Mass extinctions have a silver lining, providing
opportunities for marginalized creatures to rise to power. While
that notion seems obvious, it hadn't been demonstrated for the
end-Permian extinctions, which occurred about 252 million years ago
and wiped out about 90% of life on Earth. So, researchers took a
detailed look at the numbers and distribution of land-dwelling
species at five sites scattered across the southern part of
Pangaea, the supercontinent that existed at the time of the
die-offs. (Previous analyses had looked at only trends in marine
species or for limited regions on land, the team notes.) Of the 62
species found at the sites about 5 million years before the
die-offs, 21 (or about 34%) were found in two or more of the sites,
suggesting a wide distribution of those creatures. But10
million years after the end-Permian extinctions, only five species
out of 68—none of which matched the 62 that lived before the
die-offs—were
found at more than one site. The analysis also reveals that after the mass
extinctions, species typically had smaller, less-connected
geographical ranges than did the species living before the
die-offs, the researchers report online today in theProceedings
of the National Academy of Sciences. Altogether, the
trends suggest that when widely prevalent creatures such as the
pig-sizedDicynodon(left)
were removed from the scene, species such as the
3-meter-longAsilisaurus(right)—a
member of the archosaurs, which included dinosaurs and many groups
alive today, such as crocodilians and birds—could diversify and
thrive.
青春就应该这样绽放 游戏测试：三国时期谁是你最好的兄弟！！ 你不得不信的星座秘密Image may be NSFW.
