News
Release from Ohio University:
Ancient “terror bird”
used powerful beak to jab like an agile boxer
International team uses computer modeling
to reconstruct kills of prehistoric predator
ATHENS, Ohio (Aug. 18, 2010)—The ancient “terror bird”
Andalgalornis couldn’t fly, but it used its
unusually large, rigid skull—coupled with a hawk-like
hooked beak—for a fighting strategy reminiscent of boxer
Muhammad Ali. The agile creature repeatedly attacked and
retreated, landing well-targeted, hatchet-like jabs to
take down its prey, according to a new study published
this week in the online, open-access journal PLoS ONE
by an international team of scientists.
The study is the first detailed look at the predatory
style of a member of an extinct group of large,
flightless birds known scientifically as phorusrhacids but popularly labeled “terror birds”
because of their fearsome skull and often imposing size.
Terror birds evolved about 60 million years ago in
isolation in South America, an island continent until
the last few million years, radiating into about 18
known species ranging in size up to the 7-foot-tall (2.1
meters) Kelenken.
Because terror birds have no close analogs among
modern-day birds, their life habits have been shrouded
in mystery. Now, a multinational team of scientists has
performed the most sophisticated study to date of the
form, function and predatory behavior of a terror bird,
using CT scanning and advanced engineering methods.
“No one has ever attempted such a comprehensive
biomechanical analysis of a terror bird,” said study
lead author Federico Degrange of the Museo de La Plata/CONICET
in Argentina, who is conducting his doctoral research on
the evolution of terror birds. “We need to figure out
the ecological role that these amazing birds played if
we really want to understand how the unusual ecosystems
of South America evolved over the past 60 million
years.”
The terror bird under study is called
Andalgalornis
and lived in northwestern Argentina about six million
years ago. It was a mid-sized terror bird, standing
about 4.5 feet tall (1.4 meters) and weighing in at a
fleet-footed 90 pounds (40 kg). Like all terror birds,
its skull was relatively enormous (14.5 inches or 37
centimeters) with a deep narrow bill armed with a
powerful, hawk-like hook.
Article co-author Lawrence Witmer of the Ohio University
College of Osteopathic Medicine ran a complete skull of
Andalgalornis through a CT scanner, giving the
team a glimpse into the inner architecture of the skull.
The scans revealed to Witmer, Degrange and article
co-author Claudia Tambussi, also from the Museo de La
Plata/CONICET and Degrange’s PhD advisor, that Andalgalornis was unlike other birds because it had
evolved a highly rigid skull.
“Birds generally have skulls with lots of mobility
between the bones, which allows them to have light but
strong skulls. But we found that Andalgalornis
had turned these mobile joints into rigid beams. This
guy had a strong skull, particularly in the fore-aft
direction, despite having a curiously hollow beak,” said
Witmer, Chang Ying-Chien Professor of Paleontology and a
professor of anatomy.
The evolution of this large and rigid bony weapon was
presumably linked to the loss of flight in terror birds,
as well as to their sometimes gigantic sizes.
From the CT scans, Stephen Wroe, director of the
Computational Biomechanics Research Group at the
University of New South Wales, Australia, assembled
sophisticated 3D engineering models of the terror bird
and two living species for comparison (an eagle, as well
as the terror bird’s closest living relative, the
seriema). Using computers and software supplied by Wroe,
Degrange and Karen Moreno of the Université Paul
Sabatier in Toulouse, France, applied an approach known
as Finite Element Analysis to these models to simulate
and compare the biomechanics of biting straight down (as
in a killing bite), pulling back with its neck (as in
dismembering prey) and shaking the skull from side to
side (as in thrashing smaller animals or when dealing
with larger struggling prey). Color images created by
the program show cool-blue areas where stresses are low
and white-hot areas where stresses get dangerously high.
The engineering simulations supported the CT-based
anatomical results. “Relative to the other birds
considered in the study, the terror bird was
well-adapted to drive the beak in and pull back with
that wickedly recurved tip of the beak,” remarked Wroe,
“but when shaking its head from side to side, its skull
lights up like a Christmas tree. It really does not
handle that kind of stress well at all.”
A
key part of the engineering analysis was determining how
hard of a bite
Andalgalornis
could deliver.
To examine bite force in birds in general, Degrange and
Tambussi worked with
zookeepers
at the
La Plata Zoo
to get a seriema and an eagle to chomp down on their
bite meter.
“Combining
all this information, we discovered that
the
bite force of Andalgalornis
was a little lower than we expected and weaker than the
bite of many carnivorous mammals of about the same size.
Andalgalornis may have compensated for this
weaker bite by using its powerful neck muscles to drive
its strong skull into prey like an axe,”
Degrange said.
Taken together, the team’s results give new insight into
the lifestyle of a unique avian predator. This terror
bird was no slugger and couldn’t wade into the fray like
a feathered Joe Frazier. Its skull, though strong
vertically, was too weak from side to side, and the
hollow beak was in danger of catastrophic fracture if Andalgalornis grappled too vigorously with large
struggling prey.
Instead, the study shows that the terror bird was
required to engage in an elegant style more like
Muhammad Ali, using a repeated attack-and-retreat
strategy, using well-targeted, hatchet-like jabs. Once
killed, the prey would have been ripped into bite-sized
morsels by the powerful neck pulling the head straight
back or, if possible, swallowed whole.
Feeding on a diversity of strange, now-extinct mammals
and competing with the likes of saber-tooth marsupials,
terror birds became top predators in their environment.
At least one gigantic terror bird, Titanis,
eventually invaded North America about two to three
million years ago, but the animals disappeared from
Earth shortly after.
The research was funded by grants to Witmer from the
U.S. National Science Foundation; to Wroe from the
Australian Research Council and the Australia and
Pacific Science Foundation; and to Tambussi from the
Fondo Nacional para la Investigación Científica y
Tecnológica (Argentina).
Contacts: 1. USA (Eastern time zone): Lawrence Witmer, (740)
591-7712,
witmerL@ohio.edu;
Andrea Gibson, (740) 597-2166,
gibsona@ohio.edu
2. Argentina: Federico Degrange, (+54221) 425-7744 (int
147),
fjdegrange@fcnym.unlp.edu.ar
3. Australia: Stephen Wroe, 61 2 9385 3866 or 0408 812
702,
s.wroe@unsw.edu.au
4. France: Karen Moreno, +33 (0) 561 55 80 80,
kmoreno@cict.fr.
Note: The original journal article,
Supplementary Information, and a common language summary are available online:
terror_birds_PLoS-ONE.htm.
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