Arambourgisuchus khouribgaensis, Jouve & Iarochène & Bouya & Amaghzaz, 2005
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publication ID |
https://doi.org/ 10.5281/zenodo.13620799 |
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persistent identifier |
https://treatment.plazi.org/id/711F661D-FF90-FF9F-FF90-FE61FEFDDE21 |
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treatment provided by |
Felipe |
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scientific name |
Arambourgisuchus khouribgaensis |
| status |
sp. nov. |
Arambourgisuchus khouribgaensis sp. nov.
Etymology: Khouribga (place name), referring to the city near the type locality.
Holotype: OCP DEK−GE 300 ( Figs. 2, 5 View Fig –7), a nearly complete crushed skull, lacking the anterior part of the rostrum. Originally preserved in a phosphatic block, it has been mechanically prepared on both sides. It is very crushed and dorsoventrally flattened from the anterior level of the palatine to its posterior end. Some sutures are hardly visible, but almost all the bones can be reconstituted. All the measurements are taken for the holotype.
Type locality and horizon: The phosphate mine of Sidi Chenane, in the Ouled Abdoun Basin, Morocco; from the “couche (bed) 2a”, Thanetian (Palaeocene).
Diagnosis.—Dyrosaurid with about 20 to 21 robust but sharp teeth on the upper tooth row (on each ramus); teeth moderately elongated, with a posterior carina which ends before reaching the base of the teeth (not in the more posterior teeth), buccal and lingual surface smooth or lightly striated; interfenestral bar very narrow (sagittal crest); supraoccipital, with parietal, tapers posteriorly between the two occipital tuberosities; occipital tuberosities well developed, and dorsoventrally flattened; suture between basioccipital and exoccipital (posteriorly to basioccipital tuberosities) deeply within a groove; mandibular symphysis long, wider than high in its median part, and ending posteriorly at the level of the sixteenth tooth; splenials end dorsally between the level of the tenth and the eleventh tooth. Differs from Dyrosaurus in having less numerous, and more massive teeth, a narrower interfenestral bar, a posterior wall of the supratemporal fenestra very inclined dorsally, the occipital tuberosities dorsoventrally flattened, and the supraoccipital which tapers posteriorly; from Congosaurus in having a longer snout, more massive and more widely separated teeth; from Hyposaurus in having a longer snout, and more massive teeth, more ventrally projected basioccipital tuberosities, and the supraoccipital which tapers posteriorly; from Rhabdognathus in having more ventrally projected basioccipital tuberosities, the occipital tuberosities dorsoventrally flattened, and the supraoccipital which tapers posteriorly.
Material.—In addition to the holotype there are:
OCP DEK−GE 18 ( Fig. 3 View Fig ). An almost complete skull, with mandible. The skull is crushed, and the occipital part is strongly damaged. In the left ramus of the mandible the posterior part is missing a little behind the end of the mandibular symphysis; the right mandible is badly preserved.
OCP DEK−GE 269. A posterior part of a mandibular symphysis with five or six tooth alveoli on each side.
100 mm
quadratojugal postorbital jugal orbit tooth splenial
OCP DEK−GE 1200. The anteriormost portion of a mandibular symphysis exposed in ventral view.
Description
Cranial openings. —The external nares are poorly preserved. They seem large, dorsally directed, and surrounded by the premaxillae only.
The orbits are rounded, dorsolaterally oriented, bordered posterolaterally by a prominent anterolateral postorbital process typical of dyrosaurids.
The supratemporal fenestrae are longer (about 17 cm) than wide (about 6 cm), separated medially by a very narrow interfenestral bar constituted by the frontal (for about one fifth) and in a major part by the parietal ( Figs. 2A, 4A View Fig ). The fenestra appears to be bordered laterally more by the postorbital than by the squamosal. The posterior margin is constituted for about the same proportion by squamosal and parietal.
The infratemporal fenestra is not preserved, but can be reconstructed after the holotype ( OCP DEK−GE 300 ; Figs. 2A, 4A View Fig ). It is anteriorly limited by the postorbital bar, constituted half by the postorbital and jugal, this latter constituting the major part of the ventral margin. The quadratojugal borders the posterior margin, constitutes the posterior part of the dorsal edge, excluding the quadrate from the dorsal margin. It participates for a small length to the ventral edge .
The temporal canal, wider than high, is largely surrounded by the parietal (two third), with the squamosal contributing to its lateral margin.
The suborbital fenestra is formed medially by the palatine and the pterygoid, posterolaterally by the ectopterygoid, and anterolaterally by the maxilla ( Figs. 2B, 4B View Fig ). The medial and lateral edges are curved, and the most posterior part is acute and bears the ectopterygoid−pterygoid suture.
The choanae are deep, ventrally oriented (slightly caudally), and separated by a pterygoidian septum ( Figs. 2B, 4B View Fig ). They are largely surrounded by the pterygoid, only the most anterior border being formed by the palatine. The choanae are not very abruptly pierced within the pterygoids: the choanae lie within a depression on the ventral pterygoidal surface. The depression extends posterolaterally on to the lateral branch of the pterygoid, tapering before the pterygoid contacts the ectopterygoid. Thus, the choanal margin is not abrupt.
On the occipital face, the parietal forms the dorsomedial quarter of the posttemporal fenestra ( Fig. 5 View Fig ). The squamosal contributes to it dorsolaterally (less than the lateral half), and very slightly to the ventrolateral margin. The supraoccipital constitutes a small part of the ventral margin of the posttemporal fenestra (the rest formed by exoccipital), but constitutes the major part of this same margin to contact the squamosal more deeply within the posttemporal fenestra (excluding the exoccipital) ( Fig. 5 View Fig ).
Premaxilla.—The premaxilla is only preserved on OCP DEK−GE 18 ( Fig. 3 View Fig ). It is crushed, but its general shape can be reconstructed. Only the three first right teeth are preserved, but four teeth seem to have existed on each premaxilla. The first tooth is smaller than the two other, and a deep concavity is present between the first and the second. The second tooth is larger, but less than the third tooth which seems to be the largest (apparently confirmed by the large space between the second and third mandibular tooth). The fourth premaxillary tooth is not preserved on the skull of OCP DEK−GE 18, but the space between its third and fourth mandibular teeth is short (as in OCP DEK−GE 1200), implying the fourth tooth would have been the smallest. The space between the fourth and the first maxillary tooth is large, dues to the large size of the fourth dentary tooth, and the premaxilla−maxilla suture is at this level on the lateral surface of the snout.
The dorsal posterior process of the premaxilla is long and ends posteriorly at the level of the third maxillary tooth ( Fig. 3 View Fig ).
Maxilla.—The number of teeth on each maxilla can be estimated to about 17 ( Fig. 3 View Fig ). The snout is relatively narrow, slender, and exhibits a longirostrine type morphology ( Figs. 2–4). The maxilla is relatively sculptured laterally compared to other skull area, with longitudinal deep ridges and furrows.
The alveoli are well developed, circular, with their base in relief and very marked ventrally ( Fig. 2B). They are largely spaced (interalveolar space larger than the alveoli diameter for the teeth anterior to the thirteenth one), diameter and space decreasing posteriorly from the thirteenth tooth.
The maxilla is laterally straight, and the tooth row does not display a festooned outline in dorsal view. Occlusal pits are present from the space between the twelfth and thirteenth right maxillary alveoli, and between the thirteenth and fourteenth left alveoli. These pits, lined with the alveoli tooth row, increase in depth posteriorly. Anteriorly, the space between the right and left alveoli is large (twice the diameter of the alveoli) and increases posteriorly.
The contact with the palatines is expected between the level of the eleventh and twelfth maxillary alveoli (OCP DEK−GE 300; Fig. 4B View Fig ). The maxilla contacts the ectopterygoid medially, and ends ventrally on the jugal. Dorsally, the maxillae are separated by the nasal.
Nasal.—The nasal is a single bone (the two nasals are fused), ornamented with only discrete and sparse furrows. It is narrow between the maxillae, and its anterior process penetrates deeply between the posterior premaxillae processes, but terminates 7 cm (in OCP DEK−GE 18) posterior to the external nares, which it does not reach ( Fig. 3 View Fig ). The nasal is narrow anteriorly between the maxillae, with a constant width from the posterior contact with the premaxillae to the anterior contact with the lacrimals. Then, it widens posteriorly and finally sends a long posterior process between frontal and prefrontal ( Fig. 4 View Fig ).
Prefrontal.—Only the right prefrontal is preserved (on OCP DEK−GE 300; Fig. 2A), almost complete (the most anterior part is absent). It is short, narrow and longer than wide ( Figs. 2A, 4A View Fig ). Dorsally, the contact with the frontal is as long as its contact with the nasal.
Lacrimal.—The right lacrimal of specimen OCP DEK−GE 18 is well preserved ( Fig. 3 View Fig ), and is well anteriorly expanded, reaching the level of the tenth maxillary tooth. Its ornamentation is very light, with some shallow pits. It is large, and forms the anterior margin of the orbit.
Frontal.—It extends anteriorly within the nasal as far as the prefrontal, and its width, at the orbital level appears moderate ( Figs. 2A, 4A View Fig ). Its lateral extension is short, and contacts the postorbital to constitute the postorbital bar. Posteromedially, at the angle between the postorbital bar and the interfenestral bar, the frontal forms a very light dorsal overhang within the supratemporal fenestra. Ventrally, and below this overhang, the frontal contacts an extremely laterally elongated laterosphenoid in a flat lateroventral extension. Posteromedially, the frontal takes part in the narrow interfenestral bar (1 cm width), since its total proportion is about one−fifth of the total length ( Figs. 2A, 4A View Fig ).
The frontal is smooth, without ornamentation, with only three medial grooves between the orbits.
Parietal.—The interfenestral bar, formed by the frontal and the parietal, decreases in width just posteriorly to the contact between these two bones: the width, which reached 1 cm anteriorly, is only 0.5 cm in width posterior to the suture (OCP DEK−GE 300; Figs. 2A, 4A View Fig ). Anteroventrally, its contact with the laterosphenoid is visible, with a long anterior process between the frontal and the laterosphenoid, reducing the contact between these two bones.
Ventrally, the parietal−laterosphenoid suture appears parallel to the skull roof. Posteriorly, the interfenestral bar is broken and separated from the occipital part of the skull. In the angle between the interfenestral bar and the posttemporal bar (formed by the parietal and squamosal), the parietal sends an anterodorsal overhang into the supratemporal fenestra. This overhang is more developed than the anterior one, beginning laterally about 1 cm medial to the squamosal−parietal suture, and appears to end rapidly in the interfenestral bar. The posterior wall of the supratemporal fenestra is very inclined posteriorly, and is largely visible in dorsal view ( Figs. 2A, 4A View Fig ). The parietal−quadrate suture, visible in dorsal view on the posterior wall of the supratemporal fenestra, continues in the same direction as the parietal−laterosphenoid suture. It extends dorsally to join the squamosal−quadrate suture at the same level (in the right supratemporal fenestra) or slightly below the temporal canal (in the left supratemporal fenestra), about 1 cm laterally to the temporal canal. The ventral squamosal−parietal suture joins the temporal canal in its most lateral part, continues dorsally to this one (crosses the temporal canal medially, in its one−third dorsomedial part), and continues in a vertical direction (with zigzag).
The parietal is not ornamented on either the interfenestral bar or on the posterior skull roof. It contributes to half of the posterior wall of the supratemporal fenestra, and tapers posteromedially with a strong and acute process in the occipital face between the occipital tuberosities. The dorsal surface of this process is posteroventrally inclined, and the supraoccipital forms its ventrooccipital part ( Fig. 6 View Fig ).
Postorbital.—It is badly preserved on OCP DEK−GE 18 ( Fig. 3 View Fig ), and extremely fractured in OCP DEK−GE 300 ( Fig. 2A). The postorbital bar, comprised of the postorbital and the jugal, seems to be gently concave medially. It was probably inclined ventrolaterally, not ornamented, mediolaterally flat and longer than wide.
The postorbital is the most important part of the lateral arcade of the supratemporal fenestra ( Figs. 2A, 4A View Fig , 7). It appears dorsally and laterally ornamented with spaced pits, contacts the squamosal posteriorly, and the quadratojugal posteroventrally. It seems to participate largely to the dorsal margin of the infratemporal fenestra (Fig. 7). Anteriorly, it bears a robust lateral process, directed anteroventrally, and ornamented with deep furrows, which seems to contact the ventral margin of the orbit (jugal) ( Figs. 3 View Fig , 4A View Fig ).
Squamosal.—The squamosal forms the posterolateral part of the supratemporal fenestra. It is relatively narrow at the level of the posttemporal bar (1.5 cm in its minimum anteroposterior length) ( Fig. 2A). Weakly high in the posterior wall of the supratemporal fenestra, it constitutes the major part of the dorsal border of the temporal canal. It contacts the postorbital anterolaterally, but is separated from the quadratojugal by the quadrate. It takes part in the dorsal part of the external ear, and sends an important squamosal wing roofing the external otic aperture (Fig. 7). Posterior to the ear, the squamosal constitutes a long and high blade sinking deeply beneath the skull roof and forms the anterior wall of the paroccipital process. The paroccipital process extends more ventrally than the level of the skull roof.
In occipital view, the squamosal contributes dorsolaterally to the posttemporal fenestra (less than the lateral half), and to a small lateral part of the occipital tuberosity. It contributes to a small part to the occipital face, and more posteriorly, it participates in the dorsal edge of the paroccipital process, ending before the extremity one of the process ( Fig. 6 View Fig ).
Jugal.—Very fragmentary ( Fig. 2A), the jugal forms the lateroventral edge of the orbit, and the ventral part of the postorbital pillar ( Fig. 4A View Fig ). There is no lateral jugal edge raised bordering this pillar, and the postorbital pillar is not laterally in continuity with the lateral edge of the jugal. The postorbital bar is displaced medially and is not laterally in alignment with the lateral jugal edge. The base of the postorbital pillar is completely pierced by a foramen, anteroposteriorly directed. Apparently, the posterior aperture of this foramen is situated on the external face of the postorbital pillar. Posteriorly, the internal part of the jugal is exposed and exhibits a deep and long groove, including two distinct foramina ( Fig. 2A).
The jugal is laterally ornamented with spaced deep pits. Posteriorly, it is high, slightly convex dorsally, lateromedially narrow and ends just before the quadratojugal lateral notch (see below). Anteriorly, it reaches the level of the anterior process of the prefrontal ( Figs. 3 View Fig , 4A View Fig ).
Quadratojugal.—It is well developed, and contributes to the jaw joint for one quarter ( Fig. 2). It is laterally straight, and extends slightly ventrally in its posterior portion. A deep lateral notch just before the articulation marks off the jaw joint segment (preserved on the right quadratojugal). Medially, the contact with the jugal is long, and the space between the quadratojugal and the ectopterygoid is small on the jugal (2 cm).
The quadratojugal constitutes the posterior edge of the infratemporal fenestra, and forms a part of its dorsal margin (Fig. 7). Dorsolaterally, it is separated from the squamosal by the quadrate (there is no contact with the squamosal).
Supraoccipital.—It is a small bone, “V” shaped in posterior view, which contributes to the posteromedial occipital process with the parietal ( Figs. 2A, 4A View Fig , 6 View Fig ). It forms the medioventral mid part of the posttemporal fenestra, posteriorly on the occipital tuberosity, but contacts the squamosal one centimeter anteriorly, within the posttemporal fenestra ( Fig. 5 View Fig ). It does not seem to contribute to the occipital tuberosities.
Exoccipital.—They form the main part of the occipital face, contributing laterally to the occipital condyle (each exoccipital constitutes to one third of the half width), and almost completely surround the foramen magnum (three−quarter) ( Fig. 6 View Fig ). Dorsally, they form the occipital tuberosities, which are well developed, dorsoventrally flattened, and posteriorly directed under the posttemporal fenestra. Laterally, they constitute the main part of the robust paroccipital process, and surround dorsally, medially and ventrally to the cranio−quadrate canal. The paroccipital process is flat, composed of the exoccipital and squamosal, and its posterior extremity is quadrangular.
Ventrally, the exoccipitals contribute posterolaterally, one−third to each basioccipital tuberosity in a very broad ventral process ( Figs. 2B, 4B View Fig , 6B View Fig ). The suture between the basioccipital and the exoccipital, posteriorly to the basioccipital tuberosities, lay deeply in a cavity.
The foramen for nerve XII is small and laterally directed on the exoccipital. The vagus foramen and posterior carotid foramen are situated anterior to the foramen for nerve XII, and directed ventroposteriorly ( Fig. 6 View Fig ).
Basioccipital.—It constitutes the main part of the occipital condyle, which is very wide. Its anterior part (basioccipital tuberosities) is not strongly projected ventrally and therefore does not proceed ventrally to the occipital condyle in occipital view ( Fig. 6 View Fig ). The area between the basioccipital tuberosities and the occipital condyle is gently curved dorsally, almost horizontally oriented. In ventral view, the posterior margin of the basioccipital tuberosities is concave anteriorly, relatively thin in its medial part (just behind the medial eustachian foramen), with a small medial ridge posteriorly to the medial eustachian foramen ( Figs. 2B, 4B View Fig ). The anteroposterior thinness of the medial part of the basioccipital, posterior to the medial eustachian foramen, separates the two basioccipital tuberosities, each one having a “drop” shape in ventral view ( Figs. 2B, 4B View Fig ).
laterosphenoid parietal frontal postorbital postorbital bar jugal ectopterygoid
Basisphenoid.—It seems to enclose completely the medial eustachian foramen, but the limit between basioccipital and basisphenoid cannot be seen. The bone is narrow laterally to the medial eustachian foramen, with a lateral “pinching” ( Figs. 2B, 4B View Fig ).
Quadrate.—It is long, posteroventrally directed, and forms the jaw joint with the quadratojugal ( Figs. 2A, 4 View Fig ). In the supratemporal fenestra, it contacts the squamosal lateral to the temporal canal. Anterolaterally, it slips in between the squamosal and the quadratojugal by a thin anterior process that contacts the postorbital. Anteriorly, on its ventral face, the quadrate bears a small crest at its mid width, which probably corresponds to the “crest B” of Iordansky (1964, 1967, 1973).
Palatine.—The palatines are very crushed ( Fig. 2B). They seem enlarged and curved laterally before contacting the maxillae anteriorly. This contact, dues to the bad preservation, is not available. Its posterior border seems flattened, enlarged posteriorly and deviates laterally before joining the pterygoid (lateral border of the palatine not parallel, but laterally curved anteriorly and posteriorly, medial border of suborbital fenestra medially curved). The contact with the pterygoid is not clearly visible, but it seems to form only the anterior part of the choanae ( Fig. 4B View Fig ).
Ectopterygoid.—The left ectopterygoid is well preserved ( Fig. 2B). It is wide and twisted between its contacts with the jugal and the pterygoid. It curves gently anteriorly to form the posterolateral part of the suborbital fenestra ( Fig. 4B View Fig ). The posterior process is wide, decreasing posteriorly, and covers the pterygoid almost as far as its posterior extremity occipital tuberosities exoccipital squamosal quadrate quadratojugal Fig. 7. Arambourgisuchus khouribgaensis gen. et sp. nov., OCP DEK−GE 300, Sidi pterygoid Chenane, Morocco, late Palaeocene, detail of the left posterior part of the skull in left lateral view. Photograph (A) and explanatorus transiliens
tory drawing of the same (B).
( Fig. 2B). Its contact with the maxilla seems short, whereas that with the jugal is long.
Pterygoid.—The pterygoids are damaged ( Fig. 2B), but their shape can be trace out. Anteriorly, they almost completely surround the choanae. A septum, formed by the pterygoids separates the choanae in two openings ( Fig. 4B View Fig ).
The pterygoids diverge posterolateraly to form two lateral wings in contact with the ectopterygoid. In front and anterolaterally to the choanae, they seem flattened and enlarged laterally; they are anteroposteriorly narrow between the choanae and their contact with the ectopterygoids ( Fig. 4B View Fig ). Contact with the ectopterygoid is small, and increases rapidly lateroposteriorly with the increase of the anteroposterior length of the pterygoid wing. The lateral part of this wing is extremely thickened dorsoventrally to form a strong torus transiliens, with a very important anterior thickening, decreasing progressively posteriorly (Fig. 7).
Laterosphenoid.—Anteriorly, it is laterally expanded ventrally to the frontal, and its anterior margin is lateromedially directed ( Figs. 2A, 4A View Fig ). The posterior part is dorsoventrally crushed, and its shape is hardly distinguished ( Fig. 2). Suture with the frontal and parietal (in continuity) seems horizontal, parallel to the skull roof (dorsal limit of the interfenestral bar).
Mandible.—Two isolated mandibular fragments have been found, one anterior, preserved from the first to the twelfth tooth (OCP DEK−GE 1200; Fig 8A View Fig ), and a more posterior part, including the eleventh to the sixteenth teeth (OCP DEK−GE 269; Fig. 8B, C View Fig ). Unfortunately, only a small part of its posterior branch is preserved on the specimen OCP DEK−GE 300, but too poorly preserved to be interpreted. The first tooth is relatively robust ( Fig. 8A View Fig ), the second alveolus smaller, and the space between it and the third one is greater than between the other. The third tooth is about the same size as the second, and it is near the very enlarged fourth. This one has its alveolar edge higher dorsally. The next alveoli seem relatively regular in their spacing and diameter.
The mandible is wider than high ( Figs. 3 View Fig , 8B, C View Fig ), lacks festooned outlines, and there are occlusal pits posterior to the fifteenth teeth (OCP DEK−GE 269; Fig. 8B View Fig ).
The symphysis ends posteriorly at the level of the sixteenth tooth, and the splenial ends anteriorly between the tenth and the eleventh ( Fig. 3 View Fig ).
Teeth.—They are robust, not very slender, but relatively sharp, with posterior carinae which ends before the base of the teeth, when the anterior one reaches the base. The superficial striae are variably present on some of the teeth, and are absent or weak.
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