When the paleontologist Michael D'Emic cut into the bones of Majungasaurus, a relative of Tyrannosaurus rex that roamed Madagascar 70 million years ago, he suspected that surprises might be hiding in them. But what he found defied all expectations.
Majungasaurus adults measured up to 7 meters from snout to tail and could weigh 1,000 kilograms. Paleontologists had thought that big dinosaurs like these massive carnivores achieved their stature through rapid growth spurts. But the fossil bones revealed a different story. "Unlike carnivorous dinosaurs that had been studied up until then," D'Emic said, the Majungasaurus grew "really, really slowly."
Puzzled, he sliced up a close relative of the dinosaur — a Ceratosaurus from North America, which was roughly the same length and weight — to see if it grew slowly too. This time, "we got the opposite result," he said. "It grew just about faster than any carnivorous dinosaur I've ever seen."
What followed for D'Emic was a decade-long whirlwind of peering at bones for clues to how dinosaurs grew. His analysis of 42 different dinosaur species, recently published in Science, demonstrates that the "get big fast" mode of growth was less predominant than researchers have assumed.
[...] Whether an animal grows quicker and faster or slower and longer might seem like a nitpicky distinction. But an animal's growth trajectory provides insights into its life and the world it inhabited. Fast-growing animals can overpower potential predators and outcompete other species, but they need plenty of food and other resources. Growing slowly is riskier, but it allows an animal to survive on less during hard times. The bones of Majungasaurus, for example, confirm that, as the top predator in its ancient ecosystem, it had the luxury of developing at a leisurely pace.
Understanding growth strategies also helps explain why some dinosaurs got enormous while others stayed small. Body size can affect everything from how long an animal lives to how many offspring it has, explained Santiago Herrera Álvarez, an evolutionary biologist and doctoral student at the University of Chicago. Yet, "surprisingly, we don't have a lot of information [about] the key developmental or genetic mechanisms underlying body size variation across animals," he said. Studies like D'Emic's start to open that black box.
[...] Past studies have often suggested that a fast peak growth rate is the key to size in dinosaurs, birds and mammals. But the new analysis found that theropods were instead just as likely to control the duration of their growth — an alternative strategy previously identified in only a few groups, including crocodiles and some lizards.
What D'Emic and his colleagues found in theropods might eventually turn out to be more the rule than the exception. In their paper, they noted that previous studies of growth strategies have often been limited comparisons of a few species rather than comprehensive studies of lineages.
"My hunch would be that once other groups of animals are studied, we're going to find the same thing," he said. "We're going to find that evolution just takes the path of least resistance" and uses whatever strategy is easiest.
Journal Reference:
Michael D. D'Emic, Patrick M. O'Connor, Riley S. Sombathy, et al., Developmental strategies underlying gigantism and miniaturization in non-avialan theropod dinosaurs, Science, 379, 2023. (DOI: https://doi.org/10.1126/science.adc8714)
(Score: 3, Informative) by gawdonblue on Friday March 24, @06:17AM
Dr. Alan Grant: What kind of metabolism do they have? What's their growth rate?
Muldoon: They're lethal at eight months, and I do mean lethal.
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Random kid: It's a UNIX system! I know this!
(Score: 0) by Anonymous Coward on Friday March 24, @08:49AM (2 children)
Even if these aren't cannibalistic, aren't there other predators that would be able to eat the smaller ones?
Or do the parents/tribe help to take care of the smaller ones till they get big enough?
(Score: 1, Interesting) by Anonymous Coward on Friday March 24, @04:57PM
They're probably just like Elephants.
(Score: 2) by inertnet on Saturday March 25, @10:26AM
My guess is, they had to be smarter than the faster growing ones to survive. Or better at staying hidden.
The strategy for the faster ones seems rather simple, eat as much as you can, as fast as you can. Be the first to advance from prey to predator.