Upper Cambrian (Sunwaptan) linguliform brachiopods from the Notch Peak Formation of Utah and equivalent strata in Texas.

摘要

Bulk samples collected from the Upper Cambrian (Sunwaptan) Hellnmaria Member of the Notch Peak Formation in Utah and the Upper Cambrian--Ordovician (Sunwaptan--Skullrockian) Wilberns and Tanyard Formations in Texas have yielded faunas of linguliform brachiopods that include many new taxa. Two new genera and eight new species are described. A new genus is proposed for species originally assigned to Angulotreta Palmer, 1954. In Utah, the stratigraphic ranges of several previously described species are extended. The two collections allow biostratigraphic correlation within Laurentia as well as globally. New zonation based on linguliform brachiopods is proposed for the Sunwaptan and lower Skullrockian stages of North America.;The Hellnmaria Member was deposited in a deep subtidal environment with possible access to the open ocean. The Utah fauna has affinities to coeval faunas in Kazakhstan and includes Zhanatella rotunda Koneva, 1986. This species was described previously from Kazakhstan as well as the Montagne Noire region of France and has potential for global biostratigraphy.;In Texas, collections from the Taenicephalus and lower Idahoia trilobite zones yielded a fauna with little affinity to brachiopods at a similar stratigraphic position in Utah but with strong affinity to a fauna from the same interval in Wyoming. Upper Sunwaptan and lowest Skullrockian strata yielded a fauna with close affinities to the Utah fauna. There is complete turnover of linguliform fauna in coincidence with two trilobite extinction events.;A lingulate specimen from the Hellnmaria Member exhibits a repair scar on its larval shell. Because lingulate brachiopod larvae are planktotrophic, the individual is interpreted to have been part of the pelagic realm at injury. The injury consists of a visible break and several areas of damage to the exterior of the shell, all consistent with damage done deliberately by a predator. This implies that durophagous predation was a part of the planktic realm during the Cambrian, and that the planktic realm was more modern in its structure than previously realized. This suggests that brachiopods may have been under predation pressure as larvae as well as adults, and this pressure may have played a role in their evolution and extinction.