Irritator
Name: Irritator
(In reference to the 'irritation' of the palaeontologists -
refer to text for details).
Phonetic: Ih-re-tay-tor.
Named By: D. M. Martill, A. R. I.
Cruikshank, E. Frey, P. G. Small & M. Clarke
- 1996.
Synonyms: Possibly Angaturama
(refer to
main text for more details).
Classification: Chordata, Reptilia, Dinosauria,
Saurischia, Theropoda, Spinosauridae, Spinosaurinae.
Species: I. challengeri
(type).
Diet: Carnivore.
Size: Estimated at 8 meters long Skull estimated
at 84 centimetres long.
Known locations: Brazil - probably the Santana
Formation.
Time period: Albian of the Cretaceous.
Fossil representation: Almost complete skull and
associated vertebrae.
Irritator
is proof that palaeontologists do have a sense of humour even if it is
a dry one. The holotype specimen of Irritator was
a skull that had
been artificially elongated by illegal fossil collectors in the hope of
increasing its monetary value (plainly speaking, to get more money
for the fossil). Before the skull could be studied and described to
science the first job that had to be done was correct the lengthening
work, a long and pain staking process that needless to say irritated
those involved. The species name I. challengeri
is a little less
dramatic with the species named after Professor Challenger, a
fictional character in the classic Arthur Conan Doyle story The
Lost
World. For those not already familiar this story it is
about an
expedition that scales a plateau in the Amazon Basin where they
discover dinosaurs and other prehistoric creatures are still alive and
well.
Because
the skull was acquired from 'unofficial' sources the exact location
is unknown for certain, but the researching palaeontologists have
managed to narrow down the options to the Chapada do Araripe (often
referred to in English as the Araripe Plateau) part of the Santana
Formation. This location was deduced by analysis of micro fossils
found with the specimen that are also known to be present in this area
as well as talking to local fossil dealers. Detailed comparison of
the evidence has additionally pointed to the Romualdo Member.
Further
support for this location comes from the discovery of further
spinosaurid
material that is referred to the Angaturama
genus. Not
only can this be taken as the presence of other spinosaurids,
Angaturama may in fact be the same genus as Irritator.
The Irritator
holotype skull is missing its forward snout portion, but
interestingly Angaturma's holotype is equal to the
front
portion of the snout
that is missing in Irritator. This has led some
palaeontologists to
strongly consider the possibility that Angaturama
is not only the
same genus as Irritator, but is also the same
individual as the
holotype. The only thing that has stopped palaeontologists being one
hundred per cent certain so far is that the Angaturama
specimen seems
to have come from an individual that had a higher and flatter head than
the Irritator holotype. Both Irritator
and Angaturama were both named
in 1996, but since Irritator was named earlier
in that year, it
would have naming priority over Angaturama if they
were ever proven
without doubt to be the same.
South
America has produced steady spinosaurid remains since the 1990's,
and aside from Irritator and the dubious Angaturama,
other genera
such as Oxalaia
(possibly one of the largest spinosaurids) have
also been named. Current fossil evidence suggests that spinosaurids
may have originated in Western Europe or North Africa as indicated by
the early appearance of Baryonyx
in the fossil record. Later members
such as Suchomimus
may have then radiated out across land bridges
between Africa and South America, basically following locations of
suitable habitat.
The
spinosaurids are generally associated with environments where they have
access to water systems such as river deltas where they can use their
special hunting adaptations to pluck large fish from the water. The
skull of Irritator displays the key characteristic
of spinosaurids in
that the jaws are long and filled with large but relatively thin teeth
suitable for seizing slippery prey, giving Irritator's
skull a
crocodile like appearance. Despite this special adaptation for fish
Irritator probably supplemented its diet by
scavenging carrion,
something that all predators do when the opportunity presents itself.
Spinosaurids are known to have included other types of prey into their
diet as evidenced by the discovery of juvenile Iguanodon
remains with
Baryonyx in England, and pterosaur vertebrae with
a spinosaurid tooth
stuck into it, a fossil that was also discovered in Brazil. This
evidence can point to either scavenging or even active predation of
these animals, but the special teeth of Irritator
like other
spinosaurids work best for holding, not killing prey.
Although
not discovered with the holotype, Irritator may
have had enlarged
claws on its hands that were capable of rending flesh. These claws
are commonly associated with Baryonyx (whose name
means heavy claw
after the size of the hand claws) and Suchomimus,
and so far seem
to be a common trait in spinosaurids that may have evolved as a result
of the lack of shearing teeth in the mouth.
Another
possible trait is the presence of enlarged neural spines of the dorsal
vertebra for the purpose of either supporting a sail or a hump on the
back. These can be clearly seen in both Suchomimus
and Spinosaurus,
although not Baryonyx. However because Baryonyx
is based upon what
is thought to have been a juvenile individual, it simply may not have
had time to grow the enlarged neural spines when it died. So far the
presence of a dorsal structure on Irritator remains
unknown, but is a
potential possibility. One feature that makes Irritator
stand out
from others of its kind is the presence of a sagittal crest that is
part of the parietal bone, although the describers think that the
rear portion of this crest was enhanced by the fossil dealers.
1 - Spinosaurus, 2 - Baryonyx, 3 - Ichthyovenator, 4 - Oxalaia, 5 - Suchomimus, 6 - Irritator.
Further reading
- A new crested maniraptoran dinosaur from the Santana Formation (Lower
Cretaceous) of Brazil. - Journal of the Geological Society, London
153:5-8. - D. M. Martill, A. R. I. Cruickshank, E. Frey, P. G. Small
& M. Clarke - 1996.
- Irritator challengeri, a Spinosaurid (Dinosauria:
Theropoda) from the
Lower Cretaceous of Brazil. - Journal of Vertebrate Paleontology 22
(3): 535. - H. D. Sues, E. Frey, D. M. Martill & D. M. Scott -
2002.
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