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1 Paläontol Z (2011) 85:67 82 DOI /s RESEARCH PAPER New information about Irajatherium hernandezi Martinelli, Bonaparte, Schultz & Rubert 2005 (Eucynodontia, Tritheledontidae) from the upper triassic (Caturrita Formation, Paraná Basin) of Brazil Téo Veiga de Oliveira Agustín G. Martinelli Marina Bento Soares Received: 14 April 2010 / Accepted: 15 July 2010 / Published online: 30 July 2010 Ó Springer-Verlag 2010 Abstract In this contribution, new specimens of the tritheledontid eucynodont Irajatherium hernandezi, from the Late Triassic (Caturrita Formation) of southern Brazil, are analyzed. The new material provides significant information about incisor count, canine size and shape, basicranial morphology, and other previously unknown aspects of skull and dentition. A cladistic analysis with inclusion of the new data supports the assignment of Irajatherium to Tritheledontidae, basal to Chalimininae and Pachygenelinae. Previously unknown characters of Irajatherium revealed by the new material include: the presence of three lower incisors; the first lower incisor is enlarged; the presence of large upper and lower canines with deep paracanine fossa on the maxilla; almost complete upper and lower postcanine tooth row with a pattern similar to that of other tritheledontids (e.g. Pachygenelus and Chaliminia); there is a conspicuous crest on the inner surface of the maxilla for the attachment of the inferred maxillary turbinates; partially confluent jugular foramen and fenestra rotunda within the jugular fossa, separated by a finger-like projection of the posterolateral wall of the opisthotic; and hypoglossal T. V. de Oliveira (&) M. B. Soares Departamento de Paleontologia e Estratigrafia, Universidade Federal do Rio Grande do Sul, Instituto de Geociências, Campus do Vale. Avenida Bento Gonçalves, 9500, Bairro Agronomia, Caixa Postal 15001, CEP Porto Alegre, RS, Brazil teovoli@yahoo.com.br M. B. Soares marina.soares@ufrgs.br A. G. Martinelli Centro de Pesquisas Paleontológicas Llewellyn Ivor Price, BR-262, Km 784, Peirópolis, Uberaba, MG, Brazil agustin_martinelli@yahoo.com.ar foramina located outside the jugular fossa. Irajatherium is a key taxon for understanding the early evolution of ictidosaurs, a group of cynodonts closely related to mammaliaforms, during the cynodont mammal transition from the Late Triassic to Early Jurassic. Keywords Cynodontia Tritheledontidae Ictidosauria Irajatherium Triassic Caturrita Formation Norian Kurzfassung In dieser Arbeit werden neue Exemplare des tritheledontiden Eucynodonten Irajatherium hernandezi Martinelli et al aus der Späten Trias (Caturrita Formation) vorgestellt. Das neue Material enthüllt wichtige Informationen zur Anzahl der Incisiven, der Grösse und Form der Canini, der Morphologie des Basicraniums und anderen Aspekte von Schädel und Bezahnung. Eine cladistische Analyse mit Berücksichtigung der neuen Daten bestätigt die Zuordnung von Irajatherium zu den Tritheledontidae, welche basal der Chalimininae und Pachygenelinae stehen. Unter den vorher unbekannten Merkmale von Irajatherium sind drei untere Incisiven mit einem vergrößerten ersten Incisivus, untere und obere Canini mit einer tiefen Paracaninus-Fossa am Maxillare; eine fast komplette obere und untere postcanine Zahnreihe mit einem Bezahnungsmuster vergleichbar mit dem anderer Tritheledontiden (z.b. Pachygenelus und Chaliminia); eine auffällige, als Ansatzfläche für die Turbinalia dienende Crista an der Innenseite of the Maxilla; partiell vereinigte Jugular-Foramina und eine Fenestra rotunda in der Jugular-fossa, welche durch einen fingerartigen Vorsprung der posterolateralen Wandung des Opistothicums voneinander getrennt werden; sowie außerhalb der Jugular-Fossa liegene hypoglossale Foramina. Irajatherium ist ein Schlüsseltaxon zum Verständnis der frühen Evolution der Ictidosauriden, eine mit den Mammaliformen nahe

2 68 T. V. de Oliveira et al. verwandte Cynodontier-Gruppe aus der oberen Trias und dem unteren Jura. Schlüsselwörter Cynodontia Tritheledontidae Ictidosauria Irajatherium Trias Caturritaformation Norian Abbreviation UFRGS PV-T Introduction Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil, Paleovertebrate Collection. Non-mammaliaform probainognathian cynodonts are one of the most commom faunal elements of the Late Triassic Caturrita Formation at the localities of Faxinal do Soturno and Candelaria, Rio Grande do Sul State, southern Brazil (Fig. 1a). In these localities, probainognathians include small taxa with an average size of an extant mice and are represented by several well-preserved specimens. These cynodont fossils discovered in recent years have provided new important data on the diversity of advanced nonmammaliaform cynodonts (hereafter called cynodonts) and on sister-group relationships with mammaliaforms (Bonaparte et al. 2003, 2005; Martinelli et al. 2005; Martinelli and Rougier 2007; Martinelli and Bonaparte 2008). Among the recovered cynodonts, Riograndia guaibensis Bonaparte et al (Soares et al. 2005) and Irajatherium hernandezi Martinelli et al (Oliveira et al. 2008) are two plesiomorphic ictidosaurs (sensu Martinelli and Rougier 2007) based on relatively well preserved specimens. Pachygenelus monus Watson 1913, the best known and studied ictidosaur taxon, from the Early Jurassic of the South African Karoo, was often interpreted as the sister-taxon of the Mammaliaformes (Hopson and Barghusen 1986; Shubin et al. 1991; Crompton and Luo 1993; Luo 1994; Luo and Crompton 1994; Hopson and Kitching 2001; Luo et al. 2002). At present, Ictidosauria (defined as the clade including the most recent common ancestor of Riograndia guaibensis and Pachygenelus monus, and all its descendants; Martinelli and Rougier 2007), comprises Riograndia guaibensis (Bonaparte et al. 2001; Soares 2004), Irajatherium hernandezi (Martinelli et al. 2005), Chaliminia musteloides Bonaparte 1980 (Martinelli and Rougier 2007), Elliotherium kersteni Sidor and Hancox 2006, Pachygenelus monus (Watson 1913; Gow 1980, 2001), Diarthrognathus broomi Crompton 1958 (Crompton 1963a; Gow 1994), and Tritheledon riconoi Broom 1912 (Gow 1980). As a whole, Ictidosauria is a very important clade of cynodonts whose members have a suite of characters that shed light on the acquisition of mammalian features during the cynodont mammal transition. In this contribution, new specimens of Irajatherium hernandezi are described. These materials provide significant information about incisor count, canine size and shape, basicranial morphology, and several aspects of the skull and dentition. Geological setting and biostratigraphic comments All the known materials of Irajatherium hernandezi were recovered in outcrops of the Late Triassic Caturrita Formation (Fig. 1b, c). This unit is included in the upper portion of the Santa Maria 2 Sequence (from the Santa Maria Supersequence) (Fig. 1d). Because this unit can be difficult to distinguish from the underlying Santa Maria Formation, some authors argued that it should not be regarded as a formal stratigraphic unit or a formation (Zerfass et al. 2003). Nonetheless, despite the stratigraphic controversy, we prefer to use the Caturrita Formation in this contribution in order to distinguish it from the typical Santa Maria Formation that yields an older faunal association (Schultz and Soares 2006). The Caturrita Formation is characterized by sandstone lenses with small-scaled cross-bedding, which are interpreted as ribbon fluvial channels. Rhytmites and sandstone bodies with sigmoidal, climbing cross-bedding also occur occasionally (Zerfass et al. 2003; Martinelli et al. 2005) (Fig. 1b d). The Irajatherium holotype was collected in the Sesmaria do Pinhal locality, near Candelária city (Martinelli et al. 2005) (Fig. 1a b), whereas most of the new material was collected in the Linha São Luís locality, near Faxinal do Soturno city (Fig. 1a, c), with an additional specimen coming from Sesmaria do Pinhal locality. There are several faunal components shared between both localities, including the ictidosaur Riograndia (Bonaparte et al. 2001), the advanced probainognathians Brasilodon and Brasilitherium (Bonaparte et al. 2003, 2005), the sphenodontid Clevosaurus (Bonaparte and Sues 2006; Arantes et al. 2009), and the basal saurischian dinosaur Guaibasaurus (Bonaparte et al. 1999, 2007). The taxa unique to the Candelária region are the dicynodont Jachaleria (Araújo and Gonzaga 1980), an undetermined phytosaur (Kischlat and Lucas 2003), and an undetermined stereospondyl amphibian (Dias-da-Silva et al. 2009). These records, however, do not come from the Sesmaria do Pinhal locality but from a neighboring area. Other records such as the procolophonid Soturnia (Cisneros and Schultz 2003), a probable pterosaur, a lepidosauromorph, and a new unnamed small cynodont (Bonaparte et al. 2008) are, at present, exclusive from the Faxinal do Soturno locality. With the exception of the dinosaur Guaibasaurus,

3 New information about Irajatherium hernandezi 69 Fig. 1 Geographical location and stratigraphy of the study area: a Candelária and Faxinal do Soturno municipalities (arrows); b stratigraphic section of the Sesmaria do Pinhal outcrop (Candelária) (modified from Martinelli et al. 2005); c stratigraphic section of the Linha São Luís outcrop (Faxinal do Soturno) (modified from Bonaparte et al. 2003), with arrows indicating the levels with known vertebrates recovered in Faxinal do Soturno are small to very small-sized specimens. The absence of these small taxa in the Sesmaria do Pinhal locality could be due to low abundance of fossils or simply because of a lack of extensive fieldwork at the Faxinal do Soturno locality. The rich paleovertebrate faunal associated with both localities enabled definition of the biostratigraphic interval as the Mammaliamorph Cenozone that characterizes the Caturrita Formation (Schultz and Soares 2006) (Fig. 1d). Usually, a Carnian age has been attributed to the upper portion of the traditional Santa Maria Formation, because vertebrate fossils (the vertical scales in b and c are in meters); d Sequence stratigraphy of Brazilian Middle and Upper Triassic, with Caturrita Formation gray-colored (modified from Zerfass et al. 2003). Car Carnian, cg conglomerate, cs coarse sand, fs fine sand, Lad Ladinian, m mud, ms medium sand, Nor Norian, Rha Rhaetian of the massive presence of hyperodapedontine rhynchosaurs and the traversodontid cynodont Exaeretodon (Rogers et al. 1993; Oliveira and Schultz 2007). Consequently, the overlaying Caturrita deposits can be regarded as at least Late Carnian to Early Norian in age (Zerfass et al. 2003; Martinelli et al. 2005). This is also supported by its faunal content (Bonaparte et al. 2001, 2003, 2005, 2007; Martinelli et al. 2005). However, new stratigraphic proposals (Muttoni et al. 2004; Furin et al. 2006; Lehrmann et al. 2006; Ovtcharova et al. 2006) extends the Norian to 228 Ma, an age corresponding to the Carnian/Ladinian

4 70 T. V. de Oliveira et al. limit of Gradstein and Ogg (2004). On the other hand, Abdala and Ribeiro (2010) included the Caturrita Formation in the Late Norian Rhaetic age. The authors have justified this interpretation by the sister-group relationship of Irajatherium, from the Caturrita Formation, to the tritheledontids from the Los Colorados Formation in Argentina (e.g. Chaliminia) and the Lower Elliot Formation in South Africa (e.g. Elliotherium), that are considered Late Norian to Rhaetian according to Knoll and Battail (2001) and Knoll (2004) and along with the record of Riograndia which is interpreted by Martinelli and Rougier (2007) as the most basal ictidosaur. Additionally, Abdala and Ribeiro (2010) reinforce this interpretation with the occurrence, in the same deposits, of Brasilitherium, considered the sistergroup of the early Jurassic Mammaliaformes (Bonaparte et al. 2003, 2005; Luo 2007; Martinelli and Rougier 2007), and of Clevosaurus (Bonaparte and Sues 2006), a sphenodontid known from the Rhaetian and Lower Jurassic of England, China, South Africa, and Canada (Wu 1994; Bonaparte and Sues 2006). Systematic paleontology Cynodontia Owen 1861 Eucynodontia Kemp 1982 Probainognathia Hopson 1990 Tritheledontidae Broom 1912 (sensu Martinelli and Rougier 2007) Irajatherium Martinelli, Bonaparte, Schultz and Rubert 2005 Irajatherium hernandezi Martinelli, Bonaparte, Schultz and Rubert 2005 Holotype UFRGS PV-0599-T: fragment of left maxilla with partial dentition; natural cast of an incomplete left dentary with some bone fragments preserved, bearing an anterior postcanine; fragment of a left dentary with two postcanines; left humerus and femur; fragments of two indeterminate long bones (Fig. 2). Additional specimens UFRGS PV-1029-T: cranial fragment of a right dentary, with the canine and five postcanines, one of them incomplete (presented by Bonaparte et al. 2008, and illustrated in Soares and Dornelles 2009). UFRGS PV-1068-T: fragment of left maxilla, with the secondary palatal shelf; a right nasal; fragment of the left prootic and opisthotic; posterior portion of the left dentary with four postcanines; a fragment of a canine; a right humerus; the probable proximal portion of tibia and fibula (presented by Oliveira et al. 2008). UFRGS PV-1167-T: right incomplete maxilla with a very long canine. UFRGS PV-1169-T: right incomplete maxilla, bearing part of the canine. UFRGS PV-1170-T: left dentary fragment with two postcanines. UFRGS PV-1171-T: incomplete left maxilla with part of the canine; cranial portion of a right dentary, including empty alveoli for three incisors, a partial canine, two postcanines and two empty alveoli for postcanines; a fragment of the left dentary with two postcanines; one isolated canine and two isolated postcanines; several undetermined fragments. UFRGS PV-1172-T: distal half of a left humerus. UFRGS PV-1175-T: fragment of left maxilla with incomplete first and second postcanines, the complete third to fifth postcanines, and the anterior portion of the sixth alveolus. Remarks The additional specimens are assigned to the species Irajatherium hernandezi based primarily upon the postcanine morphology (UFRGS PV-1029-T, UFRGS PV T, UFRGS PV-1170-T, UFRGS PV-1171-T, UFRGS PV-1175-T), on the shape and size of the canine and maxilla (UFRGS PV-1167-T, UFRGS PV-1169-T, UFRGS PV-1171-T), and on the similar morphology of the humerus (UFRGS PV-1068-T, UFRGS PV-1172-T). Locality and Horizon Besides the holotype UFRGS PV T, the specimens UFRGS PV-1167-T and UFRGS PV-1175-T are also from the Sesmaria do Pinhal locality (Candelária); the specimens UFRGS PV-1029-T, UFRGS PV-1068-T, UFRGS PV-1169-T, UFRGS PV-1170-T, UFRGS PV-1171-T, and UFRGS PV-1172-T are from the Linha São Luís locality (Faxinal do Soturno). Both localities are located approximately 200 km west to Porto Alegre, Rio Grande do Sul State, Brazil (Fig. 1a). Caturrita Formation,?early-?late Norian (see the section Geological setting and biostratigraphic comments ). Emended diagnosis Small tritheledontid (sensu Martinelli and Rougier 2007) with the following combination of characters: very tall maxillary and mandibular canines, and a deep paracanine fossa placed anteromedially to the upper canine; anterior upper postcanines (PC) buccolingually narrow bearing a narrow main cusp (cusp A) and a small distal accessory cusp (cusp C); central and posterior upper PC with a high and bulbous main cusp and two small distal (cusp C) and mesial (cusp B) accessory cusps placed lingually, differing from Pachygenelus in the absence of the buccal cingulum; three lower incisors, the largest being the first one (shown by its large alveolar size); anterior mandibular postcanines (pc) with simple crown bearing only a main cusp (cusp a) and a distal accessory cusp (cusp c); middle mandibular pc with a very high main cusp and three progressively smaller distal accessory cusps whereas anterior accessory cusps are also present in the most posterior teeth, differing from Pachygenelus by the absence of a lingual cingulum; humerus with deep and narrow bicipital groove in the proximal area and a rough protuberance in the medial margin below the lesser tuberosity (for the teres major muscle attachment); large entepicondylar foramen and greatly reduced ectepicondylar

5 New information about Irajatherium hernandezi 71 Fig. 2 Holotype of Irajatherium hernandezi (UFRGS PV-0599-T). a, b partial left maxilla, with canine and five postcanines preserved, in lateral and palatal views. c, d more distal upper postcanine (sixth), in lingual and occlusal views. e partial left dentary cast (and few bone fragments) with one postcanine, in lateral view. f, g fragment of the left dentary with two postcanines, in lateral and medial views. h left humerus, in anteromedial view. i left femur, in anterior view. The drawings are from Martinelli et al. (2005). The scale bar equals 1 mm in c, d and 10 mm for the other images one; rounded trochlea and capitulum, partially confluent and dislocated towards to the lateral corner of the distal end; medial portion of the distal humerus with large entepicondyle; femur with the greater trochanter located at the level of the head and the lesser trochanter placed on the medial surface of the femoral shaft.

6 72 T. V. de Oliveira et al. Description The new and previously unpublished specimens of Irajatherium will be described and discussed in this section. The holotype UFRGS PV-0599-T was extensively described and illustrated by Martinelli et al. (2005) and the specimen UFRGS PV-1029-T was presented by Bonaparte et al. (2008) and Soares and Dornelles (2009). If necessary we used these for comparison. Snout Maxilla (Fig. 3a g). Of the five new maxillae, only one has associated postcanines (UFRGS PV-1175-T) and only one is well preserved exhibiting additional data (UFRGS PV T). In the specimen UFRGS PV-1068-T most of the maxilla is preserved. In lateral view, the facial portion of the maxilla shows a bulging area that reflects the great development of the canine root. There are four infraorbital foramina of similar size (Fig. 3a). The anterior foramen faces anteriorly and is located at the level of the posterior edge of the canine root. The second foramen opens posteriorly into a groove that is shared by the anterior opening of the third foramen. Both foramina are close to each other and are located above the level of canine root, near the alveolar border. The fourth infraorbital foramen is in a longitudinal line with the first but more posterodorsally placed than the second and third foramina. In contrast, the holotype UFRGS PV-0599-T has only one large infraorbital foramen immediately posterior to the level of the canine alveolus and another foramen above the contact between third and fourth postcanines (Martinelli et al. 2005). The last foramen could not be observed in UFRGS PV-1068-T because this portion of the maxilla is missing. In the preserved portion of the maxilla UFRGS PV-1175-T there is only a large infraorbital foramen above the level of the PC4-PC5 contact. Others foramina could not be observed. Variations in number, size, and distribution of the infraorbital foramina are common in some cynodont taxa (e.g. Kemp 1982; Martinelli et al. 2005). The paracanine fossa is deep and placed anteromedially to the upper canine alveolus. The dorsal margin of the maxilla for contacting the nasal is straight, whereas its anterior edge is irregular due to breakage; the posterior portion of the maxilla is not available in this specimen. The more remarkable feature of the maxilla UFRGS PV T is a very conspicuous crest in its inner surface (Fig. 3b). This crest is the bony base for the maxillary turbinates (Hillenius 1992, 1994; Rodrigues 2005). The palatal portion of the maxilla UFRGS PV-1068-T has a completely developed secondary palatal shelf. Near the transversal fracture of the palate (Fig. 3c) there is a small vascular foramen facing posteriorly. The posterior margin of the secondary palate could not be observed in UFRGS PV-1068-T, but it is possible that the bone was developed far posteriorly. On the palatal portion of the maxilla UFRGS PV-1175-T there is a groove parallel to the tooth row for receiving the lower sectorial postcanines when the jaw was closed (Fig. 3g). Nasal (Fig. 3h j). An isolated right nasal is preserved in the specimen UFRGS PV-1068-T. It is relatively long and narrow with at least three foramina perforating its dorsal surface (Fig. 3h). The anterior foramina face anteriorly whereas the posterior and largest foramen opens backward. Nasal foramina randomly distributed appear in several cynodonts, for example Procynosuchus, Ecteninion, Riograndia (Kemp 1979; Martinez et al. 1996; Soares 2004) and in such mammaliaforms as Morganucodon (Kermack et al. 1981) and Haldanodon (Lillegraven and Krusat 1991). The cross section of the nasal has a rotated H shape, with the dorsal plate united to the ventral one by means of a more or less vertical wall. These two plates delimitate a medial chamber, whereas in the lateral side there is another chamber divided in two portions, the anterior one to receive the premaxilla and septomaxilla and the posterior one for the lacrimal. Between these areas there is a surface probably for a maxillary contact (Fig. 3j). Basicranium Prootic and opisthotic (Fig. 4). The specimen UFRGS PV T includes a fragment of the left basicranial portion of the skull. Unfortunately, the fragment is damaged, so some structures are difficult to observe. In ventral view, the suture between prootic and opisthotic is not observed and it should be placed on the lateral striped area drawn in Fig. 4d. In this view, the fenestra ovalis is not observed because it is covered by its eroded ventral rim. In lateral view, the fenestra ovalis is large and surrounded by a salient ring, less evident in its caudal portion (Fig. 4b), as in Pachygenelus (Wible and Hopson 1993). Medially and slightly posteriorly to the fenestra ovalis is the jugular fossa. Inside the jugular fossa the jugular foramen and the fenestra rotunda are partially separated by a finger-like projection of the posterolateral wall of the fossa (Fig. 4d) similar to the condition of Probainognathus and Massetognathus (Rougier et al. 1992). The area for both the jugular foramen and the fenestra rotunda is relatively large in comparison with other cynodonts. In Riograndia and in the Jurassic Pachygenelus the jugular foramen and the fenestra rotunda (foramen cochleae) are completely separated within the jugular fossa. Because of the poor preservation of this portion of the skull, it cannot be excluded that some unossified bone participates in the separation of these

7 New information about Irajatherium hernandezi 73 Fig. 3 Maxillae and nasal of Irajatherium hernandezi. a c left maxilla UFRGS PV-1068-T, in lateral, medial and palatal views. d right maxilla UFRGS PV-1167-T with the complete canine, in lateral view. e g left maxilla UFRGS PV-1175-T, in lateral, medial and palatal views. h j right nasal UFRGS PV-1068-T, in dorsal, ventral and lateral. Scale bar = 5 mm (for e g) and 10 mm (for the remaining images). A main (central) cusp, B mesial accessory cusp, C distal accessory cusp, ctb crest for maxillary turbinates attachment, gpc groove for lower postcanines, lc lacrimal contact area, mc maxilla contact area, nf nasal foramina, PC1 5 upper postcanines, pcf paracanine fossa, psc premaxilla and septomaxilla contact area, wf wear facet openings. Small foramina which are interpreted as hypoglossal foramina (for cranial nerve XII) are observed: one outside and near the posterior rim of the jugular fossa and the other more posteriorly placed, close to the caudal border of the opisthotic (Fig. 4d). The paroccipital process of the opisthotic is large and probably contacted the missing squamosal laterally. The caudal and ventral surfaces of the paroccipital process are separated by a transversal crest, slightly reflected caudally (Fig. 4d e).

8 74 T. V. de Oliveira et al. Fig. 4 Left prootic and opisthotic of Irajatherium hernandezi (UFRGS PV-1068-T). a lateral view (the arrow indicates the trajectory of the superior ramus of the stapedial artery). b lateroventral view (mainly to show the fenestra ovalis placement). c medial view. d ventral view. e posterior view. Scale bar = 10 mm. al anterior lamina of the prootic, alc alisphenoid contact area, ec probable area In the inner side of the prootic, there are two foramina that could represent the exits of the cranial nerve VIII (Fig. 4c). The medial margin of the prootic probably contacted the basipterygoid process of the basisphenoid, consequently excluding this bone from the margin of the fenestra ovalis (Luo 1994, Luo et al. 1995). The anterior lamina and the lateral flange of the prootic are partially preserved. The lateral surface of the anterior lamina is uniform, except in its anterodorsal corner, where there is a recess probably representing a contact area for the alisphenoid (Fig. 4a b). In this region lies the trigeminal foramen, better observed medially. From the posteroventral corner of the anterior lamina arises a lateral projection that delimitates part of the groove for the superior ramus of the stapedial artery trajectory, with the contribution of the for exoccipital contact, fov fenestra ovalis, jf jugular fossa (including jugular foramen and fenestra rotunda), lf lateral flange of the prootic, pp paroccipital process, ptf posterior opening of the post-temporal foramen, tf trigeminal foramen, VIII probable foramina for the VIII cranial nerve, XII probable hypoglossal foramina, for the XII cranial nerve lateral flange of the prootic and the paroccipital process of the opisthotic (Fig. 4a). In posterior view, there is a notch in the dorsal portion of the opisthotic that probably corresponds to part of the medial and ventral edges of the post-temporal foramen, which should be closed dorsally by the squamosal (Fig. 4e). Lower jaw Several new mandibular fragments are available adding information to the holotype of Irajatherium (Fig. 5). The right dentary UFRGS PV-1071-T clearly shows the presence of an unfused mandibular symphysis (Fig. 5d) and several mental foramina of variable size (Fig. 5c, e). There are five large mental foramina in the ventral surface of the dentary close to the symphyseal line and one large, ovoid-shaped foramen below the first

9 New information about Irajatherium hernandezi 75 Fig. 5 Dentary fragments of Irajatherium hernandezi. a b left dentary UFRGS PV-1068-T, in lateral and medial views. c e right dentary UFRGS PV-1071-T (and fragments of the left dentary), in lateral, medial, and ventral views. f anterior half of right dentary UFRGS PV-1071-T in occlusal and slightly anterior view. Scale bar = 10 mm (except for F, not in scale). ap angular process of the postcanine (Fig. 5e). In this specimen, the three alveoli for incisors are clearly observed (Fig. 5f). The fragment of the dentary of specimen UFRGS PV T shows a rounded and thick angular process just slightly posteriorly projected (Fig. 5a). It is level with the lower edge of the horizontal ramus of the dentary. The masseteric fossa is well developed extending anteriorly on the horizontal ramus, approximately, until the level of the sixth or seventh postcanine (Fig. 5a). The coronoid process is prominent forming an angle of ca. 140 degrees with regard to the alveolar level. This process overlaps buccally the last functional postcanine and the one in eruption (Fig. 5b). Postdentary bones are not known in any specimens. The postdentary trough is prominent and connected anteriorly to the Meckelian groove, which runs horizontally from the symphysis to the postdentary trough without reaching the ventral edge of the horizontal ramus of the dentary (Fig. 5b). dentary, c canine (broken), cp coronoid process of the dentary, et erupting tooth, ia incisor alveolum, ld left dentary fragment, mf masseteric fossa, mg Meckelian groove, pc postcanines (their positions are those inferred in the text), pds postdentary sulcus or trough, sr symphyseal region Dentition Upper dentition (Figs. 3 and 6). Differing from the maxilla of the holotype in which the canine is not fully erupted, the specimen UFRGS PV-1167-T has an extremely large canine, being almost as high as the maxilla (Fig. 3d), indicating specialization towards carnivory in Irajatherium. In other ictidosaurs, for example Riograndia, Chaliminia, and Pachygenelus (Bonaparte et al. 2001; Martinelli and Rougier 2007) the canine is reduced. In this individual the diastema between the canine and the postcanine row is proportionally much longer than in the holotype indicating an older age for the former and the lack of replacement of the anterior postcanines. UFRGS PV-1175-T is the only specimen with new information about the postcanines of Irajatherium (Fig. 3e g). The anterior two alveoli, separated by an acute interdental process, are circular in cross section. The

10 76 T. V. de Oliveira et al. Fig. 6 Reconstruction of the left upper dentition (except incisors) of a fully grown Irajatherium hernandezi, in buccal (a) and lingual (b) views. The postcanines are numbered and the cusps are indicated by the upper case letters (not bold). The canine is based on UFRGS PV-1167-T, postcanines 1, 2 and 6 are based on the holotype, teeth 3 to 5 are based on UFRGS PV-1175-T, and tooth 7 is represented as the sixth one (the exact number of postcanines is unknown). The whole postcanine tooth row length in an adult individual should be ca. 25 mm alveolus of PC1 is slightly smaller than that of PC2. In the holotype, PC1 and PC2 are the smallest, unicuspidated teeth of the row. PC3, similar to that of the holotype specimen, has two bulbous cusps: the mesial cusp (cusp A) is the biggest with the labial surface strongly convex whereas the distal cusp (cusp C) is smaller, separated by a shallow furrow, and located in a higher position than cusp A. Both cusps have the tip slightly curved. The main cusp has a drop-shaped wear facet on the labiodistal surface. PC4 and PC5 (the first damaged and the other absent in the holotype), have three cusps; the central one (cusp A) is highest. In both postcanines, the main cusp is bulbous with a strong convex labial surface, and other two cusps are smaller, with cusp B placed on the mesiolingual margin of the crown and cusp C distal to the main cusp. All cusps have their tips worn away, precluding assessment of the height ratio of the cusps. The morphology of PC4 and PC5 of UFRGS PV-1175-T is similar to that of PC6 of the holotype specimen (Fig. 2c d) which was the basis of assignment of Irajatherium within tritheledontids (Martinelli et al. 2005). As in others probainognathian cynodonts the exact number of postcanines in Irajatherium is usually variable according to the age of the individuals. On the basis of the different size of the holotype (Fig. 2a b) with six postcanines and the other maxilla described here (Fig 3), it is highly probably that larger individuals have a greater number of teeth (perhaps seven), as presented in the tentative reconstruction shown in Fig. 6. This postcanine count matches that presented in Bonaparte et al. (2003) for Pachygenelus (however, some specimens of Pachygenelus have eight postcanines; Gow 1980) and Gow (1980) for Diarthrognathus. Lower dentition (Figs. 5, 7). UFRGS PV-1171-T provides fresh data on incisors which are relevant to understanding ictidosaur interrelationships. This specimen has three alveoli for lower incisors (Fig. 5f). The alveolus for the first incisor is the largest whereas the second and third alveoli decrease progressively in size. According to the shape of the anterior portion of the lower jaw and the alveoli, the first incisor was procumbent whereas the second and third incisors were dorsally oriented. Furthermore, there is no diastema between the last incisor and the canine, whereas the diastema between the canine and the postcanine row is relatively long (Fig. 5c). Although all the specimens, including the holotype (Martinelli et al. 2005) and that presented by Bonaparte et al. (2008), do not preserve a complete lower postcanine tooth row, the postcanine teeth morphology of Irajatherium is well known. Based on all the specimens, the reconstruction of the postcanine row of Irajatherium is shown in Fig. 7. It is probable that a fully grown individual had approximately eight postcanines. This could be argued mainly because of the conditions of two specimens, UFRGS PV-1068-T and UFRGS PV-1171-T. The latter specimen is a fragment of dentary with the first and fourth postcanines preserved and space enough for two more teeth (i.e. until the sixth tooth) (Fig. 5c). In this specimen it is possible to observe the beginning of the masseteric fossa below the level where the sixth postcanine should be

11 New information about Irajatherium hernandezi 77 Fig. 7 Reconstruction of the left lower postcanine dentition of a fully grown Irajatherium hernandezi, in buccal (a) and lingual (b) views. The teeth are numbered and the cusps are indicated by lower case letters. Teeth 1 to 4 are based on UFRGS PV-1029-T, teeth 5 and 6 placed. The other specimen, UFRGS PV-1068-T, is a posterior half of a dentary with four preserved postcanines. In this dentary, the anterior margin of the masseteric fossa is below the second preserved tooth and, by comparison with UFRGS PV-1171-T, this tooth could be regarded as the sixth postcanine. Once there are two more teeth posterior to it, the total count of postcanines could reach eight (as shown in the reconstruction). The two most mesial postcanines are the simplest with a main cusp (cusp a) and a small distal accessory cusp (cusp c). The third tooth also has one mesial (cusp b) and two distal accessory cusps (d and e). The fourth postcanine seems to have the same cusp pattern although its size is greater. The same pattern is also present in the fifth and sixth teeth. The seventh postcanine lacks the cusp e, although this can be covered buccally by the base of the coronoid process in specimen UFRGS PV-1068-T. In this specimen the eighth and ninth postcanines are not fully erupted. In the former postcanine it is possible to observe only the main cusp and the cusps b (broken during the preparation) and c and in the latter only the cusps a and c (Fig. 7b). Along the postcanine row from the third tooth and to the more distal teeth, there is an imbricate pattern in which the more distal cusp of the preceding tooth buccally overlaps the following tooth (Fig. 7). In the holotype, the imbricate pattern is less developed in the fragment of dentary with two postcanines (Martinelli et al. 2005). A are partially based on the holotype and on UFRGS PV-1171-T, and the remaining postcanines are based on UFRGS PV-1068-T. The whole tooth row length in an adult individual should be ca. 25 mm sectorial tooth imbricate pattern also occurs in some cynodonts such as Ecteninion, Therioherpeton, and Riograndia (Martinez et al. 1996; Bonaparte and Barberena 2001; Soares 2004). Postcranium Humerus (Fig. 8). The humerus of the specimen UFRGS PV-1068-T is similar to that of the holotype (Martinelli et al. 2005) (Fig. 2h) almost 50% larger than in the holotype and has an even more curved shaft. Medioventrally, in the proximal half of the humerus and near its mid portion there are two well-developed processes, possibly for the insertion of the teres major muscle (Fig. 8a, d), as in the holotype. This structure was regarded as diagnostic for Irajatherium (Martinelli et al. 2005). In this humerus and in the specimen UFRGS PV T, where the bar encircling the entepicondylar foramen is complete (Fig. 8e f), it is possible to observe the rounded trochlea and capitulum, which are missing on the damaged humerus of the holotype. These structures are confluent and placed in the lateral corner of the distal end of the humerus, whereas the medial portion of it is occupied by a greatly developed entepicondyle. Posteriorly, above the trochlea there is a shallow olecranon fossa (Fig. 8f).

12 78 T. V. de Oliveira et al. Fig. 8 Humeri of Irajatherium hernandezi. a d right humerus UFRGS PV-1068-T, in anterior, posterior, lateral, and medial views. e f left humerus UFRGS PV-1072-T distal end, in anterior and posterior views. Scale bar = 10 mm. be bar delimitating the entepicondylar foramen, bg bicipital groove, ca capitulum, dc deltopectoral crest, ef ectepicondylar foramen, enc entepicondyle, enf entepicondylar foramen, gt greater tuberosity, h head, lt lesser tuberosity, of olecranon fossa, tm teres major muscle attachment tubercle, tr trochlea Cladistic analysis Data provided by the new specimens of Irajatherium hernandezi were included in the data matrix of Martinelli and Rougier (2007) which performed a cladistic analysis including all the known species of ictidosaurs (Riograndia, Irajatherium, Chaliminia, Elliotherium, Pachygenelus, Diarthrognathus, and Tritheledon) plus a large sample of probainognathians and basal mammaliaforms. The resolution of the position of the Tritylodontidae among Eucynodontia is an issue not evaluated here that goes beyond the scope of this contribution for this purpose, see (Liu and Olsen 2010). The character list used by these authors was obtained from several sources, for example Rowe (1988), Wible (1991), Luo (1994), Martinez et al. (1996), Hopson and Kitching (2001), Abdala and Ribeiro (2003), Bonaparte et al. (2003, 2005), Martinelli et al. (2005), Sidor and Hancox (2006), and Oliveira (2006). The new scores for Irajatherium hernandezi are shown in Appendix 1. All characters were treated as non-additive and given equal weight. The data matrix was analyzed under the NONA program (Goloboff 1993) using Winclada (Nixon 1999) as interface. A heuristic search strategy was employed (Multiple TBR branch swapping; mult1000*, hold/30). Discussion and conclusion Cladistic analysis resulted in a single most parsimonious tree (length = 172; consistency index = 0.63; retention index = 0.80) (Fig. 9). The topology of the tree is exactly the same as that obtained by Martinelli and Rougier (2007) with only one difference in the diagnoses of the clade Chalimininae (Appendix 2). As expressed by these authors,

13 New information about Irajatherium hernandezi 79 Fig. 9 Most parsimonious tree (length = 172 steps; consistency index = 0.63; retention index = 0.80) depicting the phylogenetic relationships of Irajatherium hernandezi using the modified dataset of Martinelli and Rougier (2007; see text, Appendix 1, and Appendix 2). Clades: 1 Eucynodontia, 2 Probainognathia, 3 Mammaliaformes, 4 Ictidosauria, 5 Tritheledontidae, 6 Pachygenelinae, 7 Chalimininae, U unnamed clade the topology obtained does not differ significantly from the tree obtained by Martinelli et al. (2005) and Sidor and Hancox (2006). The only difference between the results from our analysis and that of Martinelli and Rougier (2007) is in the synapomorphies of the clade Chalimininae (Appendix 2). The new materials of Irajatherium described are important because they provide the first data on the lower incisor count and their relative sizes (based on the alveoli). The presence of an enlarged first lower incisor, a feature previously unknown in Irajatherium, is a synapomorphy with Ictidosauria (Martinelli and Rougier 2007). The presence of partially confluent jugular foramen and fenestra rotunda within the jugular fossa, separated by a finger-like projection of the posterolateral wall of the opisthotic is an unexpected feature for Irajatherium. In Riograndia guaibensis, the most basal ictidosaur (the sistertaxon of Tritheledontidae), the jugular foramen and the fenestra rotunda are completely separated (Soares 2004; Soares et al. 2005) as occurs in the Jurassic Pachygenelus monus (Wible and Hopson 1993). Because the basicranial region of Irajatherium is poorly preserved the separation of these openings cannot be discarded with confidence. In other tritheledontids, for example Chaliminia, Elliotherium, and Trithelodon, this portion of the skull remains unknown. The condition observed in Irajatherium occurs similarly in other cynodonts, for example Massetognathus, Probainognathus, and Brasilodon (Rougier et al. 1992; Bonaparte et al. 2005), among others. The conspicuous crest on the inner surface of the maxilla in Irajatherium is interesting because it suggests the attachment area of the maxillary turbinates. Evidence of similar crests was also reported in Thrinaxodon, Trirachodon, Massetognathus, and in the ictidosaur Riograndia, what strongly suggests the occurrence of some endothermy in these animals (Hillenius 1992, 1994; Rodrigues 2005). The presence of large upper and lower canines together with the paracanine fossa on the maxilla is a feature not found in other ictidosaurs, for example Riograndia, Chaliminia, Elliotherium, or Pachygenelus (Gow 1980; Bonaparte et al. 2001; Martinelli and Rougier 2007; Sidor and Hancox 2006). This trait in Irajatherium and the presence of sectorial lower postcanine could suggest a greater adaptation to carnivory. As was expressed by Martinelli et al. (2005) the morphology of the upper teeth of Irajatherium (partially known in the holotype UFRGS PV-0599-T) resembling those of Pachygenelus (Gow 1980) and Chaliminia (Martinelli and Rougier 2007) was one of the main characters used to include this taxon within Tritheledontidae. The specimen UFRGS PV-1175 here described has PC3 to PC5 with the same pattern as in the holotype, supporting the assignment of this specimen to Irajatherium. Moreover, the additional information provided by the new material supports the inclusion of Irajatherium within Tritheledontidae. The central and posterior upper postcanines of Irajatherium mainly differ from those of Pachygenelus (Gow, 1980) in the absence of a buccal cingulum. Furthermore, the cusp pattern of the lower postcanines is almost the same than that present in Chaliminia (Bonaparte 1980; Martinelli and Rougier 2007) and Pachygenelus (Gow 1980). Nonetheless, the lower postcanines of Pachygenelus (Gow 1980) have a lingual cingulum absent in Irajatherium postcanines. The tooth replacement of Irajatherium was described by Martinelli et al. (2005). The new material (e.g. UFRGS PV-1171-T) supports the presence of an alternate postcanine replacement. This type of replacement is also present in other ictidosaurs (Gow 1980; Crompton and Luo 1993; Martinelli and Rougier 2007) and in most carnivorous nonmammaliaform cynodonts (e.g. Crompton 1963b; Luo et al. 2004). Although several aspects of the morphology of this taxon are still unknown, the new materials support assignment of Irajatherium hernandezi to Tritheledontidae. Riograndia and Irajatherium, both coming from the same

14 80 T. V. de Oliveira et al. Late Triassic outcrops from southern Brazil, represent two basal ictidosaurs which show the first stems leading to the latest Late Triassic and/or Early Jurassic smallsized clade. In addition, this successful group developed several apomorphies in the skeleton that place its clade in close relation to the Mammaliaformes, illustrating the acquisition of mammalian features in the line leading to the mammals. Acknowledgments We thank Luiz Flávio Lopes for the photographs of several specimens and CNPq for financial support (TVO). The suggestions of the reviewers Fernando Abdala and Zhe-Xi Luo and the editor Oliver Rauhut improved the quality of this paper. Appendix 1: Score for Irajatherium hernandezi in the data matrix of Martinelli & Rougier (2007) Irajatherium?11?1? ????? ???0110?????0???? 1???????????????????1000??1?1?????0????0111??? Changes in the score for Irajatherium hernandezi presented in this paper compared with the data matrix of Martinelli & Rougier (2007): Character 2. Lower incisor number: from? to 1 (three incisors). Character 3. Some incisor enlarged: from? to 1 (present). Character 24. Sectorial postcanines with the major axis anteromedial-posterolaterally oriented, passing the distal portion of an anterior tooth medial to the mesial portion of the next tooth: from 0 to 1 (present). Character 35. Mandibular symphysis: from? to 1 (unfused). Character 36. Postdentary bones: from? to 1 (reduced to narrow rod lying in postdentary trough). Character 68. Trigeminal nerve (V 2 and V 3 ) exit: from? to 1 (foramen located entirely on the prootic, or on the anterior lamina of the petrosal). Character 69. Prootic and ophistotic: from? to 0 (unfused). Character 70. Petrosal promontorium: from? to 0 (absent). Character 71. Fenestra ovalis: from? to 0 (with thickened ring). Character 74. Perilymphatic foramen separation from jugular foramen: from? to 1 (partially separated by finger-like projection from postero-lateral wall of jugular foramen). Character 76. Hypoglossal foramen: from? to 1 (separated from the jugular fossa). Appendix 2: Diagnoses of clades (numbered as in Fig. 9; some clades are not diagnosed here). An asterisk (*) indicates ambiguous character-states Clade 4. Ictidosauria (sensu Martinelli & Rougier, 2007): presence of some enlarged incisors (Ch. 3), upper incisor 2 large and the others small (Ch. 4), lower incisor 1 large and the other small (Ch. 5), premaxilla forming the posterior border of incisive foramen (Ch. 39)*, length of palatine longer relative to maxilla in secondary palate (Ch. 47). Clade 5: Tritheledontidae (sensu Martinelli & Rougier, 2007): dominant central bulbous main cusp on upper postcanines (Ch. 11), upper posterior postcanines with cusp B and C buccally displaced and bulbous, prominent cusp A (Ch. 12), lower middle and posterior postcanines with four cusps aligned decreasing in size posteriorly (Ch. 19), posterior portion of secondary palate almost at the level of the tip of upper postcanine teeth, forming a deep groove between hard palate and tooth row (Ch. 48). Unnamed clade. Pachygenelinae (Clade 6) plus Chalimininae (Clade 7): single roots of postcanines (Ch. 25), tooth row parallel to sub-parallel from the axial plane of the cranium (Ch. 30), maxillary buccal shelf overhanging tooth row (Ch. 43). Clade 6. Pachygenelinae (sensu Martinelli & Rougier, 2007): upper postcanines with buccal cingulum (Ch. 9)*, narrow upper postcanines with lingual cingulum (Ch. 10)*. Clade 7. Chalimininae (sensu Martinelli & Rougier, 2007): more than 11 upper postcanine teeth in adult (Ch. 8)*, absence of imbrincated sectorial postcanines (Ch. 24)*. Tritheledon plus Diarthrognathus: absence of upper posterior postcanines with cusp B and C buccally displaced and bulbous, prominent cusp A (Ch. 12)*. References Abdala, F., and A.M. Ribeiro A new traversodontid cynodont from the Santa Maria Formation (Ladinian-Carnian) of southern Brazil, with a phylogenetic analysis of Gondwanan traversodontids. Zoological Journal of the Linnean Society 139: Abdala, F., and A.M. Ribeiro Distribution and diversity patterns of Triassic cynodonts (therapsida, Cynodontia) in Gondwana. Palaeogeography, Palaeoclimatology, Palaeoecology 286: Arantes, B.A., M.B. Soares, and C.L. Schultz Clevosaurus brasiliensis (Lepidosauria, Sphenodontia) do Triássico Superior do Rio Grande do Sul: anatomia pós-craniana e relações filogenéticas. Revista Brasileira de Paleontologia 12(1): Araújo, D.C., and T.D. Gonzaga Uma nova espécie de Jachaleria (Therapsida, Dicynodontia) do Triássico do Brasil. In

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