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Yutyrannus
Name:
Yutyrannus
(Feathered tyrant).
Phonetic: You-ty-ran-nus.
Named By: Xu Xing, Wang Kebai, Zhang Ke, Ma
Qingju, Xing Lida, Corwin Sullivan, Hu Dongyu, Cheng Shuqing
& Wang Shuo - 2012.
Classification: Chordata, Reptilia, Dinosauria,
Theropoda, Tyrannosauroidea.
Species: Y. huali (type).
Diet: Carnivore.
Size: Estimated at 9 meters long. Skull
estimated around 905 millimetres long.
Known locations: China, Liaoning Province -
Yixian Formation.
Time period: Aptian of the Cretaceous.
Fossil representation: Remains of three
individuals, including one adult and two juveniles.
Yutyrannus
is a good example of a tyrannosaur
that had feathers, although it is
not the first or only known tyrannosaur to have had feathers like some
news reports claimed at the time of its discovery. The first
tyrannosaur to be feathered was actually Dilong
which was named in
2004 and is actually also known from the Yixian Formation of China.
The feather covering of Yutyrannus is on different
parts of the three
specimens recovered, but when pieced together it seems that
Yutyrannus had a covering of feathers all over its
body. The feathers
themselves were most likely simple in structure and provided
insulation, but palaeontologists have not yet ruled out the
possibility that some of these feathers might have had a display
purpose.
Although
the discovery of Yutyrannus has once again raised
the question of
‘were all tyrannosaurs feathered?’ Skin impressions of Tyrannosaurus
reveal a scaly skin, suggesting that this genus at least did not.
It needs to be remembered that since feathers initially evolved for
insulation, the development and presence of feathers depends more
upon environmental conditions rather than just the size of the
dinosaur. Currently Yutyrannus is regarded as
being the biggest
feathered dinosaur, being forty times heavier than the previous
record holder, a therizinosaur named Beipiaosaurus.
Yutyrannus
is considered to be a basal tyrannosauroid, one feature revealing
this being the foot which is non-arctometatarsalian. This means that
Yutyrannus lacks the specially adapted middle toe
that helped support
the weight of the body and absorb stresses when running.
Yutyrannus also had a three fingered hand rather
than the two fingered
forms of late Cretaceous tyrannosaurs like Tyrannosaurus
and
Tarbosaurus.
When compared to other basal tyrannosaurs, Yutyrannus
is placed at being more advanced than Guanlong
which is also known from
China, but not as advanced as Eotyrannus
from England. Yutyrannus
also has a high midline crest on top of its snout that may have been
for display and identification like the crest of Guanlong
or the ridges
of Alioramus.
Yutyrannus
has not just raised more attention for large feathered dinosaurs, it
has also raised other questions regarding tyrannosaur behaviour,
specifically, ‘did tyrannosaurs hunt in packs?’ and/or ‘did they
live in family groups?’ The fact that two juveniles were found with
an adult does lend some support to the latter question, and it’s not
the first time that juveniles have been found near adult tyrannosaurs.
The pack hunting theory however is a little harder to establish.
Some palaeontologists recognise that tyrannosaurs might have formed
mixed groups where the smaller more agile juveniles would drive prey
towards the jaws of an adult tyrannosaur that was better able to make a
kill.
Others
however have hypothesised that they may have been like komodo dragons
and killed each other in competition over a carcass. The latter
theory would require the body of another dinosaur, assuming the
carcass was not one of the tyrannosaurs to begin with. However there
is a massive concentration of Albertosaurus
remains in Canada from
many individuals and so far no other types of dinosaur are known from
this bone bed. An unrelated theropod from South America called
Mapusaurus
that is also known from a bone bed of many individuals but
no other dinosaurs. Slightly less weighty evidence is the discovery
of three Daspletosaurus
with the remains of five hadrosaurs. Assuming
that the collection of three individuals is not some freak random
occurrence such as a flood washing together only three Yutyrannus
and
no other dinosaurs together, this may yet indicate further evidence
for the support of pack hunting in dinosaurs, particularly the large
theropods.
If you would like to know more about the arguments for and against pack hunting in dinosaurs in greater detail, then read the article ‘Pack Hunting Dinosaurs’.
Further reading
- A gigantic feathered dinosaur from the Lower Cretaceous of China. -
Nature 484 (7392): 92–95. - Xing Xu, Kebai Wang, Ke Zhang, Qingyu Ma,
Lida Xing, Corwin Sullivan, Dongyu Hu, Shuqing Cheng & Shuo
Wang - 2012.
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