Jakarta –
Dinosaur fossils hold a lot of information about their lives, including how they defended themselves, what they ate, and sometimes how they died. But do dinosaur fossils leave any clues about their age when they died?
The answer is yes, because there are “growth rings” on their fossil bones. These rings are arranged in a similar way to tree rings. Scientists have only discovered this in the last few decades.
Apparently most non-avian dinosaurs did not live long, although they sometimes grew to very large sizes.
For example, one of the specimens Tyrannosaurus rex most complete ever found in the Chicago Field Museum, died at the age of 28 according to his growth rings. Meanwhile, herbivorous duck-billed dinosaurs are thought to have only lived for a decade or two, Thomas Holtz, a vertebrate paleontologist at the University of Maryland, told Live Sciencequoted Wednesday (7/2/2024).
“I think many people probably have the impression that at least some dinosaurs must have been very large because they lived for such a long time,” Steve Brusatte, a vertebrate paleontologist at the University of Edinburgh in Scotland, told Live Science.
“Of course, scientists used to think that way,” he added.
How to Calculate the Age of Dinosaurs
Large modern animals tend to live long lives. African bush elephant (African Loxodonta), the largest living land animal on earth can live up to 70 years. Bowhead whale (Balaena mysticetus) can live up to 200 years.
However, dinosaurs are different. Holtz explained that thin slices of animal bone have a series of parallel lines caused by bone growth outward. New lines are produced every year, so counting these lines provides an accurate estimate of the animal’s age.
The stripes are produced by annual changes in the animal’s growth. In spring and summer, warm weather and abundant food provide animals with sufficient nutrition, allowing them to grow faster.
But in winter, when the weather is cold and food becomes scarce, growth slows. This growth retardation appears as lines between the layers of bone.
There are several complications to this growth measurement technique. One of them is caused by the medullary cavity, the space in the bone that produces bone marrow.
As the bone grows, the medullary cavity also grows, thereby eliminating some of the initial growth rings in the expansion. Holtz explained that, to get around this, researchers can place bones from smaller individuals of the same species over the missing lines of larger individuals to help estimate the potential total number.
Another complication is the type of bone. Some bones are better for identifying growth rings than others.
“Ribs, or bones like the fibula that don’t bear as much stress or load, tend to have better growth,” Brusatte says.
Large Dinosaurs Lived Longer
Although dinosaurs did not live as long as some of today’s large animals, there are some similarities between them. For example, larger animals tend to live longer than smaller animals. The same thing applies to dinosaurs.
Sauropods, a group of long-necked leaf eaters that included the largest dinosaurs that ever lived, likely had the longest lifespan of all dinosaurs. According to Holtz, the oldest known sauropod lived to be about 60 years old.
Vice versa, Stenonychosaurus inequalis weighing 110 pounds (50 kilograms) grows to its maximum size in just three to five years and likely won’t live long after that.
Why Did Dinosaurs Live Short?
There are several ideas as to why dinosaurs had such short lifespans. Brusatte thinks it’s possible that their metabolism or the body’s chemical processes, including the conversion of calories into energy, play a role in this.
Some dinosaurs were at least partially warm-blooded and had very fast metabolisms compared to reptiles. This can cause rapid growth and premature death.
Reproduction could also be a factor. Many dinosaurs produced large numbers of eggs, meaning they produced many offspring in a short period of time, Holtz explained.
In contrast, long-lived mammals such as elephants and whales reproduce more slowly, so natural selection would result in longer life spans. However, this hypothesis is not without shortcomings.
For example, the Galapagos tortoise (Chelonoidis niger) can produce large numbers of eggs but can also live well into the triple digits. So producing large numbers of offspring does not always imply a shorter lifespan.
Watch the video “Sightings of Dinosaur Fossils that Extinct 90 Million Years Ago”
(nah/pal)
2024-02-11 13:00:00
#thought #dinosaurs #short #lifespan
