Elsevier

Cretaceous Research

Volume 84, April 2018, Pages 107-119
Cretaceous Research

A supposed Gondwanan oviraptorosaur from the Albian of Brazil represents the oldest South American megaraptoran

https://doi.org/10.1016/j.cretres.2017.10.019Get rights and content

Highlights

  • A Brazilian oviraptorosaur is here reinterpreted as a megaraptoran.

  • The megaraptoran sacrum has a similar morphology to those of tyrannosauroids.

  • The oldest South American megaraptorans are Albian in age.

Abstract

A specimen composed of a partial sacrum articulated to two anterior caudal vertebrae and an ilium (SMNS 58023) from the Lower Cretaceous (Albian) Santana Formation of Brazil was originally described as an oviraptorosaur, but it is here re-interpreted as the oldest megaraptoran of South America. The phylogenetic relationships of SMNS 58023 were tested quantitatively for the first time including it in the two most comprehensive phylogenetic data sets focused on non-maniraptoran theropods –including megaraptorans. The Brazilian specimen was consistently found as a megaraptoran in both analyses because of the presence of sacral centra longer than tall, absence of a median transverse constriction of sacral centra, and the morphology and position of sacral pleurocoels. SMNS 58023 sheds light on a region of the body that is poorly known in megaraptorans and pulls back the temporal range of the clade in South America. This re-interpretation reinforces the absence of oviraptorosaurs in Gondwana.

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.

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