Abstract The Khabt-el-Hajar Formation, very rich in bryozoans and echinoderms but relatively poor in other fossil groups, has provided a brachiopod association that allows an improvement in the stratigraphic correlation of this Moroccan eastern Anti-Atlas unit with those from the Upper Ordovician of SW Europe and the rest of the Anti-Atlas. The intermediate marly beds, with bryozoan and echinoderm patches, of the Khabt-el-Hajar Formation have yielded Streptis ? sp., Paucicrura catalanica and Drabovia sp. Of these, P. catalanica , the richest in the association and known up to now exclusively from the Catalonian Coastal Ranges in NE Spain, is dated as mid to late Katian (Ka2–Ka4), since it occurs in the La Mora Slates, correlatable with horizons of that age from Iberia, Sardinia or the Montagne Noire. The analysis of the stratigraphic and palaeobiogeographical ranges of the bryozoans from the same formation agrees with the correlation above. The quartzitic sandstones that underlie the Khabt-el-Hajar Formation in the surroundings of Erfoud have yielded a different brachiopod association, including Kiaeromena ? chouberti and Rostricellula termieri among other forms more poorly represented. K. ? chouberti allows its yielding horizon to be dated as mid Katian (Ka2) and supports the identification of the sandstone-dominated unit where it occurs as the Tiouririne Formation.

Abstract The phylogeographical evolution and the consequent changing distribution and diversity of rhynchonelliform brachiopods through the Ordovician are linked to the dynamic palaeogeography of the period. The Early Ordovician (Tremadocian and Floian) is characterized by globally low-diversity faunas with local biodiversity epicentres, notably on the South China Palaeoplate; low-latitude porambonitoid-dominated faunas with early plectambonitoid and clitambonitoid representatives, as well as high-latitude assemblages mostly dominated by orthoids, can be recognized, but many taxa are rooted in Late Cambrian stocks. The Early Ordovician displays a steady increase in rhynchonelliformean biodiversity, which was mostly driven by the increasing success of the Porambonitoidea and Orthoidea, but the billingsellids and early plectambonitoids also contributed to this expansion. During the Early to Mid Ordovician (Dapingian–Darriwilian), marine life experienced an unprecedented hike in diversity at the species, genus and family levels that firmly installed the suspension-feeding benthos as the main component of the Palaeozoic fauna. However, this may have occurred in response to an early Darriwilian annihilation of existing clades, some of which had been most successful during the Early Ordovician. New clades rapidly expanded. The continents were widely dispersed together with a large number of microcontinents and volcanic arcs related to intense magmatic and tectonic activity. Climates were warm and sea-levels were high. Pivotal to the entire diversification is the role of gamma (inter-provincial) diversity and by implication the spread of the continents and frequency of island arcs and microcontinents. The phylogeographical analysis demonstrates that this new palaeogeographical configuration was particularly well explored and utilized by the strophomenides, especially the Plectambonitoidea, which radiated rapidly during this interval. The porambonitoids, on the other hand, were still in recovery following the early Darriwilian extinctions. Orthides remained dominant, particularly at high latitudes. Biodiversity epicentres were located on most of the larger palaeoplates, as well as within the Iapetus Ocean. Provincial patterns were disrupted during the Sandbian and early Katian with the migration of many elements of the benthos into deeper-water regimes, enjoying a more cosmopolitan distribution. Later Katian faunas exhibit a partition between carbonate and clastic environments. During the latest Katian, biogeographical patterns were disrupted by polewards migrations of warm-water taxa in response to the changing climate; possibly as a consequence of low-latitude cradles being developed in, for instance, carbonate reef settings. Many clades were well established with especially the strophomenides beginning to outnumber the previously successful orthides, although this process had already begun, regionally, in the mid to late Darriwilian. At the same time, atrypoid and pentameroid clades also began to radiate in low-latitude faunas, anticipating their dominance in Silurian faunas. The Hirnantian was marked by severe extinctions particularly across orthide-strophomenide clades within the context of few, but well-defined, climatically controlled provincial belts. Supplementary material: The individual localities and a reference list for the data sources are provided at: http://www.geolsoc.org.uk/SUP18667