2514: R Rotunda: ꝛ Oct 30, 2021
There are numerous examples of pairs of letters that get combined into one ligature, which does happen even today. In a sense, that is how the German ß was formed from <S> and <Z>, but as in that case, it's only a specific pair. For a time, a form of writing lower case <r> existed known as the R rotunda which looked like <ꝛ>, and, lacking a line on the left, would be tacked on to letters only if one such like existed, like <d> or even curved lines like after <o>. This was especially used for blackletter, or in other words, the font most associated with the Middle Ages. This helped to develop the modern cursive form of <r> which is notably different to its upper-case or printed counterparts. Indeed, blackletter has some characters which, without prior knowledge, would not be interpretable to a reader today, but this case was notable since there was another form of the letter used for when there was no other letter to apply the r rotunda onto. Because this character was not popular outside blackletter fonts, it more or less fell by the wayside in the 16th century with the overall decline of the script.