ZAP // DALL-E-2
Many dinosaurs followed a strategy opposite to ours (mammals): lots of offspring and little investment. But there are also signs of more direct care. One thing is certain: youth was fundamental to ecosystems.
For decades, the dominant image of dinosaurs has been filtered through a very “mammalian” lens: large animals at the top of food chains, with behaviors comparable to those of the large vertebrates that still exist today.
However, the parent dinosaurs appear to have followed very different rules—so different that they may have shaped past ecosystems as much as the dinosaurs themselves.
One of the findings that helped change this view came from a study in 2004already Chinapoints out . During an excavation, researchers discovered a fossil of Psittacosaurusa horned herbivore that lived about 120 million years ago, surrounded by the remains of 34 young grouped around it. The finding, now more than 20 years old, was seen as one of the first strong pieces of evidence that, at least in some species, there was some type of parental care.
The important detail here is that it is not known whether the adult was male or female: who was certainly doing a good job educating their children? The father or the mother? But assuming that parental care is necessarily sex-specific may say more about us mammals than it does about dinosaurs.
Among current mammals, the typical reproductive strategy involves invest a lot in few offspringwhich are born relatively large and remain dependent on their parents for a long time. But many dinosaurs appear to have followed a opposite logic: many eggs, many offspring and high mortality, in a dynamic similar to that of sea turtles, in which only a small fraction of the offspring reach adulthood.
Furthermore, the adults did not always remain close to the nests until hatching, and the chicks were born much smaller when compared to the final size of the animal.
“Ecosystem engineers”
A recent study sought to understand how this strategy could have influenced ancient ecosystems through a mechanism known as niche shift throughout development: the same animal can occupy very different ecological roles as it grows, and put pressure on different resources at different times in its life.
In practical terms, this means that a population with many juveniles can have a collective effect on the environment much greater than that suggested by adults alone.
Os sauropodsthose big long-necked dinosaurs, are a clear example of this idea.
A recent investigation into fossilized stomach contents (the first found for this group) suggests that the diet varied throughout growth. According to paleontologist Stephen Poropat, a set of offspring could quickly devastate low vegetation; adolescent individuals, larger and voracious, would press plants at different heights; and the few that did reach adults would feed mainly at the top of the trees or, in some cases, would continue to “vacuum” vegetation closer to the ground.
Throughout their lives, these dinosaurs would function as “ecosystem engineers”influencing the evolution of plants, whether favoring physical or chemical defenses, growth rates, or even the dispersal of seeds through feeding and defecation.
To more fairly compare dinosaur and mammal communities, the authors of the new study looked at “functional species” richness: instead of just counting how many species there were, they estimated how many different ecological roles a set of animals could play.
If only adults are considered, mammal communities appear richer; but when juveniles are included, dinosaurs gain an advantagesuggesting that the abundance of individuals at young stages drastically increased the range of ecological functions within the same group.
But then: were they good parents?
As for what this means in terms of “parenting styles,” the conclusion is less uniform: there was no single model.
Some dinosaurs may have laid eggs and moved on, leaving their offspring at the mercy of the environment; in other cases, there is evidence of more direct care, including the incubation of broods.
And, as in many birds, direct descendants of dinosaurs, it is plausible that in certain lineages care was not exclusive to females, and could involve males protecting and incubating eggs, similar to what happens in modern species such as emus, rheas or cassowaries.
