Study: Dinosaurs’ free-roaming parental strategy fundamentally reshaped the Mesozoic world

Thomas R. Holtz Jr., a paleontologist at the University of Maryland, has spent decades wondering how dinosaurs fit into their ancient worlds — and how those worlds differ from ours. His latest research reveals that scientists may have missed something important when comparing ancient dinosaurs to modern mammals.

“Many people think of dinosaurs as sort of equivalents to the mammals of the Mesozoic era, since they were both the dominant land animals of their respective periods,” Dr. Holtz said.

“But there is one crucial difference that scientists haven’t really taken into account when looking at how different their worlds are: reproductive and parental strategies.”

“How animals raise their young impacts the ecosystem around them, and this difference can help scientists reevaluate how we perceive ecological diversity.”

“Young mammals remain under intensive maternal care until they are almost adults.”

“Mammalian descendants essentially play the same ecological role as their parents – eating the same food and interacting with the same environment – ​​because the adults do the heavy lifting. »

“You could say that mammals have helicopter parents, and in reality, helicopter moms,” he explained.

“A mother tiger continues to hunt cubs as big as herself.”

“Young elephants, already among the largest animals in the Serengeti when they are born, continue to follow and rely on their mothers for years. »

“Humans are the same in this way: we take care of our babies until they are adults.”

“On the other hand, dinosaurs functioned very differently. Although they provided some parental care, young dinosaurs were relatively independent.”

“After just a few months or a year, the young dinosaurs would leave their parents and wander around on their own, looking out for each other.”

Dr Holtz highlighted a similar case in adult crocodilians, among the closest living analogues of dinosaurs.

Crocodiles guard nests and protect hatchlings for a limited period, but within a few months the juveniles disperse and live independently, taking years to reach adult size.

“Dinosaurs were more like latchkey children,” Dr. Holtz said.

“In terms of fossil evidence, we found groups of juvenile skeletons, all preserved together, with no evidence of adults nearby.”

“These juveniles tended to travel together in groups of similar-aged individuals, foraging for their own food and fending for themselves.”

The dinosaurs’ free-range parenting style complemented the fact that they incubated eggs, forming relatively large clutches in a single attempt.

Because multiple offspring were born at the same time and reproduction was more frequent than in mammals, dinosaurs increased their lineage’s chances of survival without expending much effort or resources.

“The key point here is that this early separation between parent and offspring, as well as the size differences between these creatures, likely led to profound ecological consequences,” Dr Holtz said.

“During different stages of its life, what a dinosaur eats changes, what species can threaten it and where it can move efficiently also changes.”

“Although adults and offspring are technically the same biological species, they occupy fundamentally different ecological niches.”

“Thus, they can be considered different ‘functional species’.”

For example, a minor Brachiosaurus the size of a sheep cannot reach vegetation 10 m from the ground like an adult Brachiosaurus.

It must feed in different areas and on different plants and face threats from carnivores that would avoid full-grown adults.

As a young person Brachiosaurus grows – from the size of a dog to the size of a horse to the size of a giraffe to its final enormous proportions – its ecological role continually changes.

“What’s interesting here is that this completely changes the way scientists think about ecological diversity in this world,” Dr. Holtz said.

“Scientists generally think that mammals today live in more diverse communities because we have more species living together.”

“But if we count young dinosaurs as functional species distinct from their parents and recalculate the numbers, the total number of functional species in these fossil dinosaur communities is actually higher on average than what we see in mammals.”

So how could ancient ecosystems assume all these functional roles? Dr. Holtz believes that two explanations could be plausible.

First, the Mesozoic world had different environmental conditions, such as warmer temperatures and higher carbon dioxide levels.

These factors would have made plants more productive, generating more food energy to support more animals.

Second, dinosaurs may have had a slightly lower metabolic rate than mammals of similar size, meaning they needed less food to survive.

“Our world might actually be somewhat starved in terms of plant productivity compared to that of the dinosaurs,” Dr. Holtz said.

“A richer base of the food chain could have supported greater functional diversity.”

“And if dinosaurs had less demanding physiology, their world could have supported many more functional dinosaur species than mammal species.”

Dr. Holtz believes that his theories do not necessarily indicate that dinosaur ecosystems were significantly more diverse than our own mammalian world – but simply that diversity could take forms that scientists do not currently recognize.

He plans to continue exploring similar patterns within this framework of functional diversity across the different stages of dinosaur life to better understand the world they lived in and how it evolved into the one humans live in today.

“We shouldn’t just think of dinosaurs as mammals covered in scales and feathers,” Dr. Holtz said.

“These are distinctive creatures that we are always looking to capture a complete picture of.”

His article appears in the Italian Journal of Geosciences.

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Thomas R. Holtz Jr. and others. 2026. Raising Baby: Preliminary exploration of the effect of ontogenic niche distribution in dinosaurs versus long-term maternal care in mammals in their respective ecosystems. Italian Journal of Geosciences 145; doi: 10.3301/IJG.2026.09