The real question of course was
why not? This puts it to rest. The mass extinction wiped out almost
everything large and vulnerable and spared partially the Sahul Continent (Australia – New Guinea ). Millions of years of evolutionary development
has then taken the handful of surviving sub species and repopulated the globe.
One thing that has not been well
understood is that this extinction preferentially depopulated the large long
lived predators. When this happens the
local biome is seriously diminished as was observed in Yellowstone . This creates a cascade of sympathetic
extinctions within the biome and that makes the recovery for large predators
pretty problematic.
This provides ample time for
smaller species to evolve into available niches. It als explains why there is evidence of former
specialists hanging on in refugia while evolving slowly if at all.
These are subtle distinctions
that I think need modeling and testing in order to properly examine the present
catalog of life forms.
Primitive birds shared dinosaur fate
by Staff Writers
The bones are from the 17 species of Cretaceous birds which went
extinct around the time of the dinosaurs. The two on the far left are foot
bones and the rest are shoulder
bones. Credit: Courtesy
Yale University .
A new study puts an end to the longstanding debate about how archaic
birds went extinct, suggesting they were virtually wiped out by the same
meteorite impact that put an end to dinosaurs 65 million years ago.
For decades, scientists have debated whether birds from the Cretaceous
period - which are very different from today's modern bird species -died
out slowly or were killed suddenly by the Chicxulub meteorite. The uncertainty
was due in part to the fact that very few fossil birds from the end of this era
have been discovered.
Now a team of paleontologists led by Yale researcher Nicholas Longrich
has provided clear evidence that many primitive bird species survived right up
until the time of the meteorite impact. They identified and dated a large
collection of bird fossils representing a range of different species, many of
which were alive within 300,000 years of the impact.
"This proves that these species went extinct very abruptly, in
terms of geological time scales," said Longrich. The study appears the
week of Sept. 19 in the journal Proceedings of the National Academy
of Sciences.
The team examined a large collection of about two dozen bird fossils
discovered in North America - representing a wide range of the species that
existed during the Cretaceous - from the collections of Yale's Peabody Museum
of Natural History, the American Museum of Natural History, the University of
California Museum of Paleontology, and the Royal Saskatchewan Museum. Fossil
birds from the Cretaceous are extremely rare, Longrich said, because bird bones
are so light and fragile that they are easily damaged or swept away in streams.
"The birds that had been discovered hadn't really been studied in
a rigorous way," Longrich said. "We took a much more detailed look at
the relationships between these bones and these birds than anyone had done
before."
Longrich believes a small fraction of the Cretaceous bird species
survived the impact, giving rise to today's birds. The birds he examined showed
much more diversity than had yet been seen in birds from the late Cretaceous,
ranging in size from that of a starling up to a small goose. Some had long
beaks full of teeth.
Yet modern birds are very different from those that existed during the
late Cretaceous, Longrich said. For instance, today's birds have developed a
much wider range of specialized features and behaviors, from penguins to
hummingbirds to flamingoes, while the primitive birds would have occupied a
narrower range of ecological niches.
"The basic bird design was in place, but all of the specialized
features developed after the mass extinction, when birds sort of re-evolved
with all the diversity they display today," Longrich said. "It's
similar to what happened with mammals after the age of the dinosaurs."
Longrich adds that this study is not the first to suggest that archaic
birds went extinct abruptly. "There's been growing evidence that these
birds were wiped out at the same time as the dinosaurs," Longrich said.
"But this new evidence effectively closes the book on the debate."
Other authors of the paper include Tim Tokaryk (Royal
Saskatchewan Museum )
and Daniel Field (Yale
University ).
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