Kaprosuchus saharicus Sereno & Larsson 2009, sp. n.

Kaprosuchus saharicus sp. n. urn:lsid:zoobank.org:act: 1951A16E-5AD8-4959-AB6B-666D02B22049 Figs. 32–36 Tables 10, 11 Etymology. Sahara, Sahara Desert; - icus, belonging to (Greek). Named for the region where the holotype was discovered. Holotype. MNN IGU12; nearly complete skull missing only portions of the right postorbital, squamosal and the middle one-third of the braincase. Type locality. Iguidi (west of In Abangharit), Agadez District, Niger Republic (N 17° 56’, E 5° 37’) (Fig. 1A). Horizon. Echkar Formation, Tegama Series; Upper Cretaceous (Cenomanian), ca. 95 Mya (Taquet 1976). In association with the crocodyliform Laganosuchus thaumastos, the abelisaurid Rugops primus, the spinosaurid Spinosaurus sp., the carcharodontosaurid Carcharodontosaurus iguidensis, an unnamed rebbachisaurid and titanosaurian sauropods. Diagnosis. Mid-sized (̴ 6 m) neosuchian with the cranium characterized by parasagittal premaxillary rugosities separated by smooth margins near the midline and along the ventral alveolar margin; median keel formed along interpremaxillary suture; circumnarial fossa absent external to the rim of the external nares; rim of external nares telescoped above snout and internarial bar; premaxillary medial process forms posterior margin of the narial rim; nasal forms all of the internarial bar; lacrimal anterior ramus extends anterior to the antorbital fossa; jugal notch for surangular shifted strongly dorsomedially; fossa on jugal dorsal to coronoid process; supratemporal bar with parasagittal orientation; rugose, posterodorsally projecting squamosal-parietal horn; pneumatic spaces within the supratemporal fossa project into the base of the squamosal-parietal horn; anterior palate transversely convex and posterior palate transversely concave; choanal fossa subquadrate; choanal septum expanded ventrally with lenticular shape; and suborbital fossa transversely narrow and facing laterally. Diagnostic features of the lower jaws include a dentary symphysis with long axis canted posteroventrally at 45° from the horizontal; surangular attachment process immediately posterior to the mandibular flange; angular ventral margin everted; hypertrophied retroarticular process (equaling quadrate length and three times the width of the quadrate condyles); retroarticular process with lateral ridge; axis of retroarticular process diverges posterolaterally; and the retroarticular ramus of the angular expands transversely toward the distal extremity of the process. Diagnostic features of the dentition include hypertrophied premaxillary, maxillary and dentary caniniforms extending dorsal and ventral to the maxilla and dentary, respectively; nearly straight, labiolingually compressed crowns; pm1 rotated so that the lingual crown surface faces posterolaterally to oppose d1 caniniform; small noncaniniform maxillary teeth; d1 and d2 project dorsally into premaxillary pits, d1 enlarged relative to d2; and d3 (rather than d4) constitutes the lower caniniform. Dorsal skull roof. The cranium of Kaprosuchus presents a unique morphological hybrid that combines aspects of two of the cranial forms commonly encountered among crocodylomorphs (Langston 1973; Brochu 2001). Th e snout has generalized proportions with a dorsally opening naris. Normally the teeth in this skull form are subconical and of moderate length, and the posterior skull of moderate depth. In Kaprosuchus, by contrast, the generalized snout is paired with hypertrophied, labiolingually compressed caniniforms and a posterior skull with deep proportions (Figs. 32–34). The external nares are telescoped dorsally with a sharp rim (Fig. 35A). In profile (Figs. 33A, 34A), the snout ascends as it joins the orbital rim and skull table, beyond which the squamosal horns project at a conspicuous angle (Fig. 36A). The antorbital fenestra is narrow but elongate and partially surrounded by a fossa (Fig. 35B). Despite the dorsoventrally flattened snout, the subcircular orbits open laterally more than vertically and are angled anteriorly, suggesting that there may have been overlap in the visual fields (Fig. 36A). Th e supra- and laterotemporal fenestrae are relatively small, reflective of the relatively short skull table (Figs. 33B, 34B). Most of the cranial surface has linear sculpting, with subcircular pitting predominant only on the frontals. Two aspects of surface texture require special comment. The anterior surface of the premaxilla has a raised rugose texture with several neurovascular openings (Figs. 35A, 36). The second unusual feature is branching impressed vessel tracts, a pair of which emerge from the anterior end of the antorbital fenestra (Figs. 33B, 34B). Th e more posterior of these tracts bifurcates distally, with one sub-branch curving ventrally to the alveolar margin by maxillary tooth 7 and a second sub-branch curving posteriorly onto the anterior end the jugal. The more anterior of these tracts courses anteriorly along the snout margin, with a pair of sub-branches curving to the alveolar margin by the diastema and by the posterior margin of the third maxillary caniniform (Figs. 33A, 34A). The premaxilla forms the broad snout end (Figs. 33, 34, 35A, 36A). Most of the external surface of the bone has a rugose texture that is sharply delimited by smooth margins along the interpremaxillary suture medially and along the alveolar margin ventrally. As a result, the paired rugosity strongly resembles a well-trimmed “mous- tache” in anterior view (Fig. 36A). Th e edges of the rugosity are elevated above the body of the premaxilla, suggesting that the rugosity is a product of secondary growth. This surface likely supported a keratinous shield of some kind, as is often the case for rugose, elevated, vascularized bone among extant amniotes. Table |0. Dimensions (mm) of the skull of Kaprosuchus saharicus (MNN IGU12). Paired structures measured on left side except as indicated. Parentheses indicate estimated measurement. 1 Measurement from right side. The alveolar margin of the premaxilla is rounded and gently scalloped between the premaxillary teeth. the alveolar margin descends toward the large alveolus of the caniniform pm3. In the midline, the interpremaxillary suture lies in a trough near the alveolar margin but projects as a crest between the rugosities (Fig. 36A). Th e rim of the external naris is gently everted (Fig. 36A). In dorsal view, swollen premaxillary processes extend the elevated rim to the posterior side of the external naris (Fig. 35A). The posterior ramus of the premaxilla meets the maxilla along a raised suture. The medial margin of the ramus approaches the midline, reducing the nasals to a narrow fused median strut (Figs. 33B, 34B). The medial two-thirds of each maxilla is oriented horizontally whereas the lateral one-third is oriented vertically. In lateral view, the anterior end of the maxilla is deeply notched to accommodate a large caniniform d3 (Figs. 33A, 34A). A large dorsal bulge is present over the caniniform m3 to accommodate its root (Fig. 36B). Three distinct ridges are present on the dorsal aspect of the maxilla. The first curves posteromedially from the notch for the caniniform d3 to the maxilla-nasal suture; the second curves from the alveolar bulge over the caniniform m3 to the maxilla-nasal suture; and the third arises along the dorsal margin of the antorbital fenestra. Th e second and third ridges join posterodorsally to form a V-shaped junction on the prefrontal, which is located dorsal to the posterior end of the antorbital fenestra. Th e posterior rami of the maxilla diverge. Th e posteroventral ramus maintains a horizontal orientation, whereas the posterodorsal ramus ascends at 45° toward the orbital rim. The nasal is elongate, transversely arched, and fused to its opposite anteriorly and along its mid-section (Figs. 33A, 34A). The nasals form all but the anteriormost extremity of the internarial bar. Th e nasals contact the frontals along a transverse interdigitating suture. The nasal-maxilla suture has a fine saw-tooth pattern, with projections on the nasal pointed anterolaterally. The prefrontal has anterior, posterior and ventral rami. Th e subrectangular anterior ramus is the longest, butting at its anterior extremity against a notch in the nasals along a slightly elevated squamous suture. At mid-length along this ramus, there is a raised, rugose V-shaped ridge, proximal to which is an arcuate groove. Th e central body of the prefrontal is inset for attachment of an anterior palpebral (Fig. 35B). Th e tapered posterior end of the subtriangular posterior process is inset into frontal along the orbital rim, which is gently everted. Its dorsal surface is recessed before meeting the frontal medially along a raised suture (Fig. 35B). Th e ventral ramus must have tapered strongly in width, angling toward the midline, where the base of the “pillar” is preserved. It expands anteroposteriorly to form a solid buttress to the palatine on the palate. The central body of the lacrimal is subquadrate, from which extend a long anterior and a short ventral ramus. Nearly all of this bone is oriented in a vertical plane. The orbital margin is beveled, presenting a smooth surface in lateral view (Fig. 35B). Th e dorsal edge of the anterior ramus is everted and rugose, joining the prefrontal along a ridge dorsal to the antorbital fenestra. Th e lacrimal forms the C-shaped posterior margin of this fenestra, contributing to its ventral margin and half of its dorsal margin. Th e lacrimal also forms most of the antorbital fossa, which is located on the dorsal side of the fenestra (Fig. 35B). The frontal is fused to its opposite. Th e composite element is diamond-shaped in dorsal view, with interdigitating nasal and parietal sutures anteriorly and posteriorly. The fused interfrontal suture is raised

Récupéré en direct depuis OpenAlex et désinversé. Les résumés ne sont pas conservés dans cette base de données : les index inversés représentent 8,6 Go des 9,3 Go de texte de la base, et le serveur dispose de 13 Go libres.