Dinosaurs are often portrayed as slow and sluggish creatures, but many of them are warm-blooded, active, and agile animals.
One of the ways to study how dinosaurs lived and grew is to look at their bones, which can reveal clues about their metabolism, activity, and growth rate.
The mystery of the holes
The researchers focused on a dinosaur species called Maiasaura, which means "good mother reptile."
Maiasaura was a herbivorous hadrosaur that lived in Montana, USA, about 76 million years ago.
Fossils from this area have shown that Maiasaura tended her eggs and raised her offspring for more than a year after hatching.
They grew very fast, reaching 200-400 kilograms by their second year, and over 3,000kg by their teens.
This is much faster than cold-blooded animals like crocodiles, which weigh only about six kilograms at the age of two and reach adulthood at between 10 and 16 years old.
Such high growth rates in Maiasaura required rapid lengthening and thickening of their long bones, such as the femur (thigh bone) and tibia (shin bone).
The researchers noticed that the shafts of these bones had holes on their surface, where the principal nutrient artery entered the bone.
This artery supplied blood to the bone tissue, which was essential for growth and repair.
The researchers measured the size of these holes in Maiasaura bones from different stages of growth and compared them with those of other animals, such as birds, mammals, and reptiles.
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The link between holes and blood flow
The researchers found that the size of the holes in Maiasaura bones was proportional to the blood flow rate in the bone tissue.
This means that the larger the hole, the more blood was flowing through the bone. They also found that the blood flow rate in Maiasaura bones was similar to that of warm-blooded animals like birds and mammals, and much higher than that of cold-blooded animals like reptiles.
This suggested that Maiasaura had a high metabolic rate, which means that it used a lot of energy and nutrients to fuel its growth and activity.
The researchers estimated that Maiasaura needed about 50 megajoules of energy per day when it was one year old, and about 300 megajoules per day when it was six years old.
This is equivalent to eating about 10 to 60 kilograms of plant matter per day.
The researchers also calculated that Maiasaura had a high aerobic capacity, which means that it could sustain prolonged and strenuous exercise without getting tired.
They estimated that the Maiasaura could run at speeds of up to 40 kilometers per hour for several minutes, or walk at speeds of up to 15 kilometers per hour for several hours.
The study by the researchers showed how holes in baby dinosaur bones can provide insights into how dinosaurs grew and lived.
By measuring the size of these holes, the researchers were able to estimate how much blood flowed through the bones, and how much energy and nutrients they needed to grow from football-sized hatchlings to three-ton teens.
The study also supports the idea that many dinosaurs were warm-blooded, active, and agile animals, capable of high levels of metabolism and aerobic activity.
This challenges the stereotype of dinosaurs as slow and sluggish creatures and reveals more about their biology and behavior.
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