Doctor of Philosophy
Dr. Jisuo Jin
This thesis, which examines the evolution of the Late Ordovician (early Katian) brachiopod fauna of Ontario, consists of two main parts: 1) a case study of the Late Ordovician Rhynchotrema–Hiscobeccus lineage of North America to investigate the morphological variations and evolutionary trends of brachiopod fauna in time and space, 2) the paleobiogeography of early Katian brachiopod fauna to explore their distribution patterns at a global scale and controlling factors.
During the Katian, the North American craton experienced a first-order marine transgression. The early stage of this event in the early Katian (Trentonian, Chatfieldian) was marked by the development of extensive new habitats for the origin and radiation of brachiopods and other shelly benthos in epicontinental seas.
Multivariate analysis, based on nine biometric characters of 171 Late Ordovician rhynchonellide specimens from nine localities in North America, demonstrated quantitatively that Hiscobeccus mackenziensis, as the earliest form of Hiscobeccus, evolved transitional characteristics between Rhynchotrema and the typical Hiscobeccus.
During the late Katian (Maysvillian and Richmondian), Hiscobeccus diversified into larger, more globular, and more strongly lamellose shells, especially in the paleoequatorially located inland marine basins. The diversification and morphological trends in the Hiscobeccus lineage are interpreted as the result of adaptation to an environment with relatively shallow, muddy substrates, and low oxygen with unsteady nutrient supply in generally overheated epicontinental seas.
Cluster and principal component analyses based on 33 brachiopod faunas of early Katian age, including 252 rhynchonelliform genera, revealed four global distinct faunal provinces, including Kazakhstan, Avalonia, epicontinental Laurentia, and Scoto-Appalachia. The late Darriwilian–early Katian brachiopod faunas of Laurentia show close similarities to those faunas of Siberia, Baltica, and other adjacent tectonic plates and terranes which indicate their semi-cosmopolitan distribution.
During the early Katian, the Scoto-Appalachian brachiopod fauna, had a closer affinity to the brachiopod faunas along the western margins of Laurentia, whereas the early Katian brachiopod fauna of the intracratonic region in Laurentia had a closer affinity to the brachiopod fauna from the platform facies of Baltica than to those in pericratonic Laurentia.
The brachiopod faunas exhibit strong provincialism during the late Katian, as the brachiopod fauna of Laurentia differentiated from those of Siberia, Kazakhstan, and South China. The faunal endemism within Laurentia was controlled by paleoecological factors related to tectonic events such as the Taconic Orogeny, as well as other factors such as paleolatitudinal faunal gradient, and varying substrate types.
Sohrabi Hashjin, Akbar, "The Trentonian (Late Ordovician) brachiopod fauna of Ontario: Evolution through a global warming event" (2013). Electronic Thesis and Dissertation Repository. Paper 1175.