[Narrator]:Teenagers are notorious for causing upheaval
as they stake their ground in social webs.
Turns out, the young of the most massive carnivorous dinosaurs
carved out a vast space for their entire species in prehistoric ecosystems.
Paleontologists have unearthed dinosaur fossils
that cover an array of species of different sizes.
On a global scale, medium-sized carnivore fossils
are slightly less common than small and large.
Within narrower geographical regions, the disparity is amplified.
This gap has been a mystery to scientists:
Did those carnivore fossils fail to survive until modern day,
or had they simply not planted their trowels in the right plot of soil?
A new study suggests another answer—
that carnivorous dinos weighing between 10 and 1000 kilograms
were replaced by young megatheropods—
hulking carnivores like T. rex that weighed over 1000 kilos fully grown—
as they developed from football-sized eggs
into more substantial juveniles
before eventually filling the shoes of their colossal parents.
The researchers examined 557 dinosaur taxa
spanning seven continents and 136 million years
across the Jurassic and Cretaceous.
Carnivores weighing between 100 to 300 kilos
were far less common in local habitats than small and large species.
It’s as if a mammal community in the modern African Savanna
had no carnivores between the size of a lion and a bat-eared fox.
The study differed from most dinosaur research because it looked at ancient ecosystems,
which are tricky to describe and confirm through fossil evidence.
So the researchers crafted mathematical models based on biomass
to make predictions about juveniles of particular species.
The models indicated that an enclave of little giants likely excluded a
more diverse range of species similar in size.
This dynamic can be found in modern ecosystems:
when animals have young whose bodies are extremely small compared to fully grown adults—
such as egg-laying reptiles like Komodo dragons
and large crocodiles— they can dominate wide swaths of ecosystems
as they progress through life,
shouldering out species that might have otherwise filled those roles.
The findings bolster efforts to understand how dinosaurs functioned in their habitats.
New ways of studying microscopic scrapes on animal teeth
could be applied to dinosaur fossils.
That would help quantify how dinosaurs hunted—
rather than typical skull analysis of how they ate—
to fill additional gaps in knowledge.
Yet another trail blaze
as we journey to conceive of a land before time.
[Music]