The end of the rapid growth phase suggests the onset of sexual maturity in Albertosaurus, although growth continued at a slower rate throughout the animals' lives. Sexual maturation while still actively growing appears to be a shared trait among small and large dinosaurs as well as in large mammals such as humans and elephants. This pattern of relatively early sexual maturation differs strikingly from the pattern in birds, which delay their sexual maturity until after they have finished growing.
By tabulating the number of specimens of each age group, Erickson and his colleagues were able to draw conclusions about life history in tyranosauridae populations. Their analysis showed that while juveniles were rare in the fossil record, subadults in the rapid growth phase and adults were far more common. Over half of the known T. rex specimens appear to have died within six years of reaching sexual maturity, a pattern which is also seen in other tyrannosaurs and in some large, long-lived birds and mammals today. These species are characterized by high infant mortality rates, followed by relatively low mortality among juveniles. Mortality increases again following sexual maturity, partly due to the stresses of reproduction. While this could be due to preservation or collection biases, Erickson hypothesized that the difference was due to low mortality among juveniles over a certain size, which is also seen in some modern large mammals like elephants. This low mortality may have resulted from a lack of predation, since tyrannosaurs surpassed all contemporaneous predators in size by the age of two. Paleontologists have not found enough Daspletosaurus remains for a similar analysis, but Erickson notes that the same general trend seems to apply.
The tyrannosaurids spent as much as half its life in the juvenile phase before ballooning up to near-maximum size in only a few years. This, along with the complete lack of predators intermediate in size between huge adult tyrannosaurids and other small theropods, suggests these niches may have been filled by juvenile tyrannosaurids. This is seen in modern Komodo dragons, where hatchlings start off as tree-dwelling insectivores and slowly mature into massive apex predators capable of taking down large vertebrates. For example, Albertosaurus have been found in aggregations that some have suggested to represent mixed-age packs.
Other articles related to "life history, life":
... During the egg stage of the lamprey’s life, it is most vulnerable to predators that prefer to eat fish eggs ... castaneus) only mates once during its entire life and dies shortly after ...
... Sexual segregation occurs during the breeding season as pregnant females move into shallow coastal waters ... The common torpedo is unusual among sharks and rays in that birthing has been documented both at higher and at lower salinities than seawater, in estuaries and lagoons ...
... The larval stage lasts for 1 to 2 weeks ... After feeding, the larvae drop to the ground and become nymphs ...
Famous quotes containing the words history and/or life:
“The history of mens opposition to womens emancipation is more interesting perhaps than the story of that emancipation itself.”
—Virginia Woolf (18821941)
“In our rhythm of earthly life we tire of light. We are glad when the day ends, when the play ends; and ecstasy is too much pain.”
—T.S. (Thomas Stearns)