Albertosaurus
Name: Albertosaurus
Phonetic: Al-ber-to-sore-us.
Named By: Henry Fairfield Osborn - 1905.
Synonyms: Deinodon sarcophagus,
Albertosaurus
arctunguis, Deinodon arctunguis.
Classification: Chordata, Reptilia, Dinosauria,
Saurischia, Theropoda, Tyrannosauridae, Albertosaurinae.
Species: A. sarcpohagus.
Type: Carnivore.
Size: Large individuals grew to over 10 meters
long.
Known locations: Canada, Alberta.
Time period: Campanian of the Cretaceous
Fossil representation: Many individuals are known
including a bone bed that contains the remains of twenty-two
individuals in the same location.
The
first remains of Albertosaurus were recovered from
the Horseshoe Canyon
Formation in 1884, and these were the type specimen along with a
smaller skull and some of the post crania. However Albertosaurus
was
not yet identified and when these parts were studied in 1892 by
Edward Drinker Cope, he assigned them to another dinosaur called
Laelaps incrassatus that he had named earlier in
1866. Now this is
where things start to get confusing because the name Laelaps
had
already been applied to a mite, and because of this Othniel Charles
Marsh had changed Laelaps to Dryptosaurus
in 1877. Anyone who
recognises the names Marsh and Cope is probably already familiar with
the 'Bone Wars' and the fierce rivalry between them. Cope refused
to acknowledge the change and it was up to the eminent palaeontologist
Lawrence Lambe to formally rename the specimens Dryptosaurus
incrassatus. This still was not the end because the
palaeontologist
Henry Fairfield Osborn disputed the renaming citing two key reasons.
The first was that Dyptosaurus incrassatus
(formerly Laelaps
incrassatus) was based only upon the description of generic
tyrannosaur teeth with no bone material to back it up, thus making
accurate comparison near impossible. The second was that the fossil
material recovered was different enough from the Dryptosaurus
type
species D. aquilunguis to be considered its own
species. So in
1905, Osborn renamed the material Albertosaurus
in reference to the
part of the world it was found.
Today
we know enough about Albertosaurus to be certain it
deserves its
own genus, but there is now another bit of contention associated with
it. Some palaeontologists have claimed that another dinosaur named
Gorgosaurus
is actually a species of Albertosaurus. Both are
members
of the tyrannosauridae group and both have a similar morphology,
being
more gracile than other members such as Tyrannosaurus
and
Daspletosaurus.
On the other hand, some palaeontologists claim that
while they are similar, there are enough differences between them to
distinguish the two and thus keep them separate. This debate is still
on going and is not likely to be settled until further study or new
fossil material can point towards which is more correct.
Like
the other tyrannosaurids, Albertosaurus had
conical 'banana
teeth'. Although not suitable for slicing flesh, they could
crunch though bone and rip flesh from a carcass. In Albertosaurus
the
teeth seem to have crack like serration in a similar fashion found in
the teeth of the ancient pelycosaur Dimetrodon.
One thing that
Albertosaurus has, that Dimetrodon
did not, is the presence of
ampulla at the base of the crack. This is a round void that displaces
stress forces placed on the teeth when Albertosaurus
bit into
something, significantly increasing their resilience. Albertosaurus
also had more teeth than the larger members of the tyrannosaurids with
over sixty in its mouth.
There
is some evidence to suggest that Albertosaurus may
have actually
been a pack hunter. The palaeontologist Barnum Brown had discovered a
bone bed containing multiple tyrannosaur remains in 1910. Brown did
not have time to excavate the site properly and so took what he could,
but after this the site was forgotten and lost. It was not until
1997 when a team led by Dr Philip J. Currie rediscovered the bed,
that its significance was realised to modern day science.
There
are enough remains in
what is now called the Dry Island bone bed to identify twenty-two
individuals of all different ages and sizes. Not all are convinced
about the pack theory stating that they may have been drawn together by
ecological factors such as a drought forcing them around a watering
hole. Others have stated they may have been killed by their own kind
in competition for feeding rights at a carcass. What has to be
remembered here is that only Albertosaurus remains
were found, and
the individuals were of different ages. Pack hunting animals today
also form groups of just one species, with individuals of different
ages represented in the same group. Regardless
of whether
Albertosaurus did or did not hunt in packs, the
fossil material
recovered from the Dry Island bone bed has allowed palaeontologists to
study the way Albertosaurus and by extension other
tyrannosaurids may
have grown. In fact Albertosaurus is now the best
known of the
tyrannosaurids.
It
is thought that
Albertosaurus would have grown steadily for the
first few years of its
life before undergoing a massive growth spurt until reaching sexual
maturity. Once this happens, growth slows down to a much slower
rate until the individual reaches its maximum potential size or it dies
from some other means. It’s possible that the stresses exerted upon
the body by such rapid growth may actually cause the body to 'burn
out' and become more susceptible to disease or other ailments in all
but the healthiest of individuals. This would explain the large
number of adult Albertosaurus specimens recovered
that had not yet
reached their maximum potential size, with most approaching nine
meters in length as opposed to the maximum recorded ten.
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