Tesselacauda Ross 1951

Tesselacauda Ross, 1951

Type species. Tesselacauda depressa Ross, 1951, from the Garden City Formation (late Tremadocian; Stairsian; Bearriverops logani Zone), southeastern Idaho, USA.

Other species. Tesselacauda kriegerae n. sp., Fillmore Formation, western Utah; T. morrisoni n. sp., Fillmore Formation, western Utah; Tesselacauda n. sp. A, Fillmore Formation, western Utah.

Diagnosis. Dorsal exoskeleton relatively flat, only slightly vaulted; anterior border forming a prominent rim; glabella large and broadly subrectangular; hypostome slightly wider than sagittally long, with small lateral spine at shoulder and slightly larger spine at posterolateral corner, entire ventral surface covered with fine, dense tubercles; twelve thoracic segments, anterior and posterior bands equally prominent, with proximal tip of anterior band extended further adaxially than posterior band, pleural furrow deep; pygidium of four segments, pleural tips bluntly terminated, anterior pleural band developed only on first two segments, sculpture of dense granules arranged into distinct rim around pygidial margin.

Discussion. Jell (1985, p. 79, pl. 32, fig. 1) assigned a partial cranidium from the Digger Island Formation (Tremadocian) of Victoria, Australia, to Tesselacauda. Peng (1990, p. 114) reassigned it with question to his new Sinoparapilekia. Boyce and Stouge (1997, p. 188) reported “ Tesselacauda sp. cf. T. depressa ” from the Boat Harbour Formation (Stairsian) of western Newfoundland, Canada, but this occurrence has never been illustrated. It is the only report of the genus from southern Laurentia (in Ordovician geography). Aitken and Norford (1967, p. 194) listed but did not describe “ Tesselacauda sp.” from the middle member of the Survey Peak Formation at Mount Wilson, Banff National Park, Alberta, Canada. The stepped nature of the proximal tips of the anterior and posterior pleural bands on the thorax is included in the diagnosis for Tesselacauda herein and is likely synapomorphic for the group. A more comprehensive examination of other “pilekiine” thoracic segments is planned and will shed light on the extent of this morphology.