Eocarcharia dinops, Sereno & Brusatte, 2008

Sereno, Paul C. & Brusatte, Stephen L., 2008, Basal abelisaurid and carcharodontosaurid theropods from the Lower Cretaceous Elrhaz Formation of Niger, Acta Palaeontologica Polonica 53 (1), pp. 15-46 : 26-35

Eocarcharia dinops sp. nov.

Figs. 9–17 , 19A , Table 3.

Derivation of the name: From Greek dinops , fierce−eyed; in reference to the massive ornamented brow above the orbit.

Holotype: MNN GAD2 , a complete left postorbital ( Figs. 9 , 10 ).

Referred material: MNN GAD3, complete left postorbital; MNN GAD4, partial right postorbital; MNN GAD5, partial right postorbital; MNN GAD6, partial right postorbital; MNN GAD7, nearly complete left maxilla ( Figs. 11–13); MNN GAD8, right maxillary fragment; MNN GAD9, left maxillary fragment; MNN GAD10, left frontal and prefrontal ( Figs. 14 , 15 ); MNN GAD11, frontoparietal ( Fig. 16 ); MNN GAD12, three teeth; MNN GAD13, tooth fragment; MNN GAD14, complete crown ( Fig. 17B ).

Type locality: “Gadoufaoua” on the western edge of the Ténéré Desert, Niger; type locality has coordinates N 16 ° 88’ and E 9 ° 88’; referred specimens come from a 10 km stretch of richly fossiliferous outcrop ( Fig. 1A ; Taquet 1975; Sereno et al. 1998; Sereno et al. 1999; Taquet and Russell 1999).

Type horizon: Elrhaz Formation (Aptian–Albian, ca. 112 Ma).

Diagnosis.—Large−bodied carcharodontosaurid with enlarged subtriangular laterally exposed promaxillary fenestra larger in size than the maxillary fenestra, a circular accessory pneumatic fenestra on the posterodorsal ramus of the maxilla, dorsoventral expansion of the antorbital fossa ventral to the promaxillary and maxillary fenestrae, postorbital brow accentuated by a finely textured ovoid swelling, or boss, positioned above the posterodorsal corner of the orbit, postorbital medial process with a plate−shaped projection fitted to an articular slot on the frontal, postorbital articulation for the jugal that includes a narrow laterally−facing facet, an enlarged prefrontal lacking the ventral process with subquadrate exposure on the dorsal skull roof and within the orbit (limiting the anterior

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ramus of the frontal to the roof over the olfactory bulbs), and a low protuberance on the frontoparietal suture.

Eocarcharia dinops also differs from other carcharodontosaurids such as Acrocanthosaurus , Giganotosaurus , and Carcharodontosaurus by the low proportions of the suborbital flange on the postorbital and from Mapusaurus , Giganotosaurus , and Carcharodontosaurus by the absence of extensive external neurovascular grooves on the maxilla and blade−shaped crowns with prominently developed, marginal, arcuate enamel wrinkles in upper and lower tooth rows. Unlike these advanced carcharodontosaurids, Eocarcharia retains the prefrontal as a separate element and has only a rudimentary lacrimal−postorbital suture. Finally, Eocarcharia has a relatively small planar sutural surface on the postorbital for the squamosal, rather than the more complex spiral articulation observed in Carcharodontosaurus , Mapusaurus , and Giganotosaurus .

Description

Maxilla.—The maxilla is represented by one nearly complete specimen ( Figs. 11–13, Table 3; MNN GAD7) and two that preserve only the central portion of the bone. The maxilla is approximately twice as long as deep and has 15 alveoli ( Table 3). Articular surfaces include the premaxilla, nasal, lacrimal, jugal and palatine. The partially preserved premaxillary contact has a fairly steep, slightly arched profile, resembling that in Acrocanthosaurus ( Currie and Carpenter 2000) more so than the straight suture in Mapusaurus (Coria and Currie 2006) or Carcharodontosaurus ( Sereno et al. 1996) . The middle portion of the nasal contact is exposed in lateral view, where it clearly forms the border of the antorbital fossa, as in other carcharodontosaurids and most allosauroids. There is no slot anteriorly for the anteroventral process of the nasal as in abelisaurids. The jugal contact is well preserved along the posterior ramus and faces dorsolaterally ( Figs. 11, 12C, D ). The anteriormost end of the jugal contact, however, is more superficial and overlaps the posterior end of the antorbital fossa ( Fig. 12C, D ). The jugal thus would have formed the posteroventral corner of the antorbital fossa as in other carcharodontosaurids and most allosauroids. The anterior ramus of the lacrimal articulates in a beveled, V−shaped slot at the end of the posterodorsal ramus of the maxilla ( Fig. 11). The ventral ramus of the lacrimal contacts the maxilla medial to the jugal suture, as best exposed in medial view ( Fig. 13). Just anterior to the lacrimal contact lies a well marked, elongate scar for the lateral ramus of the palatine.

The maxilla is a relatively flat bone. Most probably in consequence the snout was relatively narrow in transverse width as in other carcharodontosaurids. In lateral view the maxilla has a gently sinuous alveolar margin ( Fig. 11). The anterior ramus is shorter anteroposteriorly than deep, as in Carcharodontosaurus , Giganotosaurus , Acrocanthosaurus , Allosaurus , and abelisaurids. In other basal tetanurans, such as Neovenator , Afrovenator , and spinosauroids, this ramus is longer than deep. The posterodorsal ramus in Eocarcharia tapers in width once it relinquishes the edge of the antorbital fossa to the nasal. This margin in Eocarcharia and other carcharodontosaurids is gently curved. In some basal tetanurans ( Dubreuillosaurus , “ Megalosaurus ” hesperis, Afrovenator ), there is an angular bend at this point along the margin.

The posterior ramus is tapered throughout its length ( Fig. 11). The posterior portion that contacts the jugal is deflected posteroventrally at an angle of 20 ° from a horizontal line established along the alveolar margin, a condition very similar to that in Acrocanthosaurus ( Currie and Carpenter 2000) . A few other basal tetanurans, namely Afrovenator , also exhibit this condition. Other basal tetanurans exhibit posteroventral deflection of only the very tip of this ramus (e.g., Torvosaurus , Suchomimus , Monolophosaurus , Allosaurus , Carcharodontosaurus , Sinraptor , Yangchuanosaurus ; Madsen 1976; Dong and Zhang 1983; Britt 1991; Currie and Zhao 1993; Zhao and Currie 1993; Sereno et al. 1996, 1998).

The external surface of the maxilla is textured with neurovascular foramina and associated channels but lacks the pervasive pits and grooves of Carcharodontosaurus and abelisaurids. Two rows of neurovascular foramina pierce the lateral surface dorsal to the alveolar margin. The ventral, or labial, row is situated about 5 mm above the alveolar margin and has larger foramina ( Figs. 11, 12C, D ). The upper row of foramina curves dorsally above the second alveolus.

The antorbital fossa in Eocarcharia is particularly deep anteriorly under the fenestrae ( Fig. 11). Unlike most theropods the ventral rim of the antorbital fossa parallels the alveolar margin rather than rising anteriorly, and the fossa wall below the fenestrae is deeper than the remaining ventral margin of the maxilla ( Fig. 12A, B ). The anteroventral corner of the fossa is squared rather than gently arched, a condition close to that in Acrocanthosaurus ( Currie and Carpenter 2000) , Neovenator (Brusatte et al. in press), Afrovenator ( Sereno et al. 1994) , Dubreuillosaurus ( Allain 2002) , and coelophysids

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( Tykoski and Rowe 2004). The antorbital fossa is bordered ventrally by a raised, somewhat swollen and rounded rim that flattens posteriorly ( Figs. 11, 12A, B ). Some carcharodontosaurids, such as Mapusaurus and Carcharodontosaurus saharicus , have an everted and swollen ventral margin ( Sereno et al. 1996; Coria and Currie 2006). In Giganotosaurus and Acrocanthosaurus , in contrast, most of the ventral margin is not raised (Coria and Salgado 1996; Currie and Carpenter 2000).

Three fenestrae are present on the wall of the fossa. The promaxillary and maxillary fenestrae are subtriangular, the former the larger of the two and measuring 52 mm in height and 29 mm across its base. Sinraptor also has a promaxillary fenestra that is larger than the maxillary fenestra ( Witmer 1997; contra Currie and Zhao 1993), although this is rare among theropods. Only the anterior margin of the promaxillary fenestra is concealed in lateral view by the rim of the antorbital fossa. A small subcircular accessory fenestra posterodorsal to the maxillary fenestra measures approximately 18 mm in diameter. Other basal neotheropods exhibit an accessory fossa in this region, including Ceratosaurus , Sinraptor , and some specimens of Allosaurus ( Witmer 1997; Rauhut and Fechner 2005). These accessory depressions, however, are variable in size and form and their homology is less certain than the promaxillary and maxillary fenestrae.

The internal sinuses of the maxilla are preserved in part despite erosion of the medial aspect of the maxilla ( Fig. 13). The promaxillary fenestra opens medially into a large cavity, the promaxillary recess, which extends anteriorly into the anterior ramus ( Witmer 1997). The maxillary fenestra opens medially into a separate chamber, the maxillary antrum, the medial wall of which has broken away. A transverse septum separates promaxillary and maxillary recesses. The rim of the antorbital fossa is exposed posterior to the fifth alveolus. Swellings for each tooth crypt are visible on the floor of the antorbital fossa.

The interdental plates are fused forming a continuous lamina, as in many basal neotheropods including Carcharodontosaurus , Giganotosaurus, Neovenator , Allosaurus , Torvosaurus , and Ceratosaurus . Weathering of the entire medial alveolar region has artificially enlarged several of the replacement foramina along the groove for the dental lamina and partially opened several of the anterior crypts in medial view ( Fig. 13). The seventh crypt has been opened to expose a complete replacement crown. The medial maxillary shelf dorsal to the row of replacement foramina is low and beveled by a long palatine articular scar that extends as far forward as the seventh alveolus. The anterior end of the shelf and the anteromedial maxillary process are not preserved. The row of replacement foramina is located approximately at mid height along the ramus, which is not proportionately as deep as in advanced carcharodontosaurids such Carcharodontosaurus ( Brusatte and Sereno 2007) and abelisaurids ( Fig. 3). Ventrally, the anteroposteriorly broad alveoli are separated by narrow troughs throughout most of the tooth row, as in Carcharodontosaurus ( Brusatte and Sereno 2007) but unlike most other basal neotheropods.

There are 15 teeth in the maxillary tooth row ( Fig. 13), posterior to which the maxilla is declined posteroventrally as in Acrocanthosaurus ( Currie and Carpenter 2000) . Fully erupted teeth were present in positions 2, 5, 6, 10, and 13 but were eroded away. Replacement teeth are exposed in most alveoli medial to the functioning crown as in other theropods ( Edmund 1960). We opened the crypt of the seventh alveolus to fully expose an erupting crown ( Fig. 17A ). Based on comparison to this tooth, we have tentatively referred several isolated teeth from the field area to Eocarcharia dinops (MNN GAD12–14; Fig. 17B ). Although these crowns are more transversely compressed than those of most theropods ( Smith et al. 2005), they are not strongly blade−shaped or characterized by a straight posterior carina or high relief enamel wrinkles (Brusatte et al. 2007), as occurs in Tyrannotitan , Mapusaurus , Giganotosaurus , Carcharodontosaurus , and an isolated tooth from Japan ( Coria and Salgado 1995; Sereno et al. 1996; Chure et al. 1999; Novas et al. 2005; Coria and Currie 2006).

The distal carina extends much further basally than the mesial carina, a common condition in theropods that also occurs in Allosaurus , Acrocanthosaurus , and a large carcharodontosaurid tooth from Patagonia ( Vickers−Rich et al. 1999). In contrast, both carinae extend basally to the same level in maxillary teeth of Carcharodontosaurus and Giganotosaurus . Serrations are present across the tip of the crown, as in Acrocanthosaurus ( Harris 1998) , Carcharodontosaurus , and most coelurosaurs ( Currie and Carpenter 2000). The serrations are fine and unilobate, rather than bilobate, as in Tyrannotitan ( Novas et al. 2005) .

Using descriptive metrics by Smith et al. (2005), the bestpreserved referred tooth ( Fig. 17B ) exhibits crown−base length (CBL) of 24 mm, crown base width (CBW) of 11 mm, crown height ( CH) of 48 mm, apical length (AL) of 57 mm, crown base ratio (CBR = CBW/CBL) of 0.46, crown height ratio (CHR = CH /CBL) of 2.0, average mesial serration density (MAVG) of 13 per 10 mm, average distal serration density (DAVG) of 15 per 10mm, and serration (= denticle) size density index of 0.87 (DSDI = MAVG/DAVG). Only one replacement crown is exposed in situ on the maxilla, and average mesial serration density (MAVG) is the only measure possible. This tooth has 11 serrations per 5 mm near its apex and 17 per 5 mm toward the base, resulting in a MAVG of 28 serrations per 10 mm, a serration size considerably smaller than those in the isolated crown. We have no explanation for this difference except to note that serration count may be subject to individual variation and also variation along the tooth row.

Prefrontal.—The prefrontal ( Figs. 14 , 15 ) articulates in a deep, squared notch in the frontal. The posteromedial corner is more deeply inset on the ventral side, where the frontal process for the nasal is narrower transversely than the prefrontal. A process of the prefrontal extends posteriorly from the posteromedial corner into a pit in the frontal; the pit is exposed only on the anterior margin of a disarticulated frontal ( Fig. 16C, D ). The prefrontal is absent in advanced carcharodontosaurids, such as Carcharodontosaurus ( Fig. 18B ). This region of the skull roof is occupied by the lacrimal, which like the prefrontal in Allosaurus and many other neotheropods has a cone−shaped posterior process that inserts into a deep pit in the frontal. For this reason, it seems likely that the “lacrimal” in advanced carcharodontosaurids is actually a coossified lacrimal−prefrontal.

The prefrontal and frontal are joined by an interdigitating suture posteriorly and posterolaterally, which is doubtless why they have remained in contact ( Fig. 14 ). The anterolateral suture with the lacrimal, in contrast, is pitted and sinuous but not interdigitating. Just before the suture reaches the lacrimal laterally, it opens into a narrow vertical fissure ( Fig. 14C, D ). Toward the anterior end, the anteromedially facing nasal articulation is developed as a vertical butt joint ( Fig. 14C, D ).

In most theropods that retain the prefrontal as a separate element, the bone is exposed on the skull roof as a relatively small, subtriangular element with a narrow anterior apex that tapers to a point between the nasal and lacrimal. A slender ventral process extends along the posteromedial aspect of the lacrimal just medial to the lacrimal foramen. By contrast, the form of the prefrontal in Eocarcharia is very unusual. First, there is no development of a ventral process, which is present in Acrocanthosaurus ( Currie and Carpenter 2000) , Allosaurus ( Madsen 1976) , Sinraptor ( Currie and Zhao 1993) , Monolophosaurus ( Zhao and Currie 1993) , and other theropods. There are no broken areas that might otherwise account for the absence of this process via postmortem damage. Second, the prefrontal is enlarged relative to the frontal, its transverse width is fully one−half the maximum width of the frontal, and its area nearly one−third that of the frontal in ventral view ( Fig. 14C, D ). Third, it has a subrectangular rather than subtriangular shape on the dorsal skull roof ( Fig. 14A, B ). And fourth, it is considerably thickened, especially its posterior margin, which is swollen and pitted similar to the adjacent surface of the frontal ( Figs. 14 , 15 ). The anterior portion of the prefrontal angles anteroventrally at about 45 ° in lateral view ( Fig. 15 ). In Eocarcharia , thus, the prefrontal is not only retained as a separate ossification in contrast to advanced carcharodontosaurids, but it is enlarged relative to the condition in Acrocanthosaurus ( Currie and Carpenter 2000) . Frontal.—A complete left frontal is preserved as well as a pair of similar−sized coossified frontals ( Figs. 14–16 ; Table 3). Coossification of the frontals and their firm attachment posteriorly to the parietals in the second specimen suggests that it had achieved maturity. Both specimens have an articular surface for the postorbital that receives the slots and grooves on the opposing postorbital articular surface. When the frontal−prefrontal and holotypic postorbital are joined, furthermore, the articular slots and processes accommodate one another and the margin of the supratemporal fossa runs continuously across both, strongly suggesting that they belong to the same species. Articular contacts on the frontal also include the nasal, lacrimal, parietal, laterosphenoid and orbitosphenoid.

In dorsal view the frontal is particularly broad at mid length ( Figs. 14A, B ). Although frontals that are at least one−half as broad as long characterize some abelisaurids, allosauroids, and tyrannosaurids, the frontal in carcharodontosaurids is especially broad. In Carcharodontosaurus maximum transverse width of the frontal is approximately 60% its length. In Eocarcharia the frontal is broader still, with a maximum transverse width 70% its maximum length. The frontal is thickened throughout and has an interdigitating interfrontal suture that fuses with maturity, as in other carcharodontosaurids and several other theropods ( Fig. 16 ). Anteriorly the fluted nasal suture angles steeply at about 45 ° when the body of the frontal is held horizontal ( Figs. 15C, D ). On the skull roof, the frontal−nasal suture appears to angle posteromedially to the midline without a median frontal reentrant ( Figs. 14A, B , 18A ). The prefrontal, as described in detail above, inserts into a squared notch in the frontal, which is deeper ventrally than dorsally ( Fig. 12 ). The lateral portion of the frontal, which is swollen, rugose, and marked by a well defined vascular groove and foramen, forms the medial portion of the brow ( Figs. 14A, B , 15 ).

Posteriorly, the supratemporal fossa is broadly exposed, the rim of which rises as a rounded ridge as it passes medially and joins the parietal suture not far from the midline ( Figs. 14A, B ). In advanced carcharodontosaurids such as Carcharodontosaurus , in contrast, the supratemporal fossa has negligible exposure dorsally, is displaced laterally far from the midline, and extends under the ridge so that both the frontal and parietal overhang the anteromedial corner of the fossa ( Fig. 18 ). Acrocanthosaurus (OMNH 10146) has an intermediate condition, in which the fossa on the frontal is invaginated with a low overhanging rim, whereas the fossa on the parietal is developed only as a near vertical wall.

In ventral view, the transversely narrow proportion of the anterior ramus of the frontal is well exposed and is devoted entirely to roofing the olfactory portion of the endocranium ( Figs. 12C, D , 14C, D ). In Acrocanthosaurus , Carcharodontosaurus , and other tetanurans (e.g., Sinraptor ; Currie and Zhao 1993), the broader anterior ramus of the frontal extends to each side of the endocranial roof. The narrow anterior ramus of the frontal is a very unusual feature of the skull roof of Eocarcharia , which clearly identifies the conjoined frontoparietal as pertaining to the same species ( Fig. 14C, D ). In this specimen, the arcuate articular trough for each orbitosphenoid is well preserved tapering to an end at mid orbit.

In lateral view the articular edge of the frontal has a subtriangular articular surface anteriorly for the lacrimal, the broadest portion of which is near the prefrontal ( Fig. 13A, B). This is opposite the condition in more advanced carcharodontosaurids, such as Acrocanthosaurus and Carcharodontosaurus , in which the articular surface on the frontal for the lacrimal (or lacrimal−prefrontal) is broadest posteriorly. Although the frontal is removed from the orbital margin by the lacrimal−postorbital contact, there appears to be a short nonarticular notch where these lateral bones join ( Fig. 15A, B ). The frontal−postorbital suture in Eocarcharia differs in detail from that in Acrocanthosaurus (OMNH 10146) and Carcharodontosaurus (SGM−Din 1). It features a deep articular slot for a long, thin process of the postorbital ( Fig. 15A, B ).

In medial view the rugose interfrontal suture ( Fig. 15C, D ) fuses with maturity ( Fig. 16 ). The dorsal surface of the frontal near the midline is gently concave ( Fig. 14A, B ), in contrast to the condition in Acrocanthosaurus (OMNH 10146) and Carcharodontosaurus (SGM−Din 1), in which the dorsal surface is gently convex.

Parietal.—The parietal, the anterior portion of which is preserved, has an interdigitating frontoparietal suture marked by a protuberance where the suture intersects the rim of the supratemporal fossa ( Fig. 16 ). This frontal portion of the protuberance is also present on the isolated frontal ( Fig. 14A, B ), suggesting again that these bones represent individuals of the same species. The supratemporal fossae are separated from the midline by a flat skull table, which is much narrower than that in Carcharodontosaurus ( Fig. 18 ). Acrocanthosaurus again shows an intermediate condition (OMNH 10146). In ventral view, the anterior portion of the parietal forms the roof over the endocranial cavity. Near the midline, the roof is flat across the frontal and parietal ( Fig. 16A, B ).

Lacrimal.—Although the lacrimal is not preserved, some of its unusual features can be ascertained from articular scars on the prefrontal, frontal, and postorbital. First, the lacrimal extended posteriorly along the orbital margin to contact the postorbital and exclude the frontal from that margin; this is shown by the small, but well defined, articular facet for the lacrimal on the postorbital ( Figs. 9 , 10B ). Second, the lacrimal thus would likely have contributed to the robust orbital brow as in other carcharodontosaurids; this is indicated by the broad and rugose articular area for the lacrimal on the frontal. And third, the lacrimal was likely strengthened to sustain considerable stress; this is indicated by the broad and rugose articulation with the prefrontal.

Postorbital.—The postorbital exhibits diagnostic features for Eocarcharia dinops for the referral to Carcharodontosauridae and for its relationships within that clade. The robust brow appears to resist breakdown, which may account for the preservation of four similar−sized postorbitals (MNN GAD3–6) in addition to the holotype (MNN GAD2; Figs. 9 , 10 ). The postorbital contributes to the border of the orbit, laterotemporal fenestra, and supratemporal fenestra ( Figs. 9 , 10 , 18A ; Table 3). The most prominent feature of the postorbital in lateral view is the thickened brow, which is divisible into an anterior portion with subquadrate proportions that is canted anterodorsally and a posterior portion with an ovate shape, here termed the orbital boss, that is canted posterodorsally ( Fig. 9 ). The anterior portion of the brow is divided by a horizontal vascular groove that leads to a foramen that enters the central portion of the brow. The most prominent portion of the brow, the orbital boss, is weakly divided into two parts, anteroventral and posterodorsal. All of the referred postorbitals show these structural details.

Contact between the postorbital and lacrimal is important to establish, given the absence of the latter among preserved bones. A small but definitive lacrimal articular surface is present at the anterior end of the orbital ramus, measuring 9 mm deep and 12 mm long ( Figs. 9 , 10B ). Although this contact excludes the frontal from the orbital margin, its surface is absolutely and proportionately smaller than in other carcharodontosaurids ( Acrocanthosaurus , Mapusaurus , Giganotosaurus , Carcharodontosaurus ) ( Fig. 19A 3, B 3). Removal of the frontal from the orbital margin ( Fig. 18 ), an initial stage of which is preserved in Eocarcharia , evolved independently in abelisaurids and later within Coelurosauria ( Tyrannosauridae ).

The texturing of the brow in Eocarcharia and other carcharodontosaurids suggests it was covered in keratin. The large and complex postorbital−frontal suture provides great stability against lateral impact. In advanced carcharodontosaurids, the already elaborated postorbital−lacrimal and postorbital−squamosal sutures, likewise, become even larger and more complex. The head of the laterosphenoid, which braces the postorbital medially, is set in a socket in the postorbital, which is particularly deep in advanced carcharodontosaurids ( Fig. 19B 2). All of these contacts seem enhanced to handle increased stress ( Byron et al. 2004).

The brow is clearly overbuilt for were primarily for display. We speculate here that the carcharodontosaurid brow may have been used for intraspecific lateral head−butting. Most large−bodied theropods such as allosauroids and spinosauroids do not have bony orbital swellings, or bosses, on the orbit margin. In those that do, such as abelisaurids and some large tyrannosaurids, the swelling differs in structural detail from that of Eocarcharia and other carcharodontosaurids. Although the swollen postorbital brow in Tyrannosaurus is solid ( Brochu 2003: fig. 17), it does not form a prominent lateral feature along the skull margin ( Brochu 2003: fig. 3) as in carcharodontosaurids ( Fig. 18 ). In Carcharodontosaurus saharicus , furthermore, there is a nonarticular, pitted pyramidal projection on the lateral aspect of the ventral ramus of the postorbital ( Fig. 19B 1 ). Both the brow and this ornamental feature project laterally, and both may have played a role in lateral head−butting.

Coria and Currie (2006: 80) describe a portion of the orbital brow in Giganotosaurus and Mapusaurus as a separate “palpebral” ossification distinct from the postorbital. No trace of such an accessory element is present in any of the well preserved postorbitals of Eocarcharia dinops or Carcharodontosaurus saharicus ( Fig. 19B ). The presence of the element in two taxa suggests that it is not an anomaly or artifact of preservation. Either these elements are already fused without trace in Eocarcharia and Carcharodontosaurus , or the accessory ossification in Giganotosaurus and Mapusaurus is a shared derived character.

The ventral ramus has a subrectangular cross−section at mid shaft in contrast to the derived U−shaped cross−section in spinosauroids ( Afrovenator , Torvosaurus , Dubreuillosaurus ; Sereno et al. 1994; Allain 2002). A small, rugose, distally positioned infraorbital process is present, which differs from the larger, subtriangular, more proximally positioned process in Acrocanthosaurus and advanced carcharodontosaurids ( Mapusaurus , Giganotosaurus , Carcharodontosaurus ; Figs. 9 , 19 ). In Eocarcharia , other carcharodontosaurids and abelisaurids, the suborbital process is formed solely by the postorbital, whereas in tyrannosaurids it is often joined ventrally by the jugal ( Chure 2000; Brochu 2003).

Medially the articular contacts with the frontal, parietal, and laterosphenoid are clearly demarcated ( Figs. 10A , 19A 2). The rugose frontal contact, which is canted along an anterodorsal−posteroventral axis, has a distinctive plate−shaped process that inserts into a matching slot on the frontal. This plate−shaped process, an autapomorphy of Eocarcharia dinops gen. et sp. nov., is not present in Carcharodontosaurus . More posteriorly a deep notch accommodates the remainder of the frontal and anterior end of the parietal. Posteroventral to the parietal contact, a shallow oval concavity accommodated the articular head of the laterosphenoid. In Carcharodontosaurus this cavity is deeper and bounded by a thin rim ( Figs. 10A , 19A 2).

Articular contact with the jugal and squamosal is exposed in medial and lateral views ( Figs. 9 , 19A 2). The postorbital articulates with the jugal along an elongate, articular surface that begins at mid length on the medial aspect of the ventral ramus and twists to face laterally at its ventral tip ( Fig. 9 ). Unlike any other theropod described to date, the jugal wraps around the posterior margin of the ventral ramus, where it lies in a narrow inset along its posterior edge. This interlocking postorbital−jugal articulation constitutes an autapomorphy for Eocarcharia dinops . The short posterior ramus is triangular in lateral view and has a wedge−shaped articular process for the squamosal, which is best exposed in dorsal view ( Figs. 10 , 19A 3). The anterior ramus of the squamosal splits to accommodate dorsal and ventral sides of this articular wedge. The dorsal articulation is subtriangular and inset. The ventral articulation extends anteroventrally just beyond the base of the posterior ramus of the postorbital, its tip exposed in lateral view near the margin of the laterotemporal fenestra ( Figs. 9 , 19A 1 ). In advanced carcharodontosaurids, the postorbital−squamosal articulation is developed as a more elaborate spiral articulation involving a lengthened posterior ramus of the postorbital ( Sereno et al. 1996; Fig. 19B ).

In dorsal view ( Figs. 10B , 19A 3) the postorbital forms the anterolateral corner of the supratemporal fossa as in most theropods but unlike abelisaurids, in which the supratemporal fossa does not reach the postorbital ( Wilson et al. 2003).

Orbitosphenoid.—The edge of the right and left orbitosphenoid is preserved in articulation within an articular trough on the frontal ( Fig. 16C, D ). It is clear from the limited extent of the orbitosphenoid and absence of articular scars farther anteriorly on the frontal that the olfactory tracts and bulbs were not surrounded by bone. Several independent lineages of theropods, in contrast, have enclosed the anterior end of the endocranial cavity by extending the ossified orbitosphenoid anteriorly between the orbits and by ossifying a median mesethmoid (or “interorbital septum”) between the olfactory tracts and bulbs. This has occurred in larger, more derived species within Ceratosauria ( Sampson and Witmer 2007), Allosauroidea (Larson 2001; Franzosa and Rowe 2005), and Tyrannosauroidea ( Brochu 2003). Among basal allosauroids such as Sinraptor ( Currie and Zhao 1993) and Allosaurus ( Hopson 1979) , it is clear that the anterior end of the endocranium remains unossified. Eocarcharia exhibits this basal condition, as shown by the limited anterior ossification of the orbitosphenoid of a mature individual ( Fig. 14C, D ). Acrocanthosaurus (Franzosa and Rowe 2005) , Giganotosaurus ( Coria and Currie 2002) , and Carcharodontosaurus ( Larsson 2001) , on the other hand, exhibit the fully−ossified derived condition.

Maturity and body size.—The cranial bones attributed to Eocarcharia pertain to mature, or near mature, individuals. Among the referred cranial bones are fused frontals ( Fig. 16 ), and these articulate well with the holotypic postorbital ( Fig. 9 ). Adult skull size appears to have been attained. The maxilla of Eocarcharia is approximately 70% and 50% of the linear dimension of the maxilla in adult specimens of Acrocanthosaurus (NCSM 14345) and Carcharodontosaurus (SGM−Din 1), respectively. This serves as a rough approximation of the size differential between these genera. Adult Eocarcharia thus appears to be about one−half of the linear dimensions of the derived carcharodontosaurids Giganotosaurus , Mapusaurus , and Carcharodontosaurus , and therefore would have had a body length of about 6 to 8 meters.

Figures

Fig. 9. Carcharodontosaurid theropod Eocarcharia dinops gen. et sp. nov. MNN GAD2 from the Lower Cretaceous Elrhaz Formation of Niger. Left postorbital (holotype) in lateral view; stereopair (A) and pencil drawing (B). Cross−hatching indicates broken bone; dashed lines indicate estimated edge.

Fig. 10. Carcharodontosaurid theropod Eocarcharia dinops gen. et sp. nov. MNN GAD2 from the Lower Cretaceous Elrhaz Formation of Niger. Stereopairs of left postorbital (holotype) in medial (A) and dorsal (B) views.

Fig. 19. Left postorbital in two carcharodontosaurids. A. Basal carcharodontosaurid Eocarcharia dinops gen. et sp. nov. MNN GAD2 from the Lower Cretaceous Elrhaz Formation of Niger. B. Advanced carcharodontosaurid Carcharodontosaurus saharicus (Deperet and Savornin, 1927) SGM−Din 1 from the Upper Cretaceous Kem Kem beds of Morocco. Line drawings in lateral (A1, B1), medial (A2, B2), and dorsal (A3, B3) views.

Fig. 14. Carcharodontosaurid theropod Eocarcharia dinops gen. et sp. nov. MNN GAD2 from the Lower Cretaceous Elrhaz Formation of Niger. Frontal and prefrontal in dorsal (A, B) and ventral (C, D) views; photographs (A, C) and line drawings (B, D). Cross−hatching indicates broken bone; grey tone indicates matrix.

Fig. 15. Carcharodontosaurid theropod Eocarcharia dinops gen. et sp. nov. MNN GAD2 from the Lower Cretaceous Elrhaz Formation of Niger. Frontal and prefrontal in lateral (A, B) and medial (C, D) views; photographs (A, C) and line drawings (B, D).

Fig. 16. Carcharodontosaurid theropod Eocarcharia dinops gen. et sp. nov. MNN GAD2 from the Lower Cretaceous Elrhaz Formation of Niger. Frontals, parietal and fragmentary right and left orbitosphenoids in dorsal (A, B) and ventral (C, D) views; photographs (A, C) and line drawings (B, D). Cross−hatching indicates broken bone.

Fig. 17. Carcharodontosaurid theropod Eocarcharia dinops gen. et sp. nov. from the Lower Cretaceous Elrhaz Formation of Niger. A. Crown of a replacing tooth in the seventh alveolus of the left maxilla (MNN GAD7) in medial view. B. Isolated crown (MNN GAD14) in medial (B1) and anterior (B2) views.

Fig. 1. A. The region of central Niger known as Gadoufaoua (black) and the sites (white dots) where the holotypic specimens of Kryptops palaios gen. et sp. nov. (site G88) and Eocarcharia dinops gen. et sp. nov. (site G138) were discovered. B. Site map for Kryptops palaios (MNN GAD1) gen. et sp. nov. with cranial elements shown at twice natural size. The maxilla, located 15 m from the other bones, was not in place and probably was originally closer to the other bones.

Fig. 12. Carcharodontosaurid theropod Eocarcharia dinops gen. et sp. nov. MNN GAD2 from the Lower Cretaceous Elrhaz Formation of Niger. Left antorbital region in left lateral view (A, B) and posterior ramus in lateral view (C, D); photographs (A, C) and line drawings (B, D). Cross−hatching indicates broken bone; dashed lines indicate estimated edge; grey tone indicates matrix.

Fig. 18. Posterior skull roof in dorsal view reconstructed in two carcharodontosaurids. A. Basal carcharodontosaurid Eocarcharia dinops gen. et sp. nov. B. Advanced carcharodontosaurid Carcharodontosaurus saharicus (Deperet and Savornin, 1927).