Figuring out the age that dinosaurs could potentially reach is no easy feat to say the least. It's even somewhat difficult with living species, let alone extinct ones! There are various factors to consider, most of which we don't actually know for sure. There is the metabolism of the dinosaur, wild animals not usually living until their oldest age and the fact that we simply don't have a time machine. But we can estimate how old a dinosaur could get, based on living relatives, convergent evolutionary examples and what factors affect age in general, so let's get into it!
How definitive is a life expectancy?
As I've said, figuring out the life expectancy of an organism is no easy feat, even when they are still alive today. This is mainly because average life expectancies are just that: averages. They are not always an accurate representation of an animal that has reached adulthood. For example, the average life expectancy of people during the 1600s was around 30-40. That isn't because most people were dropping dead at that age, but because infant mortality was so high, bringing down that average. If you managed to live into teenage-hood back then, you were likely to live well into your 60s.
The same is especially true for wild animals. Most infants will not live into adulthood, especially if they are a species not known for their nurturing, such as turtles. A dinosaurian example of this would be the sauropods, of which only around 10% who are born would survive childhood. If we were to take a mean average life expectancy of a sauropod, including the infants, a sauropods average life expectancy would be very low indeed. Of course, we know this not to be the case.
Not only this, but there are a near infinite amount of variables that will affect an animal's life expectancy. We don't even know how long a human's potential for lifespan is, since advances in medical knowledge and attempts at better lifestyles means that number is reaching ever higher! However, when you're a wild animal, there are mortal dangers around every corner, from diseases to predators and everything in between. The best estimations we have for life expectancies for an animal would be one who remains in captivity, receiving proper care and medical attention. Even then, the animal could have defects that causes an early grave.
In other words, a dinosaur's potential age limit could be 500 years old, but it wouldn't matter all that much when the vicious wild will kill them somehow by the time they reach 30.
But that answer is no fun, so let's explore further
A question of metabolism...
If we want to figure out how old a dinosaur could get, we really need to look first at its metabolism. The metabolism of an animal is essentially how quickly its body goes through all of its usual processes. It dictates the speed of digestion, how often it has to eat, how quickly and for how long it can move, whether or not it is exothermic or endothermic (cold-blooded or warm-blooded) and how long it can potentially live for! It specifically refers to the body's ability to convert food into energy, but that energy isn't just spent moving, it's spent doing everything.
The phrase 'live fast, die young' rings especially true here. Ever wondered how some tortoises get to live to the age of 150+? Well, them being so slow is no coincidence. You see, every single function in their body runs much more slowly and so they burn energy at a much slower rate, meaning that race towards death is also taken at a much slower rate. Of course, other factors are at play in this case. Tortoises also have very special genetics, with specialised immune systems, cancer suppression and general DNA repair, but the metabolic rate plays a major role in all of this.
Yes, yes, but get to the dinosaurs!
Ok, ok.
When it comes to the question of how old dinosaurs got, paleontologists originally concluded that, given how 'reptilian' they thought dinosaurs were, they must have had a very slow metabolism. Applying the tortoise metabolism along with the general correlation between body size and longevity, paleontologists concluded that the biggest of dinosaurs could live up to 300 years old!
However, we know better about dinosaurs by now. Dinosaurs, whilst reptiles, were likely not exothermic (cold-blooded) like other reptiles. They are in fact thought to have had a much more avian system, being warm-blooded and having a much more energetic, fast paced lifestyle (relatively speaking, of course). They were not slow, lumbering, tail-dragging lizards!
Given this fact, higher energy meant faster metabolism, which meant a shorter life expectancy than 200 years. A better model to apply would be to estimate potential lifespans by scaling a birds life expectancy to size. For example, the lifespan of Microraptor would likely be similar to that of a crow, at about 8-10 years (with a good life, of course). Slightly larger dinosaurs, such as medium sized theropods or smaller ornithopods (basically anything a similar size to an ostrich) can be expected to have a similar life expectancy to an ostrich, which is between 30-40 years old (though some in captivity are known to live until 70).
Things get a little more hazy as we get bigger though. We can, of course, use mammals as an analogy, but the accuracy will be reduced considering mammals are not as directly related to dinosaurs as birds are. As a summative example, birds will actually live longer than a mammal of similar size. So, if we compare an African elephant (which has a potential lifespan of 70, second only to humans in Mammalia) to a non-avian dinosaur of a similar size, say, Triceratops, we'd likely find that Triceratops could live longer!
Another method of estimating a dinosaur's age is through the use of bone histology. Histology is the study of bones at a microscopic level, in which you can observe a feature that bones have in common with trees: growth lines. These growth lines, made by differing rates in which an animal grows by adding new bone to the outside of the old one, have helped paleontologists to not only estimate the age of a dinosaur at its time of death, but also may give some clues as to how old it could potentially get. Of course, you need a very well preserved specimen for this (which doesn't come up that often) but what we do have has led to an interesting conclusion, but one that makes sense.
In general, herbivores could live for much longer than the carnivores, regardless of size! This makes sense when we look back at metabolic rates playing a role in aging. Carnivores had a much more active lifestyle, spending almost every day hunting and fighting for food, or covering vast distances in order to scavenge some. Plants, however, aren't known for their running or martial arts capabilities, so a herbivore would only need to expend energy when fending off or escaping a threat (something that would have happened far less often than a carnivore would need to eat, considering the carnivore/herbivore ratio of any given ecosystem). Besides, those sauropods would need every calorie they could get to grow to such sizes, not wasting them on getting the quickest marathon time!
So...what's the limit?
Well, again, early estimates of a dinosaur's lifespan were based mainly on reptilian parameters, but knowing now that they had a much more avian physiology, those numbers have changed. So, here are the current estimates that paleontologists give for how long a dinosaur could live:
Largest sauropods (such as Argentinosaurus and Patagotitan): up to 100 years old
Mid sized sauropods (such as Diplodocus): up to 80 years old
Ornithopods (such as Iguanodon and Parasaurolophus): up to 70-80 years old
Largest theropods (such as T.rex and Giganotosaurus): up to 30-40 years old
Smaller theropods (such as Deinonychus and Velociraptor): up to 20 years old
Now remember, those are maximum lifespan estimates, not averages. The wild is a dangerous place, believe it or not, more dangerous when you are a carnivore, since you spend a lot more time exposing yourself to fights!
Nevertheless, those are (as of the time of writing this) the best estimates we have of how old a dinosaur could get. Until next time!