon skull morphotype is carried out in unexplored areas of the Urumaco Formation Mourasuchus, a genus of caimanine crocodylian exclusive to the (Venezuela), resulting in the discovery of some associated cranial Miocene of South America (Bona et al. 2013; Cidade et al. 2017, and postcranial elements belonging to Mourasuchus arendsi. 2019a) that is one of the most peculiar crocodylians of all time Therefore, the main goal of this paper is to describe these new (Brochu 1999; Cidade et al. 2019b). Mourasuchus is characterised elements of M. arendsi in order to improve the knowledge of the by a long, broad, duckbill-like preorbital snout, with a thin lower anatomy of the species and the genus. From the information obtained jaw and a relatively small postorbital skull table (Langston 1965; through this description and a survey of the literature, our study also Brochu 1999; Bona et al. 2012, 2013; Cidade et al. 2017). Four has another objective: to reassess the palaeoecology and feeding species of Mourasuchus have been recognised: Mourasuchus ama habits of Mourasuchus through the performing of analyses regarding zonensis Price (1964), from the late Miocene of Brazil (Price 1964; these issues that had not yet been made for this taxon. Cidade et al. 2019c); Mourasuchus atopus (Langston 1965) from the Although studies on the phylogenetics and taxonomy of middle Miocene of Colombia (Langston 1965; Langston and Mourasuchus have increased in recent years (Cidade et al. 2017, Gasparini 1997) and Peru (Salas-Gismondi et al. 2015); 2018, 2019b, 2019c), the lifestyle of this bizarre caimanine is not Mourasuchus arendsi Bocquentin-Villanueva (1984) from the late completely understood. Recently, Cidade et al. (2019d) reviewed Miocene of Venezuela, Brazil, Argentina and Bolivia (Bocquentin- hypotheses on the feeding habits and palaeoecology of Villanueva 1984; Souza-Filho and Guilherme 2011; Scheyer and Mourasuchus, proposing that it was a ‘gulp-feeder’ animal that fed Delfino 2016; Cidade et al. 2018, 2019b); and Mourasuchus patter on preferably small animals (fish and arthropods) that inhabited soni Cidade et al. (2017) from the late Miocene of Venezuela preferentially shallow, lentic waters. However, mechanical studies (Cidade et al. 2017). Additionally, records of Mourasuchus sp. on issues relating to the feeding habits of Mourasuchus are still come from the early–middle Miocene Castilletes Formation, lacking. As such, in this study we performed estimations of total Colombia (Moreno-Bernal et al. 2016), middle Miocene body length, total body mass and an analysis of the ‘“death roll” Fitzcarrald Local Fauna, Peru (Salas-Gismondi et al. 2007), Pebas capability indicator (DRCI)’ – see Blanco et al. (2015) – to provide, CONTACT Giovanne M. Cidade [email protected] Laboratório De Estudos Paleobiológicos, Departamento De Biologia, Universidade Federal De São Carlos, Sorocaba, São Paulo, Brazil Supplementary data for this article can be accessed here. © 2020 Informa UK Limited, trading as Taylor & Francis Group Published online 29 Jul 2020 2 G. M. CIDADE ET AL. for the first time, empirically-based information on the palaeoecol Urumaco Formation has been mostly taxonomic and in a few ogy and feeding habits of Mourasuchus. cases phylogenetic, whereas little has been discussed specifically on the adaptations or palaeoecology of these animals (Aguilera 2004; Scheyer and Sánchez−Villagra 2007; Sánchez-Villagra et al. Geological setting 2010). Lithologically, the Urumaco Formation can be informally Three successive geological units are exposed as outcrops in the divided into three members: lower, middle, and upper. The Urumaco area (northern Falcón State, northwestern Venezuela; lower member is dominated by mudstone, with coarsening- Figure 1), the Socorro, Urumaco and Codore formations. They upward sandstone beds, whereas the middle member is char are middle Miocene to early Pliocene in age (Díaz de Gamero acterised by a similar coarsening-upward sandstone beds but 1989; Linares 2004; Carlini et al. 2006a, 2006b; Quiroz and also present limestone and channelled sandstone up 20 metres Jaramillo 2010; Smith et al. 2010), and mostly represent thick, and the upper member lithologically broadly resembles a complex of marginal and near-shore coastal environments, the lower member with the predominance of mudstone (see including nearshore marine, deltaic systems and continental set more details in Quiroz and Jaramillo 2010). The specimen tings (Díaz de Gamero and Linares 1989; Hambalek et al. 1994; here described was collected in a mudstone of the lower mem Quiroz and Jaramillo 2010; Smith et al. 2010). ber of the Urumaco Formation, Buchivacoa Municipality, The specimen here described was collected in the Urumaco Falcón State, Venezuela (Figure 1). This member has very few Formation, which consists of complex intercalations of medium localities and levels with vertebrate fossils (Rincón et al. 2015; to fine-grained sandstone, organic-rich mudstone, coal, shale, and Cáceres et al. 2016). The described specimen is poorly preserved thick-bedded coquinoidal limestones with abundant mollusc frag and covered by a thin gypsum crust, with all elements having ments (Quiroz and Jaramillo 2010). The predominant paleoenvir suffered physical and chemical weathering during diagenesis onment during the sedimentation of the Urumaco Formation is still and surface exposure. In some areas, the bones are partly unclear. According to Díaz de Gamero and Linares (1989) and

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