The first Jurassic theropod from the Sergi Formation, Jatobá Basin, Brazil

Abstract

Archosaur osteological remains are abundant in Brazil, particularly from the Triassic and Cretaceous strata, but in Jurassic, the record is predominantly represented by ichnofossils. The Upper Jurassic archosaur records comprise the Paralligatoridae Batrachomimus pastosbonensis, from the Pastos Bons Formation (Parnaíba Basin), remains of Mesoeucrocodylia from the Aliança Formation (Jatobá Basin), and fragments of Dinosauria from the Brejo Santo Formation (Araripe Basin) with a dubious assignment. Here, we present the first undoubted Dinosauria record for the Jurassic of Brazil, MCT 2670-LE, a middle to distal caudal vertebra belonging to a theropod. MCT 2670-LE was excavated in the 60s by prof. Ignacio Machado Brito, being primarily attributed to strata of the Aliança Formation but the rock matrix involving the specimen allows us to correlate MCT 2670-LE to Sergi Formation, marking this specimen as the first archosaur record of this unit. The caudal vertebra is assigned to Carcharodontosauria based on the hourglass shaped centrum and the deep and narrow ventral groove. The specimen provides new data to the paleogeographic distribution of carcharodontosaurians before the South America-Africa break-up, as well as understanding the theropod faunal turnover of paleoenvironments during the Jurassic-Cretaceous transition in Brazil.

Key words
Theropoda; Carcharodontosauria; Caudal Vertebra; Upper Jurassic; Sergi Formation; Jatobá Basin

INTRODUCTION

In Brazil, archosaur remains are well-known, especially those dating from the Mesozoic Era, and the Triassic and Cretaceous deposits are the main fossiliferous ones (Bittencourt & Langer 2011). The Cretaceous represents the most expressive interval with abundant vertebrate fossil record (Bittencourt & Langer 2011, Brusatte et al. 2017), both on the Lower (e.g, Pereira et al. 2020a, b) and Upper levels (e.g., Pinheiro et al. 2018, Bandeira et al. 2019, Delcourt et al. 2020). Archosaurs are the predominant fossil records especially on the Upper Cretaceous strata (Bandeira et al. 2018). However, rock exposures from the Brazilian Jurassic are scarce (Bittencourt & Langer 2011), due to the sedimentation and tectonic conditions unfavorable to the preservation of bone elements (e.g., Milani 2007).

This scenario makes challenging the study and the consequent interpretations of Jurassic fossil data on Brazil (e.g., Gallo & Brito 2004, Gallo 2005, Bittencourt & Langer 2011). Thus, the Jurassic record for Brazil is best represented by the ichnofossils (e.g., Leonardi et al. 2007, but see Table I), while the Araripe Basin (Brejo Santo Formation and Missão Velha Formation), the Parnaíba Basin (Pastos Bons Formation) and the Jatobá Basin (Aliança Formation), all from Upper Jurassic, are the only units with tetrapod bone elements - mostly, archosaurs. The Paralligatoridae Batrachomimus pastosbonensis Montefeltro et al. 2013, from the Pastos Bons Formation, is the only archosaur species described so far for the Brazilian Jurassic (Montefeltro et al. 2013).

Table I
Jurassic sedimentary basins in Brazil, and their respective fossil contents, (when found). Abbreviations: Fm, Formation, Mb, Member.

geological unit	lithology and depositional context	distribution	fossil record	age	references
Parecis Basin
Fm. Anari	fine-grained to aphanitic basalts, with subordinate coarsed diabase bodies. Volcanic flows	southeast of Rondônia (RO) to the Northwest of Mato Grosso (MT) state	no fossils related	Lower Jurassic - Hettangian	Schobbenhaus et al. 1984, Marzoli et al. 1999, Silva et al. 2003. Pedreira & Bahia 2004
Fm Tapirapuã	similar to basalts from Anari Formation, with columnar disjunction and spheroidal exfoliation	comprises the Tapirapuã massif in Mato Grosso (MT) state	no fossils related	Lower Jurassic - Hettangian	Schobbenhaus et al. 1984, Marzoli et al. 1999, Silva et al. 2003. Pedreira & Bahia 2004
Fm Rio Ávila	reddish, friable and eolic sandstones with rounded grains, well to poorly selected	Outcrops in north of General Carneiro, in the valley of the Culuene river and northwest of Vilhena, Mato Grosso (MT) state	no macrofossils related	Jurassic	Silva et al. 2003, Bahia, 2007
Fm. Botucatu	large scale cross-bedded bimodal sandstones. Aeolian dunes	Outcrops in West of Rondônia (RO) and small exposures in southeast of Mato Grosso (MT)	no macrofossils or ichnofossils related	Jurassic	Pedreira & Bahia 2000, 2004
Parnaíba Basin
Fm Mosquito	tholeiitic flood basalts, interbedded with sandstones	arround the municipality of Fortaleza dos Nogueiras, Maranhão (MA) state	no macrofossils related	Lower–Middle Jurassic	Schobbenhaus et al. 1984, Bellieni et al. 1992, Santos & Carvalho 2004
Alparcata Basin
Fm Pastos Bons	for the base, se- quences of siltstone, dark shale, and greenish and brownish mud- stones. The upper strata consist of gray to green shales with wavy lamination	occurs as a south-central belt in Maranhão (MA) state, with some exposure in west of Piauí (PI)	ostracods; conchostracans; palynomorphs; plant cuticles; fishes (Lepidotus piauhyensis, probable Semionotus and pleuropholids); Crocodyliformes (i.e., Batrachomimus pastosbonensis);	Upper Jurassic - Oxfordian–Kimmeridgian	Schobbenhaus et al. 1984, Gallo, 2005, Montefeltro et al. 2013
Paraná Basin
Fm Botucatu	mostly composed of fine-to medium-grained quartz sandstones. Friable, rounded and with large-scale cross-bedding related to a wide eolian dunes field. Sand sea of large eolian dunes	widespread occurrence in the Paraná Basin, which cover great áreas of São Paulo (SP), Paraná (PR), Santa Catarina (SC), Rio Grande do Sul (RS), Mato Grosso (MT) and Mato Grosso do Sul (MS) states, with some portions in Goias (GO) and Minas Gerais (MG) states	abundant ichnofossils: as footprints and tracks produced by invertebrates (arachnids and insects) and tetrapods (small to medium dinosaurs [i.e., ceratosaurid theropods, ornithopods?] and mammals [e.g., Brasilichnium elusivum]), also urolites attributed to dinosaurs.	Upper Jurassic - Lower Cretaceous	Schobbenhaus et al. 1984, Scherer, 2000, Fernandes et al. 2004, Scherer & Lavina 2006, Leonardi et al. 2007
Fm Guará	composed of fine- to coarse-grained sandstones and rare mudstones of fluvial and eolian depositional systems	south region of Rio Grande do Sul state (RS)	ichnoassemblage formed by theropod, ornithopod and sauropod tracks	Upper Jurassic–Kimmeridgian-Tithonian	Scherer & Lavina 2005, 2006, Francischini et al. 2017
Almada Basin
Fm Sergi	fluvial and eolic deposits. Mostly composed by sandstones, but wiht conglomerates in a finning upward granulometry	south-central coast of Bahia state (BA)	no macrofossils related	Upper Jurassic (Tithonian, Dom Joao local age)	Scherer et al. 2007, Bongiolo & Scherer 2010, Adegas et al. 2012
Camumu Basin
Fm Sergi	similar as above	central coast of Bahia state (BA)	no macrofossils related	Upper Jurassic (Tithonian, Dom Joao local age)	Ferreira et al. 2009, Kuchle et al. 2011,
Recôncavo Basin
Fm Sergi	similar as above	central-eastern of the State of Bahia (BA)	ostracods (e.g, Bisulcocypris pricei); silicified wood attributed to coniferous Dadoxilon benderi	Upper Jurassic (Tithonian, Dom Joao local age)	Pedreira, 2000, Kuchle et al. 2011, Guzmán et al. 2015, Vilas Boas et al. 2018
Fm Aliança	formed by Capianga e Boipeba members. A gondwanic pre-rift sequence	central-eastern of the State of Bahia (BA)	permineralized wood reported (from Tucano and Jatobá deposits) ostracods (e.g., Darwinula, Bisulcocypris pricei, B. uninodosa) conchostracans (e.g., Cyzicus brauni); fish remains (e.g., hybodontid sharks, coelachants [e.g., Mawsonia gigas], Lepidotes and ceratodontid dipnoics); mesoeucrocodylian remains	Upper Jurassic (Tithonian, Dom Joao local age)	Netto & Oliveira, 1985, Ricardi-Branco 2004Kuchle et al. 2011, Silva et al. 2011, Guzmán et al. 2015, Vilas Boas et al. 2018, Carvalho et al. 2021
Mb Capianga	lacustrine muddystones. A gondwanic pre-rift sequence	central-eastern of the State of Bahia (BA)	no macrofossils related	Upper Jurassic (Tithonian, Dom Joao local age)	Scherer et al. 2007, Kuchle et al. 2011, Vilas Boas et al. 2018
Mb Boipeba	fluvial sandstones, compacted and cemented by quartz, anhydrite and calcite toward the base. A gondwanic pre-rift sequence	central-eastern of the State of Bahia (BA)	no macrofossils related	Upper Jurassic (Tithonian, Dom Joao local age)	Salem et al. 2000, Scherer et al. 2007, Kuchle et al. 2011, Vilas Boas et al. 2018
Tucano Basin
the same depositional units as observed for Recôncavo Basin	the same lithostratigraphy as observed for Recôncavo Basin units (sup. cit.)	Observations: Subdivided in North-Jatobá-Tucano and South-Central Tucano. Synchronic depositional sequence with Reconcavo and Jatobá units as consequence of Recôncavo-Tucano-Jatobá aborted intracontinental rift			Vita & Cupertino 1988, Milani et al. 2007, Costa et al. 2007a, Kuchle et al. 2011
Jatobá Basin
except by Boipeba Member, the same depositional units as observed for Recôncavo and Tucano basins	expected by Boipeba Member, the same lithostratigraphy as observed for Recôncavo and Tucano depositional units (sup. cit.)	Observations: Synchronic depositional sequence with Reconcavo and Tucano units as consequence of Recôncavo-Tucano-Jatobá aborted intracontinental rift			Vita & Cupertino 1988, Milani et al. 2007, Costa et al. 2007b, Kuchle et al. 2011
Sergipe Basin
Fm Serraria	coarse grained, poorly sorted, kaolinitic sandstones of fluvial braided depositions	coastal margin of Sergipe state (SE)	no macrofossils related	Upper Jurassic (Tithonian, Dom Joao local age)	Azambuja Filho 1998, Melton 2008, Borba et al. 2011, Kuchle et al. 2011, Freitas & Silveira 2017, Franco 2018
Fm Bananeiras	lacustrine red shales	coastal margin of Sergipe state (SE)	no macrofossils related	Upper Jurassic (Tithonian, Dom Joao local age)	Azambuja Filho, 1998, Melton 2008, Borba et al. 2011, Kuchle et al. 2011, Freitas & Silveira 2017
Alagoas Basin
Bananeiras and Serraria formations are same depositional units as observed for Sergipe Basin	the same lithostratigraphy as observed for Bananeiras and Serraria sequences (sup. cit.)	coastal margin of Alagoas state (AL)	same as Sergipe Basin		Azambuja Filho, 1998, Melton 2008, Borba et al. 2011, Kuchle et al. 2011, Freitas & Silveira 2017
Fm Candeeiro	iterbedding of fine to medium-grained sandstones with reddish siltstones and shales	coastal margin of Alagoas state (AL)	no macrofossils related	Upper Jurassic (Tithonian, Dom Joao local age)	Azambuja Filho, 1998, Freitas & Silveira 2017
Araripe Basin
Fm Missão Velha	consists of quartz sandstones, sometimes feldspar and/or kaolinic, locally conglomeratic. River plains of interlaced systems characterized by shallow, high-energy channels. A gondwanic pre-rift sequence	south of Ceará state (CE)	abundant silicified wood, attributed to coniferous Dadoxilon benderi	Upper Jurassic (Tithonian? Dom Joao local age)	Assine, 1992, 2007, Fambrini et al. 2009 Kuchle et al. 2011
Fm Brejo Santo	shales and red lamitos from a lacustrine deposition. A gondwanic pre-rift sequence	south of Ceará state (CE)	ichnofossils; continental ostracodes (e.g., Bisulcopypris pricei, Darwinula oblonga, Theriosynoecum miritiensis); conchostraceans (i.e., Cyzicus pricei); gastropods; bivalves; fishes (i.e., Mawsonia gigas, Lepidotes sp.); crocodyliforms teeth and dinosaurians remains	Upper Jurassic (Tithonian? Dom Joao local age)	Assine 1992, 2007, Kuchle et al. 2011, Vieira de Melo & Carvalho 2017
Tacutu basin
Fm Pirara	consists of halites in the areas central for granite and laterally interdigitated schists and, less frequently, siltstones and carbonates	central-northeast sector of Roraima state (RO). The Tacutu hemigraben deposits extends between Brazil and Guyana	no macrofossils related	Upper Jurassic	Crawford et al. 1984, Eiras & Kinoshita 2006, Vaz et al. 2007
Fm Manari	siltstones, shales and, locally, calcisiltites and dolomites, produced by a lake sedimentary environment	central-northeast sector of Roraima state (RO). The Tacutu hemigraben deposits extends between Brazil and Guyana	no macrofossils related	Upper Jurassic	Crawford et al. 1984, Eiras & Kinoshita 2006, Vaz et al. 2007
Fm Apoteri	massive tholeiitic basalts to amigdaloidals, occasionally interspersed with sandstones at the base of Takutu basin; diabase dikes	central-northeast sector of Roraima state (RO). The Tacutu hemigraben deposits extends between Brazil and Guyana	no macrofossils related	Upper - Jurassic	“BRASIL, Radambrasil Project”1975, Crawford et al. 1984, Schobbenhaus et al. 1984, Eiras & Kinoshita 2006, Milani, et al.2007, Vaz et al. 2007
Mangabeira, Lavras da Mangabeira and Iborepi
Fms Serrote do Limoeiro and Iborepi	fluvial depositions, generally formed by conglomeratic layers to the base, with fining upward red sandstones with interbedded pelites to the top	three small basins (63km2 total area) for the south of Ceará state (CE)	rhizolites and ichnofossils related to invertebrates (e.g., Skolithos sp.); conchostraceans (i.e., “Pseudestheria” pricei); and fragments of other invertebrates (e.g., Anodontites), plants, and vertebrates (indet.)	Lower Jurassic (Iborepi and Serrote do Limoeiro [?] formations) / Upper Jurassic ? (Lavras da Mangabeira)	Carvalho 1993, Carvalho & Fernandes 1993, Rocha et al. 2008Hessel, 2014

Other records consist of small axial elements (about 3-4 cm) found in the Brejo Santo Formation (Melo & Carvalho 2017), along with Mesoeucrocodylia teeth. These axial elements (which do not have a collection number) were proposed as the first Dinosauria record for the Brazilian Jurassic (Melo & Carvalho 2017). However, the authors provided no diagnostic feature for this classification, and the description of these elements is superficial. The specimen images also depict just a ventral view of the material, and more detailed comparisons become impossible. Due to the difficulty of knowing the origin in which institution these specimens are allocated, as well as unclear diagnostic characteristics that allow a more accurate systematic assignment, we assume here that the attribution to Dinosauria of these specimens is doubtful. The Missão Velha Formation has a rich fossil assemblage, including anurans, lizards, turtles, mesoeucrocodylians and even nonavian dinosaurs (sensu Brito et al. 1994), but most elements require a formal description and systematic review.

Finally, for the Upper Jurassic of Aliança Formation, there is a brief report of some Mesoeucrocodylia remains (Silva et al. 2011) which are more recently reviewed and described together with new mesoeucrocodylian findings (Carvalho et al. 2021). Thus, we present the first confirmed Dinosauria record for the Jurassic of Brazil, MCT 2670-LE, collected in 1962 by prof. Ignacio Machado Brito at São Francisco riverbank (see Geological Settings). MCT 2670-LE is identified as a middle caudal vertebra of a carcharodontosaurian theropod. The new specimen improves the understanding of the rare archorsaur remains from the Jurassic period in Brazil. It is also possible to link MCT 2670-LE to theropods of other basins with Jurassic outcrops, allowing an evaluation of the paleogeographic distribution of tetrapods recognized in these formations, as well as the evolutionary and faunal changes of paleoenvironments during the Jurassic-Cretaceous transition in Brazil.

HISTORICAL REMARKS

We describe a new fossil material collected close to the municipality of Petrolândia (Pernambuco) in 1962 by Prof. Dr Ignacio Machado Brito. In the notes associated with the specimen, Brito mentioned that it was recovered in the margins of the São Francisco River upstream the Petrolândia municipality.

This contribution is a tribute to Diogenes de Almeida Campos, the paleontologist of the Museu de Ciências da Terra (Serviço Geológico do Brasil – CPRM), who had prof. Ignacio as advisor and paleontology undergraduate professor. Ignacio led Diogenes to his first collecting fossils fieldwork at this same region. Besides this, Diogenes made a prospect in the area in the 1980s aiming for the rescue of paleontological material prior to the construction of the Luis Gonzaga hydroelectric plan. Therefore, the material here described connects Diogenes with his past advisor and to a region on which he had important historical action.

Geological settings

The Recôncavo-Tucano-Jatobá (or RTJ System, Santos et al. 1990, Costa et al. 2007) is a well-known rift system in Northeastern Brazil (Almeida, 1967, Magnavita & Cupertino 1988 , Guzmán et al. 2015). The RTJ System is part of the Borborema Province (Almeida et al. 1977) which strata records the intracontinental evolution of the Gondwana break up in South America and Africa continents (Guzmán et al. 2015, Guzmán-González et al. 2016). The Jatobá Basin - the northern end of the RTJ System - marks the inflection of the general orientation of the aborted intracontinental rupture in the referred system from NS to N70’E (Magnavita & Cupertino 1988, Magnavita et al. 2012). The Jatobá Basin (Figure 1) has an expressive sedimentary record known since last century (e.g., Derby 1879 ), where the rift phase is much less pronounced than the other rift Northeastern Basins (Guzmán-González et al. 2016).

Figure 1
Geological setting. Map of South America (A), close-up of Northeastern Brazil (B), and a close-up of the Tucano-Recôncavo-Jatobá Basins system (C). World map (Tithonian) showing localities of Upper Jurassic carcharodontosaurians (D): MCT 2670-LE (red star), Veterupristisaurus (blue square), and Lusovenator (yellow circle). Surroundings of Petrolândia (corresponding to the red square in C), showing the São Francisco River dam in function in 1969, possibly where the specimen was collected (see text for discussion) in (E), deactivated in 1984, exhibiting greater area of the Sergi Formation along the river in (F), and activated in 2020, flooding a good part of the fossiliferous areas in (G). (A) and (B) extracted from Google Maps; (C) modified from the CPRM database; (D) modified from Palaeobiology Database; (E-G) extracted from Google Earth. Numbers in (C): 1, Sergipe-Alagoas Basin; 2, Recôncavo-Tucano-Jatobá system; 3, Paleozoic Formations; 4, Estância and Palmares Basins; 5, Sergipana Range (Sub-Domain Vaza-Barris); 6, Sergipana Range (Sub-Domain Macururé); 7, Canindé-Marancó Terrain; 8, Pernambuco-Alagoas Terrain; 9, Alto Pajeú and Alto Moxotó Terrains; 10(A), Salvador-Curaçá Orogen; 10(B) Salvador-Esplanada Belt; 11, Serrinha Block.

The Jatobá Basin is divided into its three major sedimentation phases: syneclise (Silurian to Devonian); rift (Upper Jurassic-Lower Cretaceous) and post-rift (Lower Cretaceous; Costa et al. 2007, Guzmán et al. 2015, Guzmán-González et al. 2016). The Brotas Group (Figure 1) represents the rift and post-rift phases and is present in the entire RTJ rift system (Cota et al. 2007, Silva et al. 2011, Guzmán et al. 2015), consisting of the Aliança and Sergi formations. The Aliança Formation is composed mainly by packages of massive reddish laminated claystone, interbedded with limestone (Leite et al. 2001, Guzmán-González et al 2016). Normally the claystone packages are also interbedded with sandy limestone or calcareous quartz-arenite with a minor proportion of greenish-grey claystone and thin evaporate layers (Leite et al. 2001, Guzmán-González et al. 2016). The Aliança Formation was dated to the Tithonian based on biostratigraphic zones (Viana et al. 1971, Brito 1987, Magnavita & Cupertino 1988, Silva et al. 2011, Guzmán et al. 2015, Guzmán-González et al. 2016).

Despite more than a century of exploration, few is known about the vertebrate fauna of the Jatobá Basin as a whole. Most of the reports are fish remains (Silva et al. 2011), predominantly coelacanths and Lepidotes, dorsal fin spines and isolated teeth from hybodontid sharks, as well as dipnoic dental plates (Silva et al. 2011) and some mesoeucrocodylian remains (Silva et al 2011, Carvalho et al. 2021). Finally, from the limestone strata came most of the ostracods record (e.g., Guzmán-González et al. 2016).

Nevertheless, little was given about the exact layer where MCT 2670-R was collected, albeit the specimen was previously encased in a massive clast supported conglomerates, fashioned in pebble granules with sub-rounded to rounded clasts, moderately selected. As said before, the personal annotations of prof. Ignacio Brito pointed out that the specimen came from riverbanks of the São Francisco River, in Petrolândia (Pernambuco state). He set this place as belonging to Aliança Formation (Brito 1987), whose lithological composition is distinct from the rock matrix in the specimen. However, coarse to fine-grained sandstones intercalated with massive clast supported conglomerates, as described above, are typical of other Jurassic strata from Brotas Group: the almost unknown Sergi Formation (Viana et al. 1971, Rocha 2011, Adegas et al. 2012, Guzmán et al. 2015). It is also known that the contact between the Aliança and the Sergi formations is transitional (Rocha 2011, Guzman et al. 2015), which may have misleading the original geological assignment made by Brito

Finally, the Sergi Formation is interpreted as a braided river system (Rocha 2011, Adegas et al. 2012), in an environment characterized by climatic changes, where extensive forests developed after reworked under more dry conditions (Rocha 2011). The extensive wood fossil record, mainly on Petrolândia (Braun 1966, Silva et al. 2003, Guzmán et al. 2015), also corroborates this scenario. Most of the wood fossil is assigned to gymnosperms, vastly Dadoxylon benderi Mussa, 1959 (Mussa & Muniz 1985). The Jurassic age for the Sergi Formation is based on the similar occurrence of D. benderi on the Missão Velha Formation (Braun 1966, Mussa & Muniz 1985). The abundant remains of D. benderi on strata of Sergi Formation suggests an extensive tree cover in the marginal areas of higher regions of the Brazilian northeast at that time (Freitas et al. 2008). This made MCT2670-LE as the first vertebrate remain collected on the Sergi Formation, expanding our information about the fauna of the Jatobá Basin.

MATERIALS AND METHODS

Material

The specimen MCT 2670-LE comprises a theropod mid caudal vertebra. Our dataset (Supplementary Appendix) was compiled from the literature and comprises 25 abelisaurid (six specimens; Méndez 2014, O’Connor 2007); 10 megalosauroid (five specimens; Benson 2010, Malafaia et al. 2017, Mateus et al. 2011, Rauhut et al. 2016), 18 allosauroid (six specimens; Brusatte et al. 2008, Rauhut 2011, Malafaia et al. 2019, Coria et al. 2020, Pereira et al. 2020b); six megaraptoran caudal vertebrae (five specimens; Martinelli et al. 2013, Méndez et al. 2012, Motta et al. 2016, Pereira et al. 2020b) and one indeterminate theropod material (Pereira et al. 2020b). We focused in large theropod taxa that present some degree of constriction in the mid region of the centrum to observe the distribution of this feature among these groups and if it is possible so distinguish them.

Mechanical Preparation

The specimen MCT 2670-LE was still fixed to the rock matrix since the specimen was collected, which led one of us (PVLCP) to mechanical preparation using specialized pneumatic tools at the preparation lab (DEGEO/UFRJ). Once the matrix was removed, the fragile specimen was treated with a 10% paraloid solution to confer resistance. After this step, the specimen was able to be handled for diagnosis statements.

Institutional abbreviations

BMNH, Natural History Museum, London, UK; CPPLIP, Centro de Pesquisas Paleontológicas “Llewellyn Ivor Price”, Uberaba, MG, Brazil; DGM or MCT, Museu de Ciências da Terra (ancient Companhia de Pesquisa de Recursos Minerais (CPRM) and now Agência Nacional de Mineração (ANM)), Rio de Janeiro, RJ, Brazil; MACN-PV-RN, Museo Argentino de Ciencias Naturales “B. Rivadavia”, Paleontología de Vertebrados, Buenos Aires, Argentina (RN, colección Río Negro); MB, Museum fur Naturkunde, Berlin, Germany; MIWG, Isle of Wight Museum Service, Sandwown, UK; ML, Museu da Lourinhã, Lourinhã, Portugal; MLL-Pv, Museo Municipal de Las Lajas, Las Lajas, Neuquén Province, Argentina; MPMA, Museu de Paleontologia de Monte Alto “Prof. Antonio Celso de Arruda Campos”, Monte Alto, SP, Brazil; SNH, Sociedade de História Natural, Torres Vedras, Portugal; UFRJ-DG, Departamento de Geologia da Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ, Brazil; Vb, Institut fur Palaontologie of the Free University, Berlin, Germany.

Anatomical and systematic terms

Following Wilson (2006), we use the “Romerian” anatomical terms and their respective orientations (e.g., “anterior” instead of “cranial’”). All measurements of the specimen are provided in Table II. For brevity and clarity, MCT 2670-LE is mainly compared with theropod taxa: Aerosteon riocoloradensis Sereno et al. 2008; Allosaurus fragilis Marsh 1877; Acrocanthosaurus atokensis Stovall & Langston 1950; Baryonyx walkeri Charig & Milner, 1986; Concavenator corcovatus Ortega et al. 2010; Dilophosaurus wetherilli (Welles 1954); Giganotosaurus carolinii Coria & Salgado 1995; Lajasvenator ascheriae Coria et al. 2020; Lusovenator santosi Malafaia et al. 2020; Majungasaurus crenatissimus (Depéret 1896); Mapusaurus roseae Coria & Currie 2006; Megalosaurus bucklandi Mantell, 1827; Neovenator salerii Hutt et al. 1996; Siamraptor suwati Chokchaloemwong et al. 2019 and Veterupristisaurus milneri Rauhut, 2011. Additional comparisons are made with the following specimens: the Bajo de La Carpa Formation (Neuguén Group) abelisaurid material (MACN-PV-RN 1012; Ezcurra & Méndez 2009); the Açu Formation carcharodontosaurian remains (UFRJ-DG523-R and UFRJ-DG524-R; Pereira et al. 2020b); the Freixial Formation (Lusitanian Basin) carcharodontosaurid remains (SNH.019/4; Malafaia et al. 2019); the Wadi Milk Formation caudal (Vb-871, Rauhut 1999) and the Bauru Group megaraptoran material (CPPLIP 1324 and MPMA 08-003-94; Méndez et al. 2012, Martinelli et al. 2013). For systematic terminologies, we follow Padian et al. (1999), which consider Neotheropoda the least inclusive clade containing Coelophysis bauri and extant birds, and Tetanurae the most inclusive clade containing extant birds but not Ceratosaurus nasicornis.

Table II
Selected measurements of MCT 2670-LE.

Anatomical measurements of the centrum	Measurements expressed in mm
maximum length	44
width at mid-length	15
proximal facet height	29
proximal facet width	31
distal facet height	30
distal facet width	32

Phylogenetic inference

In this work, we present a phylogenetic inference based on a data matrix modified from Malafaia et al. (2020). Two new characters (i.e., unpublished) relative to mid-caudal centrum anatomy are proposed: character 359 (Mid and posterior caudal vertebrae, centrum, mid-width: 0 – over half of articular facets width; 1 – half or less); and character 360 (Mid and posterior caudals, centrum, ventral surface: 0 – flat, 1 – with a thin sulcus, 2 – with a broad groove). Furthermore, we have added four taxa: Veterupristisaurus, Siamraptor, UFRJ DG 524-R, and MCT 2670-LE. The analysis itself was performed using the free software TNT v. 1.5 (Goloboff & Catalano 2016). To heuristic search, we followed the same protocol (default New Technology Search, driven search stabilizing consensus twice by a factor of 25) as employed by Malafaia et al. (2020), though we highlight that revisions of both matrix and protocol may be welcome in future contributions.

Linear morphometrics

We performed a linear morphometrics to the mid caudal vertebrae (from 8th to 23rd caudal) with the parameters adapted from Welles (1952) and Brown (1981), which are: height/length ratio (HI = 100*H/L); breadth/length ratio (BI = 100*B/L); and rate of vertebral elongation (VLI = 2*10²L/(H+B)). We also added mid centrum width/breadth ratio (MBI = 100*M/B) to observe the variation and segregation among the analyzed neotheropod groups. The measurements were compiled from literature and/or taken from images via ImageJ v. 1.46r (Schneider et al. 2012).

We used the linear bivariate regressions to test the correlation between parameters and, subsequently, linear discriminant (LDA) and principal component analyses (PCA). Due to the low sample sizes, we considered nonparametric tests to verify the significance between group means with Kruskal-Wallis, followed by Mann Whitney pairwise tests. All statistical analyses were performed in the software PAST v. 4.02 (Hammer et al. 2001), considering p-value of 0.05 as significant.

RESULTS

Systematic paleontology

Dinosauria Owen, 1842

Theropoda Marsh, 1881

Tetanurae Gauthier, 1986

Avetheropoda Paul, 1988

Allosauroidea Marsh, 1878

cf. Carcharodontosauria Benson, Carrano and Brusatte, 2010

Description

The specimen MCT 2670-LE (Figure 2) comprises an isolated vertebral caudal centrum. Although the neural arch is not preserved, the neurocentral junction exhibits a rugose surface, which indicates that the neurocentral junction was unfused and the neurocentral suture was visible. The amphicoelous vertebral centrum is elongated (Table II) and transversely constricted in its middle length showing an hourglass shape, as it is in several allosauroids middle and posterior caudal centra (e.g., Madsen 1976, Britt 1991, Rauhut 1999, Chure 2000) but especially carcharodontosaurian ones (e.g., Malafaia et al. 2019, Chokchaloemwong et al. 2019, Pereira et al. 2020b). The articular facets are subcircular, with the anterior facet being mostly flat and the posterior smoothly concave (Figure 2). MCT 2670-LE shows a slight offset between articular facets. In lateral view, the specimen MCT 2670-LE exhibits a slight concavity in its ventral surface. Close to the neurocentral joint, in the mid-region of the centrum, the neurocentral depressions are shallow. The ventral surface of the centrum has a narrow longitudinal groove extending along its anteroposterior length. This longitudinal groove is bounded by faint paired keels, which are slightly eroded. In ventral view, the facets for chevrons joints are quite visible next to the posterior face.

Figure 2
Plate of the allosauroid specimen MCT 2670-LE, a putative carcharodontosaurian, in dorsal (a), ventral (b), right (c) left (d), anterior (e) and posterior views (f), with a scheme on the right. Abbreviations: fo, foramen; nc, neural canal; ncj, neurocentral junction; pcd, pleurocentral depression; vk, ventral keel; vg, ventral groove. Scale bar equals 10 mm.

Comparisons

The offset between articular facets is a feature spread among basal Neotheropoda, being observed in Dilophosaurus (Welles 1984), abelisaurids (Méndez 2014), Allosaurus (Madsen 1976), Acrocanthosaurus (Stovall & Langston 1950) as well as in other carcharodontosaurian mid and posterior caudal vertebrae (e.g., Rauhut 1999, Coria & Currie 2006, Malafaia et al. 2019). However, MCT 2670-LE does not show the ventrolateral ridges (Figure 3) that normally seems to accompany this ventral pronounced offset (e.g., present in Dilophosaurus Welles, 1984 and several abelisaurids, Méndez et al. 2012). The hourglass shaped centrum is typical to the middle and posterior caudal centra of several allosauroids (e.g., Madsen 1976, Britt 1991, Rauhut 1999, Chure 2000) but especially carcharodontosaurian ones (e.g., Malafaia et al. 2019, Chokchaloemwong et al. 2019, Coria et al. 2020, Pereira et al. 2020b, Figure 3). Such feature is distinct in the caudal observed in abelisauroids (e.g., MACN-PV-RN 1012; see Ezcurra & Méndez 2009) The narrow longitudinal groove in the ventral surface, bounded by faint keels in the caudal centrum is also commonly found in Abelisauroidea, Allosauroidea, especially carcharodontosaurids and Megalosauroidea (Ezcurra & Méndez 2009, Benson 2010, Mateus et al. 2011, Carrano et al. 2012, Rauhut et al. 2016, Malafaia et al. 2017, 2020, Coria et al. 2020). The absence of the ventrolateral ridges when the ventral pronounced offset is present could be a character that can be ascertained in the future phylogenetic approaches. Such feature is something putatively present in Avetheropoda, suggesting a secondary loss of these ventrolateral ridges at least within Allosauroidea, as observed in MCT 2670-R and carcharodontosaurids. Although the hourglass shape is observed in megaraptorans, as Aerosteon (see Sereno et al. 2008) and in the specimens CPPLIP 1324 (see Martinelli et al. 2013), MPMA 08-00394 (see Méndez et al. 2012), they have pneumatic foramina and/or lack a ventral groove. Therefore, the hourglass shaped centrum and the presence of a narrow longitudinal groove, bounded by ventral keels along its ventral surface allows referral of the specimen MCT 2670-LE to Allosauroidea.

Figure 3
Comparative left lateral (a) and ventral (b) views between MCT 2670-LE and other caudal vertebrae from allosauroid specimens: UFRJ-DG524-R (modified from Pereira et al. 2020b); Veterupristisaurus milneri (MB R 2166, modified from Rauhut 2011); Vb-607, Wadi Milk Formation caudal (modified from Rauhut 1999); referred specimen of Lusovenator santosi (SHN.19/04, modified from Malafaia et al. 2019); Neovenator salerii (MIWG 6348, modified from Brusatte et al. 2008), Lajasvenator ascheriae (MLL-Pv-005, modified from Coria et al. 2020); Megalosaurus bucklandi (BMNH R9672, modified from Benson 2010); Baryonyx walkeri (ML 1190, modified from Mateus et al. 2011); CPPLIP 1324 (modified from Martinelli et al. 2013); MPMA 08-003-94 (modified from Méndez et al. 2012); Aerosteon riocoloradensis (MACN-PV-3137, modified from Méndez et al. 2012); and MACN-PV-RN-1012 (modified from Ezcurra & Méndez 2009). Scale bars equal 10 mm.

The phylogenetic placement of Megaraptora is uncertain, as the group may fall within neovenatorids (as after the dataset Malafaia et al. 2020, which we have utilized here) or as basal coelurosaurs (e.g., Delcourt & Grillo 2018). We highlight that the phylogenetic placement of Megaraptora within or outside the Carcharodontosauria has no bearing on the taxonomic referral of MCT 2670-LE, which differs from megaraptorans (as expressed above) whether they are considered as carcharodontosaurians or not.

Among Allosauroidea, MCT 2670-LE is quite similar to the holotypic (SHN.036, Malafaia et al. 2020) and the referred (SHN.19, Malafaia et al. 2019) mid caudal vertebrae of Lusovenator santosi, as it is similar to Lajasvenator ascheriae. The specimen MCT 2670-R, L. santosi and L. ascheriae share the moderately elongated centra. However, the Brazilian specimen differs from SHN.019 due to the development of the pleurocentral depression well visible in the European specimen. The extremely reduced pleurocentral depression is shared with the vertebra of L. ascheriae (Coria et al. 2020), Veterupristisaurus milneri (MB R 1938; Rauhut 2011), differing from the comparatively deeper depression in the derived carcharodontosaurids Giganotosaurus carolinii (see Coria & Salgado 1995) and expanded depression in Acrocanthosaurus atokensis (see Storval & Langston 1950). However, the centrum of MCT 2670-LE has a much shallower dorsolateral depression, similar to L. ascheriae and Mapusaurus roseae (see Coria & Currie 2006, Coria et al. 2020). MCT 2670-LE also differs from L. santosi caudal vertebrae (SHN.06 and SHN.19) for the absence of the lateral lamina in Brazilian specimen, which is also absent in G. carolinii (see Coria & Salgado 1995) M. roseae (Coria & Currie 2006) and in the carcharodontosaurian remains from Açu Formation (UFRJ-DG523-R and UFRJ-DG524-R), although those are more anterior caudal vertebrae compared to MCT 2670-LE.

The amphicoelous centra with the anterior articular surface being slightly more concave than the posterior face is a feature shared with MB R 1938 (Rauhut 2011). The round articular surface is widely spread in the mid to posterior caudal vertebrae of Torvosaurus (Hanson & Makovicky 2014) and several allosauroids, such as Allosaurus (Madsen 1976), Acrocanthosaurus (Stovall & Langston 1950, Currie & Carpenter 2000), Concavenator (Cuesta et al. 2019) and in several carcharodontosaurids, but not in Mapusaurus (Coria & Currie 2006) and Siamraptor (Chokchaloemwong et al. 2019), which in turn shows subtriangular articular surfaces on mid to posterior caudal vertebrae (Coria & Currie 2006) - albeit Siamraptor has a subrectangular posterior face (Chokchaloemwong et al. 2019). MCT 2670-LE shares the ventrally pronounced border of the articular facets with Vb-871 (Rauhut 1999), MB R 1938 (Rauhut 2011), UFRJ-DG523-R and UFRJ-DG524-R (Pereira et al. 2020b) but differs from those specimens due to the less pronounced ventral keels. Such faint ventral keels, surrounding a longitudinal groove, is observed in basal carcharodontosaurids (Figure 3), as in the caudal of Lajasvenator ascheriae (see Coria et al. 2020).

Phylogenetic inference results

Our phylogenetic inference produced eight minimum-length trees, with 1085 steps, a consistency index of 0.399 and retention index of 0.687. Near the base of the Carcharodontosauria, we have recovered a small clade that includes Lusovenator, Veterupristisaurus, Siamraptor, UFRJ DG 524-R, and MCT 2670-LE (Figure 4). This small clade is recovered in a polytomy including Siats and the node that joins Neovenatoridae + Carcharodontosauridae. This small clade is supported by a single synapomorphy: character 359(1): mid and posterior caudals, centrum, mid-width: half or less of articular facets width.

Figure 4
Consensus tree showing the assignment of MCT 2670-LE within Carcharodontosauria (Allosauroidea) (to access the full tree, see Supplementary Appendix).

Linear morphometrics results

The centrum width lacks correlation with all other parameters (r² < 0.5; see graphics in Supplementary Appendix). Only the elongation shows strong correlation with both height (r² = 0.892) and breadth (r² = 0.799). Therefore, the multivariate analyses lack support based on these parameters (Table SI), with LDA correctly assigning only 38.98% of the specimens. Our results could not significantly segregate the proposed groups in morphospaces based in all parameters and evaluate the mid centrum width.

We regard only the mid centrum width among the theropod groups to evaluate this feature. The specimen MCT 2670-LE is close to the mean of megalosauroids and allosauroids (Figure 5), while the indeterminate theropod UFRJ-DG 528-R is close to the mean of abelisaurids and megaraptorans. However, the Kruskal-Wallis shows no significant difference between the sample medians (H (chi-square) = 1.701; p = 0.637) and the Mann Whitney pairwise shows no significance (Table III). Therefore, the difference between samples regarding the mid centrum width is not significant to distinguish between groups. We also evaluate the variation along the caudal series in more complete specimens (e.g. Majungasaurus and Neovenator) with more incomplete specimens. The mid centrum width is more constricted in more posterior caudal vertebrae and we observed a wide variation along the anteroposterior caudal sequence, which contributes to the wide standard deviation observed among the samples (Figure 5 and 6).

Figure 5
Mean and Whisker plot of vertebral caudal MBI values from Abelisauridae, Megalosauroidea, Allosauroidea, Megaraptora, MCT 2670-LE and UFRJ-DG 528-R.

Figure 6
Plotted MBI values of caudal vertebrae from Abelisauridae, Megalosauroidea, Allosauroidea, Megaraptora, MCT 2670-LE and UFRJ-DG 528-R. When specimens show more than one preserved caudal, it follows the anteroposterior order.

Table III
Pairwise Mann-Whitney test (raw p values, uncorrected significance) based on MBI main groups for caudal vertebrae.

	Abelisauridae	Megalosauroidea	Allosauroidea	Megaraptora
Abelisauridae	-	0.547	0.382	0.708
Megalosauroidea	-	-	0.829	0.212
Allosauroidea	-	-	-	0.368
Megaraptora	-	-	-	-

• No value is significant.

DISCUSSION

Distribution of carcharodontosaurians among Jurassic-Cretaceous boundary

Up-to-date, most of the carcharodontosaurid record from Brazil comprises teeth from the Albian to early Cenomanian (Vilas Bôas et al. 1999, Medeiros & Schultz 2002, Medeiros et al. 2014), and some caudal vertebrae from the Albian-Cenomanian of Potiguar Basin (Pereira et al. 2020b). Although the discussion in the literature points out that the latest carcharodontosaurian fossil records are restricted to the Lower Cretaceous strata, with the decline of the lineage in the mid-Cretaceous and a niche occupation by abelisaurids (Novas et al. 2013). However, some records of Upper Cretaceous outcrops from Bauru Group have been previously assigned to Carcharodontosauridae (Candeiro et al. 2004, 2006, 2012, Azevedo et al. 2013). The isolated teeth material was reanalyzed, as well as the unique osteological record (a partial maxilla with a tooth in situ; Azevedo et al. 2013) and all were reassigned to Abelisauridae (e.g., Delcourt et al. 2020). Therefore, the current data and analyses in the literature support that carcharodontosaurids were rare at the end of the Early Cretaceous and became extinct up to the Turonian (Apesteguía 2002, Coria & Salgado 2005, Novas et al. 2005, 2013).

Carcharodontosaurians are generally recognized because of global Cretaceous-age radiation of those distinctive allosauroid theropods (Sereno et al. 1996), being most present in southern landmasses (Coria & Salgado 1995, Sereno et al. 1996, Calvo & Coria 1998). Although most of the fossil record of carcharodontosaurians are mainly associated with southern landmasses, there were some exceptions. The Laurasian records consist of fragmentary materials from Upper Jurassic strata of China (Brusatte et al. 2009), Portugal (Malafaia et al. 2019, 2020), Lower Cretaceous of England (Brusatte et al. 2008) and Spain (Ortega et al. 2010, Cuesta et al. 2018). The analysis of a tooth from Romania also indicates the presence of carcharodontosaurids in the Valanginian of Laurasia, but such assignment is still dubious due to the fragmentary nature of the fossil material (Csiki-sava et al. 2016). The report of MCT 2670-LE is one of the oldest for Carcharodontosauria in Gondwana, after Veterupristisaurus, from the Kimmeridgian (Jurassic) of Tendaguru (Rauhut 2011).

From the Jurassic to the Lower Cretaceous, the sole occurrence is the allosauroid Acrocanthosaurus which could be a putative carcharodontosaurian from North America (Harris 1998, Currie & Carpenter 2000). Among the Gondwanan carcharodontosaurian record, is remarkable the diversification of the clade especially from South America (Patagonia, Argentina; Novas et al. 2013). This diversification probably occurred just before the Albian-Cenomanian interval, since it is markedly by the origin of carcharadontosaurines (Brusatte et al. 2009, Brusatte & Sereno 2008, Canale et al. 2015, Carrano et al. 2012) and the subsequent occurrence of the Giganotosaurini (the last is endemic to South America; Canale et al. 2015).The oldest record of a carcharodontosaurian to South America is from the upper Valanginian (Lower Cretaceous) of Patagonia, with the species Lajasvenator ascheriae (Coria et al. 2020).

The MCT 2670-LE resembles the caudal vertebrae found among basal carcharodontosaurians species and is the first record of the group in Brazil (Figure 7) before the vicariant event. Such record suggests the presence of these animals in South America since the Jurassic, which corroborates the wide distribution of the group through Gondwana before the Early Cretaceous.

Figure 7
Paleoartistic reconstruction of the specimen MCT 2670-LE in the environment of the Sergi Formation. The first plan shows a medium-sized carcharodontosaurian walking in a dry area, close to a Lepidotes carcass. The background shows aeolian and shallow lacustrine/fluvial depositional systems, with the occurrence of gymnosperm forests, based on Pierini et al. (2010). Reconstruction scheme by Arthur S. Brum.

Comments on diversification and decline of Carcharodontosauria

The length of the caudal centrum MCT 2670-LE is 44 mm. Comparing with other carcharodontosaurians, Neovenator exhibits middle-posterior caudal around 103-106 mm, with body length estimates of 8 m, while in Acrocantosaurus, 160 mm and 11.5 m, and Veterupristisaurus, 123 mm and 8.5-10 m of body length (Figure 5; Currie & Carpenter 2000, Brusatte et al. 2008, Rauhut 2011). Based on these measurements, we estimate that MCT 2670-LE could represent a 3-4 m body length individual (Figure 7). Although it shows a smaller size in comparison to the pattern observed in Carcharodontosauria (5-12 m in body length), the unfused neurocentral synchondrosis indicates that the individual could be at least a juvenile (for discussion about neurocentral synchondrosis as maturity criteria see Souza 2018) or subadult carcharodontosaurian. Therefore, MCT 2670-LE could grow more than 4 m (Figure 7). The recovery of MCT 2670-LE in the Upper Jurassic of South America indicates that carcharodontosaurians were already widely distributed at this time (e.g., Concavenator, Lajasvenator and Lusovenator). The specimen MCT 2670-LE also supports the medium-sized pattern found among basal carcharodontosaurians. Such medium size in the Jurassic corroborates the pattern of increase in the body length, with the largest derived forms recovered from mid-Cretaceous outcrops (e.g., Currie & Carpenter 2000, Canale et al. 2015, Coria et al. 2020). Although the occurrence of an indeterminate carcharodontosaurian from the Tithonian of Portugal suggests a medium to a large-sized individual (Malafaia et al. 2019, 2020), which could weaken such hypothesis, the phylogenies still mark the trend in the increase in body length among derived forms (e.g., Carrano et al. 2012, Novas et al. 2013, Canale et al. 2015, Malafaia et al. 2020). The fossil record of Carcharodontosauria is fragmentary and sparse, reaching its diversity with large forms along the Early-middle Cretaceous (e.g., Coria & Currie 2006, Novas et al. 2013, Canale et al. 2015), which is encompassed by the rarefaction of the group in post-Turonian. At the same time, the Abelisauridae diversified and increased in body size after the Cenomanian with the group Brachyrostra (Grillo & Delcourt 2018).

Along the Early Cretaceous, the Aptian-Turonian interval is marked by some horizons exhibiting the co-occurrence of a diverse medium-large sized theropod fauna, with abelisauroids, spinosaurids and carcharadontosaurians, such as in North Africa (Novas et al. 2005, 2013, Rauhut 2011), and ceratosaurians, allosauroids and megalosauroids in North America and Iberian Peninsula (Mateus 2006, Mateus et al. 2006, Malafaia et al. 2020). The inferred semi-aquatic habits of spinosaurids (e.g., Ibrahim et al. 2020) exclude this group from a niche overlap or competition with other medium-large sized predatory theropods in such environments. Regarding the ecological relationship between abelisaurids and carcharodontosaurids in such habitats, Gillo & Delcourt (2017) pointed out a competition between abelisaurids and carcharodontosaurians, which could be observed by similar cranial biomechanical advantages (Sakamoto 2010) and the teeth morphology (Canale et al. 2009), with the post-Turonian replacement of the huge derived carcharodontosaurids by abelisaurids. Recently, Candeiro et al. (2018) discussed niche partitioning and competition attributed to the cohabitation of spinosaurids, abelisaurids and carcharodontosaurians in the Early-middle Cretaceous. They supported the niche partitioning, based on the theropod fauna observed in North Africa (see Rauhut 2011). Such co-existing between different taxa of medium-large body sizes is also well-known in the Morrison Formation and outcrops from the Iberian Peninsula (Mateus 2006, Mateus et al. 2006, Malafaia et al. 2020). In the case of the Morrison Formation, the fossil record and the distinct body sizes between theropods reveals a niche partitioning, mainly based on factors that include the influence of facultative scavenging, the potential foraging area and energy demand by the body mass among different theropod size classes (Kane et al. 2016).

As many dinosaur taxa, basal theropods also show some pattern in the development of body size dimensions that encompass the Cope’s rule (Hone et al. 2005), in which the diversification of a group is also followed by the increase of body mass and niche specificity. Among basal theropod lineages, we observed such a trend in both abelisauroids and allosauroids, but in distinct times of diversification. The earlier diversification and decline process of the lineage is evidenced by the change from the occurrence of medium-sized Jurassic forms, with a wide distribution, to large carcharodontosaurians through the Early Cretaceous and the endemicity in this period, as observed in Giganotosaurini (Canale et al. 2015). Regarding abelisauroids, especially abelisaurids, they show an advantage in cursorial potential (Person IV & Currie 2011) over carcharodontosaurians, as indicated by Grillo & Delcourt (2018). The rarefaction of the derived large carcharodontosaurids in the Turonian would enable the abelisaurids diversification, with the increase of their body sizes and occupation of a niche once occupied by carcharodontosaurids. Such occupation may reflect convergent features, as the cranial biomechanics and teeth (Sakamoto 2010, Canale et al. 2009, Delcourt et al. 2020). However, both competition and niche partitioning scenarios should be better delimited with more fossil material of these groups, especially during the Jurassic-Early Cretaceous (Figure 8), which is marked by a gap in both carcharodontosaurian and abelisauroid lineages. Therefore, we provided an alternative scenario, and we could not discard the competition hypothesis.

Figure 8
Hypothetical cladogram of abelisauroids and allosauroids (with the assignment of MCT 2670-LE), showing estimated body lengths and distribution from Middle Jurassic to Upper Cretaceous. Body lengths to abelisauroids based on Grillo & Delcourt (2018). Cladogram based on the phylogenies of Langer et al. (2019) to Noasauridae, Filippi et al. (2016) to Abelisauridae, Malafaia et al. (2020) to basal Allosauroidea, Canale et al. (2015) and our phylogenetic results to Carcharodontosauridae. Silhouettes from PhyloPic, by Ian Reid and Scott Hartman.

Comments on the phylogenetic relationships of MCT 2670-LE

An interesting result of our phylogenetic inference is the recovery of a small clade at the base of the Carcharodontosauria, comprehending the earliest records of the group – the Late Jurassic OTUs Lusovenator, Veterupristisaurus, and MCT 2670-LE. This clade further includes the Early Cretaceous Siamraptor and the Albian-Cenomanian UFRJ DG 524-R. All these five taxa share a single synapomorphy: character 359(1): mid and posterior caudals, centrum, mid-width: half or less of articular facets width. This small clade was recovered in a polytomy involving Siats as well as (Neovenatoridae + Carcharodontosauridae) and is thus comprised within the Carcharodontosauria, since it is defined as a branch-based clade containing Carcharodontosaurus and Neovenator but not Allosaurus or Sinraptor (Benson et al. 2010).

The carcharodontosaurian nature of each of these OTUs is well supported (e.g., see Rauhut 2011, Chokchaloemwong et al. 2019, Malafaia et al. 2020). In fact, we replicate the results of Malafaia et al. (2020) regarding the phylogenetic position of Lusovenator as a carcharodontosaurian; we simply add to its branch the OTUs Veterupristisaurus, Siamraptor, MCT 2670-LE and UFRJ DG 524-R based on the synapomorphy mentioned above, character 359(1). The position of Lusovenator itself is supported by three carcharodontosaurian synapomorphies (characters 160(2), 273(2) and 294(1); see the Supplementary Material). However, the monophyly of this possible new clade is still questionable and must be viewed with caution, since it is based on a single synapomorphy and very fragmentary specimens. Future discoveries are needed to shed light on this possible clade.

The new character proposed on this study, 360(2): mid and posterior caudals, centrum, ventral surface with a thin and deep sulcus, is recovered as a synapomorphy of the Allosauroidea, corroborating the allosauroid nature of MCT 2670-LE. This character state is reversed in Shaochilong + Carcharodontosaurinae (see Coria & Currie 2006 for Mapusaurus, and Benson et al. 2010 for Shaochilong). The presence of this feature indicates that MCT 2670-LE could be a basal carcharodontosaurian, or at least an allosauroid taxon closely related to the Carcharodontosauria clade.

Therefore, despite the fragmentary status of the newly described specimen, our phylogenetic results demonstrate the presence of a combined set of features that undoubtedly resolves MCT 2670-LE as a carcharodontosaurian. Therefore, our results are in agreement with previous work that demonstrates that, despite fragmentary, some fossil specimens have enough combination of features that enable a precise recognition of their evolutionary affinities (e.g., Kearney 2002, Wiens 2003a, b, Kearney & Clark 2003).

CONCLUSIONS

The Sergi Formation has a yet unexplored potential for understanding the relationships of Mesozoic fossil vertebrates. The faunistic content discussed here provides a significant contribution to South American paleontology, especially the knowledge of the Upper Jurassic in Brazil. MCT 2670-LE is the first confirmed dinosaur record for the Jurassic of Brazil and it is assigned to the Allosauroidea, with affinities to the Carcharodontosauria, due to the hour-glass shaped centrum and the ventral surface showing a narrow longitudinal groove, bounded by ventral keels. Within Carcharodontosauria, the specimen is quite similar to Lusovenator santosi, Lajasvenator ascheriae and Veterupristisaurus milneri. Based on this, the material could represent one of the oldest carcharodontosaurian remains known. Further studies are needed to promote the stratigraphic and temporal refinement of the formation, which in the future may bring more data on a putative Gondwanan origin of the carcharodontosaurians.

ACKNOWLEDGMENTS

We are grateful to Dr. Rodrigo Machado and Dr. Rafael Costa for allowing us to study the specimen deposited at the Museu de Ciências da Terra (MCT-DNPM-CPRM). We are grateful to Profa. Dra. Lilian P. Bergqvist for allowing us to use of equipment in the preparation laboratory. Also, we make a posthumous thanks to Prof. Dr. Ignacio Machado Brito, for all his contributions to vertebrate paleontology in Brazil, in which without his effort, the present work would not exist. The authors would like to acknowledge Dr. Federico Agnolin and the two anonymous reviewers for their comments that helped to improve this article. We thank Victoria Barros for the English revision. Credits for silhouettes from PhyloPic (Figure 8): Ian Reid and Scott Hartman (https://creativecommons.org/licenses/by/3.0/). This study was funded by Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP #2019/10231-6 to RVP), Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES-PROANTAR #88887.336584/2019-00 to ASB), Coordenação de Aperfeiçoamento de Pessoal de Nível Superior and Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro (FAPERJ #PDR10E-26/201.995/2020 to PVLGCP). LGS thanks to the financial support granted by Paleo and Geohistory exhibition at Museu da Amazônia (PRONAC 183808) and the postdoctoral scholarship granted by Fundação de Amparo à Pesquisa do Estado do Amazonas (FAPEAM #062.00166/2020).

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SUPPLEMENTARY MATERIAL

Supplementary Appendix. Phylogenetic dataset (character list and scorings) and supplementary figures.

Figure S1. Strict consensus tree from our phylogenetic analysis.

Figure S2. Linear regressions of the caudal vertebrae of abelisaurids, megalosauroids, carcharodontosaurians, megaraptorans, MCT 2670-LE and UFRJ-DG 528-R.

Figure S3. Principal component (a) and linear discriminant analyses (b) of abelisaurids, megalosauroids, carcharodontosaurians and megaraptorans.

Table SI. Linear morphometrics dataset.

Publication Dates

• Publication in this collection
  02 Aug 2021
• Date of issue
  2021

History

• Received
  1 Oct 2020
• Accepted
  24 Apr 2021