Araripesuchus wegeneri Buffetaut & Taquet, 1979

Sereno, Paul & Larsson, Hans, 2009, Cretaceous Crocodyliforms from the Sahara, ZooKeys 28 (28), pp. 1-143 : 34-55

Araripesuchus wegeneri Buffetaut & Taquet, 1979

Figs. 14–26

Tables 6–8

Buffetaut and Taquet (1979, fig. 1)

Ortega et al. (2000, fig. 9)

Turner (2006, figs. 5–7)

Holotype. MNHN GDF700 ; snout composed of articulated upper and lower jaws and preserved to mid-orbit on the right side with several teeth preserving their crowns.

Type locality. Gadoufaoua, Agadez District, Niger Republic (more precise locality unknown) (Fig. 1A, C).

Horizon. Elrhaz Formation, Tegama Series; Lower Cretaceous (Aptian-Albian), ca. 110 Mya ( Taquet 1976).

Referred material. MNN GAD 19, nearly complete cranium lacking only portions of the left lacrimal and prefrontal, the palpebrals, and some of the teeth (Figs. 14–17, 19); MNN GAD 20, partial skeleton on block preserving the left side of the skull exposing the dentition in medial view and an articulated tail with dermal armor ( Figs. 20 , 21, 25A); MNN GAD 21, partial skeleton on block preserving the ventral portion of the skull, an articulated partial forelimb, and an articulated tail with dermal armor ( Fig. 24 , 25B ); MNN GAD 22, partial skeleton on block preserving the ventral portion of the skull, an articulated right manus and pes, a right calcaneum, and an articulated tail with dermal armor ( Fig. 26 ); MNN GAD 23, isolated snout on block composed of articulated upper and lower jaws and preserved to mid-orbit on the right side; MNN GAD 24, isolated left maxilla on block preserving the dentition; MNN GAD 25, partial skeleton preserving the posterior ends of the lower jaws and most of the postcranial skeleton except the tail; MNN GAD 26, edentulous right dentary from a juvenile (Fig. 18).

An exceptional series of specimens are preserved in close proximity on a single block of sandstone ( MNN GAD 20–24) ( Fig. 23 ). Th ree individuals are fairly complete, partially articulated skeletons with their axial columns aligned side-by-side pointing in the same direction ( MNN GAD 20–22). One of the three ( MNN GAD 20) is slightly small- er than the other two. Also present are portions of at least two additional individuals, one represented by an articulated snout ( MNN GAD 23) and the other by an isolated maxilla ( MNN GAD 24). A minimum of five individuals thus are represented on the block.

The close proximity and alignment of the three best preserved skeletons and the presence of additional individuals on a small block is unusual. Portions of the three best preserved skeletons ( MNN GAD 20–22) and the isolated snout ( MNN GAD 23) have been lost to postmortem surface erosion and would have been more complete. Some postmortem disarticulation is evident in all three of the most complete specimens ( MNN GAD 20–22), although there is no obvious preferred direction or orientation to displaced elements. Th e strong curvature of the distal tail in three skeletons, in addition, is diffi cult to attribute to postmortem water transport, as the curvature in one of the skeletons opposes the curvature in the other two.

Revised diagnosis. Small-bodied metasuchian (<1.0 m) characterized by an anterior premaxillary foramen anterior to the first premaxillary tooth; infratemporal bar of jugal with marginal fossa; supratemporal fossa with marked anteromedial corner; scalloped posterior margin of skull table with median process; reduction of the premaxillary palate to parasagittal shelves; median elliptical incisive foramen; dentary with prominent labial alveolar margin that obscures all alveoli in lateral view; caniniform (d4) to the largest crowns in the postcaniniform series (d13) with relatively low, mesiodistally broad (crown width 60–80% of crown height), denticulate crowns; and largest postcaniniform crowns with lingually deflected mesial carina and associated trough.

Discussion. The referred cranium (MNN GAD19; Figs. 14–17, 19) removes any doubt about the assignment of the African species to Araripesuchus ; the shape of the cranium and many of its structural details are close or identical with the type species Araripesuchus gomesii ( Price 1959) .

Figure |4. Skull of the crocodyliform Araripesuchus wegeneri . Cranium (MNN GAD19). A Lateral view (reversed). B Dorsal view. C Ventral view. Scale bar equals 5 cm.

Secondly, there is no doubt that cranium MNN GAD19 is correctly referred to A. wegeneri , because there are many features it shares only with the holotype, a partial snout ( MNHN GDF700 ; Buffetaut and Taquet 1979). It is approximately 90% of the size of the holotype, based on measurements of the snout. Both have five premaxillary teeth. Th e jugal in both specimens expands in depth toward its anterior end and has a shallow sculpted fossa under the orbit. Other shared features found thus far only in the holotype and MNN GAD19 include a premaxillary sinus, small posterior spine on the maxilla that projects into the antorbital fenestra, flat strap-shaped border between the

Figure |5. Skull of the crocodyliform Araripesuchus wegeneri . Drawings matching the cranium (MNN GAD19) in Fig. 14. A Lateral view (reversed). B Dorsal view. C Ventral view. Parallel lines indicate broken bone surface; dashed line indicates missing bone or tooth crown; grey tone indicates matrix. Scale bar equals 5 cm. Abbreviations: am3, 14, alveolus for maxillary tooth 3, 14; antfe, antorbital fenestra; antfo, antorbital fossa; apap, articular surface for palpebral; apm1, alveolus for premaxillary tooth 1; apmf, anterior premaxillary foramen; aqj, articular surface for the quadratojugal; be, buccal emargination; bo, basioccipital; bs, basisphenoid; bt, basal tubera; ch, choana; cqp, cranioquadrate passage; ec, ectopterygoid; Ef, Eustachian foramen; en, external naris; f, frontal; fl, flange; fo, foramen; gef, groove for ear flap; j, jugal; l, lacrimal; lf, lacrimal foramen; ls, laterosphenoid; m, maxilla; m1, 3, 7, maxillary tooth 1, 3, 7; n, nasal; nfo, narial fossa; oc, occipital condyle; ot, otoccipital; p, parietal; pf, prefrontal; pl, palatine; pm, premaxilla; pm3, 5, premaxillary tooth 3, 5; pmmf, premaxilla-maxilla foramen; po, postorbital; popr, paroccipital process; pos, preotic siphonium; pt, pterygoid; q, quadrate; qj, quadratojugal; se, septum; sq, squamosal; so, supraoccipital; sof, suborbital fenestra.

choana and suborbital fenestra, and a V-shaped anterior margin of the choanae (Figs. 14, 15, 17). Finally, the fifth maxillary crown is preserved in both skulls and corresponds in detail regarding orientation, shape, and surface detail; the subcircular crown is angled posteroventrally, has a low short primary ridge near the crown apex laterally, has finely denticulate carinae, and has fine striations on the crown surface, some of which extend from the denticles.

Dorsal skull roof. The following abbreviate description is based primarily on the well preserved cranium MNN GAD19 (Figs. 14–17, 19, 22; Table 7) and a nearly complete dentition in skull MNN GAD20, which was hemisected by erosion ( Figs. 20 , 21).

The premaxilla exhibits many features important for determining phylogenetic position, the monophyly of Araripesuchus , and the distinction of A. wegeneri . Most of the external surface of the bone is smooth, except for the tip of the posterodorsal ramus (Figs. 14A, B, 15A, B, 16A). At the anterior tip of the premaxilla, an anterior premaxillary foramen is present and passes posterodorsally into the nasal passage (Fig. 16A). On the lateral aspect of the premaxilla, the posterior boundary of the narial fossa is indicated by an arcuate depression, posterior to which are located two large neurovascular foramina (posterior premaxillary foramina) and one smaller accessory foramen. One large foramen with a similar anteroventral groove has been described or shown in A. gomesii ( Price 1959) (also AMNH 24450), A. patagonicus ( Ortega et al. 2000) and A. tsangatsangana ( Turner 2006) . Posterior to these foramina is located the larger premaxillamaxilla foramen, which opens between these bones and extends ventrally to the alveolar margin as a narrow slit (Fig. 16A). In cross-section the body of the premaxilla posterior to the external nares is hollow (Fig. 17A), a highly unusual feature that is at least partially responsible for the inflated appearance of the premaxilla (Fig. 16A). Th is space, a premaxillary sinus, is also visible on the holotype, the cavity filled with matrix and exposed by erosion (MNHN GDF700). In the scan of A. wegeneri and in an acid-prepared skull of A. gomesii (AMNH 24450; Hecht 1991), the canal of the premaxilla-maxilla foramen appears to have an anterior diverticulum that may pneumatize the premaxilla. The scan also shows that the pair of large lateral foramina on the body of the premaxilla anterior to the premaxilla-maxilla foramen also communicate with the premaxillary sinus.

The external surface of the maxilla is textured, except for a smooth surface along the arched, ventral alveolar margin dorsal to the postcaniniform teeth (Figs. 14A, 15A, 16A). Th e root of the caniniform tooth fills the swelling at the anterior end of the maxilla. Th e maxilla extends posteriorly to form the anterior margin of the antorbital fenestra and fossa. Above the fossa, a narrow prong of the maxilla contacts the prefrontal, separating the nasal and lacrimal. Th is is a sutural configuration present in A. tsangatsangana but absent in A. gomesii and A. patagonicus ( Turner 2006) , where the nasal contacts the lacrimal separating the maxilla and prefrontal.

The nasal is textured most deeply with circular pits in its mid-section and has a more elevated median nasal bridge than in other species (Figs. 14B, 15B). The nasalfrontal suture is interdigitated as in A. gomesii ( Price 1959) and A. patagonicus ( Ortega et al. 2000) , a sutural configuration present in juveniles of A. gomesii (AMNH 24450).

structures measured on left side except as indicated.

The nasal-frontal suture shows less interdigitation in A. tsangatsangana ( Turner 2006) , and the frontal has a narrow anteromedian process in A. buitreraensis ( Pol and Apesteguia 2005) .

The L-shaped lacrimal forms nearly all of the smooth surface of the antorbital fossa, which has subequal margins posterior and ventral to the antorbital fenestra as in A. gomesii (Figs. 14A, 15A). Th e narrow continuation of the smooth margin of the fossa extends around the anterior corner of the antorbital fenestra and along the ventral margin of a posterior prong of the maxilla that partially divides the fenestra. None of the other species of Araripesuchus have a similar maxillary prong. In both A. gomesii and A. patagonicus ( Ortega et al. 2000) , the antorbital fossa is approximately twice the size of the opening in A. wegeneri relative to the orbit and does not appear to change much in rela-

Figure |6. Skull of the crocodyliform Araripesuchus wegeneri . Detailed views of the cranium (MNN GAD19). A Snout margin in anterolateral view. B Posterior portion of the skull in left lateral view. C Posterior palate in ventral view. Scale bars equal 2 cm. Abbreviations: apap, articular surface for the palpebral; apmf, anterior premaxillary foramen; be, buccal emargination; cqp, cranioquadrate passage; ch, choana; ec, ectopterygoid; fo, foramen; fov, fenestra ovalis; gef, groove for the ear flange; j, jugal; pm, premaxilla; qj, quadratojugal; m, maxilla; m3, maxillary tooth 3; mco, medial condyle; n, nasal; nf, narial fossa; p, parietal; pl, palatine; pm, premaxilla; pm3, 5, premaxillary tooth 3, 5; pmmf, premaxilla-maxilla foramen; po, postorbital; pos, preotic siphonium; ppmf, posterior premaxillary foramen; pt, pterygoid; ptfl, pterygoid flange; q, quadrate; se, septum; sof, suborbital fenestra; sq, squamosal.

Figure |7. Skull of the crocodyliform Araripesuchus wegeneri . Computed-tomographic cutaway views of the cranium (MNN GAD19). A Snout posterior to the external nares in anterior view. B Posterior portion of the skull in anterior view. C Cranium in sagittal section near midline. Scale bar for A and B equals 2 cm; scale bar for C equals 3 cm. Abbreviations: ch, choana; cr, crest; ec, ectopterygoid; Euc, Eustachian canal; f, frontal; fm, foramen magnum; j, jugal; lu, lumen; m, maxilla; m3, 7, maxillary tooth 3, 7; n, nasal; np, narial passage; pl, palatine; pm, premaxilla; pm3, 5, premaxillary tooth 3, 5; po, postorbital; popr, paroccipital process; prf, prefrontal; pt, pterygoid; ptfl, pterygoid flange; q, quadrate; se, septum; sq, squamosal; v, vomer.

tive size after reaching subadult size in A. gomesii ( Price 1959; Hecht 1991). The opening is proportionately largest in A. tsangatsangana and appears to lack any smooth surface attributable to an antorbital fossa ( Turner 2006). A prominent knob and ridge are situated on the lacrimal dorsal to the fossa and are continuous posteriorly with the edge of a large anterior palpebral. Th e lacrimal foramen is located ventral to this knob within the orbit.

The anterior and posterior palpebrals are missing in cranium MNN GAD19, exposing articular fossae on the lacrimal and prefrontal anteriorly and on the postorbital posteriorly (Figs. 14B, 15B). Disarticulated palpebrals have been discovered on the large block ( Fig. 23 ). In A. wegeneri the interdigitating prefrontal-frontal suture contrasts with the broad scarf joint described in A. tsangatsangana ( Turner 2006) . The prefrontal pillar is anteroposteriorly flattened and angles ventromedially and slightly posteriorly, tapering strongly from the skull roof to the palate.

The frontal and parietal are fused to their opposites and join each other by an interdigitating frontoparietal suture. Th e frontals have a distinct median crest, and the parietal skull table between the supratemporal fossae is noticeably narrower than in other species of Araripesuchus . In A. wegeneri a parasagittal line extending along the orbital margin passes across the supratemporal fossa rather than along its lateral rim as in other species (Figs. 14B, 15B). Th e frontal enters the supratemporal fossa to a greater degree than in other species of Araripesuchus , reaching the inner margin of the fossa in dorsal view. The rim of the fossa in A. wegeneri also has a marked anteromedial corner with parasagittal and transverse edges, whereas in other species the rim of the fossa is nearly uniformly curved. Th e posterior margin of the skull table in A. wegeneri is scalloped to each side of the supraoccipital, differing from the nearly straight posterior margin in other species.

The postorbital is notched by an articular facet for a small posterior palpebral, as in other species of Araripesuchus and most stem crocodyliforms. Th e surface of the postorbital between this facet and the supratemporal fossa varies, remaining textured with pits in some species, such as A. gomesii ( Price 1959) and A. tsangatsangana ( Turner 2006) , and smooth in others such as A. patagonicus ( Ortega et al. 2000) . In A. wegeneri this surface is smooth and convex (Figs. 14B, 15B) rather than flat with a sharp medial and lateral rims as in many protosuchians and neosuchians.

The squamosal is distinctly triradiate in dorsal view in A. wegeneri and all other species except A. gomesii . The difference lies in the length and orientation of the posterior process, which has more subdued pitting and is offset below the skull table. The posterior process appears to be both shorter and angled more steeply posteroventrally in A. gomesii , such that it appears to be of negligible length in dorsal view of the skull ( Price 1959; Hecht 1991). Th e pitted dorsal surface of the squamosal in A. wegeneri has an L-shaped fossa where the pitted texture is depressed, a condition more strongly expressed in Simosuchus ( Buckley et al. 2000) .

The anterior ramus of the jugal extends as a broad process as far anteriorly as the lacrimal, approaching the border of the antorbital fossa with a narrow fingerlike process. The anterior ramus is not as deep or extended anteriorly in either A. patagonicus ( Ortega et al. 2000) or A. tsangatsangana ( Turner 2006) . The base of the smooth rod-shaped dorsal ramus, which is inset from the textured body of the jugal and pierced by a si- phonal foramen, is situated on the posterior one-half of the jugal (Figs. 14A, 15A). The posterior ramus of the jugal is distinctive. As in A. gomesii but unlike other species, the ramus tapers to a point below the posterior corner of the laterotemporal fenestra rather than at mid-length along the infratemporal bar. Unique to A. wegeneri , a marginal fossa with reduced texture is present along the dorsal margin of the posterior ramus.

The L-shaped quadratojugal has an inset articular facet for the posterior ramus of the jugal. Th e quadratojugal-quadrate contact adjacent to the condyles and along the shaft is an interdigitating suture. Texturing of the external surface of the quadratojugal is limited to the posteroventral corner, where the bone approaches, but does not contribute to, the articular surface for the lower jaw.

Palate. The configuration of the anterior palate in A. wegeneri is unusual compared to that in A. gomesii ( Price 1959) and other basal metasuchians. The premaxillary contribution is limited to the periphery of the anterior palate adjacent to the alveolar margin. Opposing premaxillae have very little contact on the palate. Th ey join in the midline only anterior and posterior to an elliptical incisive foramen (Figs. 14C, 15C). Most of the palate between the premaxillary tooth rows is formed by the maxillae. A pit for reception of the tip of the dentary caniniform is present at the premaxilla-maxilla suture medial to the premaxilla-maxilla foramen. Th e tip of the dentary caniniform in this location can be seen in the articulated dentition of MNN GAD20 ( Fig. 20B ).

The configuration of the remainder of the palate, including the palatine, ectopterygoid and pterygoid, is quite similar to that in A. gomesii ( Price 1959) and A. tsangatsangana ( Turner 2006) . Th e semicircular suborbital fenestra is larger than the adjacent choana, which is situated farther posteriorly on the palate, although not butted against the posterior transverse edge of the pterygoids (Figs. 14C, 15C). A. patagonicus is unusual in this regard, with the posterior margin of the choana positioned farther anteriorly than the posterior margin of the suborbital fenestra, although breakage may have artificially expanded the fenestra ( Ortega et al. 2000). A. wegeneri shares with A. gomesii the presence of a distinctive wedge-shaped flange on the pterygoid at the posterior margin of the palate (Figs. 14C, 15C, 16C, 17C), a process that is either very reduced or absent in other species of the genus.

Three palatal features differentiate A. wegeneri from other species (Figs. 14C, 15C, 16C). Th e anterior margin of the choanae is V-shaped rather than transverse; there is a flat, strap-shaped border between the suborbital fenestra and choana rather than a narrow, ventrally directed edge; the choanal septum is narrow, its rounded ventral edge only slightly thickened posteriorly rather than developed as a horizontal flange.

The main shaft of the quadrate angles posteroventrally from the recessed otic region to the quadrate condyles, which are directed ventrally. In the otic region, there is a preotic siphonium, ventral to which is a marked fossa and posterior to which is a large opening housing the fenestra ovalis and confluent cranioquadrate passage (Fig. 16B). A sharp vertical crest on the quadrate contributes to the posterior skull margin, joining the paroccipital process with the rim of the medial condyle. In posterior view, a foramen aërum opens on the posterior aspect of the quadrate shaft just above the medial condyle. Th e relatively flat quadrate condyles, which are well preserved on the left side, are separated by a marked V-shaped cleft.

Braincase. Poorly exposed in other species, the braincase in A. wegeneri is well preserved with visible sutures and foramina (Figs. 14C, 15C, 16B, 17C). The supraoccipital is exposed along the posterior margin of the skull table as a pitted subtriangular surface sutured to a notch between the fused parietals. A thin nuchal crest projects posteriorly and recedes ventrally at the contact with the exoccipitals.

Although the ventral portion of the occipital condyle on the basioccipital is weathered away, the hemisphere of the condyle is prominent and fully exposed in ventral view. The ventral prominence of the condyle is a key difference when compared to the condyle in an extant crocodylian. A ventrally deflected condyle characterizes notosuchians, such as Anatosuchus and Simosuchus , but is less common among other crocodylomorphs. In Hamadasuchus , for example, a comparable profile of the occipital condyle is achieved with the braincase held in posteroventral view ( Larsson and Sues 2007: fig. 5B).

The remainder of the basioccipital angles anteroventrally at approximately 45°. In the midline moving anteriorly from the condyle, there is a small posterior Eustachian foramen, a wedge-shaped median crest, and a large anterior Eustachian foramen opening between the basioccipital and basisphenoid. The Eustachian foramen opens anterodorsally into the pituitary fossa (Fig. 17C). Th e lateral edge of the basioccipital curls up against the low basal tubera to each side, between which is located a relatively small lateral Eustachian foramen.

In posterior view, the otoccipital (exoccipital + opisthotic) meets its opposite over the foramen magnum as a protruding rim, excluding the supraoccipital from its border. The rim, which provides an articular surface for the proatlas, overhangs the foramen magnum in A. wegeneri , a condition coincident with ventral deflection of the occipital condyle. In non-notosuchian crocodylomorphs such as Hamadasuchus ( Larsson and Sues 2007), in contrast, the exoccipital rim projects posteriorly. Th e paroccipital processes project to each side, their central axis following a sigmoid curve.

The otoccipital forms the extreme dorsolateral edge on each side of the occipital condyle and then extends anteroventrally to the basioccipital, tapering to a point against a crest formed by the quadrate and basisphenoid. Th e anteroventral tip of the otoccipital is raised as a low, rugose basal tuber, which is held between the basioccipital, basisphenoid and quadrate. Four foramina open to each side of the occipital condyle for passage of the posterior cranial nerves and internal carotid artery. Th e carotid foramen is larger than the others and opens ventrally rather than ventrolaterally.

Exposure of the basisphenoid is very limited in A. wegeneri . Th e more extensive exposure shown in A. patagonicus ( Ortega et al. 2000) may well be due to erosion of the ventral surface of the braincase. Turner described “large posteroventral exposure” of the basisphenoid in A. tsangatsangana ( Turner 2006: 286) , although this cannot be verified in images of the specimens. In A. wegeneri the basisphenoid is pinched between the pterygoids and quadrates anteriorly and the basioccipital and otoccipital posteriorly (Figs. 14C, 15C). Th e basisphenoid contributes to the medial portion of the more posterior of two crests running anteromedially from the quadrates to the pterygoids. This paired posterior crest converges in the midline running across the center of the exposed surface of the basisphenoid.

Endocast. An endocast, generated from a computed-tomographic scan of cranium MNN GAD19 ( Fig. 22 ), closely resembles the endocast of Anatosuchus (Fig. 10). Both have spade-shaped, dorsoventrally compressed cerebral hemispheres separated dorsally by a shallow sinus. In Araripesuchus there is also a median fossa separating the hemispheres ventrally ( Fig. 22C ).

The optic lobe is differentiated as a low swelling posterior to each cerebral hemisphere. In the cerebellar region, the sagittal sinus ascends to a height level with the cerebral hemispheres, creating a steeply angled pontine flexure resembling that in theropod dinosaurs ( Hopson 1979; Larsson 2001). On the ventral side of the endocast, the exit for the optic nerves and a pendant pituitary fossa are visible ( Fig. 22A, C ).

Lower jaw. Except for the dentary (Fig. 18), the lower jaw has yet to be well exposed in any available specimens. Th e dentary in A. wegeneri is unusual in several regards. No alveoli are visible in lateral view. Th e lateral alveolar margin is dorsally prominent as compared to its medial counterpart, which appears to be lacking entirely posterior to dentary tooth 10 (Figs. 18B, 20). Th e alveolar margin is sinuous in lateral view as in many crocodyliforms. Th e most prominent, convex portions of the alveolar margin house the largest teeth and oppose smaller teeth in the upper tooth row set in a dorsally concave alveolar margin ( Fig. 20A ). In lateral view, the alveolar margin adjacent to the postcaniniforms is smooth and bordered ventrally by a connected row of large neurovascular foramina (Fig. 18A, D).

The dentary symphysis is rugose and fairly shallow (Fig. 18B, D). Th e articular scar for the splenial covers the anterior end of Meckel’s canal and then curves onto the dorsal aspect of the dentary between the tooth rows (Fig. 18B, C). As a result, the splenial appears to have formed most of the dorsal surface of the symphysis between the tooth rows posterior to the caniniform.

Dentition. There are 5 premaxillary, 14 maxillary, and 16 dentary teeth in the best preserved subadult and adult dentitions (MNN GAD19, GAD20). Th e teeth in A. wegeneri are regionalized. For descriptive purposes, we identify upper and lower teeth as incisiforms, caniniforms, and postcaniniforms, although tooth form grades between these functional types.

Incisiforms have subconical crowns with a bulbous base separated from an expand- ed root by a gentle constriction. Th e crown tip is slightly recurved posterolingually, and the crown is asymmetrical with a longer mesial than distal carina. Th e carina is both smooth and unornamented or has apically inclined, relatively fine denticles numbering about 5–6 per mm. The crown surface of incisiforms in A. wegeneri is ornamented with fine wrinkles toward its apex and very rounded ridges toward the crown base that are occasionally visible under high magnification of well preserved, unworn crowns.

Caniniforms are discordantly (20–50%) larger than adjacent teeth, their principal defining feature. Like the incisiforms, the caniniform teeth have a bulbous crown with a basal constriction, are asymmetrical with a longer mesial carina, may have either smooth or denticulate carinae, and have crown surfaces characterized by fine wrinkles and low rounded ridges.

Figure |8. Right dentary of the crocodyliform Araripesuchus wegeneri . Isolated, edentulous right dentary from a subadult (MNN GAD26). A Lateral view (reversed). B Medial view. C Dorsal view. D Anterior view. Scale bar equals 1 cm. Abbreviations: ad1, 4, 8, 11, 14, 15, alveolus for dentary tooth 1, 4, 8, 11, 14, 15; asp, articular surface for the splenial; be, buccal emargination; dsym, dentary symphysis; fo, foramen; Mc, Meckel’s canal.

Postcaniniforms are located posterior to caniniform teeth. Crown form is quite variable, from tall pointed crowns that are asymmetrical with longer mesial carinae to squat symmetrical crowns that are longer mesiodistally than deep apicobasally. All have a marked constriction between crown and root, and all have denticulate mesial and distal carinae.

There are five premaxillary teeth in A. wegeneri , the first four of which have the centroid of the tooth base or alveolus aligned in a straight row. The centroid of the small fifth premaxillary tooth (or its alveolus if missing) is inset slightly lingual to a line through the other teeth/alveoli. In palatal view, the straight portions of the premaxillary tooth rows converge anteriorly at an angle of 85° as in A. gomesii ( Price 1959) . A similar morphology appears to be preserved in A. tsangatsangana ( Turner 2006) . Although no specimen of A. tsangatsangana preserves the premaxillary tooth row in place, the anterior five dentary teeth are aligned in a straight row [12: fig. 41A]. Libycosuchus has a similar linear configuration of alveoli, although the tooth rows converge more abruptly at an angle of approximately 100° ( Stromer 1914). The straight premaxillary tooth rows are reflected in the external margin of the premaxilla, which appears straight or slightly concave, rather than convex, in dorsal view of the cranium.

All but the first premaxillary tooth are preserved in both MNN GAD19 and GAD20 (Figs. 19A, 20B). All of the crowns are incisiform as described above. The first three alveoli are virtually identical in size in MNN GAD19, yet the second premaxillary tooth preserved on the left side is slightly smaller than the third premaxillary tooth preserved on the right side. It is probable, thus, that there is a continuous increase in crown size from pm1 to pm4 and that pm5 is the smallest of the premaxillary series.

Crown shape is remarkably similar in the premaxillary series and is asymmetrical in labial and apical views. In labial view, the longer mesial carina is convex, displacing the crown tip distally. Th e shorter distal carina is also convex in all but the large pm4, where it is straight. All of the premaxillary crowns have low vertical fluting and sharp, unornamented mesial and distal carinae. Th e lingual crown face is slightly less convex than its labial counterpart, and a shallow trough is present adjacent to both carinae on the lingual side of the crown (Figs. 19A, 20B). Given these asymmetries, it is possible to determine whether an isolated premaxillary crown is from left or right premaxillae.

The maxillary teeth can be divided into two anterior incisiforms (m1, m2), a caniniform (m3), and 11 postcaniniforms (m4-m14). All have finely denticulate carinae upon eruption (approximately 5–6 denticles per millimeter) and low fluting on both crown surfaces, as preserved in both MNN GAD19 and GAD20 ( Figs. 20 , 21). Fine denticles are present on the carinae of an erupting m1 crown in the mature individual MNN GAD19. Apical wear, however, has reduced or obliterated the denticles on other crowns in the same tooth row (Fig. 19B, C). Th e mesial and distal carinae of the caniniform (m3) in MNN GAD19 have been truncated by wear, giving the misleading appearance that the crown is recurved (Figs. 16A, 19A). An unworn m3 is partially exposed in MNN GAD20 and shows that the caniniform tooth in the upper jaw is not recurved but rather has an asymmetrical leaf shape in labial or lingual view ( Fig. 20B ).

Crown shape in the maxillary series changes rapidly from leaf-shaped in m1–3 to the squat proportions of the postcaniniforms (Fig. 21). Th e denticles in postcaniniforms are restricted to the apical margin, and there is often a low primary ridge leading to the apical denticle.

All of the dentary teeth have finely denticulate margins, although information is limited for d2 and absent for d1. Th e fourth dentary tooth is enlarged as a caniniform, which has a crown shape similar to that of pm4 and m 3 in the upper tooth row; the longer mesial carina is convex whereas the distal carina is straight. Postcaniniform

Figure |9. Worndentition of the crocodyliform Araripesuchus wegeneri . Detailed views of the dentition (MNN GAD19). A Right premaxillary teeth 3–5 in ventromedial view. B Left maxillary teeth 6–11 in ventromedial view. C Left maxillary teeth 9–11 in ventromedial view. Scale bars equal 5 mm. Abbreviations: apm2, alveolus for premaxillary tooth 2; awf, apical wear facet; ca, carina; de, denticle; fl, fluting; m, maxilla; m6, 9, 11, maxillary tooth 6, 9, 11; mwf, medial wear facet; ne, neck; pm, premaxilla; pm3, 5, premaxillary tooth 3, 5; pmmf, premaxilla-maxilla foramen; rt, root; wf, wear facet.

crowns decrease in size to d7 followed by an increase in size to d11 and d12 ( Fig. 20 ). The trough adjacent to the mesial carina on the lingual crown face is marked, giving the appearance that the mesial edge of the crown is curled lingually ( Fig. 20C ).

Three aspects of the dentition deserve special note. The first involves crown orientation along the tooth row. Many postcaniniform maxillary and dentary crowns

Figure 2 |. Unworn dentition of the crocodyliform Araripesuchus wegeneri . Detailed views of the middle and posterior portions of the tooth rows (MNN GAD20). A Middle portion of left tooth rows in medial view. B Posterior portion of left tooth rows in medial view. C Close-up view of maxillary tooth 7 and dentary tooth 10 and 11 in medial view. Scale bar for A and B and scale bar for C equal 5 mm. Abbreviations: aca, anterior carina; ad, apical denticle; ad12, alveolus for dentary tooth 12; d9–11, 14, 16, dentary tooth 9–11, 14, 16; de, denticle; m4, 7–9, 13, maxillary tooth 4, 7–9, 13; ne, neck; pca, posterior carina; pri, primary ridge; rt, root; se, septum; tr, trough.

are canted mesiolingually (anteromedially) relative to the tooth row, creating an en echelon arrangement reminiscent of the condition in basal sauropodomorph and ornithischian dinosaurs. Th is can be seen in m 5–7 in MNN GAD19 and d 9–11 in MNN GAD20 (Figs. 14C, 15C, 20C). Secondly, the postcaniniform maxillary teeth and mid- and distal dentary teeth are set into a trough with alveoli incompletely divided by bony septa. Th e maxillary trough is best seen in MNN GAD19, and the lingually open alveoli in the dentary series are best seen in MNN GAD20. Th irdly, blunt apical wear occurs throughout the dentition in MNN GAD19. Th e prevalence of blunt apical tooth wear, denticulate carinae, crown surfaces with fluting, en echelon crown orientation and the absence of recurved caniniforms suggest that A. wegeneri may have been an opportunistic, or even an obligate, herbivore. A detailed study of occlusion and wear is warranted on the materials here described.

Axial skeleton. Portions of the axial column are preserved and differ little from that preserved in A. gomesii ( Hecht 1991) . Th e centra are amphicoelous. Th e thin subquadrate dorsal and caudal osteoderms have low parasagittal keels and no articular processes. Th e tail is surrounded by osteoderms, including paired dorsal osteoderms extending at least over the proximal two-thirds of the tail, a single lateral row in the proximal tail, and paired ventral osteoderm rows ( Fig. 24 ).

Appendicular skeleton. The limbs are the best exposed portion of the appendicular skeleton. Th e humerus, radius and ulna in A. wegeneri have straight and relatively slen- der shafts with proximal and distal articular surfaces consistent with upright posture ( Fig. 25 ). In extant crocodylians with a habitual posture that is less erect, the humeral shaft has a sigmoidal axis and the distal condyles face anteriorly. Th e radiale, ulnare and metacarpals ( Figs. 25B , 26A ), likewise, are proportionately elongate compared to those in extant crocodylians ( Mook 1921).

Articulated forelimb elements in two individuals permit measurement of proportions within the forelimb of adult Araripesuchus for the first time ( Table 6). Compared to extant crocodylians, distal forelimb segments in A. wegeneri are longer relative to proximal segments. Th us the radius is longer relative to the humerus, and the radiale is longer relative to the radius in A. wegeneri by a factor of between 10–15%. Comparison of the radiale and metacarpal three, however, is more striking. The radiale is more than 150% of metacarpal three length in A. wegeneri , whereas the radiale is only about 75% the length of metacarpal three in extant crocodylians. In other words, the elongate proximal carpals in A. wegeneri are approximately twice their length relative to the metacarpus in extant crocodylians. Relative lengthening of distal limb segments also suggests greater relative speed and a more upright limb posture. Th e proximal end of each metacarpal is flattened and expanded to enhance overlap, and the distal end is marked by pits that allow considerable extension of the proximal phalanges ( Fig. 26A ).

The long bones in the hind limb also have straight shafts. A calcaneum near skeleton MNN GAD22 ( Fig. 23 ) has a deep calcaneal tuber that is only moderately laterally deflected. An articulated pes has straight, proportionately long metatarsals with flattened proximal shafts to enhance overlap and distal pits for extension of the proximal phalanges ( Fig. 26B ). Th ese features, again, suggest that during terrestrial locomotion, limb posture in A. wegeneri was more upright than in extant crocodylians.

Figures

Figure 2. Skull and cervical vertebra of the crocodyliform Stomatosuchus inermis. A Cranium in ventral view. B Right lower jaw in medial view. C Right lower jaw (reversed) in dorsal view. D cervical vertebra in anterior view. E Right quadrate in ventral view. F Skull reconstruction in dorsal view. G Skull reconstruction in lateral view. Scale bar for A-E equals 50 cm. A-E from Stromer (1925); F and G from Stromer (1936).

Figure 20. Unworn dentition of the crocodyliform Araripesuchus wegeneri. Detailed views of the anterior and middle portions of the tooth rows (MNN GAD20). A Left tooth rows in medial view. B Anterior portionof left tooth rows in medial view. C Middle portion of left tooth rows in medial view. Scale bar equals 1 cm in A and 5 mm in B and C. Abbreviations: ca, carina; d2, 4, 5, 7, 9, 11, 14, 16, dentary tooth 2, 4, 5, 7, 9, 11, 14, 16; m1, 3, 5, 7, 9, 13, maxillary tooth 1, 3, 5, 7, 9, 13; ne, neck; pm2–5, premaxillary tooth 2–5; rt, root.

Figure 22. Endocast of the crocodyliform Araripesuchus wegeneri. Endocast (UCRC PVC5) prototyped from a computed-tomography scan of skull MNN GAD19. Th e endocast lacks a portion of the pituitary fossa and right and left labyrinths. A Lateral view. B Dorsal view. C Ventral view. Scale bar equals 1 cm. Abbreviations: cer, cerebrum; cnII, cranial nerve II (optic nerve); lsin, longitudinal sinus; opt, optic lobe; pit, pituitary fossa; vfo, ventral fossa.

Figure 23. Block containing skeletons of the crocodyliform Araripesuchus wegeneri. Three aligned and partially articulated skeletons (MNN GAD20–22) and a partial skull (MNN GAD23) in dorsal view. Weathered portions of the crania were restored based on MNN GAD19. Scale bar equals 20 cm. Abbreviations: cda, caudal dermal armor; ma, manus; pe, pes.

Figure 24. Caudal skeleton of the crocodyliform Araripesuchus wegeneri. Flexed, articulated tail showing paired dorsal osteoderm rows in dorsal view, lateral osteoderm row in lateral view and ventral osteoderm rows in ventral view (MNN GAD20). Scale bar equals 5 cm. Abbreviations: k, keel; l do, left dorsal osteoderm; l vo, left ventral osteoderm; r do, right dorsal osteoderm; r lo, right lateral osteoderm; r vo, right ventral osteoderm.

Figure 25. Forelimb bones of the crocodyliform Araripesuchus wegeneri. A Left humerus in anterior view (MNN GAD20). B Partial right forelimb in anterior view (MNN GAD21). Scale bars equal 2 cm. Abbreviations: dcon, distal condyles; dpc, deltopectoral crest; hd, head; mc1–3, metacarpal 1–3; ra, radius; rae, radiale; sh, shaft; ul, ulna; ule, ulnare.

Figure 26. Manus and pes of the crocodyliform Araripesuchus wegeneri. A Right manus in dorsal view (MNN GAD22). B Right pes in dorsal view (MNN GAD22).Scale bar equals 1 cm in A and 2 cm in B. Abbreviations: I-V, digits I-V; mc1–5, metacarpal 1–5; mt1–4, metatarsal 1–4; ph, phalanx; un, ungual.