Titanis
Name: Titanis
(Titanic).
Phonetic: Tie-tan-is.
Named By: Pierce Brodkorb - 1963.
Classification: Chordata, Aves, Cariamae,
Phorusrhacidae, Phorusrhacinae.
Species: T. walleri (type).
Diet: Carnivore.
Size: Estimated at 2.5 meters tall.
Known locations: USA, Florida, Texas.
Time period: Zanclean of the Pliocene through to
Gelasian of the Pleistocene.
Fossil representation: Multiple but fragmentary post
cranial remains.
Large flightless birds are well known in the fossil records of the world’s southern continents, but it is usually the ‘terror birds’ of the Phorusrhacidae that usually steal the thunder of the others. Titanis manages to stand out from these other terror birds, not because it was one of the largest or most terrifying, but because it was the first and so far only one known in North America. It is thought that Titanis appeared in North America as a result of the Great American Interchange, an event that happened as a result of the creation of the Isthmus of Panama. Further support for this theory comes from the presence of other typically South American animals such as giant ground sloths like Megalonyx being found in North America. It also allowed North American animals such as the sabre toothed cat Smilodon to enter South America.
Titanis the
bird.
Because
only fragmentary remains of the post cranial skeleton are known, much
of what we ‘know’ about Titanis has been the
result of comparison
to other better known and preserved phorusrhacids. This is especially
true for the skull which to date (Dec 2011) remains unknown to
science. How this comparison works is Titanis
fossils are measured
and compared to other more complete remains which then allows the
missing gaps to be filled in. These more complete reconstructions are
then assembled to get a better idea of the complete bird, which in
the case of Titanis resulted in a two and a half
meter tall terror bird.
Titanis
has a strong similarity with other large members of the Phorusrhacidae
which has made the reconstruction much easier. However this same
similarity has also raised the question of if Titanis
actually deserves
to be classed as its own genus, something that is very hard to
establish with certainty due to the fragmentary nature of original
remains. The main synonym contender is the similarly sized
Phorusrhacos, the first of the terror birds to be named and
discovered. Both are so similar to one another that they both qualify
as members of the Phorusrhacinae. However, Titanis
lived during a
much later time than Phorusrhacos, and the fragmentary remains of
Titanis actually do point to a much more robust,
heavily built bird.
These differences themselves are enough to convince most
palaeontologists that Titanis represents a specific
genus.
Many
entries regarding Titanis mention that it had
grasping hands similar to Theropod dinosaurs like Tyrannosaurus.
This
is based upon research by R. M. Chandler, who in 1994
described the construction and orientation of the arms which may have
resulted in a clawed fingered hand in a more complete specimen.
However this wing structure can actually be seen today in the South
American seriema birds which do not have clawed hands. In fact
seriema birds are thought to be the closest living relatives to the
extinct phorusrhacid terror birds, which is why they often get used
as living analogies to the terror birds. Today most researchers
discount the idea of clawed hands on Titanis as
highly unlikely.
When did Titanis
live, and how did its ancestors reach North America?
Estimating
the temporal range of Titanis was initially
difficult to ascertain
because the first fossils were found in Florida’s Santa Fe River.
Aside from the fact that divers had to be used to recover the
fossils, the fragments would have been washed down from their
original locations and were also mixed up with the fragments of other
animals. Some of these animals were known from the end of the
Pleistocene and because Titanis was found in
association to them,
some reports erroneously placed Titanis at the end
of the Pleistocene
as well, some even going so far as to suggest it came into conflict
with early human settlers.
A
2006 study undertaken by B. McFadden, J. Labs-Hochstein, R.
C. Hulbert and J. A. Baskin Jr. took a much more scientific
approach to estimating the real age of Titanis.
Usually fossils are
age estimated by the level of stratum that they are recovered from.
This basically means that the strata is studied and dated, and the
fossils dated by location, something that was made impossible by the
river washing the Titanis fossils from the original
location.
Different strata however do have differing levels of minerals which in
turn are absorbed by the fossils lying within them. By analysing the
mineral content of fossils from known locations where the date has
already been established, the team was able to build up a collection
of comparative data which allowed for the identification of a fossils
temporal place in the fossil record based upon its mineral content.
When
the mineral content of the Titanis fragments was
established, they
were found to most closely match fossils that were created around two
million years ago, placing the fragments within the second half of
the Gelasian stage of the Pleistocene. Titanis
remains from Texas
however have been found to be around five million years old, giving
Titanis a full temporal range of at least three
million years. This
also suggests that Titanis was one of the first
animals to take part in
the Great American Interchange when North and South America became
connected. Titanis may have even had an early
start by a process of
‘island hopping’ as land masses between the two continents changed
in connection to fluxuating sea levels as well as tectonic and volcanic
activity that would ultimately lead to the establishment of a permanent
land bridge.
Titanis hunting
Aside
from looking similar, Titanis probably had
similar hunting behaviour
to other phorusrhacids. Titanis itself would
probably have been a
visually orientated predator, relying upon eyesight for everything
from prey identification to gauging distances between itself and prey.
Analysis of the brain area of the skull in other phorusrhacids has
revealed an underdeveloped sense of smell, and while it is not yet
possible to know this for certain with Titanis,
it is probably likely
that as a member of the group, Titanis would also
have had limited
olfactory ability. This suggests that Titanis was
more actively
involved in predation than scavenging carcasses, although it does not
mean that Titanis never scavenged as most
carnivorous animals do when
the opportunity presents itself.
Titanis
was probably able to match almost any other animal in its ecosystem for
speed. While more robust in build than other terror birds, Titanis
still had very long legs, particularly the lower legs and modified
metatarsals (foot bones) that added extra length to the leg. This
resulted in a digitigrade stance that essentially means that Titanis
would have balanced upon its toes rather than the flats of it feet
(like humans do). All together the leg construction resulted in
increased mechanical advantage from the levering of longer leg and foot
bones as well as a longer stride that allowed Titanis
to cover more
ground with each step. This would have allowed for a very efficient
means of locomotion that would have allowed Titanis
to run down prey,
as well as being potentially more manoeuvrable thanks to its bipedal
stance and short frame that would have allowed for tighter turning.
Reconstruction of the inner ears also shows that Titanis
had a
well-developed sense of balance.
Assuming
that Titanis’s skull was similar to other
phorusrhacids, and
currently there is no reason to think that it was not, then the beak
would have been the primary killing weapon. The tip of the beak would
have been strongly curved down to a sharp point, as can be seen in
other carnivorous birds today. In feeding this hook tip pulls at the
meat while the lower jaw closes, shearing through the meat so that
the bird has a bite sized chunk. In actual killing however the point
could be brought down onto the neck or the back of the prey’s skull.
This penetrating strike could hit an artery, damage the spine and
even pierce the cranium and enter the brain causing instant death to
the prey in question.
Smaller
prey may have actually been swallowed whole, although observation of
seriema birds suggests that small prey may have been thrown against the
ground to stun or kill it outright before it was swallowed. Impacts
against a hard ground would also break the bones of smaller prey
resulting in easier swallowing. It’s also possible that Titanis
may
have regurgitated gastric pellets, especially after feeding on whole
animals. This is seen today in owls which typically swallow rodents
whole but are unable to digest the fur and the bones. After the bird
has finished digesting the flesh, the bones and fur are packed
together inside the stomach and are then brought up and regurgitated in
the form of a pellet.
Extinction
The
fact that Titanis existed for at least three
million years, and also
comes from a lineage of birds that lasted even longer, has led to a
lot of thought as to what could have caused it to go extinct. Because
Titanis was a fast runner and capable of tackling
anything from small
to medium and possibly even some larger prey, it seems unlikely that
the cause could have been a loss of prey species. A possible
alternative could be competition from newly evolving predators such as
larger big cats as well as new forms of canids including the rising
numbers of wolves which would have been hunting in packs. These new
predators may have begun to displace Titanis as the
top predator of its
ecosystem, with other carnivores such as Arctodus
(better known as
the short faced bear) denying Titanis ready
access to carrion from
these other predators’ kills as well.
Another
possibility that may have had a part in the downfall of Titanis
is a
changing climate. A trend of global cooling that happened in the
Pliocene resulted in the climate of the Americas shifting from forest
to drier open savannahs. Titanis was not just big
it was tall, and
when travelling in open grassland it could have easily been spotted by
grazing herbivores who would have had plenty of warning to get away.
This meant that Titanis would have steadily become
a less successful
predator, and even when it was successful it may have had to expend
even greater amounts of energy when chasing prey. This situation
combined with new predators that were better adapted to make use of the
environment in their hunting may have combined to steadily overwhelm
Titanis to the point where it could not continue to
survive.
Further reading
- A Giant Flightless Bird from the Pleistocene of Florida. - The Auk
80(2):111-115 - P. Brodkorb - 1963.
- The wing of Titanis walleri (Aves:
Phorusrhacidae) from the Late
Blancan of Florida - Bulletin of the Florida Museum of Natural History,
Biological Sciences 36: 175–180. - R. M. Chandler - 1994.
- The giant flightless bird Titanis walleri (Aves:
Phorusrhacidae) from
the Pleistocene coastal plain of South Texas. - Journal of Vertebrate
Paleontology 15 (4): 842–844 - J. A. Baskin - 1995.
- Systematic revision of the Phorusrhacidae (Aves: Ralliformes) -
Pap�is Avulsos de Zoologia 43 (4): 55–91 - H. M. F. Alvarenga &
e. H�fling - 2003.
- Titanis walleri: bones of contention - Bulletin
of the Florida Museum
of Natural History 45: 201–229. - Gina C. Gould & Irvy R.
Quitmyer - 2005.
- Refined age of the late Neogene terror bird (Titanis)
from Florida
and Texas using rare earth elements - Journal of Vertebrate
Paleontology 26 (3): 92A (Supplement). - B. McFadden, J.
Labs-Hochstein, R. C. Hulbert Jr, J. A. Baskin - 2006.
- Revised age of the late Neogene terror bird (Titanis)
in North
America during the Great American Interchange - Geology 35 (2): 123–126
- B. McFadden, J. Labs-Hochstein, R. C. Hulbert Jr, J. A. Baskin -
2007.
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