Domningia sodhae, Thewissen & Bajpai, 2009

Thewissen, J. G. M. & Bajpai, Sunil, 2009, A new Miocene sirenian from Kutch, India, Acta Palaeontologica Polonica 54 (1), pp. 7-13 : 8-12

Domningia sodhae sp. nov.

Figs. 1–3.

Etymology: In honor to Mohan Singh Sodha from Kutch, India, who collected the holotype specimen.

Holotype: IITR−SB 3091 , well−preserved, complete adult skull with left and right dentaries (Figs. 1, 3). The type specimen is in the collections of the “Fossil Park” in the village Vithon , Taluka Nakhatrana , District Kutch , State of Gujarat, India. The “Fossil Park” is a small, private museum run by Mohan Singh Sodha , who collected the specimen. As this museum does not keep a catalogue, the specimen has been entered in the catalogue of the Vertebrate Palaeontology Laboratory , Indian Institute of Technology , Roorkee, and casts of the specimen have been deposited with the institutions of the authors. Vertebrae were associated with the holotype, but only some of these can be positively identified among the large amount of uncatalogued sirenian material in this collection.

Type locality: Nangia , Kutch. The type specimen was found in a (dry) tributary of the Nithi River . This tributary crosses the road between the villages of Nangia and Sujapur 500 meters NW of Nangia, and the specimen was found near this intersection. The specimen is from a yellow sandstone near the top of the exposed section. The sandstone overlies a sandstone rich in Turritella and oysters. Co−ordinates of the locality are 23 ° 22.337’N, 68 ° 54.866’E .

Type horizon: The beds are part of the Khari Nadi Formation, and is generally presumed to be Aquitanian (lower Miocene) in age ( Biswas 1992).

Material.—Additional material of this species is present in the collection of the “Fossil Park”, but locality information is lacking for much of it. A fragmentary skull with some vertebrae and ribs (IITR−SB 3092) of another specimen was recovered by the authors at this locality in 2005. It is here tenta− Condylobasal length 510 Maximum height of jugal inferior to orbit 65 Zygomatic breadth 248 Distance between superior and inferior occipital condyle 42 Breadth across occipital condyles 102 Breadth of braincase at posterior frontoparietal suture 80 Greatest width of foramen magnum 50 Length of external nasal opening 190 Maximum width of external nasal opening 76 Length of orbit 96 Length of upper molar row 80 Maximum width between labial edges of upper cheek teeth 94

tively referred to Domningia , in addition to another braincase from the Fossil Park (IITR−SB 3099).

Diagnosis.—As for the genus, by monotypy.

Description.—The holotype skull (measurements are summarized in Table 1) is nearly complete and undeformed, with only the rostral part of the premaxillae slightly damaged, and the right zygomatic arch missing. Incisors are broken off, and the only tooth crowns preserved are the molars. The left zygomatic arch is preserved completely in place. Left and right tympanics are preserved. The orbits, temporal fossae, and tympanic regions have been left unprepared and are filled with sediment in order to protect the delicate areas underlying the sediment from storage and handling.

The premaxillae are large and ventrally deflected, housing the roots for the large tusks. These tusks are flattened mesiodistally, and are described with the other tooth crowns. The tusks are the only teeth in the premaxilla. Rostrally, the palatal side of the premaxillae bears fused palatine fissures that extend as a long and narrow slit in the median plane. Caudal to this opening are bilateral grooves on the palate located lateral to the median plane. The median suture of the palatines is raised in a crest. On the palate, the suture between premaxilla and maxilla is unclear. The part of the palate caudal to the incisors is broad, whereas the palate rostral to the cheekteeth is narrow (Fig. 1D). The lateral edge of the palate is sharp immediately behind the incisors, but flattens out into an irregularly shaped plane which extends onto the maxilla. The suture between left and right premaxillae makes up approximately 30% of the length of the skull.

The suture between premaxilla and maxilla is clear on the side of the face (Fig. 1D), extending dorsal and caudal from a point approximately halfway between the tip of the rostrum and the zygomatic arch. The suture can also be traced on the dorsal side of the skull, where the premaxilla contacts the dorsal side of the lacrimal, and then extends caudomedially, reaching the nasal opening at its posterior third (Fig. 1F). The rostral point of the nasal opening extends approximately to frontoparietal suture nasal lacrimal

Fig. 1. Holotype ( IITR−SB 3091 ) of the sirenian Domningia sodhae gen. et sp. nov., Khari Nadi Formation , Aquitanian ( lower Miocene ), Nangia , District Kutch, India, in lateral (A, B) and ventral (C–F) views. Photographs (A, C, E) and explanatory drawings (B, D, F).

frontoparietal suture the level of the rostral part of the suture between premaxilla and maxilla.

The maxilla is the largest contributor to the palate in the molar region. The grooves on the rostral palate fuse caudally and form a sharply delineated, broad median trough (Fig. 1D). The palate narrows caudally and its edge is sharp. Caudally, this edge separates into two crests which extend on lingual and buccal sides of the teeth. There are no teeth in the rostral part of the maxilla. A triangular flat region, bounded by the two low crests occurs rostral to the upper molars, and held premolars earlier in life. One lingual and one labial alveolus for a premolar occur rostral to the first molar. The area rostral to these premolar alveoli is rugose and lacks alveoli. It is possible that an additional premolar was lost during life and the alveoli resorbed. The palatine contribution to the palate extends from the rostral area to the anterior edge of M1 and caudally to the middle of M3, and the bony palate bears a median groove between the molars.

The maxilla surrounds the oval infraorbital foramen, which is 30 mm in diameter mediolaterally, its greatest dimension. Lateral to the infraorbital foramen is the projecting rostral rim of the orbit. The zygomatic−orbital bridge of the maxilla is broad and forms the floor of the infraorbital canal, jutting out laterally behind the rostrum. This bridge is nearly level with the palate. The maxilla has a long suture with the jugal (Fig. 1B), and this suture extends rostral to the orbit. The lacrimal is a small, triangular bone articulating ventrally with the jugal and dorsally with the premaxilla (Fig. 1F). There is a long and stout lacrimal process, which projects into the orbit ( Fig. 2A ).

The frontal forms the supraorbital process. This process is large, triangular and projects lateroventrally, reaching within a centimeter of the jugal arch. Directly dorsal to the process, the frontal bears a strong crest−like tubercle, which extends from laterorostral to mediocaudal. Posteriorly this tubercle continues as the temporal crest ( Fig. 2F ). The frontal slopes rostrally between these crests toward the nasal opening. The premaxilla−frontal suture is on the rostral face of this tubercle ( Fig. 2F ). This suture extends vertically in front of the orbit and caudomedially on the forehead. No sutures are visible near the caudal edge of the nasal opening, but two symmetrical cracks suggest that the nasals are present and triangular, sharing a median suture and indenting the frontals in the midline ( Fig. 2A ). This part of the caudal part of the nasal opening is convex and projects into the nasal opening. The fronto−parietal suture is clear (Fig. 1F). On the dorsal surface of the skull, this suture extends from the temporal crest mediocaudally. The fronto−parietal suture reaches the temporal ridge well caudal to the caudal edge of the nasal opening. The dorsal side of the frontal is more or less flat. The frontal surrounds the caudal one−third of the nasal opening. In the median plane, left and right frontal (or fused nasals) share a symphyseal suture. Lateral to the temporal crests, the fronto−parietal suture changes direction and extends caudally in the temporal fossa on the lateral side of the skull (Fig. 1F).

The parietal forms most of the dorsal wall of the braincase. The temporal crest of the frontal continues on the parietal and increases in height caudally, making the bone concave near the nuchal crest. The parieto−squamosal suture (Fig. 1B) extends on the lateral side of the braincase in a broad arch, and the parietal forms most of the wall of the braincase.

The jugal (zygomatic) contacts the lacrimal, and forms most of the rostral and ventral rim of the orbit (Fig. 1B). The most ventral part of the jugal is situated directly ventral to the lowest point of the orbit. The jugal forms the entire height of the zygomatic arch where it makes up the rim of the orbit, and forms a dorsal projection behind the eye, which nearly contacts the supraorbital process. Caudal to this process, the squamosal is the main contributor to the zygomatic arch, and the jugal is reduced to a narrow process. The jugal projects beyond the orbit both ventrally and caudally.

The orbit and temporal fossa are filled with sediment and cannot be studied. The pterygoid process is oval in cross−section and has a rugose tip. On the caudal side of the pterygoid process are two crests that converge proximally, and form a narrow and sharp crest dorsally, at the root of the process. The area between these crests is the weak pterygoid fossa.

The squamosal projects between parietal and supraoccipital on the lateral side of the skull. Ventral to the suture between squamosal and supraoccipital is a large mastoid foramen (Figs. 1B, 2B), basically an ossification defect between squamosal and supraoccipital. This defect extends ventrally between exoccipital and squamosal. A small part of the mastoid is exposed in the ventral half of this defect. Ventral to this part of the mastoid, the squamosal forms the posttympanic process ( Fig. 2B ). It is blunt and its lateral side bears a longitudinal groove. This process borders the caudal side of the external auditory meatus. The external auditory meatus is broad, approximately equally wide as long. Dorsal to the external auditory meatus, the squamosal bears a sigmoid ridge. Rostral to the external auditory meatus is the root of the zygomatic arch and the depressed mandibular fossa. The zygomatic process of the squamosal is broad and more or less horizontal. The caudal part of the zygomatic arch reaches far posterior on the skull, and is 21 mm from the paroccipital process.

The supraoccipital forms the dorsal half of the occipital side of the skull. Its dorsal surface is rugose, and its dorsal suture (the nuchal crest) is more or less straight. The occipital side of the skull is narrower centrally than dorsally and ventrally. The ventral suture of the supraoccipital extends from laterodorsal to medioventral, shaping the bilateral suture between supraoccipital and exoccipitals as a wide−open V ( Fig. 2B ). Laterally, the exoccipital extends in a ventral direction between occipital condyle and squamosal, and ends in a sharp but low paroccipital process which curves medially. There is a large supracondylar fossa extending along the dorsal and lateral sides of the occipital condyle. Left and right exoccipitals touch in the median plane dorsal to the foramen magnum. The occipital condyles are large and do not touch in the median plane. The basioccipital is narrow. A blunt bilateral process occurs on the anterior part of the basioccipital. The middle ear is deeply recessed and much of the ear region is covered with sediment. The tympanic is horseshoe−shaped and thick.

Among the upper teeth, crowns are only preserved for the molars. The first molar is strongly worn and the entire rostrobuccal side of the tooth is missing because of wear. The second molar is also worn, but still shows that the tooth had four main cusps with strong mesial and distal cingula. The M3 has a well−preserved crown that is lightly worn. It is bilophodont, with rostrally convex lophs and a strong mesial cingulum, but no other cingula. A cusp is present distal to the hypocone, and there is a basin buccal to this cusp. M1 is 21 mm long and 26 mm wide, M2 is 25 mm long and 28 mm wide, and M3 is 31 mm long and 24 mm wide. Only the root of the first incisor is preserved on left and right sides. This tooth is a tusk and is more−or−less oval in cross−section. Its maximum (mesio−distal) and minimum (labio−lingual) dimensions are 46 and 14 mm. Enamel is not visible on the part of the tusk that remains.

The lower jaw of the holotype has an evenly downturned, strongly concave lower margin, and a single, large mental foramen ( Fig. 3A ). The mandibular symphysis is firmly fused and the rostral tip of the mandible is narrow: it widens to form a rugose occlusal area which has three shallow bilateral depressions lined up from rostral to caudal. Three molar crowns are preserved on both sides. Rostral to these, there are three premolar alveoli. The rostral alveolus is narrow and long and the two caudal alveoli are broader and closely spaced. The two tooth rows are parallel ( Fig. 3B ). The caudal edge of the ascending ramus is damaged.

The ascending ramus originates buccal to m3 and covers the distal aspect of this tooth in lateral view. The rostral edge of this ramus is vertical and the area of insertion for the temporal muscle on the coronoid process reaches further dorsal than the mandibular condyle.

The m1 is strongly worn and all enamel is missing from its mesial side ( Fig. 3C ). The m2 is also worn, but the undulations in its enamel suggest that there were four cusps and a strong distal cingulid. The m3 preserves cusp morphology, it is bilophodont, and there are two cusps posterior to the hypolophid. The labial of these cusps is connected to the hypolophid. The dimensions of the lower molars are:

Figures

Fig. 2. Nasal opening and superior left orbit (A) and oblique occipital view (B) of the sirenian Domningia sodhae gen. et sp. nov. (IITR−SB 3091), Khari Nadi Formation, Aquitanian (lower Miocene), Nangia, District Kutch, India.

Fig. 3. Right lateral (A), oblique anterior (B), and occlusal (C) view of mandible of the sirenian Domningia sodhae gen. et sp. nov. (IITR−SB 3091, holotype), Khari Nadi Formation Aquitanian (lower Miocene), Nangia, District Kutch, India.