Evolution of the Rhynchotrema–Hiscobeccus lineage: implications for the diversification of the Late Ordovician epicontienntal brachiopod fauna of Laurentia.

چکیده مقاله

the Late Ordovician mass extinction was the first mass extinction in Phanerozoic life history. This mass extinction Eliminated 49-60% of marine genera and nearly 85% of marine species. More than 50% of the brachiopods and bryozoans in North America were wiped out and biodiversity recovered rapidly in the Early Silurian. Brachiopods became extinct at the onset of the Hirnantian glaciation (casualties of the first extinction pulse). The latest Ordovician Mass Extinction is partly the result of a mass dying of the epicontinental marine fauna that evolved during the great Late Ordovician marine transgression (just before the latest Ordovician glaciation). Previous qualitative studies have indicated that Hiscobeccus most likely evolved from Rhynchotrema during the early Katian and developed a large, globular and strongly lamellose shell. The quantitative multivariate analysis in this study based on 171 rhynchonellide specimens (Rhynchotrema and Hiscobeccus) from nine upper Sandbian–upper Katian localities in North America provided strong support for the hypothesis and demonstrated that the earliest Hiscobeccus, H. mackenziensis, exhibits transitional characteristics between Rhynchotrema and the typical Hiscobeccus. The shells of this early form cluster more closely with Rhynchotrema than with younger species of Hiscobeccus of Maysvillian–Richmondian age.