Vetulicolians from the Lower Cambrian Sirius Passet Lagerstatte, North Greenland, and the polarity of morphological characters in basal deuterostomes

Vetulicolians are problematic Cambrian fossils with a debated phylogenetic history. Here, we describe two vetulicolian specimens from the Lower Cambrian Sirius Passet locality in North Greenland. One of the specimens is assigned to Ooedigera peeli gen. et sp. nov, whereas the other is retained under open nomenclature. The mode of tail flexibility has been debated in the literature, and we argue here that the tail normally flexed laterally to generate power strokes rather than dorsoventrally. The phylogenetic relationships of vetulicolians are discussed in the light of current knowledge of deuterostome phylogeny and morphology, and it is concluded that the best hypothesis on currently available evidence is that vetulicolians are a clade or paraphyletic assemblage of stem-Deuterostomata. The presence of a voluminous, sediment-filled anterior chamber suggests that the atrium may be a synapomorphy of deuterostomes.