Article: A euthycarcinoid arthropod from the Silurian of Western Australia
Kenneth J. McNamara and Nigel H. Trewin
The Euthycarcinoidea is a superclass of the arthropod phylum Uniramia and one of the rarest groups of fossil arthropods. Only seven species in five genera have been described, from rocks of Late Carboniferous age in France and the USA, and of Middle Triassic age in France and eastern Australia. Here, a much older euthycarcinoid, from a mixed sequence of fluviatile and aeolian sandstones of probable Late Silurian age in Western Australia, is described as Kalbarria brimmellae gen. et sp. nov. Because of their uniramian affinities, it has previously been suggested that euthycarcinoids may be the closest ancestral relatives of hexapods. Although previous evidence had indicated that the earliest hexapod predated the earliest euthycarcinoid, the discovery of a euthycarcinoid about 120 million years older than the previous oldest record, and predating the oldest known hexapod, provides strong support for the view that the hexapods may have evolved from the Euthycarcinoidea. A model illustrating euthycarcinoid origins from myriapods, and hexapod origins from euthycarcinoids is proposed, based on paedomorphic loss of appendages.