Troodon
Name: Troodon
(wounding tooth).
Phonetic: Tru-don.
Named By: Joseph Leidy - 1856.
Classification: Chordata, Reptilia, Dinosauria,
Saurischia, Theropoda, Troodontidae, Troodontinae.
Species: T. formosus (type).
Diet: Carnivore.
Size: Unknown.
Known locations: USA, Monatana - Judith River
Formation.
Time period: Campanian of the Cretaceous.
Fossil representation: Teeth.
Remarkably
when Troodon was first 'discovered' it was only
known from a
tooth, and it was the description of this tooth that gave rise to the
genus. Although naming a creature after only discovering its teeth is
hard to imagine today, it was a common place practice in the
nineteenth century, and at least in the case of Troodon
the teeth
were different to most others. Two problems arose from describing
Troodon from only teeth. One, while these teeth
were curved like in
a carnivore, they had curved serrations similar to some herbivores.
Two, because no one knew of any skeletal remains, no one knew what
kind of dinosaur it actually was, or even if it really was a dinosaur
for that matter.
When
named by Joseph Leidy in 1856, Troodon was
classed as a lizard.
When classed as a dinosaur in 1901, Troodon
was assigned to the
megalosauridae, a wastebasket group at the time that was used as a
dumping ground for any carnivorous dinosaur whose kind and position
among others was not known. In 1924 Troodon
'became' a
pachycephalosaur,
a herbivorous kind of dinosaur known for having
dome headed skulls, with the grouping made on the basis of
similarities between their teeth, notably the serrations. It should
also be mentioned that as Troodon was grouped with
them, all
pachycephalosaurs
known at the time were classed under Troodontidae,
until 1945 when Troodon was removed from the
group on the basis
that its teeth were for a carnivorous purpose. Because the group
could not be called after a dinosaur that was no longer a part of it,
they were re-named the pachycephalosuars after Pachycephalosaurus.
Skipping
back to 1932, and another genus of dinosaur, Stenonychosaurus,
was formally described to science. This was a small predator,
later realised to have had teeth similar to Troodon.
But for over
fifty years Stenonychosaurus and Troodon
were kept separate, until
1987, when palaeontologist Philip J. Currie found Stenonychosaurus
to be a synonym of Troodon. This was done on the
basis that
differences in tooth and jaw form of known troodonts seemed to have
been down to age and growth and were probably representing a single
species of dinosaur.
The
addition of this fossil material to Troodon
allowed the first
accurate reconstructions of the genus. As a small predator with a
sickle shaped claw on each foot, Troodon was
often recreated in
popular science, as a small but fierce and deadly predator that
terrorised Late Cretaceous North America. This depiction was common
throughout the late twentieth/early twenty-first centuries.
Now
it seems things were not so clear cut, and questions over assigning
all of this fossil material to Troodon began to be
asked as to whether
this was the correct thing to do. This questioning was not just done
by some other palaeontologists, but by Philip Currie himself.
Throughout the 1990s and opening years of the twenty-first century
new ideas that fossils from different formations could represents at
least different species of Troodon, perhaps even
different genera of
troodontid dinosaurs, were often discussed.
Ultimately
the problem of Troodon always came down to the same
issue. Troodon
was established upon the basis of teeth, and like all creatures
described by only teeth, it is almost impossible to refer fossils on
bone material. On the principal of extra fossil bones later
assigned to Troodon, there was just not a clear
example to prove a
connection, just superficial similarity.
Thirty
years after Troodon and Stenonychosaurus
were synonymised together,
they were split again in 2017. Fossils of bones once used to
reconstruct Troodon now either placed back into
the resurrected
Stenonychosaurus genus, or moved into an
additional new genus called
Latenivenatrix.
This conclusion is the culmination of work by many
palaeontologists again including Philip Currie. While some
palaeontologists have not been quick to accept the removal of bone
fossils from Troodon, at the time of writing
(2020) most
palaeontologists are working with the resurrection of Stenonychosaurus
and description of Latenivenatrix as valid.
With
Troodon being dubbed a ‘tooth taxon’ (known only
from teeth),
Troodon itself is now once again regarded as a
dubious genus of
dinosaur.
Further reading
- Notices of remains of extinct reptiles and fishes, discovered by
Dr. F. V. Hayden in the bad lands of the Judith River, Nebraska
Territory. - Proceedings of the Academy of Natural Sciences of
Philadelphia 8:72-73. - J. Leidy - 1856.
- The dentary of Tro�don, a genus of theropod
dinosaurs. -
Journal of Paleontology 22(5):625-629. - L. S. Russel
- 1948.
- A new specimen of Stenonychosaurus from the
Oldman Formation
(Cretaceous) of Alberta. - Canadian Journal of Earth Sciences
6:595-612. - D. A. Russel - 1969.
- Reconstruction of the small Cretaceous theropod Stenonychosaurus
inequalis and a hypothetical dinosauroid. - Syllogeus
37:
1–43. - D. A. Russel & R. S�guin - 1982.
- Theropods of the Judith River Formation of Dinosaur Provincial
Park, Alberta, Canada, by P. J. Currie. - In Fourth
Symposium on Mesozoic Terrestrial Ecosystems. Tyrrell Museum of
Paleontology, Drumheller, Alberta 52-60. - P. J. Currie
& E. H. Koster (eds.) - 1987.
- Bird-like characteristics of the jaws and teeth of troodontid
theropods (Dinosauria, Saurischia). - Journal of Vertebrate
Paleontology 7: 72–81. - P. J. Currie - 1987.
- Bone microstructure of the Upper Cretaceous theropod dinosaur
Troodon formosus. - Journal of Vertebrate
Paleontology 13,
99-104. - D. V. Varricchio - 1993.
- Denticle Morphometrics and a Possibly Omnivorous Feeding Habit for
the Theropod Dinosaur Troodon. - Gaia 15. - Thomas R.
Holtz, Daniel L. Brinkman & Christine L. Chandler -
1998.
- Embryos and eggs for the Cretaceous theropod dinosaur Troodon
formosus. - Journal of Vertebrate Paleontology 22
(3):
564–576. - David J. Varricchio, John R. Horner &
Frankie D. Jackson - 2002.
- The last polar dinosaurs: high diversity of latest Cretaceous
arctic dinosaurs in Russia. - Naturwissenschaften - P.
Godefroit, L. Golovneva, S. Shchepetov, G. Garcia
& P. Alekseev - 2008.
- On the Occurrence of Exceptionally Large Teeth of Troodon
(Dinosauria: Saurischia) from the Late Cretaceous of Northern
Alaska. - Palaios volume 23 pp.322-328. - Anthony R.
Fiorillo - 2008.
- Description of two partial Troodon braincases
from the Prince Creek
Formation (Upper Cretaceous), North Slope Alaska. - Journal
of Vertebrate Paleontology 29(1):178-187. - A. R.
Fiorillo, R. S. Tykoski, P. J. Currie, P. J.
McCarthy & P. Flaig - 2009.
-A new species of troodontid theropod (Dinosauria: Maniraptora)
from the Horseshoe Canyon Formation (Maastrichtian) of Alberta,
Canada. Canadian Journal of Earth Sciences. 54 (8):
813–826. - D. C. Evans, T. M. Cullen, D. W.
Larson & A. Rego - 2017.
- Troodontids (Theropoda) from the Dinosaur Park Formation,
Alberta, with a description of a unique new taxon: implications
for deinonychosaur diversity in North America . Canadian Journal of
Earth Sciences 54:919-935. - A. J. van der Reest &
P. J. Currie - 2017.
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