The Emerging Graminivores

Grass is, quite simply, a terrible food source. It's difficult to eat, difficult to digest, and to top it off it's nutritionally poor. However, it is also abundant, fast growing, and doesn't require a lot of effort to get it into your mouth. Because of this a lot of animals specialise in eating grass, the benefits of a nearly limitless food source outweighing the downsides of it being rubbish.

As rats- the common garden variety- were unable to digest grass, the first step to becoming graminivores was to develop a digestive system able to absorb nutrients such materials. The stomach and gut gradually became enlarged, acting as fermenting tanks where tough grass could be steadily broken down by enzymes. The resulting increase in gut size also lead to an increase in body mass, with the graminivores growing larger in size to match. This also resulted in the graminivores becoming obligate quadrupeds; although rats are quadrupedal they can easily stand on their hind legs to reach higher objects or gain a better viewpoint. For the graminivores- whose food was squarely on the ground- this was no longer as beneficial as having a sturdy foundation to support their weight. As a result the forelegs have become thicker and larger, more homogenous with the hind legs, which in turn are becoming more adapted to walking than scurrying. This gives the graminivores an appearance similar to that of a capybara.

Once rats had overcome the initial hurdle of being able to actually extract nutrients from grass, the next stage was being able to graze it efficiently. Grass contains silica, the tiny sharp crystals of which slowly wear away teeth as it's being chewed. Over time this will eventually completely destroy the eater's teeth; in the wild graminivores never die of old age, rather of starvation as they no longer have any teeth with which to chew.

Taking advantage of the phenomenal strength of jaw muscles inherited from their rat ancestors, the graminivores have evolved a molar mastication strategy; that is, the chewing is done with their molars. The premaxilla has greatly shortened, reducing the gap (the diastema) between incisors and molars. The incisors are used to snip and slice blades of grass, which are moved further back into the mouth by the tongue to then be chewed.

Taking advantage of the rat ability to move both halves of their jaw independently, the graminivores have a peculiar method of chewing. The two halves of their bottom jaw slide forward and backwards in alternating movements, grinding the grass with a horizontal movement of the molars. Once ground down far enough the grass is then swallowed. This alternating forward and backward movement of the lower jaw is a very bizarre sight for an observer, as the animals face appears to warp and distort as it chews.

Although this method means a graminivore cannot graze and chew at the same time, it is a highly effective means of grinding down food as a form of pre-digestion.

As the grazers of Loki are still poorly adapted to a grass diet, all graminivores engage in coprophagy- eating their own droppings. By eating the partially-digested grass in their droppings the graminivores are able to extract even more nutrients from a second pass through their system.

Graminivores have begun to live in larger groups than their rat ancestors; rather than a single family group, a collection of families stick closer together. More members means more eyes, ears and noses to detect predators, and a reduced risk of an individual being targeted by an attacker. Each family group retains an alpha (who aggressively defends their group from unwanted attention), but as a whole the groups tolerate each other's close proximity for mutual benefit.

Another noticeable change in the graminivores is their body clocks. Rats are crepuscular- active in the twilight hours. The graminivores are evolved almost the opposite; being active at day and night and resting during twilight. This rhythm comes with its advantages; it mainly evolved as a defence strategy against predators, who still retain their crepuscular ways. By resting together in a group more individuals are able to keep watch, increasing the group's chance of spotting a predator before it strikes. Secondly, it gives the graminivore a chance to digest their food and eat their droppings. When settling down for twilight an individual will defecate and then rest beside the pile, having a nibble every now and again. At the end of rest, when the group move away, the individual will pass its second lot of droppings; digested twice and too nutritionally poor to bother eating.

Due to their increased size graminivores are currently the largest land animals on Loki; albeit only the size of a large dog at most. The benefits of a large size in terms of digestion and protection from predators however is driving natural selection, and one day these humble grazers will achieve very big things indeed.