Kaprosuchus saharicus Sereno &amp; Larsson 2009, sp. n.
Creators: name: Sereno, Paul
name: Larsson, Hans
Publisher: name: Zenodo
Year: 2009
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Reptilia
Crocodilomorphi
Mahajangasuchidae
Kaprosuchus

description: <i>Kaprosuchus saharicus</i> sp. n. urn:lsid:zoobank.org:act: 1951A16E-5AD8-4959-AB6B-666D02B22049 Figs. 32–36 Tables 10, 11 <b>Etymology.</b> <i>Sahara</i>, Sahara Desert; - <i>icus</i>, belonging to (Greek). Named for the region where the holotype was discovered. <b>Holotype.</b> MNN IGU12; nearly complete skull missing only portions of the right postorbital, squamosal and the middle one-third of the braincase. <b>Type locality.</b> Iguidi (west of In Abangharit), Agadez District, Niger Republic (N 17° 56’, E 5° 37’) (Fig. 1A). <b>Horizon.</b> Echkar Formation, Tegama Series; Upper Cretaceous (Cenomanian), ca. 95 Mya (Taquet 1976). In association with the crocodyliform <i>Laganosuchus thaumastos</i>, the abelisaurid <i>Rugops primus</i>, the spinosaurid <i>Spinosaurus</i> sp., the carcharodontosaurid <i>Carcharodontosaurus iguidensis</i>, an unnamed rebbachisaurid and titanosaurian sauropods. <b>Diagnosis.</b> 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. <b>Dorsal skull roof.</b> The cranium of <i>Kaprosuchus</i> 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 <i>Kaprosuchus</i>, 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 <i>premaxilla</i> 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. <b>Table |0.</b> Dimensions (mm) of the skull of <i>Kaprosuchus saharicus</i> (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 <i>maxilla</i> 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 <i>nasal</i> 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 <i>prefrontal</i> 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 <i>lacrimal</i> 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 <i>frontal</i> 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 into a low sagittal crest (Figs. 33B, 34B). The orbital margin is slightly everted (Figs. 33A, 34A). Th e frontal is excluded from entering the supratemporal fossa by the parietal and postorbital, the latter contacting the frontal along an interdigitating suture. The <i>parietal</i> is fused to its opposite forming a very narrow skull table between the supratemporal fossae (Figs. 33B, 34B). Th at surface is rugose, depressed in the midline, and raised into a sharp edge along the medial rim of the supratemporal fossa, closely resembling the condition in <i>Mahajangasuchus</i> (Turner and Buckley 2008). The posterior edge of the parietals overhangs the occiput forming a posterior cranial margin that would have extended at least 1 cm beyond the occiput. Th e posterolateral portions of the parietals extend even further posterodorsally to form the medial portion of the base of the squamosal horn. Th at interdigitating parietal-squamosal suture passes anterolaterally along the medial margin of the enlarged foramen within the fossa. The ventral contact with the supraoccipital has a pneumatic recess, suggesting that the mastoid antrum in the supraoccipital likely passed dorsally into the parietal. The triradiate <i>postorbital</i> forms the posterior margin of the orbit, anterolateral margin of the supratemporal fenestra, and anterior margin of the laterotemporal fenestra. The medial process is broad, its posterior one-third devoted to the smooth margin of the supratemporal fossa. The subtriangular posterior process is deeply notched laterally for the anterior process of the squamosal. Th e ventral process is inset and continuous posteriorly within the auditory fossa. The tetraradiate <i>squamosal</i> has anterior, medial, posterior and posterodorsal rami, although only the medial and posterodorsal rami are preserved. Th e medial ramus forms most of the posterior margin of the supratemporal fenestra and surrounds the enlarged pneumatized opening to the posttemporal canal. Th e novel posterodorsal ramus is an elaboration of the posterior margin of the skull table (Fig. 32). It extends posterodorsally from the skull table at least two centimeters posterior to the occiput and has a markedly pitted and rugose surface. Broken along its distal edge, the process may have been longer and/or continued in keratin. Even at its preserved length, it is particularly prominent in anterior view of the skull (Fig. 36A). Other crocodylians have been reported with squamosal horns, the most exaggerated occurring in <i>“ Crocodylus ” robustus</i> (Brochu 2006). In this case and other crocodylids, the horn is an elaboration of the lateral edge of the squamosal rather than the posterior margin, and there is no contribution from the parietal. The <i>jugal</i> has anterior, dorsal and posterior rami and forms the slightly everted ventral margin of the orbit. The anterior ramus is tongue-shaped and particularly broad, whereas the posterior ramus is strap-shaped. Both are oriented so they are more broadly exposed in dorsal than lateral views (Figs. 33A, B, 34A, B), as in <i>Mahajangasuchus</i> (Turner and Buckley 2008). Furthermore, as in <i>Mahajangasuchus</i>, the anterior and posterior rami are separated by a deep embayment, such that in lateral view the ventral margin of the anterior ramus is angled posterodorsally whereas that of the posterior ramus angles posteroventrally (Figs. 33A, 34A). Distinctive fossae are also present on each ramus, facing laterally on the anterior ramus and ventrally on the posterior ramus, again as in <i>Mahajangasuchus</i> (Turner and Buckley 2008). The V-shaped <i>quadratojugal</i> forms a broad plate at the posterior corner of the laterotemporal fenestra. The anterior ramus and the anterior one-half of the dorsal ramus are textured. Th e quadratojugal extends toward the lateral quadrate condyle, wrapping onto its ventral side, but does not participate in the jaw articulation. The quadratojugal-quadrate suture is visible near the jaw articulation but fuses as it passes anterodorsally. Th e dorsal contacts of the quadratojugal are not preserved. <b>Palate.</b> The premaxillary palate is exposed only near the alveolar margin, where there are located two deep fossae, which accommodate the crowns of the first and second dentary teeth. The first dentary tooth is larger than the second, and the fossa on the premaxilla is correspondingly very large, its anterior margin extending between pm1 and pm2 to reach the anterior margin of the premaxilla (Figs. 33C, 34C). A second smaller fossa for the smaller d2 is located posterior to pm2. Although uncommon, an enlarged anteriorly placed fossa on the premaxillary palate separating pm1 and pm2 occurs in some extant crocodylians such as <i>Osteolaemus</i> (Iordansky 1983). <i>Mahajangasuchus</i> has an enlarged d1 (Buckley and Brochu 1999) and apparently has a premaxillary palate with a similarly positioned enlarged fossa (Turner and Buckley 2008). The palatal shelves of the maxillae contact along their length and form a broad, U-shaped secondary palate that appears to curve ventrally from the premaxillary palate (Figs. 33C, 34C). The <i>palatine</i> forms most of the broad posterior one-half of the secondary palate (Figs. 33C, 34C). A slender process extends between the maxillae anteriorly. Posteriorly, the palatine forms the straight, nearly transverse anterior margin of the choana. Laterally, the palatine expands but does not reach the narrow suborbital fenestra, separated from that opening on both sides of the palate by a narrow contact between the maxilla and pterygoid. Th is unusual condition is absent in <i>Anatosuchus</i> (Figs. 5C, 6C), <i>Araripesuchus</i> (Figs. 14C, 15C), <i>Mahajangasuchus</i> (Turner and Buckley 2008) and may be unique among crocodyliforms. The suborbital fenestrae are shifted to the lateral edge of the palate. Because the lateral margin formed by the maxilla and ectopterygoid ui shifted dorsally, the fenestra opens laterally as much as ventrally and is nearly obscured in ventral view (Figs. 33C, 34C). In this regard, <i>Kaprosuchus</i> is clearly derived and quite distinct from the aforementioned crocodyliforms (Turner and Buckley 2008). The <i>pterygoid</i>, fused to its opposite, has a broad palatal ramus that forms the remainder of the border of the choana and extends laterally over the palatines to border the suborbital fenestra. Th e lateral border of the choana is flat and lacks a discrete edge (Figs. 33C, 34C). At the anterolateral corner of the choana, the pterygoid has a short medial process that supports the palatine. Th e choanal septum is strut-shaped anteriorly and posteriorly but has an expanded ventral margin centrally. Lenticular fossae are present on either side of a thin median septum. The posterior rim of the choana is sturdy and rod-shaped without any processes. The choanal fossa is invaginated under this rim. The pterygoids extend laterally and posteriorly, so the posterior margin of the palate is deeply U-shaped, unlike the less embayed margin in <i>Anatosuchus</i> (Figs. 5, 6), <i>Araripesuchus</i> (Figs. 14C, 15C), and <i>Mahajangasuchus</i> (Turner and Buckley 2008) but similar to the deeply embayed posterior margin of the palate in baurusuchids such as <i>Stratiotosuchus</i>. The <i>ectopterygoid</i> twists into a vertical plane, anteriorly, forming the lateral edge of the suborbital fenestra. Posteriorly, the ectopterygoid extends as the swollen lateral margin of the pterygoid flanges. The <i>quadrate</i> angles posteroventrally to the jaw articulation in lateral view (Figs. 33A, 34B). Th e condyles are broad and transversely oriented, the lateral condyle larger and more convex. A subcircular fossa is present dorsal to the condyles. A foramen on the medial edge of the fossa just dorsal to the medial condyle is identified as the opening of the siphoneal foramen. <b>Braincase.</b> The parasphenoid and posterior two thirds of the braincase are not preserved. Th e ventral portion of the <i>basioccipital</i> and <i>basisphenoid</i> are present, their ventral surface inclined anteroventrally at approximately 45°. A low median crest is present on the basioccipital, anterior to which is a large Eustachian foramen. The basisphenoid has limited ventral exposure between the pterygoids and basioccipital, as in <i>Anatosuchus</i> and <i>Araripesuchus</i>. Two crests are present on the basisphenoid to either side of the Eustachian opening (Figs. 33C, 34C). <b>Lower jaw.</b> The jaws are shut with prominent crowns fitted snugly into notches in the opposing jaw margin (Fig. 32). Separation of the jaws would have risked damage to the teeth and alveolar margins. Th e skull was subjected to a computed-tomographic scan to locate small dentary crowns covered from view by the maxilla, and then a cast of the skull was cut apart with hidden teeth restored (Figs. 33A, 34A). Unlike the sculpted bones of the cranium, most of the external surface of the lower jaw is lightly textured. Only the symphyseal margin and posterior one-quarter of the lower jaws are sculpted. The <i>dentary</i> is dorsoventrally deep with a nearly vertical lateral surface marked by shallow vertical undulations (Figs. 33A, 34A). Posteriorly, in the region of the coronoid process, the depth of the dentary exceeds that of the dorsal skull roof, as in <i>Mahajangasuchus</i> (Buckley and Brochu 1999; Turner and Buckley 2008). As in that genus, the prominence of the coronoid process is accommodated by a marked embayment in the jugal. Anteriorly, the s
description: Published as part of <i>Sereno, Paul &amp; Larsson, Hans, 2009, Cretaceous Crocodyliforms from the Sahara, pp. 1-143 in ZooKeys 28 (28)</i> on pages 63-77, DOI: 10.3897/zookeys.28.325, http://zenodo.org/record/576570
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