Journal of South American Earth Sciences 39 (2012) 16e23 Contents lists available at SciVerse ScienceDirect Journal of South American Earth Sciences journal homepage: www.elsevier.com/locate/jsames Footprints of large theropod dinosaurs and implications on the age of Triassic biotas from Southern Brazil Rafael Costa da Silva a, *, Ronaldo Barboni b, Tânia Dutra b, Michel Marques Godoy c, Raquel Barros Binotto d a CPRM e Companhia de Pesquisa de Recursos Minerais e Serviço Geológico do Brasil, Departamento de Geologia, Divisão de Paleontologia, Av. Pasteur, 404, Urca, 22290-240 Rio de Janeiro, RJ, Brazil Graduation Program in Geology, Universidade do Vale do Rio dos Sinos e UNISINOS, Av. Unisinos, 950, 93022-000 São Leopoldo, Rio Grande do Sul, Brazil c CPRM e Companhia de Pesquisa de Recursos Minerais e Serviço Geológico do Brasil, Gerência de Recursos Minerais, Rua Banco da Província, 105, Santa Teresa, 90840-030 Porto Alegre, RS, Brazil d CPRM e Companhia de Pesquisa de Recursos Minerais e Serviço Geológico do Brasil, Gerência de Relações Institucionais e Desenvolvimento, Rua Banco da Província, 105, Santa Teresa, 90840-030 Porto Alegre, RS, Brazil b a r t i c l e i n f o a b s t r a c t Article history: Received 31 January 2012 Accepted 23 June 2012 Dinosaur footprints found in an outcrop of the Caturrita Formation (Rio Grande do Sul State, Southern Brazil), associated with a diverse and well preserved record of fauna and ﬂora, reopen the debate about its exclusive Triassic age. The studied footprints were identiﬁed as Eubrontes isp. and are interpreted as having been produced by large theropod dinosaurs. The morphological characteristics and dimensions of the footprints are more derived than those commonly found in the CarnianeNorian, and are more consistent with those found during the RhaetianeJurassic. The trackmaker does not correspond to any type of dinosaur yet known from Triassic rocks of Brazil. Recent studies with the paleoﬂoristic content of this unit also support a more advanced Rhaetian or even Jurassic age for this unit. Ó 2012 Elsevier Ltd. All rights reserved. Keywords: Eubrontes Dinosaur Caturrita Formation Gondwana 1. Introduction The study of tetrapod fossil tracks provides a great amount of data about diversity, functional morphology, behavior and ecological relationship of extant animals, beyond sedimentological features of the substrate and paleoenvironmental aspects. Traditionally, they are not used for biostratigraphic purposes, although they may be important for determining the age of successions lacking body fossils or for the reﬁnement of ages when associated with them (e.g. Lucas, 1998; Lucas and Tanner, 2007). In southernmost Brazil (state of Rio Grande do Sul), the Linha São Luiz outcrop exposes levels of the Caturrita Formation and has provided numerous and well preserved fossils, including cynodonts, dinosaurs, possible pterosaurs, sphenodontids, procolophonids, ﬁshes, insects, conchostraca, invertebrate ichnofossils and remains of several distinct types of gymnosperms. The diverse fossil record of the Caturrita Formation and its lithological * Corresponding author. E-mail addresses: [email protected], [email protected] (R.C.da Silva), [email protected] (R. Barboni), [email protected] (T. Dutra), [email protected] (M.M. Godoy), [email protected] (R.B. Binotto). 0895-9811/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jsames.2012.06.017 relationships indicate an Early Norian age (Late Triassic) for this unit (Rubert and Schultz, 2004), although more recent studies suggest a NorianeRhaetian age (Abdala and Ribeiro, 2010). Recently, two footprints were found in the upper portion of the outcrop. Together with some paleoﬂoristic and other paleofaunistic data, it reopens the debate about the age of the Caturrita Formation. This study aims to analyze these tracks and their paleontological and geological context. 2. Material and methods The studied material was identiﬁed at the Linha São Luiz outcrop (29 330 4500 S; 53 260 4800 W), municipality of Faxinal do Soturno, state of Rio Grande do Sul (Fig. 1), and consists of two footprints preserved in a tabular sandstone layer that represents the upper part of a rhythmic succession of sand and mud layers and overbank deposits (crevasse splay). They received the ﬁeld code FSSL-01 and FSSL-02 (FS ¼ Faxinal do Soturno; SL ¼ São Luiz). The ﬁrst one was collected in 2008 and housed at the paleontological collection of Museu de Ciências Naturais, Fundação Zoobotânica do Rio Grande do Sul, Porto Alegre, Rio Grande do Sul, under the number MCN-PIC.030. The second footprint, FSSL-02, was found in 2009 less than a meter away from the ﬁrst, covered by a layer of R.C.da Silva et al. / Journal of South American Earth Sciences 39 (2012) 16e23 17 Fig. 1. Location of the Linha São Luiz outcrop in the state of Rio Grande do Sul, Southern Brazil (based on Schultz et al., 2000). sandy siltstone. It was studied and prepared in situ and kept in place. This footprint was moistened to enhance the contrast for the photographic record. A plaster model was made in the ﬁeld and deposited in the mentioned institution. The specimens were prepared by mechanical processes. Footprint parameters were based on Leonardi (1987) and measured using the computer program ImageJ (Abramoff et al., 2004). 3. Geological context The Caturrita Formation is considered a Triassic independent unit from the Paraná Basin (Andreis et al., 1980; Faccini, 1989). It was subdivided in two parts based on its fossil content (Zerfass et al., 2003; Faccini, 2007). The basal one was considered Early Norian due to its vertebrate fauna (Barberena, 1977; Schultz et al., 2000; Rubert and Schultz, 2004), and the youngest one (“Mata Sandstones”), probably Rhaetian by the presence of allocthonous Araucarioxylon wood logs (Faccini, 1989, 2007; Guerra-Sommer and Cazzulo-Klepzig, 2000). According to sequence stratigraphic concepts, the Caturrita Formation corresponds to a transgressive tract system that includes two possibly incomplete third order sequences, deposited in a tectonically and structurally disturbed area (Zerfass et al., 2003, 2004). Deposition occurred in high energy, low sinuous and ephemeral river systems with associated plains or lakes in an extensional basin, contemporaneous to those from Waterberg, South Africa, and Cuyo and Ischigualasto, western Argentina (Zerfass, 2007). The active tectonism that affected the Triassic successions from Rio Grande do Sul (Andreis et al., 1980; Da-Rosa and Faccini, 2005; Zerfass, 2007) led to a progressive increase in accommodation rate that supported delta progradation and longitudinal and transversal faults. The related block dislodgement affect correlations. The Linha São Luiz outcrop (Fig. 2) is about 20 m high and composed of sandstones in the basal portion, mudstones in the middle, and rhythmic sandstones and mudstones at the top. The basal portion is composed of low angle cross bedded and well sorted ﬁne to medium sandstones, as well as short scale trough cross-bedded sandstones (ﬂuvial system) followed by massive or sigmoidal trough cross-laminated ﬁne sands associated with crevasse deposits (Faccini, 2007), generated into a ﬂuvio-deltaic system (Faccini, 1989; Zerfass, 2007). The following laminated mudstone-siltstone interval represents a more permanent lake and yielded autochthonous and parautochthonous gymnosperm wood material (Pires and GuerraSommer, 2004; Dutra and Crisafulli, 2009), branches of diversiﬁed conifers and rare Equisetales, and impressions of sterile and reproductive parts of Bennettitales (Wilberger et al., 2004; Barboni and Dutra, in press), accompanied by conchostraca, insects and ﬁsh scales. The upper portion of the outcrop is represented by heterolithic sandstone and mudstone deposits with evidences of episodically subaerial exposure. These are considered to represent a crevasse splay deposition and contain the two large dinosaur footprints herein discussed, associated with desiccation cracks, in the surface of a thick tabular sandstone layer. 4. Systematic ichnology Ichnogenus Eubrontes Hitchcock, 1845 Eubrontes isp. Material: MCN-PIC.030 and FSSL-02, isolated footprints (Fig. 3). Description: The footprints are digitigrade, tridactyl and mesaxonic, with acute digital extremities and hypices and with a rear margin indented by a posteromedial notch or a heel-like bulge. The footprint MCN-PIC.030 is incomplete due to erosion and corresponds to the impression of a left foot with the plantar portion, digit IV and the proximal portion of the digits II and III preserved. Digit IV presents three phalangeal pads and a claw mark. This footprint is oriented approximately to northwest, having 11 cm 18 R.C.da Silva et al. / Journal of South American Earth Sciences 39 (2012) 16e23 Fig. 2. Detailed section of Linha São Luiz outcrop, Paraná Basin, Southern Brazil. A, General view of the outcrop; B, Fluvial (base), lacustrine (middle) and crevasse splay (top) deposits; C, General view of the crevasse splays deposits. of sole length and 22 cm of sole width. The footprint FSSL-02 corresponds to the complete impression of a right foot, with the digits medially curved. It is longer than wide and there are no phalangeal or plantar pads. Digits II and IV are almost equal in length while digit III is longer. This footprint is oriented approximately southeast and presents 43 cm of length and 39 cm of width. Measurements of both footprints are given in Table 1. Remarks: The footprints clearly fulﬁll the criteria of impressions made by dinosaurs and cannot be confused with archosaurian chirotheroid footprints due to the strong mesaxonic and digitigrade pattern. The studied footprints can be attributed to Eubrontes due to the totally digitigrade instance, the typical tridactyl theropod morphology and the big size, longer than 28 cm (as deﬁned by Olsen et al., 1998). Morphologically, the studied material is closer to Eubrontes veillonensis Lapparent and Montenat, 1967. However, given the absence of trackways or more speciﬁc details, the identiﬁcation at ichnospeciﬁc level is not possible. The footprints differ from other ichnogenera of similar size like Gigandipus Hitchcock, R.C.da Silva et al. / Journal of South American Earth Sciences 39 (2012) 16e23 19 Fig. 3. Eubrontes isp., footprints from Caturrita Formation at Linha São Luiz outcrop. A, MCN.PIC.030, specimen at the ﬁeld and after collecting; B, FSSL-02, specimen at the ﬁeld on the surface and cutted; C, Composite photograph illustrating the original position of the two footprints; D, Original and cast of the specimen FSSL-02. 1855 by the absence of hallux impressions, and Tyrannosauropus Haubold, 1971 by the presence of longer digits in relation to the sole. Gigandipus was also considered a behavioral variant of Eubrontes (Rainforth, 2004, 2005). An isolated footprint resembling the studied material was illustrated and brieﬂy described by Turner et al. (2009: 63) as “.Large ornithopod footprint cf. Wintonopus, ca. Table 1 Parameters of the footprints from Caturrita Formation (L ¼ length, W ¼ width, SL ¼ sole length, SW ¼ sole width, D ¼ divarication, TD ¼ total divarication). Linear measures in cm. MCN-PIC.030 FSSL-02 L W SL SW L II L III L IV D IIeIII D IIIeIV TD e 43 e 39 11 17 22 31 e 19 e 29 17 22 44 28 25 24 69 52 48 cm long.”, but this footprint does not match the diagnostic patterns of that ichnogenus like the smaller size, broad digits with rounded or bluntly angular tips, and digits III and IV close together, parallel or slightly divergent. 5. Discussion The two footprints identiﬁed as Eubrontes isp. are typical of large theropod dinosaurs (e.g. Haubold, 1971; Thulborn, 1990; Lockley, 1991). The footprints are preserved in a tabular sandstone layer and show signs of deformation. During the preparation in the ﬁeld, it was observed that the sandy siltstone layer that covers the footprints was also deformed and revolved above them, what means that the trackmaker stepped on the fresh silty sediment, crossing through it and reaching the sand below (e.g. Brand and 20 R.C.da Silva et al. / Journal of South American Earth Sciences 39 (2012) 16e23 Kramer, 1996; Milàn and Bromley, 2006). The imprints are not recognizable in the siltstone because of the semi-ﬂuid nature of the original substrate, but they are preserved in the sandstone. This process may enhance the preservation potential of the footprints, because eliminates the aerial exposure after their generation. It can also explain the differences in size between the two footprints, because the original footprint was probably larger than the preserved one, with their size controlled by the depth of the impression (Fig. 4). This kind of preservation can be understood as a variation of the classic undertracks and ghostprints, and is similar to what was called “cut undertracks” by Goldring and Seilacher (1971). It was also noted in tracks preserved in grainﬂows of dune deposits of the Lower Jurassic Navajo Sandstone, southwestern USA (Loope, 2006). Also, there are no other, smaller tracks on the same surface, which probably results from the “Goldilocks” effect as noted by Falkingham et al. (2011). In such cases, only a narrow range of loads can produce tracks, given that small animals failed to indent the substrate. The total divarication of the studied footprints is slightly higher than the average for the ichnogenus Eubrontes, indicating that they were produced on a softer and wetter ground. Footprints produced on this kind of substrate tend to show higher divarication angles than those produced on ﬁrm ground (Currie and Sargeant, 1979; Thulborn, 1990). The heel-like bulges at the rear margin of the footprints are occasionally produced when the foot does not sink deeply into the substrate. Such features are usually found in theropod footprints (Haubold, 1971; Thulborn, 1990), as those from Northeast Brazil (Carvalho, 2000, 2004; Leonardi, 1994). It is not possible to determine if the footprints were made by a single trackmaker, because their size and direction are different. The footprint FSSL-02 corresponds to a complete impression of a right foot with 31 cm of sole width and 43 cm of total length. This footprint was the base to estimate the size of the trackmaker according to the equations used by Thulborn and Wade (1984) and Thulborn (1989). Employing both methods discussed by those authors: morphometric ratios (h ¼ 4.9 FL when footprint length [FL] is higher than 25 cm, for large theropods) and allometric equations (h ¼ 8.6 FL0.85, when FL > 25 cm), it was possible to estimate the height at the hip joint (h) at 2.10 m, what corresponds to an animal with up to 8 m long, similar in size to a big Allosaurus. Currently, the known paleofauna of Linha São Luiz outcrop includes mainly small animals, like the sphenodontian Clevosaurus riograndensis (Bonaparte and Sues, 2006), the procolophonid Soturnia caliodon (Cisneros and Schultz, 2003), the lepidosauriformes Cargninia enigmatica (Bonaparte et al., 2010a), the cynodonts Riograndia guaibensis (Bonaparte et al., 2001), Brasilodon quadrangularis, Brasilitherium riograndensis (Bonaparte et al., 2003) and Minicynodon maieri (Bonaparte et al., 2010a), the possible pterosaur Faxinalipterus minima (Bonaparte et al., 2010b), and the medium-sized dinosaur probably Guaibasaurus candelariensis (Rubert and Schultz, 2004; Bonaparte et al., 2006). All of them are restricted until now to the massive sandstones of the basal crevasse splay deposits of São Luiz outcrop (Bonaparte et al., 1999, 2001, 2003, 2006, 2010b; Cisneros and Schultz, 2003; Martinelli et al., 2005; Bonaparte and Sues, 2006; Arantes et al., 2009; Soares et al., 2011a,b). As a whole, the paleofauna of Caturrita Formation includes also the medium-sized dicynodont Jachaleria candelariensis (Araújo and Gonzaga, 1980), an indeterminate phytosaur (Kischlat and Lucas, 2003), the cynodont Irajatherium hernandezi (Martinelli et al., 2005), indeterminated sphenodontians, a stereospondyl temnospondyl (Dias-da-Silva et al., 2009), the dinosauromorph Sacisaurus agudoensis (Ferigolo and Langer, 2006) and Unaysaurus tolentinoi (Leal et al., 2004), beyond more fragmentary archosaur and cynodont remains (Dornelles, 1990; Ribeiro et al., 2011). Other dinosaurs recorded in the Brazilian Triassic include Pampadromaeus, Staurikosaurus, Saturnalia and also Grallator footprints from the lower Santa Maria Formation (Colbert, 1970; Langer et al., 1999; Silva et al., 2008; Cabreira et al., 2011). In addition, tracks were previously recorded in the Caturrita Formation at the Novo Treviso site and assigned to prosauropod dinosaurs (Silva et al., 2007). However, those rocks were reinterpreted in a recent mapping of the region as belonging to the Guará Alloformation, Late Jurassic to Early Cretaceous in age (Scherer et al., 2000, 2001; Zerfass, 2007). Dinosaur footprints were also recorded in other outcrops of the Guará Formation and assigned to Sauropoda and Theropoda (Schultz et al., 2003; Dentzien-Dias et al., 2005; Dias and Schultz, 2005; Dentzien-Dias and Bertoni-Machado, 2005; Scherer and Lavina, 2005). Thus, the structures found in Novo Treviso are similar in age and shape to the other imprints from Guará Formation and could be related to the same trackmakers. Of the above mentioned taxa, none represent potential producers for the footprints dealt with here. The largest known dinosaurs from Caturrita Formation, U. tolentinoi and G. candelariensis, are considerably smaller than the Eubrontes trackmaker, as well as the others known dinosaurs from the Triassic of the Paraná Basin (Fig. 5). In fact, the Grallator footprints from Santa Maria Fig. 4. Preservation of the footprints (specimen FSSL-02) as “cut undertracks”, in which the semi-ﬂuid nature of the original substrate controlled the depth of the impression and allowed the impression in already buried layers. R.C.da Silva et al. / Journal of South American Earth Sciences 39 (2012) 16e23 21 Fig. 5. Dinosaurs recorded in the Brazilian Triassic, based on body fossils and ichnofossils. Note the incongruent size of Eubrontes trackmaker compared to the others. Formation (Silva et al., 2008) correspond to what would be expected for the Brazilian Triassic dinosaurs. Ichnologists have long debated about the age of the oldest occurrence of the ichnogenus Eubrontes. Haubold (1971) regarded the occurrence of Eubrontes as spanning both Late Triassic and Early Jurassic. Olsen and Galton (1984) proposed that its lowest occurrence matches with the base of the Jurassic, due to the correspondence between the appearance of this ichnogenus in the Newark Supergroup and the Passaic palynoﬂoral event (but see Lucas and Tanner, 2007). Thereafter, most ichnologists began to consider Eubrontes tracks as indicative of Jurassic age (e.g. Haubold, 1986; Lockley and Hunt, 1994). Indeed, Olsen et al. (2002a, 2002b) concluded that the sudden appearance of Eubrontes giganteous in the Early Jurassic of the Newark Supergroup indicates a dramatic size increase in theropod dinosaurs at the TriassiceJurassic boundary. However, E. giganteous appears to also occur in the latest Rhaetian based on the new deﬁnition of the base Hettangian GSSP (Olsen et al., 2011). Triassic theropod tracks were revised by Lucas et al. (2006), who assigned all tridactyl footprints longer than 25 cm to Eubrontes. They listed distinct tracks, with varied sizes, from Australia (Carnian? 43 cm long), Southern Africa (Norian, up to 35 cm), Great Britain (NorianeRhaetian, 26 cm), Switzerland (Norian, 25e30 cm), France (Norian, 50 cm?; Rhaetian, 40 cm), Germany (Rhaetian, 25 cm), Sweden (Rhaetian, 32 cm) and Greenland (Norian, 28 cm). However, the size criteria applied alone cannot provide a solid ichnotaxonomic basis, and morphological elements should be considered for an appropriated identiﬁcation. They also argued that the footprints from Great Britain, France, Germany and Greenland are of grallatorid morphology. Lucas and Tanner (2007) also cited that theropods large enough to have made at least some Eubrontessize tracks are known from the Late Triassic body-fossil record as Liliensternus (Norian of Europe, estimated length of 5 m) and Gojirosaurus (Norian of the USA, estimated length of 5.5 m), but animals of this size do not explain the occurrence of footprints with more than 30 cm long as those described. The problem of the identiﬁcation of some Triassic footprints as theropodan in origin also has been discussed by several authors (e.g. Olsen et al., 1998; Olsen et al., 2003; Lucas et al., 2006). Although the subject is still far from being closed, it seems clear that the emergence of Eubrontes trackmarkers occurred before the beginning of the Jurassic, and that there are Triassic animals capable of producing at least mid-sized Eubrontes-like footprints. Nevertheless, there is an agreement between most researchers that most Eubrontes tracks are clearly Jurassic, or at least that theropod footprints with more than 40 cm in length, and with eubrontid morphology, are more characteristic of the Jurassic. The age of Caturrita Formation is also subject of discussion in the literature. Rubert and Schultz (2004) proposed the Ictidosauria Cenozone to the upper part of Caturrita Formation. Soares et al. (2011a,b) have proposed to replace the “Ictidosauria Cenozone” for the Riograndia Assemblage Zone. It was correlated with the faunas of Los Colorados Formation, from Argentina, traditionally placed in the Norian. A Norian age for the Caturrita Formation has been used ever since, despite earlier works considered the deposition of the Los Colorados Formation as Rhaetian in age (Heckert and Lucas, 1998; Lucas, 1998; Arcucci et al., 2004). According to Abdala and Ribeiro (2010), a late NorianeRhaetian age is more plausible for the cynodonts, as indicated by its correlation with the Los Colorados (Argentina) and the Elliot (South Africa) formations faunas. The difﬁculties to correlate the faunistic content of São Luiz exposition results from the different positions of regional structural blocks due to fault displacements (Da-Rosa and Faccini, 2005) and the endemic character of most of its faunal components. Other elements, such as J. candelariensis, apparently constrain the age of the Caturrita Formation to the Triassic due to correlations with the argentine basins and the extinction of the group at the end of the Triassic (Schwanke and Araújo-Barberena, 2002; Rubert and Schultz, 2004). However, remnants of dicynodonts with plesiomorphic characters have recently been identiﬁed in the Lower Cretaceous of Australia (Thulborn and Turner, 2003). At this time, however, no record of J. candelariensis occurs at São Luis outcrop, which is known exclusively from one outcrop near Candelária, 50 km east of the site herein studied. In relation to paleoﬂoristic content, Barboni and Dutra (in press) recently registered Bennettitales “ﬂowers” in the São Luis outcrop. The derived morphology of the female cone Williamsonia reinforces a Rhaetian or younger age, which is also supported by comparisons with other fossil ﬂoras, mainly those from Argentine basins (Artabe et al., 2005; Menéndez, 1966; Barboni, 2010). 6. Conclusion The studied footprints were identiﬁed as Eubrontes isp., and their trackmarkers were most likely large theropod dinosaurs. The morphological characteristics and dimensions of the footprints are not commonly found in the CarnianeNorian, but more consistent with those found after the RhaetianeJurassic. The trackmaker does not correspond to any type of dinosaur known in Triassic rocks from Brazil. The occurrence of the footprints, along with paleoﬂoristic and paleofaunistic data, indicate a Triassic age younger than previously suggested for the Santa Maria Supersequence for the upper portion of the Caturrita Formation or at least for the Linha 22 R.C.da Silva et al. / Journal of South American Earth Sciences 39 (2012) 16e23 São Luiz site, although an Early Jurassic age cannot be discarded. More data and detailed studies of the fossil content are needed for a better age estimate. Acknowledgments Thanks go to: Jorge Ferigolo and Ana Maria Ribeiro, Fundação Zoobotânica do Rio Grande do Sul (FZB-RS), for receiving the material in the collection; to Henrique Zerfass (Petrobras) for assistance on the ﬁeld and discussions on geology; and to CONDESUS (Consórcio de Desenvolvimento Sustentável da Quarta Colônia) for technical support; and to Peter L. Falkingham (University of Manchester) for the revision of the manuscript. 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