This is the offering … and rams’ skins dyed red, and sealskins (Exod. 25:3). R. Judah and R. Nehemiah discussed this verse. R. Judah said: It was a large pure animal, with a single horn in its forehead and a skin of six different colors that roamed the desert. They captured one of them and from its skin made a covering for the ark. R. Nehemiah contended that it was a miraculous creature He created for that precise moment, and that it disappeared immediately thereafter from earth. Why is it called orot tahashim (“sealskins,” lit. “skins of tahashim”)? Because the verse states: The length of each curtain shall be thirty cubits (Exod. 26:8).
What known animal could supply enough skin for a curtain of thirty cubits? It must, indeed, have been a miraculous creation, which disappeared (immediately after it was created).