In my next ATU (non-OTU) I'll probably use the Celirans, a race of warm-blooded, egg-laying sentient "lizard-birds" who have evolved from
theropods transplanted from Earth to what has later become their homeworld of Renya by a long-extinct alien race about 70 million years ago (as part of a hunting preserve). Celirans are a bit smaller than Humans, have green skin with soft scales, large yellow (or orange in some cases) eyes and a long, flexible prehensile tail (which is also a bit useful when swimming). They are bipeds but don't exactly walk upright (their pelvis is similar to those of their theropod ancestors or to that of birds - they walk bent forward from a Human perspective). They have bird-style legs and three fingers in each hand (one opposing two). They also have a crest of feathers on their heads and a bunch of feathers at the tip of their tail. They also have chirpy voices and are better singers than humans on average (especially the males).
Courtship in their ur-species was similar to that of songbirds - the female chose the male: the more colorful a male was and the better he sang, the greater chances he had to find a mate. As a sentient species, of course, interpersonal relations vary from this, but the biological adaptations for this form of courtship remain: males and females have the same muscle mass; males have chirpier voices than females and sing better than them; and males are more colorful than females (all of these taken together was the source for some embarrassing incidents when the first Human explorers reached Renya). As both parents could roost and feed the young (originally with chewed insects and fruits; in modern times with a mash of insects and fruits made in a blender or bought ready), family structure tends to vary more greatly between Celiran cultures than between different Human cultures (as except for laying the eggs, both Celiran parents could fill the same rules). Most Celiran societies are slightly matriarchal, but not overly so, though religious leaders are almost always female (among other things, due to the fact that psionics manifest only in females in this species, and were known since a very early period in their history). Their most common religion is the faith in Meya Enna ("One Mother"), a monotheistic agrarian (originally, that is) goddess; Renya itself is a constitutional theocracy with the Council of Matriarchs sharing power with the elected Assembly. There are, of course, other religions (as well as multiple sects within this faith), most notably shamanic faiths, some of which have been adopted (in a modern form) by Celiran spacers.
Celirans have evolved in a swamp-forest, and are well adapted to eating insects, fish and soft fruits: they have many small, very sharp teeth. Due to their terragen origin, they could easily eat some Earth foods, though they find most kinds of meat - not to mention cereals and most "harder" baked goods - quite hard to chew; also, as non-mammals, they are incapable of digesting lactose.
In that ATU, Celirans are considered a "Minor Race" by the main Human polity because they've received jump technology from Humans. However, this title is a bit unfair as Celirans had space exploration when Humans were struggling with early gunpowder weapons, interplanetary colonies when Human naval exploration was just beginning, and interstellar STL sleeper-ships when Humans have barely invented the first primitive steam-engines. However, for various reasons, they haven't invented gravitics or jump-drives for centuries and were limited to TL8 and early TL9 for that time. This has several implications. First, while they had no gravitics or jump-drives, they have a long history of perfecting interplanetary and interstellar STL craft and had many research advances in the fields of life-support, hydroponics, medicine and cryogenics (and their low-berths are better than Human ones even today). Second, their ship design paradigm is still very influenced by the needs of pre-gravitics ships (they have gravitics only for a century or so), with engines places "below" the decks rather than at the ship's "rear", with unstreamlined large ships using aerodynamic smaller craft for atmospheric operations, and with a tendency to build distributed-structure ships and modular ones. Third, Celiran spacers had quite a long time to develop their own sub-culture, as without FTL there was a huge amount of space colonization in the Renya system rather than just colonizing planets and moons. Fourth, Celiran gravitics and jump-drives, reverse-engineered from Human tech, typically lag a bit behind the current Human tech (they have the same ranges but less efficiency). And fifth, there is a number of Celiran worlds settled by STL sleeper-ships, many of which had quite a time to develop their own cultures (and national identity in some cases).