This is an interesting idea, although it poses the question of why female water deer grow canines, albeit it typically only very small ones, given that upper and lower canines are lost in almost all female ungulate species in which the males use them in combat (e.g. In her 2020 paper to PeerJ, Museum für Naturkunde Berlin biologist Nicola Heckeberg suggests that the presence, and possibly also the size, of upper canines is genetically linked with antlers, such that the underlying mechanism prompting their development is the same for both structures. Comparison of the tusk of the Reeve's muntjac (left) and Chinese water deer (right), the only two of Britain's deer exhibiting enlarged canines. As deer grew larger and more sociable, they could ill afford to do each other serious damage as wounds could draw predators to the herd, so antlers evolved as a way of managing largely bloodless combat. Furthermore, for a largely antisocial group, small weapons that could inflict maximum damage on an opponent without risking being tangled among tall vegetation were perfect. Writing in the Journal of Mammalian Evolution during 2020, Doreen Cabrera and Theodore Stankowich point out that tusks are a better choice of weapon for the smaller, slinking artiodactyls that live in well-vegetated environments with low visibility, while larger species inhabiting more open ground can bear the cost of elaborate headgear.

That said, however, Bedfordshire-based deer manager Paul Childerley has come across a few does with reasonably well-developed canines on his ground, although it should be mentioned that this is uncommon (see: Sexing). Instead, tusks seem primarily a weapon of territorial combat in this species, having evolved in lieu of antlers, and are consequently sported primarily by the males. While it is conceivable that the canines evolved for use in general defence, water deer make no obvious attempt to fight back when caught by humans or dogs. The skull of a mature Chinese water deer buck illustrating enlarged upper canines (tusks). Leaving aside the musk and mouse deer, both of which grow large canines but, despite their deer-like appearance, aren't true deer, the presence of such hypertrophied dentition is uncommon among the Cervidae, Hydropotes being one of only three members of the family sporting them the others being the muntjacs ( Muntiacus spp.) and the Chinese tufted deer ( Elaphodus cephalophus), native to northeast Myanmar and southern and central China. Chinese water deer don't hold the vernacular name of “vampire deer” for nothing, and it's perhaps the enlarged canines, commonly referred to as tusks or (incorrectly, given that they neither inject nor suck liquid) “fangs”, for which they are best known.

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