If any of you have played in such a group, what was it like? I am going to make this a + thread FYE.
you may want to edit the thread title just to make that as clear as possible, that can get ignored even when it isn't displayed front and centre.
It might not be quite what you were looking for since it's so unusual. I ran a 3.5 campaign where everyone was a dragon hatchling (different varieties) with advancement in regular PC class/PrC levels once they bought off their level adjustment.To me, parties composed of mixed species seem to be the norm in D&D, as each player wants to role-play as their favorite species. But are there any examples out there where a group decided to role-play as members of the same species?
. The most fun for everyone was the way it let me creatively word noc behavior in ways that leaned into the differences (No not fear/scared/terrified... Prey like/adrenaline scented/etc) and use skill checks to do the same in reverse sometimes. Once it started to click with everyone that sometimes started going both ways even when doing it would obviously result in the party arguing about how Bob is scaring the cheer-leader(elder mayor duke whatever) with an effort to reassure him by "slinking around him I'm kind of a c shape so he feels less vulnerable with a dragon protecting his back and sides from unseen predators lurking in the shadows that prey always fears" while another tries to reassure him that they consider him worthy of a quick death and would never let it happen slowly in an effort to calm the poor prey-leader. Nature of predators kinda gets into some of that "we are the aliens and holy crap we are bizarre" cultural misunderstanding but with omnivorous humans instead of apex predator carnivorous dragons & I highly recommend it both as a story as well as ways of widening interspecies interaction gaps to the players 
To me, parties composed of mixed species seem to be the norm in D&D, as each player wants to role-play as their favorite species. But are there any examples out there where a group decided to role-play as members of the same species?
It's cool.It might not be quite what you were looking for since it's so unusual. I ran a 3.5 campaign where everyone was a dragon hatchling (different varieties) with advancement in regular PC class/PrC levels once they bought off their level adjustment.
The physical limitations were a shock to a couple players who showed up wanting to world a weapon of some form other than claws/bite/breath, but there were a lot of interesting monstrous and draconic feats that allowed weapon using classes to dial it up in unique & interesting ways that wouldn't normally be an option. The players were often significantly hindered by not being able to use silver/cold iron/etc weapons and sometimes needed to accept that or work around it in creative ways.
Beyond the mechanical differences it allowed a rather fun theme where the party was always the alien culture of scary predators trying to interact with a world that viewed the PCs as hard to trust scary predators with what they were sure was always sound reasoning.its a totally different thing when a party of humanoid PCs gets back from dealing with a bandit threat still bloody and tarnished from the deed than when a party of dragon hatchlings trot up still bloody and scuffed after being beaten by one of the bandits to a town alerted to the dragon invasion or whatever
Before 4e, Dragon Magazine had two articles where you could play a Dragon PC as though they were a class. One article covered the Chromatic Dragons, the other covered the Metallic Dragons. Each Chromatic and Metallic Dragon had their own class, and each class was designed to cover the first four age categories (Wyrmling to Very Young, I believe).
