Dakotaraptor
Name:
Dakotaraptor
(Dakota thief).
Phonetic: Da-ko-tah-rap-tor.
Named By: Robert A. DePalma, David A.
Burnham, Larry Dean Martin, Peter Lars Larson & Robert
Thomas Bakker - 2015.
Classification: Chordata, Reptilia, Dinosauria,
Saurischia, Theropoda, Dromaeosauridae, Dromaeosaurinae.
Species: D. steini (type).
Diet: Carnivore.
Size: Estimated at about 5.5 meters long.
Known locations: USA, South Dakota - Hell
Creek Formation.
Time period: Late Maastrichtian of the Cretaceous.
Fossil representation: Partial post cranial skeletal
remains.
The
one thing that immediately stands out about Dakotaraptor
at first
glance is simply the large size of this dromaeosaurid
dinosaur. Most
dromaeosaurid dinosaurs measure in at under two meters in length,
with a few genera ranging between two and three meters long. The
Holotype individual of Dakotaraptor however has a
reconstructed length
of five and a half meters. At the time of the 2015
description, this makes Dakotaraptor the second
largest
dromaeosaurid dinosaur known, with the largest being Utahraptor.
As
far as comparison between Dakotaraptor and Utahraptor
goes,
Utahraptor lived in North America around Utah
(clue is in the name)
during the Early Cretaceous roughly one hundred and twenty-six million
years ago. Dakotaraptor also lived in North
America but around South
Dakota towards the end of the Late Cretaceous some sixty-six million
years ago. Not only are Dakotaraptor and Utahraptor
separated by a
wide temporal gulf, study of the known fossils of Dakotaraptor
show
that in body proportions this genus was actually more like genera
such as Deinonychus
and Dromaeosaurus
than it was Utahraptor,
making
a direct link between Dakotaraptor and Utahraptor
unlikely.
Studies
of dromaeosaurid dinosaurs going back to the late twentieth century
indicate that dromaeosaurid dinosaurs almost certainly had feathers.
These feathers were not necessarily all over the body, but were
likely on the thorax and abdomen and almost certain on the arms.
Dakotaraptor supports this theory in that fossils
of the ulna (one
of the forearm bones) show attachment points for large pennaceous
feathers. It is unknown to what extent feathers would have covered
Dakotaraptor, but smaller insulating feathers are
known to have
covered the body in even larger theropod dinosaurs such as the
tyrannosaur
Yutyrannus.
However other dinosaurs living in North
America during the late Cretaceous such as the ornithomimosaur
Ornithomimus
are known to have had small feathers on the back and
sides of the body, but have legs that were devoid of feathers. The
coverage of feathers on Dakotaraptor were likely a
reflection of
environmental factors first, and additional functions such as display
and egg insulation second.
In
the early twenty-first century there has been a lot of debate
concerning the relationship between dromaeosaurid dinosaurs and the
evolution of birds, with the classic idea being that birds evolved
from maniraptoran dinosaurs. There are now alternate theories that
maniraptoran dinosaurs may have evolved from birds, or perhaps even
to birds and back again, but the ideas are simply too long to explain
and off topic for this article. The key point is that some
dromaeosaurs may have had a limited flight ability even if only gliding
as has been speculated for genera such as Microraptor.
As far as
Dakotaraptor is concerned, flight was almost
certainly an
impossibility, mainly for the simple fact that at about five and a
half meters long Dakotaraptor would have simply
been too big. There
was also no way for Dakotaraptor to use its arms to
generate anywhere
near enough lift. The original study of the forearms of Dakotaraptor
into wings, indicated the total ‘wingspan’ of Dakotaraptor
would
have been about one hundred and twenty centimetres, which is even
less than what an average human adult could achieve if they held their
arms out to the side.
Although
certainly too big to fly, Dakotaraptor was still
no slouch on the
ground. Proportions of the leg show that the lower leg bones of the
tibia and fibula were longer than the femur which makes up the upper
leg. This allows for a significantly longer stride of the leg which
directly translates to an increase in speed and ability to run fast.
The vertebrae of Dakotaraptor were also
pneumatised, meaning that
they had air spaces within them. This dramatically reduces the weight
of the bone, and with this factor in mind, Dakotaraptor
would have
actually been quite lightweight for its size. Not only would this
allow for larger size growth, but it would also allow Dakotaraptor
to
retain some of the speed and agility that dromaeosaurid dinosaurs are
known for.
At
the original fossil site of Dakotaraptor, remains
of more than one
individual were found. The Holotype individual is the most complete
of these, however there also seems to have been a notable
difference in build between the holotype which is by far the most
robust (heavily built), and the others which are more gracile
(lightly built). All individuals seem to have been fully grown
adults, so one train of thought is that these may represent a
collection of male and female individuals. However that still does
not make it certain which is which, as while in the animal kingdom
males are usually the more robustly built, it is not unknown for
females to have been the larger (the moa
bird Dinornis
is a good
example). Only further study and fossil remains can tell us for
sure.
Dakotaraptor
is the second dromaeosaurid dinosaur known from the Hell Creek
Formation, with the first being the much smaller Acheroraptor.
The
only predator known to have been around at the same time and location
and also be bigger than Dakotaraptor is the mighty Tyrannosaurus.
Possible prey dinosaurs for Dakotaraptor could
include anything from
ceratopsian
dinosaurs such as Triceratops
and Leptoceratops,
ankylosaurs
and nodosaurs such as Ankylosaurus
and Edmontonia,
pachycephalosaurs
such as Pachycephalosaurus,
and hadrosaurs
and
ornithopods such as Edmontosaurus
and Thescelosaurus.
Further reading
- The First Giant Raptor (Theropoda: Dromaeosauridae) from the
Hell Creek Formation. Paleontological Contributions (14). -
Robert A. DePalma, David A. Burnham, Larry Dean Martin,
Peter Lars Larson & Robert Thomas Bakker - 2015.
- The furculae of the dromaeosaurid dinosaur Dakotaraptor
steini are
trionychid turtle entoplastra. - PeerJ. 3. - V. M. Arbour, L. E. Zanno,
D. W. larson, D. C. Wvans & H. Sues - 2015.
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