Page 28 - AT

A28 SCIENCE
Friday 25 OctOber 2019
Fossil trove shows life's fast recovery after big extinction

By MALCOLM RITTER
AP Science Writer
NEW YORK (AP) — A remark-
able trove of fossils from
Colorado has revealed de-
tails of how mammals grew
larger and plants evolved
after the cataclysm that
killed off the dinosaurs.
The thousands of speci-
mens let scientists trace
that history over a span of
1 million years, a mere eye-
blink in Earth's lifespan.
Sixty-six million years ago,
a large meteorite smashed
into what is now the Yucat-
an Peninsula of southeast-
ern Mexico. It unleashed
broiling waves of heat and
filled the sky with aerosols
that blotted out the sun
for months, killing off plants
and the animals that de-
pended on them.
More than three-quarters
of species on Earth died
out. But life came back,
and land mammals began
to expand from being small This photo provided by HHMI Tangled Bank Studios in October 2019 shows some of the mammal skull fossils retrieved from Corral
creatures into the wide ar- Bluffs, Colo.
ray of forms we see today Associated Press
— including us. wide a geographic region and perhaps more broad- kilograms). Soon after the than the mammals that
So the new find taps into the fossils' story of recov- ly, he wrote in an email. disaster, the environment survived the extinction,
"the origin of the modern ery applies to, but that he Stephanie Smith of the Field was blanketed with ferns "which I think is pretty fast"
world," said Tyler Lyson, an thinks they show what hap- Museum in Chicago said and the biggest mam- for growth, Lyson said.
author of a paper report- pened over North America. the study's detailed focus mal around was about as What drove mammals to
ing the fossil finds Thursday "We just know so little about on a single area can help heavy as a rat. The world get bigger? The main fac-
in the journal Science. this everywhere on the scientists understand the was in a warming period, tor was the disappearance
The fossils were recovered globe," he said. "At least complexity of recovery as documented in previous of the dinosaurs, leaving
from an area of steep bluffs now we have at one spot when combined with re- studies. By about 100,000 an ecological niche to be
covering about 10 square a fantastic record." sults from elsewhere. years after the meteor- filled, he said. But the qual-
miles (17 square kilometers) Experts not connected to Scientists have previously ite impact, the forest was ity and types of food on the
near Colorado Springs, the study were enthusias- found little evidence about dominated by palm trees landscape probably also
starting three years ago. tic. what happened in the af- and mammals had grown played a role, he said. The
Lyson, of the Denver Mu- It's "an unparalleled docu- termath of the meteorite to the weight of raccoons, simultaneous appearance
seum of Nature and Sci- mentary of how life on land crash, especially on land, almost as big as before the of legume plants and big-
ence, found little in that recovered" after the aster- said Jin Meng of the Ameri- meteorite crash. "That's a ger mammals suggests the
area when he followed oid impact, said P. David can Museum of Natural His- pretty rapid recovery, or at plants may have provided
the standard practice of Polly of Indiana University tory in New York. The new least one aspect of recov- a "protein bar moment," Ly-
scanning for bits of bone. in Bloomington. "The sheer work, he said in an email, ery," Lyson said. son said.
But that changed when he number of fossil specimens appears to provide "the By 300,000 years, the walnut He said the mammals were
began looking instead for and the quality of their best record on Earth to tree family had diversified, creatures that evolved
rocks that can form around preservation are excep- date." and the biggest mammals from animals that had sur-
bone. When the rocks were tional" for this time period, The study reports on hun- were plant eaters about as vived extinction or those
broken open, skulls and he said. dreds of mammal fossils heavy as a large beaver. that immigrated from else-
other fossils within were re- The fossils' story certainly representing 16 species Based on other studies of where.
vealed. represents what happened and more than 6,000 plant their diet, they may have Zhe-Xi Luo of the University
Lyson said it's not clear how in central North America fossils. Researchers also an- evolved along with those of Chicago, who did not
alyzed thousands of pollen trees, Lyson said. participate in the work,
grains to see what plants By 700,000 years, the fos- said the report is remark-
were alive at various times. sil record shows the first able for tying together re-
Analysis of leaves indicat- known appearance of cords for plants, mammals
ed several warming peri- legume plants, the fam- and temperature, giving a
ods during the period. ily that includes peas and "holistic picture."
Here's the recovery story beans. And it reveals the Scientists expected mam-
the fossils tell: two largest mammals mals to recover after the di-
The area had been a forest found in the study, with the nosaur extinctions, he said,
before the meteorite hit, larger one weighing about and the new work "is a huge
home to dinosaurs like T. rex 100 pounds (50 kilograms), step forward in getting a
and mammals no bigger roughly like a wolf. That is firm understanding about
than about 17 pounds (8 about 100 times heavier just how it happened."q