Redescription and phylogenetic relationships of Meridiosaurus vallisparadisi, a pholidosaurid from the Late Jurassic of Uruguay

Authors

  • DANIEL FORTIER,

    Corresponding author
    1. Departamento de Paleontologia e Estratigrafia, IG, UFRGS, Avenue Bento Gonçalves, 9500, Cx. P. 15001, Porto Alegre, RS, Brazil
    2. Department of Geoscience, University of Iowa, 121 Trowbridge Hall, Iowa City, IA 52242, USA
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  • DANIEL PEREA,

    1. Departamento de Evolución de Cuencas, Facultad de Ciencias, Iguá 4225, 11400 Montevideo, Uruguay
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  • CESAR SCHULTZ

    1. Departamento de Paleontologia e Estratigrafia, IG, UFRGS, Avenue Bento Gonçalves, 9500, Cx. P. 15001, Porto Alegre, RS, Brazil
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E-mail: daniel.fortier@ufrgs.br

Abstract

Meridiosaurus vallisparadisi Mones, 1980, a freshwater pholidosaurid from the Late Jurassic of Uruguay, is redescribed herein. It can be diagnosed by the possession of the following combination of features: (1) lateral constriction of the rostrum at premaxilla–maxilla contact, strong lateral expansion of the premaxilla with the fifth tooth placed in the widest portion; (2) sinusoidal premaxilla–maxilla suture in palatal view, posteromedially directed on its lateral half, and anteromedially directed along its medial region; (3) evaginated maxillary alveolar edges forming a discrete collar at each alveolus, lateroventrally oriented; (4) greater number of maxillary teeth (at least 27) with respect to Elosuchus (less than 20 maxillary teeth); (5) nasals do not meet premaxilla dorsally; (6) strong sinusoidal lateral contour of snout in dorsal view, with respect to the similar condition of Elosuchus, forming two waves (‘festooned’); and (7) third, fourth, and fifth alveoli are equally enlarged. A phylogenetic analysis was performed, including six pholidosaurids: Elosuchus, Meridiosaurus, Oceanosuchus, Pholidosaurus, Sarcosuchus, and Terminonaris. The analysis confirmed the monophyly of Pholidosauridae, and a new definition is proposed: a stem-based group name including Pholidosaurus schaumburgensis Meyer, 1841 and all taxa closer to it than to Dyrosaurus phosphaticus (Thomas, 1893) or Pelagosaurus typus Bronn, 1841. Pholidosauridae originated in Europe during the Middle Jurassic, dispersed to Africa, and North and South America, in several dispersal events, and completely disappeared in the Late Cretaceous.

© 2011 The Linnean Society of London, Zoological Journal of the Linnean Society, 2011, 163, S257–S272.

INTRODUCTION

Pholidosauridae is a group of fossil longirostrine crocodylomophs adapted to aquatic environments, reported from the Middle Jurassic (Owen, 1884; Mook, 1942) to Late Cretaceous (Mook, 1934; Wu, Russell & Cumbaa, 2001; Hua et al., 2007). Remains of Pholidosauridae occur in marine, estuarine, and fluviolacustrine sediments of North America (Shimada & Parris, 2007), South America (Buffetaut & Taquet, 1977), Africa (Sereno et al., 2001), and Europe (Salisbury, 2002). Despite some well-known species, like Terminonaris and Sarcosuchus, some pholidosaurids are still rather poorly known, like Pholidosaurus and Anglosuchus.

There are three main Mesozoic longirostrine crocodylomorph groups: Thalattosuchia, Dyrosauridae, and Pholidosauridae. The latter have been included in some phylogenetic analysis, but there is still no consensus as regards to the monophyly of the group. Some authors consider Pholidosauridae as a monophyletic group (Jouve et al., 2006; Jouve, 2009), whereas others postulate its paraphyly (Sereno et al., 2001; Wu et al., 2001; Young & Andrade, 2009). Nevertheless, all those works show the close relationship between Pholidosauridae and Dyrosauridae. However, the relationship among them and Thalattosuchia is controversial. Previous cladistic hypotheses have considered at least two main positions for Thalattosuchia: as the sister clade of most mesoeucrocodylians (Buckley et al., 2000; Sereno et al., 2001, 2003; Tykoski et al., 2002; Larsson & Sues, 2007; Sereno & Larsson, 2009; Young & Andrade, 2009); or as closely related to Pholidosauridae and Dyrosauridae (Clark, 1994; Buckley & Brochu, 1999; Larsson & Gado, 2000; Wu et al., 1997, 2001; Brochu et al., 2002; Pol & Apesteguía, 2005; Jouve et al., 2006; Jouve, 2009; Pol & Gasparini, 2009). Although recent works have explored improvements, either in cladistic methods or in taxon sampling, the phylogenetic relationships among those groups are still under debate and are far from a conclusion.

A partial skull of a longirostrine crocodylomorph was discovered in the 1970s, from the Late Jurassic–Early Cretaceous continental sediments of Uruguay (Fig. 1). Mones (1980), in a brief note, described the specimen and tentatively assigned it as a member of Pholidosaudidae. Named Meridiosaurus vallisparadisiMones, 1980, it was the first amniote found in the Tacuarembó Formation, and the only one for at least 20 years (Mones, 1980; Perea, Ubilla & Rojas, 2003).

Figure 1.

Map showing the Tacuarembó Formation (shaded area) and Valle Edén locality.

After a reanalysis of the type specimen, it was found necessary to redescribe the incomplete skull, along with a few elements not mentioned in the original description, such as a mandibular fragment. Meridiosaurus vallisparadisi is redescribed herein and its phylogenetic relationship is tested through a cladistic analysis, including most of the pholidosaurid species.

GEOLOGICAL SETTINGS

The sediments of the Tacuarembó Formation outcrop in northern Uruguay (Fig. 1), mainly in the departments of Tacuarembó and Rivera (Martínez et al., 1993). The sediments were formed in fluviolacustrine and aeolian depositional systems (Perea et al., 2009). Sprechmann, Bossi & Da Silva (1981) distinguished two members within the formation: Batoví (lower) and Rivera (upper) members (Perea et al., 2009). The latter unit is afossiliferous.

The fossil remains are preserved in the sandstones of the Batoví Member, widespread around the city of Tacuarembó. The formation yields fossils from freshwater and terrestrial environments, including bivalves, gastropods, ostracods, conchostracans, dipnoans, ‘semionotiform’-like halecostomes, freshwater hybodontid sharks, testudines, crocodylomorphs, theropod dinosaurs, and ichnofossils (Mones, 1980; Martínez et al., 1993; Yanbin, Gallego & Martinez, 2004; Soto & Perea, 2008; Perea et al., 2001, 2003, 2009).

Until recently, the age of the Tacuarembó Formation has been estimated on the basis of purely stratigraphic criteria, and there was no agreement in the published literature. It was considered as Late Triassic (Bossi & Navarro, 1991; Bossi, 1996), Late Triassic–Late Jurassic (Herbst & Ferrando, 1985), Early Jurassic–Early Cretaceous (Sprechmann et al., 1981), and Late Jurassic–Early Cretaceous (Mones & Figueiras, 1981). Since the discovery of Priohybodus cf. Priohybodus arambourgi d'Erasmo, 1960 (Perea et al., 2001), the age of the Tacuarembó Formation has been considered as Late Jurassic–Early Cretaceous. Later works also confirmed that age (Perea et al., 2001, 2003; Soto & Perea, 2008), and the recent work of Perea et al. (2009) performed a complete lithographic and biostratigraphic study, and confirmed that the Tacuarembó Formation cannot be older than Kimmeridgian or younger than Hauterivian. The fossil assemblage of the Batoví Member suggests a Kimmeridgian–Tithonian age (Soto & Perea, 2008; Perea et al., 2009). Meridiosaurus vallisparadisi was discovered in sediments of the Batoví Member, in the Valle Edén locality, near Tacuarembó city.

SYSTEMATIC PALEONTOLOGY

MesoeucrododyliaWhetstone& Whybrow 1983

NeosuchiaBenton& Clark 1988

PholidosauridaeZittel & Eastman 1902

New definition: a stem-based group name including Pholidosaurus schaumburgensis (Meyer, 1841) and all taxa closer to it than to Dyrosaurus phosphaticus (Thomas, 1893) or Pelagosaurus typusBronn, 1841.

Composition: Elosuchus cherifiensis (Lavocat, 1955), Elosuchus felixiLapparent de Broin, 2002, Meridiosaurus vallisparadisiMones, 1980, Oceanosuchus boecensisHua et al., 2007, Pholidosaurus purbeckensis (Mansel-Pleydell, 1888) Pholidosaurus schaumburgensis (Meyer, 1841), Sarcosuchus hartii (Marsh, 1869), Sarcosuchus imperatorde Broin & Taquet, 1966, Terminonaris browni (Osborn, 1904), Terminonaris robusta (Mook, 1934). Putative pholidosaurids are Anglosuchus geoffroyi (Owen, 1884) and A. laticeps (Owen, 1884), Crocodilaemus robustus Jourdan in Gervais (1871), and Pholidosaurus meyeri (Dunker, 1843). Sarcosuchus hartii, from the Early Cretaceous of Brazil, could be the same species of S. imperator, as stated in de Broin & Taquet (1966). The group ranges temporally from the Middle Jurassic (Bathonian) to Late Cretaceous (Late Turonian).

Emended diagnosis: Longirostrine mesoeucrocodylians distinguished by the possession of the following unambiguous synapomorphies: (1) anterodorsal margin of the external naris without the premaxillary dorsal projection; (2) the medial margin of the orbit is formed mostly by the prefrontal, with little or no participation of the frontal; (3) the fifth premaxillary tooth is anterolaterally placed in relation to the maxillary tooth row; (4) the posterior premaxillary teeth are longer then the anterior teeth; (5) the ventral edge of the premaxilla is located deeper than the ventral edge of the maxilla; (6) the distance between the tip of the snout and the anteriormost position of the premaxilla–maxilla suture in dorsal view is smaller than the distance between this and the posterodorsal extremity of the premaxilla (except in Elosuchus); (7) absence of postorbital–ectopterygoid contact; and (8) the maximal width of premaxillae is wider than the maximal width of the rostrum at the level of the fourth or fifth alveoli.

Meridiosaurus vallisparidisi mones, 1980 (Fig. 2)

Figure 2.

Meridiosaurus vallisparadisi, holotype and unique specimen, FC-DPV-2322. A and C, rostrum in dorsal view; B and D, rostrum in dorsal view; E, rostrum in right lateral view; F, zoom of the dashed area in D, showing the details of two maxillary teeth; G–I, right lower jaw fragment in lateral, medial, and dorsal views, respectively; J, caudal osteoderm in dorsal view. Abbreviations: d, dentary; dn, notch for dentary teeth; if, incisive foramen; mx, maxilla; mg, Meckelian groove; pmx, premaxilla; sp, splenial. Scale bars: A–E, 5 cm; F–J, 1 cm.

Etymology: Genus from meridionalis, Latin for ‘southern’, and saurus, Greek for ‘lizard’, referring to the southernmost record of a pholidosaurid. Specific epithet from vallis, Latin for ‘valley’, and paradisus, latin for ‘paradise, Eden’, referring to its geographic provenance, the Valle Edén locality.

Holotype: FC-DPV-2322 (formerly SPV-FHC-27-II-78-1), anterior part of rostrum, mandible fragments, one osteoderm, and unidentifiable fragments. No referred specimens. Housed in the Colección de Vertebrados Fósiles, Faculdad de Ciencias, Montevideo (FC-DPV).

Horizon and locality: The fluviolacustrine sandstone facies of the Batoví Member, Tacuarembó Formation, in the Valle Edén locatily near Tacuarembó city.

Emended diagnosis: Longirostrine mesoeucrocodylian with the following combination of features: (1) lateral constriction of the rostrum at premaxilla–maxilla contact, strong lateral expansion of the premaxilla with the fifth tooth placed in the widest portion; (2) sinusoidal premaxilla–maxilla suture in palatal view, posteromedially directed on its lateral half and anteromedially directed along its medial region; (3) evaginated maxillary alveolar edges forming a discrete collar at each alveolus, lateroventrally oriented; (4) greater number of maxillary teeth (at least 27) with respect to Elosuchus (less than 20 maxillary teeth); (5) nasals do not meet premaxilla dorsally; (6) strong sinusoidal lateral contour of snout in dorsal view, with respect to the similar condition of Elosuchus, forming two waves (‘festooned’); and (7) third, fourth, and fifth alveoli are equally enlarged.

DESCRIPTION

State of preservation: The specimen is very fragmented. Practically all teeth are missing, and even small elements, like an osteoderm, are fragmented. Nevertheless, there is no evidence of water abrasion. The sutures are visible and external ornamentation is preserved, as well the delicate details of a carinated maxillary tooth. There is no evidence of diagenetic distortion.

Gerenal features: The nearly tubular rostrum measures 27.8 cm in length, 2.6–7.6 cm in width, and 1.5 cm in height. The external surface is ornamented with deep pits and grooves, but the evaginated alveolar margins are smooth. The lateral and ventral edges of the rostrum are sinusoidal in dorsal and ventral views, forming waves, constricted anteriorly at the level of premaxilla–maxilla suture in ventral view, and posteriorly at the level of the seventh maxillary teeth. The heart-shaped external naris is longer than wide, not divided, and completely surrounded by the premaxillae. It faces dorsally and is separated from the anterior edge of the rostrum by the premaxillary bar. There is no premaxilla–nasal contact, an autapomorphic feature of Meridiosaurus.

Premaxilla: Both premaxillae were preserved and show fractures of compression oriented dorsoventrally. Each has a maximum length of 7.5 cm. The width for each is 2.6 cm at the level of the premaxilla–maxilla constriction, and the maximum width is 4.2 cm at the level of the fourth tooth. Each premaxilla has five teeth. The alveoli are ventrally long and ventrally oriented. The first two are aligned transversely at the anterior margin of the bone. The other three teeth are positioned in a posteriorly curving arch. Alveoli for the first four teeth enlarge to the fourth tooth. The fifth is the smaller, placed anterolaterally to the maxillary tooth row, and is in close contact with the fourth tooth. In ventral view, there is a deep notch for the first dentary teeth, at the level of the third tooth, and a shallow notch for the second dentary teeth behind it. Dorsally, the acute posterior process extends to the level of the fifth maxillary tooth, and in ventral view to the level of the first maxillary tooth. The distance between the tip of the rostrum and the anteriormost position of the premaxilla–maxilla suture in dorsal view is smaller than the distance between this and the posterodorsal extremity of the premaxilla. The premaxilla–maxilla suture is smooth in dorsal view, and slightly serrated in lateral view. Laterally, the suture is oriented anteroventrally, and ventrally is sinusoidal, with the medial part directed anteriorly and the lateral part directed posteriorly. The premaxilla is constricted at the contact with the maxilla, and expands anteriorly forming a concave notch, similar to the condition in Goniopholis simus (Salisbury et al., 1999). It is more expanded than the maxillae until the thirteenth maxillary teeth, where the maxillae become wider. The anterior part is expanded dorsoventrally, and the ventral edge is placed slightly deeper than the maxilla edge, not as far as in Sarcosuchus imperator (Sereno et al., 2001) or Terminonaris robusta (Wu et al., 2001). A small ovate incisive foramen is placed in the middle of the premaxillae in ventral view, and is also visible in dorsal view. Some small to large foramina are located in the ventral view, parallel with the tooth row.

Maxilla: Both maxillae are present, but fragmented. The right maxilla has 27 alveoli preserved. Each alveolus is surrounded by the unsculptured evaginated maxillary edge. The anterior alveoli are subcircular, and the posterior alveoli are anteroposteriorly oval. Among the first eight alveoli, the third, fourth, and fifth are larger. One complete and nine incomplete teeth are preserved. The teeth have a smooth root (based on the left thirteenth tooth) and a carinated crown (based on the left fourteenth and right third teeth; Fig. 2F). The tooth rows form sinusoidal waves, and at the level of the fifteenth tooth, the maxillae expand posteriorly. In ventral view, there is an acute anterior process, extended to the level of the fourth premaxillary tooth, close to the incisive foramen. The anterior teeth have a large interalveolar space, whereas the posterior alveoli are close to each other. Notches for dentary teeth follow the tooth rows medially, from the eighth tooth to the end of the maxillae. The maxillae are well sutured in the midline. Some small foramina are located in ventral view, medially to the notches for dentary teeth.

Dentition: Alveolar proximodistal diameters vary between 2.6 mm (fifth premaxillary tooth) and 6.3 mm (fourth premaxillary tooth). The maximum interalveolar space is 5.1 mm, between the first and the second maxillary teeth. The teeth have a smooth root and carinated crown, forming ridges (Fig. 2F). The last maxillary alveoli are lingolabially compressed, oriented parallel with the longitudinal axis of the rostrum. However, all the preserved teeth are circular to subcircular in cross section. No teeth show constriction at the base of the crown, and the width of the root is nearly equal to the width of the crown. No premaxillary alveoli are inturned, as in Sarcosuchus and Terminonaris (Sereno et al., 2001). All dentary teeth occlude lingual to maxillary teeth, as suggested by the presence of notches in the premaxillae and the maxillae for occlusion of the dentary teeth. The tooth margins are slightly higher than the medial portion of the palate.

Mandible: Only a post-symphysial dentary fragment was preserved, probably from the right ramus, bearing three incomplete teeth (Fig. 2G–I). The ornamentation is formed by shallow grooves. The alveolar edges are evaginated, forming discrete evaginations at each alveoli, covering the base of the teeth. All alveoli lie in a 30° angle, postero-anteriorly. As in the maxilla, the dentary teeth have a smooth root and a carinated crown. In lingual view, a thin sheet of the splenial was preserved, forming the ventral edge of a reduced Meckelian groove.

Bone armour: Only one osteoderm was recovered associated with Meridiosaurus remains, from the caudal armour (Fig. 2J). The osteoderm is strongly ornamented, with ridges, grooves, and punctuations, and is not keeled. It is slightly convex dorsally, and it bears an anteriorly depressed overlap margin for articulation with the preceding osteoderm. It is very similar to the caudal osteoderm of Sarcosuchus (Sereno et al., 2001).

Remarks on size and weight: Usually, the ratio between the preorbital length and the total skull length is used in longirostrine crocodylomorphs (e.g. Hua et al., 2007). However, this measure cannot be made for Meridiosaurus. Elosuchus have a ratio between the length of the tip of the snout to the last maxillary tooth, and the total skull length equal to 68%. There is little variation in this percentage among other pholidosaurids, e.g. 65% for Sarcosuchus and 70% for Terminonaris. Considering the last preserved maxillary tooth of Meridiosaurus as its last tooth, we can suppose a skull length of 40 cm. This value is the minimum size of the skull, but it is possible that more teeth were present posterior to the last preserved tooth. Plotting this size in the regression formulae of Sereno et al. (2001), the body length should vary between 2.3 and 2.8 m, which would make it the smallest know pholidosaurid. Using the regression formulae of Farlow et al. (2005), Meridiosaurus weighed between 45 (2.3 m body length) and 85 kg (2.8 m body length). Nothing can be inferred about the age of the specimen.

DISCUSSION

Pholidosauridae is well supported by eight unambiguous synapomorphies. However, some are homoplastic and are shared with other neosuchian crocodylomorphs, or can vary inside the group. The distance between the tip of the snout and the anteriormost position of the premaxilla–maxilla suture in dorsal view is longer than the distance between this and the posterodorsal extremity of the premaxilla in Elosuchus, differing from all other pholidosaurids that have this feature preserved. This autapomorphy may be associated with the anterior elongation of the nasal that borders the external naris in this taxon. In pholidosaurids, the maximal width of the premaxillae is more expanded than the maximal width of the rostrum at the level of the fourth or fifth alveoli, as well as in Gavialis gangeticus (Gmelin, 1789) and some teleosaurids (Jouve, 2009). The medial margin of the orbit in dorsal view is formed mostly by the prefrontal, and the frontal is excluded or participates only slightly, as in Goniopholis simus Owen, 1878, Metriorhyncus superciliosus (Blainville, 1853), Dakosaurus andiniensis Vignaud & Gasparini, 1996, ‘Teleidosaurusgaudry Collot, 1905, and Chenanisuchus (Salisbury et al., 1999; Jouve, Bouya & Amaghzaz, 2005; Jouve, 2009; Pol & Gasparini, 2009).

All known pholidosaurids possess all the diagnostic features, expect when not preserved. Nevertheless, there are features that are not included in the diagnosis because of ambiguity (either ACCTRAN or DELTRAN optimizations) or primitivity (simplesiomorphies), but in fact they are useful for the identification and differentiation between Pholidosauridae and other longirostrine groups, particularly Thalattosuchia and Dyrosauridae. The supratemporal fenestrae are relatively short, but are still longer than the orbits, the basioccipital lacks well-developed bilateral tuberosities, and the quadrates are ornamented in the base. Pholidosaurids and Teleosaurus share five premaxillary teeth (Jouve, 2009). Pholidosaurids have a broad sculpted region separating the supratemporal fenestrae, as well as Teleosaurus cadomensis (Lamouroux, 1820) (Jouve, 2009) and Chenanisuchus (Jouve et al., 2005). Dyrosaurids and pholidosaurids share a squamosal longer than the postorbital. In Terminonaris, the squamosal is about as long as the postorbital (Wu et al., 2001).

When compared with other longirostrine groups – Thalattosuchia and Dyrosauridae – several characters exclude Meridiosauris vallisparadisi from them. It differs from Thalattosuchia in characters that include the heavy external ornamentation, the presence of a strong lateral expansion of the premaxilla, the presence of five premaxillary teeth, the sinusoidal premaxilla–maxilla suture in ventral view, the sinusoidal contour of the snout in dorsal and lateral views, and the evaginated maxillary alveolar edges. Meridiosaurus differs from dyrosauridae in the presence of five premaxillary teeth rather than four (Barbosa, Alexander & Viana, 2008), the expanded premaxilla, the anterolateral position of the last premaxillary tooth, the absence of the nasal–premaxilla contact, and the sinusoidal contour of snout in dorsal and lateral views. Meridiosaurus vallisparadisi is diagnosed as a Pholidosauridae with the presence of: (1) a deep ventral edge of premaxilla in respect to the ventral edge of maxilla in lateral view; (2) an expanded premaxilla; (3) the anterolateral position of the fifth premaxillary tooth; (4) the maximal width of premaxillae is wider than the maximal width of the rostrum at the level of the fourth or fifth alveoli; and (5) the distance between the tip of the snout and the anteriormost position of the premaxilla–maxilla suture in dorsal view is smaller than the distance of that and the posterodorsal extremity of the premaxilla. Meridiosaurus vallisparadisi differs from any other pholidosaurid in the absence of a premaxilla–nasal contact in dorsal view, an autapomorphic feature for this taxon. Interestingly, Kälin (1955) illustrated a Pholidosaurus schaumburgensis skull with no premaxilla–nasal contact. Andrews (1913) commented that the Pholidosaurus purbeckensis nasal anterior process ‘probably’ just reaches the posterior process of the premaxilla. However, Köken (1887) illustrated a skull of Pholidosaurus schaumburgensis with clear premaxilla–nasal contact. This feature seems to vary among Pholidosaurus species and specimens. Even if this condition is confirmed for Pholidosaurus, Meridiosaurus would still be differentiated from Pholidosaurus in the presence of the sinusoidal contour of the snout in dorsal and lateral views, the large notch on ventral edge of the snout at premaxillae–maxilla contact, the sinusoidal premaxillae–maxilla suture in palatal view, posteromedially directed on its lateral half and anteromedially directed along its medial region, and the arched orientation of the premaxillary tooth row.

PHYLOGENETIC ANALYSIS

To test the phylogenetic relationships of Meridiosaurus vallisparadisi, a comprehensive cladistic analysis was performed. The analysis presented herein also has the objective to test the monophyly of pholidosaurids. The phylogenetic analysis is based on an extension of the data matrix of Pol & Gasparini (2009). Seven characters and three new taxa were added, and the coding for some taxa were modified, based on recent data or on a different interpretation (see Appendix 1–3). Thus, the total data set is based on 62 taxa and 264 morphological characters. Six pholidosaurids are included in the analysis (Fig. 3): Elosuchus cherifiensis (Lavocat, 1955), Meridiosaurus vallisparadisi, Oceanosuchus boecenis Hua et al., 2007, Pholidosaurus purbeckensis, Sarsocusuchus imperator, and Terminonaris robusta.

Figure 3.

Pholidosaurids included in the phylogenetic analysis, and their relationships. Scale bars: 10 cm, except for Meridiosaurus (5 cm).

The phylogenetic data set was analysed with equally weighted parsimony using TNT 1.1 (Goloboff et al., 2008), with 1000 heuristic tree search replicates plus tree bisection and reconnection (TBR) branch swapping, and holding ten trees per replicate. Zero-length branches were collapsed if they lacked support (rule 1 of Coddington & Scharff, 1994). This analysis resulted in a single most parsimonious tree of 910 steps (consistency index, CI = 0.35; retention index, RI = 0.70).

The most parsimonious hypothesis (Fig. 4) shows the monophyly of Pholidosauridae, supported by five unambiguous and eight ambiguous synapomorphies (see Appendix 4). The main reason for the great number of ambiguous synapomorphies is the high degree of missing data among pholidosaurids. Two main clades were formed, one grouping Pholidosaurus as the sister taxon of Sarcosuchus and Terminonaris, and the second grouping Oceanosuchus as the sister taxon of Elosuchus and Meridiosaurus. Figure 4 shows the phylogenetic relationships of Pholidosauridae, calibrated on the temporal scale. Non-pholidosaurid taxa follow the topology as described in Pol & Gasparini (2009).

Figure 4.

Temporally calibrated cladogram showing the phylogenetic relationships of Pholidosauridae. The ghost lineages are in grey. 1, temporal range based on Sarcosuchus hartii. 2, temporal range based on two putative pholidosaurids, Anglosuchus and Crocodilaemus. First appearances based on: Dyrosauridae, Buffetaut & Lauverjat (1978) and Buffetaut, Bussert & Brinkmann (1990); Thalattosuchia, Buffetaut et al. (1981); other neosuchians, Tykoski et al. (2002; Calsoyasuchus valliceps). Stratigraphic chart based on Ogg, Ogg & Gradstein (2008).

PALEOBIOGEOGRAPHY

Pholidosaurids were longirostrine crocodylomorphs adapted to aquatic environments, but without as many aquatic adaptations as Thalattosuchians and Dyrosaurids (Buffetaut, 1982; Hua & Buffetaut, 1997; Hua, 2008). In spite of the longirostrine proportions, the relatively large limbs suggest the possibility of ambulatory behaviour (Watson, 1911). Pholidosaurs inhabited three different types of aquatic ecosystem. Terminonaris and Oceanosuchus were probably marine forms (Hua et al., 2007; Shimada & Parris, 2007), whereas the well-known species Pholidosaurus and Sarcosuchus, along with Elosuchus and Meridiosaurus, where freshwater forms. However, the first pholidosaurids were probably adapted to live in a mixed environment. Anglosuchus was recovered from the English Great Oolites limestones of Bathonian age (Ziegler, 1990), interpreted as a mixing zone between freshwater and marine waters (McLimans & Videtich, 1989), and Crocodilaemus from the French Cerin Lagerstätte of Kimmeridgian age, interpreted as a near-shore lagoon with clear marine influence (Gaillard et al., 2006). Even though they were not true marine forms, these two species had at least the ability to live in, or at least withstand, saltwater ecosystems. This ability may be the main factor for the dispersal events in the biogeographic history of the group.

Although the phylogenetic analysis presented here has weak support on the internal nodes of Pholidosauridae, and its fossil record is fairly incomplete, some considerations can be stated about its geographical distribution (Fig. 5). The paleobiogeographical history of Pholidosauridae shows wide temporal lapses and sparse remains. Given the phylogeny presented here (Fig. 4), there is a long ghost lineage through the Toarcian–Bajocian (c. 15 Myr). The oldest record of the group is Anglosuchus, from the Bathonian of England, and Crocodilaemus, from the Kimmeridgian of France (Mook, 1942; Steel, 1973). It suggests the group, or at least this lineage, originated in Europe during the Middle Jurassic. This hypothesis is coherent with the biogeographical history of a closely related group, the thalattosuchians. The oldest record of teleosaurids are also from Europe (Buffetaut, Termier & Termier, 1981). In this scheme, the biogeographical origin of the dyrosaurids may be related to the European origin of pholidosaurids. However, Dyrosauridae has a ghost lineage of at least 65 Myr (this work), without record from the Middle Jurassic to the Early Late Cretaceous. The known dyrosaurid lineage, from Cenomanian (Buffetaut & Lauverjat, 1978) to Early Eocene (Buffetaut, 1978a–c), originated in northern Africa and then dispersed to the south, following two possible dispersal routes (Barbosa et al., 2008).

Figure 5.

Paleogeographic map of the Late Jurassic (modified from Paleogeographic Globes available at http://jan.ucc.nau.edu/~rcb7/globehighres.html) indicating the pholidosaurid localities and dispersion routes. See text for explanation. Legend: 1, Pholidosaurus; 2, Terminonaris; 3, Sarcosuchus; 4, Oceanosuchus; 5, Elosuchus; 6, Meridiosaurus.

After the Middle–Late Jurassic endemism in Europe, Pholidosauridae may have dispersed in a relatively short period of time. During the Late Jurassic–Early Cretaceous, the group may have dispersed to Africa and South America in two independent events: the first, a dispersion of the Sarcosuchus lineage to Africa and South America (Fig. 5, black dashed line); and the second, a dispersion of the Elosuchus–Meridiosaurus lineage to Africa and southern South America (Fig. 5, dotted line). After the break-up of Gondwana, the South American lineages no longer persisted, as there is no confirmed Late Cretaceous record in that continent (Gasparini, 1996; Fortier & Schultz, 2009). In Europe, the group remained until the Berriasian (Pholidosaurus; Salisbury, 2002), reappeared during the Early Cenomanian (Oceanosuchus; Hua et al., 2007), and had completely disappeared by the Late Cenomanian (Terminonaris; Buffetaut & Wellnhofer, 1980).

The group may have dispersed to South America during the Oxfordian–Kimmeridgian, or even earlier (Toarcian), considering the ghost lineages involved. However, there is no record in Africa until the appearance of Sarcosuchus in Aptian–Albian (Buffetaut & Taquet, 1977). The group possibly inhabited Africa during these 30 Myr, considering the Sarcosuchus from the Neocomian of Brazil (Buffetaut & Taquet, 1977), but no trace remains. The same phenomenon occurred in the Elosuchus lineage, showing a ghost lineage from the Kimmeridgian to the Late Albian (this work) of approximately 50 Myr.

Another dispersal event occurred in the Terminonaris lineage (Fig. 5, white dashed line). Terminonaris is assumed to have been an inhabitant of marginal marine environments (Shimada & Parris, 2007), thus the dispersal through the narrow Atlantic Ocean was possible. The genus first appeared in the Late Cenomanian from Germany (Buffetaut & Wellnhofer, 1980), after a long ghost lineage since the earliest record of Sarcosuchus during the Berriasian (see Fig. 4), and then dispersed to North America sometime in the Late Conomanian or Early Turonian. All the specimens are from the Turonian, recorded in USA (Osborn, 1904; Mook, 1934; Erickson, 1969; Shimada & Parris, 2007) and Canada (Wu et al., 2001). The group had a short but important history in North America, as Pholidosauridae had its last record there.

CONCLUSION

Meridiosaurus vallisparadisi Mones, 1980 is a valid taxon and a member of Pholidosauridae, from the Late Jurassic–Early Cretaceous Tacuarembó Formation, Uruguay. It represents one of the earliest species and the southernmost record of the group. Also, it is the most complete record of a pholidosaurid from South America.

The phylogenetic hypothesis herein presented confirm the monophyly of Pholidosauridae, redefined here as a stem-based group name including Pholidosaurus schaumburgensis and all taxa closer to it than to Dyrosaurus phosphaticus or Pelagosaurus typus, and is diagnosed by several characteristics. However, the relationships among members of Pholidosauridae are weakly supported because of a high degree of missing data. Certainly, this problem requires further study, such as increasing taxon and character sampling. Putative pholidosaurids, like Anglosuchus and Crocodilaemus, strongly need a reappraisal of their anatomy in order to have phylogenetic relationships recovered. The genus Pholidosaurus needs a systematic revision, as regards to the taxonomic status of P. schaumburgensis and P. meyeri. Nevertheless, some paleobiogeographical considerations can be stated.

Pholidosaridae probably originated in Europe during the Middle Jurassic, and remained only there until the Tithonian–Oxfordian, when two dispersal events probably occurred to Africa and South America. The group possibly inhabited Africa during the Neocomian, but no trace was left. The record in Africa ranges from Late Aptian to Early Cenomanian. In Europe, the group remained until the Berriasian, reappeared during the Early Cenomanian, and completely disappeared in the Late Cenomanian. Another dispersal event occurred from Europe to North America sometime in the Late Cenomanian or Early Turonian, a time when Pholidosauridae disappeared. There is no specific explanation for the Early Creataceous ghost lineage among Dyrosauridae and Pholidosauridae. For dyrosaurids, the temporal gap is even longer. The reason that could be stated is the incompleteness of the fossil record or an incorrect phylogenetic hypothesis.

ACKNOWLEDGEMENTS

The authors thank Hans Larsson, Diego Pol, and two anonymous reviewers for many suggestions that improved the article, and Martín Ubilla (Departamento de Paleontología, Faculdad de Ciencias, Montevideo) for collection support. For access to and assistance with comparative collections, we thank Carl Mehling (American Museum of Natural History), Richard Butler and Oliver Rauhut (Bayerische Staatssammlung für Paläontologie und Geologie), Peter Woodward (Dorset County Museum), Lorna Steel (Natural History Museum) and Rainer Schoch (Staatliches Museum für Naturkunde Stuttgart). Financial support for this research was provided by ANII-Uruguay (project number FCE2007-110) and the Jurassic Foundation, for partial fieldwork support (granted to DP), and CNPq (Proc. 490340/2006–7 – PROSUL, granted to CS). DF also thanks CNPq and CAPES for a PhD scholarship, and the University of Iowa for lending its computational and bibliographical resources.

Appendices

APPENDIX 1

Institutional abbreviations and list of reference pholidosauridae used in the phylogenetic analysis

Collection numbers of the specimens that were revised first-hand by the authors are added before the bibliographic reference. Six pholidosaurids have been considered in the present work, included in the data matrix from Pol & Gasparini (2009).

AMNH, American Museum of Natural History, New York, USA; BSP, Bayerische Staatssammlung für Paläontologie und Geologie, Münich, Germany; DORCM, Dorset County Museum, Dorchester, UK; FC-DPV, Faculdad de Ciencias, Departamento de Paleontología de Vertebrados, Montevideo, Uruguay; MNHN, Museum National d'Histoire Naturelle, Paris, France; NHM, Natural History Museum, London, UK; SMNS, Staatliches Museum für Naturkunde Stuttgart, Stuttgart, Germany.

Elosuchus cherifiensis: Lavocat (1955); Lapparent de Broin (2002).

Meridiosaurus vallisparadisi: FC-DPV-2322 (formerly SPV-FHC-27-II-78–1); Mones (1980).

Oceanosuchus boecenis: Hua et al. (2007); Lepage et al. (2008).

Pholidosaurus schaumburgensis: DORCM G97; NHM R3414; NHM R3956; NHM 28432; NHM 28966; Owen (1878); Koken (1887; for P. meyeri and P. schaumburgensis); Mansel-Pleydell (1888); Watson (1911); Andrews (1913); Salisbury (2002).

Sarcosuchus imperator: MNHN uncatalogued cast of the holotype; Taquet (1976); Sereno et al. (2001).

Terminonaris robusta: AMNH 5849, AMNH 5850; Osborn (1904); Mook (1933, 1934); Sereno et al. (2001); Wu et al. (2001).

Steneosaurus bollencis: AMNH 5138, BSP 1890.I.510, BSP 1945.XV.1, BSP 1949.XV.1, BSP 1972.V.11, BSP 1973.VII.592, SMNS 115, SMNS 4554, SMNS 9427, SMNS 9428, SMNS 15951, SMNS 16848, SMNS 17484, SMNS 18878, SMNS 20280, SMNS 20282, SMNS 20283, SMNS 53422.

Pelagosaurus typus: NHM R32599, BSP 1925.I.34, BSP 1990.VIII.68, SMNS 8666, SMNS 80066, Pierce & Benton 2006.

APPENDIX 2

List of characters employed in the phylogenetic analysis

The following list presents the characters added in the original data matrix from Pol & Gasparini (2009). No modification was made to the original list. The additional characters are listed here and their respective sources are cited along with the character number of the original publication. These characters were set as non-additive.

Character 258 (modified from Jouve, 2004; character 178): Anterior process of the frontal extending far anteriorly, or slightly anteriorly, at the same level (0) or posteriorly (1) to the anterior margin of the orbits.

Character 259 (modified from Jouve, 2004; character 197): Posterior surface of basioccipital ventral to the occipital condyle short and gently curved, lower than the occipital condyle (0), or long, flat, and nearly vertical, at least as high as occipital condyle (1).

Character 260 (Jouve, 2009; character 326): Medial margin of the orbit in dorsal view: formed mostly by the frontal (0), or mostly by the prefrontal, the frontal is excluded or participates only slightly (1).

Character 261 (Jouve, 2009; character 341): Maximal width of premaxillae less (0), or more (1) expanded than the maximal width of the rostrum at the level of alveoli 4 or 5.

Character 262 (Wu et al., 2001; character 114): Maxilla terminating behind anterior margin of orbit (0), or anterior to orbit (1).

Character 263 (Jouve, 2004; character 205): Distance between the tip of the snout and the anteriomost position of the premaxilla–maxilla suture in dorsal view is larger (0), or smaller (1) than the distance between the anteriormost position of premaxilla–maxilla suture in dorsal view and the posterodorsal extremity of the premaxilla.

Character 264 (modified from Jouve, 2004; character 3): Anterodorsal margin of the external nares with small dorsal projection at the level of the suture between right and left premaxillae (0), or without premaxillary dorsal projection (1).

APPENDIX 3

List of character scores

Coding for characters 258–264 of taxa from the original data set (Pol & Gasparini, 2009), and for all 263 characters of the three species included (Elosuchus cherifiensis, Meridiosaurus vallisparadisi, and Oceanosuchus boecensis) and five modified taxa (Pholidosaurus purbeckensis, Sarcosuchus hartii, Terminonaris robusta, Steneosaurus bollensis and Pelagosaurus typus).

Gracilisuchus stipanicicorum???????

Terrestrisuchus gracilis???????

Dibothrosuchus elaphros 1010000

Protosuchus richardsoni 1000000

Hemiprotosuchus leali?1??0?0

Orthosuchus stormbergi 1000000

Kayenta form???0000

Edentosuchus tienshanensis 1?100??

Zaraasuchus shepardi???????

Gobiosuchus kielanae 11?0000

Sichuanosuchus shuhanensis 1?10000

Shantungosuchus hangjinensis?1?00??

Zosuchus davidsoni 110000?

Fruita form???????

Hsisosuchus chungkingensis 000?1??

Notosuchus terrestris 1100001

Comahuesuchus brachybuccalis 1000001

Mariliasuchus amarali 1?000??

Uruguaysuchus aznarezi 1?00001

Chimaeresuchus paradoxus???0?01

Malawisuchus mwakayasyunguti 1?1000?

Candidodon itapecurense???????

Simosuchus clarki 1100000

Sphagesaurus huenei???0001

Bretesuchus bonapartei???0000

Baurusuchus pachecoi???????

Iberosuchus macrodon???????

Lybicosuchus brevirostris?1?00?0

Araripesuchus gomesii 1100000

Araripesuchus patagonicus 110?0??

Araripesuchus buitreraensis???????

Araripesuchus wegeneri???????

Lomasuchus palpebrosus 11?000?

Peirosaurus torminni???0000

Theriosuchus pusillus 0?00001

Alligatorium???????

Metriorhynchus superciliosus 1010000

Metriorhynchus casamiquelai???????

Geosaurus araucanensis 1000000

Geosaurus suevicus???????

Dakosaurus maximus 1?00000

Dakosaurus andiniensis 0010000

Rhabdognathus 010?0??

Sokotosuchus ianwilsoni???????

Dyrosaurus phosphaticus 0100000

Hyposaurus rogersii???????

Goniopholis 1110000

Eutretauranosuchus delfsi 0?0?0??

Bernissartia fagessi 0?00001

Hylaeochampsa vectiana 110?0??

Borealosuchus formidabilis 010000?

Gavialis gangeticus 0001001

Crocodylus niloticus 0100001

Alligator mississippiensis 0100000

Pholidosaurus purbeckensis

212?121101??1??1110[01]10011?10010001012110101?01112?11?1010?10?100?131[12]???0???1?0????1?2???0??0??200?????????0??0??????0?1?1??10110?????0?001001??1???00??????000?0010102?100????0?0000?0???000?00?10?0?10??01?100?0010???0??????0??00???0?102?1011?1???0?0001?0?00001101?

Sarcosuchus imperator

203?12110100101?100010011001010001012?10101[01]01?12?1??10100?0?100?131213??000210101?112????[01]00?1200?00??010[01]0??00[01]001?0?101??121100??0000001001011???00???110?0[02]11010[01]022100?0000?000000?000000?00?01001000?1?100?0010?00000000?0?0100000?100011110100?0?000100?101011111

Terminonaris robusta

202?[01]2?1010010?11??01001??01010001012?1010[01]1??????11?1010??0??0??13[01][12]13?000?2100011112??00000?1200?10??0?010210?1001001101??12010??0??0?0010???11???000011100?0?1?101[01]2[12]10?????0?0000?0?0000?0001?0?00?0?0?11100?00?0??00???00?0?0100?00?1020111101?0?0?00?100??00011011

Meridiosaurus vallisparadisi

2?2?121111??11???????????????????????????????????????????????????1???????????12??????????????????????????010???????????1??0?11????????0?0010?????????????????????010???????????0?1????11???0??????????????????0??????????????????00???0????20?001??????????1????????1?11

Elosuchus cherifiensis

203?12111100001?1??010????11????01012???????????????????0??????????1????????112?????????????????0????????0????0??????0???1???010?????????????0?11???????????????0?1??02?0????????1????1???????????????????????????????????????????0????????2??001??????????1?????1011101

Oceanosuchus boecensis

202?12110100101????11001???101??01012???????????????????0??????????1????????1?00???1?????????????????????0????0??????0???1???110????????????????????????????????0?1??0???????????0????0???????????????????????????????????????????0????????2??001??????????1?????1011111

Steneosaurus bollensis

[02]02?[01]111?10011020100[01]00010000000110021101000?0011011?1001011?1?00120103?000?20000110111100000?120001[01]1?011?02100[01]001001101??10?10000??0?0010?1?00??00000110000010000110?0001001000200?0?000000000101[12]01000[01]1100010010?0000000000?0010?00?100000000?1000010?0[01]01001001000

Pelagosaurus typus

202?[01]111?1001102010[01][01]00000000000[01]1002110100000011011?1001001?10001201?300000200001101?1?00000012000111?011002100???101?101??1??10000??00001010100??[01]00???100000??0001102000100?000200?0??0?0?00001011010000110000001??0000000??0???10?00?10[01]00000021000[01]100110?00100?000

APPENDIX 4

List of apomorphies

The apomorphy list is provided here for Pholidosauridae and its internal nodes only. Legend: italicized, ACCTRAN; underlined, DELTRAN; bold, unambiguous transformations.

Pholidosauridae

33(0), 57(0), 68(1), 78(1), 78(1), 106(0), 144(1), 145(1), 163(1), 241(1), 259(0), 260(1), 261(1), 263(1), 264(1)

Pholidosaurus + Sarcosuchus, Terminonaris

128(1), 142(1), 169(1), 240(1)

Pholidosaurus

2(1), 18(1), 28(0), 126(0), 256(0)

Sarcosuchus + Terminonaris

27(0), 77(2), 78(1), 126(2), 155(1), 161(1), 227(1), 239(1)

Sarcosuchus

3(3), 80(1), 100(0), 236(0), 256(1), 258(1), 262(1)

Terminonaris

100(1), 127(0), 193(1)

Oceanosuchus + Elosuchus, Meridiosaurus

N: 128(0), 142(0), 258(1), 262(1)

Oceanosuchus

20(1), 126(1)

Elosuchus + Meridiosaurus

9(1), 79(2), 178(1), 183(1)

Elosuchus

3(3), 13(0), 126 (0), 263(0)

Meridiosaurus

14(1), 126(1)

Ancillary