The oldest raphe-bearing diatoms: Evidence from the Upper Cretaceous of western and northern Canada

Diatoms, with their unique siliceous cell walls, are among the most successful eukaryotic lineages on Earth. They inhabit virtually every wet environment and are central organisms in aquatic food webs and biogeochemical cycles. A highly diverse number of species with an impressive array of morphological designs have evolved since the late Mesozoic, and especially since the Late Cretaceous. Pennate diatoms comprise the largest clade, and include those forms that evolved a raphe, an advancement that yielded motility and the ability to move across surfaces. We report multiple raphe-bearing freshwater diatoms from two Cretaceous fossil localities in Canada, the Battle Formation in Alberta (67Ma), and the Wombat locality in the Northwest Territories (82 Ma). A new species of the genus Adlafia, A. wolfeii sp. nov., is reported from the Battle Formation. Multiple species of the genus Eunotia were uncovered from the Wombat locality pushing back the minimum earliest age for this taxon by similar to 30 Ma. The discoveries represent two of the oldest known records of raphe-bearing diatoms and support the hypothesis that the raphe evolved in a freshwater environment during the Cretaceous. These new records are placed in context with previous fossil records, and provide new age constraints for use in linking diatom molecular-based phylogenies to the geological record.(c) 2022 Elsevier Ltd. All rights reserved.