A couple of questions about dinosaurs lifespan

I was reading a science article today that stated dinosaurs might have had a lifespan of several hundred years. First question, is this true and is there anyway to know? (I fully realize that there many, many types of dinos spanning many millions of years. I’m hoping to avoid bogging down in that. For the sake of this thread assume we talking about the popular things most people call dinosaurs - brontos, T-rex, triceratops, etc)

Googling I found conflicting information. Some sites saying maybe as short as 40 years. Some dates were claimed by something called bone growth rings. Which brings me to question two: since dino “bones” are really fossils are there really still growth rings to count. I am completely ignorant on the subject but it doesn’t seem like the fossilization process would preserve growth rings.

Fossilisation does or, more correctly can preserve internal detail of bone under the right conditions.

Some bones develop ‘rings’ or at least grow differentially at different times of the year, and this incremental differential growth can be seen and, more importantly counted

If you get your dinosaur-descendant ducks in a row - right bone->right fossilisation->right discovery->right palaeontologist, then perhaps you can work out how old the bone is.

When humans have developmental delays that can leave permanent marks of altered growth in the bone, which are known as Harris lines and can mark, for example childhood periods of malnourishment.

There are some specimens which display such “growth rings” (not too much unlike those found in trees) and they can give an approximation of age; in the case of the famous “Sue” the T.rex we can guess an age of late 20s to early 30s. However, it’s not one size fits all when it comes to dinosaurs. Think about the variation in longevity in fish, in reptiles, birds, mammals… same deal. Larger animals seem to have longer lifespans, and an Argentinosaurus might have lived over 100 years, smaller animals like Compsognathus might have had less than ten years (I’m not basing these on any evidence, that’s the point, we DON’T have evidence either way); we won’t really know unless we crack open a bone and measure growth rings, or we develop some new method of estimating age.

Here is some speculation for you:

Please take with a grain of salt the article’s claim that “the very large herbivores - things like brachiosaurs and Diplodocus” “were comparable in size to an elephant.” An African elephant can grow to about 13,000 pounds – that’s 6.5 tons. A Brachiosaurus is estimated to have eight as much as 62 tons – ten times more.

Some dinosaurs nowadays can live to 50 or 60 years. And they’re much smaller than elephants, so I think that it’s safe to say that even if there’s a correlation between size and longevity within a class, it doesn’t hold very well between classes.

I knew someone who determined the age of fish in archaeological contexts by looking at the layers in the ear-bones (otoliths). I’m reasonably sure that something like that could provide the ages of dinosaurs.

Or even older at the extremes. Cookie is the best documented, but there are other contenders that claim ages closer to a century. And of course there are koi and tortoises that put them to shame.

ETA:

My understanding from my long ago ichthyology class is that otoliths can be tricky sometimes. Like putting down multiple layers during a particularly productive growth season tricky. Though I’ll admit my info on that might be a little dated.

I once met someone who was present at the Battle of Sevastopol. Admittedly she was a tortoise, but she was already mature during the Crimean War.
https://en.wikipedia.org/wiki/Timothy_(tortoise)

Multiple partial growth rings are mostly seen during the first year or two of a fish’s life when growth is rapid, after which a lot of species will slow down and more regular single growth rings are laid down annually. Fish which grow slowly and get old can also be problematic to age because the growth rings become progressively smaller and more tightly packed and how the otolith is prepared can influence whether they are all visible.

A quick bit of googling shows that under some circumstances fossilization can indeed preserve microscopic details; one page I saw described how researchers were looking at the cellular wall structure of petrified trees for their study (though I wouldn’t think every fossil is preserved this well). I don’t know enough about dinosaur growth rings to comment on their ages, but it does appear that in some cases such details can be preserved for millions of years.

Correct, I certainly didn’t necessarily mean absolute size in comparison to all animals, ever. Giant Tortoises, Alligator Snapping Turtles, and Leatherback Turtles are far smaller than cetaceans in general but have pretty impressive longevity compared to, say, Red-Eared Sliders. That’s more of what I meant.