Sidneyia is an extinct marine arthropod known from fossils found from the Early to the Mid Cambrian of China and the Mid Cambrian Burgess Shale of British Columbia, Canada. It is thought to have been a durophagous (crushing) predator that used its spine-covered leg bases (gnathobases) to feed on hard-bodied animals like trilobites and brachiopods, as well as possibly soft bodied animals. It was historically placed in the group "Xenopoda" alongside Emeraldella. It is now placed within the clade Vicissicaudata along with aglaspidids, chelonellids, as well as Emeraldella, among others. Vicissicaudata forms part of the broader group Artiopoda, which includes trilobites.
Description
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File:Sidneyia size comparison.svg|Size comparison of Sidneyia species
File:Bicknell et al. 2018 Sidneyia inexpectans.png|Biramous limb of Sidneyia inexpectans Key: basipod with gnathobasic spines (green) exopod (orange), endopod (blue)
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Sidneyia inexpectans reached lengths of at least . The head shield is short, with notches present on the sides to accommodate stalked eyes, with the underside having a hypostome. The head has a pair of segmented antennae, as well as three pairs of post-antennal appendages. This was followed by a thorax, which had eight to ten segments/tergites, each associated with a pair of biramous (two branched) appendages, this was followed with one to three abdomen segments/tergites, with the body terminating with a telson, which comprised a pair of tail flukes. In S. minor, the biramous appendages have 8 podomeres/segments on the endopod (the inner leg like branch), with the last segment being a terminal claw. The exopod (the outer branch) of these limbs is flattened and bears lamellae.
Taxonomy
thumb|Reconstruction of Sidneyia minor
Sidneyia was discovered in 1910 during the first day of Charles Walcott's exploration of the Burgess Shale. He named it after his elder son, Sidney, who had helped to locate the site and collect the specimen. The species name, Sidneyia inexpectans, is derived from the meaning of "Sidney's surprise".
144 specimens of Sidneyia are known from the Greater Phyllopod bed, where they comprise 0.27% of the community.
Sidneyia sinica was named in 2002 from a specimen found in the Chengjiang Biota of South China. However, it has since been rejected from the genus, and other indeterminate specimens assigned to the genus from the Spence Shale and Sirius Passet lack key diagnostic characters. Specimens that can confidently assigned to the genus include Sidneyia cf. inexpectans, known from the Wuliuan Mantou Formation of North China, Sidneyia minor from the Early Cambrian (Cambrian Stage 3) Xiaoshiba Biota of Yunnan, China,
Cladogram of Artiopoda including Sidneyia after Berks et al. 2023.
Cladogram of Vicissicaudata after McCoy et al. 2025:
See also
- Paleobiota of the Burgess Shale
- Paleobiota of the Maotianshan Shales