According to a statement from Iona, Anna Holm Baumeister placed 55th out of 157 runners during the Sunday morning race.
The gold medalist, Kenya's Jemina Jelagat, finished the marathon 15:45 earlier, according to Iona.
Baumeister was the second Danish finisher and 25th European overall.
Baumeister's performance was the third and final performance for a former Iona runner in Rio.
Germany's Maya Rehberg finished 15th in her heat in the women's 3,000-meter steeplechase preliminary round Saturday morning while the United States' Leonard Korir finished 14th in the men's 10,000-meter final Saturday night.
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