Dyrosaurus maghribensis, Jouve & Iarochène & Bouya & Amaghzaz, 2006

Jouve, Stéphane, Iarochène, Mohamed, Bouya, Baâdi & Amaghzaz, Mbarek, 2006, A new species of Dyrosaurus (Crocodylomorpha, Dyrosauridae) from the early Eocene of Morocco: phylogenetic implications, Zoological Journal of the Linnean Society 148 (4), pp. 603-656 : 606-622

DYROSAURUS MAGHRIBENSIS SP. NOV.

Etymology: From ‘Maghrib’, Morocco in arabic language, referring to the distribution of this species, known up to now in Morocco only.

Holotype: OCP DEK-GE 255 , a nearly complete specimen, with skull, mandible, and postcranial material ( Fig. 2A ), housed in the geological survey of the OCP in Khouribga , Morocco.

Type horizon and locality: The phosphate mine of Mera el Arech, in the Oulad Abdoun Basin, Morocco; from the ‘layer 1’, according to the miner’s terms, corresponding to the early Eocene (Ypresian).

Diagnosis: Dorsal margin of parietal almost smooth, ornamented with very light furrows only; interfenestral bar wide and strongly T-shaped in transverse section; choanae widely opened and prolonged on the pterygoids by lateral shallow depressions; short distance between the posterior margin of the choanae (posterior margin of the septum) and the medial eustachian foramen; lateral and medial dorsal osteoderms not sutured, with all their margins without serration; anterolateral margin of medial row of the dorsal osteoderms with rounded lateral lobe; lateral row of the dorsal osteoderms square in shape with rounded corner.

Referred specimens: OCP DEK-GE 36, OCP DEK-GE 43, OCP DEK-GE 78, OCP DEK-GE 88, OCP DEK-GE 252, OCP DEK-GE 253, OCP DEK-GE 254, OCP DEK-GE 255, OCP DEK-GE 256, OCP DEK-GE 257, OCP DEK-GE 258, OCP DEK-GE 259, OCP DEK-GE 263, OCP DEK-GE 362, OCP DEK-GE 323, IRSNB R146, Rhin. Coll. phosphate 1; all from the Ypresian of the Oulad Abdoun Basin, Morocco.

Skull

General shape: The rostrum is very long and narrow, with the snout proportion (antorbital portion) reaching 75% of the total skull length in the largest specimen. This proportion varies ontogenetically from 66 to 75%. The dorsal surface of the rostrum is slightly sculptured with shallow anteroposterior grooves and ridges ( Figs 3 , 4 ).

Cranial openings: The unpaired external naris is almost oval and dorsally orientated ( Figs 3 , 4 ). The lateral margin is lower than the posterior margin and the anterior suture between the two premaxillae makes a distinct dorsal protuberance anterior to the external naris. In lateral view, the lateral margins of the naris are anteroventrally inclined.

The foramen incisivum is small and heart-shaped, with its anterior extremity penetrating anteriorly between the first premaxillary alveoli. It is posteriorly bordered by the maxillae and ends posteriorly at the same level as the posterior margin of the second tooth.

The orbit, because of the anterolateral postorbital process, appears circular in dorsal view ( Fig. 4 ). Its anterior margin comprises the prefrontal and lacrimal. The ventral margin is formed by the jugal, the frontal, constituting the posteromedial quarter, and the postorbital, constituting the posterolateral quarter.

The anterior wall of the orbit is exposed. The postnasal fenestra, which pierces the antorbital wall, enables a communication between the antorbital cavity (sensu Witmer, 1995) and the suborbital cavity. It is small, and situated in the ventral part of the antorbital wall. Three-quarters of the prefrontal pillar is formed by the prefrontal, and only its base by the palatine. The lacrimal forms a high, anteriorly convex vertical wall, dorsal to the postnasal fenestra. The right and left prefrontal pillars are medially separated by a narrow and dorsoventrally high slit [passage for the olfactory nerve (I) (dorsally) and the nasal septum (ventrally)]. Ventrally, the sulcus septalis is formed by the pterygoid.

The supratemporal fenestra is extremely large, much longer than wide, with rounded anterior and posterior margins, giving a general longitudinally ovate shape to this opening. The right and left supratemporal fenestrae are separated by a wide interfenestral bar, which is wider above than below (Tshaped in transverse section) ( Figs 3 , 4 ). This interfenestral bar widens gently and slightly anteriorly, but more strongly posteriorly. The frontal participates in one-fifth of the interfenestral bar, and in slightly more than half of the anterior margin of the supratemporal fenestra. The anteromedial corner of the fenestra is more angular than the other corners; the anterolateral corner, formed by the postorbital, is very rounded. Posteromedially, the corner is also rounded. The posterior wall of the supratemporal fenestra is nearly vertical and weakly exposed in dorsal view.

The temporal canal is small and slightly wider than high, surrounded by the squamosal in its dorsolateral quarter, and by the parietal in the remainder of its margin.

The infratemporal fenestra is extremely elongated anteroposteriorly, extending posteriorly beyond the posterior margin of the supratemporal fenestra ( Fig. 5 ). It is limited anteriorly by the lateromedially flattened postorbital bar and ventrally by the jugal (and for a weak posterior portion by the quadratojugal). The quadratojugal forms less than the posterior half and the postorbital more than the anterior half of the dorsal margin ( Fig. 6 ).

The post-temporal fenestra is located above the occipital tuberosity ( Fig. 7 ). It is elongated lateromedially, and thin dorsoventrally. The squamosal forms the dorsolateral quarter of its margin, and the exoccipital a part of the ventral border. The participation of the parietal, supraoccipital, and exoccipital cannot be estimated because of the absence of visible sutures in the area of the post-temporal fenestra.

The foramen magnum is large, mostly surrounded by the exoccipital, the basioccipital forming only a weak portion of its medioventral margin.

On the ventral side of the skull, the suborbital fenestra is well developed and rounded in shape anteriorly. It is sharp posteriorly, and reaches the level of the mid-length of the choanae ( Figs 8 , 9 ).

The choanae are large, wide, divided by a pterygoid septum, and open posteroventrally. They are not abruptly pierced within the pterygoids, but are laterally prolonged by a depression on the pterygoids ( Fig. 9 ). The depression extends posterolaterally on to the lateral branch of the pterygoid, tapering before the pterygoid contacts the ectopterygoid. They are almost completely surrounded by the pterygoids, the palatines narrowly entering the anteromedial margin.

Premaxilla: The premaxillae are relatively narrow and very slightly inflated laterally relative to the width of the maxillary ( Figs 4 , 5 ). The anterior suture between the right and left premaxillae forms a distinct dorsal protuberance anterior to the external naris ( Fig. 6 ). The premaxillae are slightly ornamented with shallow furrows. The posterodorsal processes reach the level of the third maxillary tooth. Each premaxilla bears four alveoli, the third tooth being the largest, the three others being nearly equal in diameter. Sulci for the occlusion of the mandibular teeth separate the alveoli. The first notch, between the first and second alveolus, is particularly well marked, and the first right and left premaxillary alveoli are very close to each other.

Ventrally, the premaxillae do not contact each other posterior to the foramen incisivum ( Fig. 9 ).

Maxilla: The maxillae are ornamented with shallow longitudinal and spaced furrows ( Figs 3 , 4 , 7 ). The two maxillae are separated dorsally by the nasal bone throughout their length, and each maxilla bears 19–21 teeth. The lateral margin of the maxilla runs straight posteriorly and progressively curves laterally from the level of the ninth maxillary alveolus.

The last premaxillary and the first maxillary alveoli are widely separated (due to the passage of the large occlusal notch for the large fourth dentary tooth) ( Figs 5 , 9 ). The alveoli are relatively small, circular, with their base in relief ventrally in lateral view. They are widely spaced, the interalveolar distance being larger than the alveoli diameter for the teeth anterior to the 15th.

The lateral margin of the maxilla is linear, and the occlusal sulci are present between the alveoli, but not sufficiently deep dorsally to be seen in dorsal view ( Figs 3 , 4 ). The occlusal pits are present from the space between the 15th and 16th alveoli. These pits, lined with the alveoli tooth row, increase in depth posteriorly.

The distance between the tooth rows is narrow and constant to the eighth maxillary tooth (slightly wider than the diameter of the alveoli) and increases progressively posteriorly ( Figs 8 , 9 ).

Ventrally, the contact with the palatines is expected between the level of the 15th and 16th alveoli. The maxilla contacts the ectopterygoid medially, and terminates below the jugal in a long edentelous posterior process ( Fig. 11 ).

Nasal: The single nasal bone (the two nasals are fused) is ornamented with discrete and scarce furrows ( Figs 3–5 ). Its anterior process penetrates deeply between the posterior processes of the premaxillae, but does not reach to the external naris. The nasal is narrow anteriorly between both maxillae, and has a constant width from its posterior contact with the premaxillae to the level of the 11th maxillary tooth. It widens posteriorly and divides into posteriorly tapering processes which are inserted for a short distance between the anterior ends of the frontal and the prefrontals.

Lacrimal: The lacrimal is not well expanded anteriorly, and its contact with the nasal is much shorter than the prefrontal–nasal suture ( Fig. 5 ). Its ornamentation is light, with some shallow pits. It is large, and forms with the prefrontal the anterior margin of the orbit.

Prefrontal: The prefrontal is short, narrow, and longer than wide ( Fig. 5 ). Dorsally, its contact with the frontal is as long as that with the nasal.

The prefrontal forms three-quarters of the prefrontal pillar (its height). It is dorsally wide, narrowing ventrally before contacting the palatine. Medially, the right and left prefrontal pillars are separated from each other by a narrow and high slit-like opening that is interpreted as the passage for the nasal septum and the olfactory nerve (I). The frontal forms the dorsal margin of this opening. The ventral margin (sulcus septalis) is formed by the pterygoid.

Frontal: The frontal extends wedge-like between posterior processes of the nasal bone. It extends slightly beyond the tip of the lacrimal but before the end of the prefrontal. Its interorbital space is narrow ( Figs 3–5 ). Its lateral extension is small, and it contacts the postorbital to form the posteromedial margin of the orbit. Posteriorly, the frontal, forming the anteromedial margin of the supratemporal fenestra, overhangs the anteromedial part of the supratemporal fenestra. It continuous posteriorly, forming a strong overhang along the edge of the interfenestral bar. Consequently, the interfenestral bar is strongly T-shaped in crosssection. The frontal forms nearly one-fifth of the interfenestral bar.

The frontal is ornamented with shallow anteroposterior furrows ( Figs 3–5 ).

Jugal: The jugal forms the lateroventral edge of the orbit, and the ventral part of a strong, anteroposteriorly oval and mediolaterally flattened postorbital bar ( Figs 3 , 4 ). There is no raised lateral jugal lamina bordering this bar, although the lateral surface of the postorbital bar is not continuous laterally with the lateral edge of the jugal, being slightly displaced from it medially. The postorbital bar is slightly located on the dorsomedial edge of the jugal bar, dorsomedially inclined and gently medially concave. The anterior elevation of the orbital edge begins to decrease at the level of the contact with the anterolateral postorbital process, and decreases rapidly posteriorly to reach the same level as the base of the postorbital bar.

The jugal is laterally ornamented with spaced deep pits and furrows ( Figs 3 , 4 ). Its posterior ramus is high, slightly convex dorsally, compressed transversely, and ends slightly anteriorly to the quadrate condyle. Anteriorly, it terminates slightly anterior to the orbits, but remains posterior to the anterior process of the prefrontal ( Figs 5 , 6 ).

Quadratojugal: The quadratojugal is well developed and contributes to more than one-quarter of the craniomandibular joint ( Figs 5 , 9 ). It is straight laterally and extends slightly ventrally posteriorly.

The quadratojugal forms the posterior edge of the infratemporal fenestra and participates in less than half of its posterodorsal margin. It takes part shortly in the ventral margin of the infratemporal fenestra ( Fig. 6 ). Dorsally, it widely contacts the quadrate, but only slightly the postorbital. There is no contact between the quadratojugal and the squamosal.

Medioventrally, the contact with the jugal is long, and the distance between the quadratojugal and the ectopterygoid is short on the jugal (2 cm).

Postorbital: The postorbital represents the largest part of the lateral arcade of the supratemporal fenestra ( Fig. 5 ). It appears to be dorsally and laterally ornamented with spaced pits, and contacts the squamosal posteriorly and the quadratojugal posteroventrally, above the infratemporal fenestra.

Anteriorly, it bears a robust anteroventral lateral process that is ornamented with strong ridges and furrows. It contacts the ventral margin of the orbit (jugal), giving a circular shape to the orbit in dorsal view ( Figs 3–6 ). The postorbital process is not ventrolaterally continuous with the postorbital bar, but a slight crest, continuous with the ventral border of the postorbital process, separates the lateral margin of the postorbital bar from the lateral margin of the postorbital process.

The postorbital bar is half formed by the postorbital and half by the jugal, and is gently concave mediodorsally. It is inclined dorsomedially, its ventral portion being inclined because of its concave shape. It is unornamented, mediolaterally flat, and much longer than wide.

Parietal: The frontoparietal suture zigzags in a vertical plane and the frontal–parietal–laterosphenoid contact lies anteriorly beyond the frontoparietal suture on the interfenestral bar ( Fig. 5 ). The parietal bears a thin projection between the frontal and the laterosphenoid. Ventrally, the parietal– laterosphenoid suture descends posteriorly relative to the skull roof. Like the frontal in the interfenestral bar, the parietal is T-shaped in cross-section, and the dorsal overhang continues on the posterior wall of the supratemporal fenestra. The posterior wall of the supratemporal fenestra is nearly vertical and weakly visible in dorsal view. The parietal–quadrate suture, on the posterior wall of the supratemporal fenestra, is parallel with the parietal–laterosphenoid suture. It joins the squamosal–quadrate suture largely beneath and lateral to the temporal canal. The parietal forms half of the posterodorsal margin of the supratemporal fenestra, and its suture with the squamosal crosses the dorsal margin of the temporal canal in its mid-width. The ventral squamosal– parietal suture is bowed medially and is continuous with the laterosphenoid–quadrate suture, a condition that prevents a contact between the quadrate and the parietal.

The parietal is seen on the occipital face of the skull between the occipital tuberosities. It is W-shaped in occipital view, and bears a dorsoventrally orientated medial ridge. It forms the dorsomedial margin of the post-temporal fenestra ( Fig. 7 ).

In the interfenestral bar, the parietal is ornamented in its anteriormost portion, but is posteriorly and posterolaterally smooth. Its posterior margin is straight or slightly concave anteriorly in dorsal view, according to the specimens.

Squamosal: The squamosal forms the posterolateral part of the supratemporal fenestra ( Fig. 5 ). It is thin in the posterior wall of the supratemporal fenestra dorsal to the temporal canal, and forms half of its dorsal margin. It contacts anterolaterally the postorbital, but is separated from the quadratojugal by the quadrate. It takes part in the dorsal margin of the external otic aperture, and sends off a narrow squamosal wing roofing the recessus oticus externus. Posterior to the external ear, the squamosal forms a long, high blade which sinks deeply beneath the squamosal skull roof (squamosal). It forms the dorsal margin of the paroccipital process, which extends ventrally beyond the level of the skull roof.

In occipital view, the squamosal contributes dorsolaterally to the post-temporal fenestra (about half the dorsolateral margin), and to a small lateral part of the occipital tuberosity. It contributes slightly to the occipital face and forms the dorsal edge of the paroccipital process. Its occipital face bears a relatively wellmarked furrow, parallel and immediately beneath the skull roof. Its suture with the exoccipital lies in a furrow parallel to the first one.

Supraoccipital: The supraoccipital is V-shaped, located below the parietal and between the occipital tuberosities ( Fig. 7 ). It is a small bone separated from the foramen magnum by the exoccipitals. It does not participate in the occipital tuberosities, but seems to participate modestly in the medioventral margin of the post-temporal fenestra.

Exoccipital: The exoccipitals form the major part of the occipital face, contributing approximately onethird to either side of the occipital condyle, and surrounding more than three-quarters of the foramen magnum. Dorsally, the exoccipital forms the occipital tuberosity, which is moderately developed, rounded, and posteriorly directed below the post-temporal fenestra. Laterally, it constitutes the ventral portion of the robust paroccipital process ( Fig. 7 ), and surrounds dorsally, medially, and ventrally the cranioquadrate canal. Ventrally, the exoccipital forms one-third of the basioccipital tubera lateroposteriorly.

The foramen for the hypoglossal nerve (XII) is small and laterally orientated on the exoccipital. The foramen vagi (X–XI) and the foramen caroticum posterius are located anterior to the foramen for the nerve XII, and orientated ventroposteriorly.

Quadrate: The quadrate is long, directed posteroventrally, and forms the jaw joint with the quadratojugal ( Figs 5 , 9 ). The quadrate contacts the squamosal within the supratemporal fenestra ventral and lateral to the temporal canal. It has an extensive contact with the parietal, and bears a relatively long process between the parietal and the laterosphenoid beyond the foramen for the trigeminal nerve (V). It also bears a long ventral process, located at the same level as the ventral margin of the basisphenoid rostrum. The quadrate contacts the laterosphenoid ventral to the foramen for the trigeminal nerve, and slightly the posterior margin of the basisphenoid rostrum. Anterolaterally, it slips in between the squamosal and the quadratojugal, ends slightly anterior to the external ear, and it contacts anteriorly the postorbital. It forms half of the anterior margin, and the ventral and the posterior margins of the external ear.

Palatine: The palatine is wide and long anterior to the suborbital fenestra. It reaches the level of the interalveolar space between the 15th and 16th maxillary teeth ( Fig. 9 ). The maxilla–palatine suture crosses the edge of the suborbital fenestra at its anteriormost extremity. The two palatines constitute a wide, ventrally flattened tube which transmits the nasopharyngeal duct. The palatine bridge is curved dorsally towards the posterior end, and ventrally behind. Its portion immediately anterior to the internal nares is more flattened than its anteriormost part.

The contact with the pterygoid is large and located anterolaterally to the internal nares ( Fig. 9 ). The palatines participate in the anteromedial border of the internal nares.

Pterygoid: Anteroventrally, the pterygoids surround the choanae almost completely. A pterygoid septum separates the choanae in two openings ( Fig. 9 ).

The pterygoid extends posterolaterally to form a lateral ‘wing’ in contact with the ectopterygoid. Anterolaterally to the choanae, the pterygoid is flattened and expanded laterally in the suborbital fenestra, whereas it is relatively narrow anteroposteriorly between the choanae and its contact with the ectopterygoids ( Fig. 9 ). This contact is at first small, but increases lateroposteriorly with the increase in the anteroposterior length of the pterygoid wing. The lateral part of this wing is extremely dorsoventrally thickened to form the torus transiliens, with a very strong anterior thickening, progressively decreasing posteriorly.

Posterodorsally, on the braincase, the pterygoid sends a short process between the posterior margin of the basisphenoid rostrum and the quadrate, and another longer process between the quadrate and the basisphenoid. A strong crest, probably crest B of Iordansky (1973), located on the quadrate, isolates the basioccipital tubera from the basicranium, and forces the pterygoidian process between the quadrate and the basisphenoid to be in a different plane from the basicranium.

Anterodorsally, the united pterygoids form the roof of the palatine bridge above the ducts. They taper and extend anteriorly beyond the level of the prefrontal pillar, that they separate ventrally (sulcus septalis).

Ectopterygoid: The ectopterygoid is wide and twisted between its contacts with the jugal and the pterygoid. It curves gently anteriorly to form the posterolateral margin of the suborbital fenestra ( Fig. 9 ).

The posterior process is wide, decreasing in thickness posteriorly, and covers the pterygoid ventrally almost up to its posterior extremity. Its contact with the maxilla seems to be as long as its contact with the jugal and reaches anteriorly, in the suborbital fenestra, the level of the last maxillary tooth. Medioventrally, it participates slightly in the base of the postorbital bar, but does not contact the postorbital.

Basioccipital: The basioccipital forms most of the occipital condyle, which is very wide. The anteroventrally situated basioccipital tubera are moderately projected ventrally and they proceed ventrally to the occipital condyle in occipital view. The area between the basioccipital tubera and the occipital condyle is relatively arched dorsally, nearly vertically orientated.

In ventral view, the posterior margin of the basioccipital tubera is anteriorly concave, relatively short in its medioventral part (immediately behind the medial eustachial foramen), and with a dorsoventral strong medial ridge posterior to the medial eustachian foramen ( Fig. 9 ). The narrow medial part of the basioccipital separates the tubera in two parts, which are teardrop-shaped in ventral view. The posterolateral part of the tubera is situated more dorsal than the medial part.

The basioccipital is visible in lateral view as a thin wedge between the basisphenoid and the exoccipital, its dorsal margin tapering to contact slightly the lateral eustachian foramen.

Laterosphenoid: The laterosphenoid does not contact the squamosal. Its ventral limit with the anterior process of the basisphenoid seems to be located slightly ventral to the level of the foramen for the trigeminal nerve (V). Anteriorly, it is laterally expanded ventrally to the frontal, and its anterior margin (capitate process) is directed lateroposteriorly. The suture with the frontal and the parietal is linear, descending posteriorly compared to the skull roof (dorsal limit of the interfenestral bar).

The opposing laterosphenoids meet each other medially, below the olfactory foramen (I), with a modest expansion for the optic foramina (II).

Posteroventrally, the laterosphenoid sends a short process between the quadrate and the basisphenoid, greatly narrowing the contact between these two bones.

The laterosphenoid forms the anterior margin of the trigeminal foramen. No laterosphenoid bridge forming a distinct foramen for the ophthalmic branch (V1) was observed. A shallow anteroposterior groove prolongs this foramen, indicating the external pathway of the ophthalmic branch. Anteriorly, in this groove, the laterosphenoid is pierced by the foramen for the trochlear nerve (IV).

Ventral to the laterosphenoid, at the limit with the basisphenoid, the foramen for the oculomotor nerves (III) is directed anteriorly and prolonged anteriorly by a deep groove on the laterosphenoid.

Basisphenoid: The basisphenoid is narrow lateral to the medial eustachian foramen, and constricted laterally in ventral view. The lateral narrowing of the basisphenoid gives a particular triangular shape to the basioccipital tubera in ventral view. The basisphenoid is narrow anteroposteriorly (posterior to the pterygoids) and surrounds the medial eustachian foramen.

The lateral eustachian foramen is long and narrow and located dorsally at the top of the lateral exposure of the basioccipital. The basisphenoid forms its anterior margin. Posterodorsally, the basisphenoid contacts largely the quadrate.

Anteriorly, the basisphenoid rostrum is high, extremely elongated, narrow anteriorly, and sutured dorsally with the laterosphenoid. Its posterior margin is vertical, contacting the quadrate and the pterygoid ventrally. The existence of a dorsal contact with the pro-otic cannot be asserted. Dorsally on the pterygoid, the basisphenoid bears a second anterior process, largely separated from the basisphenoid rostrum by a narrow slit. It extends beyond the basisphenoid rostrum, ending slightly posterior to the prefrontal pillar, and located in the dorsomedial depression between the pterygoids.

Pro-otic: The shape and extension of the pro-otic cannot be distinguished.

Palpebral: The palpebral is only preserved in Rhin. Coll. phosphate 1. It is a single bone, as long as the orbit, relatively large, but longer than wide.

Mandible

General shape: The mandible is extremely elongated, narrow in its anterior half ( Fig. 8 ), and the symphysis reaches posteriorly the level of the 21st dentary tooth in the largest specimens [from the 17th to the 21st, varying according to the size and age of the animal (S. Jouve, pers. observ.)]. The external mandibular fenestra is very small, largely surrounded anteriorly by the dentary and slightly posteriorly by the angular in lateral view. Medially, the surangular participates in its posteroventral margin, but does not participate in the fenestra in lateral view. The glenoid fossa is formed medially by the articular and laterally by the surangular. The retroarticular process is extremely elongated, curved posterodorsally ( Fig. 10A, B ), and Lshaped in cross-section, the articular forming a deep posteromedial depression ( Fig. 10C–F ).

Dentary: The dentary is long, narrow, and about as wide as high (even if the remains have been deformed diagenetically) ( Fig. 8 ).

The first alveolus is relatively wide and opened anterodorsally (more dorsally than anteriorly). The second is smaller, and closer to the first than to the third. A large notch separates the second and third teeth for the passage of the largest premaxillary tooth (the third). The fourth dentary tooth is the largest and the seventh is extremely reduced and close to the eighth.

The dentary ventrally ends at the mid-length to the external mandibular fenestra, and sends off a short and sharp process dorsally between the angular and the surangular, which extends posteriorly beyond the external mandibular fenestra. In medial view, it ends ventrally at the mid-length of the external mandibular fenestra, and dorsally at the level of the posterior margin of the external mandibular fenestra ( Fig. 10A, B ).

Splenials: The splenials are very long anteriorly, participating broadly in the symphysis in a long, sharp, and wedge-shaped anterior process located between the dentary. The splenials reach anteriorly the level of the 11th to the 14th teeth (varying according to the animal) and consequently participate broadly in the mandibular symphysis.

Posteriorly, the splenials send off dorsal and ventral processes to the Meckelian fossa ( Fig. 10E, F ). They stop slightly posterior to the mid-length of the distance between the last dentary tooth and the anterior margin of the glenoid fossa. In medial view, there is a deep anterior concavity between the posteroventral and posterodorsal process of the splenial, the posteroventral process being slightly more extended posteriorly. The anterior foramen intermandibularis oralis pierces the splenial in the posterior margin of the symphysis. Right and left foraminae are separated from each other by nearly 1 cm.

Angular: The angular participates medially and laterally in the posterior margin of the external mandibular fenestra ( Fig. 10A, B ). Anteroventrally, it bears a ventral process that almost reaches the level of the mandibular symphysis. Posteriorly, it forms the ventrolateral margin of the retroarticular process and extends posterolaterally beyond the posterior end of the surangular, between half and three-quarters of the length of the retroarticular process.

Surangular: The surangular reaches anteriorly the level of the last dentary tooth as a thin dorsolateral process, and it displays two occlusal pits for the two last maxillary teeth. It contributes to half of the lateral margin of the glenoid fossa, and its suture with the articular deviates laterally in the retroarticular process. The surangular is long posteriorly, narrow, facing dorsolaterally, and ends a few centimetres anterior to the end of the retroarticular process.

Laterally to the posterior process of the glenoid fossa, it bears a lateral rim orientated anteroposteriorly ( Fig. 10A, B ). A second longitudinal rim, separated from the first rim, continues posteriorly for a short distance before progressively ending posteriorly. This rim displays several foramina, the largest being the foramen aereum.

Articular: The articular forms the medial half of the glenoid fossa ( Fig. 10A, B ). It sends off an anteromedial process. Consequently, the anterior margin of the glenoid fossa is concave posteriorly. This process is continuous ventrally with a narrow ventromedial lamina which reaches anteroventrally the medioventral margin of the mandible, within a ventral gutter of the angular. Posterior to the glenoid cavity, the articular is abruptly depressed medioventrally ( Fig. 10C–F ) and L-shaped in transverse section, giving the same shape to the transverse section of the retroarticular process. The articular forms all of the medial part of the retroarticular process, its medial wing being in a ventral position behind the joint, at the same level as the ventral margin of the retroarticular process. This ventromedial wing progressively disappears posteriorly.

Coronoid: In all specimens examined, there is no indication on the medial surface of the jaw that the coronoid was present ( Fig. 10A, B ).

Dentition: The dentition is homodont, conical, and slender. The teeth are curved distally. The anterior maxillary and dentary teeth are long, slender, and cylindrical in cross-section, whereas the fifth or sixth most posterior are shorter, more robust and lateromedially compressed in cross-section. The teeth are divided into asymmetrical labial and lingual surfaces by well-developed anterior and posterior carinae. In the shorter teeth, the anterior carina is sometimes modest, deflected ventromedially. Striae are present on all surfaces. The tooth size decreases from front to back, the posterior teeth being shorter, more robust, and their striations being weaker or absent.

Postcranial skeleton

Vertebrae: All preserved vertebral centra are weakly amphicoelous ( Fig. 11 ). The first nine vertebrae, plus the proatlas ( Fig. 12 ), are usually considered to belong to the cervical section in crocodylomorphs ( Steel, 1973) on the basis of the relationships between the parapophysis and the centrum–neural arch suture. In the first nine vertebrae, the parapophysis is located ventral to this suture. Posterior to the ninth vertebra, the parapophysis is located more dorsally on the centrum. In D. maghribensis , there are nine vertebrae corresponding to the description of cervicals ( Fig. 13B ). The difference in the position of the parapophyses between the ninth and tenth vertebrae is minor.

The proatlas is small and arched in shape ( Fig. 12A–C ). The lateral margins are orientated anteromedially and the posterior margin slightly concave anteriorly, giving the proatlas a triangular dorsal shape. The anterior portion displays two anterior protuberances separated from each other by a deep posterior concavity. The dorsal margin is convex dorsally, and the ventral margin is concave ventrally. The posterior margin is inclined anterodorsally.

Only the neural arch of the atlas is known ( Fig. 12D–I ). In ventral view, its articular surface is square rounded in shape, divided into two articular facets, inclined at two different angles. The anteroventral surface is articulated with the occipital condyle, and the posteroventral surface with the odontoid process of the axis. The dorsal portion forms a large medial wing that surrounds the nervous system dorsally. The postzygapophysis is nearly orientated vertically.

The axis is almost completely known ( Fig. 11 ). The odontoid process is sutured to the centrum, with a large wedge-shape in lateral view ( Fig. 12J–N ). It has a deep dorsoventrally elongate lateral fossa surrounding an anterior well-developed diapophysis directed posteroventrally. The anterior margin is gently concave, with a dorsomedial pit, which is orientated dorsoventrally. The very short ventral margin bears a small medial crest. The dorsal margin is concave, with a central smooth crest orientated anteroposteriorly, separating two lateral foraminae. The articular surface for the axis neural arch is inclined posteroventrally on the posterodorsal margin, and the articular surface for the atlas neural arch is triangular in shape, and orientated anterodorsolaterally. The centrum has a low but long neural spine, which tapers posteriorly in a sharp end. The articular surface of the prezygapophysis is almost orientated vertically.

In the cervical vertebrae, the parapophyses are directed much more ventrally than laterally, and the diapophyses are strongly directed ventrally from the third to the sixth cervicals ( Fig. 13A, B ). In these cervicals, the diapophyses and parapophyses are located on the anterior part of the centrum and have an elongate anteroposterior shape. In the third to the fifth cervical vertebrae, the neural spine is short, and sharp dorsally relative to the more posterior ones ( Fig. 13A– C ). The neural spine is strongly directed posteriorly in the third cervical, slightly posteriorly in the fourth, and vertically in the fifth. The sixth and most posterior vertebrae are inclined posteriorly. The anterior margin of the neural spine is straight in the third and fourth cervical and convex anteriorly in the most posterior vertebrae. The antero- and posterodorsal margins of the third cervical spine are thinner than the median part. In the fifth to the seventh spines, only the anterior margin is thinner. The difference between the thin and thick parts is less marked in the sixth cervical vertebra. The height of the neural spine increases progressively to the seventh cervical and the neural spine of the sixth has a dorsal extremity slightly more rounded than the most anterior ones. The presence of cervical ribs still articulated with diapophyses and parapophyses precludes access to the ventral part of the centrum. From the seventh cervical vertebra, the diapophyses and parapophyses are circular in shape, and move dorsally and posteriorly. Their neural spines are higher, with a dorsal spine much longer and rounded in shape. The three last cervicals (seventh to ninth) have neural spines of the same height. The presence of a hypapophysis on the ventral margin of the centrum is attested only on the last two cervicals ( Fig. 13 ). Its presence in more anterior cervicals can be supposed on the seventh, which only preserved its base on the centrum, but cannot be deduced on the anteriormost. On the eight and ninth cervicals, the hypapophyses are blades flattened laterally, very rounded ventrally, long anteroposteriorly, and located anteriorly on the centrum. The hypapophysis on the ninth cervical is higher than in the eighth.

There are 15 dorsal vertebrae, followed by two sacrals ( Figs 11 , 13A ). The two first dorsals have separated diapophyses and parapophyses ( Fig. 13C ). These apophyses are joined in the third and more posterior vertebrae on a transverse process slightly orientated posterodorsally. From the fourth to the tenth, the transverse process is inclined anteroventrally, this inclination decreasing from front to back. The posteriormost vertebrae, from the tenth, bear horizontal processes. From the third dorsal vertebra, the transverse process is completely located dorsally to the neural arch–centrum suture. The first to fifth dorsal vertebrae have a neural spine lower than the last cervical ones, and their height progressively decreases posteriorly. The height of the neural spine is constant from the seventh to the eleventh dorsals, and progressively increases posteriorly. The neural arch is more inclined posteriorly in the anterior dorsals than in the posterior cervicals. This inclination decreases from the ninth, the five last dorsal vertebrae (11–15) having a vertical neural spine. All neural spines of the dorsal vertebrae are narrow, without any dorsal widening for the osteoderms. The hypapophysis of the first dorsal is higher than that of the last cervical. It is inclined posteriorly and located anteriorly on the centrum in OCP DEK-GE 254, but higher, longer, and less inclined in OCP DEK-GE 252. In some vertebrae, there is a very short space between the anterior margin of the hypapophysis and the anterior margin of the centrum. The hypapophyses increase in height ventrally and length posteriorly in the second and third dorsals. In this last vertebra, the hypapophysis is the highest of all the vertebrae, its posterior margin almost reaching the posterior margin of the centrum. The hypapophysis of the fourth is weak, nearly equal in size to the last cervical, and it only forms a small rounded anterior keel in the fifth ( Fig. 13C ). The posteriormost vertebrae, from the sixth to the fifteenth, do not have hypapophyses. The neural arch of the last dorsal vertebra is not preserved and the centrum exhibits the trace of the insertion for the first sacral rib. The first sacral rib is located one-third on the last dorsal vertebra and two- thirds on the first sacral vertebra. The area for the insertion of this rib is vertical, and directed posterolaterally on the last dorsal.

There are two sacral vertebrae. The sacral rib is attached to the anterolateral side of its centrum in sacral 1, and the second is attached to the posterolateral side of sacral 2. The surface of insertion of the second sacral rib covers almost all the lateral surface of the second sacral vertebra. Their zygapophyses are orientated almost vertically.

Twenty-one caudal vertebrae are known ( Fig. 11 ). The first two centra have a nearly circular transverse section. This shape becomes rapidly quadrangular in the posteriormost vertebrae. The angle of the zygapophyses seems rapidly to verticalize posteriorly. The neural spines, higher than in the posterior dorsals, increase rapidly in height posteriorly to reach their maximal height in the ninth caudal. This height seems to be constant up to the thirteenth vertebra and progressively decreases posteriorly. The neural spines of the first to fifth caudals are long anteroposteriorly. The sixth and seventh decrease in length, the posteriormost from the eighth having the same anteroposterior length and being much narrower. In the first to fifth caudals, there are anterior and posterior concavities in the neural spine just dorsal to the zygapophyses. The neural spine is longer dorsally, the dorsalmost part having subparallel anterior and posterior margins. From the sixth caudal, because of the decrease in the anteroposterior length of the neural spine, the anterior and posterior margins of the neural spine are increasingly concave, giving it an anteroposteriorly elongated dorsal to the zygapophyses, with their anterior and posterior margins parallel. After this, the neural spine becomes narrow dorsally. Only the base of the transverse processes is known. They are flattened dorsoventrally, and their anteroposterior length is about half the length of the centrum, this length progressively decreasing posteriorly. Some haemal arches are preserved, but only a few are complete. The haemal arch is nearly complete in the third caudal vertebra. It is constricted medially, anteroposteriorly short, and higher than the neural spine. The height of the haemal arches decreases posteriorly, as the haemal arch is nearly half the height of the neural spine in the eighth caudal.

The axial rib has only its capitulum in contact with the odontoid process and axis centrum in the specimen OCP DEK-GE 254, whereas the tuberculum is long and contacts the axial diapophysis in OCP DEK GE 43. In OCP DEK-GE 254, the tuberculum is reduced; nevertheless the incisura capitulotubercularis is relatively deep, and the anteroventral part is marked by a small tuberosity, probably the rudiment of the tuberculum seen in OCP DEK GE 43. Only cervical ribs 3–6 are preserved in articulation. They all have the same shape, with a short corpus costalis, as long as the cranial process.

Scapula: The posterior margin of the scapula is nearly straight, with only the most ventral part slightly concave. The ventral coracoidal articular surface is large, and the scapula forms a high ventral process anteriorly, ending by a high and straight margin anteriorly, perpendicular to the scapulocoracoid suture. The articular surface for the humerus is directed caudoventrally and is gently concave. Dorsal to this quadrangular process, the anterior margin of the scapula displays a deep concavity. Lateroposteroventral to this concavity, the scapula bears a long and low crest, orientated obliquely, located in the same axis as the anterior margin. The dorsal termination is strongly broadened ( Fig. 14 ).

Coracoid: The maximal length of the coracoid is shorter than the maximal length of the scapula. The anterodorsal margin of the coracoid is nearly straight, nearly perpendicular to the scapulocoracoid suture. It extends as anteriorly as the anteroventral margin of the scapula ( Fig. 14 ). The shaft is narrow, more or less circular in cross-section, with a slightly more flattened medial surface, and its posterior part is very slightly broadened and flattened. The posteroventrally projected glenoid process of the coracoidal head bears a humeral articular surface that is slightly directed posteroventrally and triangular-shaped in outline. A dorsoventrally oval coracoidal foramen is positioned slightly anterodorsally from the centrum of the coracoidal head.

Interclavicle: The interclavicle is a long and narrow bone, sharp anteriorly and posteriorly with a nearly constant width ( Fig. 15 ).

Humerus: The left humerus is exposed in anterior view in OCP DEK-GE 362. The proximal and distal extremities are not twisted against each other. The humeral shaft seems to have been circular in crosssection. The proximal head of the humerus ends with a convex articular surface. The deltopectoral crest extends on the lateral margin of the humerus, parallel to the lateral margin of the proximal extremity. It extends on nearly one-third of the length of the humerus, and appears as a rounded crest moderately developed. Both condyles of the distal extremity of the humerus are divided from each other by a deep intercondylar sulcus.

Ulna: The right ulna is preserved and exposed in anterior view in OCP DEK-GE 252. The ulnar shaft is circular in cross-section, and the condyle of the proximal head is one-third wider than the shaft in its distal half. The articular surface for the humeral head is strongly medially deflected. The distal head of the ulna is not available, but seems to be strongly less wide than the proximal head.

Radius: The right radius is preserved in OCP DEK- GE 252, but it is poorly preserved. Its proximal head is not available, and its shaft is circular in cross-section. The distal head, even if it is damaged, would have been slightly flatter and wider than the shaft.

Manus: The left manus is preserved in the specimen OCP DEK-GE 252 ( Fig. 16A ). The ulnare is much smaller than the radiale, and is broader distally than proximally. The radiale is flat, wide, and its proximal head is broad. The pisiform is a small bone, triangular in shape, and its poor preservation does not permit the examination of some details. Only one carpal is observed, probably the fused carpals 4 + 5 ( Buscalioni et al., 1997). The others have not been found, possibly due to their unossified condition. Because the particularly good conditions of preservation enable the preservation of the small pisiform, it can be supposed that if the central 2 and 3 had been present and ossified, they also would have been found. The metacarpals are relatively short and massive, the third being the longest, followed by the second and the fourth. The phalanges are short and massive.

Ilium: The ilium is visible in lateral (OCP DEK-GE 252; Fig. 17A ) and medial (OCP DEK-GE 254; Fig. 17B ) view, and parts of the sacral ribs are still in contact with the ilium ( Fig. 17B ). It is a large iliac blade, with a smoothly convex dorsal margin, a gently rounded posterior margin, and a concave anterior margin. The anterodorsal process is strong, and projected more anteriorly than dorsally ( Fig. 17D ). The ventral margin of the ilium bears anterior and posterior peduncles, as long as each other. The articular surface for the femur is wide and covers almost all the lateral surface of the posterior peduncle. Between the two ventral peduncles, the semicircular dorsal margin of the acetabular foramen is small. The lateral surface of the ilium bears a strong crest, which begins at the level of the anteroventral margin of the anterodorsal process, and extends posteriorly for two-thirds of the length of the ilium. The insertion of the first sacral rib on the ilium is higher than long, and is kidney-shaped, with its anterior margin concave. Insertion of the second sacral rib is much longer than high, with the shape of a nearly horizontal oval.

Ischium: The ischium is well developed ventrally. Dorsally, the posterior process is not much more developed than the anterior process ( Fig. 17D ). The anterior process is inclined at about 30° to the posterior process. The anterior process bears a strong knob-shaped process for articulation with the pubis. The anterior margin of the ventral shaft of the ischium is concave ventral to this knob-shaped process. The posterior margin is more gently curved. The ventral margin of the ischium is long and straight, slightly longer than the dorsal length. The ischium bears a strong protuberance on its posteroventral surface, probably for the insertion of the ilioischiocaudalis muscle ( Schwarz, 2003).

Pubis: The pubis is wide ventrally, and the anterior and posterior margins seem symmetrically concave, forming a wide anteroventral plate ( Fig. 17C ).

Femur: The femur is curved sigmoidally. The proximal and distal extremities are twisted relative to each other. The femoral shaft is semicircular in cross-section. The fourth trochanter is a prominent tuberosity positioned at the border between the medial surface of the proximal femoral extremity and the posterior surface of the femoral shaft. A shallow, proximodistal oval paratrochanterical fossa is developed anterior to the fourth trochanter.

Tibia: The tibia is preserved in anterior view in OCP DEK-GE 254. The tibial shaft is circular in crosssection. The proximal extremity is bent from the tibial shaft in a posterior direction, and the distal extremity is wider than the shaft.

Pes: The left foot bones are preserved in OCP DEK- GE 252 ( Fig. 16B ). The calcaneum is preserved in ventral view, with the facet for tarsal IV, which is flat and rounded in outline. The massive astragalus is preserved in anterior view, with shallow fossae between the rounded surface for articulation for tarsals III and metatarsals I and II, and the dorsal margin. The articular surface for tarsal III is anteroventrally orientated, whereas the surface for metatarsals I and II is orientated anteriorly.

The fourth tarsal articulates with the calcaneum along a flattened, roughly triangular, posterior surface that curves slightly forward above. The third tarsal is an irregularly shaped block of bone whose orientation on the tarsus is uncertain.

The first four metatarsals are massive bones with thick proximal and distal ends. The second and third metatarsals are nearly the same size, whereas the first and fourth are slightly shorter. A small triangular damaged bone seems to be the fifth.

Osteoderms: In OCP DEK-GE 252, some anterior dorsal osteoderms are preserved in place ( Fig. 18C ). There are two longitudinal rows, and six transverse rows. The anteriormost is located at the level of the ninth cervical, and the posteriormost preserved at the level of the fifth dorsal. They are from the left side, and exposed in ventral view. Their ornamentation is thus not observed. The first medial osteoderm, located at the level of the ninth vertebra, is short (4 cm long), whereas the posterior medials are longer (6 cm for the osteoderm at the level of the first dorsal vertebra, and 6.9 cm for the osteoderm at the level of the fifth dorsal vertebra). Except for the two first osteoderms, the medial osteoderms are rectangular in outline, with rounded corners, the first being nearly triangular, the second being square. Their width progressively increases posteriorly, and a small anterolateral lobe is present on the sixth medial osteoderm. The first lateral osteoderm would have been on the second transverse row, but is not preserved. The first preserved is on the third transverse row. It has the shape of a rightangled triangle with rounded corners. The lateral osteoderms become progressively square, and the fifth is square ( Fig. 18D ).

In OCP DEK-GE 43, some dorsal osteoderms are preserved, still in place on the body at the level of the ninth to 11th dorsal vertebrae ( Fig. 18A, B ). The dorsal shield is formed by several medial and lateral longitudinal parallel rows with four preserved transverse rows. Their anterior margins are overlapped by their neighbours immediately anterior to them. The plates are strongly ornamented with numerous large, deep, round pits widely separated from each other. A regular area (about 1 cm width) without ornamentation surrounds the external margin of the plates. The pits of the lateral row are more marked than those of the medial row. The lateral margin of the pits forms a small dorsal overhang within the pit (cross-section of the bone separating the pits in the shape of a wide ‘T’). The plates of the medial row are wider than long (about one-third more), regularly rectangular with rounded corners. The lateroanterior margin is prolonged laterally to form a flat, smooth, and rounded lateral lobe, spreading on the lateral plate. The lateral margins of the osteoderms of this medial row are not serrated, indicating that they are not sutured to the lateral ones. The lateral row is formed by square plates and about as wide as long, with rounded corners, without any trace of a lateral lobe ( Fig. 18D ).

Gastroliths: In all complete skeletons, many stones have been found in situ at the location of that was probably the animal stomach. These stones are small and rounded, no more than 5 cm in diameter.

Figures

Figure 2. Dyrosaurus maghribensis sp. nov., Ypresian of Mera el Arech, in the Oulad Abdoun Basin, Morocco: A, skeleton of OCP DEK-GE 255, holotype; B, skeleton of OCP DEK-GE 252.

Figure 3. Skull of Dyrosaurus maghribensis sp. nov., OCP DEK-GE 88, Ypresian of Daoui, Oulad Abdoun Basin, Morocco, in dorsolateral view.

Figure 4. Skull, cervical and dorsal vertebrae of Dyrosaurus maghribensis sp. nov., OCP DEK-GE 43, Ypresian of Daoui, in the Oulad Abdoun Basin, Morocco, in dorsal view.

Figure 5. Reconstruction of the skull of Dyrosaurus maghribensis sp. nov., Ypresian of the Oulad Abdoun Basin, Morocco, in dorsal view. See Appendix 5, for explanation of abbreviations here and in Figures 6–17.

Figure 6. Reconstruction of the skull and mandible of Dyrosaurus maghribensis sp. nov., Ypresian of the Oulad Abdoun Basin, Morocco, in lateral view.

Figure 7. Stereoscopic photograph of the occipital face of Dyrosaurus maghribensis sp. nov., OCP DEK-GE 263, Ypresian of Mera el Arech, Oulad Abdoun Basin, Morocco.

Figure 8. Skull, mandible, and postcranial remains of Dyrosaurus maghribensis sp. nov., OCP DEK-GE 253, Ypresian of Mera el Arech, Oulad Abdoun Basin, Morocco.

Figure 9. Reconstruction of the skull of Dyrosaurus maghribensis sp. nov., Ypresian of the Oulad Abdoun Basin, Morocco, in ventral view.

Figure 10. Posterior part of the left mandibular ramus of Dyrosaurus maghribensis sp. nov., OCP DEK-GE 253, Ypresian of Mera el Arech, Oulad Abdoun Basin, Morocco: A, lateral view; B, dorsal view; C, medial view.

Figure 11. Vertebral column of Dyrosaurus maghribensis sp. nov., OCP DEK-GE 254 and OCP DEK-GE 255, Ypresian of Mera el Arech, Oulad Abdoun Basin, Morocco, in lateral view. Cervicals and dorsals are from OCP DEK-GE 254, sacrals and caudals are from OCP DEK-GE 255.

Figure 12. Dyrosaurus maghribensis sp. nov., Ypresian of Mera el Arech, Oulad Abdoun Basin, Morocco: proatlas (OCP DEK-GE 263) in ventral (A), dorsal (B) and posterior (C) views; neural arch of atlas (OCP DEK-GE 254) in dorsal (D, E), medial (F, G) and ventral (H, I) views; odontoid process (OCP DEK-GE 254) in right lateral (J), dorsal (K), ventral (L), anterior (M) and posterior (N) views.

Figure 13. Reconstruction of the vertebral column of Dyrosaurus maghribensis sp. nov., OCP DEK-GE 254, Ypresian of Mera el Arech, Oulad Abdoun Basin, Morocco in lateral view: A, cervical and dorsal vertebrae; B, cervical 1–6; C, cervical 8 to dorsal 6.

Figure 14. Right scapula and coracoid of Dyrosaurus maghribensis sp. nov., OCP DEK-GE 254, Ypresian of Mera el Arech, Oulad Abdoun Basin, Morocco: A, lateral view; B, lateroventral view; C, interpretative drawing of (A) and (B).

Figure 15. Interclavicle of Dyrosaurus maghribensis sp. nov., OCP DEK-GE 254, Ypresian of Mera el Arech, Oulad Abdoun Basin, Morocco, in lateral view.

Figure 16. Dyrosaurus maghribensis sp. nov., Ypresian of Mera el Arech, Oulad Abdoun Basin, Morocco, in dorsal view: A, left manus of OCP DEK-GE 252 in dorsal view; B, left foot of OCP DEK-GE 252.

Figure 17. Pelvic girdle of Dyrosaurus maghribensis sp. nov., Ypresian of Mera el Arech, Oulad Abdoun Basin, Morocco: A, left illium and ischium (OCP DEK-GE 252) in lateral view; B, right illium and ischium (OCP DEK-GE 254) in medial view; C, pubis (OCP DEK-GE 259) in ventral view; D, reconstruction of the pelvic girdle in left lateral view.

Figure 18. Dyrosaurus maghribensis sp. nov., Ypresian of Mera el Arech, Oulad Abdoun Basin, Morocco: A, B, dorsal view of the dorsal osteoderms (OCP DEK-GE 43); C, ventral view of the anterior dorsal osteoderms (OCP DEK-GE 252); D, reconstruction of an anterior part of the dorsal armour.