Growth and Lifecycle
No dinosaur egg has been found that is larger than a basketball and embryos of large dinosaurs have been found in relatively small eggs, e.g. Maiasaura. Like mammals, dinosaurs stopped growing when they reached the typical adult size of their species, while mature reptiles continue to grow slowly if they have enough food. Dinosaurs of all sizes grew faster than similarly sized modern reptiles; but the results of comparisons with similarly sized "warm-blooded" modern animals depend on their sizes:
| Weight (kg) | Comparative growth rate of dinosaurs | Modern animals in this size range |
|---|---|---|
| 0.22 | Slower than marsupials | Rat |
| 1 - 20 | Similar to marsupials, slower than precocial birds (those that are born capable of running) | From guinea pig to Andean Condor |
| 100 - 1000 | Faster than marsupials, similar to precocial birds, slower than placental mammals | From Red Kangaroo to Polar Bear |
| 1500 – 3500 | Similar to most placental mammals | From American Bison to rhinoceros |
| 25000 and over | Very fast, similar to modern whales; but about half that of a scaled-up altricial bird (one that is born helpless) - if one could scale up a bird to 25,000 kilograms (25 long tons; 28 short tons) | Whales |
Tyrannosaurus rex showed a "teenage growth spurt":
- ½ ton at age 10
- very rapid growth to around 2 tons in the mid-teens (about ½ ton per year).
- negligible growth after the second decade.
A 2008 study of one skeleton of the hadrosaur Hypacrosaurus concluded that this dinosaur grew even faster, reaching its full size at the age of about 15; the main evidence was the number and spacing of growth rings in its bones. The authors found this consistent with a life-cycle theory that prey species should grow faster than their predators if they lose a lot of juveniles to predators and the local environment provides enough resources for rapid growth.
It appears that individual dinosaurs were rather short-lived, e.g. the oldest (at death) Tyrannosaurus found so far was 28 and the oldest sauropod was 38. Predation was probably responsible for the high death rate of very young dinosaurs and sexual competition for the high death rate of sexually mature dinosaurs.
Read more about this topic: Physiology Of Dinosaurs
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