Yi
Name: Yi
(wing).
Phonetic: Yee.
Named By: X. Xu, X. Zheng, C. Sullivan,
X. Wang, L. Xing, Y. Wang, X. Zhang, J. K.
o’Connor, F. Zhang & Y. Pan - 2015.
Classification: Chordata, Reptilia, Dinosauria,
Theropoda, Scansoriopterygidae.
Species: Y. qi (type).
Diet: Insectivore/Carnivore.
Size: Wingspan roughly about 60 centimetres across.
Known locations: China, Hebei - Tiaojishan
Formation.
Time period: Callovian/Oxfordian Jurassic.
Fossil representation: Skull, lower jaws and
partial post cranial skeleton, mostly articulated.
Yi
is certainly one of the more bizarre dinosaurs that were named in
2015. In fact this is reflected in the full type species name of Yi
qi which translates to English as ‘strange wing’. This
is a
reference to how the hands of Yi not only had
elongated fingers, but
how there also seems to have been a membrane of skin between them,
forming a wing similar in appearance to what we see in bats today.
The
membrane is known to have connected the fingers and the styliform bone
(a newly evolved bone not seen in other theropod dinosaurs) of the
hand area, but it is still not yet known with certainty if the
membrane reached all the way to the main torso. Also, the position
of the styliform bone in flight is not known for certain, and these
two unknown factors have led the original describers to postulate three
main theories about how the wing was formed. First is that if the
membrane did not connect to the torso and terminated at the styliform
bone, then Yi may have just had pads that opened
up like those of
gliding tree frogs. If the membrane did connect to the torso though,
then it is the shape of the wing that is unknown. If the styliform
bone was held out to the side then the wing membrane would have been
long but thin. If the styliform bone faced backwards however then
the wings would have been shorter but broader. If the membrane
reached the torso, and if Yi lived in forested
areas which seem to
have covered extensive parts of China in the Jurassic, then a
shorter, broader wing may perhaps be more likely as this would reduce
the chance and frequency of the wings clipping branches and trunks as
Yi flew through such an environment.
The
exact method of flight for Yi is also unknown for
certain but we can
also speculate as to what is more probable for this dinosaur. Yi
probably could not rely upon powered flapping of the wings even though
Yi probably had the range of motion necessary.
This is because the
sternum (breast bone) of Yi did not have a deep
keel, meaning
that there was no enlarged area for the attachment of enlarged pectoral
muscles like we can see in birds. With only relatively small pectoral
muscles similar to other small theropod dinosaurs, Yi
would have only
been capable of flapping its arms for a short while before becoming too
tired to flap them anymore, making a reliance upon powered flapping
flight for long distances impossible.
This
might make gliding more possible, but again, Yi
does not seem to be
perfectly adapted to gliding either as it would have had a different
wing form to other gliding animals that we know today. This does not
discount the idea entirely however, this dinosaur may have simply
done something different to what we can observe today. It may be that
Yi actually used a hybrid form of gliding, where
travel from a launch
point to landing site was primarily done by gliding, but short bursts
of flapping were undertaken to launch, steer and then perhaps slow
down before finally landing.
Yi
is yet another genus that hints that flight evolved several times in
the dinosaurs, and not always along the same route. However,
while Yi can be seen as an example of convergent
(similar but not
direct) evolution when compared to mammalian bats, Yi
also likely
represents and evolutionary dead end. This is because at the time of
writing Yi and other scansoriopterygid dinosaurs
are only known from a
relatively narrow scope of time in China. When Yi
was named the only
other two members of this group are the type genus Scansoriopteryx
and
Epidexipteryx,
and both are noted for having enlarged fingers like
Yi, though no membranes were reported when they
were first
described. However one palaeontologist named Andrea Cau did speculate
about the presence of skin membranes on these two dinosaurs in 2008
and 2012, years before Yi would be described.
This begs the
question, did these two genera also have skin membranes, or is Yi
a
further offshoot from these two dinosaurs?
The
skull of Yi is reconstructed as being very short
and blunt, while the
lower jaw curves downwards. The teeth in the upper and lower jaws
are angled to face forwards, the lower jaw more so than the upper.
Altogether this loosely resembles the form of the anurognathid
pterosaurs
some of which such as Dendrorhynchoides
and Jeholopterus
were flying around Chinese forests during similar times as Yi.
This
may indicate that Yi was an insectivore, hunting
for flying insects
in the Jurassic forests of China.
Thanks
to modern electron microscope analysis, melanosomes (pigment
bearing organelles) have been located and studied on the Yi
holotype
fossils, meaning that we actually have an idea as to what colour this
dinosaur was. For the most part Yi seems to have
been black in
colour (eumelanosomes), while the head, skin membranes seem to
have been yellow-brown (phaeomelanosomes). Because of the family
connection to Epidexipteryx, Yi
is also thought to have sported a few
elongated tail feathers.
As
of 2015, Yi is the shortest dinosaur name
recorded in science,
replacing the previous record holder Mei
which was named in 2004.
The total name Yi qi is also the shortest possible
name under
zoological nomenclature given that the minimum is four letters long.
This means that while one day there may be other dinosaurs with names
as short as Yi qi, no other dinosaur will ever
attain a name shorter
than this.
Further reading
- A bizarre Jurassic maniraptoran theropod with preserved evidence of
membranous wings. - Nature. - X. Xu, X. Zheng, C.
Sullivan, X. Wang, L. Xing, Y. Wang, X. Zhang, J.
K. o’Connor, F. Zhang & Y. Pan - 2015.
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