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A new genus and species of giant crocodylomorph from the Upper Triassic of New Mexico is described.Redondavenator quayensis n. gen. et n. sp. (Crocodylomorpha: Sphenosuchia) has a very long posterior process of the premaxilla that fits between the nasal and the maxilla, and a long postglenoid process on the coracoid. These synapomorphies place it within the Crocodylomorpha.Redondavenator also has a System of grooves and pits that cover the anterior portions of the maxillae, the entire premaxillae, and the anterior part of the nasal. Possible foramina among the network of grooves and pits on the anterior portion of the skull may represent a rudimentary sensory System that is common to many extinct and ail extant crocodilians. Its exact phylogenetic position could not be determined from the preserved material, but key characters suggest a phylogenetic position near the base of Sphenosuchia.

Macelognathus vagans was described by O.C. Marsh in 1884, based on a mandibular symphysis from the Upper Jurassic Morrison Formation of Wyoming. Often considered a dinosaur but later tentatively referred to the Crocodylia, its phylogenetic identity has until now been enigmatic. New material of this species from the Morrison Formation of western Colorado demonstrates its affinities with basal crocodylomorphs commonly grouped together as the Sphenosuchia, which are characterized by a gracile postcranial skeleton with erect limb posture. Macelognathus shares features with Kayentasuchus from the Lower Jurassic Kayenta Formation of Arizona and Hallopus, which may be from the Morrison Formation of eastern Colorado. The new material constitutes the youngest definitive occurrence of a sphenosuchian, previously known from the Late Triassic to the Middle or Late? Jurassic.

A new taxon of sphenosuchian crocodylomorph, Dromicosuchus grallator, is described on the basis of a well-preserved, largely articulated partial skeleton from Late Triassic strata in the Durham sub-basin of the Deep River basin (Newark Supergroup) of Durham County, North Carolina. The holotype was preserved directly beneath the skeleton of a rauisuchian archosaur; this association, along with apparent bite marks to the head and neck of the crocodylomorph, suggests that the two animals died and were buried together during the act of predation. Dromicosuchus grallator is most closely related to Hesperosuchus agilis from the Petrified Forest Member of the Chinle Formation (late Carnian or early Norian) of Arizona and New Mexico and Saltoposuchus connectens from the Middle Stubensandstein (Lowenstein Formation; middle Norian) of Wurttemberg, Germany. The monophyly of Sphenosuchia is only weakly supported at present.

We report on and name two new taxa of basal crocodylomorph archosaurs from the Lower Jurassic, Litargosuchus leptorhynchus gen. et sp. nov., from the upper Elliot Formation (Stormberg Group) of South Africa, and Kayentasuchus walkeri gen. et sp. nov., from the Kayenta Formation (Glen Canyon Group) of Arizona, USA. Examination of this material led to a reconsideration of basal crocodylomorph interrelationships. A phylogenetic analysis found no support for the monophyly of Sphenosuchia. © 2002 The Linnean Society of London. Zoological Journal of the Linnean Society, 2002, 136, 77–95.

Much of a skeleton of Dibothrosuchus elaphros from the Lower Lufeng Group (Lower Jurassic) of Yunnan, China permits a detailed review of the anatomy and relationships of sphenosuchian crocodylomorphs. The skull is strongly built, akinetic, and monimostylic. The quadrate shows three dorsal processes that are firmly sutured to the skull roof and the braincase. The otic capsule is essentially crocodilian, and the tympanic pneumaticities are more elaborate than in extant forms. The animal possessed refined hearing ability and was probably vocal. The coracoid has an extremely elongated, posteriorly directed postglenoid process. The humerus bears an oval depression anteriorly near the head, and the radiale and ulnare are longer than the metacarpals. The limbs are long and slender, adapted for quadrupedal terrestrial gait. The estimated total length was 1.3 m. Phylogenetic analysis of 65 characters indicates the monophyly of the Sphenosuchia. Within the Sphenosuchia, Saltoposuchus (=Terrestrisuchus), Ps...

The skull of living crocodylians is highly solidified and the jaw closing muscles are enlarged1, allowing for prey capture by prolonged crushing between the jaws. Living species are all semi-aquatic, with sprawling limbs and a broad body that moves mainly from side-to-side2; however, fossils indicate that they evolved from terrestrial forms. The most cursorial of these fossils3,4,5,6 are small, gracile forms often grouped together as the Sphenosuchia, with fully erect, slender limbs; their relationships, however, are poorly understood5,7,8,9,10. A new crocodylomorph from deposits in northwestern China of the poorly known Middle Jurassic epoch possesses a skull with several adaptations typical of living crocodylians. Postcranially it is similar to sphenosuchians but with even greater adaptations for cursoriality in the forelimb. Here we show, through phylogenetic analysis, that it is the closest relative of the large group Crocodyliformes, including living crocodylians. Thus, important features of the modern crocodylian skull evolved during a phase when the postcranial skeleton was evolving towards greater cursoriality, rather than towards their current semi-aquatic habitus.

LITARGOSUCHUS LEPTORHYNCHUS SP. NOV. 1988 Pedeticosaurus sp. Gow & Kitching, p. 518. Etymology. From Greek leptos, thin, delicate, and Greek rhynchos, snout, muzzle. Diagnosis. Parietals partially fused and devoid of sagittal cresting. Squamosal broad transversely and without dorsolateral crest. Dentaries forming extensive symphysis, with little or no splenial involvement. Holotype. BP/1/5237, skull, mandible and much of the postcranial skeleton, first identified as Pedeticosaurus sp. by Gow & Kitching (1988). The postcranium is represented by the mostly articulated presacral vertebral column and scattered parts of caudal series, both scapulae and coracoids, both humeri, left radius and ulna, part of the left ilium, both ischia, left hindlimb (with the exception of the proximal portion of the femur and most of the pes), and distal portion of right femur. In view of its small size and gracile build, BP/1/5237 possibly represents a juvenile. Closure of the neurocentral sutures along the vertebral column provides a particularly useful osteological criterion for ontogenetic assessment (Brochu, 1996). Open neurocentral sutures are apparent on the cervical vertebrae, but preservation and current state of preparation do not permit identification of this feature in the dorsal column. Type horizon and locality. Upper Elliot Formation (Stormberg Group), 2 m below the contact with the Clarens Formation, on the farm Eagles Crag, Barkley East, South Africa. Age: Early Jurassic. SKULL Gow & Kitching (1988) provided only a brief account of the structure of the skull, and examination of the specimen revealed much additional detail. The skull (Figs 1, 2) was dorsoventrally flattened during fossilization. As a result of this crushing, the mandibular rami are now tightly appressed to the skull. The individual bones, with the exception of those constituting the palate and ventral portion of the braincase, are well-preserved, but some are traversed by fractures. They are delicate, smooth and devoid of sculpturing. The specimen was preserved in a hard, haematite-rich matrix, and removal of the encrusting haematite layer by mechanical means resulted in local loss of surficial bone. The occipital region is partially obscured by unidentified pieces of bone. In dorsal view, the skull has a narrow snout and a transversely broad temporal region (although its width was accentuated by dorsoventral compression). It is 63 mm long (measured along the midline of the skull roof from the anterior tip of the snout to the anteromedial end of the occipital embayment). The orbit is large, with an anteroposterior diameter of about 16 mm. The supratemporal fossae are delimited medially and posteriorly by faint ridges on the parietal and squamosal. The supratemporal fenestrae are much longer than wide, resembling those of Terrestrisuchus (Crush, 1984). On the better preserved left side, the recurved posterolateral process of the small premaxilla overlaps the nasal and maxilla on the side of the snout, excluding the latter element from participation in the posterior margin of the laterally directed external naris. The anterior ends of the premaxillae appear to be drawn out into a point. The left premaxilla holds four teeth, the first of which is the smallest; three teeth are preserved in the more incomplete right premaxilla. Contra Gow & Kitching (1988), the presence of a lateral notch between the premaxilla and maxilla cannot be ascertained due to poor preservation of this region on either side of the snout. The low but long maxilla forms most of the rostral portion of the skull. In lateral view, its alveolar margin is almost straight. The facial portion of the maxilla is vertical. Its ascending process projects posteriorly as well as slightly dorsally and contacts the anterior ramus of the lacrimal half way along the dorsal rim of the antorbital fenestra, excluding the nasal from participation in the dorsal margin of the antorbital fossa. The ventral margin of the large, subtriangular antorbital fossa is deeply recessed relative to the remainder of the lateral surface of the maxilla. The antorbital fenestra is situated in the posteroventral corner of the antorbital fossa. It is long anteroposteriorly but low dorsoventrally. The more completely preserved left maxillary tooth row comprises at least 18 teeth (16 of which are completely or partially preserved) and terminates posteriorly just behind the anterior margin of the orbit. The nasal extends back almost to the level of the anterior margin of the orbit. Its lateral sutural contacts with the maxilla, lacrimal and prefrontal are nearly straight. Its tapered anterior portion forms most of the dorsal margin of the narial fenestra. The dorsal surface of each nasal bears several neurovascular foramina, especially a large one in the posterior quarter. The contact between the ascending process of the maxilla and the anterior process of the lacrimal excludes the nasal from the dorsal margin of the antorbital fossa. The lacrimal has the shape of an inverted L and is inclined forward in lateral view. It forms the preorbital bar and contributes a broad medial lamina to the medial wall of the antorbital fossa. The lateral surface of its vertical portion bears a thin but distinct ridge. Posteriorly, the lacrimal forms an extensive lateral contact with the prefrontal along the preorbital bar. Dorsally, it is narrowly exposed on the skull roof. The prefrontal forms the anteromedial portion of the dorsal rim of the orbit. It is overlapped by the frontal posterolaterally. The dorsal surface of the prefrontal is subtriangular in outline. The posterior process of the jugal is deep dorsoventrally and faces ventrolaterally (although this may be due to dorsoventral compression of the skull). Its dorsal process for contact with the descending process of the postorbital is short and delicate. The anterior process of the jugal forms the ventral margin of the orbit but does not extend to the posteroventral corner of the antorbital fenestra and fossa anteriorly. The dorsoventral crushing of the skull has pushed the quadrates up through the supratemporal fenestrae. Few details are visible. The frontal is much longer than wide and forms most of the skull roof as well as the slightly raised dorsal rim of the orbit. Its dorsal surface is concave transversely. Although the frontals are somewhat thicker along their median sutural contact they do not form a distinct ridge as in Hesperosuchus (Clark et al., 2001) and Sphenosuchus (Walker, 1990). Anteriorly, the frontals extend forward for a short distance between the posterior ends of the nasals along the midline of the skull roof. Posteriorly, they contact the parietals along a transverse suture. The frontal does not participate in the anterior margin of the supratemporal fenestra. The interparietal suture is present only on the anterodorsal portion of the skull roof and cannot be traced more posteriorly. The parietals lack extensive posterolateral wings and form a weakly concave embayment in the occipital margin of the skull roof. Their dorsal surface is very slightly concave transversely between the medial margins of the supratemporal fossae. The sutural contact betwen the parietal and squamosal posterior to the supratemporal fenestra is short. The postorbital is triradiate in lateral view. It forms the anterior half of the dorsal margin of the supratemporal bar and overlaps the squamosal posteriorly. Anteromedially, the postorbital contacts the posterolateral end of the frontal. Its ventral process for contact with the ascending process of the jugal is delicate. No palpebral bones are preserved. The rather broad squamosal forms the posterolateral corner of the skull roof and resembles the homologous element in Crocodyliformes. It is thin and ventrally somewhat concave. The lateral edge of the squamosal is deflected and overhangs the infratemporal region and suspensorium laterally. Anteriorly, the squamosal extends ventral to the postorbital to participate in the formation of the postorbital bar. The dorsal surface of the squamosal is broad and gently convex transversely. It lacks the posterolateral crest bordering the supratemporal fossa found in most basal crocodylomorph archosaurs except Terrestrisuchus (Crush, 1984). The distal end of the paroccipital process formed by the otoccipital (fused exoccipital and opisthotic) is expanded dorsoventrally. The post-temporal foramen is located at the sutural contact between the squamosal, otoccipital, and supraoccipital and is very small. The palate is poorly preserved; it is represented by the posterior portions of the vomers, the palatines and fragments of the pterygoids. The vomers contact each other along the midline. The long medial portion of the ectopterygoid extends posteriorly along the anterolateral edge of the transverse flange of the pterygoid. Long, rod-like bones preserved on both sides of the palate probably represent the ceratobranchialia I of the hyoid apparatus, as in extant crocodylians. They have been somewhat warped during fossilization. MANDIBLE The mandibular rami are long and very slender. The external mandibular fenestra is long and low. The number of dentary teeth cannot be determined due to the tight contact between the mandibular rami and the skull. The dentaries form a rather long symphysis, which extends back to the level of the third maxillary tooth. The splenial either did not enter into the symphysis or contributed only minimally to its formation. The articular forms a distinct, dorsomedially directed process. DENTITION All teeth have labiolingually flattened crowns with anterior (mesial) and posterior (distal) carinae. Preservation of individual teeth is poor, and it cannot be determined whether the carinae were serrated or smooth; the carinae are serrated in all other known basal crocodylomorphs. The premaxillary and anterior maxillary teeth have slender and distinctly recurved crowns. In the left maxilla, the teeth in positions 4���6 appear to have the tallest crowns. The more posterior teeth have shorter and less recurved crowns., Published as part of Clark, James M. & Sues, Hans-Dieter, 2002, Two new basal crocodylomorph archosaurs from the Lower Jurassic and the monophyly of the Sphenosuchia, pp. 77-95 in Zoological Journal of the Linnean Society 136 (1) on pages 78-81, DOI: 10.1046/j.1096-3642.2002.00026.x, http://zenodo.org/record/4634400, {"references":["Gow CE, Kitching JW. 1988. Early Jurassic crocodilomorphs from the Stormberg of South Africa. Neues Jahrbuch fur Geologie und Palaontologie, Monatshefte 1988: 517 - 536.","Brochu CA. 1996. Closure of neurocentral sutures during crocodilian ontogeny: Implications for maturity assessment in fossil archosaurs. Journal of Vertebrate Paleontology 16: 49 - 62.","Crush PJ. 1984. A late upper Triassic sphenosuchid crocodilian from Wales. Palaeontology 27: 131 - 157.","Clark JM, Sues H-D, Berman DS. 2001. A new specimen of Hesperosuchus agilis from the Upper Triassic of New Mexico and the interrelationships of basal crocodylomorph archosaurs. Journal of Vertebrate Paleontology 20: 683 - 704.","Walker AD. 1990. A revision of Sphenosuchus acutus Haughton, a crocodylomorph reptile from the Elliot Formation (late Triassic or early Jurassic) of South Africa. Philosophical Transactions of the Royal Society of London B 330: 1 - 120."]}

LITARGOSUCHUS GEN. NOV Etymology. From Greek litargos, running fast, and Greek soukhos, crocodile, in reference to the inferred cursorial habits of this crocodylomorph reptile. Type species. Litargosuchus leptorhynchus sp. nov. (by monotypy). Diagnosis. As for the type and only known species, given below., Published as part of Clark, James M. & Sues, Hans-Dieter, 2002, Two new basal crocodylomorph archosaurs from the Lower Jurassic and the monophyly of the Sphenosuchia, pp. 77-95 in Zoological Journal of the Linnean Society 136 (1) on page 78, DOI: 10.1046/j.1096-3642.2002.00026.x

KAYENTASUCHUS GEN. NOV. Etymology. Kayenta, in reference to the formation from which the holotype was collected, and Greek soukhos, crocodile. Type specie s. Kayentasuchus walkeri sp. nov. (by monotypy) Diagnosis. As for the type and only known species, given below., Published as part of Clark, James M. & Sues, Hans-Dieter, 2002, Two new basal crocodylomorph archosaurs from the Lower Jurassic and the monophyly of the Sphenosuchia, pp. 77-95 in Zoological Journal of the Linnean Society 136 (1) on page 81, DOI: 10.1046/j.1096-3642.2002.00026.x, http://zenodo.org/record/4634400

KAYENTASUCHUS WALKERI SP. NOV. Etymology. In memory of Alick D. Walker for his many contributions to our understanding of Sphenosuchus and other archosaurs. Holotype. University of California Museum of Palaeontology (UCMP) 131830, a nearly complete but fragmented skeleton including an incomplete skull with articulated mandibular rami, articulated trunk region, articulated right ilium and femur, and other as yet unprepared postcranial bones. Type horizon and locality. Near the middle of the Kayenta Formation (Glen Canyon Group) in the ���silty facies��� of that unit (Clark & Fastovsky, 1986). Badlands at Willow Springs, Rock Head 7.5 Minute Quadrangle, NE Arizona, USA. Age: Early Jurassic (Sues et al., 1994). Diagnosis. Anterior process on maxilla projecting into well-developed, slit-like recess between premaxilla and maxilla. Outline of antorbital fenestra forming equilateral triangle. Squamosal descending along lateral edge of paroccipital process. Elongate mandibular symphysis with only minimal involvement of splenial. Dentary without enlarged anterior caniniform tooth and lacking teeth at anterior tip. Shares with Crocodyliformes presence of a groove along lateral edge of squamosal on dorsal surface. SKULL The skull of the specimen (Figs 3, 4) was compressed laterally during fossilization but otherwise appears undistorted. It broke into several fragments during excavation. The left side of the rostrum is wellpreserved and intact, and is preserved in articulation with the left dentary. The right nasal is preserved with this piece, but the fragmentary right maxilla, premaxilla and dentary and a large fragment of the frontals were recovered separately. The posterior portions of the right and left mandibular rami are also preserved separately. The dorsal part of the braincase and skull roof have been assembled from individual fragments into right and left halves, preserving most details; the ventral part of the prootic and part of the basisphenoid are preserved on the right side only. The snout (Fig. 3) is relatively deep and narrow; even allowing for distortion, it is at least four times higher than wide at the level of the antorbital fenestra. It is comparable in length to Sphenosuchus (Walker, 1990) and Dibothrosuchus (Wu & Chatterjee, 1993) and shorter than in Pseudhesperosuchus (Bonaparte, 1972a) and Terrestrisuchus (Crush, 1984). The external nares are terminal and laterally directed. They are divided by a bony bar composed of the nasals and premaxillae (although the premaxillary portion is no longer preserved). Each naris narrows posterodorsally and thus has a slightly oval outline. An antorbital fenestra is present just anterior to the orbit. It forms a roughly equilateral triangle in outline, with a vertical posterior margin, an horizontal dorsal edge, and an oblique anteroventral margin; the dorsal edge descends to a slight degree anteriorly. The maxilla forms the ventral margin, the lacrimal the posterior, and the two bones meet midway along the dorsal edge; the jugal may enter into the posterior margin of the fenestra, but, if this is indeed the case, it forms only a very small part of that margin. The fenestra, which is about one third the length of the maxilla, is relatively shorter than in Saltoposuchus and Pseudhesperosuchus, but is similar in length to the opening in Sphenosuchus and Dibothrosuchus. Its shape differs from that in the latter, which is more nearly circular, and those of the other three, which are more elongate and oval. A fossa is present in the maxilla anterior to the fenestra. The squamosals are broadened to form a ���skull table��� as in crocodyliforms, but, unlike the flat surface of crocodyliform squamosals, that of Kayentasuchus bends ventrally lateral to the quadrate and faces laterally. This may be due to some extent to lateral compression during fossilization, but a ridge along the edge of the occiput at the bend in the squamosal indicates that the bend is natural. The supratemporal fenestrae are relatively elongate, similar in length to those of other sphenosuchians except for Dibothrosuchus, in which the fenestrae are shorter. The fenestrae of Kayentasuchus are much longer than wide, and although this has been accentuated by the lateral compression of the specimen the original dimensions could not have been significantly different from the observed condition. The post-temporal fenestra is small but is not absent (as in Dibothrosuchus). It lies at the junction of the squamosal, parietal, otoccipital, and supraoccipital. This area is crushed on the better preserved left side of the skull, but the smooth ventral edge of the fenestra is present on the right side. On the left side the squamosal appears to form a groove which enters the lateral edge of the fenestra, but this may be due to crushing. The surfaces of most of the skull bones, with the exception of the frontal and squamosal, are smooth and devoid of sculpturing. The dorsal surface of the frontal bears weakly developed pitting along the midline. The squamosal is rugose near its lateral edge. The sculpturing composed of small pits and grooves typical of crocodyliform cranial bones is absent. The premaxilla is a small and slender bone forming most of the border of the external naris (Fig. 3). A slender posterodorsal process overlies the nasal and maxilla in what appears to be a weak suture behind the naris, rather than abutting against them as in crocodylians. The body of the premaxilla forms the anterior edge of a laterally open notch between it and the maxilla; this edge is gently convex posteriorly, and the premaxilla and maxilla do not meet below the notch. A process must have ascended from the anterior part of the premaxilla near the midline to form the ventral half of the internarial bar, but it has been broken away. The premaxillae meet only at the tip of the rostrum and do not meet posterior to the incisive foramen, so they do not form part of the secondary bony palate. The nasals form the dorsal surface of the snout between the naris and the frontals. Each extends anteriorly to form the posterodorsal half of the internarial bar, although the tips are broken off. The nasal borders the maxilla and lacrimal along their medial edges, and this contact is straight. Between the level of the antorbital fenestra and the nares, the lateral part of the nasal is bent ventrolaterally and faces dorsolaterally. A longitudinal ridge occurs where the bone bends. More posteriorly, the entire bone faces dorsally and meets the frontal at the level of the anterior end of the orbit. It presumably also contacted the prefrontal in this region, but neither prefrontal has been preserved on the rostral fragment. The nasal does not form any part of the fossa associated with the antorbital fenestra. The maxilla forms most of the facial region of the snout as well as a short secondary bony palate (Fig. 3). Its facial portion is vertical. The length of the maxilla is more than twice its maximum height. It is lower anteriorly and gradually increases in depth posteriorly. The combined length of the antorbital fossa and fenestra is approximately one-half that of the maxilla. The fossa has the same shape as the fenestra but is longer anteriorly and shorter posteriorly. The anterior end of the fossa narrows to a rounded end opposite the sixth tooth. The anterior tip of the fossa enters into a large foramen which communicates with the interior surface of the maxilla. The anterior edge of the maxilla forms the posterior part of the notch with the premaxilla and has a short anterior process that projects into the notch. The dorsal part of the maxilla contacts the lacrimal half way along the dorsal edge of the antorbital fenestra and at the posteroventral angle of the fenestra. The full extent of the contact between the maxilla and jugal is not obvious on the specimen, but most of it lies ventral to the lacrimal so that the maxilla does not extend posteriorly beneath the orbit. At its contact with the jugal the ventrolateral part of the maxilla has a thin lamina which ascends dorsally to overlie part of the jugal, although the jugal overlies the maxilla along most of the contact. The ventral border of the maxilla is straight, lacking the ���festooning��� commonly found in crocodyliforms. Small neurovascular foramina are present on the lateral surface of the maxilla dorsal to the tooth row; there are slightly fewer foramina than teeth. The anterior halves of the maxillae form a secondary bony palate, which extends back to the level of the sixth maxillary tooth. From here it continues posteriorly as a narrow palatal shelf. The palatine contacts the maxilla posterior to this narrow shelf. The ventral surface of the secondary palate is covered with many tiny pits in a pattern similar to that seen on the occipital surface of the squamosal. At the midline, the bone rises dorsally to form a longitudinal ridge along the dorsal surface of the secondary palate. Slightly posterior to the secondary bony palate, a ridge arises from the dorsal surface of the palatal shelf and ascends a short distance anterodorsally onto the medial surface of the facial part of the maxilla; possibly soft tissue forming the dorsal roof of the narial passage attached to this ridge. The vomer articulates bluntly with the maxilla at the posterodorsal edge of the secondary bony palate along the midline. The vertically oriented lacrimal separates the antorbital fenestra and orbit (Fig. 3). Most of the left element is preserved on the rostral fragment except for its posterodorsal part near the contact with the prefrontal. The ventral portion of the lacrimal is vertical and forms the posterior border of the antorbital fenestra and the anterior border of the orbit. The dorsal portion of the bone is horizontal and extends anteriorly dorsal to the antorbital fenestra. It is narrow, as in Sphenosuchus, rather than having a broad ventral lamina extending into the antorbital fossa, as in Pseudhesperosuchus (Bonaparte, 1972a) and Terrestrisuchus (Crush, 1984). The ventral part of the lacrimal is gently concave posteriorly and gently convex anteriorly. It bears a thin vertical ridge on its lateral surface and broadens medially. The lacrimal broadens ventrally at the contact with the maxilla (and possibly jugal), and it may also meet the palatine in this area. The contact between the lacrimal and prefrontal is not preserved. The posterior entrance of the lacrimal canal could not be identified. The jugal is represented only by the anterior end of the left element lying beneath the orbit. It is relatively narrow compared with that of crocodylians. Its contact with the lacrimal is not evident, but it clearly did not ascend far dorsally as in some basal archosaurs. The medial surface of the anterior end is concave, wrapping around the posterior end of the maxilla. The squamosal lies at the posterolateral corner of the upper temporal region, extending laterally over the quadrate. It is thin and similar to that of Saltoposuchus (Sereno & Wild, 1992) and Terrestrisuchus (Crush, 1984). Laterally, it bends downward so that this part of the bone is orientated vertically (Fig. 3). This may be partly owing to the lateral compression of the fossil, but the shape of the occipital portion of the bone suggests that the bend is for the most part a natural feature. The border of the occipital portion of the bone has a smoothly curved edge that follows the bend in the body of the bone, so that, had the body of the bone been essentially horizontal before crushing, the fragmentation of the occiput would have been more severe. The medial part of the squamosal also bends downward abruptly along the lateral edge of the supratemporal fenestra, although a true descending process as seen in primitive archosaurs and dinosaurs is absent. This portion of the bone is relatively short and of an even height throughout. The contact between the quadrate and squamosal lies along this part of the bone. Anteriorly, lateral to the supratemporal fenestra, this contact is a lap joint, with the squamosal lying medial to the quadrate. Posteriorly, in the area where the quadrate contacts the prootic, the quadrate abuts directly against the ventral surface of the squamosal, although there is a small ventral extension of the squamosal lateral to the quadrate. The dorsal part of the quadrate continues posteriorly beneath the squamosal to contact the anterior surface of its occipital part. There is no indication of a socket within the squamosal for the quadrate, as in Sphenosuchus (Walker, 1990) and more primitive archosaurs. As in crocodyliforms (with the exception of Eopneumatosuchus; Crompton & Smith, 1980), the anterior part of the quadrate is not sutured to the squamosal, but merely underlies it. However, a break in the right squamosal reveals that, unlike in crocodyliforms, the quadrate is not sutured to the squamosal posterior to the supratemporal fenestra. The anteroposterior development of the quadrate beneath the squamosal suggests that little, if any, movement was possible along this contact, especially in an anteroposterior direction. The occipital portion of the squamosal (Fig. 3) is extensive, being equal in height to the supraoccipital bone. It descends ventrally along the posterior surface of the paroccipital process to opposite the dorsal border of the foramen magnum. Its ventral edge is straight and horizontal. The squamosal appears to underlie the parietal posteriorly on the occipital surface. The two bones meet along an extensive contact so that the squamosal has no, or a very slight, contact with the supraoccipital. In posterior view, the contact between the squamosal and parietal is oblique, extending ventromedially from the dorsal surface of the skull. The occipital surface of the squamosal is covered with tiny pits. The lateral surface of the squamosal is broadest posteriorly, its ventral edge being orientated obliquely at an angle of about 45 ��. The occipital portion of the squamosal extends ventrally along the lateral edge of the paroccipital process to cover its lateral surface. The lateral edge of the squamosal on the occiput forms a strong ridge that extends posteriorly. It has a rough surface, especially dorsally. The lateral surface of the squamosal is sculptured in a complex pattern. The area along the anteroventral edge is roughened, and a low ridge is developed paralleling this roughness posterodorsally. Together these two features form a groove extending most of the length of the bone (Fig. 3). Anteriorly, this groove extends onto the dorsal surface of the bone as the descending portion of the bone gradually narrows. The ridges and groove terminate posteriorly opposite the level of the occiput where the groove turns downward and reaches the ventral edge of the bone. The groove may have served for the attachment of muscles for an ear flap as in extant crocodylians (Shute & Bellairs, 1955). A raised area is situated within the groove at its posterior end, as seen on the right side. Posterior to the groove, the lateral surface of the squamosal is roughened in a more regular pattern. The contact between the parietal and squamosal posterior to the supratemporal fenestra on the dorsal surface of the skull is very short, especially in comparison with crocodyliforms. It is less than one quarter the length of the squamosal, compared to about half the length of the squamosal in crocodylians. The squamosal does not appear to border the anterior temporal foramen (for the passage of a. temporo-orbitalis) as it does in Dibothrosuchus and crocodyliforms. The contact of the squamosal with the postorbital is not preserved. The parietals appear to be fused, but this is difficult to determine with certainty because they have separated along the midline and the contact surface is damaged. Anteriorly, they appear to have separated along an open suture, but posteriorly the break is not directly through the midline and no suture is apparent. It is possible that, as in Litargosuchus, the parietals were fused posteriorly but suturally separated more anteriorly. The anterior end of the bone is missing from the braincase pieces, but a fragment containing the anterior end of the left parietal and the posterior end of the frontal is preserved. In dorsal view, the parietal broadens posteriorly and, to a lesser extent, anteriorly; thus the lateral edge of the bone is concave where it borders the supratemporal fenestra. Anteriorly, near the frontal contact, the lateral edges become parallel. The parietal is similar in length to that of Sphenosuchus, Saltoposuchus, Terrestrisuchus, and Pseudhesperosuchus. A distinct rugose ridge along the lateral edge of the parietal clearly marks the dorsal limit of m. adductor mandibulae within the supratemporal fenestra. These ridges are separated by a broad expanse of bone on the skull roof, in contrast with Sphenosuchus and Dibothrosuchus in which a very narrow sagittal crest is formed along the dorsal midline. The dorsomedial surface is broadly rounded transversely, and the lateral edge of the dorsal surface is turned upward. The parietal extends ventrally from its lateral ridge to meet the endochondral bones of the braincase (Fig. 4). It contacts the laterosphenoid ventrally along the medial surface of the supratemporal fenestra, and in this area the lateral surface of the parietal is relatively flat. Posterior to the supratemporal fenestra the parietal contacts the prootic. Here its lateral surface is concave, with the ventral edge flaring laterally at the prootic contact. The parietal contacts the supraoccipital at the posterior end of the braincase, where it entirely overlies the supraoccipital dorsally. The extensive occipital portion of the parietal (Fig. 4) is wedge-shaped, thinning ventrally. It has broad contacts with the squamosal laterally and the supraoccipital medially on the occiput, and it has only limited (if any) ventral contact with the otoccipital. In dorsal view, the posterior edge of the parietal is concave posteriorly. The area dorsal to the supraoccipital is strongly concave, but flattens out laterally. The frontals roof the orbits. They are incompletely preserved; the medial parts of both bones are preserved together as an isolated fragment, and the posterior region of the left frontal forms another isolated fragment with the anterior part of the left parietal. The parietal extends anterolaterally along the edge of the supratemporal fenestra to separate it from the frontal. The ridge on the dorsal midline of the parietal continues anteriorly onto the frontals. The ridge becomes broader anteriorly, and its surface is slightly sculptured with narrow grooves. The lateral portion of the frontals is not preserved, but the broken edges are thinner than the medial part of the bones. Thus it is likely that the frontals are similar to those of Sphenosuchus and Hesperosuchus (Walker, 1970) in having depressions lateral to a midline ridge. The frontals of Kayentasuchus lack the three longitudinal ridges on their dorsal surface that are diagnostic for Dibothrosuchus (Wu & Chatterjee, 1993). The ventral surface of the frontals is poorly preserved, but the cristae cranii bordering the olfactory tracts were well-developed. A single small foramen marks the frontal lateral to the right crista. A fragment underlying the right nasal is probably part of the frontal, so that, Published as part of Clark, James M. & Sues, Hans-Dieter, 2002, Two new basal crocodylomorph archosaurs from the Lower Jurassic and the monophyly of the Sphenosuchia, pp. 77-95 in Zoological Journal of the Linnean Society 136 (1) on pages 82-90, DOI: 10.1046/j.1096-3642.2002.00026.x, http://zenodo.org/record/4634400, {"references":["Clark JM, Fastovsky DE. 1986. Vertebrate biostratigraphy of the Glen Canyon Group in northern Arizona. In: Padian K, ed. The Beginning of the Age of Dinosaurs: Faunal Change across the Triassic - Jurassic Boundary. New York: Cambridge University Press, 285 - 301.","Sues H-D, Clark JM, Jenkins FA Jr. 1994. A review of the Early Jurassic tetrapods from the Glen Canyon Group of the American Southwest. In: Fraser NC, Sues H-D, eds. The Shadow of the Dinosaurs: Early Mesozoic Tetrapods. Cambridge and New York: Cambridge University Press, 284 - 294.","Walker AD. 1990. A revision of Sphenosuchus acutus Haughton, a crocodylomorph reptile from the Elliot Formation (late Triassic or early Jurassic) of South Africa. Philosophical Transactions of the Royal Society of London B 330: 1 - 120.","Wu X-C, Chatterjee S. 1993. Dibothrosuchus elaphros, a crocodylomorph from the Lower Jurassic of China and the phylogeny of the Sphenosuchia. Journal of Vertebrate Paleontology 13: 58 - 89.","Bonaparte JF. 1972 a. Los tetrapodos del sector superior de la Formacion Los Colorados, La Rioja, Argentina. Opera Lilloana 22: 1 - 183.","Crush PJ. 1984. A late upper Triassic sphenosuchid crocodilian from Wales. Palaeontology 27: 131 - 157.","Sereno PC, Wild R. 1992. Procompsognathus: theropod, ' thecodont' or both? Journal of Vertebrate Paleontology 12: 435 - 458.","Crompton AW, Smith KK. 1980. A new genus and species of crocodilian from the Kayenta Formation (Late Triassic?) of Northern Arizona. In: Jacobs LL, ed. Aspects of Vertebrate History. Flagstaff: Museum of Northern Arizona Press, 193 - 217.","Shute CCD, Bellairs A. 1955. The external ear in Crocodilia. Proceedings of the Zoological Society of London 124: 741 - 749.","Walker AD. 1970. A revision of the Jurassic reptile Hallopus victor (Marsh), with remarks on the classification of crocodiles. Philosophical Transactions of the Royal Society of London B 257: 323 - 372.","Clark JM, Sues H-D, Berman DS. 2001. A new specimen of Hesperosuchus agilis from the Upper Triassic of New Mexico and the interrelationships of basal crocodylomorph archosaurs. Journal of Vertebrate Paleontology 20: 683 - 704.","Busbey AB III. 1989. Form and function of the jaw apparatus of Alligator mississippiensis. Journal of Morphology 202: 99 - 127.","Romer AS. 1923. Crocodilian pelvic muscles and their avian and reptilian homologues. Bulletin of the American Museum of Natural History 48: 533 - 552.","Hutchinson JR. 2001. The evolution of femoral osteology and soft tissues on the line to extant birds (Neornithes). Zoological Journal of the Linnean Society 131: 169 - 197."]}

The basis of this classificatory essay includes a reconsideration of the Thecodontia-Crocodylia boundaries, an evaluation of the temporal region of the thecodont skull, and some observations on the carpus, pelvis and tarsus of the group. The Proterosuchia include the Lower Triassic families Proterosuchidae-Erythrosuchidae and also the Middle and Late Triassic families Rauisuchidae and Cerritosauridae-Proterochampsidae, and the suborder is made up of two different lineages: the infraorders Rauisuchia and Proterochampsia. The Pseudosuchia is restricted to the families Euparkeriidae, Ornithosuchidae, Lagosuchidae and Scleromochlidae, with crurotarsal and mesotarsal tarsi, and short carpus. The Sphenosuchia are defined as the crocodilelike thecodonts, lightly built, with derived characters in the temporal region of the skull, elongated carpus and coracoid, and mesotarsal tarsi. The Aetosauria include the Stagonolepididae and the Doswelliidae, the latter recently described by R.E. Weems (1980) . The Phytosauria are briefly cited as it is a very well defined natural group.