The osteology of the pectoral limb of small captorhinids is described and figured in detail. A cartilaginous sternum was present. The glenoid was not a simple sliding or rocking joint, as was previously supposed, but considerable rotation was also an integral part of the humeral movement. The structure of the elbow joint is such that when the lower arm was extended, its distal end swung forward and extended the anterior reach of the hand. When the lower arm was flexed, the posterior reach of the hand was extended. Articulated specimens allow a recontruction of the manus. There was no well developed wrist joint, but rather the manus, as a whole, was a flexible structure. A pisiform was present. Sesamoid bones were developed in the tendons of the palmaris communis profundus muscle. Study of forelimb musculature of living reptiles based on dissections and the literature indicates that its evolution has been very conservative. The forelimb musculature of small captorhinids probably was very similar to that of all living reptiles except turtles.

No abstract

The fossil record provides no evidence supporting a unique common ancestry for frogs, salamanders and apodans. The ancestors of the modern orders may have diverged from one another as recently as 250 million years ago, or as long ago as 400 million years according to current theories of various authors. In order to evaluate the evolutionary patterns of the modern orders it is necessary to determine whether their last common ancestor was a rhipidistian fish, a very primitive amphibian, a labyrimhodom or a ‘lissamphibian’. The broad cranial similarities of frogs and salamanders, especially the dominance of the braincase as a supporting element, can be associated with the small size of the skull in their immediate ancestors. Hynobiids show the most primitive cranial pattern known among the living salamander families and “provide a model for determining the nature of the ancestors of the entire order. Features expected in ancestral salamanders include: (1) Emargination of the cheek; (2) Movable suspensorium formed by the quadrate, squamosal and pterygoid; (3) Occipital condyle posterior to jaw articulation; (4) Distinct prootic and opisthotic; (5) Absence ol otic notch; (6) Stapes forming a structural link between braincase and cheek. In the otic region, cheek and jaw suspension, the primitive salamander pattern (resembles most closely the microsaurs among known Paleozoic amphibians, and shows no significant features in common with either ancestral frogs or the majority of labyrinth odonts. The basic pattern of the adductor jaw musculature is consistent within both frogs and salamanders, but major differences are evident between the two groups. The dominance of the adductor mandibulae externus in salamanders can be associated with the open cheek in all members of that order, and the small size of this muscle in frogs can be associated with the large otic notch. The spread of different muscles over the otic capsule, the longus head ol the adductor mandibulae posterior in frogs and the superficial head of the adductor mandibulae internus in salamanders, indicates that fenestration of the skull posterodorsal to the orbit occurred separately in the ancestors of the two groups. Reconstruction of the probable pattern of the jaw musculature in Paleozoic amphibians indicates that frogs and salamanders might have evolved from a condition hypothesized for primitive labyrinthodonts, but the presence of a large otic notch in dissorophids suggests specialization toward the anuran, not the urodele condition. The presence of either an einarginated cheek or an embayment of the lateral surface of the dentary and the absence of an otic notch in microsaurs indicate a salamander‐like distribution of die adductor jaw muscles. The ancestors of frogs and salamanders probably diverged from one another in the early Carboniferous, Frogs later evolved from small labyrinthodonts and salamanders from microsaurs. Features considered typical of lissamphibians evolved separately in the two groups in the late Permian andTriassic.

No abstract

Proterogyrinus scheelei Romer, from the Upper Mississippian of Greer, West Virginia, is one of the earliest known members of the am phibian infraorder Embolomeri. The primitive, eogyrinid-like skull conforms to Panchen’s allometric plot of the British eogyrinids. It has no identifiable autapomorphies, but shares with two other, as yet undescribed genera attributed to the same family, a unique skull table with a raised pineal foramenrim and an acuminate median ridge on the skull table posteriorly, flanked on each side by a deep depression. The kinetic junction extends from the otic notch anteriorly to the posterodorsal corner of the orbit. The braincase, bearing no ossified roof, is composed of separate otic-occipital and sphenethmoid units, the latter bearing no sagittal or parasagittal septa. The vertebrae are similar to those of other embolomeres, except that the pleurocentrum retains a dorsal suture in adults, and the intercentrum , unossified dorsally in adults, is a ventral cresent. The presacral count is 32. The atlas-axis is reptiliomorph. The limbs and girdles are similar to those of Archeria ,except that they are slightly stouter. Humerus structure is primitive. Range of limb movement, at least in the pectoral limb, is very restricted. The possession of few autapomorphies indicates that P roterogyrinus is a member of the stem family (Proterogyrinidae) of the infraorder Embolomeri. Although most of the putative autapom orphies of anthracosaurs that were formerly thought to preclude them from reptile ancestry are not considered to be valid, there are no undisputed synapomorphies with reptiles either, making it impossible to support close relationship between the two groups.

BackgroundThe chasmosaurine ceratopsid Chasmosaurus is known from the Upper Cretaceous (Campanian) Dinosaur Park Formation of southern Alberta and Saskatchewan. Two valid species, Chasmosaurus belli and C. russelli, have been diagnosed by differences in cranial ornamentation. Their validity has been supported, in part, by the reported stratigraphic segregation of chasmosaurines in the Dinosaur Park Formation, with C. belli and C. russelli occurring in discrete, successive zones within the formation.Results/ConclusionsAn analysis of every potentially taxonomically informative chasmosaurine specimen from the Dinosaur Park Formation indicates that C. belli and C. russelli have indistinguishable ontogenetic histories and overlapping stratigraphic intervals. Neither taxon exhibits autapomorphies, nor a unique set of apomorphies, but they can be separated and diagnosed by a single phylogenetically informative character—the embayment angle formed by the posterior parietal bars relative to the parietal midline. Although relatively deeply embayed specimens (C. russelli) generally have relatively longer postorbital horncores than specimens with more shallow embayments (C. belli), neither this horncore character nor epiparietal morphology can be used to consistently distinguish every specimen of C. belli from C. russelli.Status of Kosmoceratops in the Dinosaur Park FormationKosmoceratops is purportedly represented in the Dinosaur Park Formation by a specimen previously referred to Chasmosaurus. The reassignment of this specimen to Kosmoceratops is unsupported here, as it is based on features that are either influenced by taphonomy or within the realm of individual variation for Chasmosaurus. Therefore, we conclude that Kosmoceratops is not present in the Dinosaur Park Formation, but is instead restricted to southern Laramidia, as originally posited.

Chasmosaurus irvinensis (sp. nov.) is distinguished from other species of this genus by the possession of a broad snout, absence of a brow horn (the position of which is occupied by a pit or rugosities suggestive of bone resorption), broadly rounded and open jugal notch, subrectangular squamosal, straight posterior parietal bar bearing 10 epoccipitals, eight of which are flattened, strongly curved anterodorsally, and nearly indistinguishably coossified to their neighbours, and small, transversely oriented parietal fenestrae restricted to the posterior portion of the frill. This species, restricted to the upper part of the Dinosaur Park Formation, is significantly younger than the other recognized Canadian Chasmosaurus species, C. belli and C. russelli. Phylogenetic analysis shows that C. irvinensis is most closely related to the other Canadian Chasmosaurus species and more distantly related to Chasmosaurus mariscalensis from Texas.Résumé : Chasmosaurus irvinensis (sp. nov.) se distingue des autres espèces de ce genre par son large boutoir, l'absence d'une corne sur le front (cette position est occupée par une fossette ou des rugosités qui suggèrent une résorption osseuse), une encoche jugale généralement arrondie et ouverte, un temporal presque rectangulaire, une barre pariétale postérieure droite comportant 10 époccipitaux, dont huit sont aplatis et fortement recourbés, dirigées en position antéro-dorsale et co-ossifiés à leurs voisins de façon presque indistincte, ainsi que de petites fenêtres pariétales à orientation transversale restreintes à la partie arrière de la collerette. Cette espèce, limitée à la portion supérieure de la Formation de Dinosaur Park, est beaucoup plus jeune que les autres espèces canadiennes de Chasmosaurus, C. belli et C. russelli. Une analyse phylogénique montre que C. irvinensis est plus étroitement lié aux autres espèces canadiennes de Chasmosaurus et moins étroitement lié au Chasmosaurus mariscalensis du Texas.[Traduit par la Rédaction] 1438Holmes et al.

Arrhinoceratops brachyops is a poorly understood chasmosaurine ceratopsid from the Upper Cretaceous Horseshoe Canyon Formation of Alberta, previously described on the basis of only a single skull. Here, we report on a second specimen attributable to this species, including a relatively complete skull, syncervical, and partial left forelimb. This second specimen clarifies aspects of morphology not visible in the holotype, and also elucidates variation in A. brachyops. The species is distinguished by a square-shaped triangular process of the premaxilla, a steeply inclined triturating surface of the predentary, and a triangular nasal horncore in horizontal section. The dentary is also distinctive in bearing a bony lateral ridge similar to that of Anchiceratops ornatus, but more strongly developed. Phylogenetic analysis cannot resolve the relationships of Arrhinoceratops beyond the level of Chasmosaurinae, owing to both missing data and conflicting characters. However, we do find some support for a deep split within Chasmosaurinae, contrary to conventional topologies. We also report on other fragmentary specimens plausibly attributable to A. brachyops that suggest a minimum age range of approximately 750 ka for this species.