New camerate crinoid genera from the Upper Ordovician (Katian) of Estonia: evolutionary origin of family Opsiocrinidae and a phylogenetic assessment of Ordovician Monobathrida

Abstract

Most major crinoid clades first appear in the fossil record during the Ordovician, but the evolutionary origins of many higher taxa remain unresolved. Here, the first camerate crinoids from the Katian (Upper Ordovician) of Estonia with complete calyces are described. Phylogenetic analyses are conducted to determine the affinities of two new genera and to assess the evolutionary origins of the families Opsiocrinidae (Diplobathrida) and Glyptocrinidae (Monobathrida). Sakucrinus krossi gen. et sp. nov. is identified as the earliest known member of Opsiocrinidae and demonstrates that: (1) the family originated much earlier than was previously assumed; (2) features previously considered plesiomorphic for the family are instead derived; and (3) the family is likely closely related to the Dimerocrinitidae. Family Pachycephalocrinidae fam. nov. is established to accept the monocyclic glyptocrinid Pachycephalocrinus jaanussoni gen. et sp. nov. Pachycephalocrinus jaanussoni displays morphological features that are unique among monobathrid crinoids, including a large periproct in the calyx side. Inclusion of Pachycephalocrinus in the first phylogenetic analysis focusing on Ordovician monobathrid crinoids elucidates evolutionary relationships among Ordovician monobathrids and calls into question the validity of superorder Compsocrinina. The new genera described here provide important insight into the timing of origination and morphological diversity of higher taxa during the early evolutionary history of camerate crinoids.

http://zoobank.org/urn:lsid:zoobank.org:pub/28B337ED-1008-40CD-8B86-51DAD81B45F6

Keywords:

• systematics
• Echinodermata
• Baltica
• Sakucrinus
• Pachycephalocrinus

Acknowledgements

Funding to SRC was provided through an Ohio State University Presidential Fellowship and a Smithsonian Institution Springer Postdoctoral Fellowship. We thank S. K. Donovan and J. Sprinkle for thoughtful reviews of the manuscript, and D. F. Wright for comments on an early draft. This paper is a contribution to the International Geoscience Programme (IGCP) Project 653 The onset of the Great Ordovician Biodiversification Event.

Data archiving statement

Data for this study are available in the Dryad Digital Repository: https://doi.org/10.1080/14772019.2018.1447519

Additional information

Funding

United Nations Educational, Scientific and Cultural Organization