The ants’ endosurgical techniques also progressed rapidly. For example, when performing surgery in the digestive system, it was no longer necessary for a long line of ants to trek down the dinosaur’s oesophagus. Instead, they entered by means of an ‘ant pellet’. Approximately 1,000 ants would cling tightly to one another and form a ball ten to twenty centimetres in diameter. The dinosaur patient would then wash down one or more of these pellets with water, as though swallowing a pill. This technique improved surgical efficiency substantially.

As the Ivory Citadel continued to mushroom, some of the dinosaurs who came for treatment stayed on, establishing a city of their own not far from the ant megalopolis. Because the dinosaurs constructed their homes with massive stones, the ants called it Boulder City. The Ivory Citadel and Boulder City would later become the capitals of the Formican and Saurian Empires of Gondwana.

There was also significant movement in the opposite direction. Some of the dinosaurs who returned home after having received treatment took groups of ants with them to other dinosaur cities and ant colonies all across Gondwana. When the émigré ants settled in these faraway places, they passed on the Ivory Citadel’s medical technology to the locals. And so dinosaur–ant cooperation gradually spread throughout Gondwana, cementing the foundations for a dinosaur–ant alliance.

Up till now, the cooperation between Earth’s two dominant species could only be classified as an advanced symbiotic relationship. The ants provided medical services to the dinosaurs in exchange for food, and the dinosaurs traded food for medical care. Although the character of the transaction had evolved considerably since the ants had picked that first dinosaur’s teeth, the essence of the contract had remained unchanged.

In fact, this sort of mutualistic association between different species had long existed on Earth and persists to the present day. The practice is as old as the hills – older than most hills, actually. Consider, for example, the cleaning symbioses among marine organisms. Cleaner species rid certain fish of ectoparasites, fungi and algae, as well as damaged tissue and wayward scraps of food, and in the process they get to eat their fill. They assemble at fixed ‘cleaning stations’ to wait for client fish to swim by. Cleaners and clients establish ways of signalling to each other: for example, when a cleaner shrimp wants to approach a large fish, it will nudge it with its antennae. If the fish wishes to be cleaned, it will tilt its body, flare its gills and open its mouth to indicate its acceptance. Only then will the cleaner shrimp proceed; otherwise, it runs the risk of being eaten. Cleaning associations are extremely important to fish, and whenever a cleaner species is removed from an area, there’s a decline in both the health and abundance of the client fish species.