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Quadrupedal dinosaurs and other archosaurs are hypothesized to alleviate differences in height between shorter forelimbs and longer hindlimbs via digitigrady (standing on fingers). An alternative hypothesis suggests that they trend toward metacarpogrady (vertical, columnar palms with finger reduction and loss) to abandon semi-pronated (mechanically misaligned) wrist and finger joints. Range of motion (ROM) studies provide support for the latter hypothesis by showing that some dinosaurian fingers were held hyperextended away from the palm at metacarpophalangeal (MCP) joints. However, recent studies dispute traditional MCP hyperextension characters. Moreover, in vivo ROM is assumed to be less than fossil ROM because of the constraining influence of lost soft tissues, further implying that reports of MCP hyperextension in fossil archosaurs may be overstated. Because crocodilian fingers reportedly hyperextend during the high walk, a ROM study of their MCP joints could clarify these issues. Here a repeated-measures analysis was used to gather ex vivo finger joint ROM data in degrees from fully fleshed to skeletonized conditions in digit III of the American alligator Alligator mississippiensis. Results verify that MCP joints hyperextend, and show that soft tissues significantly affect ex vivo ROM. Skeletal ROMs were greater than fleshed ROMs in the three interphalangeal joints; however the MCP joint had the opposite result after losing curved articular cartilages. These results suggest that studies of flattened metacarpo- and metatarsophalangeal joints in fossil archosaurs may underestimate in vivo hyperextension. A comparison of characters in Alligator mississippiensis and the rauisuchid Postosuchus suggests that Postosuchus metacarpal adaptations represent a transitional stage toward vertical quadrupedal support with hyperextended MCP joints. This information provides support for the preexisting hypothesis that quadrupedal archosaurs tend to transform their wrist + palm into a rigid stilt-like extension of the forearm, which implies that locomotor abandonment of semi-pronated wrist/finger joints and alleviation of limb disparity evolve synchronously.

A new Early Triassic thecodont from the Donskaya Luka locality is described. A new species and genus of Rauisuchidae, Bystrowisuchus flerovi gen. et sp. nov., the first East European and earliest known member of the family Ctenosauriscidae is established. The taxonomy and phylogeny of Rauisuchidae and their stratigraphical and geographical distribution in connection with new finds are discussed.

In the 1970s the Upper Triassic strata of the Arg- ana Basin yielded archosaurian remains that were tentatively attributed to the rauisuchian Ticinosuchus. Restudy of this material together with new remains reveal new anatomical data and show that it in fact belongs to a new taxon, Arga- nasuchus dutuiti gen. et sp. nov. The systematics of the Rau- isuchia are still unresolved; nevertheless, a monophyletic suprageneric group can be defined within the probable non- monophyletic rauisuchians. Arganasuchus dutuiti differs from all adequately known rauisuchians in three autapomorphies: acetabular rim on pubis runs anteroventrally parallel to pubic shift rather than being terminal and perpendicular to it; large contribution of pubis to acetabular depression; pala- tal process of maxillary low and confluent with interdental crest, rather than separated from it by a large area. The max- illa of Arganasuchus resembles those of Batrachotomus and Fasolasuchus in having a Y-shaped rather than a U-shaped form. As in rauisuchids, Arganasuchus dutuiti has short cervi- cal vertebrae and a dorsal border of the proximal extremity of the pubis that is convex in lateral view. It shares one derived character state with Batrachotomus and Postosuchus (a tear-shaped and anteriorly orientated rugosity on the lateral side of the pubis, lying on a deep, longitudinal depression) and one more derived character state with Batrachotomus (narrow ante-acetabular part of the pubis; hence, the anterior border of the proximal extremity of the pubis is almost contiguous with the actabular rim).

GENUS RAUISUCHUS VON HUENE, 1938 A Type and only known species Rauisuchus tiradentes von Huene, 1938a. Diagnosis As for the type species (by monotypy)., Published as part of Lautenschlager, Stephan & Rauhut, Oliver W. M., 2015, Osteology of Rauisuchus tiradentes from the Late Triassic (Carnian) Santa Maria Formation of Brazil, and its implications for rauisuchid anatomy and phylogeny, pp. 55-91 in Zoological Journal of the Linnean Society 173 (1) on page 58, DOI: 10.1111/zoj.12196, http://zenodo.org/record/5330952, {"references":["von Huene F. 1938 a. Die fossilen Reptilien des sudamerikanischen Gondwanalandes. Ergebnisse der Sauriergrabung in Sudbrasilien 1928 / 29. Neues Jahrbuch fur Mineralogie, Geologie und Palaontologie, Referate 1938: 142 - 151."]}

RAUISUCHUS TIRADENTES Rauisuchoid ilium The only known ilium (BSPG AS XXV 88; Fig. 17A, B) originally assigned to R. tiradentes is a left element and comes from the secondary fossil site as part of ‘ Find 1025’. Compared with the pubis of the lectotype it shows a notable difference in size and is from an individual that was at least 20–25% smaller than the lectotype. The ilium consists of an acetabular area and the iliac blade with two processes: an anterior preacetabular process and a posterior postacetabular process. The lateral surface of the main body is nearly entirely occupied by a deep acetabulum. A prominent supraacetabular rim surrounds the dorsal margin. Anteriorly, the main body possesses a spike-like, dorsally flattened projection, which forms the pubic process. In this region the supra-acetabular rim is strongly developed. Anteroventrally, below the pubic process, the ilium bears a longitudinal groove with a depression on the ventralmost part, forming the articulation socket for the pubis. The parallel acetabular rim is not interrupted, indicating that the pubis only marginally contributed, or did not contribute at all, to the acetabulum. The posteroventral part of the ilium is partly broken. The area where the ischiadic process would be located is missing. The preacetabular process is short and projects anteriorly, but does not extend anterior to the pubic process. It has a blunt outline and is only slightly separated from the main body. The postacetabular process is considerably elongated and projects posteriorly and slightly laterally, although the latter might be a preservational artefact. Its cross section is triangular with a rounded lateral side. The medial(?) side is covered by a ventromedially excavated depression. Posteriorly it tapers to a blunt tip. Above the supra-acetabular rim, located between the preacetabular and the postacetabular process, the ilium possesses a prominent supra-acetabular ridge or buttress. It is perpendicular to the longitudinal axis of the iliac blade and contacts the dorsal margin to the supra-acetabular rim. According to Colbert (1961) and Chatterjee (1985), this ridge represents the attachment point for the iliofemoralis or the iliotibialis muscle, although this inference has been debated (Gower, 2000). On the medial side of the ilium, four distinct depressions are visible, which most probably represent the articulation sockets for the two-pronged sacral ribs of the sacral vertebrae. As no corresponding or overlapping elements are preserved in the lectotype, the ilium cannot be referred to R. tiradentes, although the following characteristics support its classification as a rauisuchoid ilium: (1) the ilium contributes to the major part of the acetabulum; (2) presence of a supraacetabular rim; (3) a short preacetabular and an elongated postacetabular process; (4) presence of a supraacetabular ridge connecting the supra-acetabular rim and the dorsal margin of the ilium; (5) closed acetabulum (Gower, 2000; Nesbitt, 2011). The fact that the acetabulum is almost entirely or even entirely placed on the ilium might indicate that it was correctly assigned to R. tiradentes, as the latter lacks an acetabular facet on the pubis; however, this can only be confirmed by additional material., Published as part of Lautenschlager, Stephan & Rauhut, Oliver W. M., 2015, Osteology of Rauisuchus tiradentes from the Late Triassic (Carnian) Santa Maria Formation of Brazil, and its implications for rauisuchid anatomy and phylogeny, pp. 55-91 in Zoological Journal of the Linnean Society 173 (1) on pages 82-83, DOI: 10.1111/zoj.12196, http://zenodo.org/record/5330952, {"references":["Colbert EH. 1961. The Triassic reptile Poposaurus. Fieldiana Geology 14: 59 - 78.","Chatterjee S. 1985. Postosuchus, a new thecodontian reptile from the Triassic of Texas and the origin of tyrannosaurs. Philosophical Transactions of the Royal Society, London 309: 395 - 460.","Gower DJ. 2000. Rauisuchian archosaurs (Reptilia, Diapsida): an overview. Neues Jahrbuch fur Geologie und Palaontologie, Abhandlungen 218: 447 - 488.","Nesbitt SJ. 2011. The early evolution of archosaurs: relationships and the origin of major clades. Bulletin of the American Museum of Natural History 352: 1 - 292."]}

Spondylosoma absconditum (Ladinian, Middle Triassic) lacks certain Dinosauriformes-Dinosauria characters (sigmoid curve and epipophyses in neck, distally placed deltopectoral crest on humerus) and those present (accessary hyposphene-hypantra vertebral articulations, three sacral vertebrae, elongate pubis) also occur in the Rauisuchia (Crurotarsi, Suchia, Rauisuchiformes).Spondylosoma is tentatively referred to the Rauisuchidae because, as indicated by the ventrolaterally directed sacral ribs, the ilium was held obliquely (and not vertically as in the Poposauridae).Staurikosaurus pricei (Carnian, Upper Triassic), one of the oldest dinosaurs, possesses autapomorphies of Dinosauriformes, Dinosauria, Saurischia, and Herrerasauridae, but it retains certain plesiomorphic characters (subcircular distal end to tibia, ?proximally placed deltopectoral crest, axially unshortened neural spine to sacral 1, ?scapular spine unreduced distally) not present inHerrerasaurus (Carnian, Ischigualasto Formation, Argentina). However, the femur is more derived in the loss of the trochanteric shelf and reduction of the lesser trochanter (as also occurs in some prosauropods). The two vertebrae sacrum ofStaurikosaurus is a plesiomorphic character for Dinosauria (also in other herrerasaurids, German Upper Triassic prosauropodSellosaurus gracilis — ?males), to which was added either a caudosacral (e.g. Santa Maria prosauropodSaturnalia, Sellosaurus gracilis — ?females) or a dorsosacral (e.g. Ischigualasto theropodEoraptor and prosauropodRiojasaurus). Agrosaurus (Upper Triassic, Durdham Down, England — not Australia) is not a herrerasaurid; it is referred to the prosauropod dinosaurThecodontosaurus antiquus (Upper Triassic, Durdham Down).

Postosuchus kirkpatricki Chatterjee, 1985 (fig. 11C) AGE: Norian, Late Triassic (Lehman and Chatterjee, 2005). OCCURRENCE: Post (5 Miller) Quarry, Cooper Canyon Formation, Dockum Group (Chatterjee, 1985). HOLOTYPE: TTU-P 9000, skull and partial skeleton. PARATYPE: TTU-P 9002, skull and skeleton. REMARKS: See Nesbitt et al., 2009a. KEY REFERENCES: Chatterjee, 1985; Long and Murry, 1995; Weinbaum, 2002; Peyer et al., 2008., Published as part of Nesbitt, Sterling J., 2011, The Early Evolution Of Archosaurs: Relationships And The Origin Of Major Clades, pp. 1-292 in Bulletin of the American Museum of Natural History 2011 (352) on page 37, DOI: 10.1206/352.1, http://zenodo.org/record/5405335, {"references":["Chatterjee, S. 1985. Postosuchus, a new thecodontian reptile from the Triassic of Texas and the origin of tyrannosaurs. Philosophical Transactions of the Royal Society of London B 309: 395 - 460.","Lehman, T., and S. Chatterjee. 2005. Depositional setting and vertebrate biostratigraphy of the Triassic Dockum Group of Texas. Journal of Earth Systems and Science 114: 325 - 351.","Nesbitt, S. J., M. R. Stocker, B. Small, and A. Downs. 2009 a. The osteology and relationships of Vancleavea campi (Reptilia: Archosauriformes). Zoological Journal of the Linnean Society 157: 814 - 864.","Long, R. A., and P. A. Murry. 1995. Late Triassic (Carnian and Norian) tetrapods from the southwestern United States. New Mexico Museum of Natural History and Science Bulletin 4: 1 - 254.","Weinbaum, J. C. 2002. Osteology and relationships of Postosuchus kirkpatricki (Archosauria: Crurotarsi). Lubbuck: Texas Tech University, 78 pp.","Peyer, K., J. G. Carter, H. - D. Sues, S. E. Novak, and P. E. Olsen. 2008. A new suchian archosaur from the Upper Triassic of North Carolina. Journal of Vertebrate Paleontology 28: 363 - 381."]}

Archosaurs have a nearly 250 million year record that originated shortly after the Permian-Triassic extinction event and is continued today by two extant clades, the crocodylians and the avians. The two extant lineages exemplify two bauplan extremes among a diverse and complex evolutionary history, but little is known about the common ancestor of these lineages. Renewed interest in early archosaurs has led to nearly a doubling of the known taxa in the last 20 years. This study presents a thorough phylogenetic analysis of 80 species-level taxa ranging from the latest Permian to the early part of the Jurassic using a dataset of 412 characters. Each terminal taxon is explicitly described and all specimens used in the analysis are clearly stated. Additionally, each character is discussed in detail and nearly all of the character states are illustrated in either a drawing or highlighted on a specimen photograph. A combination of novel characters and comprehensive character sampling has bridged previou...

The Crocodylotarsi are a group erected by Benton and Clark (1988) for archosaurs that share the “crocodile-normal” ankle structure. In this study, the phylogeny of the Crocodylotarsi was re-examined based on study of most relevant fossil material of the early non–crocodyliform members of the clade. Relationships among the major archosaurian taxa (Ornithodira, Ornithosuchidae, and Crocodylotarsi) and their proximal outgroups (Proterochampsidae, Euparkeria) were also considered. The monophyly of the Archosauria, Crurotarsi, and Crocodylotarsi is supported by the current analysis. The Parasuchia are the most plesiomorphic clade within the Crocodylotarsi. The Suchia comprise the crocodylotarsans excluding the phytosaurs. The taxon Prestosuchidae is placed near the base of this clade, as are Lewisuchus and Turfanosuchus dabanensis. The new taxon Rauisuchiformes includes the last common ancestor of Aetosauria and Crocodylia and its descendants. Rauisuchia (new combination) includes Rauisuchidae, Gracil...

The osteology of an almost complete braincase of the rauisuchian archosaur Batrachotomus kupferzellensis Gower from the Middle Triassic of Germany is described. There is a possibly discrete epiotic ossification, the metotic fissure is undivided by bone (i.e. there is a metotic foramen), the medial wall of the otic capsule is mostly ossified, the cerebral branch of the internal carotid artery entered the lateral surface of the parabasisphenoid, the ventral ramus of the opisthotic is more prominent laterally than a strong subvertical ridge on the exoccipital and basioccipital that lies posterior to the external foramen for the hypoglossal nerve, and the perilymphatic foramen faces away from the otic capsule in a posterior direction. Braincase morphology in the rauisuchians Saurosuchus galilei, Postosuchus kirkpatricki, and Tikisuchus romeri is reviewed. A matrix of 27 braincase characters for 12 archosaurian taxa is analysed. The most parsimonious hypothesis is consistent with the currently orthodox view of archosaurian phylogeny, except in that aetosaurians are more closely related to crocodylomorphs than is any rauisuchian. This phylogeny is used in a brief interpretation of the evolution of derived braincase features present in extant crocodilians. © 2002 The Linnean Society of London, Zoological Journal of the Linnean Society, 2002, 136, 49–76.

TIKISUCHUS ROMERI Tikisuchus romeri Chatterjee & Majumdar is a rauisuchian from the Upper Triassic Tiki Formation of India, known from a single incomplete specimen, ISI R 305. The osteology of this taxon has been described only briefly by Chatterjee & Majumdar (1987). These authors figured a restoration of the braincase in posterior view and presented the following description: ‘braincase very deep with elongated and well pronounced basipterygoid processes; supraoccipital tapers dorsally and makes a movable contact with parietal’ (Chatterjee & Majumdar, 1987: 788). Furthermore, they (p. 787) included ‘ossified laterosphenoid’ in a list of archosaurian features possessed by the specimen. I have re-examined this material as part of this study. The surface preservation of ISI R 305 is very crumbly, and sutures and other details are hard to make out. In addition, several regions of the braincase are not preserved or could not be located at the time of this study. This makes it impossible to comment on the laterosphenoids (which could not be located), exoccipitals, metotic region, fenestra ovalis. The paroccipital processes are fairly short with strong distal expansions. The basioccipital bears dorsal facets that indicate that the ventral ends of the exoccipitals met along the midline to form the ventral border of the foramen magnum. The basal tubera of the basioccipital are barely bilobed. There is no sign that the entrance foramina for the cerebral branches of the internal carotid arteries were located on the posterior or posteroventral wall of the parabasisphenoid. The anterolateral surfaces of the same element are even less perfectly preserved, but I tentatively interpret that this is where the foramina for the cerebral branch of the internal carotid artery are positioned. The braincase of T. romeri resembles that of P. kirkpatricki, particularly in the elongated region of the parabasisphenoid between the basipterygoid processes and the basal tubera, and in the way this region harbours a dorsoventrally elongate median pharyngeal recess. This is a derived feature within Suchia, and it represents a potential synapomorphy shared by P. kirkpatricki and T. romeri to the exclusion of other known suchians, including B. kupferzellensis (although the braincase UMMP 7473 appears to possess a similar feature, see above). One clear difference between the parabasisphenoids of P. kirkpatricki and T. romeri lies in the presence of paired short hook-like (in the transverse plane) processes on the parabasisphenoid of the latter taxon. These are not apparent in Chatterjee & Majumdar’s (1987) figure 2, but they can be clearly detected on the posterior surface of the element between the bases of the basipterygoid processes. In summary, rauisuchian braincases are slowly becoming better known. The braincases of B. kupferzellensis, S. galilei, P. kirkpatricki and T. romeri share many features. Most of these are apparently plesiomorphic for Archosauria (e.g. undivided metotic foramen, external foramina for hypoglossal nerve not posterior to subvertical ridge), some are probably derived for Archosauria (e.g. well ossified otic bullae, lateral foramen for the cerebral branch of the internal carotid artery), but few if any seem to be both derived for Suchia and restricted to rauisuchians. The elongate median pharyngeal recess of P. kirkpatricki and T. romeri is perhaps the only such character. B. kupferzellensis and P. kirkpatricki share a separate foramen possibly for the posterior cerebral/cephalic vein above the dorsal end of the metotic foramen, but a probable equivalent is also present in at least some crocodilians, and the condition in S. galilei and T. romeri is unknown., Published as part of Gower, David J., 2002, Braincase evolution in suchian archosaurs (Reptilia: Diapsida): evidence from the rauisuchian Batrachotomus kupferzellensis, pp. 49-76 in Zoological Journal of the Linnean Society 136 (1) on pages 66-67, DOI: 10.1046/j.1096-3642.2002.00025.x, http://zenodo.org/record/5436041, {"references":["Chatterjee S, Majumdar PK. 1987. Tikisuchus romeri a new rauisuchid reptile from the late Triassic of India. Journal of Paleontology 61: 787 - 793."]}

Postosuchus kirkpatricki(n.g., n.sp.) is a large, gracile, carnivorous thecodontian from the late Triassic Dockum Group of Texas. The species is characterized by its erect and facultative bipedal gait, highly advanced pelvis with slightly open acetabulum and footed pubis. The teeth are large, highly serrated, deeply set in sockets, and show a wave-like replacement pattern. Some flexibility in the palate and the lower jaw permitted the animal to swallow large chunks of flesh.Postosuchuswas the arch predator of its time, and lived in the interfluves or upland regions along with aetosaurs, coelurosaurs, and ictidosaurs. The quarry’s thanatocoenose probably reflects autochthonous burials of a Dockum community, perhaps in consequence of a catastrophic event such as a flash flood. AlthoughPostosuchusexhibits many carnosaurian traits, its ankle joint is of ‘crocodile-normal’ pattern, which suggests its pseudosuchian affinity. All Triassic reptiles previously thought to be carnosaurs are considered herein as advanced thecodontians; true carnosaurs probably appeared in post-Triassic time.Postosuchusis grouped withPoposaurus,Teratosaurus,Arizonasaurusand the unnamed 'Warwick archosaur’ in the family Poposauridae. The Poposauridae and Rauisuchidae are placed in the infraorder Rauisuchia. Tyrannosaurs probably evolved from poposaurids, as indicated by the correlation between skull, pelvis and ankle structure.

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.