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      New small-bodied ornithopods (Dinosauria, Neornithischia) from the Early Cretaceous Wonthaggi Formation (Strzelecki Group) of the Australian-Antarctic rift system, with revision of Qantassaurus intrepidus Rich and Vickers-Rich, 1999

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          Abstract

          The Flat Rocks locality in the Wonthaggi Formation (Strzelecki Group) of the Gippsland Basin, southeastern Australia, hosts fossils of a late Barremian vertebrate fauna that inhabited the ancient rift between Australia and Antarctica. Known from its dentary, Qantassaurus intrepidus Rich and Vickers-Rich, 1999 has been the only dinosaur named from this locality. However, the plethora of vertebrate fossils collected from Flat Rocks suggests that further dinosaurs await discovery. From this locality, we name a new small-bodied ornithopod, Galleonosaurus dorisae n. gen. n. sp. from craniodental remains. Five ornithopodan genera are now named from Victoria. Galleonosaurus dorisae n. gen. n. sp. is known from five maxillae, from which the first description of jaw growth in an Australian dinosaur is provided. The holotype of Galleonosaurus dorisae n. gen. n. sp. is the most complete dinosaur maxilla known from Victoria. Micro-CT imagery of the holotype reveals the complex internal anatomy of the neurovascular tract and antorbital fossa. We confirm that Q. intrepidus is uniquely characterized by a deep foreshortened dentary. Two dentaries originally referred to Q. intrepidus are reassigned to Q. ? intrepidus and a further maxilla is referred to cf. Atlascopcosaurus loadsi Rich and Rich, 1989. A further ornithopod dentary morphotype is identified, more elongate than those of Q. intrepidus and Q. ? intrepidus and with three more tooth positions. This dentary might pertain to Galleonosaurus dorisae n. gen. n. sp. Phylogenetic analysis recovered Cretaceous Victorian and Argentinian nonstyracosternan ornithopods within the exclusively Gondwanan clade Elasmaria. However, the large-bodied taxon Muttaburrasaurus langdoni Bartholomai and Molnar, 1981 is hypothesised as a basal iguanodontian with closer affinities to dryomorphans than to rhabdodontids.

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          On the Classification of the Fossil Animals Commonly Named Dinosauria

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            Homology of facial structures in extant archosaurs (birds and crocodilians), with special reference to paranasal pneumaticity and nasal conchae

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              Time resolution in fluvial vertebrate assemblages

              Calibrating levels of time resolution that are accessible in the fossil record is important in understanding what evolutionary phenomena can be profitably studied using fossils. A model for attritional bone assemblage formation in fluvial deposits, based on observations of taphonomic processes in modern environments, provides order-of-magnitude estimates for time intervals represented in single unit, ‘contemporaneous' vertebrate samples. In order to form units with adequate material for analysis of morphological variation or paleoecological associations, it appears that bones must be spatially concentrated or stratigraphically condensed by sedimentary processes or biological agencies. In many cases this means that significant periods of time will be represented by single unit assemblages. According to predictions from modern environments, carcasses contributed through normal attrition can accumulate in the soil to ‘fossiliferous' densities over time intervals of 102–104 yrs. Attritional channel assemblages include bones from three sources: floodplain land surfaces, floodplain deposits, and the active channel, and represent time intervals on the order of 102–104 yrs. Given additional limitations on the composition of the fossil sample imposed by circumstances of preservation, outcrop availability and collecting strategy, attritional fluvial assemblages probably can be resolved only to 103 years even under the best conditions. Time intervals represented by fossils are not necessarily the same as those represented by sedimentary events in fluvial systems because bones can continue to accumulate and may be concentrated during times of erosion or non-deposition. Fluvial vertebrate assemblages of comparable taphonomic history can be used to document evolutionary changes over periods longer than their finest level of time resolution. While they may not be applicable to questions of punctuated or gradual transitions over shorter time scales, the longer-term patterns should have their own evolutionary significance.
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                Author and article information

                Journal
                applab
                Journal of Paleontology
                J. Paleontol.
                Cambridge University Press (CUP)
                0022-3360
                1937-2337
                March 11 2019
                : 1-42
                Article
                10.1017/jpa.2018.95
                8ac05841-04e9-4825-9006-256d88832660
                © 2019

                http://creativecommons.org/licenses/by/4.0/

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