Name:
Phorusrhacos
(Rag thief).
Phonetic: Foe-roos-rah-coss.
Named By: Florentino Ameghino - 1887.
Synonyms: Callornis giganteus,
Darwinornis copei, D. socialis, D. zittelli, Eucallornis
giganteus, Liornis floweri, L. minor, Mesembriornis
quatrefragesi, M. studeri, Owenornis affinis, O. lydekkeri,
Phororhacos longissimus P. platygnathus, P. sehuensis,
Stereornis gaundryi, S. rollieri, Titanornis mirabilis.
Classification: Chordata, Aves, Cariamae,
Phorusrhacidae, Phorusrhacinae.
Species: P. longissimus (type).
Diet: Carnivore.
Size: 2.4-2.5 meters tall, Skull up to 65
centimetres long.
Known locations: Argentina, Santa Cruz Province.
Time period: Mid Miocene.
Fossil representation: Many known specimens.
Like
similar predatory birds of its day, Phorusrhacos
was flightless
with its wings greatly reduced in size. The wings of Phorusrhacos
also had sharp hooks that seem to be more suited for gripping. These
hooks have been suggested as being used to secure struggling prey as
Phorusrhacos dispatched it with its beak, but it
is also possible
that they may have had a use in combat between Phorusrhacos
individuals. Either purpose is possible, but birds like
Phorusrhacos are usually depicted as hunting small
to medium sized prey
which may have been too small to be gripped with the wings.
The
beak of Phorusrhacos is large and strongly curved
to form a hook tip
shape that is commonly seen in other birds that eat meat. This beak
seems to have been the primary tool for killing prey with two main
possible uses now generally accepted. The first method has been
derived from observing the South American seriema birds which are
thought to be the closest living relatives to terror birds like
Phorusrhacos. Seriema birds pick up prey in their
beaks and then
throw it against the ground as hard as they can. Not only does this
stun and kill prey, it breaks the bones so that small prey can be
more easily swallowed as well as making it easier to use their claws to
tear parts off prey too large to swallow. Many palaeontologists think
that Phorusrhacos would have killed and eaten in a
similar way, just
on a larger scale.
The
second method of killing prey involves using the beak to make precision
strikes on critical body parts. As mentioned above, the beak is
strongly curved and pointed, more so than necessary just for the
purpose of feeding. It’s possible that this beak hook was brought
down on top of prey for a quick strike to the back of the preys skull.
This strike would have pierced the skull, causing damage to the
brain resulting in instant death to the prey.
In
order for Phorusrhacos to deliver a fatal strike it
would first have to
catch its prey, something it was well adapted to do. While the
wings were too small for flight, the legs were very long and
powerful. Across open ground Phorusrhacos would
have easily been
capable of chasing and catching up smaller mammalian prey. In
hunting, Phorusrhacos may have stayed near thin
outcroppings of
shrubs and trees where its body form could more easily blend in with
the tree trunks. Once prey approached close it could then ambush it
with devastating speed before it had time to react. Once prey was
caught and killed, Phorusrhacos probably used a
combination of its
sharp beak and the sharp claws of its feet to tear up the carcass so
that it could be more efficiently eaten. While the beak of
Phorusrhacos was sharp, the advantage of using the
claws on its feet
is clear because with these it could use its entire body weight
(estimated to be as much as 130 kilograms) to push its claws
through its preys body.
The
suggestion has been made that Phorusrhacos and
another ‘terror bird’
named Titanis
are actually the same genus. However, while both
birds are very similar, Titanis has a more robust
build,
particularly a shorter neck and heavier support for a skull. Because
of this the majority of researchers continue to recognise Titanis
as an
independent genus, although because it is very similar it continues
to belong to the same sub-family as Phorusrhacos,
the Phorusrhacinae.
Further reading
- Systematic revision of the Phorusrhacidae (Aves: Ralliformes). -
Pap�is Avulsos de Zoologia. 43 (4): 55–9. - Herculano M. F. Alvarenga
& Elizabeth H�fling - 2003.
- New skull remains of Phorusrhacos longissimus (Aves, Cariamiformes)
from the Miocene of Argentina: implications for the morphology of
Phorusrhacidae. - Journal of Paleontology. 93 (6): 1221–1233. -
Federico J. Degrange, Drew R. Eddy, Pablo F. Puerta & Julia
Clarke - 2019.