University of Maryland paleontologist Thomas R. Holtz Jr. has explored how dinosaurs adapted to their ancient environments and the differences between those worlds and our own for decades. His recent research suggests that crucial factors may have been overlooked in comparing ancient dinosaurs with modern mammals.

“Many people view dinosaurs as the Mesozoic equivalent of mammals since both groups were the dominant land animals of their respective eras,” says Holtz.

“However, a crucial difference relates to their reproductive and child-rearing strategies, which scientists haven’t fully considered when comparing these worlds.”

“The methods by which animals raise their young significantly influence their ecosystems. Understanding these differences can help scientists reevaluate ecological diversity,” he explains.

“Young mammals often receive extensive care from their mothers until they are nearly fully grown.”

“In essence, mammal offspring fulfill similar ecological roles as their parents; they consume similar food and interact within the same environment because adults handle most of the responsibilities.”

“You could say mammals have ‘helicopter’ parents—particularly helicopter mothers,” he continues.

“For example, mother tigers continue to hunt for cubs that are nearly their size.”

“Even young elephants, among the largest animals in the Serengeti at birth, rely on their mothers for years.”

“Humans exhibit similar behavior, caring for our children until they reach adulthood.”

“Conversely, dinosaurs exhibited different parenting behaviors. They offered some parental care, but their young were relatively independent.”

“After a short period, from a few months to a year, young dinosaurs left their parents to roam independently, often cautious of one another.”

Dr. Holtz notes that adult crocodiles, closely related to dinosaurs, demonstrate a similar trend.

Crocodiles guard their nests and protect their young for a limited duration; however, within a few months, the young disperse and lead independent lives, taking years to reach adulthood.

“Dinosaurs could be likened to ‘latchkey kids,'” Holtz states.

“Fossil evidence shows that juvenile skeletons were often found together, with no adults nearby.”

“These juveniles congregated in groups of similar ages, learning to feed themselves and fend for their safety.”

This parenting style suited the fact that dinosaurs laid eggs and produced relatively large chicks at once.

By producing multiple offspring at a time and reproducing more frequently than mammals, dinosaurs increased the chances of their lineage’s survival without significant resource investment.

“The key takeaway is that this early separation between parents and offspring, alongside size differences, likely had significant ecological implications,” Holtz noted.

“The dietary needs of dinosaurs shifted as they matured, as did their vulnerabilities to predators and their mobility.”

“Even though adult and juvenile dinosaurs belong to the same biological species, they occupy distinctly different ecological niches.”

“Therefore, they can be regarded as different ‘functional species.’

For instance, a juvenile Brachiosaurus, comparable in size to a sheep, couldn’t access food 10 meters above ground like its adult counterparts.

Juveniles faced different predators, feeding in different locations and avoiding fully grown adults.

As young Brachiosaurus grow from dog-sized to horse-sized to giraffe-sized, their ecological roles evolve significantly.

“This understanding has transformed how scientists perceive ecological diversity,” Holtz emphasized.

Typically, scientists argue that modern mammals inhabit more diverse ecosystems because of the coexistence of varied species.

However, if young dinosaurs are counted as separate functional species and their numbers recalculated, the total functional species in dinosaur fossil assemblages likely exceeds that of mammalian fossil assemblages.

How did ancient ecosystems accommodate all these functional roles? Dr. Holtz proposes two potential explanations.

First, the Mesozoic era featured unique environmental conditions, such as warmer temperatures and elevated carbon dioxide levels.

These factors likely enhanced plant productivity, generating more food energy to sustain larger populations.

Secondly, dinosaurs may have had lower metabolic rates than similarly sized mammals, demanding less food for survival.

“Our world might actually be less productive in terms of plant resources than the age of dinosaurs,” claims Holtz.

“A more robust food chain could support greater functional diversity.”

“If dinosaurs’ physiological demands were lower, their ecosystems might have accommodated far more functional species than found in mammalian systems.”

Dr. Holtz emphasizes that his theory doesn’t necessarily imply that dinosaur ecosystems were vastly more diverse than those of mammals, but rather that diversity may have existed in forms that have yet to be identified by scientists.

He intends to further explore similar patterns within the context of dinosaur functional diversity across different life stages to gain deeper insights into their world and its evolution into our contemporary ecosystem.

“We shouldn’t merely consider dinosaurs as scaled and feathered versions of mammals,” Holtz concludes.

“They are remarkable creatures in their own right, and the full scope of their existence is still being uncovered.”

This research will be detailed in Holtz’s paper, set to appear in the Italian Journal of Geosciences.

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Thomas R. Holtz Jr. et al. 2026. Raising Babies: A Preliminary Investigation into Ontogenetic Niche Partitioning in Dinosaurs and Long-term Maternal Care in Mammals within Their Ecosystems. Italian Journal of Geosciences 145; doi: 10.3301/IJG.2026.09