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Rhynchosaurs were quadrupedal, bulky herbivorous archosauromorph diapsids with a highly specialized dental apparatus. This group is restricted to the Triassic Period and became extremely abundant w...

Proterochampsids are one of the several diapsid groups that originated, flourished and became extinct during the Triassic Period. The current fossil record of this group indicates that its species ...

Teraterpeton hrynewichorum is an unusual archosauromorph reptile from the Upper Triassic (Carnian) Evangeline Member of the Wolfville Formation in Nova Scotia (Canada). Its long snout has transvers...

Three small and gracile jaw fragments are recovered from the Boren Quarry, one of the lowest fossil quarries of the Upper Triassic Dockum Group of Texas. The specimens are referred to archosauromorphs, where the morphology of the dentary and teeth of two specimens resemble what is observed in basal saurischians. Growing numbers of early dinosaur fossils from the lowest quarries of the Dockum Group of Texas which correspond to the lowermost Norian raises doubts concerning early dinosaur dispersal during the late Carnian-early Norian interval and the first occurrence of North American dinosaurs which might have happened earlier than previously suggested.

The so-called historical Polish discoveries of Triassic ‘dinosaurs’ have been repeatedly cited in papers and popular science books. Here, we re-evaluate each historical and purported Triassic dinosaur find from Poland. Additionaly, we describe several supposed ‘dinosaur’ bones collected by Polish geologists but only briefly mentioned: in regional geological journals, on collection labels, or in field notes. We attempt to assign all investigated specimens to the least inclusive taxon possible. Our revision indicates that part of this material represents non-dinosaur archosauromorph taxa. Most of the analysed specimens are fragmentary bones or isolated teeth and are indistinguishable from skeletal elements described from other well-known Triassic archosauromorph taxa. We conclude that fossils of dinosauriforms are present in the Upper Triassic of Silesia and Holy Cross Mountains. New analysis of Velocipes guerichi von Huene, 1932 holotype specimen from Kocury shows that it is the proximal part of fi...

Proterosuchids are a clade of quadrupedal, carnivorous Permo-Triassic diapsids crucial to understand the successful evolutionary radiation of archosaurs during the Mesozoic. The importance and good fossil record of proterosuchids nourished a renewed interest in recent years, but no function has been proposed for their bizarre snouts. An oversized and downturned premaxilla with up to nine teeth with continuous replacement is present in all proterosuchid species and seems to have represented a physiologically costly phenotype that increased towards adulthood. A non-functional or a species recognition hypothesis are not supported as evolutionary mechanisms that drove this phenotype because features expected for these explanations tend to have a very low or zero physiological cost. There is no evidence favouring –but neither rejecting− that this morphology can be explained by non-sexual and non-social natural selection alone. Mutual social and/or sexual selection is favoured here as the most unambiguously supported explanation for the function and origin of the bizarre snout of proterosuchids based on several lines of evidence, including costliness, positive allometry, positive changes in growth rates and modern analogues. Social and/or sexual selection may have been important evolutionary mechanism in the dawn of the lineage that gave rise to crocodiles and dinosaurs. Fil: Ezcurra, Martin Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; Argentina. University of Birmingham; Reino Unido

European Russia has yielded several fragmentary but potentially important archosauriform specimens from the Middle Triassic, but these have been only briefly described in the literature. One of these puzzling taxa is Dongusuchus efremovi Sennikov, 1988, described from the Donguz Svita. We present a redescription of Dongusuchus efremovi, which includes the first photographic atlas and thorough anatomical description of the holotype and referred specimens. This taxon is shown to be a gracile, probably fast-running species with elongate and slender limbs. A phylogenetic analysis recovers Dongusuchus efremovi as an early-diverging, non-archosaurian archosauriform. Previous work had suggested that this taxon was a ‘rauisuchid’. The gracile proportions of the femur and somewhat wedge-shaped head, however, are unusual for basal archosauriforms and are similar to the plesiomorphic state in crocodile and avian-line crown archosaurs. Several Early-Middle Triassic basal archosauriforms and early members of the croco...

A previous analysis of the phylogenetic position of the Pterosauria argued that pterosaurs were not closely related to dinosaurs as is generally accepted, but rather were outside the crown group Archosauria. However, that study was dismissed for the use of inappropriate methods. Here, the data set from that analysis was divided into five partitions: one with characters associated with cursorial digitigrade bipedal locomotion and the other four with characters from the skull and mandible, postcranial axial skeleton, forelimb and hindlimb, respectively. The partitions were subjected to homogeneity testing, and the Cursorial partition was found to be incongruent with other partitions and all other characters at the α = 0.01 probability level. Deletion of the Pterosauria removed all significant incongruence, demonstrating that the incongruence results from the coding of pterosaurs for the cursorial characters. The cause of the incongruence was interpreted as homoplasy in hindlimb morphology, and after re-eval...

The best-known South American Early Triassic archosauriform belongs to a putative proterosuchid briefly reported by Jose Bonaparte in 1981, collected from the Quebrada de los Fosiles Formation (Puesto Viejo Group, Argentina). This specimen consists of well-preserved natural external molds of a partial postcranium that preserve dorsal vertebrae, osteoderms, a dorsal rib, a possible gastralium, a chevron, a humerus, an ilium, two metapodials, and an ungual. We re-describe this specimen and identify autapomorphies that allow us to recognize Koilamasuchus gonzalezdiazi, gen. et sp. nov. The presence of an iliac blade with a slightly convex dorsal margin and with a maximum length more than 3 times its maximum height places Koilamasuchus within Archosauriformes. A cladistic analysis of basal Archosauriformes positions Koilamasuchus more crownwards than Proterosuchus, Sarmatosuchus, Fugusuchus, and Osmolskina, as the sister taxon of the clade that includes Erythrosuchidae and Archosauria. Proterosuchida...

A detailed redescription of the Late Triassic archosauromorph reptile Doswellia kaltenbachi Weems, 1980 from the Poor Farm Member of the Falling Creek Formation in the Taylorsville basin (Newark Supergroup) in Virginia is presented based upon additional preparation of the holotype. The euryapsid skull has a distinctive occiput with a prominent supraoccipital process that is flanked by posterior “horn-like” projections of the squamosals. Postfrontals, tabulars, and postparietals are absent. Plesiomorphic features of the palate and braincase include a plate-like horizontal parabasisphenoid, a pair of foramina for the internal carotid arteries on the ventral surface of the basisphenoid, and two fields of teeth on the palatal surface of the pterygoid. A sharp angle along the cervical and anterior dorsal ribs clearly separates the dorsal and lateral sides of the neck and anterior thoracic region. The posterior thoracic region has shorter ribs that project laterally with only a slight curvature. The il...

A new tetrapod taxon from the Upper Triassic Cow Branch Formation of Virginia is described solely on the basis of computed tomography (CT) scans of 2 individuals. The new form is characterized by the presence of extremely elongate thoracolumbar ribs that presumably supported a gliding membrane in life. It differs from all other known gliding tetrapods in possessing a very pronounced elongate neck. The grasping hindfoot is consistent with an arboreal habit. A gliding habit has been reported in a handful of fossil reptiles, with the oldest occurrence in Coelurosauravus (Carroll, 1978; Evans, 1982: Evans and Haubold, 1987) from the Permian of Europe and Africa. Elongate ribs were originally described in this form and these were thought to have supported a gliding membrane in life, but it has since been shown that the membrane-supporting structures are not true ribs, but separate bundles of rodlike neomorph ossifications (Frey et al., 1997). However, 3 closely related forms (Icarosaurus, Kuehneosaurus and Kuehneosuchus) from the Upper Triassic of Europe and North America do have exceptionally elongate thoracolumbar ribs, and all have been referred to a single family, the Kuehneosauridae (Robinson, 1962; Colbert, 1970). They are further characterized by the ribs forming hinge joints with the markedly elongate transverse processes on the dorsal vertebrae. This contrasts with the living gliding agamid Draco (Colbert, 1970), in which the elongate thoracolumbar ribs are flexible and lack the hinge-joint with the vertebral transverse processes. A fourth Triassic tetrapod, Sharovipteryx from the Triassic of Kirghizia, also possessed a gliding membrane (Gans et al., 1987) but in this form it is stretched between the hind limbs. Here we describe a new Triassic tetrapod with elongate ribs that is comparable in size to the contemporaneous Icarosaurus, but differs significantly from kuehneosaurs in having a long neck, a character that is potentially very unstable in a gliding animal. The 2 specimens of the new tetrapod were recovered from

Four different species belonging to three genera of South African proterosuchids have been described: Proterosuchus fergusi (Broom, 1903), Chasmatosaurus vanhoepeni (Haughton, 1924), Elaphrosuchus rubidgei (Broom, 1946), and Chasmatosaurus alexandri (Hoffman, 1965). The specimens and descriptions suggest that all four are subjective synonyms for the same concept. The type specimen is specifically determinable and the senior synonym, Proterosuchus fergusi Broom, 1903, is selected as the valid name for the South African proterosuchid species. The diagnosis for the species includes features such as: the dentigerous borders of the premaxilla and maxilla form an angle of about 120 degrees; the palatal teeth are arranged in a specific pattern; the laterosphenoid is not reduced in its anterior development; and the epipterygoid is axe-shaped and has an anteroventral medial process.

A new diapsid reptile, Jesairosaurus lehmani, gen. et sp. nov., is described on the basis of cranial and postcranial remains from the base of the Zarzaitine Series (Triassic) of Algeria. Jesairosaurus is a small prolacertiform with a low skull and an elongated neck; the snout is narrow and elongated and the post-orbital region short and narrow; the quadratojugal is lost; the posterior process of the jugal is reduced and spur-shaped; the hind-limb is large in comparison with the forelimb and the rest of the postcranial skeleton. The relationships of basal archosauromorphs and the interrelationships of the prolacertiforms are examined. The analysis of 71 binary characters leads to the identification of Jesairosaurus lehmani as a prolacertiform and suggests that Prolacertiformes forms a monophyletic group within the Archosauromorpha. The analysis indicates that the Rhynchosauria is the sister group of a clade comprising Trilophosaurus, Prolacertiformes, and Proterosuchus. The Choristodera is the mos...

A detailed description of the early archosaur Sarmatosuchus otschevi Sennikov, 1994, from the Middle Triassic Donguz Formation of southern European Russia, is presented. New morphological data forms the basis of a preliminary investigation of the phylogenetic relationships between a selection of the earliest archosaurs. A parsimony analysis based on 9 taxa and 35 characters recovers two most parsimonious trees that support the referral of Sarmatosuchus and Fugusuchus to a proterosuchid clade, as well as the paraphyly of the Proterosuchia. Characters from the structure of the braincase are more homoplastic than those from the rest of the skeleton. The presence of Sarmatosuchus in the Middle Triassic affords evidence that the proterosuchids were a more diverse and persistent clade than has been previously envisaged. Evidence suggesting that proterosuchids may have existed with erythrosuchids and early crown-group archosaurs in the Middle Triassic requires a revision of our understanding of the earl...

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 laterosphenoid is an ossification of the pila antotica neurocranial cartilage in the anterior sidewall of the braincase of crocodylians and birds. Contrary to published reports, the bone is present in the basal archosauriforms Proterosuchus fergusi, Euparkeria capensis, and Erythrosuchidae, taxa that diverged prior to the origin of the archosaurian crown group. Its presence is thus a synapomorphy of Archosauriformes rather than of Archosauria. The bone appears to have been induced by shifting jaw muscle origins from the skull roof to the anterolateral wall of the braincase. Additional innovations in the archosauriform feeding apparatus, such as a mandibular fenestra, appear to reflect changes in jaw muscles that may, in turn, facilitate predaceous habits. We review the historical development of the names of bones in the anterior sidewall of the amniote braincase and argue for the use of the term laterosphenoid, rather than either pleurosphenoid or orbitosphenoid, for this bone in all Archosau...

The Erythrosuchidae are a late Early to early Middle Triassic lineage that represent the first radiation of large terrestrial carnivores within the Archosauriformes. Erythrosuchid monophyly can be established by their possession of a suite of seven shared derived characters. At least five valid genera of erythrosuchids can be recognized. The most plesimorphic of these is Fugusuchus from China, followed by Garjainia from Russia and Erythrosuchus from South Africa. Vjushkovia and Shansisuchus share a later common ancestry. Vjushkovia is represented by two species, V. triplicostata from Russia and V. sinensis from China. Shansisuchus, also from China, is the only erythrosuchid with two fenestrae in the antorbital region. Erythrosuchids had a nearly worldwide distribution, although individual species appear to have restricted geographical ranges. The greatest diversity is in Russia and China but this probably reflects the fact that the most complete continental sequences spanning the stratigraphic ra...

Archosaurs first appeared in the Middle Triassic and within a short interval of time came to dominate all faunas of large vertebrates for the remainder of the Mesozoic. It is widely held that short...

We report on tanystropheids from the Late Triassic (middle Norian) Hayden Quarry of northern New Mexico (Chinle Formation, Hayden Quarry). These elements, consisting of isolated vertebrae and appendicular bones, represent the first unambiguously identified tanystropheid from western North America and likely the latest occurrence of the group, postdating Tanytrachelos in the eastern United States. A new phylogenetic analysis of early saurians identifies synapomorphies of tanystropheid subclades, which are recognized in the recovered vertebrae and a calcaneum. The femora are consistent with referral to Tanystropheidae. There is no clear association of the remains, however, so we refrain from erecting a new taxon. The analysis also indicates that the Hayden Quarry tanystropheid fossils belong to a newly recognized clade including the Late Triassic taxa Langobardisaurus and Tanytrachelos. Because most tanystropheid specimens are two-dimensionally crushed skeletons, the Hayden Quarry tanystropheid foss...

A partly complete skeleton from the late Paleocene of western North Dakota is described as Simoedosaurus dakotensis, n. sp., and is compared with European individuals of the genus. This specimen represents the earliest occurrence of the genus and is the first species to be recognized from North America. Skull characters that differ from the type species and indicate an early stage of development are: shorter muzzle; marginal teeth of more uniform size; larger lachrymal and a broader and longer skull table. Postcranial distinctions from its close ally Champsosaurus, with which it is often confused, are also presented, and its association with crocodilians is noted.