An Ordovician variation on Burgess Shale-type biotas

Abstract

The Cambrian Burgess Shale-type biotas form a globally consistent ecosystem, usually dominated by arthropods. Elements of these communities continued into the Early Ordovician at high latitude, but our understanding of ecological changes during the Great Ordovician Biodiversification Event (GOBE) is currently limited by the paucity of Ordovician exceptionally preserved open-marine faunas. Here we clarify the early stages of the GOBE by describing a new open-marine Konservat-Lagerstätte from the Early Ordovician of Wales. The Afon Gam Biota includes many lineages typical of the Cambrian Burgess Shale-type biotas, but the most abundant groups were sponges, algae and worms, with non-trilobite arthropods being unexpectedly rare. Labile tissues occur abundantly in the sponges and are also present in other groups, including brachiopods and hyoliths. Taphonomic biases are considered and rejected as explanations for arthropod rarity; the preserved biota is considered to be an approximation to the original community composition. We note that other exceptionally preserved communities in the Welsh Ordovician are also sponge-dominated, suggesting a regional change in benthic ecology during the early stages of the GOBE.

The Fezouata fossils of Morocco; an extraordinary record of marine life in the Early Ordovician

“…Exceptional preservation in the deeper water deposits of the Llanfallteg Formation (Darriwilian) is rare, but the fauna does include a few Burgess Shale-type taxa (Whittington 1993;Legg & Hearing 2015). The slightly older early late Tremadocian Afon Gam fauna (Botting et al 2015) is from a comparable water depth and palaeolatitude to the Fezouata biota (c. 60°S for Afon Gam, versus c. 65°S for Fezouata; Martin et al 2015). However, the Afon Gam fauna is dominated by algae and Burgess Shale sponge taxa, with other groups being of minor importance.…”

The dawn of a dynasty: life strategies of Cambrian and Ordovician brachiopods

“…However, lingulate brachiopods have been reported from the Ordovician of Wales that display a slim, bulb‐terminating pedicle that is comparable to Cambrian anchoring forms (Botting et al . ). An anchored lifestyle is also frequently shown in palaeoecological reconstructions (McKerrow ; Carrera ; Waisfeld et al .…”

“…Their large, flat shells certainly aided stability and prevented submersion; however, their precise life orientation and degree of facultative motility is still a matter of debate (Rudwick 1970;Richards 1972;Thayer 1975; The rarity of brachiopod soft-part preservation in the Ordovician has impeded recognizing brachiopods that anchor their pedicle in the sediment. However, lingulate brachiopods have been reported from the Ordovician of Wales that display a slim, bulb-terminating pedicle that is comparable to Cambrian anchoring forms (Botting et al 2015). An anchored lifestyle is also frequently shown in palaeoecological reconstructions (McKerrow 1978;Carrera 2000;Waisfeld et al 2003;Harper 2006;Santos et al 2014) and has been suggested for a range of brachiopod genera (Richards 1972;Curry 1981), and it is probable that the lifestyle was common among Ordovician taxa.…”

Three-dimensionally preserved digestive systems of two Cambrian hyolithides (Hyolitha)

“…Most published reconstructions of the internal anatomy of hyolithides preceded the discovery of hyolithide soft-parts and were based on orthothecide anatomy (Marek & Yochelson 1976, Dzik 1980, Missarzhevskiy 1989. Until the present report, hyolithide guts were known only from well-preserved specimens compressed in shale (Babcock & Robison 1988, Mao et al 1992, Butterfield 2003, English & Babcock 2010, Botting et al 2015, Robison et al 2015.…”