Aristotle [ca. 350 BCE] (De animalibus Book 9, chapter 32.1-3): The bonassus is found in Pæonia, in Mount Messapius, which forms the boundary between Pæonia and Mædia. The Pæonians call it monapus. It is as large as a bull, and more heavily built; for it is not a long animal... In form it resembles a bull, but it has a mane as far as the point of the shoulder like the horse, but its hair is softer than that of the horse, and shorter. ... Their voice is like that of the ox. Their horns are crooked and bent together, of no use for defense, a span long or a little more, so thick that each of them would hold half a measure or a little more. ... When wounded it retreats, and stays when it can proceed no farther. It defends itself by kicking and ejecting its dung, which it can do to the distance of four fathoms from itself. It uses this means of defense easily and frequently. Its dung is so caustic as to burn the hair from dogs. The dung is only caustic when the creature is disturbed and alarmed. It is not so when undisturbed. - [Cresswell translation, 1887]

Pliny the Elder [1st century CE] (Natural History, Book 8, 16): There are reports of a wild animal in Paeonia called the bonasus, which has the mane of a horse but in all other respects resembles a bull; its horns are curved back in such a manner as to be of no use for fighting, and it is said that because of this it saves itself by running away, meanwhile emitting a trail of dung that sometimes covers a distance of as much as three furlongs, contact with which scorches pursuers like a sort of fire. - [Rackham translation]

Aelianus [170-230 CE] (On the Characteristics of Animals, Book 7, chapter ): There is an animal in Paeonia called Monops, and it is the size of a shaggy bull. Now when this creature is pursued, in its agitation it excretes a fiery and acrid dung, so I am told; and should this happen to fall on any of the hunters, it kills him. - [Scholfield translation]

Gaius Julius Solinus [3rd century CE] (De mirabilibus mundi / Polyhistor, Chapter 40.10-11): [Chapter 40.10] In these parts [Phrygia] an animal called the bonacus is produced. Its head and the body which follows is like that of an ox, except that it has a mane like a horse's. Its horns run back on themselves with such multitudinous winding that if someone bumps against them, he is not wounded. [Chapter 40.11] The protection the forehead denies to this monster is provided by its belly. When it turns to flee, it discharges dung with a quick evacuation of its stomach, for a length of three acres. The heat of the dung burns whatever it touches. Thus it wards off pursuers with its noxious secretion. - [Arwen Apps translation, 2011]

Aberdeen Bestiary [circa 1200 CE] (folio 12r) In Asia an animal is found which men call bonnacon. It has the head of a bull, and thereafter its whole body is of the size of a bull's with the maned neck of a horse. Its horns are convoluted, curling back on themselves in such a way that if anyone comes up against it, he is not harmed. But the protection which its forehead denies this monster is furnished by its bowels. For when it turns to flee, it discharges fumes from the excrement of its belly over a distance of three acres, the heat of which sets fire to anything it touches. In this way, it drives off its pursuers with its harmful excrement.

Thomas of Cantimpré [circa 1200-1272 CE] (Liber de natura rerum, Quadrupeds 4.11; 4.37): [Thomas describes the bonnacon under the names bonachum and hemchires]. [Quadrupeds 4.11] Bonachum is an animal, as Solinus says, having the head of a bull and the body and the mane of a horse, Its horns are so bent back upon themselves that if any one stumbles upon them, he will not be wounded. When this animal turns to flight, by the flow of its stomach it sends dung behind it over the space of one acre, the heat of which burns whoever it touches. With these weapons it subdues its pursuers. This animal signifies good prelates, who have austerity in them like the horns of life, and while they exercise it in their subjects, they do the least harm to their subjects, because they show in themselves to be what they exhort. [Quadrupeds 4.37] Hemchires is an animal from the region of the East, as Aristotle says. It is about the size of a bull, and somewhat resembles it, but long hairs are found in it descending to the shoulders, as in a horse. And the hair itself is softer and shorter than horse hair. And the color of its body is between black and red, but rather inclining towards blackness. Accordingly, the hairs that are on its limbs are like other hairs. The voice of this animal is like the voice of a bull, and its horns are much curved and are not suitable for fighting. The hairs of its forehead part here and there over its eyes. It lacks the upper teeth of a bull. Its legs have sparse hair, and it has horny soles on its feet; and its tail is short in relation to its body. It digs the ground. And it has a very hard skin and endures many blows. Its flesh is very sweet, and for this reason it is pursued by hunters. And when it is pursued, it flees, and sometimes it stops and rests, and when it is weakened, it fights, and in the fight it throws dung for four paces, and this because of fear. But it is an animal with much dung. When the time for the birth of this animal approaches, many animals of the same kind gather around it, and those gather dung to form a wall around the animal. - [Badke translation/paraphrase]

Bartholomaeus Anglicus [13th century CE] (Liber de proprietatibus rerum, Book18.15): Also there is a manner wylde Oxe, that Aristotle libro. 8. cirea finem calleth Bonboricus, and saith, it is a great Beast, as a great Bull, and is lyke a Bull, and hath haire shad on either side on the necke, as it fareth on the haire of an horse: and his haire is more softer than horse haire, and more shorter, and is haired continually unto the eyen, and is some deale redde or citrine, and his voyce is lyke to the voyce of a Bull, & his hornes are some deale redde or citrine, and be some deale crooked: and in to eyther of his hornes, maye halfe the measure that is called Bos, and hath no téeth above, but is toothlesse above, as a Bull: and his legges be not full hairy, but they be lyke to a speare, and is cloven footed, with two clées in one foote: and his tayle is short in comparison to his bodye: and he diggeth the earth, and teareth him in digging, as a Bull doth, and hath an harde skinne, and suffereth well strokes, and his flesh is full swéet, and is therefore hunted and beaten, and flyeth, and resteth when he is hunted, & throweth dirte foure paces from him, & doth so for dread, and houndes that run after him, smell to the dirte: and while the hounds be occupied about such smelling, the beast dyeth and runneth, and passeth farre away. - [Batman]