Young dinosaurs lived alone while mammal babies stayed close to parents

A young Brachiosaurus the size of a golden retriever foraged with its siblings, alert for predators. Forty feet away, its parents went about their day, largely indifferent to their offspring's survival. This wasn't neglect — it was how dinosaurs worked.

New research from the University of Maryland suggests this parenting gap fundamentally shaped how the Mesozoic world functioned, and it's forcing scientists to rethink how diverse those ancient ecosystems actually were.

Why parenting style matters

Mammals invest heavily in their young. A tiger mother hunts for cubs nearly as large as herself. Elephant calves, already massive at birth, follow their mothers for years. This extended dependence means young mammals occupy the same ecological role as adults — they eat similar food, face similar predators, and move through similar terrain.

Dinosaurs did the opposite. After a few months to a year, juvenile dinosaurs left their parents and roamed independently. Fossil evidence shows pods of young dinosaurs preserved together, no adults nearby, traveling in age-matched groups and fending for themselves. Thomas R. Holtz Jr., a principal lecturer in the University of Maryland's Department of Geology, describes them as "latchkey kids."

This matters because as dinosaurs grew, everything about them changed — what they ate, which predators could threaten them, where they could move. A juvenile Triceratops occupied a completely different ecological niche than its adult self. Count those as separate functional species, and the math shifts dramatically.

"If we recalculate the numbers treating young dinosaurs as separate functional species from their parents, the total number of functional species in dinosaur fossil communities is actually greater on average than what we see in mammalian ones," Holtz said.

This reframes how scientists understand ancient diversity. We assume modern mammal-dominated ecosystems are more diverse because more species live together. But the Mesozoic world, structured around this parent-offspring separation, may have supported more ecological roles than we've been counting.

How did dinosaur worlds sustain all that diversity?

Holtz proposes two possibilities. The Mesozoic climate — warmer, with higher carbon dioxide levels — likely made plants more productive, generating more food energy to support more animals. Alternatively, dinosaurs may have had lower metabolic rates than similarly sized mammals, requiring less food to survive.

"Our world might actually be kind of starved in plant productivity compared to the dinosaurian one," Holtz suggested. "A richer base of the food chain might have been able to support more functional diversity."

The research doesn't just explain the past. It highlights how fundamentally different dinosaurs were from the mammals that eventually replaced them. They weren't simply "mammals cloaked in scales and feathers," Holtz emphasizes. They operated by entirely different rules — rules that allowed their world to function in ways ours cannot.

As Holtz continues exploring these patterns across different dinosaur life stages, the picture of the Mesozoic becomes less familiar and more strange. That strangeness is where the real science lives.