Phylogenetic position and stratigraphic uncertainty of a new flexible crinoid from the Ordovician–Silurian boundary of Anticosti Island (Quebec, Canada)

Fossil crinoids from the Ordovician–Silurian boundary interval (~ 443.8
million years) are known from relatively few locations worldwide due to a
near-global unconformity that formed from eustatic sea level fall. This
rock record bias has severely hindered study of the timing, magnitude,
biogeographic signature, and extinction mechanisms of the Late Ordovician
mass extinction (LOME). Crinoids underwent a significant faunal transition
between the Late Ordovician and early Silurian that resulted in major
shifts between dominant clades, but the driving mechanisms and precise
timing of this transition remain unclear. Anticosti Island (Quebec,
Canada) preserves one of the few Late Ordovician–early Silurian
successions of highly fossiliferous, shallow-water rocks that includes the
O–S boundary, making fossils from this region instrumental for better
understanding the LOME and Ordovician–Silurian crinoid faunal turnover.
Here, we report on a new flexible crinoid, Anticosticrinus natiscotecensis
n. gen. n. sp., from the Ordovician-Silurian boundary of Anticosti Island.
Phylogenetic analysis of Middle Ordovician-early Silurian flexibles
recovers Anticosticrinus natiscotecensis n. gen. n. sp. as a member of
Family Anisocrinidae. We quantified stratigraphic age uncertainty of A.
natiscotecensis using a Bayesian approach for estimating tip-occurrence
times in a phylogenetic context. Although results do not provide
unequivocal support for the specimen’s precise stratigraphic age, the
maximum a posteriori estimate indicates a late Hirnantian age. Regardless
of its true age, recognition of Anticosticrinus natiscotecensis provides
additional data for evaluating the timing of extinction in flexible
crinoids, their diversification and increasing dominance during the
Silurian, and crinoid faunal turnover between the Ordovician and Silurian.