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. Their evolutionary ancestors relied on their agility and speed in short sprints to catch their prey. This strategy differs from early humans and hominins, who used persistence hunting as their primary predation strategy, outrunning otherwise faster opponents over long periods of time. Consequently, while they are much faster and stronger than humans, the Sangheili's stamina and means of thermal regulation in sustained exertion are not as effective (for example, they do not perspire). Their impressive 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. This transition did come with some loss in speed, causing the Sangheili's hunting tactics to be increasingly ambush-oriented. Pack hunting formed an integral 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. The early Sangheili organized themselves into tight-knit tribal units in which eggs were brooded and young raised communally - early predecessors to the species' later standard group families and clans. Depending on the latitude, the proto-Sangheili were crepuscular or metaturnal, hunting for food in twilight or in sporadic intervals throughout Sanghelios' somewhat atypical day-night cycle.

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.

Biology
The Sangheili are tall, four-limbed bipeds of a taxonomic clade dubbed by human xenobiologists as Cardomandibulae. These are part of a class of reptile-like organisms characterized by their distinctive quadruple jaw structure. One of the most successful forms of being to arise on Sanghelios, their biology has various parallels to terrestrial saurians, though as they are independently-evolved aliens, most of these similarities are merely superficial.

Diet
The primitive Sangheili were opportunistic mesocarnivores, favoring animal-based nutrient sources ranging from sea life and insectoids to other sauroids, but they would often supplement their diets with plant-based foods such as fruits, roots, algae and fungi by necessity. 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 to themselves. Even now, grain such as irukan is mostly grown for livestock's consumption, as well as non-Sangheili serfs; Sangheili are able to digest it, but it does not give them much in the way of nutrition.

Facial anatomy
One of the Sangheili's most distinctive morphological characteristics is their quad set of hinged mandibles. Many related species on Sanghelios share this trait, which originally evolved for feeding purposes while the species' ancestors were still quadrupedal and largely unable to use their forelimbs for feeding. The mandibles, much stronger and more prominent at the time, were used to both immobilize and kill prey as well as guide it into the mouth. The modern Sangheili's smaller mandibles are actually a neotenic trait retained from an ancestral mutation at one point in the species' evolution. Normally, as their ancestors would mature into adulthood, the mandibles would grow considerably larger. However, this would also directly limit the brain size, as the muscles responsible for moving them took up considerable space around the cranium. This can be seen with several of the species' surviving relatives, which retain a thinner, elongated skull, with some even having an additional head crest to which the muscles attach. As the species shifted increasingly from quadrupedal to bipedal locomotion and began using the forelimbs to manipulate objects, the need for the mandibles for their original purpose grew less acute, and the retention of the more neotenic, less pronounced and weaker mandible structure freed up space in the cranium for a larger brain to develop. Now, the mandibles are largely vestigial and only have limited utility in their original function; their most notable use is as one of the Sangheili's primary means of conveying expressions.

There exists some variety in the shape and size of the mandibles between different Sangheili ethnic groups and, to some extent, individual phenotypes. Because of their evolutionary history, larger and more forward-jutting mandibles exhibited by some phenotypes are generally seen as more atavistic or "primitive" traits in Sangheili. An interesting trait which once manifested in the Quun, a now-extinct subspecies of Sangheili, is the fusing of the two mandibles on each side into one, while retaining the quadruple bone structure; similar developments can also be seen in other extant members of their clade. As the subspecies could interbreed by what are now regarded as Sangheili, vestiges of this trait still manifest in some isolated population groups.

Languages
The Sangheili are known for attributing almost painstaking significance to their use of both language and nonverbal communication. Even the little details of everyday interaction are often tacit cultural or political statements, and language is no exception. One of the distinctions where language makes a difference is the axis from Common to High Sangheili - a simplification of the variance in dialects within the Qers'nok language family, now widely known as Sangheili. "Common" Sangheili, often known simply as the Common Speech, is the Covenant's everyday language. Over time, it has become considerably simplified from its roots; a lot of Common Sangheili's more complex grammar (and accompanying expressive power) have fallen by the wayside due to its long history non-native, non-fluent usage, and many alien loanwords have entered the language.

High Sangheili is a grouping of dialects used among the higher aristocracy, in governance, as well as in poetry and literature. It retains many of the "archaic" constructions and vocabulary that have long disappeared from the Common Speech, and is often claimed by its speakers to be Sangheili distilled to its "purest" form, retaining the classical Sangheili of old literature and poetry; at times, influential authors and philologists attempt to introduce what some other scholars wryly recognize as more or less artificial constructions that seek to make the language even more artful or "classical" in style. To the average speaker of common Sangheili, many of the elaborate word constructions and obscure inflections used in High Sangheili would be almost unrecognizable. It is a matter of pride for orators, poets and philosophers to master these nuances as well as the associated ideogrammatic systems. In spite of its complexity, High Sangheili is still able to be used in casual conversation. This sets it apart from the Covenant's liturgical language, which is only truly useful for discussing the finer points of theology.