ISSN:0272-4634    

DOI:10.1671/0272-4634(2000)020[0001:ADREFT]2.0.CO;2

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

ISSN:0272-4634    

DOI:10.1671/0272-4634(2000)020[0007:ANTTFU]2.0.CO;2

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Joffrichthys triangulpterus, sp. nov. is a new species of the family Osteoglossidae, and is described based on two nearly complete, and two partial, articulated specimens from the Sentinel Butte Formation in the Fort Union Group (Paleocene) of central North Dakota, USA. The familial placement is based on three diagnostic characters: uroneurals absent; six hypurals; and a kidney shaped opercle. The generic placement intoJoffrichthysis based on two diagnostic characters and eight similar morphologies and meristics shared between the new species and previously describedJ. symmetropterus: two complete or partial neural spines present on preural 2; one spine or no spines present on ural 1; similar shapes of the maxillary, dentary, preopercle, opercle, and frontal; a similar body silhouette; and a similar vertebral and supraneural count. The specimens are identified as a new species by nine diagnostic characteristics distinguishing it fromJ. symmetroptems, the most closely related taxon: more posteriorly-placed pelvic fins; a greater dorsal fin ray count (30 total); a triangular dorsal and anal fin; asymmetrically positioned dorsal and anal fins (anterior pterygiophore insertions separated by 8 to 9 vertebrae); the third dorsal and fifth anal pterygiophores being the longest; and two complete spines on preural 2. The North Dakota fish is important because it represents a new species ofJoffrichthysand represents the most southern occurrence of the genus to date.

ISSN:0272-4634    

DOI:10.1671/0272-4634(2000)020[0012:ANSOJT]2.0.CO;2

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The braincase ofLeptopleuron lacertinumOwen, a leptopleuronine procolophonid from the Late Triassic (lower Norian) of Scotland, is described for the first time. Morphologically, the braincase ofLeptopleuronis similar to that of the Early Triassic genusProcolophon, and to a number of other procolophonids currently included in the subfamily Procolophoninae Romer, 1956. Several features of the braincase ofLeptopleuronare derived within the Procolophonidae, but others are unique to this genus. Apomorphies include a strongly tripartite occipital condyle, a metotic foramen that is not walled by bone anteriorly, an ‘ascending process’ of the basisphenoid that forms a robust flat-ended expansion, and bears ventrally a thin laterally directed lamella, a ‘processus infrastapedialis columellae’ of the stapes that is aligned with the long axis of the footplate, loss of the foramen for nerve IX on the ventral ramus of the opisthotic, and a greatly expanded, vertical basisphenoid rostrum. These features may be autapomorphic forLeptopleuron, or represent synapomorphies of the Leptopleuroninae Ivakhnenko, 1979.

ISSN:0272-4634    

DOI:10.1671/0272-4634(2000)020[0021:TBSOLL]2.0.CO;2

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The dentition ofNicrosaurus kapffi, a phytosaur from the Norian of central Europe, consists of three distinct dental sets in the upper jaw, and two in the mandible. Dental sets are defined by: (1) gradual, linear transformations of dental characters within an array that results in characteristic end members; and (2) the position of each array within the jaws. The tip-of-snout set in the upper jaw comprises mainly the large fang-like anteriormost teeth. In the premaxilla set, the teeth grade from a conical, unspecialized form anteriorly to high, D-shaped and bicarinate teeth posteriorly. In the maxilla set the teeth grade from stout, conical, unspecialized forms anteriorly to triangular forms with expanded flanges posteriorly. The tip-of-mandible and the dentary set correspond to the tip-of-snout, and to an elongated maxilla set, respectively, but were studied in less detail. The presence of tripartite and bipartite dentitions (three versus two dental sets in the upper jaw) is suggested as a criterion for defining the degree of heterodonty in phytosaurs. By taking into account positional variation, it is suggested that dental characters can be used to identify the relative position of some isolated teeth and can contribute valuable information to the diagnosis of a phytosaur taxon, although the application of the latter is still limited due to incomplete knowledge. The tooth morphology suggests that the more derived, tripartite phytosaur dentition is differentiated functionally into greatly enlarged anterior teeth probably used to kill smaller prey instantly by stabbing, strong posterior premaxillary teeth to seize and subdue large-sized prey, and trenchant posterior maxillary teeth to effectively dismember larger prey items.

ISSN:0272-4634    

DOI:10.1671/0272-4634(2000)020[0031:HITEPN]2.0.CO;2

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Protosuchus haughtonifrom the Lower Jurassic Stormberg series of southern Africa is closely similar to the contemporaneousP. richardsonifrom the Moenave Formation of North America. The taxon is based on two well preserved braincases; the rest of the skull is described here, based on an exceptionally well preserved and virtually complete skull.

ISSN:0272-4634    

DOI:10.1671/0272-4634(2000)020[0049:TSOPHA]2.0.CO;2

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A new species of the genusAraripesuchusfrom the Albian-Cenomanian locality of the El Chocón (Neuquén Province, Argentina) is described. The diagnosis of the genus is reviewed and its phylogenetic placement within Crocodylomorpha discussed.Araripesuchusis proposed here as being the sister taxon of Neosuchia, corroborating previous phylogenetic analysis. The new species,Araripesuchus patagonicus, differs from the type species,A. gomesiiin the relationships of the prefronto-nasal and lachrymo-nasal sutures, the dermal placement of the postorbital bar on the medial side of the jugal, and the greater extension of the squamosals in the skull dorsum. The African species,“Araripesuchus” wegeneri, does not share the diagnostic traits of the genus, and its reassignment to a new genus needs to be considered. The phylogenetic contextof Araripesuchusand “A.”wegeneripermits a reanalysis of the role played by their amphiatlantic distribution in the Aptian-Albian.“Araripesuchus” wegeneriand the South American forms might share a pre-Aptian common ancestor, and have been already differentiated and isolated in the African and South American continents by the time of the Aptian-Albian.

ISSN:0272-4634    

DOI:10.1671/0272-4634(2000)020[0057:ANSOAC]2.0.CO;2

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Re-examination of the surviving specimens ofThecodontosaurus antiquusindicates that this plesiomorphic sauropodomorph can be diagnosed on the basis of elongate basipterygoid processes, a relatively short dentary, and a squared posterior process of the ilium. Although much of the original topotype material found in the 1830s in Bristol, England, has now been lost, some 245 specimens remain. These indicate a small, gracile prosauropod, up to 2.5 m in length, distinguished primarily on the absence of derived characters seen in other prosauropods. Although attempts were formerly made to subdivide the Bristol specimens into several dinosaurian, and other, taxa, most appear to pertain to the prosauropodThecodontosaurus antiquus. The specimens do indicate a clear separation into two morphs, a gracile and a robust form, presumably evidence of sexual dimorphism. A juvenileThecodontosaurussp. from South Wales may belong to the same species. A cladistic analysis indicates that Prosauropoda is probably a clade, rather than a series of outgroups to Sauropoda, but support for this conclusion is weak. Echoing other recent cladistic analyses, stronger support is found for the existence of a clade Sauropodomorpha, made up from Prosauropoda + Sauropoda, for the clade Sauropoda itself, and for the clade Eusauropoda within Sauropoda.

ISSN:0272-4634    

DOI:10.1671/0272-4634(2000)020[0077:AASOTP]2.0.CO;2

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Sauroposeidon proteles, a new brachiosaurid sauropod, is represented by an articulated series of four mid-cervical vertebrae recovered from the Antlers Formation (Aptian–Albian) of southeastern Oklahoma. Most Early Cretaceous North American sauropod material has been referred toPleurocoelus, a genus which is largely represented by juvenile material and is not well understood. Regardless of the status and affinities ofPleurocoelus, the new taxon is morphologically and proportionally distinct. Among well-known sauropod taxa,Sauroposeidonis most similar toBrachiosaurus; particularly noteworthy are the neural spines, which are set forward on the centra and are not bifurcate, and the extremely elongate cervical ribs.SauroposeidonandBrachiosaurusalso share a derived pattern of pneumatic vertebral ultrastructure and a mid-cervical transition point, at which neural spine morphology changes from very low (anteriorly) to very high (posteriorly). Autapomorphies ofSauroposeidoninclude posterior placement of the di apophyses, hypertrophied pneumatic fossae in the lateral faces of the neural spines and centra, and an extraordinary degree of vertebral elongation (e.g., C8 = 1.25 m; 25% longer thanBrachiosaurus). Additional sauropod material from the Early Cretaceous Cloverly Formation may be referrable to the new Oklahoma sauropod, which appears to be the last of the giant North American sauropods and represents the culmination of brachiosaurid trends towards lengthening and lightening of the neck.

ISSN:0272-4634    

DOI:10.1671/0272-4634(2000)020[0109:SPANSF]2.0.CO;2

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Ontogenetic changes in the bone histology ofMaiasaura peeblesorumare revealed by six relatively distinct but gradational growth stages: early and late nestling, early and late juvenile, sub-adult, and adult. These stages are distinguished not only by relative size but by changes in the histological patterns of bones at each stage. In general, the earliest stages are marked by spongy bone matrix with large vascular canals. Through growth, the cortical bone differentiates into fibro-lamellar tissue that tends to become more regularly layered in the outer cortex. By the sub-adult stage, lines of arrested growth (LAGs) begin to appear regularly. Resorption lines and substantial Haversian substitution in many long bones also begin to appear at this stage, and the external cortex has a lamellar-zonal structure in some bones that indicates imminent cessation of growth.

ISSN:0272-4634    

DOI:10.1671/0272-4634(2000)020[0115:LBHOTH]2.0.CO;2

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor