Saurischia Seeley, 1887

Díaz, Verónica Díez, Suberbiola, Xabier Pereda & Sanz, José Luis, 2011, Braincase anatomy of the titanosaurian sauropod Lirainosaurus astibiae from the Late Cretaceous of the Iberian Peninsula, Acta Palaeontologica Polonica 56 (3), pp. 521-533 : 523-527

publication ID	https://doi.org/ 10.4202/app.2010.0043
persistent identifier	https://treatment.plazi.org/id/101A87D7-2D19-1C5A-8BBA-F81FFA4AD107
treatment provided by	Felipe
scientific name	Saurischia Seeley, 1887
status

Treatment

Sauropoda Marsh, 1878

Titanosauria Bonaparte and Coria, 1993

Lithostrotia Upchurch, Barrett, and Dodson, 2004 Eutitanosauria Sanz, Powell, Le Loeuff, Martínez, and Pereda Suberbiola, 1999

Genus Lirainosaurus Sanz, Powell, Le Loeuff, Martínez, and Pereda Suberbiola, 1999 Lirainosaurus astibiae Sanz, Powell, Le Loeuff, Martínez, and Pereda Suberbiola, 1999

Figs. 2–8 View Fig .

Type material: Holotype: MCNA 7458 View Materials , anteriormost caudal vertebra ( Sanz et al. 1999: pl. 2) . Paratypes: MCNA 7439 View Materials , incomplete braincase consisting of the basioccipital, the right prootic and exoccipital−ophistotic complex, and fragments of the basisphenoid−parasphenoid ( Figs. 2–4 View Fig ). See Sanz et al. (1999: 237, pls. 1, 5, 6) for a complete list of paratypes, which also includes isolated teeth, dorsal and caudal vertebrae, scapula, coracoid, sternal plate, humeri, fragments of ilium and pubis, femora, tibia, fibula and osteoderms ( MCNA collection) .

Referred specimen: MCNA 13913, incomplete braincase consisting of fragments of the basioccipital, and basisphenoid−parasphenoid ( Figs. 5–8 View Fig View Fig View Fig ).

Type locality: Laño quarry, between the towns of Laño and Albaina ( Condado de Treviño ), about 25 km south of Vitoria−Gasteiz, Spain .

Type horizon: L1A level; S3U1 unit of Astibia et al. (1987, 1990); upper zone of the B unit of Baceta et al. (1999); unit equivalent to the Sedano doi:10.4202/app.2010.0043

Formation of the North−Castilian Platform ( Floquet 1991; Berreteaga 2008); Upper Cretaceous, probable late Campanian to early Maastrichtian.

Revised diagnosis (only skull features).—Presence of a foramen in the distal surface of each basal tubera. The absence of median subcondylar foramina in the basioccipital, below the occipital condyle and between the basal tubera, may be an autopomorphic trait or a feature due to ontogenetic growth. See Sanz et al. (1999) for postcranial autapomorphies of L. astibiae .

Description

The elements of the two braincases of Lirainosaurus astibiae are partially fused; only a suture is visible between the basioccipital and the basisphenoid, just anterior to the basal tubera. MCNA 7439 lacks the laterosphenoid and orbitosphenoid, and MCNA 13913 lacks the dorsal braincase bones. These braincases probably belonged to both subadult individuals, as the absence of the laterosphenoid and orbitosphenoid appears to be due to lack of ossification, as there is not a broken surface in the anterior face of the right prootic in MCNA 7439. This absence is typical in subadult sauropods (e.g., immature specimen of Jainosaurus ; Wilson et al. 2009). The basipterygoid and paroccipital processes are not preserved in the specimens. Both braincases are covered by iron oxides in some areas, as is typical in the Laño fossils ( Elorza et al. 1999).

Exoccipital−opisthotic complex.—Only MCNA 7439 has preserved the right exoccipital−opisthotic complex, and only the base of the right paroccipital process is preserved. The contribution of the exoccipital−opisthotic complex to the occipital condyle cannot be observed, as the matrix obscures the surface where the suture between the exoccipital−opisthotic complex and the basioccipital should be. But it can be confirmed that the exoccipital−opisthotic complex forms the lateral margin of the foramen magnum.

DÍEZ DÍAZ ET AL.—LATE CRETACEOUS TITANOSAURIAN FROM SPAIN 525

20 mm

In posterior view, the exit for the hypoglossal nerve ( XII) could be located in the exoccipital−opisthotic complex near the occipital condyle, though the iron oxides hinder the observation of this area.

Prootic.—Only MCNA 7439 has preserved the right prootic. This element is fused to the anterior surface of the exoccipital−opisthotic complex. Two ridges appear near the base of the ventral margin of the paroccipital process ( Figs. 3A, 4C View Fig ). The posteriormost ridge—probably formed by the exoccipital−opisthotic complex—is sharp and prominent, and the anteriormost or crista prootica is less prominent. The crista prootica extends ventrally to the basipterygoid process, although it is truncated at the height of the occipital condyle. In lateral view, between these two ridges, opens the metotic foramen. This foramen, filled by iron oxides, is ellipsoid. Though the metotic foramen run the glossopharyngeal ( IX), vagus (X), and accessory ( XI) cranial nerves, as well as the jugular vein ( Chatterjee and Zheng 2002, 2005). Anterior to this foramen there is a broken surface where the crista prootica is truncated, showing a small channel. This channel probably belongs to the foramen of the facial nerve ( VII). A groove begins ventral to this opening and extends ventrally to the basipterygoid processes; the crista prootica occurs in its anterior margin. This groove is probably for the branch of the facial nerve ( VII). As the laterosphenoid and orbitosphenoid are not preserved, only the posterior margin of the trigeminal nerve (V) is visible, anterior to the crista prootica ( Figs. 3A, 4C View Fig ). This foramen is the largest one of the braincase. Ventral to this opening is a groove, which is anterior and shorter than the one for the foramen of the facial nerve ( VII). This groove is probably for the mandibular and/or maxillary branches of the trigeminal nerve (V). In medial view, posterior to the margin of the trigeminal nerve (V), there is a deep groove and, dorsal to it, a small foramen. A similar foramen is present in Bonatitan reigi ( Martinelli and Forasiepi 2004) and in an indeterminate titanosaur from Patagonia ( Paulina Carabajal et al. 2008). Both structures are probably for cranial vascularization.

Basioccipital−basisphenoid complex.—This complex forms the floor of the braincase. Only MCNA 7439 preserves the occipital condyle. The basioccipital probably forms the occipital condyle, which is slightly heart−shaped in posterior view, and its neck. The neck of the occipital condyle is short and wide, and it has a concave dorsal surface. When the doi:10.4202/app.2010.0043

basicranium is oriented vertically, the prootic and the base of the basipterygoid processes are aligned in the same vertical plane, the floor of the braincase is horizontal and the occipital condyle projects posteroventrally. It can be inferred that the occipital condyle is wider than the foramen magnum, as is common in other titanosaurs.

The basioccipital shows a median cavity for the pons variolii ( Fig. 7A View Fig ), which is situated in the posterior surface of the floor of the braincase (as in Jainosaurus septentrionalis ISI R 162 in Table 1; Chatterjee and Rudra 1996). More anteriorly, the floor of the braincase is pierced by the foramina for the abducens nerve ( VI). The surface of the basioccipital below the occipital condyle and between the basal tubera is continuous and smooth in MCNA 7439, and exhibits a small ridge joining the basal tubera in MCNA 13913 ( Figs. 5A View Fig , 7C View Fig ). This surface does not have any median subcondylar foramen, recess, depression or pit. The basioccipital forms the basal tubera, which are rounded, wide and robust and posterolaterally oriented. A foramen pierces the distal surface of each basal tuber, a feature unknown in other titanosaurian basicrania ( Figs. 2A View Fig , 3, 4A, C View Fig , 5A View Fig , 6 View Fig , 7B, C View Fig , 8B). Anterior to the suture between the basioccipital and basisphenoid, a rugose zone extends in lateral view, probably for muscle attachment ( Curry Rogers and Forster 2004).

In MCNA 13913, the lagena of the osseous inner ear is exposed by fracture, and can be observed in right lateral view ( Figs. 6 View Fig , 8B), surrounded by a rugose surface to receive the prootic. Posterior to it, the metotic fissure runs ventrally to the basal tubera.

The basisphenoid forms the basipterygoid processes, but in both specimens of Lirainosaurus these processes are broken at their base. Their cross−section is slightly triangular and flattened anteroposteriorly. The foramina for the internal carotid arteries are near the base of the basipterygoid processes, at the ventral end of the crista prootica. Each channel runs inside the basisphenoid to open in the floor of the pituitary fossa.

Parasphenoid.—The parasphenoid is fused with the basisphenoid. It forms the anterior wall of the pituitary fossa. In both specimens of Lirainosaurus only the base of the parasphenoid rostrum is preserved, and the pituitary fossa is open dorsally. In anterior view, the dorsum sellae forms the posterior wall of the pituitary fossa, and separates the floor of the braincase and the pituitary fossa ( Paulina−Carabajal and Salgado 2007). At both sides of the pituitary fossa the openings for the abducens nerve ( VI) can be found ( Figs. 2B View Fig , 4B View Fig , 5B View Fig , 8A). Their passages run inside the basisphenoid, without piercing the pituitary fossa, and exit in the floor of the braincase. In MCNA 13913 two small foramina appear anterior to the opening for the abducens nerve ( VI), probably for cranial vascularization ( Fig. 8B).

doi:10.4202/app.2010.0043