Image courtesy of Davide Bonadonna
Joel Kontinen
When
according to evolution, did the dinosaurs die? In most cases,
they say it was around 66 million years ago, but new research shows they did
not die,
Dinosaurs likely
weren’t declining before an asteroid wiped them all out; instead, there may
just be limited fossils from that time period, according to a new study.
It has been hotly debated whether dinosaur populations
were thriving or dwindling when a huge asteroid slammed into the planet about
66 million years ago. Specifically, a drop in the availability of dinosaur
fossils from the years leading up to the asteroid has led some scientists to
believe the giants were doomed regardless of the impact.
Christopher Dean at
University College London and his team analysed a dataset of more than 8000
fossils from four types of dinosaurs that lived between 84 million and 66
million years ago in North America, including the famed Tyrannosaurus rex and Triceratops.
They
found many fossils of dinosaurs from 84 million to 75 million years ago – and
then that number drops in the following 9 million years leading up to the
Chicxulub impact. But there was more.
When calculating how much land is currently accessible
to palaeontologists from the years leading up to the asteroid’s impact and how
many excavation expeditions have been undertaken in those areas, Dean’s team
found there simply aren’t many of the right rocks available for today’s
scientists to study.
Because palaeontologists look for fossils in ancient
layers of Earth’s crust that have since been exposed to the surface, it is like
working on “a puzzle where half the pieces are missing,” says Dean.
When the team used ecological models to estimate the
plausible number of dinosaurs in those areas — including information about the
geology and geography at the time — their calculations suggested that overall
dinosaur numbers stayed stable before the asteroid impact. There weren’t fewer
dinosaurs at the time; we are just less likely to find them, says Dean: “It
looks like our ability to detect dinosaurs is influencing the patterns that we
see in the fossil records more than anything else.”
This adds to the
growing body of research suggesting there is a bias in how many fossils
palaeontologists can access from North America in the 9 million years leading
up to the asteroid hit, according to Manabu Sakamoto from Reading
University in the UK, who was not involved in the study. Yet,
he says, this doesn’t change the bigger picture of dinosaurs being in decline
before the asteroid hit.
Even if dinosaurs were still populous and dominant
towards the end of the Cretaceous period, there doesn’t seem to be a lot of
variation in their species. Sakamoto’s
research suggests that, during the 175 million years dinosaurs roamed
Earth, the rate at which new species of dinosaurs appeared was slowing down
overall, leading to more dinosaur species going extinct than new ones evolving.
This long-term decline in dinosaur diversity still
holds true, says Sakamoto, despite the new research suggesting a bias in the
available fossils: “Those two things are not mutually exclusive of each other.”
According to the creation based timeline, dinosaurs did not die off so
suddenly but they have been around much later.
Sofia Quaglia 2025 Rethink of fossils hints dinosaurs still thrived before asteroid hit | New Scientist 8 April
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