The Kugel Celestial Globe, an antique silver celestial globe dated to the second or third century A.D., shows Boötes holding two dogs. However the dogs are engraved rather crudely compared to many of the other constellations so perhaps they were added at a later time. Unless the Kugel globe canines were added very much later (and there is no reason to assume that they were added after Johannes Stöffler's dogs of 1493) they represent the earliest known depiction of Boötes' dogs that I know of. Kugel Celestial Globe at the Galerie J. Kugel.
Top Drawing: The Dolphin of the Ancients taken near (symbol) Line, called by our seamen a Porpus.
Bottom Drawing: A Dolphin as it is usually called by our seamen taken in the open sea.
- from "A Voyage to New - Holland, &c. In the Year 1699" by Captain William Dampier.
There is infrequently some confusion between Hevelius' alternative name for this constellation, Tigris, with the name of an obsolete Plancius constellation called Tigris flu (ie. fluvius, meaning river). These two Tigris constellations were totally different and were located in opposite regions of sky.
The word monoceros is from the Greek, monokeros, meaning one horn. This constellation name is often misspelled as Monocerus (note the 'u' instead of an 'o'). If after reading the pdf download you are curious about the Unicorn Tapestries you can find out more about them here.
There is some argument as to who should get credit for the 12 new southern constellations that were first published on a celestial globe in late 1597 or early 1598. The candidates include Plancius (see 'Who's Who'), Keyser (see 'Who's Who), Houtman (see 'ETC' in Tucana), Pieter Stockmans (ref. Globi Neerlandici, page 153), and Vechter Willemsz (ref. Filling the Sky, page 39). I credit Plancius and Keyser because although many people may have been involved in the effort the only aforementioned names to appear on the published globe are those of Plancius and Keyser. Keyser's fellow observers are collectively referred to as "other students..." Modern writers variously credit the new southern constellations to either: 1) Plancius, 2) Keyser, 3) Plancius and Keyser, 4) Keyser and Houtman, 5) Plancius, Keyser and Houtman, or 6) Plancius, Keyser, Houtman, and others. [By the way, I do not have the source at hand for the inclusion of Vechter Willemsz but if I ever get around to it I will look into my old notes to find out where I got his name from.]