Tesselacauda, Ross, 1951

Adrain, Jonathan M. & Karim, Talia S., 2019, Revision of the Early Ordovician (late Tremadocian; Stairsian) cheirurid trilobite Tesselacauda Ross, with species from the Great Basin, western USA, Zootaxa 4661 (2), pp. 201-255 : 216

Tesselacauda n. sp. A

( Plate 12 , figs 13–16, 18–29)

Material. Assigned specimens SUI 147587–147594, from Section MME 36.4m, Fillmore Formation (upper Tremadocian; Stairsian; Rossaspis leboni Zone ), southern Confusion Range, Ibex area, Millard County, western Utah.

Discussion. Specimens retrieved from Section MME 36.4 m are from lower in the same zone as those of T. morrisoni . The sample from MME 36.4 m is in general fragmentary and sparse, but most species seem to occur also in the assemblage at MME 49.8 m. The Tesselacauda specimens, however, definitely do not belong to T. morrisoni . The dorsal pygidial surfaces of most specimens are almost completely effaced, and lack the clusters of tubercles on the distal parts of the pleurae which characterize T. morrisoni . The terminal piece, while relatively large, is about as wide as it is long, whereas those of pygidia of T. morrisoni are much longer than wide. The MME 36.4 m material seems to represent a poorly known but distinct species, the oldest member of the genus thus far recovered.

Figures

PLATE 12. 1–12, 17. Tesselacauda morrisoni n. sp., from Section MME 49.8 m, Fillmore Formation (upper Tremadocian; Stairsian; Rossaspis leboni Zone), Middle Mountain, Ibex area, Millard County, western Utah, USA. 1, 4, 6, 11. Thoracic segment, SUI 147584, dorsal, anterior, posterior, and left lateral views, x10. 2, 3, 5, 7, 9. Thoracic segment, SUI 147585, right lateral, dorsal, ventral, anterior, and posterior views, x8. 8, 10, 12, 17. Thoracic segment, SUI 147586, dorsal, posterior, anterior, and left lateral views, x10. 13–16, 18–29. Tesselacauda n. sp. A, from Section MME 36.4 m, Fillmore Formation (upper Tremadocian; Stairsian; Rossaspis leboni Zone), Middle Mountain, Ibex area, Millard County, western Utah, USA. 13. Cranidial fragment (probably from same individual as fig. 14), SUI 147587, dorsal view, x7.5. 14. Cranidial fragment (probably from same individual as fig. 13), SUI 147588, dorsal view, x7.5. 15. Pygidium, SUI 147589, dorsal view, x15. 16, 20, 21. Pygidium, SUI 147590, dorsal, right lateral, and posterior views, x12. 18. Pygidium, SUI 147591, dorsal view, x12. 19, 23, 24. Pygidium, SUI 147592, dorsal, posterior, and right lateral views, x15. 22, 28, 29. Pygidium, SUI 147593, dorsal, posterior, and left lateral views, x12. 25–27. Pygidium, SUI 147594, posterior, right lateral, and dorsal views, x12.