Historical Biology 115 section of these regions would be elliptical and proportionally flat. The symphysis is mostly horizontal, but the anterior section shows a small dorsal inclination anteriorly. The right mandibular ramus is mostly preserved, showing a well developed coronoid process. The tooth-bearing portions are highly divergent (over 45 degreees) and contain four teeth. At the middle section, where the mandibular fenestra is partially preserved, the right ramus is only slightly divergent from the sagittal plane, and both rami would be almost parallel. The mandibular fenestra is only partially preserved on the right ramus, and likely was elliptical or elongated. The dentary supports most teeth, but the splenial apparently forms the medial edges of the posteriormost alveoli for teeth pairs 6– 9. The splenials meet on the posterior section of the symphysis and this contact is slightly exposed in ventral view, with no projection over the suture of the dentaries. Only the anterior section of the right angular was preserved. It barely projects over the dentary beyond the maxillary fenestra and is mostly exposed on the lateral part of the mandible. The right surangular is also preserved only on its anterior portion (Figure 11), and is divided into internal and external rami. Both rami are subequal in size and well developed. The external ramus seems to be bilobate, projecting over the dentary and beyond the anterior border of the mandibular fenestra. The internal ramus is single, projecting over the splenial, but not beyond the anterior border of the mandibulary fenestra. No part of the articular is preserved.
Figure 10. Quadrate and basicranium from MPMA 15-001/90 Sphagesaurus montealtensis sp. nov., holotype, seen in lateroventral view. Note the pneumatic structure of the quadrate and its triangular cross-section.
Alveolar margin and dentition The alveolar margin (premaxillae and maxillae) is evidently differentiated, with lateroventral inclination, due to the prominent maxillary longitudinal ridge. The mandibular alveolar margin is inclined laterodorsally. Only a few neurovascular foramina are present over the alveolar margin (premaxillae, maxillae and mandible). A small foramen is preserved at the premaxillary – maxillary suture on the right side of the specimen, while the corresponding area on the left side is not preserved. Five maxillary foramina are easily identifiable on the right maxilla, only four of them preserved on the left element. The first three pairs correspond to the first two pairs of maxillary teeth. The fourth foramen (only preserved on the right maxilla) is located above the fourth maxillary tooth and the fifth pair, over the fifth tooth. Between the third and fourth foramina there is a considerable distance where there is no evidence of other neurovascular structure. This gap could be interpreted as an artefact of preservation, but the same pattern can be seen also on the left side (Figure 12). There seems to be at least five pairs of neurovascular foramina on the mandible, though preservation hinders a definite identification. On the left side, a small foramen is located below the mandibular teeth pairs 2 – 3, but the structure is absent from the right side. Below the third mandibulary teeth, there is an elongated damaged area on each side of the specimen, which probably correspond to two foramina on each side. Below the fourth mandibular tooth there are other two small foramina, reasonably preserved on both sides of the specimen. A single additional foramen may be present below the fifth tooth, and also below the sixth. The presence of the last two pairs is uncertain though, due to preservation problems. Furthermore, foramina may have occurred anteriorly, below the first mandibulary tooth, but the area is not preserved. In all cases, neurovascular foramina are positioned distant to the alveoli. The dentition bears several characters previously used to diagnose Sphagesaurus, and some distinctive characters for S. montealtensis. Only one pair of hypertrophied caniniform teeth is present on the premaxilla. Just the right premaxillary caniniform is present, and its crown was mostly eroded. Seven pairs of teeth were present on the maxilla (Figure 13), and the series shows an arched disposition in ventral view. The maxillary teeth increase in size from pairs 1–3, and then decrease to the end of the series. Most of them are well preserved, apart from the seventh from the right series. The first pair of maxillary teeth in MPMA 15-001/90 is very small, but instead of creating a functional diastema, the corresponding pair of dentary teeth is well developed and occludes with this first pair of maxillary ones (Figure 13).