Jars of tiny platypus and echidna specimens, collected in the late 1800s by the scientist William Caldwell, have been discovered in the stores of Cambridge's University Museum of Zoology.
source https://www.lifetechnology.com/blogs/life-technology-science-news/museum-discovers-150-year-old-platypus-and-echidna-specimens-that-proved-some-mammals-lay-eggs