Kiisortoqia soperi, Stein, 2010, Stein, 2010

Stein, Martin, 2010, A new arthropod from the Early Cambrian of North Greenland, with a ‘ great appendage’ - like antennula, Zoological Journal of the Linnean Society 158 (3), pp. 477-500 : 497

AFFINITIES OF KIISORTOQIA SOPERI GEN. ET SP. NOV.

Kiisortoqia soperi gen. et sp. nov. exhibits three characters that are considered to be part of the ground pattern of Euarthropoda ( Waloszek et al., 2007).

1. A head incorporating the antennular plus three limb-bearing segments.

2. Postantennular limbs with a rigid, anteroposteriorly flattened, spine-bearing basipod, extended mediodistally into the endopod, and carrying the exopod on its lateral sloping edge.

3. A flap-like exopod fringed with setae.

Consequently, K. soperi gen. et sp. nov. rests comfortably within the Euarthropoda. The position within Euarthropoda, however, is difficult to resolve because of the many plesiomorphies of K. soperi gen. et sp. nov. The potential absence of eyes and the trilobate, semicircular tail shield may represent autapomorphies. None of the known arthropod taxa with ‘great appendages’ has such a tail shield, but a somewhat similar tail can be found in trilobite-like taxa, where it frequently includes limb-bearing segments, forming the pygidium. Apart from the tail shield, there is, however, no character that would support the affinities of K. soperi gen. et sp. nov. with trilobites or allied taxa. According to Chen et al. (2004) and Maas et al. (2004), the large, potentially raptorial antennula may represent a synapomorphy with Chelicerata, but a true raptorial function remains speculative, and a mere function in food gathering of the antennula is considered to be a ground-pattern character of Arthropoda s.s., retained e.g. in the ground pattern of Crustacea ( Waloszek et al., 2007). Scholtz & Edgecombe (2006) considered even a large, raptorial antennula to be part of the ground pattern of Euarthropoda, although this assumption is based partly on equivocal data from Fuxianhuia protensa (see above). Resolving the phylogenetic position of anomalocaridids should help to settle this issue, but their phylogenetic position remains controversial ( Chen et al., 2004; Scholtz & Edgecombe, 2006), mainly because of the insufficient preservation of the material available. The phylogenetic position of K. soperi gen. et sp. nov., therefore, cannot be resolved at present.