Complex sentence: They mainly eat lichens in winter, especially reindeer moss--a unique adaptation among mammals, and they are the only animals except for some gastropods where the enzyme lichenase, which breaks down lichenin to glucose, have been found.
Split into simpler sentences: They mainly eat lichens in winter, especially reindeer moss. A unique adaptation among mammals, and they are the only animals except from some gastropods where the enzyme lichenase, which breaks down lichenin to glucose, have been found.