29-4 New Drumian deuterostomes from western Utah

Session: Evolution of Life in the Cambrian Seas: Biotic, Biogeochemical, and Sedimentological Contexts (Posters)

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Abstract:

Deuterostomes include major phyla in modern ecosystems such as echinoderms, pterobranchs and chordates, and it is possible to date their origins back to the Cambrian Explosion. Fossil deuterostomes are minor components of Drumian-aged exceptionally preserved biotas in western Utah; although their main diversity and abundance consists mainly of early pterobranchs and echinoderms, deuterostomes in these deposits are also represented by enigmatic forms such as vetulocystids and eldoniids, as wells as recently described chordates. Nuucichthys represents the first soft-bodied stem-group vertebrate in the Cambrian of the American Great Basin Region, whereas Megasiphon is the oldest confirmed tunicate in Laurentia. Here we report the discovery of new deuterostome fossils from the Drumian Wheeler Formation in the Drum Mountains and the Marjum Formation in the House Range of western Utah from the collections at the Utah Museum of Natural History. We confirm the presence of additional tunicates that can be assigned to, or closely related to, Megasiphon based on the presence of a barrel shaped main body bearing a pair of large siphons with a fibrous texture that represent muscle bundles. This specimen extends the occurrence of Megasiphon to the lower Drumian of the Drum Mountains. A second enigmatic taxon features tapering stalk, a discoidal body with a large visceral mass filling most of its upper half, and at least two, multibranched tentacles. The fossil striking similarities with the genus Phlogites from the lower Cambrian Chengjiang biota and to a lesser extent to the vetulocystid Thylacocercus from the Drumian Wheeler strata in the Drum Mountains. Finally, we report a composite specimen with two, possibly three individuals that show the presence of an elongate transversally striated stalk, a long fusiform main body and up to two siphon-like structures. This new taxon is reminiscent of the putative early Cambrian tunicate Shankouclava from Chengjiang in its gross anatomy, although it does possess at least one siphon-like structure. If confirmed this would represent the second ascidiacean-like tunicate known from the Cambrian of North America, and highlights the morphological and ecological conservatism of this clade in deep time.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-8090

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