Well, first clarification, it could sound contradictory "I want a humanoid shape that not looks like a common human", well for this reason I thought necessary say what I consider "humanoid", simply a stickman shape, you know just a head above a neck of part of a "vertical" column connected with a hip with two legs under, sure we can change this a few, for example add or remove arms or change the posture but this in general traits is what I will consider humanoid.
There is already similar questions but I could not find this specific, something like viability of humanoid non primate humanoids" or What will the abdominal muscles of non-primate humanoids look like? and a little bit less related with facial musculature of humanoid reptiles
So I am gonna explain, the human sexual dimorphism characteristics which I want discard.
For males is easier, just problems with muscle and fat distribution, for example (till where I know) mammals have a bigger concentration of fat and muscle at the scapular girdle, that permits the hump from bison, the strong for felids are the arms and pectoral muscles from apes, in difference with birds (dinosaurs had this concentration at the pelvic girdle) that have a very different distribution or amphibian and reptiles that are very uniform with this.
The problem is bigger with females, usually fantasy artists just add breasts without nipples and the curvy body shape caused by the fat the hips. So this give two options or justify why these characteristics are present or find other way to have sexual dimorphism.
First I will mention why the breasts and hips are not an option (till now) if I want something more "realistic", so the secondary function, at apes the growing of the breasts and the hips is an indicator of ovulation then for humans is an indicator of a constant ovulation, but this happens for the primary function, lactation, indicating a good health for provide the breast milk to the babies, something that comes hand in hand with a suitable mouth of the young to be able to consume the food without harming their mother.
So maybe I can let this happen for other mammal humanoids, but not for snake-women, "mermaids" or "harpies" and I honestly don't know how to denote that they are different from the males of their species. I don't think that add breast can have sense without the initial presence of nipples and with the hips I said I do not know how change the fat and muscle distribution keeping some of the most interesting characteristics.
The first option that I will mention is justify a reason for why this animals developed "human-like breasts and nipples", not my favorite, but I saw a very interesting justification at the anatomically correct arachne, the pluckedkiwi's answer in which explains why this arthropods evolved for a convergent shape with humans but for very different reasons, removing the secondary use for breasts and using very different structures for nipples. Anyways this still needing many other characteristics.
And the other option is find other visual/anatomical characteristic that can show which is the male and which is the female, there are some examples like different colors (like paradise birds or peacocks, maybe are not for reptiles or fishes) or sizes, this last I thought is ambiguous. And I will not like something like pokemon's "gender" differences, like "oh yea, males have two black lines at the nape and the females just one".
So in short what I want is:
- Should be an anatomical feature.
- A way to difference between female and male humanoid animals.
- In this case just for reptiles, amphibians, birds and fishes.
- Should be visual enough notorious for not be explained many times.
- Alternative way, a some scientific justification of why keep the human characteristics (breasts and hips principally or pectoral muscles).
- Keep the majority of the most notorious characteristics from initial species, for example flying for birds or swimming for fishes