Rumbling Helmethead

Serinarcta's most abundant grazer by numbers is a tribbethere species known as the rumbling helmethead, a crested thorngrazer notable for its specialized hollow nasal cavity, which serves as a resonating chamber that amplifes its calls through two bony horns formed from its nostrils. 

Rumbling helmetheads are widely distributed over Serinarcta from the polar basin to the southern coastline, and while most associated with soglands these animals are also present along drier uplands. The most basic unit of their social structure are familial groups usually less than twenty five, in which only females have enduring social bonds and a dominance hierarchy, while a single male guards them as a resource from competing males. These groups aggregate into far larger herds for protection from enemies, and the total population of this species alone across Serinarcta is roughly six hundred million animals, though their populations are prone to booms and busts and adapted to quickly recover numbers after collapses from disease. Reproductive age is reached in females in only eight months, around 250 lbs, but in males in three years or sometimes two in good conditions, as they must compete with older males for dominance to mate and so be as massive as possible. Full adult size of 350-450 lbs attained around two years of age. These thorngrazers grow very fast, and often die young, with females  bearing one to two calves annually which are born small and defenseless, without any teeth, and so rely on regurgitated feeding by their mother of a nutritious milk-like secretion of fatty cells produced in the throat (this is typical for thorngrazers, whose often barely edible diets are not suitable for growing juveniles without the large specialized gut of the adult). Females can live up to seven years if they survive adolescence, but most males die before the age of five, and very few animals reach their potential lifespans due to heavy parasite loads, predation and pathogen infection. 

Male helmetheads are much more colorful than females, and their horns are larger, but these structures are fragile and so are ornamental - they would be easily damaged in physical confrontations, and so helmetheads rely heavily on display and vocalization to proclaim their dominance. Their calls are complex and slightly melodic, carrying several miles in good weather conditions, and function like the songs of birds to proclaim a territory, only that in their case their territory is mobile and restricted to the area immediately around their group of females. When males do fight, they utilize a side to side posture in which each tries to push the other off its feet with sideways shoves and hits with their tusks. Both sexes have two tusks remaining on the lower jaw, but in females they serve a mainly defensive role.