The Hirnantian mass extinction is recognized as the first of the “big three” extinctions and, along with the end-Permian and end-Cretaceous events, is the result of an acceleration in biotic extinctions concomitant with a rise in originations. The Hirnantian mass extinction is characterized by high taxonomic impact and within-community extinctions. The Hirnantian mass extinction is also unusual in that (1) it is associated with glaciation, but there is little evidence elsewhere in the younger Phanerozoic that glaciations have been a cause of mass extinction, and (2) there is limited understanding of how glaciation could directly cause mass extinction, particularly in the marine realm. In this review, we argue that coordinated extinctions occurred at the onset and termination of glaciation and were due to climatically induced changes in relative sea level, ocean redox stratification, and sea-surface temperature gradients. These earth system changes resulted in a reduction in prospective niche space, both in the water column and on the seafloor, which in turn led to increased competition and selection pressures, resulting in extinctions where the carrying capacities of particular ecological niches were exceeded. The long-term ventilation of the oceans broke the link between glaciation and mass extinction.

The Ordovician Period (ca. 488–444 Ma) witnessed profound changes in the biodiversity and biocomplexity of marine life, marked by the installation of a benthos dominated by suspension-feeding animals, most notably the brachiopods. The Ordovician brachiopod fauna was dominated by rhynchonelliformeans in contrast to that of the underlying Cambrian System, characterized by a diversity of various non-articulated groups. Over an interval of some 25 m.y., accelerating γ (inter-provincial), β (inter-community), and α (intra-community) diversity was initiated by high diversities among Early Ordovician brachiopod faunas associated with the dispersal of the continents and the high frequency of volcanic arcs and microcontinents (γ diversity). During the Early and Middle Ordovician, community types expanded particularly into deeper water and around carbonate platforms and structures (β diversity). Moreover, during the period the α diversity of individual assemblages increased from <10 species during the Late Cambrian to ~30 in the Late Ordovician, with the canalization of ecological niches and the opportunity for more densely packed communities. The end-Ordovician extinction event was a severe crisis for the more common Ordovician taxa, the orthide and strophomenide brachiopods. Whereas some widespread taxa, characteristic of deep-water environments, survived, many from shallower-water, together with those from the deep shelf and slope, disappeared. The subsequent Silurian fauna became increasingly dominated by atrypide, athyridide, spiriferide, and rhynchonellide brachiopods.

Thirteen species of fossil articulate brachiopod are documented from the Cretaceous and Cenozoic rocks of Jamaica. Dyscritothyris sp. cf. D. cubensis and Terebratulina? sp. are described from the upper Cretaceous; the Cenozoic fauna comprises the rhynchonellide Probolarina? sp., the thecideid Lacazella sp. cf. L. caribbeanensis and the terebratulides Gryphus ? sp., Tichosina sp., Argyrotheca sp. cf. A. barrettiana, A. sp. cf. A. magnicostata, A. sp. 1 and A. sp. 2, Terebratulina sp. cf. T. palmeri, Terebratulina sp., and Hercothyris sp. cf. H. semiradiata.