Some of the smallest mammals that lived 65 million years ago are distantly related to the largest ones alive today. The mass extinctions that took place during the Anthropocene gave a handful of surviving species a world of opportunities; as populations recovered and grew they rapidly diversified. Rodents in particular thrived in new environments and branched into two main groups: slow quadrupedal herbivores and fast bipedal carnivores. For the first ten million years or so, the former group was largely composed of medium-sized, non-specialised creatures similar to capybaras, but as ecosystems grew more complex and new biological niches appeared new species evolved to fill them.





Today’s herbivores include the largest land mammals yet seen. Anachrotherium Giganteus (giant beast misplaced in time) can grow up to 20 metres long and weigh up to 15 tons. These creatures’ resemblance to the long-vanished sauropods bespeaks a similar lifestyle. Their long necks help them eat plants that would otherwise be out of reach and graze wider areas without expending as much energy. Their multiple stomachs aid digestion and their sheer size helps them retain heat in colder environments. Healthy adults are almost immune to predation, though young, sick, injured or exhausted individuals are naturally more vulnerable. Despite their resemblance to sauropods, their breeding cycles are more like those of other large land mammals: each mother bears a single calf after eighteen months’ gestation. Adult females live in herds together with their offspring and the males that fathered them. Young adult males range more widely and when possible join other herds, driving older bulls away and forming new relationships. This reduces the risk of inbreeding in smaller populations and increases genetic diversity.





Anachrotheres can change whole landscapes by stripping trees of leaves and removing undergrowth, though their dung provides fertilizer and their corpses are jackpots for scavengers. The herds themselves could be considered smaller moving ecosystems; many insect species live on or around anachrotheres, drawing warmth and sustenance from their bodies, blood and waste, and they in turn are eaten by swarms of small diurnal bats. Besides removing parasites, these bats can also act as scouts, leading herds to food and water or alerting them to dangers they could not see from the ground.



