Tulaneia amabilia, a new erniettomorph from the Wood Canyon Formation, Nevada and the age of the Ediacaran-Cambrian transition in the Great Basin

Specimens of Tulaneia amabilia n. gen n. sp. [previously Ernietta
plateauensis Pflug] discovered by RJH in 1991 at a site in the Montgomery
Mountains near Johnnie, Nevada, are described for the first time. All of
the material from the original locality was from float, but its
stratigraphic position was clearly within the lowest siliciclastic to
dolostone interval of the lower member of the Wood Canyon Formation
(LMWCF); this was confirmed by subsequent discoveries. As the upper part
of the LMWCF contains Treptichnus pedum (Seilacher), the
Ediacaran-Cambrian boundary has long been drawn at its first appearance.
However, in the Esmeralda Member of the Deep Spring Formation in the
White-Inyo Mountains, California and at Mount Dunfee, Nevada, another
Cambrian ichnofossil—‘Plagiogmus’ [now Psammichnites gigas arcuatus
(Roedel)]—is found just beneath the nadir of the basal Cambrian isotope
excursion (BACE). As the nadir of the BACE excursion is older than ~539 Ma
in Mexico, the oldest occurrences of Treptichnus pedum in the LMWCF are
latest—not earliest— Fortunian in age, and there is no need to reduce the
age of the eon boundary from ~539 to ~533 Ma. Tulaneia resembles Ernietta
and other erniettomorphs in being composed of tubular modules with planar
common surfaces, but its overall shape was tabular and unidirectional
rather than sack or frond shaped. We also illustrate and briefly describe
other trace and body fossils from the LMWCF and re-illustrate previously
published specimens of Psammichnites gigas arcuatus in order to document
its earliest occurrence in the Great Basin.