Halisaurus ARAMBOURGI BARDET & PEREDA SUBERBIOLA 2005, SP. NOV.
Creators: name: Bardet, Nathalie
name: Suberbiola, Xabier Pereda
name: Iarochene, Mohamed
name: Bouya, Baadi
name: Amaghzaz, Mbarek
Publisher: name: Zenodo
Year: 2005
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Reptilia
Squamata
Mosasauridae
Halisaurus

description: HALISAURUS ARAMBOURGI BARDET & PEREDA SUBERBIOLA, SP. NOV.
Etymology: In honour of the late Prof. Camille Arambourg, for his pioneering work on fossil vertebrates from the phosphates of North Africa and the Middle East.
Holotype: MNHN PMC 14, incomplete skeleton including a disarticulated skull and 27 associated articulated vertebrae (seven cervicals, 18 dorsals, two distal caudals) (Figs 2, 3).
Type locality and horizon: Grand Daoui area, near Khouribga, central Morocco; phosphates of the Oulad Abdoun Basin, upper Couche III, Late Cretaceous, Late Maastrichtian (Cappetta, 1987).
Referred specimens from the same locality and horizon: MNHN PMC 15, disarticulated cranium with three cervical vertebrae (Figs 4A, 5A); MNHN PMC 16, disarticulated incomplete cranium; OCP-DEK/GE 100, incomplete disarticulated skeleton with cranial remains, vertebrae, girdle and limb bones (Figs 4B, 5B, 8A, 9A, 10A, 11A, 12B, 13B); OCP DEK/GE 101, incomplete skeleton including caudal vertebrae, pelvic girdle and hindlimb bones (Figs 6, 7, 10B, 11B); OCP DEK/GE 102, incomplete disarticulated skeleton with cranial remains, vertebrae and forelimb bones (Figs 8B, 9B, 12C, 13C); OCP DEK/GE 103, incomplete skeleton with vertebrae and forelimb bones (Figs 12A, 13A). Other incomplete specimens are kept in the OCP collections (OCP DEK/GE 12, 23, 39, 53, 73, 73 bi, 104–108, 150, 176, 185, 244, 272– 277) as well as in private collections (Figs 8C–H, 9C– H, 14C).
Remarks: Isolated teeth from the Maastrichtian Phosphates of the Ganntour Basin of Morocco (N. Bardet, pers. observ.), the Early Maastrichtian phosphates of Syria (Plioplatecarpinae indet. in Bardet et al., 2000) and Jordan (Bardet & Pereda Suberbiola, 2002) and, tentatively, the Maastrichtian of Negev (as Platecarpus (?) sp. in Raab, 1963: pl. 3, figs 17–19) and Angola (as Mosasauridae indet. in Telles Antunes, 1964: pl. 26, fig. 5-5a) could also belong to this taxon.
Diagnosis: Small mosasaurid (adult total length 3– 4 m). External nares extend from 6th to 12th maxillary teeth, V-shaped anteriorly and U-shaped posteriorly; prefrontal contributes moderately to margin of naris and possesses small anterior supraorbital ridge; frontal with median dorsal ridge extending on two-thirds of the bone length, and two anterior oblique ridges; parietal with triangular table ornamented by transverse undulated ridges and a lenticular foramen, the anterior end of which is located half its length from the frontal suture; quadrate with a vertical oval stapedial notch; pterygoid with short palatine process at about 45∞ relative to the ectopterygoid process; dental formula: 2 premaxillary, at least 16 maxillary and 12 pterygoid teeth, 19 dentary teeth; teeth very fine and sharp, abruptly posteriorly recurved, with a circular basal cross-section, two carinae and enamel ornamented by minute ridges; estimated vertebral formula: 7 cervicals, at least 20 dorsals and pygals, more than 29 median and 45 distal caudals; humerus length approximately 1.6 times distal width; femur length approximately 1.5 times distal width.
DESCRIPTION
GENERAL PRESERVATION
Several incomplete but complementary specimens are known (see list of material above); reconstructions of skull and mandible have been attempted (Fig. 15). Most skulls are disarticulated and range from 30 to 45 cm in length (Fig. 15). The total body length is estimated as approximately 3–4 m in adults. Although most of the skull and mandibular bones remain unfused, indicating a high degree of cranial kinetism, the studied specimens are regarded as belonging to subadult or to adult individuals.
Skull (Fig. 15)
The premaxilla is short anteriorly, U-shaped and without a rostrum (Figs 2A, B, 3A, B). It bears two pairs of teeth and two rows of large foramina (3–5) for the dorsal ophthalmic ramus of the cranial nerve V. The suture with the maxilla is long and reaches the level of the 6th or 7th maxillary tooth. In lateral view, the suture is vertical, then oblique and becomes horizontal posteriorly. The internarial bar is slender, triangular in cross-section and bears a prominent dorsal longitudinal crest.
The long and narrow maxilla (Figs 2A, B, 3A, B, 4A, 5A) bears at least 16 teeth, exhibits a lateral row of large foramina located above the entire length of the gum line and has a posterodorsal process. The lingual parapet is slightly shorter than the labial one.
The nares are located between the 6th or 7th and the 12th maxillary teeth. They are V-shaped anteriorly and U-shaped posteriorly (Fig. 16C). There is no evidence of the septomaxilla or nasal bones.
The prefrontal is a large triangular bone that contributes moderately to the margin of the external naris (Figs 4A, 5A). Its posterior ramus extends far posteriorly along the lateral margin of the frontal and bears a small, anteriorly located supraorbital process.
The frontal is long and narrow, with concave posterolateral margins, sharp lateral corners and straight parietal suture (Figs 2A, 3A, 4A, 5A, 16C). Facets for reception of the prefrontal and postorbitofrontal on its ventral surface indicate that these two bones did not made contact. Anteriorly, the emarginations for the nares are rounded. The lateral borders are slightly sinusoidal. The dorsal surface bears three distinctive features: a median longitudinal ridge on the anterior two-thirds of the bone; a prominent, finely ridged, posteromedian triangular area; and two anterior oblique ridges, less marked on larger specimens. The ventral surface of the frontal bears a wide median groove for the olfactory stalks and a triangular posteromedian roof for the cerebral hemispheres. The ventral sutural surface for the prefrontal is larger than that for the postorbitofrontal. The frontal orbital margin is reduced.
The postorbitofrontal is not well known in any specimen. It overlaps the frontal and parietal and has a larger contact with the frontal (Figs 4A, 5A). The short posterior squamosal ramus does not reach the posterior margin of the supratemporal fenestra.
The long and slender jugal lacks posteroventral process (Figs 2B, 3B, 4, 5). The horizontal ramus is very long compared with the vertical ramus. The ascending ramus, forming an angle of more than 90∞ with the horizontal one, is mediolaterally compressed and expands distally.
The parietal is long and broad, occupying more than one-quarter of the skull length (Fig. 16C). The parietal table is roughly triangular and bears a median surface ornamented by transversal undulated ridges (Figs 2A, 3A, 4, 5, 10B, 11B). The margin of the large, lenticular parietal foramen is elevated with respect to the dorsal surface of the parietal table. Its anterior margin is located half way from the frontal suture. The foramen opens ventrally on a triangular boss. It is obliquely orientated, so that its ventral opening is located more posteriorly than the dorsal one. The suspensorial rami are long and mediolaterally compressed, and the surface of articulation for the supratemporal is obliquely orientated.
The supratemporal is a narrow lamina of bone located between the parietal, squamosal and the paroccipital process of the opisthotic-exoccipital (Figs 2A, 3A).
The squamosal is a comma-shaped, slender bone (Figs 4A, 5A).
The quadrate has a question-mark shape in lateral view (Figs 2A, B, 3A, B, 8C–H, 9C–H, 14C). The suprastapedial process is very large and strongly swollen distally, so that it seems divided into two parts that include a circular depression, probably for the origination of m. depressor mandibulae (Russell, 1967: 48). The infrastapedial process is also well developed medially, forming a very large oblique process. Both are coalescent but not fused. The stapedial notch (tympanic meatus) is oval, vertical and located in the dorsal portion of the bone. The stapedial pit is small, narrow and oval. The broken tympanic ala was probably thin. The distal condyle is convex from side to side and orientated perpendicular to the proximal head.
The braincase unit preserved only parts of the basioccipital (Figs 8B, 9B), basisphenoid, prootic, opisthotic-exoccipital and supraoccipital (Figs 4B, 5B, 8A, 9A). The basioccipital has a typically crescentic condyle. The basal tubera (sphenoccipital tubercles) are of medium size and anterolaterally directed. The suture between the basioccipital and the basisphenoid is transverse. The square basipterygoid bears short, small processes that are not fan-shaped. The prootic preserves only the posterior ascending branch (suspensorial process) for the supratemporal. It is long, narrow and widens distally and dorsally. The prootic covers the opisthotic anterolaterally. The large opening for the internal auditory meatus is located beneath a sulcus near the base of the suspensorial process of the prootic. There is a small otosphenoidal crest obscuring the foramen for cranial nerve VII (internal jugular vein). The paroccipital process of the opisthotic-exoccipital is long, narrow and expands distally. It bears longitudinal ridges on its medial surface, probably for the insertion of the m. obliquus capitis magnus. There are two oblique lenticular foramina separated by a thin sheet of bone for the exits of cranial nerves X–XI (jugular foramen, the largest) and XII (condylar foramen, the smallest). The supraoccipital is a rectangular, roof-shaped bone firmly attached to the parietal. The foramen magnum is large and dorsally elongated.
The pterygoid is poorly preserved in all specimens (Figs 2B, 3B, 4A, 5A). It bears at least 12 teeth on specimen OCP DEK/GE 23. The teeth are delicate, strongly posteriorly recurved, without carinae and only slightly smaller than the marginal ones. The short palatine process is broad anteriorly and tapers posteriorly. The ectopterygoid process projects from the main body of the bone at an angle of about 45∞ to the palatine process. The basisphenoid process is long, narrow and rounded at its extremity.
Some palatine fragments are available (Figs 4, 5) and resemble those of Platecarpus ictericus (Russell, 1967: fig. 6). It is a subrectangular bone with a curvilinear medial margin.
Mandible (Fig. 15)
This is the only species of Halisaurus that preserves the complete mandible. In general terms, its resembles that of H. platyspondylus.
The dentary is long and narrow, without rostrum (Figs 2A, B, 3A, B). It bears 19 teeth. There is a large edentulous process posterior to the last tooth. The dorsal and ventral margins are almost straight. The medial parapet is lower than the lateral one. The lateral surface is gently convex with a dorsal row of foramina for the mandibular terminal branch of the cranial nerve V. Anteriorly, there is a ventral second row of foramina. The medial surface is concave with a deep Meckelian canal beginning near the anterior tip of the bone and widening posteriorly to form the mandibular channel. The posterior margin of the dentary is posteroventrally oblique, strongly striated and bears a median groove.
The long, triangular splenial (Figs 4A, 5A) extends far anteriorly spanning more than half the length of the dentary. The lateral wing is oblique posteriorly but rotated to be horizontal anteriorly. The medial wing is poorly preserved but is higher than the lateral one. Ventroposteriorly, it bears a large foramen for the inferior alveolar nerve. The well-developed concave articulation for the angular is elliptical and bears an oblique comma-shaped groove located lateral to the centre of the articulation. There is no anteromedial contact with the coronoid.
The long and narrow angular tapers posteriorly (Figs 4A, 5A). The lateral wing is low and largely exposed below the surangular. The medial wing is triangular and very well developed. Near its articulation with the splenial it bears a large foramen for the angular branch of the mandibular nerve.
The large, rectangular surangular is widely exposed in lateral view and occupies most of the surface of the posterior part of the mandible (Figs 4A, 5A). The lateral surface bears a nearly horizontal sharp crest for the insertion for the m. adductor mandibulae externus. The coronoid buttress is low and rounded. The coronoid suture extends onto the anterior half of the bone. The anterior margin of the surangular is oblique. The posterior lateral suture with the articular is posteriorly convex. The surface for the glenoid fossa is smaller than that of the articular.
The coronoid is long, narrow and regularly curved, forming a saddle-shaped bone (Figs 4, 5). There is no posteromedial process and the lateral and medial wings are poorly developed. The posterior ascending process is large.
As in other mosasauroids, the prearticular and articular are fused to form a unique bone (DeBraga & Carroll, 1993) (Figs 4, 5). The prearticular process extends anteriorly through the mandibular joint. The contribution of the articular to the glenoid surface is greater than that of the surangular. The glenoid fossa is surrounded posterolaterally by a large conical buttress process. The square retroarticular process is nearly vertical.
Marginal dentition
The teeth of Halisaurus arambourgi resemble those of Plioplatecarpus, suggesting a diet probably based on soft and small prey (Massare, 1987). They are poorly differentiated both in shape and in size along the jaw margins (Figs 2A, B, 3A, B, 4A, 5A). The crowns are delicate and small, approximately 1 cm high (the largest ones can reach 2 cm in height). They bear a pointed apex and are abruptly posteriorly recurved from about the midpoint of the crown, as in Plioplatecarpus. The basal cross-section is circular and both lingual and labial surfaces are convex. On the largest specimens, the base of the root exhibits a slight fluting. The enamel crown bears anterior and posterior carinae and is ornamented by minute ridges, more marked at the base of the crown, giving it a silky aspect. The crowns of the teeth are generally shorter, with a more delicate ornamentation, than those of Plioplatecarpus.
Axial skeleton
No specimen has a complete vertebral column. Based on complementary specimens, the vertebral formula could be estimated as follows: seven cervicals, at least 20 dorsals and pygal caudals (with transverse processes), more than 29 median caudals (both transverse processes and haemal arches) and more than 45 distal caudals (only haemal arches). There is no zygosphene– zygantrum complex and the zygapophyses extend on the cervical and dorsal vertebrae as in most mosasaurids. There are no sacral vertebrae.
The atlas consists of paired arches, centrum and intercentrum. The axis comprises a centrum with a fused neural spine and bears a facet for hypapophysis and small synapophyses. In addition to the atlas-axis, there are five cervical vertebrae bearing a hypapophyseal peduncle (Figs 2B, C, 3B, C). The articulation surfaces are roughly subrectangular, strongly dorsoventrally compressed (height/width ratio approximately 0.5) and slightly obliquely orientated. The condyle is slightly constricted from the main body of the centrum. The peduncle for the hypapophysis is located posteriorly on the ventral surface of the centrum. It is large, elliptical and slightly obliquely orientated. The pre- and postzygapophyses are very large and almost horizontal. The synapophyses are large, located anteriorly on the centrum and are connected to the prezygapophyses by a sharp crest. Their ventral border extends well below the ventral surface of the centra.
The dorsal vertebrae are wide and short and bear anteriorly located transverse processes. As in the cervicals, the articulating surfaces are strongly dorsoventrally compressed and slightly obliquely orientated (Figs 2C, D, 3C, D, 4B, 5B).
As no specimen preserves a complete vertebral series, it is difficult to estimate the number of dorsal and pygal vertebrae. There is no evidence of a direct contact between the vertebrae of the sacral region and the pelvic girdle. The pygal caudals bear a large and stout transverse process (Figs 6, 7). The median caudals have vertical elliptical articular surfaces, transverse processes and fused haemal arches (Figs 6, 7). The distal caudal centra are as high as long. They have circular articular surfaces, no synapophyses and fused haemal arches (Figs 6, 7).
Appendicular skeleton
All girdle elements are ossified separately, as typically in mosasaurids (DeBraga & Carroll, 1993). The limb bones remain plesiomorphic but are more derived than those of Varanus and Aigialosaurus in the following characters: the propodial and mesopodial bones are flat and have reduced length relative to width; propodial diaphyses and epiphyses lay in the same plan; and antebrachial and crurial foramina are lenticular (see DeBraga & Carroll, 1993).
Shoulder girdle: The scapula appears to be larger than the coracoid (Figs 4B, 5B, 10A, 11A), although it could be an artefact of poor preservation of the coracoid. The scapula is fan-shaped and overall resembles that of Platecarpus ictericus. The anterior margin is slightly shorter than the posterior one. The posterior margin is deeply concave just dorsal to the glenoid and then straight, as in Platecarpus, Plioplatecarpus, Ectenosaurus and Tylosaurus. The dorsal margin is regularly convex. The coracoid bears a short neck ventral to the glenoid. It is difficult to say whether the anterior margin is longer or shorter than the posterior one. The posterior margin is concave just ventral to the glenoid. The coracoid foramen is large.
Forelimb. The humerus is longer than wide (length approximately 1.6¥ distal width) and slightly expanded at both extremities (Figs 4B, 5B, 12, 13). The proximal articular end is almost flat, elliptical in shape and strongly grooved and pitted. It is well separated from both the deltoid crest and the postglenoid process. The postglenoid process is expanded. The deltoid and pectoral crests are separated. The deltoid crest is located more distally from the condyle than the postglenoid process. The pectoral crest is developed on the anteroventral portion of the humerus. A large oval scar is present on the anteromedian ventral part of the shaft. The distal end of the humerus is flat, without well-defined articular facets for radius and ulna. The ectepicondylar and entepicondylar tuberosities are moderately developed. The ectepicondylar foramen for the radial nerve is an oblique and narrow groove on the anteromedian dorsal part of the shaft. The radius is long, and its distal extremity is wider than the proximal one (Figs 4B, 5B, 10A, 11A, 12A, 13A). The proximal articular surface is nearly straight whereas the distal one is gently convex. The radius bears a well-developed preaxial ridge extending on the distal two-thirds of its length. The ulna is long and hourglass-shaped (Figs 12A, 13A). The proximal end is wider than the distal one. The olecranon is prominent. The distal extremity is slightly convex and undifferentiated.
Pelvic girdle: The slender club-shaped ilium (Figs 6, 7, 10, 11) expands ventrally to include the articular facets for pubis and ischium and the lateral acetabular facet, which is broad and well defined. The proximal shaft is elliptical in cross-section and anteriorly inclined, as in other mosasaurids. The distal part of the shaft tapers and does not articulate with vertebrae. Both pubes are preserved in OCP DEK/GE 101 but are broken at about their anterior third (Figs 6, 7, 10B, 11B). The size, shape and orientation of the pubic tubercle are unknown. The obturator foramen is not visible. Ventral to the rounded acetabular facet, the pubes become very narrow. The ischium is long and slender (Figs 6, 7, 10B, 11B), particularly distally. The ischiadic tubercle is small and located very close to the acetabular face.
Hindlimb: The femur is long and slender (length approximately 1.5¥ distal width) (Figs 6, 7, 10B, 11B). The proximal and distal ends are gently convex and undifferentiated. The shaft is slender and straight. The anterior surface is less concave than the posterior one. The internal trochanter is well developed and located anteriorly and proximally on the ventral surface of the bone. The tibia is slightly wider and shorter than the fibula (Figs 6, 7, 10B, 11B). The proximal end of the tibia is wider than the distal one and bears an anterior flange. The anterior margin is more concave than the posterior one. There is a distinct astragalar facet on the posterior part of the distal articular surface. The fibula has a distal extremity wider than the proximal one. Both are regularly convex. A possible astragalus, roughly elliptical, is preserved in OCP DEK/GE 101 (Figs 6, 7, 10B, 11B). Only a few metapodials and phalanges are known (Figs 4B, 5B, 6, 7, 10B, 11B). They are long and hourglass-shaped. The proximal ends of the metapodial bones are larger than the distal ones. The phalanges of both extremities are similar in size.
description: Published as part of Bardet, Nathalie, Suberbiola, Xabier Pereda, Iarochene, Mohamed, Bouya, Baadi & Amaghzaz, Mbarek, 2005, A new species of Halisaurus from the Late Cretaceous phosphates of Morocco, and the phylogenetical relationships of the Halisaurinae (Squamata: Mosasauridae), pp. 447-472 in Zoological Journal of the Linnean Society 143 (3) on pages 449-462, DOI: 10.1111/j.1096-3642.2005.00152.x, http://zenodo.org/record/4687311