A new cretaceous notosuchian (Mesoeucrocodylia) with bizarre dentition from Brazil

Authors

  • ALEXANDER W. A. KELLNER,

    Corresponding author
    1. Departamento Nacional de Produção Mineral, Museu de Ciências da Terra, Avenida Pasteur, 404, Urca, RJ-22290-040, Brazil
      E-mail: kellner@mn.ufrj.br
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  • RODRIGO G. FIGUEIREDO,

    1. Departamento Nacional de Produção Mineral, Museu de Ciências da Terra, Avenida Pasteur, 404, Urca, RJ-22290-040, Brazil
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  • SERGIO A. K. AZEVEDO,

    1. Departamento Nacional de Produção Mineral, Museu de Ciências da Terra, Avenida Pasteur, 404, Urca, RJ-22290-040, Brazil
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  • DIOGENES A. CAMPOS

    1. Departamento Nacional de Produção Mineral, Museu de Ciências da Terra, Avenida Pasteur, 404, Urca, RJ-22290-040, Brazil
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E-mail: kellner@mn.ufrj.br

Abstract

A new species of Notosuchia, Labidiosuchus amicum gen. et sp. nov., is described based on an incomplete lower jaw (DGM 1480-R) from the Upper Cretaceous Marília Formation (Maastrichtian) recovered from a quarry near the Peirópolis municipality, Minas Gerais State, Southeastern Brazil. The mandibular symphysis is long, strong anterodorsally projected and ‘Y-shaped’. The bizarre dentition is formed by at least eight teeth placed in a symphyseal tooth battery, some located lateral to each other. The first pair is larger than all others and procumbent. Some teeth are obliquely implanted (anterolabially to posterolingually) and have sub circular to elliptical outline. At least the posterior teeth are single cuspidate with acute apex. Labidiosuchus amicum shows a rather bizarre dentition, increasing the taxonomic diversity and potential feeding strategies of notosuchian crocodylomorphs.

© 2011 The Linnean Society of London, Zoological Journal of the Linnean Society, 2011, 163, S109–S115.

INTRODUCTION

The crocodylomorph fossil record of South America is notably rich and diverse (e.g. Price, 1955; Gasparini, 1982; Kellner, 1987; Kellner & Campos, 1999; Brochu, 2003; Aguilera, Riff & Villanueva, 2006; Calvo et al., 2007; Barbosa, Kellner & Viana, 2008; Campos et al., 2011), especially the Notosuchia, which were well adapted to terrestrial environments (e.g. Carvalho & Bertini, 1999; Pol, 2003; Pol & Apesteguía, 2005; Nobre & Carvalho, 2006; Andrade & Bertini, 2008a; Kellner et al., 2009). This clade was first defined by Gasparini (1971) and comprises small terrestrial crocodylomorphs that except for one species (Wu & Sues, 1996) are typically found in Cretaceous deposits of Gondwana. The phylogenetic content of Notosuchia are still debated, and some authors include groups like Baurusuchidae and Araripesuchidae in this clade (Ortega et al., 2000; Sereno et al., 2001; Pol, 2003; Sereno et al., 2003; Turner, 2006; Pol & Gasparini, 2009). Furthermore, the taxonomic status of some taxa, such as Sphagesaurus, is presently being reviewed (Kellner et al., 2011).

Amongst the striking features of notosuchians is the diversified dentition of several species, which supports a variety of feeding habits including omnivorous and possibly herbivorous animals (e.g. Clark, Jacobs & Downs, 1989; Andrade & Bertini, 2008c; Lecuona & Pol, 2008).

In 1987, the Departamento Nacional da Produção Mineral, associated with the Municipality of Uberaba, reopened the palaeontological excavation for vertebrate remains in the Peirópolis neighbourhood, Minas Gerais State, Brazil, where several important fossil quarries were opened by Llewellyn Ivor Price between 1948 and 1969 (Campos & Kellner, 1999). Those quarries have yielded particularly dinosaur remains (Kellner & Campos, 2000) but other fossil vertebrates have also been found (e.g. Price, 1955; Bertini et al., 1993; Kellner & Campos, 1999; Carvalho, Ribeiro & Avilla, 2004). During an excavation at the quarry close to the ‘Serra do Veadinho’, one of us (S. A. K. A.) collected a fragmentary bone embedded in sandstone that was preliminary identified as a dinosaur element (Campos & Azevedo, 1992). Further preparation revealed that this specimen is a lower jaw of a new notosuchian crocodylomorph that shows a quite distinct dentition and is described here.

Anatomical abbreviations

ang, angular; den, dentary; for, foramen; emf, mandibular fenestra; spl, splenial; syp, symphyseal platform; sur, surangular; d1−d8, dentary tooth 1–8.

SYSTEMATIC PALAEONTOLOGY

Crocodylomorpha Walker, 1970

Crocodyliformes Hay, 1930

Mesoeucrocodylia Whetstone & Whybrow, 1983

Notosuchia Gasparini, 1971

GenusLabidiosuchusgen. nov.

Type species: Labidiosuchus amicum gen. et sp. nov.

Etymology: The generic name is derived from the Greek word labis for forceps, tongs and souchos that means crocodile.

Diagnosis: As for the type and only species.

Labidiosuchus amicumsp. nov.

Holotype: Incomplete lower jaw housed at the Earth Science Museum of the Departamento Nacional da Produção Mineral under the number DGM 1480-R (Figs 1–5). Cast at the Museum Nacional/UFRJ (MN).

Figure 1.

Right lateral view of Labidiosuchus amicum gen. et sp. nov. lower jaw (DGM 1480-R). A, drawing; B, photograph. Abbreviations: ang, angular; den, dentary; emf, external mandibular fenestra; sur, surangular; syp, symphyseal platform. Scale bars = 10 mm.

Figure 2.

Dorsal view of Labidiosuchus amicum gen. et sp. nov. mandible (DGM 1480-R). The white arrows indicate the anterior bifurcation of the surangular. Abbreviations: den, dentary; spl, splenial; sur, surangular. Scale bar = 10 mm.

Figure 3.

Anterior view of the mandibular symphysis of Labidiosuchus amicum gen. et sp. nov. (DGM 1480-R). Abbreviation: for, foramen. Scale bar = 10 mm.

Figure 4.

Detail of the symphysis of Labidiosuchus amicum gen. et sp. nov. (DGM 1480-R) in occlusal view. A, drawing; B, photograph showing the dentition. Abbreviations: d1−d8, dentary teeth 1 to 8. Scale bars = 5 mm.

Figure 5.

Last tooth (d8) of Labidiosuchus amicum gen. et sp. nov. (DGM 1480-R), positioned on the mandibular ramus. A, photograph and B, drawing of labial view; C, photograph and D, drawing of lingual view. Scale bars = 1 mm.

Etymology: The specific name comes from the Latin amicus for friend, honouring the community that has helped to protect the palaeontological site at Peirópolis, especially the members of the Associação dos Amigos do Sítio Paleontológico de Peirópolis (Association of the Friends of the Peirópolis Palaeontological Site).

Type locality: ‘Serra do Veadinho’, Municipality of Peirópolis, Minas Gerais State, south-eastern Brazil.

Type horizon: Upper Cretaceous (Maastrichtian) Marília Formation of the Bauru Group (Dias-Brito et al., 2001).

Diagnosis: Notosuchian that can be separated from all other members of this clade based on the following combination of characters (autapomorphies are indicated with an asterisk): the mandible is strongly anterodorsally projected; there is a symphyseal platform holding the teeth*; the surangular is anteriorly bifurcated; strong heterodont dentition both in size and shape, formed by teeth with circular and elliptical cross section; discrepancy of size of the first anterior pair of teeth that are much larger than all other mandibular teeth*; first anterior teeth strongly inclined anterodorsally; presence of small teeth on the medial side of the anterior portion of the dentary*; proportionally large number of the teeth, tightly packed, at the anterior symphysis*; presence of a symphyseal tooth battery.

Description and comparisons

The holotype of Labidiosuchus amicum consists of an incomplete lower jaw (DGM 1480-R) with the anterior part of the dentary complete, lacking most of the right mandibular ramus and the posterior end of the left mandibular ramus (Figs 1–4). The preserved part is about 70.5 mm long and clearly suggests that the jaw had a Y-shaped outline in dorsal view (Fig. 2).

Although the surface of some parts of this specimen is broken, there are no perceptible taphonomic deformations. The preservation of DGM 1480-R is the same as observed in other dinosaur bones collected in this area, also including other crocodylomorphs (e.g. Campos & Kellner, 1999; Kellner & Campos, 2000; Carvalho et al., 2004).

The dentaries are strongly bent dorsally with a concave dorsal and convex ventral margin, respectively. The anterior portion is projected anterodorsally at about 35°, similar to Adamantinasuchus navae (Nobre & Carvalho, 2006). Opposite dentaries are not fused to form an actual symphysis but one probably developed in ontogenetically older individuals. The contact region of opposite dentaries is longer than wide as in other notosuchians, differing from the putative notosuchians Anatosuchus and Simosuchus (Buckley et al., 2000; Sereno et al., 2003). The distal-most end of the dentaries forms a symphyseal platform, which consists of a horizontal shelf with a tightly packed set of teeth.

The lateral surface of the dentary ramus is flat and slightly compressed in the anterior to mid-sections, which can also be observed in Comahuesuchus, Chimaerasuchus, Malawisuchus, Mariliasuchus, Notosuchus, Simosuchus, the skull attributed to Sphagesaurus huenei (see Kellner et al., 2011 for details about the taxonomic status of Sphagesaurus), and Uruguaysuchus (Gasparini, 1971; Bonaparte, 1991; Wu & Sues, 1996; Gomani, 1997; Carvalho & Bertini, 1999; Buckley et al., 2000; Martinelli, 2003; Pol, 2003; Fiorelli & Calvo, 2008). The alveolar margins of the dentaries are flat and smooth and they do not project. All anterior-most alveoli are separated by thin septa; however, the distal-most alveoli are well separated by thick walls.

The mandibular fenestra is large and elliptical with the dorsal margin formed by the dorsal branch of the dentary and the anterior border of the surangular. The latter is bifurcated and has a lateral ramus contacting the dentary and a medial ramus directed to the splenial (Fig. 2), similar to Mariliasuchus and ‘Sphagesaurusmontealtensis (Carvalho & Bertini, 1999; Andrade & Bertini, 2008a). The anteromedial margin of the surangular is dorsally arched as in Comahuesuchus, Mariliasuchus, Notosuchus, Simosuchus, and ‘Sphagesaurusmontealtensis (Bonaparte, 1991; Carvalho & Bertini, 1999; Buckley et al., 2000; Andrade & Bertini, 2008a; Fiorelli & Calvo, 2008; Kellner et al., 2011), differing from the straight to near-straight margins observed in Anatosuchus, Araripesuchus gomesii, Malawisuchus, and Uruguaysuchus (Price, 1959; Gasparini, 1971; Gomani, 1997; Sereno et al., 2003).

The most striking feature of L. amicum is the dentition, with the teeth tightly packed in the symphyseal platform made by the dentaries. Altogether there are eight teeth present in this region, which is at a higher level relative to the remaining part of the lower jaw. As already noted, there is no taphonomic modification that could account either for the shape of the mandibular symphysis or for the particular position of the teeth. No tooth is complete, but almost every alveolus shows a partial tooth inside (Fig. 4). The first tooth (d1) is projected anterodorsally at about 35°, similar to the condition observed in Adamantinasuchus, Armadillosuchus, and Mariliasuchus (Carvalho & Bertini, 1999; Nobre & Carvalho, 2006; Marinho & Carvalho, 2009). However, in L. amicum this tooth is much larger than all others. Three teeth (d2−d4) follow, separated from each other by thin septa. The most anterior one (d2), the smallest of the jaw, is placed close to the midline. This tooth is unlikely to be a replacement tooth because it is far too small compared to the first tooth and located in the wrong position to be replacing the fourth tooth (d4), which is located posteriorly at the medial half of the jaw. The next tooth (d3) reaches the lateral margin of the dentary and has a rather elliptic transverse section (Fig. 4). Two other teeth (d5 and d6) follow, with elliptic and rounded transverse sections, respectively. These teeth are strongly obliquely implanted relative to the lateral margin of the dentary, with giroversion of about 50 and 40°, respectively. The oblique implantation of teeth is typical of the Sphagesauridae, although Mariliasuchus and Notosuchus also have some teeth with the main axis at an angle relative to the lateral margin of the jaw (Andrade & Bertini, 2008b, c). In Coringasuchus anisodontis the obliquely implanted teeth differ by their anterolingual to posterolabial direction (Kellner et al., 2009).

Posterior to those, a much larger tooth (d7) with a subcircular transverse section can be found, situated in a slightly dorsally projected part of the mandible. It is followed by a similar but slightly smaller tooth (d8), both being somewhat obliquely implanted.

The last tooth (d8) is positioned at the diverging point of the mandibular rami and can only be observed on the right side (Fig. 5). It is not fully broken and shows a well striated surface. Small ridges are located in a small posterolingual carina, differing from the robust ridges observed in sphagesaurids (Price, 1950; Pol, 2003). The tooth apex is acute like in Chimaerasuchus, Malawisuchus, and Uruguaysuchus (Gasparini, 1971; Wu & Sues, 1996; Gomani, 1997) with a single cusp. There is no constriction at the transitional region from the crown to the root as reported in some notosuchians, such as Candidodon, Malawisuchus, Mariliasuchus, and ‘Sphagesaurus huenei’ (Gomani, 1997; Andrade & Bertini, 2008b, c).

DISCUSSION AND CONCLUSIONS

The phylogenetic position of L. amicum is not easy to establish because of the incompleteness of the holotype. The overall shape of the lower jaw allows the allocation of this new species to the Notosuchia, a rather diverse group of crocodylomorphs that shows a great variety of dentition. Labidiosuchus amicum is the only one where the teeth are so closely placed in a horizontal platform with medial and lateral teeth positioned close to each other. Anterior projection of the lower jaw is also recorded in Adamantinasuchus. Some teeth show an oblique implantation that is typical of the Sphagesauridae. The Y-shaped condition of the lower jaw is shared with Adamantinasuchus, Notosuchus, Mariliasuchus, and ‘Sphagesaurus montealtensis’ and probably with Candidodon. The strong protruding forward inclination of the first pair of teeth (commonly referred to as incisiforms) present in L. amicum is also present in Adamantinasuchus, Armadillosuchus, and Mariliasuchus (Carvalho & Bertini, 1999; Nobre & Carvalho, 2006; Marinho & Carvalho, 2009). However, in Notosuchus and Sphagesaurus they are slightly anteriorly projected (Gasparini, 1971; Andrade & Bertini, 2008a). Furthermore, L. amicum lacks the typical sphagesaurid dentition (Price, 1950; Pol, 2003). Therefore, although L. amicum can be regarded as a notosuchian, the close relationship of this taxon within the clade remains to be established.

The occurrence of yet another notosuchian with a quite distinctive dentition corroborates previous suggestions that this group of crocodylomorphs have developed a quite diverse range of feeding habits. Although it is not easy to establish what L. amicum might have been feeding on, the tightly packed teeth located on a platform made of the dentaries indicate that this species could have used the jaws for crushing food, suggesting that it was feeding on rather resistant material. Although seeds and similar items could have been a possibility, making this another potential omnivorous or even herbivorous species (e.g. Clark et al., 1989; Buckley et al., 2000; Andrade & Bertini, 2008a, b, c; Lecuona & Pol, 2008), at present the feeding preferences of L. amicum cannot be determined with certainty. Nevertheless, the new species shows yet another bizarre variation of the notosuchian dentition adding to the diversity of this clade.

ACKNOWLEDGEMENTS

We thank Alejandro Kramarz and Fernando Novas from the Museo Argentino de Ciências Naturales and Marcelo Reguero and Zulma Gasparini from the Museo de La Plata for access to specimens under their care. We are also grateful to Gustavo Oliveira for help with the photographs and André Pinheiro (Museu Nacional/UFRJ) is thanked for the drawings that illustrate this paper. We also acknowledge Marco Brandalise de Andrade (University of Bristol) and an anonymous reviewer for comments on the original manuscript. This project was partially funded by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) (fellowship to R. G. F.) and by the Fundação Carlos Chagas de Amparo à Pesquisa do Rio de Janeiro (FAPERJ, grant number E-26/152.885/2006 to A. W. A. K.) and Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq, grants 486313/2006-9 and 501267/2008-5 to A. W. A. K.).

Ancillary