Wikipedia is your friend:
Tones
See also: Four tones
The Qieyun classified characters in four parts according to their tone: even tone (píngshēng 平聲), rising tone (shǎngshēng 上聲), departing tone (qùshēng 去聲), and entering tone (rùshēng 入聲). The "entering tone", also known as a "checked tone", actually refers to syllables characterized by a final stop consonant (/p/, /t/, or /k/) rather than a distinct pitch.[48]
It is difficult to determine the exact contours of the other tones. Karlgren interpreted the names literally as level, rising and falling pitches, respectively.[48] The oldest known description of the tones is found in a Song dynasty quotation from the early 9th century Yuanhe Yunpu 《元和韻譜》 (no longer extant): "Level tone is sad and stable. Rising tone is strident and rising. Departing tone is clear and distant. Entering tone is straight and abrupt."[m]
Every topolect has their own ancient Chinese as well. For example 四川话 has 蜀语 as its "Classical Chinese" - so your assumption that ancient Chinese is root of all modern Chinese would be wrong. Chinese has a lot of variants - that does not mean that they stem from each other or that they are strictly speaking even dialects.
入声 was originally considered a tone - it is your so-called "coda" as you can see from the quote from Wikipedia above. This can still be found in a few Sinitic topolects today, which you obviously already know.