PHILYDOSAURUS PROSEILUS SP. NOV. (FIGS 2���5) Etymology: Philydros + sauros (Gr.), water-loving lizard, referring to the presumed aquatic life style of the animal; proseilos (Gr.), meaning toward the sun, similar in meaning to the place name Chaoyang. Holotype: PKUP V2001, nearly complete skull and lower jaws in association with partial postcranial skeleton. Type locality and horizon: China, western Liaoning Province, Shangheshou near the city of Chaoyang; Early Cretaceous Chiufotang Formation. Known distribution: China, western Liaoning Province, Early Cretaceous Chiufotang Formation. Diagnosis: A medium-sized monjurosuchid choristodere sharing with Monjurosuchus the following derived character states: frontal markedly narrow and hourglass-shaped; anterior extension of lacrimal close to nasal/prefrontal suture; supratemporal fenestra small; infratemporal fenestra closed by expansion of surrounding elements, including postorbital, quadratojugal and squamosal. Differing from Monjurosuchus in having a more elongate skull; elongate narial openings and orbits; presence of a ���supratemporal trough��� formed by the postorbital and postfrontal and containing the supratemporal fenestra; a distinct antorbital ridge on dorsal surface of prefrontal; postfrontal ridge forming medial border of ���supratemporal trough���; hypertrophied postorbital and squamosal carrying a dorsal ridge to form lateral border of the ���supratemporal trough���; temporal process of parietal short, roughly 1/ 3 of parietal length; a deep U-shaped post-temporal incision at the midline of the occiput; low-crowned dentition; strongly elongated iliac blade with parallel dorsal and ventral borders; presence of a distinct spike-like posterior process of ischium. Anatomical description The holotype (PKUP V2001) includes a nearly complete skull, mandibles and postcranial skeleton missing minor parts of the limbs (Fig. 2). The entire skeleton is preserved in a volcanic shale slab, and was exposed in dorsal view after preparation of the specimen. Skull roof. The cranial skeleton is nearly completely preserved, and is dorsoventrally compressed as in other choristoderes (Fig. 3). The general configuration of the skull in dorsal view, however, is sharply different from the type genus Monjurosuchus, as the skull of the new form is substantially more elongated, with the antorbital portion slightly longer than the postorbital portion. The total length of the skull is approximately 103 mm, with the antorbital portion 40 mm, the orbit 25 mm, and the postorbital portion 38 mm long. The external narial openings are paired, elongated and are nearly terminal in position. With a strong interorbital constriction, the orbit is large but more dorsally than laterally orientated. The orbit is longer than wide, differing from that in Monjurosuchus (Gao et al., 2000). The supratemporal fenestra of Philydrosaurus proseilus is unique: it is small and connects with an anterior trough formed by the postorbital and postfrontal (Fig. 3). The infratemporal fenestra is completely closed by expansion of the surrounding bones, including the postorbital, quadratojugal and squamosal. The closing of the infratemporal fenestra is apparently a synapomorphic feature of the Monjurosuchidae, as it also occurs in the type genus Monjurosuchus (Gao et al., 2000). No post-temporal fenestra is developed: the extremely short temporal process of the parietal is in full contact with the squamosal and the quadrate (see below). The premaxillae are small, paired elements that meet along a midline suture. The body of the premaxilla is penetrated by several foramina for nerves and vessels, and these are associated with small bumps developed as surface ornamentation. Each premaxilla has a slender but well-defined dorsal process that forms 1/3���1/2 of the medial border of the external nares (the dorsal process of the left premaxilla extends to the level of the posterior border of the narial openings). The posterior end of the dorsal process narrows between the slender anterior processes of the nasals that form the posterior part of the medial border of the external nares. The posterior margin of the premaxillary body is notched for the anterior border of the narial opening, and lateral to the opening is the irregular suture that marks the articulation between the premaxilla and maxilla. Posteroventrally, the premaxilla has a well-developed tooth-bearing process extending to the midlevel of the narial opening. The nasals are paired, very narrow, elongated (20 mm long) and extend posteriorly to contact the prefrontal at the midlevel of the snout. Anteriorly, the nasal forms the posterior, but not part of the lateral, border of the narial opening. A slender anterior process of the bone contacts the dorsal process of the premaxilla to form a large part of the internarial septum. Laterally, the nasal has a long, straight suture with the maxilla, and posteriorly it is developed as a slender process that pinches between the anterior process of the prefrontal and the dorsal rim of the maxilla. The prefrontals are paired and elongated, being the same length (20 mm) as the nasals. A midline sutural contact between the prefrontals is clearly visible as in other choristoderes generally; however, a narrow opening is evident within the midline suture; such a prefrontal fontanel has never previously been recorded in other choristoderes, including a small subadult skull of Champsosaurus (RTMP 94.163.1, see Gao & Fox, 1998) from the Upper Cretaceous Dinosaur Park Formation of western Canada. The dorsal surface of the prefrontal of this new animal is unique in having a sharp elongate ridge running anteriorly from the orbital rim to the level of nasal/prefrontal articulation. The prefrontal contacts the nasal anteriorly, the frontal posteriorly, and the lacrimal and maxilla laterally. The frontals are paired, elongated and hourglassshaped, with a strong interorbital constriction. Having a greatest length of 26 mm, the frontal is longer than the prefrontal, and equal in length to the parietal (26 mm). The anterior part of the frontal is broken bilaterally, but it seems to lack an anteromedial process. The anterolateral processes are in articulation with the prefrontal but barely contact the lacrimal. The anterior and posterior width of the paired frontals is 11 mm, and the interorbital width, 5 mm. The frontal contacts the postfrontal posterolaterally along a short straight suture, and meets the parietal posteriorly at a contact that is roughly transverse to the long axes of these bones. The latter suture is at about the same level as the anterior border of the ���supratemporal trough��� or the posterior border of the orbits. The parietals are paired, having a total length of 26 mm, including the short temporal process. The dorsal surface of the parietal table is smooth, but a prominent longitudinal ridge is developed that flanks the lateral border of the table. This lateral ridge also forms the medial border of the small supratemporal fenestra, and is continuous anteriorly with the ridge of the postfrontal that extends to the posteromedial border of the orbit. There is no parietal foramen. The temporal process of the parietal is extremely short (9 mm long), roughly 1/3 of the total length of the bone (26 mm). The two temporal processes form a deep Ushaped post-temporal incision medially on the occiput (Fig. 3). The maxillae are well preserved on both sides. As in other choristoderes, the maxilla lacks a well-defined dorsal process, but inrolls medially to contact the elongated nasal bone. The maxilla has a short anterior process that is in articulation with the premaxilla and forms the lateral border of the narial opening. Medially, the maxilla has a long suture with the nasal and posteriorly contacts the lacrimal: the lateral wall of the maxilla sharply descends to meet the lacrimal and jugal. The slender posterior process of the maxilla is largely obscured on the right side, but the betterexposed left side seems to show it terminates at a level close to the posterior border of the orbit. This interpretation is supported by the fact that the lower dentition also terminates at this level, as shown by the disarticulated left mandible (Fig. 3). Anterior to the orbit, the lacrimal is located in a longitudinal depression that is deep and wide in its posterior part but gradually becomes narrow and shallow anteriorly, terminating not far behind the narial opening. The lacrimal is quite narrow and elongated (25 mm long), with its anterior extremity reaching beyond the level of the nasal/prefrontal suture. Medially, it meets the prefrontal, and laterally the maxilla and anterior process of the jugal. The medial edge of the lacrimal contacts the prefrontal in the longitudinal depression developed dorsally on the snout (Fig. 3). The posterior border of the lacrimal is deeply notched for the anterior border of the orbit, and the dorsal rim of the orbit is ornamented with prominent tuberosities. The lacrimal foramen is identifiable on both sides, despite the dorsoventral compression of the skull. This foramen penetrates the lacrimal, the primitive condition differing from the derived pattern in which the foramen is bordered by the lacrimal, prefrontal and palatine as in neochoristoderes (see Gao & Fox, 1998). The postorbital and postfrontal are separate, and both enter the posterior border of the orbit (Fig. 3). This morphology is primitive in diapsids and differs from the fused condition in some but not all derived choristoderes (Gao & Fox, 1998; Evans & Manabe, 1999; Ksepka, Gao & Norell, 2005). In dorsal view, the postfrontal is substantially smaller than the postorbital, but overlaps the latter element in the ���supratemporal trough.��� Dorsally, the postfrontal displays a short but prominent ridge that runs from the posterior border of the orbit to meet the lateral ridge of the parietal. Medial to this ridge, the postfrontal contacts both the frontal and the parietal along a short, straight suture; the posterior extension of this suture enters obliquely into the ���supratemporal trough��� that separates the postfrontal from a small lateral projection of the parietal. Also within the trough, the postfrontal overlaps the postorbital to form much of the anterior border of the supratemporal fenestra. Lateral to the postfrontal, the postorbital is greatly hypertrophied as the main element that closes the infratemporal fenestra. Dorsally, the postfrontal displays a strongly developed ridge that joins with the ridge from the squamosal to form the lateral border of the ���supratemporal trough���. Lateral to the dorsal ridge, the postorbital has an extensive sutural contact posteriorly with the squamosal and ventrally with the quadratojugal. As a diagnostic feature of the family Monjurosuchidae, these three elements together have entirely closed the infratemporal fenestra, leaving no trace of the opening. The jugal and the quadratojugal are preserved on both sides in the holotype. The anterior process of the jugal forms the lower border of the orbit and extends anteriorly to the lateral surface of the posterior process of the maxilla. The anterior tip of the process is damaged on both sides, but it probably terminated at a level slightly anterior to the orbit, as interpreted from the articular surface of the jugal on the maxilla. The postorbital, or dorsal, process of the jugal is low but well defined, forming a small part of the posteroventral border of the orbit. From the postorbital process, the dorsal margin of the jugal descends posteriorly to meet the quadratojugal. The short posterior process of the jugal fits into a small notch on the quadratojugal slightly anterior to the craniomandibular joint. The quadratojugal is a much smaller bone in comparison to the jugal and squamosal. It is located between the jugal and the squamosal, and dorsally contacts the enlarged postorbital. The squamosal is greatly expanded as a major element that closes the infratemporal fenestra. The dorsolateral exposure of the squamosal is roughly a triangular plate, with a flattened surface rugosely ornamented. In dorsal view, the medial extension of the squamosal forms part of the floor of the ���supratemporal trough���, and meets the temporal process of the parietal. The anterior border of this medial extension is thin, slightly concave and overlaps the quadrate. Posteriorly, this extension has two prominent processes separated from one another by a small notch (Fig. 3). The medial process forms a small part of the lateral border of the narrow U-shaped post-temporal incision, and the lateral process forms the posterior extremity of the temporal region. Braincase and palate: Only a small part of the lateral wall of the braincase is exposed in the supratemporal fenestra within the ���supratemporal trough���, and the lateral wall is badly crushed on both sides. However, it is clear that a downgrowth of the parietal forms a small part of the braincase wall, and it has a dorsally concave border for articulation with a small bone, presumably the neomorph as in other known choristoderes (Fox, 1968). A neomorph occurs in neochoristoderes and possibly in Cteniogenys (Evans, 1990), but this element cannot be identified positively for this new form because of breakage and distortion of the braincase. By the same token, a pterygoquadrate foramen is not identifiable on the new specimen, and the ventral parts of the braincase cannot be exposed without damaging the specimen; therefore, knowledge of the morphology of this part of the skull must await discovery of better preserved material. Within the orbit, the pterygoid and ectopterygoid are partly exposed in dorsal view. The short medial process of the ectopterygoid forms the posterior border of the suborbital fenestra and overlaps the short lateral process of the pterygoid. A slender anterior process of the ectopterygoid extends along the medial side of the anterior process of the jugal, terminating slightly anterior to the midlevel of the suborbital fenestra; therefore, the short anterior extension of the process allows a small part of the jugal to enter the lateral border of the suborbital fenestra (Fig. 3). The anterior extension of the pterygoid is greatly widened as a plate that forms the entire medial border of the suborbital fenestra. The midline suture of the pterygoids is obscured by the frontal, and thus, the taxonomically significant feature of the interpterygoid foramen cannot be observed in this specimen. The anterior end of the pterygoid is badly damaged on both sides, and the pattern of the pterygoid/palatine articulation cannot be determined. Posterior to the suborbital fenestra, only a small part of the subtemporal fenestra is exposed behind the medial process of the ectopterygoid; therefore, the actual size of the fenestra is unknown in the holotype of the new taxon. Disarticulated from the palate, the left palatine is exposed in close association with the skull (partly obscured by the left maxilla). Most of the palatine is a thin plate, but it is slightly thickened posteriorly at the notch for the suborbital fenestra. Along the dorsomedial border of the palatine, the articular surface for the greatly elongated vomer can be seen. This surface is about half the width of the palatine, indicating an extensive articulation between the two bones. Although exposed in dorsal view, the exposed lateral edge seems to show that the palatine has a toothed ventral surface, but the distribution pattern of the palatal teeth cannot be ascertained in the absence of a ventral view. Also disarticulated from the skull, the right vomer is nearly completely preserved in close association with a hyoid bone. Exposed in dorsal view, the vomer is greatly elongated, with a total length of 50 mm. The anterior extremity of the vomer is narrowly pointed but deeply bifurcated by a fissure 10 mm in length. About 19 mm from the anterior tip, a small vomerine foramen opens close to the medial border of the bone. Along this border, a well-defined ridge runs from the vomerine foramen to the posterior end of the anterior fissure. The vomer posteriorly has a notch for articulation with the pterygoid and posterolaterally an articular surface for the palatine. Lying to the side of the vomer is a slender bone 32 mm in length. This is probably one of the hyoid elements that are also known for some champsosaurs (Gao & Fox, 1998: fig. 5). Mandibles: Before burial, both mandibles of the holotype (PKUP V2001) were disarticulated from the skull (Fig. 3). The left mandible is nearly completely preserved and is exposed in medial view; the dentary of the right mandible is exposed in lateral view but the postdentary parts are missing. The total length of the mandible is 83 mm as measured from the nearly complete left element. With a total length of 63 mm, the dentary is the longest mandibular bone and covers a large part of the lateral side of the lower jaw. As shown in the right mandible, the strongly convex lateral surface of the dentary is penetrated by rows of small foramina. The foramina on the anterior part of the jaw are closely spaced, while those on the posterior part are increasingly widely spaced; they are accompanied by narrow and posteriorly extending grooves that housed lateral cutaneous branches of the mandibular ramus of the trigeminal nerve and accompanying blood vessels. The posterior end of the dentary is bifurcated for articulation with the surangular bone (missing on the right mandible along with the other postdentary elements). Medially, the dentary carries a well-developed subdental shelf, the depth of which is roughly equal to the tooth height. Below the shelf is the Meckelian canal that opens medially as a narrow groove for the anterior one-third of the dentary length, but is closed by the splenial for the posterior twothirds. Anteriorly, the mandibular symphysis is extremely short and lacks a posterior extension as seen in advanced neochoristoderes. The splenial has been crushed into the Meckelian canal, but it shows that its posterior extremity terminates as a short tongue slightly beyond the posterior end of the tooth row. This tongue is wedged between the coronoid and the anterior extension of the prearticular, but may have a short ventral sutural articulation with the angular bone. The coronoid is a small triangular bone without a prominent dorsal process. It sends a short posteroventral process to articulate with the splenial and the prearticular, thereby contributing to a small part of the lower border of the mandibular fossa. Behind the fossa is the articular surface for the craniomandibular joint. From the length of the mandible, this joint is interpreted as being located roughly at the same level as the occipital condyle. The articular surface is at the posterior extremity of the jaw, and thus a retroarticular process is undeveloped in this animal. Dentition: On the holotype specimen, marginal teeth are observed on both upper and lower jaws. Anteriorly, the upper dentition is exposed on both sides, but its more posterior parts are imbedded in matrix making the total number of the maxillary teeth indeterminable. As a result of the disarticulation of the lower jaws from the skull, the lower dentition on the left is exposed in medial view and that on the right in lateral view (Fig. 3). The left dentary has as many as 41 teeth preserved, with, Published as part of Gao, Ke-Qin & Fox, Richard C., 2005, A new choristodere (Reptilia: Diapsida) from the Lower Cretaceous of western Liaoning Province, China, and phylogenetic relationships of Monjurosuchidae, pp. 427-444 in Zoological Journal of the Linnean Society 145 (3) on pages 428-437, DOI: 10.1111/j.1096-3642.2005.00191.x, http://zenodo.org/record/4687363, {"references":["Gao K, Evans S, Ji Q, Norell M, Ji S. 2000. 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