A supposed Gondwanan oviraptorosaur from the Albian of Brazil represents the oldest South American megaraptoran
Introduction
The Cretaceous theropod record of South America is mainly restricted to Argentina and Brazil (Novas, 2009). In particular, the Argentinean record of the group is taxonomically diverse, including ceratosaurids, noasaurids, abelisaurids, carcharodontosaurids, basal coelurosaurs, megaraptorans, alvarezsaurids, basal paravians, and birds (e.g., Novas, 2009, Novas et al., 2013; Ezcurra and Novas, 2016). The theropod Brazilian record is less abundant, but considerably diverse though, including abelisaurids, noasaurids, carcharodontosaurids, spinosaurids, megaraptorans, basal coelurosaurs, and birds (e.g., Kellner and de Campos, 2002, Novas, 2009, Bittencourt and Langer, 2011, Lindoso et al., 2012, Martinelli et al., 2013, Carvalho et al., 2015, Brusatte et al., 2017).
Most Brazilian theropod nominal species and the best-known specimens come from the Lower Cretaceous Santana Formation in the northeast of the country (i.e., Irritator challengeri, Angaturama limai, Santanaraptor placidus, Mirischia asymmetrica; Kellner and de Campos, 1996, Martill et al., 1996, Kellner, 1999, Sues et al., 2002, Naish et al., 2004, Carvalho et al., 2015). However, in recent years a more diverse Late Cretaceous theropod assemblage has been described in other geological units of the country, but still known from mostly fragmentary specimens, including abelisaurids (e.g., Pycnomemosaurus nevesi; Kellner and de Campos, 2002, Delcourt, 2017, Delcourt and Grillo, 2017), spinosaurids (e.g., Oxalaia quilombensis; Kellner et al., 2011), probable carcharodontosaurids (Vilas Boas et al., 1999, Candeiro et al., 2004, Candeiro et al., 2006), megaraptorans (Méndez et al., 2012, Martinelli et al., 2013, Sales et al., 2017), and possibly noasaurids (Lindoso et al., 2012) and maniraptorans (Elias et al., 2004, Bittencourt and Langer, 2011). As part of the Early Cretaceous theropod record, Frey and Martill (1995) described a partial sacrum articulated to two caudal vertebrae and a partial right ilium (SMNS 58023) from the Albian beds of the Santana Formation. This specimen was interpreted tentatively as an indeterminate oviraptorosaur on the basis of the presence of pleurocoels in the sacral vertebral centra (Frey and Martill, 1995). Subsequently, Kellner (1996) considered that the taxonomic assignment of SMNS 58023 should be considered with caution. Makovicky and Sues (1998) criticized more explicitly the identification of SMNS 58023 as a possible oviraptorosaur and considered it doubtful, stating that sacral pleurocoels are present in some other coelurosaurs (e.g., tyrannosauroids, some dromaeosaurids) and that this specimen differs from oviraptorosaurs in the presence of an arched sacrum in lateral view with much expanded intercentral articulations. This view was followed more recently by Novas (2009), who added that the posterior end of the ilium of SMNS 58023 differs from that of oviraptorosaurs in being transversely broader and possessing a notched posterior margin. As a result, although the identification of SMNS 58023 as an oviraptorosaur was criticized by some previous authors, no alternative hypothesis for its affinities has been proposed.
Two other previous reports of Gondwanan oviraptorosaurs were based on an isolated cervical vertebra from the Maastrichtian Lecho Formation of northern Argentina (Frankfurt and Chiappe, 1999) and a possible surangular bone associated to an isolated dorsal vertebra from the Aptian−Albian of southeastern Australia (Currie et al., 1996). The Argentinean specimen was reinterpreted as belonging to an indeterminate abelisauroid or to Noasaurus leali (Agnolín and Martinelli, 2007), and the Australian specimens were reinterpreted as an indeterminate theropod (i.e., possible surangular) (Agnolín et al., 2010) and an indeterminate maniraptoran (i.e., vertebra) (Benson et al., 2012a). As a result, the currently most suggestive evidence for the presence of oviraptosaurs in Gondwana is the specimen from the middle Cretaceous Santana Formation of Brazil. Here we revisit the anatomy and phylogenetic relationships of this specimen because of its potential implications for the palaeobiogeography and evolutionary history of Cretaceous theropods.
IVPP: Institute of Vertebrate Paleontology and Paleoanthropology, Beijing, China.
MACN-Pv CH: Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”, Paleovertebrados (Pv), Colección Chubut (CH), Buenos Aires, Argentina.
MPCA-Pv: Museo Provincial “Carlos Ameghino”, Cipolletti, Río Negro, Argentina.
MUCPv: Museo de Geología y Paleontología, Universidad Nacional del Comahue, Neuquén, Argentina. SMNS: Staatliches Museum für Naturkunde Stuttgart, Stuttgart, Germany.
Section snippets
Geological setting
The Araripe Basin is a worldwide known sedimentary deposit. It is the most extensive intracratonic basin of northeastern Brazil, covering an area of about 9000 km2 in the Ceará, Pernambuco, and Piauí states (Fig. 1). It is laid upon the Proterozoic basement that corresponds to the Borborema Tectonic Province. The depositional history was mainly related to the reactivation of faults in the basement during the Late Jurassic–Early Cretaceous, when tectonic movements led to the separation between
Phylogenetic analysis
In order to test the phylogenetic affinities of SMNS 58023, this specimen was included in two independent data matrixes focused on the higher-level phylogenetic relationships of non-maniraptoran averostrans, namely Carrano et al. (2012) and Porfiri et al. (2014) (following the modifications implemented by Apesteguía et al., [2016] in both data matrixes).
Both data matrixes mainly overlap in the sampling of allosauroid theropods, but the matrix of Carrano et al. (2012) includes a broader sample
Systematic palaeontology
Theropoda Marsh, 1881
Tetanurae Gauthier, 1986
Avetheropoda Paul, 1988
Megaraptora Benson et al., 2010
Gen. et sp. indet.
Material. SMNS 58023, last three sacral vertebrae and ribs, two caudal vertebrae, and postacetabular process of the right ilium.
Locality and horizon. Unknown locality, Romualdo Member (Albian) of the Santana Formation, Araripe Basin, northeastern Brazil (Frey and Martill, 1995).
Sacral vertebrae
The preserved portion of the sacrum of SMNS 58023 is composed of the last three vertebrae and ribs (Fig. 2, Fig. 3, Fig. 4). The postacetabular process of the ilium is apparently attached to the last two sacral vertebrae (see below), a condition broadly distributed among theropods with five to seven sacral vertebrae (e.g., Carnotaurus: Bonaparte et al., 1990; Tyrannosaurus: Brochu, 2003; Shixinggia: Lü and Zhang, 2005).
The most anteriorly preserved vertebra lacks its anterior region and the
Concluding remarks
Frey and Martill (1995) assigned, with doubts, SMNS 58023 to Oviraptorosauria on the basis of the presence of pleurocoels in the sacral centra. However, discoveries conducted in the last twenty years have shown that this feature is more widely distributed among theropods and homoplastic than previous thought (e.g., Benson et al., 2010, Novas et al., 2013). By contrast, we found in SMNS 58023 a series of character-states that are not present in oviraptorosaurs and are listed as follows: 1)
Acknowledgements
We thank the curators Rainer Schoch (SMNS) and Susana Devinvenzi González (MCNAM) that provided access to specimens under their care for the purpose of this research. Access to the free version of TNT 1.5 was possible due to the Willi Henning Society. We thank Federico L. Agnolín and Ariel H. Méndez for the comments and suggestions on the manuscript.
References (85)
- et al.
Did oviraptorosaurs (Dinosauria: Theropoda) inhabit Argentina?
Cretaceous Research
(2007) Branch support and tree stability
Cladistics
(1994)- et al.
Morphology and internal structure of two new abelisaurid remains (Theropoda, Dinosauria) from the Adamantina Formation (Turonian-Maastrichtian), Bauru Group, Paraná Basin, Brazil
Cretaceous Research
(2016) - et al.
Dinosaurs remains from western São Paulo state, Brazil (Bauru Basin, Adamantina Formation, Upper Cretaceous)
Journal of South American Earth Sciences
(2004) - et al.
Tetrapods from the Upper Cretaceous (Turonian Maastrichtian) Bauru Group of Brazil: a reappraisal
Cretaceous Research
(2006) - et al.
Problems with zero-length branches
Cladistics
(1994) - et al.
Controlled excavations in the Romualdo Member of the Santana Formation (Early Cretaceous, Araripe Basin, northeastern Brazil): stratigraphic, palaeoenvironmental and palaeoecological implications
Palaeogeography, Palaeoclimatology, Palaeoecology
(2005) - et al.
Improvements to resampling measures of group support
Cladistics
(2003) - et al.
Masiakasaurus-like theropod teeth from the Alcântara Formation, São Luís Basin (Cenomanian) northeastern Brazil
Cretaceous Research
(2012) - et al.
Halite pseudomorphs in the Crato Formation (Early Cretaceous, Late Aptian–Early Albian), Araripe Basin, northeast Brazil: further evidence for hypersalinity
Cretaceous Research
(2007)