University of Maryland paleontologist Thomas R. Holtz Jr. has spent decades puzzling over how dinosaurs fit into their ancient worlds—and how those worlds differed from ours. His latest research suggests that scientists may have missed something important when comparing ancient dinosaurs to modern mammals.
Some sauropod dinosaurs such as Alamosaurus sanhuanaformed herds divided by age. Image credit: DiBgd.
“Many people think of dinosaurs as sort of the mammal equivalents of the Mesozoic era, since they were both the dominant land animals during their respective time periods,” Dr Holtz said.
“But there's a critical difference that scientists haven't really taken into account when looking at how different their worlds are: reproductive and parental strategies.”
“The way animals raise their young affects the ecosystem around them, and this difference may help scientists reevaluate how we perceive ecological diversity.”
“Young mammals remain under intensive maternal care until they are almost adults.”
“Mammalian offspring perform essentially the same ecological role as their parents: eating the same foods and interacting with the same environment because the adults do most of the heavy lifting.”
“You could say that mammals have helicopter parents, but in reality they have helicopter moms,” he explained.
“The mother tiger still hunts for cubs the same size as herself.”
“Young elephants, already among the largest animals in the Serengeti at birth, continue to follow and rely on their mothers for many years.”
“In this sense, people are the same: we take care of our babies until they become adults.”
“Dinosaurs, on the other hand, acted very differently. Although they provided some parental care, young dinosaurs were relatively independent.”
“After just a few months or a year, the young dinosaurs left their parents and wandered around alone, looking out for each other.”
Dr. Holtz pointed to a similar case in adult crocodiles, some of the closest living analogs to dinosaurs.
Crocodiles guard nests and protect hatchlings for a limited period of time, but within a few months the young disperse and live independently, taking years to reach adult size.
“Dinosaurs were more like children with a castle,” Dr. Holtz said.
“In terms of fossil evidence, we found groups of juvenile skeletons, all preserved together, with no trace of adults nearby.”
“These young adults typically traveled together in groups of similarly aged individuals, foraging for food and fending for themselves.”
The dinosaurs' free-ranging style of rearing was complemented by the fact that they incubated eggs, forming relatively large broods in a single attempt.
Because multiple offspring were born at the same time, and reproduction occurred more frequently than in mammals, dinosaurs increased the chances of survival of their lineage without expending much effort or resources.
“The key point here is that this early parent-offspring separation, and the size differences between these creatures, likely had profound ecological consequences,” Dr Holtz said.
“Different life stages change what a dinosaur eats, what species might threaten it, and where it can move effectively.”
“Although adults and offspring are technically the same 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 above the ground, like an adult. Brachiosaurus.
It must feed in different places and on different plants and face threats from predators that avoid mature adults.
Being young Brachiosaurus grows – from the size of a dog, to the size of a horse, to a giraffe, and to the latest enormous size – its ecological role is constantly changing.
“What's interesting is that this completely changes the way scientists look at ecological diversity in this world,” Dr. Holtz said.
“Scientists generally believe that mammals today live in more diverse communities because we have more species living together.”
“But if we count young dinosaurs as separate functional species from their parents and crunch the numbers, the total number of functional species in these fossil dinosaur communities is actually on average larger than what we see in mammals.”
So how could ancient ecosystems fulfill all of these functional roles? Dr. Holtz believes two explanations are plausible.
First, the Mesozoic world had different environmental conditions, such as higher temperatures and higher levels of carbon dioxide.
These factors would make plants more productive, producing more food energy to support more animals.
Second, dinosaurs may have had a slightly lower metabolic rate than similarly sized mammals, meaning they required less food to survive.
“It may be that our world actually lacks plant productivity compared to the world of dinosaurs,” Dr Holtz said.
“A richer food web base could support greater functional diversity.”
“And if dinosaurs had a less demanding physiology, their world could support many more functional species of dinosaurs than mammals.”
Dr Holtz believes his theories do not necessarily indicate that dinosaur ecosystems were significantly more diverse than our own mammalian world – just that this diversity may take forms that scientists do not currently recognize.
He plans to continue studying similar patterns of functional diversity across dinosaur life stages to better understand the world they lived in and how it evolved into the world we live in today.
“We shouldn't just think of dinosaurs as mammals with scales and feathers,” Dr Holtz said.
“These are unique creatures that we are still trying to get a complete picture of.”
His paper appears in Italian Journal of Geosciences.
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Thomas R. Holtz Jr. etc.. 2026. Raising a child: a preliminary study of the influence of ontogenetic niche partitioning in dinosaurs compared with long-term maternal care in mammals in their respective ecosystems. Italian Journal of Geosciences 145; doi: 10.3301/IJG.2026.09
