 Subjects -> PALEONTOLOGY (Total: 46 journals)
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- Robert “Bob” Lynn Carroll (1938 - 2020)
Authors: Michael Caldwell, Hans Larsson
Pages: 1 - 6
Abstract: NA
PubDate: 2020-05-04
DOI: 10.18435/vamp29364
Issue No: Vol. 8 (2020)
- CSVP Abstracts 2020
Authors: Alison M Murray, Victoria Arbour, Robert Holmes
Pages: 7 - 66
Abstract: n/a
PubDate: 2020-05-05
DOI: 10.18435/vamp29365
Issue No: Vol. 8 (2020)
- A subadult individual of Styracosaurus albertensis (Ornithischia:
Ceratopsidae) with comments on ontogeny and intraspecific variation in
Styracosaurus and Centrosaurus.
Authors: Caleb Brown, Robert Holmes, Phillip Currie
Pages: 67 - 95
Abstract: Styracosaurus albertensis is an iconic centrosaurine horned dinosaur from the Campanian of Alberta, Canada, known for its large spike-like parietal processes. Although described over 100 years ago, subsequent discoveries were rare the last few decades, during which time several new skulls, skeletons, and bonebeds were found. Here we described an immature individual, the smallest known for the species, represented by a complete skull and fragmentary skeleton. Although ~80% maximum size, it possesses a suite of characters associated with immaturity, and is regarded as a subadult. The ornamentation is characterized by a small, recurved, but fused nasal horncore; low, rounded postorbital horncores; and short, triangular, and flat parietal processes. Using this specimen, and additional skulls and bonebed material, the cranial ontogeny of Styracosaurus is described, and compared to Centrosaurus. Styracosaurus shows a similar early ontogeny of the nasal horncore, starting thin, recurved, and unfused, but retains the recurved morphology into large adult size, and never develops the procurved morphology common in Centrosaurus. The postorbital horncores of Styracosaurus are lower and more rounded than those of Centrosaurus throughout ontogeny, and show greater resorption later in ontogeney. The length and thickness of the parietal processes increase drastically through ontogeny, but their position and orientation are static across the size series. Several diagnostic Styracosaurus albertensis specimens now preserve medially orientated P3 spikes, causing issues for the diagnosis of S. ovatus. Variability in parietal ornamentation, either expression of P1 and P2 parietal processes, or other cranial ornamentations, does not appear to correlate with stratigraphy.
PubDate: 2020-05-11
DOI: 10.18435/vamp29361
Issue No: Vol. 8 (2020)
- A New Specimen of Xiphiorhynchus sp. cf. aegyptiacus (Istiophoriformes,
Xiphioidei, Xiphiidae) and Billfish Diversity in the Oligocene of South
Carolina
Authors: William McCuen, Aika Ishimori, Robert Boessenecker
Pages: 98 - 104
Abstract: A partial billfish rostrum from the Chandler Bridge Formation (Early Chattian, Oligocene) near Ladson, South Carolina, U.S.A., is described and identified as Xiphiorhynchus sp. cf. aegyptiacus. The angle of taper, depth to width ratio of the cross section, and other morphological features (including dorsolateral grooves and a planoconvex cross-section), indicate that this specimen (and an earlier published speccimen) is closest in morphology to X. aegyptiacus from the Eocene Birket Qarun Formation of Egypt. This confirms the presence of a second xiphiid in the Chandler Bridge Formation besides the well-documented giant swordfish X. rotundus. This is an unusual example of two Xiphiorhynchus species existing in known sympatry, and strongly contrasting morphologies and morphometrics may point to niche partitioning between the two forms. The occurrence of specimens strongly resembling X. aegyptiacus in the western Atlantic also further substantiates past arguments that easy dispersal across the Atlantic was possible for this genus, and, by extension, that it shared the open-sea, migratory epipelagic lifestyle of modern swordfish. Moreover, the Chandler Bridge Formation boasts the most diverse billfish assemblage in the world, including Xiphiorhynchus sp., cf. X. aegyptiacus, X. rotundus, an early istiophorid, and 4-7 species of blochiid billfish in the genera Aglyptorhynchus and Cylindracanthus.
PubDate: 2020-07-13
DOI: 10.18435/vamp29367
Issue No: Vol. 8 (2020)
- Caenagnathids of the Dinosaur Park Formation (Campanian) of Alberta,
Canada: anatomy, osteohistology, taxonomy, and evolution
Authors: Gregory Funston
Pages: 105 - 153
Abstract: Our understanding of caenagnathid anatomy, diversity, and ecology has improved considerably in the past twenty years, but numerous issues still remain. Among these, the diversity and taxonomy of caenagnathids from the Dinosaur Park Formation of Alberta, Canada, have remained problematic. Whereas some authors recognize three genera, others suggest only two were present, and there is considerable disagreement about which specimens are referable to which genus. This study aims to resolve this issue by reviewing the known specimens and using osteohistology, to establish a testable taxonomic framework of Dinosaur Park Formation caenagnathids. Numerous new specimens from all regions of the skeleton provide insight into morphological variation in caenagnathids, and three morphotypes are recognized based on a combination of morphological features and body size. Osteohistology shows that representatives in each body size class are at skeletal maturity, and therefore supports the delineation of three taxa: the smaller Citipes elegans gen. nov., the intermediate Chirostenotes pergracilis, and the larger Caenagnathus collinsi, new material of which shows it rivalled Anzu wyliei in size. However, these analyses also raise concerns about the referral of isolated material to each taxon in the absence of skeletal overlap between specimens or osteohistological analysis. Caenagnathids are consistently recovered throughout the Dinosaur Park Formation interval, and two geographic clusters of increased abundance probably reflect collection and taphonomic biases. The coexistence of three taxa was apparently facilitated by differences in both adult body size and functional morphology of the dentary and pes, which suggests that caenagnathids minimized niche overlap rather than subdividing niche space. Regardless, little is known of the exact roles caenagnathids played in Late Cretaceous ecosystems. Incorporation of the new material and taxonomic framework into a phylogenetic analysis drastically improves our understanding of the relationships between caenagnathines, and sheds light on the evolution of body size in caenagnathids and its role in their diversification.
PubDate: 2020-07-27
DOI: 10.18435/vamp29362
Issue No: Vol. 8 (2020)
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