Pliny the Elder [1st century CE] (Natural History, Book 8, 52): The reindeer [tarandrus] of Scythia also changes its colors... The reindeer [tarandrus] is the size of an ox; its head is larger than that of a stag but not unlike it; it has branching horns, cloven hooves, and a fleece as shaggy as a bear's but, when it happens to be self-colored, resembling an ass's coat. The hide is so hard that they use it for making cuirasses. When alarmed it imitates the colors of all the trees, bushes and flowers and places where it lurks, and consequently is rarely caught. It would be surprising that its body has such variety of character, but it is more surprising that even its fleece has. - [Rackham translation]

Gaius Julius Solinus [3rd century CE] (De mirabilibus mundi / Polyhistor, Chapter 30.25-26): [Chapter 30.25] Aethiopia also engenders the parandrus, which is the size of an ox. It has cloven footprints, branching horns, and a deer-like head. It is the color of a bear, and has equally shaggy hair. This parandrus, it is asserted, changes its shape when alarmed; when it takes cover, it becomes similar to whatever is near to it, be it white like a stone, green like a thicket, or whatever else it prefers. [Chapter 30.26] It is, then, an extraordinary and remarkable thing that the parandrus’ rough hair should give rise to changes in color. Because of this, parandri are difficult to catch. - [Arwen Apps translation, 2011]

Thomas of Cantimpré [circa 1200-1272 CE] (Liber de natura rerum, Quadrupeds 4.88): Pirander, as Solinus says, is a beast of the size of an ox, with branched horns, a stag'shead, a pig's feet, a bear's color, and woolly and matted hair. They affirm that this animal changes its color in a variety of ways, so that when it hides in a place, whether it is a white rock or a green bush, it is changed to their likeness. From this it follows that it can be taken with difficulty - [Badke translation/paraphrase]