Nanuqsaurus
Name:
Nanuqsaurus
(Polar bear lizard).
Phonetic: Nah-nuk-sore-us.
Named By: Anthony R. Fiorillo & Ronald
S. Tykoski - 2014.
Classification: Chordata, Reptilia, Dinosauria,
Theropoda, Tyrannosauroidea, Tyrannosauridae, Tyrannosaurinae.
Species: N. hoglundi (type).
Diet: Carnivore.
Size: Uncertain due to lack of remains, but
reconstructions of the skull place the length of the whole skull at
between 60 and 70 centimetres. This in turn has led to rough
estimates for the total length of the animal of around 6 meters
long.
Known locations: USA, Alaska - Prince Creek
Formation.
Time period: Early Maastrichtian of the Cretaceous.
Fossil representation: Partial remains of skull and
lower jaw.
Back
in the Cretaceous North America was divided into two land masses due to
the presence of the Western Interior Seaway, a shallow sea that
submerged the central portions of North America all the way from Canada
to Mexico. These two land masses were Appalachia in the east, and
Laramidia in the west, and with the Nanuqsaurus
holotype fossils
coming from Alaska, we know that this tyrannosaur
lived in northern
Laramidia. This is considerably further north than many of the more
famous and larger North American tyrannosaurs, which has led to a lot
of sudden interest about Nanuqsaurus.
Because
Nanuqsaurus seem to have lived so far north, they
would have lived in
a much colder environment than that experienced by the Southern
tyrannosaurs. This in turn has led to the suggestion that Nanuqsaurus
may have had at least a covering of insulatory feathers over its body
in order to better survive this environment. There is no direct
fossil evidence that proves that Nanuqsaurus had
feathers, but the
discovery of Yutyrannus
in China, and also interpreted as living
in a cool environment, proves that at least some of the larger
tyrannosaurs were feathered all over.
If
Nanuqsaurus spent most of its time living in the
region were the
holotype was found and was not merely passing through, then these
tyrannosaurs would have experienced a greater seasonal variation that
other tyrannosaur genera living further south. This variation could
include extended periods of daylight in summer months, and extended
periods of darkness in winter months. This may have also brought
about a seasonal availability of prey with dinosaurs such as
ceratopsians
and hadrosaurs
moving further north to feed upon fresh
plant growth in summer, then migrating further South in winter.
Because
of the incomplete state of preservation for the holotype remains,
only a best guess is available for the size estimate of Nanuqsaurus.
This however does show that if the adult size was about six meters
long, then Nanuqsaurus would have been relatively
small for a
tyrannosaur, especially a genera alive in the late Cretaceous. It
is possible that the small size of Nanuqsaurus may
have been a result
of living in its environment, especially if prey resources were
scarce. Also of interest is that other predatory dinosaurs of the
region such as Troodon
are known to have grown half as big again as
their southern relatives. Gigantism is a surprisingly common method
that animals adopt to cope with colder climates because the greater
mass of their bodies offers more insulation for the internal organs,
so the reduction in size for Nanuqsaurus again
seems to be driven by
the availability of food.
Although
the skull of Nanuqsaurus is incomplete, is does
show that Nanuqsaurus
would have had a heightened sense of smell, perhaps proportionately
even greater than that of Tyrannosaurus.
This would suggest that
smell was an integral part of the Nanuqsaurus
survival method, but
how is likely to further the scavenger debate about tyrannosaurs. A
sense of smell could be used to track living animals that otherwise
might not have been easy to spot in the polar gloom. In addition this
sense of smell may have been used to sniff out carrion, or perhaps
even the kills of Troodon which had exceptionally
good eyesight and so
were probably still able to hunt in the dark. Even though small at
six meters, Nanuqsaurus was still much bigger
than Troodon and so
may have still been capable of driving them away from their kills.
This is pure conjecture however, as a good sense of smell can serve
both a predator and a scavenger. There is also a world of difference
between opportunistic scavenging, something that most meat eaters
do, and obligate scavenging which is when an animal only scavenges.
The
partial remains of Nanuqsaurus were first thought
to represent remains
of either Gorgosauurs
or Albertosaurus
until they were finally realised
to actually represent a whole new genus of tyrannosaur. Even though
Nanuqsaurus was once thought to represent an
albertosaurine
tyrannosaur, it is now thought to be a tyrannosaurine, and
phylogenetically be close to Tyrannosaurus, Tarbosaurus
and
Zhuchengtyrannus.
Further reading
- A Diminutive New Tyrannosaur from the Top of the World. - PLoS
ONE 9 (3): e91287. - Anthony R. Fiorillo &
Ronald S. Tykoski - 2014.
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