Sangheili

The Sangheili are a sapient species of sinewy, bipedal sauroids. As a founding species and primary ruling class of the Covenant alongside the San'Shyuum, the Sangheili are one of the oldest active spacefaring species in the Orion Arm.

Evolution and prehistory
The Sangheili are semi-predatory omnivores (or mesocarnivores) that evolved from larger predators. As opposed to humans, who began as nomadic endurance hunters who could outrun their prey over long periods of time, the Sangheili relied on their speed and agility to do the same; this also means their means of thermal regulation in sustained exertion are not as effective (for example, they do not perspire). Their physical prowess is less of an indication of an apex predator role, but rather the harsh and competitive evolutionary environment of Sanghelios, where they are a lower mid-tier predator at best, having sacrificed strength and size for brain capacity. Their primitive cousins would often be forced to resort to scavenging rather than hunting for live prey, although as they grew more intelligent, their hunting strategies also diversified, and with pack tactics they could best even far physically superior prey. It was also around this point that they transitioned from primarily quadrupedal to bipedal locomotion, first intermittently and later near-exclusively. Pack hunting formed an important part of the Sangheili's formative millennia, and is suspected to have been a key contributor to their development of language and intelligence. Indeed, in more than one early Sangheili civilization, their word for themselves translated to "hunters" or some close equivalent. Their ancestors usually hunted in twilight, at night or the break of dawn.

As opportunistic mesocarnivores, the primitive Sangheili favored animal-based nutrient sources ranging from insectoids to sauroids and various mammal-equivalents, but they would often supplement their diets with plant-based foods such as fruits, roots, algae and fungi. The eventual development of agriculture saw a handful of additions to this. Sanghelios does not exactly have direct equivalents to terrestrial grain, and their staple crops are most akin to legumes and algae, as well as some types of fungi. The Sangheili may have genetically modified some crops early on in their history to be more nutritious or easily digestible. Even now, grain such as irukan is mostly grown for livestock's consumption, as well as non-Sangheili serfs; Sangheili can eat it, but it does not give them much in the way of nutrition. The Sangheili's quad mandibles, a trait shared by many related species on Sanghelios in various forms, originally evolved for feeding purposes at the time the species' evolutionary ancestors were still quadrupedal. The mandibles were much larger and more functional on their ancestors; now, on most Sangheili ethnicities, they are largely vestigial especially with the feeding habits of most modern Sangheili.

The development of agriculture eventually led to the formation of small tribal communities, which quickly settled down; the species never experienced a prolonged and nearly-universal nomadic phase, as they never relied as much on routinely crossing long distances as humans did.