Trimerellida

Trimerellida is an extinct order of craniate brachiopods, containing the sole superfamily Trimerelloidea and the families Adensuidae, Trimerellidae, and Ussuniidae. Trimerellidae was a widespread family of warm-water brachiopods ranging from the Middle Ordovician ("Llandeilo" / Darriwilian) to the late Silurian (Ludlow). Adensuidae and Ussuniidae are monogeneric families restricted to the Ordovician of Kazakhstan. Most individuals were free-living, though some (namely Australian populations of the genus Eodinobolus) clustered into large congregations similar to modern oyster reefs.

== Evolution == Trimerellides probably originated from tropical island arcs in the region of Kazakhstania (present-day Kazakhstan) during the "Llandeilo" (late Darriwilian stage). By the late Sandbian and early Katian stages, many dispersed eastward to nearby regions equivalent to South China and Australia. A few managed to populate the vicinity of Laurentia (North America), possibly through its diminishing proximity to the Australian portion of Gondwana. By the late Katian, trimerellides had also dispersed westward, populating the seas around Baltica (eastern Europe), Scotland, and Siberia. Trimerellides were an exclusively tropical group, with most genera endemic to a specific region. There are some exceptions: Eodinobolus and Monomerella were particularly widespread, found at low-latitude ecosystems worldwide. At their acme in the late Katian, trimerellides reached the highest diversity ever seen among craniiform brachiopods, forming a significant component of brachiopod assemblages worldwide.