The gestalt, Formisaura delacasa, is a small pachycephalosaur with a colonial lifestyle like that of an ant or a termite, from The New Dinosaurs: An Alternative Evolution. It comes from the deciduous and mixed woodlands of Eurasia.
The most remarkable animal of the Palaearctic ecozone must be the gestalt. It is unique among the vertebrates because it pursues a communal existence. The gestalt evolved fairly recently, in the Last Ice Age, when there were few reptiles and non-avian dinosaurs existing in western Eurasia and food was scarce. The animals that did survive there had to develop all kinds of strategies in order to make best use of the food available under the harsh circumstances. The gestalt evolved from one of the smaller pachycephalosaurs (the bone-headed dinosaurs) that lived in herds, mostly in mountainous areas.
The gestalt's strategy was to delegate the breeding of the herd to one individual female, freeing the rest to become food gatherers. They developed the ability to build citadels to guard their hard-won food against other animals. Within this citadel the individuals adhere to a strict discipline and a hierarchy that is based on age and sex. Now that the Last Ice Age has passed, the gestalt has found that its evolved way of life is still very efficient and successful.
Among the pachycephalosaurs the armored head developed as a display structure, particularly in the males. In the gestalt, the male still has a very specialized head, but it is not used for fighting or intimidating members of its own species. The armor has developed spines containing a lethal venom, now used when protecting the colony from predators.
In times of plenty the population tends to grow too big for the colony to sustain. Small groups of adult males and females then leave to start up new colonies. Streams in the temperate regions of Eurasia may be marked by lines of the conical citadels.
The nest is built and kept in repair by the females. It is a thatched structure, built of twigs and straw, usually around a sloping tree trunk over a stream. The interior is a mass of tunnels and chambers and each nest usually has the same layout.