Why do cows have such straight backs (parallel to the ground)? Most other animals don’t seem to…
In: Biology
(Obligatory warning: I’m on mobile)
Long story short: it appears straight but technically isn’t. What you see as the line of their back is the line that connects all the spinal processes of their vertebrae. Those do line up to create a straight line. The body of the vertebrae however do form a curve underneath that you can’t see.
Long story long: let’s look at why backs are curved for a second. In 4 legged animals, walking requires the back to undergo a slight side-to-side wave-like motion with each step. It also bends ever so slightly with each step when the hip is flexed to bring the leg forward under the animal. The spine also holds the weight of the innards, which are contained by muscles that are attached to the spine. Basic architecture tells us that an upwards curve is better at holding in weight than a straight line. Hence, the spine curves upwards a bit.
Now let’s compare some behavior and lifestyles to better understand the anatomical differences between species. Take a horse and a cow for example. A horses back is much more curved than a cows. But why is that? One good way to try to backtrack why a feature is the way it is, is to think about its function. A horse has a raised withers (the area between the shoulder blades). In this area, the spinal processes are much longer than in the rest of the back. This is also the area where a lot of the muscles and most importantly, the ligament that runs all the way along the spine from the base of the skull to the top of the tail, are attached. The raised processes give more surface for those muscles to attach to, and allow for a lever effect to take place. This all facilitates the act of raising the head. Horses are nervous prey animals that rely on their senses and their ability to escape a situation quickly to survive. They graze most of the day with their head down, but most of their non-grazing hours are spent with their heads in a more horizontal/upwards position (when they nap while standing or socialize). So they need the raised withers and more curved back to help their muscles raise their heads and support the weight of their belly.
Cows on the other hand, have a generally lower position of the head. Proportionately, they spend less time grazing because they are ruminants. They tend to spend their ruminating time lying on the ground with their legs tucked under and their heads just slightly raised above the ground, but they don’t need to raise their heads above the level of their backs as much as horses do. The fact that they also spend much more time lying down helps them carry the weight of their belly. So they don’t need as much room to attach head muscles to.
As for most carnivores, they have well developed muscles all around, but are mostly developed for motility. They are less likely to spend a lot of time in a specific position so their bones have adapted to give muscles more space. They typically have lighter, finer skeletons as well whereas grass eaters have heavier, less streamlined bones.
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