Isoxys(Arthropoda) with preserved soft anatomy from the Sirius Passet Lagerstätte, lower Cambrian of North Greenland

Abstract

M. 2010: Isoxys (Arthropoda) with preserved soft anatomy from the Sirius Passet Lagerstätte, lower Cambrian of North Greenland. Lethaia, Vol. 43, Isoxys volucris is the most commonly occurring species in the lower Cambrian Sirius Passet Lagerstätte of North Greenland. Newly identified material allows a first, limited, account of the ventral morphology of this species, hitherto known only by the morphology of its shield. The antennula is large and robust, composed of about seven articles armed with spines, and was probably not sensorial. The postantennular limbs are serially similar, biramous with a large paddle-shaped exopod fringed with setae. It is possible that the animal possessed a furca. The inner lamella, lining the ventral surface of the shield is recognised in Isoxys for the first time. Comparisons with other congeneric species of which aspects of the ventral morphology are known, show similarities with Isoxys auritus from China, reconsidered here, but indicate differences in antennular morphology with other species as currently understood. h Cambrian, Greenland, Isoxys, soft anatomy, Sirius Passet, palaeoecology.

Molaria (Euarthropoda) from the Sirius Passet Lagerstätte (Cambrian Series 2, Stage 3) of North Greenland

“…9), this might imply that the setae forming the setal fringes were more robust than the articles and the absence of exopod and endopod branches is a preservational artifact. However, the distribution of the setae in Molaria steini agrees with the reconstruction made by Stein & Selden (2012) despite the absence of recognized limb branches. Lamellae of Stein & Selden (2012, fig.…”

“…However, the distribution of the setae in Molaria steini agrees with the reconstruction made by Stein & Selden (2012) despite the absence of recognized limb branches. Lamellae of Stein & Selden (2012, fig. 9) diverging from article 1 of the exopod in E. brocki can be compared to long, straight setae in M. steini (arrows a in Fig.…”

“…Whittington (1981, p. 341) noted specimens of M. spinifera where the connecting segment had been forced diagenetically under the posterior trunk tergites and therefore not visible, but there is no evidence of this having occurred in available specimens of M. steini. Stein & Selden (2012) discussed previous interpretations of the segment that occurs between the 11 th trunk tergite and the telson in Emeraldella brocki Walcott, 1912 from the Burgess Shale. They noted that this segment was more elongate than more anterior tergites and had much reduced tergopleurae, but considered it to be a 12 th trunk tergite.…”

“…Stein & Selden (2012) reported 12 tergites in the type species Emeraldella brocki Walcott, 1912 from the Burgess Shale Lagerstätte, of which the elongate 12 th tergite had much reduced tergopleurae. Only 11 tergites are present in E. brutoni Stein, Church & Robison, 2011 from the Wheeler Shale of Utah.…”

“…Similar traces of limbs through the shield are visible in Naraoia compacta Walcott, 1912(Whittington 1971with Haug & Haug 2016) from the Burgess Shale. In a model of exopod structure such as the reconstruction of the exopod branch of limbs of Emeraldella brocki made by Stein & Selden (2012, fig. 9), this might imply that the setae forming the setal fringes were more robust than the articles and the absence of exopod and endopod branches is a preservational artifact.…”