Agglutinated tubes as a feature of Early Ordovician ecosystems

Abstract

Agglutinated tubes are produced by a variety of marine organisms. Such tubes will readily break down after the death of the producer, and hence are likely to be found only in deposits with rapid burial and/or exceptional preservation. Here we document agglutinated tubes from four localities of Early Ordovician age. The Lower Ordovician (upper Tremadocian) Afon Gam Biota of North Wales, UK, contains a diverse fossil assemblage including algae, worms, sponges, hyoliths, tergomyans, echinoderms, trilobites, and other arthropods. The biota also includes locally abundant agglutinated tubes composed largely of echinoderm fragments, in particular glyptocystitid (including Macrocystella) stem and brachiole ossicles. The tube producer appears to have preferentially selected echinoderms for use in tube building, with trilobites and tergomyans only rarely incorporated in the tubes. These tubes are named Echinokleptus anileis n. gen. n. sp. Similar tubes, although incorporating individual echinoderm ossicles rather than complete animals, occur in the Lower Ordovician (lower Floian) Tonggao Formation of South China. Possible additional agglutinated tubes are found in the Tremadocian–Floian Fezouata Shale of Morocco; these examples are composed of a range of bioclasts including echinoderm remains and hyolithids. Further possible tubes composed of mixed shelly material were observed in the Floian Landeyran Formation, Montagne Noire, France. The occurrence of morphologically similar agglutinated tubes on different continental blocks and at different palaeolatitudes indicates that the group responsible (inferred to be a polychaete annelid) was diversifying as part of the Great Ordovician Biodiversification Event, and similar interpretations should be considered for problematic bioclastic accumulations elsewhere.