Abstract
Originally considered as large, solely Cambrian apex predators, Radiodonta—a clade of stem-group euarthropods including Anomalocaris—now comprises a diverse group of predators, sediment sifters and filter feeders. These animals are only known from deposits preserving non-biomineralized material, with radiodonts often the first and/or only taxa known from such deposits. Despite the widespread and diverse nature of the group, only a handful of radiodonts are known from post-Cambrian deposits, and all originate from deposits or localities rich in other total-group euarthropods. In this contribution, we describe the first radiodont from the UK, an isolated hurdiid frontal appendage from the Tremadocian (Lower Ordovician) Dol-cyn-Afon Formation, Wales, UK. This finding is unusual in two major aspects: firstly, the appendage (1.8 mm in size) is less than half the size of the next smallest radiodont frontal appendage known, and probably belonged to an animal between 6 and 15 mm in length; secondly, it was discovered in the sponge-dominated Afon Gam Biota, one of only a handful of non-biomineralized total-group euarthropods known from this deposit. This Welsh hurdiid breaks new ground for Radiodonta in terms of both its small size and sponge-dominated habitat. This occurrence demonstrates the adaptability of the group in response to the partitioning of ecosystems and environments in the late Cambrian and Early Ordovician world.
Highlights
Lower Palaeozoic strata known for the exceptional preservation of lightly sclerotized or soft-bodied faunas (Konservat-Lagerstätten), deposited during the Cambrian and Early Ordovician (540–480 Ma), provide crucial information on the phylogenetic, morphological and ecological diversity patterns of early animals in marine environments (e.g. [1,2,3,4])
Radiodonts, a group which includes the large apex predator Anomalocaris, are among the best-known animals from these early ecosystems [5,6,7,8,9,10,11,12,13]. This diverse group of stem-group euarthropods is known from deposits ranging from China (e.g. [15,16,17,18,19,20]) to North America (e.g. [7,12,13,21,22,23,24,25,26,27,28,29]), Europe [25,30,31], North Africa [32,33] and Australia [34,35,36], reflecting the widespread nature of these nektonic animals across different palaeocontinents from the equator to the poles
The description of a miniature hurdiid from an Ordovician Konservat-Lagerstätte in Wales is the first report of a radiodont from palaeocontinent Avalonia and the modern-day UK
Summary
Lower Palaeozoic strata known for the exceptional preservation of lightly sclerotized or soft-bodied faunas (Konservat-Lagerstätten), deposited during the Cambrian and Early Ordovician (540–480 Ma), provide crucial information on the phylogenetic, morphological and ecological diversity patterns of early animals in marine environments (e.g. [1,2,3,4]). [7,12,13,21,22,23,24,25,26,27,28,29]), Europe [25,30,31], North Africa [32,33] and Australia [34,35,36], reflecting the widespread nature of these (mostly) nektonic animals across different palaeocontinents from the equator to the poles On account of their lightly sclerotized frontal appendages, head sclerites and mouthparts, which sit anterior to a segmented body with lateral swimming flaps, radiodonts are often among the first animals described from Konservat-Lagerstätten Hurdiids sometimes have one to three podomeres with reduced endites distal to the five large-endite-bearing podomeres, and the distal podomeres reduce substantially in size compared with the tall rectangular podomeres in the proximal region [24,26,27,28,29]
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