Sanajeh indicus WILSON, MOHABEY, PETERS & HEAD 2010
Creators: name: Zaher, Hussam
name: Mohabey, Dhananjay M
name: Grazziotin, Felipe G
name: Wilson Mantilla, Jeffrey A
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Reptilia
Squamata
Madtsoiidae
Sanajeh
Sanajeh indicus

description: SANAJEH INDICUS WILSON, MOHABEY, PETERS & HEAD, 2010
Hypodigm: Here, we restrict the holotype of Sanajeh indicus to GSI/GC/2901, GSI/GC/2902, GSI/ GC/2903 and GSI/GC/2906. We exclude from the holotype specimens GSI/GC/2904 and GSI/GC/2905, which were inadvertently included in the holotype (Wilson et al., 2010) but pertain to a titanosaur hatchling and egg, respectively. We refer to Sanajeh indicus (Figs 1-15) a second specimen (GSI/GC/DD4) from the Dholi Dungri locality that includes the posterior portion of the skull, comprising a partial braincase and skull roof (parietal, basioccipital, otooccipital, prootic, left postorbital, left squamosal, left supratemporal and left stapedial footplate), a partial right mandible (complete splenial, fragmentary dentary and compound bone) and right pterygoid. Found in close association with this partial skull was the posterior portion of the left compound bone, a right palatine, several precloacal vertebrae and ribs.
Referral of GSI / GC / DD4 to Sanajeh indicus: Specimen GSI / GC / DD4 was found 51 m from the holotype at Dholi Dungri, in close association with elements of a turtle shell pertaining to a young individual and a single, small (1.5 cm × 2.5 cm) crocodylomorph osteoderm. The elements we attribute to specimen GSI / GC / DD4 (i.e. skull fragment, right palatine, partial compound bone and two articulated partial vertebral series) were found within a radius of <39 cm. The palatine was found 14.3 cm from the skull fragment, and the shorter and longer articulated vertebral series were found 8.4 and 38.4 cm from the skull fragment, respectively. The proximity, size and non-duplication of these elements are all consistent with the hypothesis that they pertain to a single individual, which is corroborated further by the near-perfect articulation of the right palatine and pterygoid (Fig. 14). Referral of GSI / GC / DD4 to Sanajeh indicus is based on shared morphological similarities present in numerous overlapping cranial and postcranial elements, including the parietal, prootic, otooccipital, basioccipital, palatine, stapedial footplate, mandible, precloacal vertebrae and ribs, several of which are diagnostic (see ‘Emended diagnosis’ below).
The holotypic skull (GSI/GC/2903) includes a partial right palatine comprising a fragment of the lateral edge of the dentigerous process and an incomplete maxillary process, which is pierced by the foramen for the subocular ramus of the trigeminal nerve posteriorly. The referred specimen (GSI/GC/DD4) includes a nearly complete right palatine that preserves its four main processes and nine teeth. The holotypic and referred palatines are slightly different in size, but they bear a close resemblance to one another morphologically. Uniquely, they share an especially high posterior wall of the maxillary process of the palatine, and both have a dentigerous process. The holotypic and referred specimens also both preserve the basioccipital, which bears a wide and dorsally concave posterolateral process. The footplate of the stapes is also preserved in both specimens, which share the same general outline in lateral view. Precloacal vertebrae preserved with the holotypic and referred specimens are similar in size and possess small parazygantral foramina and posterodorsally angled neural spines.
Emended diagnosis: Wilson et al. (2010) listed four features that together distinguish Sanajeh indicus from other snakes: (1) juxtastapedial recess rectangular; (2) basioccipital posterolateral process wide and dorsally concave; (3) precloacal vertebrae with small parazygantral foramina; and (4) precloacal vertebrae with thin, posterodorsally angled neural spines.
Wilson et al. (2010) also listed a ‘broad and squaredoff supratemporal’, but we have reinterpreted this bone to be the stapedial footplate (see below in Additional description of Sanajeh indicus). Further preparation of the holotypic specimen (GSI/ GC/2903) and the referred individual (GSI/GC/DD4) suggests the following additional diagnostic features of Sanajeh indicus: (5) premaxillary teeth positioned laterally, on the maxillary processes (as in pythons); (6) maxilla with a high ascending process; (7) maxilla with palatine process expanded medially to form a large, triangular shelf; (8) palatine with an anteriorly elongated dentigerous process; (9) pterygoid and palatine bones are toothed; (10) palatine and pterygoid with tongue-and-groove articulation; (11) palatine maxillary process with especially high posterior wall; (12) supratemporal elongated and tightly appressed to the braincase; (13) supratemporal lacking a freeending process; (14) stapedial footplate enlarged; (15) stapes elongate and posteriorly curved; (16) prootic with elongate posterior process; and (17) ossified upper temporal bar formed by postorbital and squamosal.
ADDITIONAL DESCRIPTION OF SANAJEH INDICUS
In the description of the preserved bones in Sanajeh presented below, we combine the anatomical information present in the holotypic and referred specimens. There is considerable anatomical overlap between the two specimens, which allows us to determine that they are conspecific, but even among these overlapping elements there are differences in preservation and completeness that require us to rely on both in the description. Overlapping elements include the otooccipital, supraoccipital, prootic, basioccipital, parietal, palatine, stapes, dentary, splenial, angular, coronoid and compound bone. In addition to these, there are also non-overlapping elements that are preserved in only one of the two specimens. The holotype is the only Sanajeh specimen that preserves a parabasisphenoid, septomaxilla, premaxilla, maxilla, frontal and postfrontal, whereas the referred specimen is the only one that preserves a postorbital, squamosal, supratemporal and pterygoid.
Reinterpretation of preƲiously described elements of the holotype
We have reinterpreted the identifications of three cranial elements preserved with the holotype of Sanajeh indicus based on additional preparation of that specimen (Figs 1, 2). The new interpretations and rationale for each is briefly noted below. Scorings in the character–taxon matrix reflect these new interpretations.
1. ‘Supratemporal’:weinterprettheelementidentified by Wilson et al. (2010) as the supratemporal to be the stapedial footplate, based on its shape and on the presence of a broken region near its centre that represents the base of the columella.
2. ‘Palatine’: the element identified by Wilson et al. (2010) as the palatine is here interpreted to be the septomaxilla (Figs 1, 2), based on its connections with other bones and comparisons with the palatine preserved with the second specimen, which bears teeth and can be identified definitively as that element (Figs 7, 14).
3. ‘Left mandible’: further preparation has revealed that the element identified as an anterior fragment of the left mandible in the description by Wilson et al. (2010) is the premaxilla (Figs 1–3). Its alveolar margin is almost completely preserved, and its preserved dentition matches those in the premaxillae of other snakes (Fig. 3B).
Braincases of the holotypic and referred specimens
The holotypic specimen of Sanajeh preserves a partial braincase that is best preserved on its posteroventral and right ventrolateral sides. The left posterior and dorsal portions of the holotypic braincase are not well preserved. The referred braincase is much better preserved in these respects and provides more detailed information on the anatomy of the prootic, parietal, supratemporal and otooccipital regions (Figs 8–11, 15).
The holotypic specimen retains a partial parietal, left and right prootics, right stapes, parabasisphenoid, basioccipital and fragmentary left and right otooccipitals. Except for the basioccipital, which has a well-preserved outer surface on its right side, all remaining bones show different levels of abrasion of their surface and losses of significant parts. The holotypic skull does not preserve the posteriorly directed paroccipital processes of the otoocipital or their dorsolaterally adpressed supratemporals. The referred specimen, in contrast, retains a partial parietal, left prootic, left otooccipital, left squamosal, complete left stapes, supratemporal and postorbital.
The posterior extension of the prootic that roofs the otic capsule is present in the right side of the holotype, but it is badly weathered and difficult to interpret. However, the paroccipital process of the otooccipital, supratemporal and posterior part of the prootic are nicely preserved on the left side of the referred specimen (Figs 8–11). The posterior half of the left prootic and left stapes are not preserved in the holotype, revealing the inner surface of the otic capsule at the level of the lateral semicircular canal. The ventrolaterally projected process of the otooccipital that forms the crista tuberalis is almost completely preserved on the left side of the holotype and of the referred specimen. The basioccipital is mostly preserved on the right side of the holotype and only preserved in part on the left side of the referred specimen.
Snout complex
The snout complex in snakes includes the premaxilla,nasal, septomaxilla and vomer. Neither specimen preserves the nasal or vomer, and the premaxilla and septomaxilla are preserved only in the holotypic skull of Sanajeh indicus.
Premaxilla: Further preparation of the holotype revealed a partially complete premaxilla that was identified previously by Wilson et al. (2010) as the anterior tip of the left mandible (Fig. 3A, B). The premaxilla is preserved in near-life position, near the end (as preserved) of the right maxilla and perpendicular to its long axis. Much of the alveolar region of the premaxilla remains embedded in matrix, but the remainder is completely exposed, including two teeth on the left maxillary process. The premaxillary teeth possess a smooth surface, with no sign of either carinae or a fluted base. The nasal and vomerine processes of the premaxilla are not preserved, and the dorsal portion of the left maxillary ramus is damaged, revealing the inner surface of the premaxillary channels.
The premaxilla is a transversely oriented structure formed by two lobe-like maxillary processes that are separated, in part, ventrally by a median embayment. Consequenntly, the anteroventral margin of the premaxilla has an undulating surface. There is no indication that the lateral aspect of the premaxilla was sutured to the maxillae. Instead, its rounded, smooth lateral margins, as best preserved on the left side, indicate a loose contact between the premaxilla and maxilla. However, the degree of mobility between these two bones is difficult to establish. Breakage has exposed premaxillary channels on each side of the nasal process, but their posterior openings cannot be defined.
Two premaxillary teeth are exposed in posterior (lingual) view (Fig. 3B). They are recurved, needlelike and have a smooth basal surface. The two teeth are positioned at the lateral extreme of the maxillary process and are tightly appressed, diverging only slightly apically owing to the narrowing of tooth diameter. Both teeth seem to be ankylosed to the rim of shallow thecae, with only limited deposition of bone of attachment at their base. Resorption pits are not visible.
Septomaxilla: A portion of the right septomaxilla is preserved in the holotypic skull of Sanajeh indicus nearly in the natural position, located posterolateral to the right maxillary process of the premaxilla and medial to the ascending process of the maxilla (Figs 1, 2). The body of the septomaxilla is mostly missing, but the lateral flange (conchal process; sensu Cundall & Irish, 2008) is almost completely preserved. It is horizontally directed, but more laterally the flange curves abruptly to form a vertically directed lamina that bears a long, partly preserved posterior spine. Its anterior edge is broken; therefore, we cannot ascertain whether it possessed an anteriorly directed spine.
Palatomaxillary complex
Four bones are associated with the palatomaxillary complex in snakes, namely the maxilla, palatine, pterygoid and ectopterygoid. The ectopterygoid is not preserved in either of the two partial skulls attributed to Sanajeh indicus.
Maxilla: The holotype of Sanajeh indicus preserves a partial right maxilla in contact with palatal elements (septomaxilla, palatine) and an element adjacent to the posterior end of the maxilla that we identify as the postfrontal (Figs 1, 2). The body of the maxilla is preserved in part, and it is not clear how much of its anterior and posterior ends are missing. Much of the middle portion of the maxilla is not preserved, including the orbital margin and the ascending process. Part of the alveolar margin of the maxilla is still embedded in matrix, but the remainder has been prepared completely. Six maxillary teeth are exposed; four are visible in internal (lingual) view, and two are exposed in external (labial) view (Fig. 3C). The preserved teeth span the preserved length of the maxilla, and the posteriormost tooth is on a fragment of the maxilla that has been dislodged from the main body. The maxillary teeth are circular in cross-section at their base, as indicated by the last maxillary tooth. The teeth are tall, curved and cylindrical, with a pointed distal crown and an expanded base. Their curvature indicates that they are not aligned with the maxillary axis, but have their tips directed more medially. The outer layer of enamel is eroded in all observed teeth, preventing any detailed analysis of the surface ornamentation. Internally, the teeth lack plicidentine, as shown by the posteriormost tooth on the maxilla, which is broken transversely near its proximal end (Figs 3C, 15C). The tooth attachment is clearly pleurodont, with the labial part of the crown ankylosed to a high, obliquely sloping pleura (Fig. 15C). The lingual side of the tooth base is ankylosed to a poorly developed basal plate. The longest preserved tooth is ~ 0.6 cm.
The maxilla is a low, anteroposteriorly elongate element measuring ~ 7 cm. It is slightly deeper dorsoventrally in its middle third, which is poorly preserved. In lateral view, the anterior fragment of maxilla includes an elevated ascending process that meets the prefrontal and sets off a dorsally concave and medially curved anterior process (Fig. 3C). Although the ascending process is poorly preserved, its anterior and posterior ends can be recognized easily by the sharp break in slope that they make from the body of the maxilla. Additionally, the presence of the canal for the suborbital branch of the maxillary ramus of the trigeminal nerve (cranial nerve V 2) identifies definitively the position of the contact with the palatine, which in squamates provides a reliable indicator of the anterior border of the orbit. The ascending process in Sanajeh is long, extending for approximately half the estimated length of the maxilla (Fig. 3C). In this regard, it is distinct from Dinilysia and more advanced snakes, such as Wonambi, which retain a well-defined but short ascending process. Immediately posterior to the ascending process is the orbital margin, which in Sanajeh is short. The posterior portion of the maxilla is not preserved completely, but based on comparisons with Dinilysia, which it otherwise resembles, in addition to comparisons with its own dentary, the maxilla of Sanajeh would not have extended far beyond the position of the isolated fragment preserved in the block (Fig. 1).
Palatine: Both the holotypic and referred specimens of Sanajeh indicus preserve the right palatine, which facilitates comparison of their relative size and shape (Figs 1, 2, 7). The palatine in the holotype is preserved only in part, found a near-life position (based on the relative positions of the openings for the suborbital branch of the maxillary nerve). The preserved part of the right palatine of the holotype corresponds to part of the suborbital palatine foramen, including its ventral and lateral walls and part of the dorsal wall, in addition to a small portion of the dentigerous process corresponding to its lateral margin (Figs 1, 2). The fragmented parts of the right palatine of the holotype are almost identical to the same structures present in the much better-preserved palatine of the referred specimen, allowing a direct comparison. The palatine of the referred specimen, in contrast, is nearly complete (Figs 7, 14). It was found nearly 17 cm from the posterior portion of the skull, which includes the braincase, skull roof, right pterygoid and partial right lower jaw. Segmentation of the right palatine and pterygoid of the referred specimen allowed for their digital re-articulation and identified surfaces of mutual contact (Fig. 14). The referred right palatine is well preserved and lacks only part of the anteromedial portion of the choanal process. In the description below, we rely on the referred specimen for most of the salient anatomical features; we refer to the holotypic specimen for its relationship to the maxilla.
The palatine is an anteroposteriorly elongate element (~ 2.4 cm) that contacts the maxilla laterally, the pterygoid posteriorly and the vomer anteromedially. In dorsal view, three processes of the palatine are visible: a broad, anterolaterally directed maxillary process, a posteriorly directed pterygoid process and a partly preserved choanal process (Fig. 14).
Like Dinilysia, Sanajeh lacks a typical dentigerous process of the palatine, but unlike the former, it has a conspicuous row of palatine teeth that reaches the anterolateral tip of the maxillary process, running along the lateral margin of the pterygoid process and anteromedial margin of the maxillary process (Fig. 14A, C, E). In contrast, Dinilysia retains a row of teeth on the palatine that is restricted to the lateral margin of the pterygoid process and, like Lanthanotus Steindachner, 1878 (Fig. 14B, D, F), does not extend to the maxillary process anteriorly.
The palatine bears a total of 13 complete alveoli, where at least eight small (~ 0.2 cm), recurved teeth are still preserved. The three posteriormost preserved teeth are positioned lateral to the pterygoid articulation facet on the ventral surface of the palatine. Palatine and pterygoid teeth are the same size and collinear.
The choanal process of the palatine is preserved only in part, but it is notably thick dorsoventrally (0.3 cm), especially in comparison to the more laminar pterygoid process (Fig. 14). In this way, the palatine of Sanajeh resembles that of Dinilysia and probably retained a broad contact with the vomer.
The maxillary process of the palatine is long anteroposteriorly (~ 1.5 cm) and broad transversely (~1.0 cm). It is longer than the incompletely preserved choanal, which, when complete, would have been likely to exceed it in length (Fig. 14). The posterior portion of the palatine is dorsoventrally high and traversed by the suborbital foramen, which enters its posterior wall and exits posterolaterally near its posterior contact with the maxilla (Fig. 14E). The posterior entrance of the foramen is twice as broad transversely as it is tall dorsoventrally (0.4 cm × 0.2 cm). The holotypic palatine matches the referred specimen, but it is incompletely preserved. The suborbital foramen is open medially in the holotype, owing to damage to its dorsal wall. The palatine overlaps the maxilla dorsally in a broad contact (Figs 1, 2). The pterygoid process of the palatine is a broad flange of bone that bears the articular surface for the pterygoid on its ventral surface. The main part of the pterygoid articulation in Sanajeh is planar, rectangular (0.4 cm × 0.5 cm) and almost horizontally oriented (Fig. 7B). Posterior and slightly lateral to this planar contact is a narrow, V-shaped slit that receives a corresponding projection from the pterygoid (Figs 8, 10, 14A). In this way, the condition in Sanajeh resembles that in Dinilysia and in non-ophidian lizards (Fig. 14B), in which the palatine broadly overlaps the pterygoid. It differs from that of Wonambi, Yurlunggur, pachyophiids and more advanced extant snakes, which have a U-shaped groove on the palatine that indicates a vertically oriented, complex tongueand-groove suture with the pterygoid. Sanajeh also differs from extant snakes in the position of the palatopterygoid tooth row with respect to the axis of the palatine process of the pterygoid. In extant snakes, the palatal tooth row is aligned with this axis and positioned in the middle of the palatine process, but in Sanajeh the tooth row is shifted more laterally (Fig. 14C).
Pterygoid: The right pterygoid is preserved only in the referred specimen of Sanajeh. It is nearly complete, lacking only the distal portion of its quadrate ramus (Figs 10, 14). The pterygoid has been displaced anteriorly <1 cm and rotated medially relative to its original position. It remains partly embedded in matrix, but most of the crucial details of its anatomy can be observed directly on the specimen (Figs 8–11) and on the digitally segmented CT scan images (Fig. 14).
The pterygoid is an elongate element (~ 5 cm) that has an anteriorly directed palatine ramus, a laterally directed ectopterygoid articulation, a medially directed basipterygoid articulation and a posteriorly directed quadrate ramus. The pterygoid is broadest near mid-length (1.1 cm), where the basipterygoid and ectopterygoid articulations extend medially and laterally. Posterior to this point extends the quadrate ramus, which has the form of a flattened r o d (0.4 c m × 0. 2 c m). T h e q u a d r a t e r a m u s i s incomplete, and it is unclear exactly how far it would have projected from its preserved end. The palatine ramus bears a broad articular surface for the palatine at its distal end (Fig. 8). This articular surface faces dorsally and is 0.7 cm long and nearly as broad. There is a small, elevated ridge positioned lateral to the main articular facet that fits into a corresponding notch in the palatine (Fig. 14A). The anteriormost pterygoid tooth ends slightly posterolateral to the broad articular facet, with the pterygoid tooth row lining up with the palatine tooth row (Fig. 14C). The pterygoid tooth row of Sanajeh follows the medially concave curvature of the bone, as in Lanthanotus (Fig. 13D) and Dinilysia (Estes et al., 1970).
There are 11 teeth preserved and evidence of four additional alveoli, indicating that there were 15 teeth in the pterygoid. The teeth are small (0.3 cm long), conical and recurved.
Circumorbital complex
Based on the arguments and observations presented in the Discussion section below, we suggest the following primary homology statements for the dorsal, posterodorsal and posteroventral orbital elements in fossil and extant snakes: (1) the ‘supraorbital’ is the neomorphic dorsal orbital element known to occur in Calabaria Gray, 1858, Loxocemus Cope, 1861 and pythonids; (2) the postfrontal is the posterodorsal (pachyophiids, Dinilysia, Najash and Yurlunggur) or posterior (extant snakes) orbital element intimately associated with the skull roof at the frontoparietal suture; (3) the jugal is the posteroventral element known to occur in the fossil pachyophiids, Dinilysia, Najash and Yurlunggur, inferred to be present in Sanajeh (see postorbital description), but considered to be absent in extant alethinophidian snakes; and (4) the postorbital bone is currently known only in Sanajeh among extinct and extant snakes.
Thus, up to six bones can be associated with the orbital margin in snakes: prefrontal, postfrontal, supraorbital, jugal, postorbital and maxilla. The prefrontal, postfrontal and maxilla are present in both extant and fossil snakes. The supraorbital is known to occur only in some extant snakes, whereas the jugal occurs only in the known fossil pachyophiids, Dinilysia, Najash and Yurlunggur. Below, we describe the bones bordering the upper part of the orbit as preserved in Sanajeh, which include the postfrontal and postorbital (see above for description of the maxilla).
Postfrontal: The holotypic skull preserves a nearly complete right postfrontal (Fig. 4). The postfrontal was not found in its natural articulation with other skull roof bones (i.e. frontal and parietal). It was found in a vertical orientation appressed against the lateral surface of the maxilla, at the level of the posterior border of its palatine process (Figs 1, 2). There is a small, rod-like element adhered to its dorsal surface (Fig. 4).
The postfrontal is a relatively small, subtriangular element with an anteromedially directed apex and a posteriorly directed base. The medial edge, which would have contacted the frontal, is straight, and the lateral edge, which would have bordered the orbit, is convex. The posteriorly directed base is slightly angled and provides the articular surface for the parietal. The postfrontal is slightly longer anteroposteriorly than it is broad at its base (1.1 cm × 0.9 cm) and bears a slightly dished dorsal surface; that is, it is slightly concave dorsally and convex ventrally. This dished surface contains the small, rod-like element, which we interpret to be a fragment of the right postorbital (see below in Postorbital and squamosal).
In dorsal view, the orbital margin of the postfrontal is convex laterally and measures 1.1 cm. Its ventral surface tapers toward its lateral edge, ending in a paper-thin, textured orbital margin. The postfrontal is anteroposteriorly short (1.1 cm), implying that the orbit was similarly abbreviate. This assessment is consistent with the short (0.6 cm) orbital margin identified on the maxilla.
The frontal articulation, which has an approximately anteroposterior orientation, is straight and occupies much of the length of the postfrontal. This articulation forms an angle of slightly> 90° with the parietal articulation, which itself consists of two segments that meet at an oblique angle. Near the point at which the frontal and parietal articular surfaces converge is a distinctive C-shaped articular surface extending below the plane of these other articulations. This C-shaped facet received a small process of the parietal, which can be seen in the well-preserved left parietal on the referred skull. There does not appear to be a flange that underlapped the parietal and frontal, as there is in Yurlunggur.
The frontal articulation and orbital margin meet anteromedially to form the apex of the postfrontal. There is no sign of a more transversely oriented articular surface anteriorly, which suggests that the prefrontal did not contact the postfrontal, nor is there a ventrally directed process that would have contacted the jugal.
Postorbital and squamosal: The referred specimen of Sanajeh possesses a complete upper temporal bar formed by the postorbital and squamosal bones, which are nearly complete and preserved in what appears to be close to their natural position (Figs 8–11, 13, 15). We describe these two bones together. The postorbital appears to be complete, or nearly so, but the squamosal is broken posteriorly and might have been slightly longer. The holotypic skull preserves only an eroded fragment of the left half of the skull roof, which bears no evidence of temporal arcade bones. Nevertheless, the concave dorsal surface of the postfrontal is overlain by a small rod-shaped element that might represent a fragment of the anterior postorbital (Fig. 4). This fragment is appropriate in size and shape and is in the position expected for the postorbital.
The two upper temporal arch elements are unequal in size and different in shape. The postorbital is shorter and more strap-like than is the squamosal, which is longer and more rod-like. The postorbital is 2.2 cm long, 0.3 cm tall and <0.1 cm transversely; the squamosal is 3.2 cm long and 0.2 cm tall and wide. They overlap one another by ~ 0.8 cm as preserved. The postorbital and squamosal are not tightly articulated,butthereisevidencefortheirmutualarticulation based on facets on both elements that are best viewed in 3D reconstructions based on micro-CT scan images (Fig. 13). The two bones retain their surface of contact adjacent to each other, showing that they are not individually displaced anteriorly or posteriorly from their natural positions. The CT scan sections in the horizontal and transversal planes also help to clarify the very distinct nature of the postorbital and squamosal elements (Fig. 15A–C). The curvature of the two bones individually and in contact follows that of the temporal region, which supports our interpretation of their identity. The anterior end of the postorbital slightly expands laterally to form a blunt, dorsoventrally tapering projection that is likely to have been clasped dorsally by the postfrontal and ventrally by the jugal (not preserved), as suggested by the presence of flat areas of contact on both dorsal and ventral surfaces (Fig. 13A). There is no evidence of a direct bony connection between the posterior end of the squamosal, which is not preserved, and the paroccipital region of the skull. Instead, the squamosal was probably seated loosely near the dorsal head of the quadrate, held in place by soft tissue connections in the shallow gutter formed on the dorsal surface of the suspensorium along the parietal–otooccipital contact. Extant anilioids and ‘scolecophidians’ retain an upper temporal tendon that seems to represent the remnant of the upper temporal bar of Sanajeh, in both cases receiving the more lateral adductor mandibulae muscle bundle (Rieppel, 1980; Zaher, 1994a).
Braincase and suspensorium
We describe the braincase and suspensorium together below because they form a functional complex in snakes.
Supratemporal: A complete left supratemporal is preserved in the referred skull (Figs 8–11, 15); no trace of the supratemporal is preserved with the holotypic skull. Although complete, the supratemporal in the referred skull is exposed mostly in lateral view.
The supratemporal is an anteroposteriorly elongate element (2.8 cm) that contacts the prootic ventrally, the parietal dorsally and the otooccipital medially (Figs 8–11, 15). It projects posteriorly and slightly laterally and, together with the parietal, prootic and otooccipital, it forms an elongate suspensorial process. The anterior half of the supratemporal is sandwiched between the prootic and parietal (Figs 8–11, 15). It is convex dorsally and flat ventrally, tapering toward a pointed anterior tip. Immediately posterior to the prootic, the supratemporal expands to twice its dorsoventral height to cover almost completely the entire lateral surface of the otooccipital. At that level, the contact between the prootic and the supratemporal is interrupted by a lateral expansion of the otooccipital, which is sandwiched between the former two bones on the ventrolateral surface of the suspensorium (Figs 10, 15A). Posterior to this point, the supratemporal gradually expands dorsally before tapering toward its posterior end. As a result, the posterior half of the supratemporal also has a convex dorsal surface. The supratemporal has a vertically oriented contact with the otooccipital posteriorly to form the distal part of the suspensorial process, extending ~ 1 mm beyond it posteriorly. The posterior portion of the supratemporal is slightly convex laterally and, together with the portion of the otooccipital exposed laterally on the suspensorial process, it would have received the quadrate head. In Sanajeh, a lateral contact between the prootic and otooccipital is retained below the supratemporal, with the supratemporal expanding posteriorly and ventrally to cover most of the otooccipital laterally (Fig. 10). The posterior end of the squamosal, freed from its contact with the dorsal head of the quadrate by the expansion of the supratemporal, sits on top of the suspensorium and was probably attached loosely through connective tissues to the shallow gutter formed along the parietal–otooccipital contact (Fig. 8).
Parietal: Remnants of the parietal are preserved on both holotypic and referred skulls. A fragment of the left side of the parietal is present in the holotypic skull, but it is poorly preserved. The parietal of the referred specimen is not completely preserved, but the left side is nearly complete, hence we can reconstruct its shape with confidence (Figs 8–11).
The parietal is a dorsally arched element that is much longer than it is broad (4.9 cm × 2.0 cm), owing to its elongate supratemporal processes. The parietal contacts the frontal anteriorly, the postfrontal anterolaterally, the parabasisphenoid ventrally and the supratemporal, prootic and supraoccipital posterolaterally. The parietal has a conspicuous median sagittal crest that is elevated ~ 2 mm from its surface (Fig. 8). The anterior face of the parietal bears a vertically oriented articular surface that would have contacted both the frontal and postfrontal bones (Fig. 11). This vertical surface is nearly flat except for a small median depression that received a process of the frontal; paramedian depressions that received the postfrontal and a small lip immediately lateral to this would have fitted into a groove in the postfrontal. The total height of this articular surface is 0.6 cm.
The parietal contacts the parabasisphenoid and prootic anterolaterally. The parabasisphenoid articulation can be observed only in the holotypic skull, in which it is concave ventrally and smooth. The parietal and prootic contact each other on the anterior margin of the opening for cranial nerve V and stay in contact posteriorly until they are separated by the supratemporal bone (Fig. 10). The prootic forms most of the margin of the opening for cranial nerve V, with only a small portion formed by the parietal.
The parietal has an elongate supratemporal process that extends posteriorly well beyond the foramen magnum, tapering to a pointed tip positioned at the level of the posterior extreme of the prootic (Fig. 8). The length of the supratemporal processes of the parietal is unique among snakes. In this region, the parietal is sandwiched between the supratemporal laterally and the otooccipital ventrally and medially (Fig. 15D). Along the length of its contact with each of these elements, the parietal is raised to form a gentle ridge. Between these two posteriorly converging ridges is a small sulcus, which we hypothesize received the posterior end of the squamosal (Fig. 8). Note that the squamosal is displaced only a short distance (3 mm) from this sulcus.
Prootic: The prootic is preserved in both holotypic and referred specimens. The holotypic left and right prootic are eroded; the right preserves only its posteromedial surface, which received the stapedial footplate (see below), and the left preserves only its most interior wall and lacks its superficial structures. The referred braincase preserves a fragment of the right prootic and has a nearly complete, well-preserved left prootic that lacks only part of its ventral edge, which originally contacted the parabasisphenoid (Figs 8–10).
The left prootic is roughly tetraradiate in lateral view, with two processes extending anteriorly to form the opening for the single trigeminal foramen of cranial nerve V and two processes extending posteriorly around the fenestra ovalis. The surfaces of the two anterior processes are clearly abraded, having lost their original shape. However, the longer and broader dorsal anterior (‘alar’) process retains its contact with the parietal through a broadly rounded, dorsoventrally expanded suture that overlaps the descending flange of the parietal (Fig. 10), much like in Najash rionegrina (Zaher et al., 2009). The highly abraded ventral anterior process is shorter and narrower, abutting on a small projected surface of the parietal that might also result from the process of abrasion of this bone. The two anterior processes nearly contact one another on the anterior margin of the opening for cranial nerve V, separated by only a small margin by the parietal.
The prootic expands posteriorly to embrace the fenestra ovalis, forming its anterior, dorsal and ventral margins. The posterior extension of the prootic that surrounds the fenestra ovalis ventrally is relatively short (~1.0 cm), whereas the posterodorsal process (Oelrich, 1956) surrounding it dorsally is much longer (1.7 cm) and robust (Fig. 10). The posteroventral extension of the prootic that articulates with the basioccipital and forms the part of the lower margin of the fenestra ovalis is abraded and has lost its surface. The surface within which opens the foramen for the facial nerve, posterior to the trigeminal foramen, is also damaged, and its opening occurs in the abraded surface of the prootic. A smooth surface contact and posterior opening of the Vidian canal are not visible either, because this region of the skull was originally exposed on the surface of the block. The posterodorsal process of the prootic and its contacts are mostly intact, extending well beyond the fenestra ovalis and angling slightly dorsal direction toward its sharply blunted end, which abuts the supratemporal and receives a small part of the otooccipital (Fig 10). Dorsal and anterior to the stapes, the prootic forms a well-developed crista prootica that overhangs the edge of the stapedial footplate, projecting lateral to the latter (Fig. 10).
Otooccipital: The otooccipitals are fragmentary in the holotype, and only part of the left element is preserved in the referred specimen. Nevertheless, this bone reveals an unexpected morphology that provides new insight into the evolution of the suspensorium in snakes. The otooccipital contacts the parietal, supratemporal, prootic and quadrate. In life, it would also have contacted the squamosal, which is now slightly displaced from its original position and lacks its posterior tip, and the supraoccipital, which is eroded in the referred specimen.
The otooccipital is an elongate element that projects posteriorly and slightly laterally, forming an expanded, posteriorly concave paroccipital process that receives the prootic ventrolaterally and the supratemporal dorsolaterally (Figs 8–10, 15). The left otooccipital of the referred specimen is visible laterally, sandwiched by the prootic and supratemporal (Figs 10, 15A). This small surface of the otooccipital must have contacted the quadrate in life (as confirmed by articular surfaces preserved in the region), retaining the condition present in lizards, in which the crista parotica receives the dorsal condyle of the quadrate (Bellairs & Kamal, 1981; McDowell, 2008). The left otooccipital of the referred specimen lacks the proximal portion, eroded along with the supraoccipital and its right counterpart surrounding the foramen magnum. Only the medial, inner braincase surface of the left otooccipital remains from that region of the bone, where the apertures for the vagus and glossopharyngeal nerves are visible.
Basioccipital: Only a small portion of the left part of the basioccipital is present in the referred specimen. It is completely worn on its external surface, but its medial surface is preserved (Fig. 9). The apertura medialis recessus scalae tympani is visible as an expanded, slightly U-shaped commissure pressed to the sutural contact with the ventral margin of the otooccipital.
Supraoccipital: The external surface of the supraoccipital is completely lost, and the bone is visible only in internal (medial) view (Fig. 8). It is triangular, tapering ventrally, with anterior and posterior margins contacting the prootic and otooccipital, respectively, and dorsally enclosing the posterior semicircular canal. Its concave internal surface bears a conspicuous foramen endolymphaticum.
Stapes: Stapes are preserved with both holotypic and referred specimens. In both cases, a large footplate is present. The footplate is preserved only in part in the holotypic skull (incorrectly identified as a supratemporal by Wilson et al., 2010; see above), but both the footplate and columella (stapedial shaft) are completely preserved in the referred specimen (Figs 9, 10). The referred stapes was found in near-perfect anatomical position within the fenestra ovalis; the holotypic stapes was displaced posteriorly from its original position (Zaher et al., 2017).
The footplate of the referred specimen is relatively large (1.1 cm × 0.8 cm) and elliptical in shape. The columella is nearly 2 cm long and extremely narrow at mid-length (~ 2 mm in diameter). The base of the columella is massive, and its shaft projects posterolaterally from the posterior half of the footplate, strongly curving immediately after it passes the posterior edge of the fenestra ovalis to take a posteriorly directed orientation. The columella expands to nearly twice the diameter of its shaft toward its distal end, terminating in a broad, tongueshaped process.
Mandible
The holotypic specimen of Sanajeh preserves elements of both mandibles.The left mandible is heavily damaged and has not been re-prepared since it was described originally. The right mandible is almost complete and, although damaged, it was removed for further preparation (Figs 5, 6). It is composed of the dentary, coronoid, angular and anterior portion of the compound bone. A small fragment of the splenial is present along the Meckelian groove in the midline of the medial surface of the dentary (Fig. 5B). The referred specimen also preserves a portion of both mandibles. The right mandible was found in close association with the braincase and skull roof (Figs 8–11), and a partial left mandible was found nearby (Fig. 12). All bones of the mandible are preserved to varying degrees, including the dentary, splenial, angular and compound bone. Two fragmentary teeth are preserved in the holotypic right dentary.
Dentary: A nearly complete dentary is preserved with the holotypic right mandible (Figs 5, 6), and the posteroventral process and compound bone articulation are preserved with the right mandible of the referred specimen (Figs 8–12). Together, these two specimens account for most, if not all, of the salient morphology of the dentary. Owing to coverage by matrix and adjacent bones, portions of the dentition and the medial aspect of the dentary could not be observed. The dentary is an elongate element (~ 64 mm long × 12 mm tall × 7 mm wide) that is gently bowed laterally and ventrally. The preserved curved anterior tip of the dentary bears an expanded, slightly curved, anteroposteriorly directed facet of contact for the opposite dentary (Fig. 6). The surface is rugose, suggesting a tight ligamentous contact conferring limited mobility between the dentaries. The Meckelian groove is open throughout the preserved length of the dentary, extending ventrally from the tip to the level of the anterior one-third of the bone (Figs 5B, 6). From that point, it attains a more ventromedial position and deepens dorsoventrally. The splenial articulates within the Meckelian groove, where a few fragments attributable to it are preserved. The contact for the compound bone is located on the posterolateral surface of the dentary, in an elongate fossa framed by its posterodorsal and posteroventral processes. The posterodorsal process is preserved in the holotype and the posteroventral process in the referred specimen. A contact with the coronoid was probably present on the medial aspect of the dentary immediately behind the tooth row, but corresponding portions of the dentary and coronoid are not preserved well enough in the two specimens to determine. A prominent mental foramen opens at approximately mid-height in the holotypic dentary at the level of the third alveolus (Fig. 5A). A total of 11 teeth are definitively present on the dentary, although one or more additional smaller alveoli might be present distal to the last preserved 11 th dentary tooth.
There are three nearly complete teeth and portions of several others preserved in the dentary of the holotype (Fig. 5). One complete tooth is preserved under the sediment in the right dentary of the referred specimen (Fig. 15C). The teeth are slightly recumbent and gently recurved, and they taper distally to a point from a base that is ~ 1 mm wide mesiodistally. Tooth implantation in Sanajeh is pleurodont and resembles the ‘modified alethinophidian type’ of implantation present in Najash (sensu Zaher & Rieppel, 1999b), with teeth implanted in distinct tooth sockets formed by prominent interdental ridges that extend onto the lingual wall of the subdental shelf. The orientation of the sockets with respect to the pleura is typical of a labial pleurodont condition, in which the pleura is high and the lingual dental ridge is vertically directed. These ridges provide bony support for the ankylosis of the labial part of the crown to the high, obliquely sloping pleura; the lingual part of the crown is ankylosed to a poorly developed basal plate on the dorsal surface of the well-developed subdental shelf (Fig. 15C).
Compound bone: The right compound bone is preserved in the holotypic specimen of Sanajeh (Fig. 5), and parts of both right and left compound bone are preserved in the referred specimen (Figs 8–12). Individually, these elements are incomplete, but together they preserve the complete length of the compound bone and many of its main features. However, owing to matrix cover and breakage, contacts with adjacent lower jaw elements are not apparent. The compound bone is a composite element comprising the fused prearticular, surangular and articular. In both holotypic and referred individuals, there is no trace of sutures among constituent elements. The compound bone forms the majority of the posterior portion of the mandible, contacting the dentary anteriorly, the angular medially and the coronoid anterodorsally, and articulating with the quadrate at its posterior end.
The anterior half of the compound bone is preserved in the holotype (Fig. 5). The ventral margin of the anterior surangular foramen is preserved as a sulcus on its dorsolateral surface, which is eroded in that region (Fig. 5A). The articulation between the compound bone and dentary is visible on the right mandible of the referred individual. The dorsoventral height of the compound bone diminishes gradually toward its anterior end, terminating in a blunted tip that fits within the space formed by the posterodorsal and posteroventral processes of the dentary. The posterior one-third of the right compound bone is preserved in the referred individual and in the holotype. The contact for the angular could not be identified, and a coronoid eminence of the surangular is absent. A wellpreserved posterior portion of the left compound bone was found with the referred specimen (Fig. 12). This portion of the compound bone is rod-like, with a prominent medial flange immediately in front of the articular surface for the quadrate that corresponds to the expanded medial flange of the surangular, located between the posterior margin of the adductor fossa and the anterior margin of the articular surface for the quadrate. A similarly expanded, slightly concave horizontal surface of the surangular is present in Dinilysia, Varanus Merrem, 1820 and Wonambi (Scanlon, 2005; Zaher et al., 2012). In dorsal or ventral views, this flange gradually expands medially before tapering again toward its broken anterior margin. The articular facet for the quadrate is exposed in dorsal and medial views. The articular surface is broad and saddle shaped, convex transversely and concave anteroposteriorly (Fig. 12). Immediately posterior to the quadrate articular surface is a small retroarticular process that extends posteriorly. Both the anterior tapering surface, which would have been located at the posterior border of the mandibular fossa, and the posterior retroarticular process are eroded and incomplete. A prominent opening for the chorda tympani is present on the ventromedial aspect of the compound bone (Fig. 12D). A smaller opening, the posterior surangular foramen, is present on the lateral surface of the compound bone, slightly anterior to the articular surface (Fig. 12A).
Coronoid: Portions of the coronoid are preserved in both the holotypic and referred specimens. The holotypic mandible preserves the most complete and informative fragment of the coronoid, which has been displaced a little posteriorly and medially out of position (Fig. 5). The referred specimen preserves a comparably poorer coronoid that is preserved near its original position atop the anterior portion of the compound bone, only contacting the posterodorsal edge of the splenial via its anterior process (Fig. 10). When complete, it would have extended slightly further anteriorly to reach the posterior edge of the dentary tooth row. The more complete, holotypic coronoid is roughly triradiate in medial or lateral view, with a prominent dorsal peak, an anterior facet that expands anteroventrally to form a triangular surface for insertion of the adductor externus superficialis musculature (Haas, 1973; Zaher, 1994a) and an expanded, slightly concave medial surface for the adductor externus profundus musculature (Fig. 5). The posterior margin is missing.
Splenial: Fragments of the splenial were preserved in the more complete, intact right mandible of the holotype. The referred specimen of Sanajeh preserves an almost complete right splenial, which is preserved against the medial surface of the posteroventral process of the dentary (Figs 9, 10). As such, the splenial has been slightly rotated and translated ventrally from its presumed original position on the medial aspect of the dentary. It is preserved in contact with the coronoid posterodorsally and with the compound bone posterolaterally. This preserved part of the splenial includes its articular surface for the angular, which is a fairly low, blunt process that is flush with the ventral edge of the splenial. The vertically oriented articular margin with the angular is broad and forms a shallow, concave articular surface for the angular. Medially, the splenial is excavated by a deep notch that probably received an anterior medial prong projecting from the anterior medioventral margin of the angular, forming a complex articular contact similar to the one described in extant snakes (Rieppel & Zaher, 2000). There is a large anterior mylohyoid foramen, which is enclosed within an elongate fossa that extends anteriorly ~ 6 mm. Immediately anterior to this fossa, near the preserved anterior edge of the splenial, is a small, partly preserved anterior inferior alveolar foramen enclosed in a shallow fossa. The Meckelian groove was probably covered by the splenial.
Angular: The angular is absent in the referred specimen but almost completely preserved in the holotypic right mandible, where it is partly obscured by a broken and displaced large fragment of the coronoid (Fig. 5B). It lacks its anterior articular surface. The angular is an elongate, strap-like element that measures 27 mm long by 4 mm deep. It is displaced posterodorsally from its original position within a subtriangular fossa on the ventromedial surface of the compound bone. A large foramen for exit of the posterior branch of the mylohyoid nerve is present toward the anterior end of the angular, set within a dorsoventrally shallow but anteroposteriorly elongate fossa. Apart from its articulation with the splenial, the angular maintains its dorsoventral height throughout its length. Its transverse thickness appears to taper posteriorly, such that its posterior end is approximately one-half the thickness at the splenial articulation.
description: Published as part of Zaher, Hussam, Mohabey, Dhananjay M, Grazziotin, Felipe G & Wilson Mantilla, Jeffrey A, 2023, The skull of Sanajeh indicus, a Cretaceous snake with an upper temporal bar, and the origin of ophidian wide-gaped feeding, pp. 656-697 in Zoological Journal of the Linnean Society 197 (3) on pages 661-681, DOI: 10.1093/zoolinnean/zlac001, http://zenodo.org/record/7690864