The Reptilians, like the other Xindi species, evolved on the planet Xindus in the Delphic Expanse. In the the 2030s, during their civil war, the Reptilians made an alliance with the Insectoids. In one of their last desperate actions during their Civil War, the Reptilians and Insectoids planted explosives under Xindus's eight largest seismic fissures. This had the unintentional result of destroying Xindus due to its high geological instability. They like the other species, except the Avians, went into space as part of the "Great Diaspora". (ENT episodes: "The Xindi", "The Shipment"; ST reference: Federation: The First 150 Years)
The Reptilians, like Earth reptiles, were scaly and highly textured, including many small wrinkles and ridges. The Reptilians had yellow to brown-colored scales with multiple spikes coming out of their heads and little tusks, one on either side of the face, around their mouth. They had yellow eyes with slitted vertical pupils, and were cold blooded. Like other Xindi, they had a characteristic facial feature, involving a small indentation and a series of little bumps on their cheek bones. They also had greater strength and stamina than Humans. Some Reptilian soldiers were also given a suicide gland. (ENT episode & novelization: The Expanse; ENT episode: "Rajiin")
Reptilian weapons used eel-like power cells. Their biorifles worked on a rotating modulation that self-destructed when accessed by other species. They also used a type of ray gun. (ENT episodes: "The Shipment", "Carpenter Street").