A new rebbachisaurid (Sauropoda: Diplodocoidea) from the middle Cretaceous of northern Brazil
Introduction
One of the most interesting subjects concerning the Mesozoic continental faunas is the identification of events of vicariance and dispersal throughout the history of Gondwana. In this sense, Rebbachisauridae is paleobiogeographically relevant, a clade formed by all diplodocoids more closely related to Rebbachisaurus garasbae than to Diplodocus longus (sensu Salgado et al., 2004). Their records have been useful for ascertaining the moment of definitive separation between South America and Africa (Carballido et al., 2010). Recently, phylogenetic analysis has emphasized a marked provincialism among members of Rebbachisauridae, with some of them restricted to Europe and northern Africa (e.g. Nigersaurus, Demandasaurus, Rebbachisaurus) and others only composed by Upper Cretaceous South American taxa (e.g. Limaysaurus, Cathartesaura, Nopcsaspondylus, El Chocon rebbachisaurid) (Sereno et al., 2007, Whitlock, 2011, Fanti et al., 2013, Wilson and Allain, 2015, Mannion et al., 2019). This group of neosauropods also reveals extreme adaptations for herbivory and high temperatures in habitats at tropical and subtropical paleolatitudes (Sereno et al., 2007, Ibiricu et al., 2017).
In South America, Rebbachisauridae is diverse and frequently recorded in an interval extending from the Barremian to Turonian, particularly in Argentina. Additionally, their remains are composed mainly of postcranial elements (Calvo and Salgado, 1995, Bonaparte, 1996, Calvo, 1999, Salgado et al., 2004, Gallina and Apesteguía, 2005, Apesteguía, 2007, Carballido et al., 2010, Carballido et al., 2012, Haluza et al., 2012, Ibiricu et al., 2012, Ibiricu et al., 2013). This diversity has been also complemented by a few cranial remains (Calvo and Salgado, 1995, Carabajal et al., 2016, Canudo et al., 2018). Other records of Rebbachisauridae in South America occur only in northern-northeastern Brazil (Carvalho et al., 2003, Medeiros and Schultz, 2004, Castro et al., 2007, Medeiros et al., 2014).
In the São Luís Basin, Cretaceous outcrops are mainly Cenomanian in age (Klein and Ferreira, 1979, Pedrão et al., 1993). For over 20 years, the most important fossiliferous outcrop in this basin has been the Laje do Coringa bone-bed, which records the Alcântara Formation (lower Cenomanian), at Cajual Island, São Marcos Bay (Corrêa-Martins, 1996, Medeiros and Schultz, 2001, Medeiros and Schultz, 2002) (Fig. 1). Therein, a noteworthy paleocommunity including crocodyliforms, fishes, dinosaurs, plants remains, invertebrates, and pterosaurs has been recorded (Medeiros et al., 1995, Medeiros et al., 1996, Medeiros et al., 2014, Corrêa-Martins, 1996, Vilas-Bôas et al., 1999, Vilas-Bôas and Carvalho, 2001, Medeiros and Schultz, 2001, Medeiros and Schultz, 2002, Elias et al., 2007, Pereira and Medeiros, 2008, Araújo et al., 2011, Lindoso et al., 2012, Lindoso et al., 2013a).
The Alcântara Formation records both Titanosauria and Diplodocoidea remains, although the former is less frequent in the Laje do Coringa bone bed (Medeiros et al., 2007, Medeiros et al., 2014). The fragmentary state of these materials has precluded the proposition of any nominal species, except for a few teeth tentatively assigned to Malawisaurus (Freire et al., 2007). Some rebbachisaurid remains (e.g. caudal vertebrae/neural spine) have been tentatively assigned to a more specific taxonomic level, cf. Limaysaurus tessonei (Medeiros and Schultz, 2004).
In the Parnaíba sedimentary Province (which also include the São Luís Basin to the north), Diplodocoidea remains has been found in a better preservation state, with a unique nominal species described so far, Amazonsaurus maranhensis Carvalho et al. (2003). This rebbachisaurid was described based on a partial postcranial skeleton in Lower Cretaceous (Aptian-Albian) strata of the Itapecuru Formation, southern Maranhão State, northern Brazil (Carvalho et al., 2003). Many common taxa are recorded in the Alcântara and Itapecuru formations (e.g. Theropoda and fishes), suggesting a homogeneous paleocommunity inhabiting the northeastern Brazil throughout the Albian and early Cenomanian (Medeiros and Schultz, 2002, Medeiros et al., 2007, Medeiros et al., 2014).
In the present study, a new genus and species of rebbachisaurid dinosaur is described from lower Cenomanian strata of Brazil, the first nominal diplodocoid from the Alcântara Formation. It comes from a new fossiliferous locality in Maranhão State and may help to increase our understanding concerning this sauropod group during the mid-Cretaceous worldwide.
Section snippets
Geological setting
The São Luís Basin is a marginal basin located in the north portion of South America. It has a total area of 18.000 km2 and its genesis is related to the Equatorial Atlantic opening initiated during the Late Jurassic and Early Cretaceous (Szatimari et al., 1987, Góes and Rossetti, 2001, Carvalho, 2001a). This basin represents one sub-basin on a larger intracratonic sedimentary area, the Parnaíba Province, tectonically reactivated in the Mesozoic during the South America and Africa breakup (
Material and methods
The fossils described herein are housed at the fossil collection of the Universidade Federal do Maranhão (UFMA). They were localized by a fisherman on a beach in the Cajapió municipality, Maranhão State, subsequently being recovered by a team of paleontologists of the Universidade Federal do Maranhão (UFMA), Universidade Federal do Rio de Janeiro (UFRJ), Centro de Pesquisa de História Natural e Arqueologia do Maranhão (CPHNAMA) and Universidade Estadual do Maranhão (Fig. 2A). As the specimen
Systematic paleontology
SAURISCHIA Seeley, 1887
SAUROPODOMORPHA Huene, 1932
SAUROPODA Marsh, 1878
DIPLODOCOIDEA Marsh, 1884 (sensu Upchurch, 1995)
REBBACHISAURIDAE Bonaparte, 1997
Itapeuasaurus cajapioensis, gen. et sp. nov.
(Fig. 3, Fig. 4, Fig. 5, Fig. 6, Fig. 7, Fig. 8, Fig. 9)
Diagnosis. Rebbachisauridae distinguished by the following combination of characters on the dorsal and caudal vertebrae (autapomorphies are marked with an asterisk): Presence of three shallow pneumatic fossae disposed vertically on the dorsal
Phylogenetic analysis
Rebbachisauridae was defined as all diplodocoids more closely related to Rebbachisaurus garasbae than to Diplodocus longus (Wilson [pers. comm.] in Salgado et al., 2004). Recent analysis has recovered Amazonsaurus as the most ‘basal’ member of this clade, with the European/African Histriasaurus its sister taxon. Histriasaurus forms a polytomy with the South American Zapalasaurus at the base of Rebbachisauridae and Comahuesaurus is also placed outside of Khebbashia
Conclusions
Itapeuasaurus cajapioensis gen. et sp. nov. represents the northernmost record of Diplodocoidea in South America and the second nominal Rebbachisauridae for the middle-Cretaceous of Brazil, expanding our knowledge regarding the diversity of this clade in Western Gondwana. Its set of autapomorphies confirm the pneumatic complexity inherent to this neosauropod group. The phylogenetic analysis performed herein identifies Nigersaurinae as a South American – African/European clade more than an
Acknowledgements
We would like to thank Dr. Philip Mannion for criticisms, comments and English improvement addressed to the final version of this manuscript. We are very grateful to Dr. Eduardo Koutsoukos for his valuable comments on the paleobiogeography of Western Gondwana, and the anonymous reviewer for criticisms and comments. We thank the group of locals who found the fossil on Itapeua beach and helped with the collecting work: João Francisco Costa Filho, Mosart Rogério Soares, Taísa Pinheiro, Cláudia
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