Browsing by Author "Bordy, Emese"

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    From grains to tracks: high-resolution sedimentology of track-bearing Stormberg strata, southern Africa
    (2023) Mpangala, Loyce Elesia; Abrahams, Miengah; Bordy, Emese
    Tracks registration is influenced by the dynamic interplay between the pedal anatomy of the trackmaker, its behaviour, and the substrate conditions it interacts with. Differences in substrate conditions, especially those linked to grain size and moisture content, often result in the most dramatic variations in track morphology. In the upper Stormberg Group, main Karoo Basin of southern Africa, diverse trace fossils, primarily comprising Upper Triassic– Lower Jurassic dinosaur tracks, are preserved. Extensive studies have been carried out to document these individual tracksites and to examine the variations between sites and through time, with recent studies suggesting that track abundance and anatomical fidelity increase up-stratigraphy. Despite the well-established understanding of the effects of substrate on track registration and preservation, these past studies have not specifically focused on the substrate conditions, and when substrate conditions were considered, the emphasis was primarily on macro-sedimentary features. Here, we examine the microsedimentary features of track-bearing units in the upper Stormberg Group using petrographic techniques, to better understand the palaeosubstrate and its effect on fossil track registration and preservation. The analysis revealed that very fine-grained sands and substrates modified by microbial activity tend to preserve tracks with greater abundance and higher anatomical fidelity. Furthermore, the prevalence of very fine-grained and microbially modified strata, and their associated track trends, increases in younger stratigraphic units. Across the Triassic– Jurassic boundary of southern Africa, there was a proliferation of dinosaur populations, possibly linked to the end–Triassic mass extinction events, which has been credited globally for track abundance increases in the Lower Jurassic. However, our findings suggest that, locally, the observed increase in track abundance (and anatomical fidelity) up-stratigraphy may also be linked to substrate–composition differences, which were ultimately controlled by large-scale changes in the palaeoenvironment from high-energy meandering fluvial to lowerenergy aeolian-lacustrine settings in the Late Triassic and Early Jurassic, respectively
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    The sauropodomorph biostratigraphy of the ElliotFormation of southern Africa: Tracking the evolution ofSauropodomorpha across the Triassic–Jurassic boundary
    (2017) McPhee, Blair; Bordy, Emese; Sciscio, Lara; Choiniere, Jonah
    The latest Triassic is notable for coinciding with the dramatic decline of many previously dominant groups, followed by the rapid radiation of Dinosauria in the Early Jurassic. Among the most common terrestrial vertebrates from this time, sauropodomorph dinosaurs provide an important insight into the changing dynamics of the biota across the Triassic–Jurassic boundary. The Elliot Formation of South Africa and Lesotho preserves the richest assemblage of sauropodomorphs known from this age, and is a key index assemblage for biostratigraphic correlations with other similarly-aged global terrestrial deposits. Past assessments of Elliot Formation biostratigraphy were hampered by an overly simplistic biozonation scheme which divided it into a lower “Euskelosaurus” Range Zone and an upper Massospondylus Range Zone. Here we revise the zonation of the Elliot Formation by: (i) synthesizing the last three decades’ worth of fossil discoveries, taxonomic revision, and lithostratigraphic investigation; and (ii) systematically reappraising the stratigraphic provenance of important fossil locations. We then use our revised stratigraphic information in conjunction with phylogenetic character data to assess morphological disparity between Late Triassic and Early Jurassic sauropodomorph taxa. Our results demonstrate that the Early Jurassic upper Elliot Formation is considerably more taxonomically and morphologically diverse than previously thought. In contrast, the sauropodomorph fauna of the Late Triassic lower Elliot Formation remains relatively poorly understood due to the pervasive incompleteness of many key specimens, as well as the relative homogeneity of their diagnostic character suites. Our metrics indicate that both Elliot Formation and global sauropodomorph assemblages had greater morphological disparity within the Early Jurassic than the Late Triassic. This result is discussed in the context of changing palaeoclimatic conditions, as well as macroevolutionary events associated with the end-Triassic extinction.