SILURIAN (LLANDOVERY) CRINOID FAUNAS FROM ANTICOSTI ISLAND, QUEBEC

Silurian strata on Anticosti Island record the thickest, most complete Llandovery succession that contains relatively common crinoids. These strata were deposited in a shallow-water, mixed carbonate-siliciclastic setting that supported an abundant and diverse benthic fauna. For the first time, crinoids have been systematically sampled through this section. With other faunas, new Anticosti material provides the opportunity to examine the recovery of crinoids following the end-Ordovician extinctions. This juncture was a macroevolutionary change for crinoid faunas. Crinoid calyxes are known from all Silurian formations on Anticosti Island, except the Merrimack Formation.

The Rhuddanian fauna (Becscie Formation through Merrimack Formation) consists of 10 species. Only two species cross the Ordovician-Silurian boundary, with the higher diversity in the Fox Point Member, Becscie Formation (earliest Rhuddanian). The majority of the genera are “holdovers” from the Rawtheyan with Dendrocrinus, Protaxocrinus, Xenocrinus, and a rhodocrinitid. However, new genera belonging to the Dimerocrinitidae and Paramelocrinidae are representative of the camerate expansion yet to come.

The Aeronian fauna (Gun River Formation through Richardson Member, Jupiter Formation) has 14 species. The highest diversity is in the Goéland Member, Jupiter Formation. This fauna has a Silurian character with a dimerocrinitid, carpocrinid, stipatocrinid, dendrocrinids, and Eomyelodactylus.

The Telychian fauna (Cybele Member, Jupiter Formation through Chicotte Formation), has the richest crinoid fauna with 30 species. It is composed of representatives of typical Silurian faunas, including dimerocrinitids, Abacocrinus, Eucalyptocrinites, patelliocrinids, stipatocrinids, dendrocrinids, botryocrinids, cyathocrinids, crotalocrinitids, taxocrinids, Eomyelodactylus, and Parapisocrinus, with the highest diversity in the Chicotte Formation. Although still undergoing rapid radiation, the Middle Paleozoic Crinoid Macroevolutionary Fauna was already established by the middle Llandovery.