Secondary Sexual Characteristics are elements of a creature's physiology that result from it being male or female. It is one step removed from "primary sexual characteristics" (which describes the actual reproductive organs). For example, everyone knows that only male lions have that iconic mane of fur around their neck, and that only male mallard ducks have a green head; it is one of their species' Secondary Sexual Characteristics.
Many times, fictional creatures are based on some manner of RealLife inspiration, and whether or not they have noticeable sexual dimorphism corresponds to whatever inspiration they came from -- if one author decides to [[CallARabbitASmeerp call a lion a Smeerp]], it makes sense that male Smeerps might have thick manes while female Smeerps do not, right?
Now a full discussion of these characteristics is [[http://en.wikipedia.org/wiki/Sexual_dimorphism well beyond the scope of this wiki]]; but when dealing with this subject in fiction, it can manifest itself in a variety of ways.
!!Secondary Sexual Characteristic Gender Clues
* AnimalFacialHair: Male individuals with moustaches and/or beards.
* BizarreSexualDimorphism: Sexual dimorphism played to [[UpToEleven such extremes]] that males and females are scarcely recognizable as members of the same species at all. (Can be the result of BizarreAlienBiology.)
* FurryBaldness: Older male induviduals who are bald or balding.
* FurryFemaleMane: Female individuals posessing a head of long, humanlike hair that the corresponding males do not. (A common occurence with [[SlidingScaleOfAnthropomorphism anthropomorphic animals]].)
* HartmanHips: Female individuals posessing wide hips and a narrow waist, but a small bust. (Also common with anthropomorphism.)
* HumanoidFemaleAnimal: Species where members of one sex (typically, the females) are more [[SlidingScaleOfAnthropomorphism anthropomorphized]] than their counterparts.
* ImpossibleHourglassFigure: Female individuals posessing wide hips, a narrow waist, and a large bust. (Also common with anthropomorphism.)
* NonMammalMammaries: Species whose female members have humanlike breasts, regardless of whether or not their species has any need for such things (and, frequently, they don't).
* MasculineLinesFeminineCurves: Females have curvaceous bodies while males have squarer, more angular or straighter bodies.
* PaleFemalesDarkMales: Females are lighter colored than males.
!!Other Gender Clue Tropes
* PinkGirlBlueBoy: A special case of ColorCodedForYourConvenience.
* TertiarySexualCharacteristics: Gender clues supplied by means other than the individual's inherent physiology.
!!Tropes That Get the Secondary Sexual Characteristics of Animals Wrong
No RealLife examples please. Please only list fictional examples that aren't listed in any of the tropes listed here. Anything that fits in any of the tropes listed should be listed in that trope.