Image credit: Marian78ro/wikipedia
Bringing Science Home (SteamForKids)
Written by | Seven Monarchs
Birth, old age, illness and death are natural laws that all living things cannot bypass. It is difficult for wild animals to survive to old age, and death from injury infection or being eaten is a more common outcome.
For some oversized animals, although the possibility of being eaten in adulthood is relatively low, it seems that it is also difficult to die of old age, elephants are such animals. In the wild, with the exception of poaching, elephants that die naturally die mainly from unexpected causes: starvation.
Humans and elephants are very similar in many ways, such as social animals and similar lifespans. Theoretically, elephants live to be 70 years, but few elephants live to that age. They do not die of a variety of diseases like humans, but most of them die of starvation.
But why do most elephants that die naturally die of starvation?
This is due to their special teeth. The teeth in question are not the "ivory" that poachers love. In fact, elephant tusks are their upper row of incisors. While many elephants die because of these two beautiful incisors, the elephants that die naturally are due to their other tooth, the molars.
Molars of African elephants (Credit: Wikimedia)
Among mammals, elephant teeth are very special. Almost all mammals have only 3 sets of molars, and when they reach adulthood, teeth cannot be renewed, and they grow in a manner similar to the tips of bamboo shoots.
But elephant's is different. Elephants have no canine teeth, only incisors and 6 sets of molars. However, their upper and lower jaws are relatively short and cannot accommodate 6 sets of molars (24 in total) at the same time, so these 6 sets of molars appear sequentially. The elephant's molars act like conveyor belts, gradually moving forward from the back of the mouth.
Elephants usually have only 2 sets of molars in their mouths, and the back one will slowly push the front one out. (Credit: Amboseli Trust for Elephants)
At birth, baby elephants come with 4 miniature molars and baby teeth. By the time they are 2 years old, these baby teeth will fall out, followed by larger, longer-lasting molars.
The relationship between the 6 sets of molars and life stages of elephants. (Image source: doi.org/10.1016/j.mambio.2018.12.004)
These molars fall off with wear and tear and are replaced by new ones. The new set of molars tends to last longer than the previous set and is also a little larger than the previous set. When new teeth are grown, the roots of the old teeth are absorbed by the upper and lower jaws. The procedure is quite uncomfortable, so elephants in tooth changes are usually more grumpy.
Sadly, with each new set of molars, the elephant's life countdown progresses one block. By the time the sixth set of molars appears, their lives enter the final stage.
The elephant's 1st to 6th sets of molars. (Image source: doi.org/10.1111/j.1469-7998.1988.tb03760.x)
This last set of molars appears in their prime, around the age of 30.
The sixth set of molars is clearly different from the morphology of several other sets. The end surfaces of the first five sets are all relatively rounded or flat, but the ends of the sixth set are pointed. The sixth set of molars takes twenty or thirty years, so elephants will lose their lifespan if they eat too much hard and poorly chewed food, such as bark and thorns.
The elephant had used up all its molars before it died, as there were no substitute molars left in the back row. (Credit: Amboseli Trust for Elephants)
EleAid, an elephant rescue charity, says that's why most old elephants die of starvation. Taking into account the special physiology of elephants, some zoos or rescue organizations will provide special food to captive elephants. For example, wildlife SOS, a wildlife rescue nonprofit, feeds semi-liquid food to old elephants that have reached their sixth set of molars.
In addition to elephants, there are only 3 species of manatees, 1 species of kangaroo (Petrogale concinna), and frost rat (Heliophobius argenteocinereus) whose teeth are pushed from back to front.
Heliophobius argenteocinereus (Image: Wikimedia)
That is, of the 5500 known mammal species, fewer than 10 are constantly renewing their molars.
But why do elephants have such progressive teeth?
Biology researchers Oscar W. Johnson and Irven O. Buss point out that it is generally believed that the last three sets of molars of elephants correspond to the molars of other mammals in adulthood; However, it is not clear what the first three sets of molars of elephants are.
Some researchers believe that the first three sets are equivalent to milk molars. That is, elephants are still having baby teeth in their teens.
As for why elephants slowly teeth with age, researchers have not yet figured it out.
Some researchers speculate that the secret of elephants' teeth may lie in their skeletons.
This is because, although elephants live as long as humans, elephants' bones mature very late. Elephants do not fuse with the epiphysis until they are about forty years old, which means that elephants do not stop growing until they are forty, and their last set of molars appear around this stage.
The second reason is that there is a strong positive correlation between elephant tooth stage and bone length, which is also puzzling to the researchers. Some speculate that this may be because bone growth drives tooth renewal, or vice versa.
Comparison of molar teeth of adult elephants and juvenile elephants. (Credit: Amboseli Trust for Elephants)
Does this mean that elephants can live to "old age" as long as they take good care of their teeth? In any case, the fate of elephants in natural conditions is almost certain.
Old elephants tend to get pinker as they get older because their ears and nose fade with age. And on their deathbed, hungry elephants tend to look for water, so you can see pink elephants dying near the water source.
Tikiri, an elephant in Sri Lanka who performs animals, lived to be 78 years old, which was her dying state. (Credit: Save Elephant Foundation)
The location of water sources is shared within the same elephant family, so elephants of the same family tend to die together. And this may be the origin of the so-called elephant graveyard.
After watching the natural outcome of elephants' lives, I really don't know whether to envy them or feel sorry for them.
It is enviable that they did not have any serious diseases before they died, except for hunger. Sadly, even if they escape poachers, they will inevitably die because of their unique teeth.
Human: Standing at thirty.
Elephant: Thirty chestnuts.
Resources:
https://docs.qq.com/doc/DVHZ4aFBZWWFEcHdi
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Source: Global Science