Even before the great asteroid strike, were dinosaurs on the verge of extinction? Researchers provide fresh
Shown here is an artist's reconstruction of what the North American environment may have looked like 66 million years ago.
In paleontology, there has long been a controversy about: Were dinosaurs already on the verge of extinction when the space rock struck
Earth 66 million years ago, or were they flourishing when the asteroid struck one
fateful spring day?
A group of scientists examined the fossil record of North America, concentrating
on the 18 million years preceding the catastrophic extinction at the end
of the Cretaceous epoch, in order to find explanations. The latest study, which was released on Tuesday in the journal Current Biology,
supports an increasing amount of data showing that the dinosaurs were thriving
prior to the asteroid's catastrophic hit.
The more than 8,000 fossils that are currently available for examination, however,
indicate that the number of dinosaur species peaked approximately 75 million years
ago and then decreased in the 9 million years preceding the asteroid crash.
It all boils down to the quality, or accuracy, of the fossil record. Since the 1970s, people have realized that the fossil record is not accurate but rather
a biased portrayal of the past, according to main study author Chris Dean,
a paleontology research fellow at University College London.
“It’s only in very recent years that we’ve started to see the full scope of
(the bias issue), when using these big datasets of fossil occurrences,” he said.
Dean and his colleagues used occupancy modeling, a statistical technique
to calculate the likelihood of a dinosaur being present at a site, to gain a better
understanding of what was happening at the time of the dinosaurs' death. Occupancy modeling is used in modern ecology and conservation to take into
consideration the possibility that a species may be unnoticed or undiscovered
even if it is present in a certain area. According to Dean, this study is the first time the method has been applied
to a large-scale study of dinosaurs.
Alfio Alessandro Chiarenza
"It is incredibly difficult to apply a new technique," Dean said. It will not be the final word, in my opinion. There must be a great deal more to say.
Four major dinosaur families were examined in the new study: the Ceratopsidae
A paleontologist is seen here prospecting for dinosaur fossils in North American Cretaceous rocks. The study's findings suggested that less rock from the late Cretaceous is exposed on Earth's surface, which may cloud the picture on dinosaur diversity during that window of time.
(large three-horned herbivores, including Triceratops), the Hadrosauridae
(duck-billed dinosaurs),
the Tyrannosauridae (carnivores, including Tyrannosaurus rex), and the Ankylosauridae
(armored plant-eating dinosaurs, including the club-tailed Ankylosaurus).
"In order to effectively have more data, we looked at these larger categories,"
Dean stated. "We created a large spatial grid of North America and identified
the locations
where fossils can be found, where we have actually discovered fossils, and the
number of times individuals have visited these locations to search for fossils."
After feeding the data into a computer model, Dean and his associates discovered
a discrepancy between the program's suggested fossil record and the actual fossil record.
Closing the gaps in the fossil record
According to the model, during the 18 million-year period under consideration,
the four dinosaur clades most likely inhabited a constant percentage of the land,
indicating that their potential habitat area remained steady and that there was little
chance of extinction.
The absence of rock exposed at the Earth's surface during that time period, which
would have allowed fossil hunters to examine it now, was one of the elements that
would have obscured the true diversification patterns of dinosaurs.
According to a statement from study coauthor Alfio Alessandro Chiarenza,
a Royal Society Newton International Fellow at University College London's
department of Earth sciences, "in this study, we show that this apparent decline
is more likely a result of a reduced sampling window, caused by geological
changes in these terminal Mesozoic fossil-bearing layers — driven
by processes such as tectonics, mountain uplift, and sea-level retreat — rather
than genuine fluctuations in biodiversity."
According to Chiarenza, "dinosaurs were probably not unavoidably doomed
to extinction at the end of the Mesozoic." "They might still be on this planet with mammals, lizards, and their living offspring,
birds, if it were not for that asteroid."
According to Darla Zelenitsky, a paleontologist from the University of Calgary
in Alberta who was not involved in the study, it helped to emphasize the biases
that might have affected scientists' comprehension of the true pattern of dinosaur
diversity preceding the extinction event.
"Detecting dinosaurs and understanding their diversity patterns within that window of time shortly before the mass extinction was more challenging due to the nature of the rock record," she added.
We are aware that the rock record contains biases that can mask actual biological tendencies, so it makes sense. Our chances of discovering dinosaurs in a certain rock increase with the amount of rock that is exposed at the surface (today), which helps us better understand the patterns of diversity in that rock.
Although he described the paper as "thorough and detailed," Mike Benton,
a professor of vertebrate paleontology at the University of Bristol in the
United Kingdom, stated that it does not establish that dinosaur diversity was
not reduced prior to the extinction event. According to Benton's research, dinosaur populations were declining prior
to the asteroid's destruction. The latest study did not include him.
Benton emailed, "The current article suggests that the'reduction' can be explained
as a statistical artefact." "What it demonstrates, in my judgment, is just that the decline might be genuine
or could be explained by less sample."
Source edition.cnn.com
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