Olympidytes

Content sourced from Wikipedia, licensed under CC BY-SA 3.0.

Olympidytes is an extinct genus of plotopterids, a family of large, flightless marine birds that looked like penguins but were more closely related to cormorants and gannets. It lived during the Late Eocene to Early Oligocene in what are now Washington state (USA) and Japan. The first remains were found in 2012: a partial skeleton from the Lincoln Creek Formation in Washington, and another specimen from the Makah Formation. In 2016, Mayr and Goedert named Olympidytes thieli after the holotype SMF Av 608. In 2021, a fragment from Japan was tentatively referred to as cf. Olympidytes sp. Today, Olympidytes is the only known tonsalin plotopterid genus found on both sides of the Pacific.

Olympidytes was comparatively small for a plotopterid, about the size of its relative Tonsala. Its tail bones (the pygostyle) resemble those of penguins more than modern wing-propelled divers, which fits the idea that the tail helped on land. The femur was long and stout, and the holotype tibiotarsus was complete and robust; the referred foot bone (tarsometatarsus) lacked a distal foramen, a trait shared with Klallamornis and suggesting a close relationship. A cf. Olympidytes sp. from Japan may represent another species. A distinctive trait of Olympidytes is the absence of a deep groove near a muscle attachment on the leg bone, helping to identify the genus. Like related birds, Olympidytes swallowed pebbles (gastroliths). A well-developed tibial trochlea hints at adaptations for leg-propelled diving, suggesting Olympidytes and its relative Hokkaidornis could have used both leg and tail-wing propulsion. Throughout the Late Eocene to Early Oligocene seas, Olympidytes lived alongside Klallamornis abyssa and Klallamornis clarki. The discovery of remains in both North America and Asia makes Olympidytes the only plotopterid genus known from both sides of the Pacific, and its diversity, along with other plotopterids, may have been influenced by global cooling at the Eocene–Oligocene boundary, which increased ocean nutrients and plankton.