Stenonychosaurus
Name:
Stenonychosaurus
(narrow claw lizard).
Phonetic: Ten-on-e-ko-sore-us.
Named By: Charles M. Sternberg - 1932.
Synonyms: Troodon inequalis.
Classification: Chordata, Reptilia, Dinosauria,
Saurischia, Theropoda, Troodontidae, Troodontinae.
Species: S. inequalis
(type).
Diet: Carnivore.
Size: Up to 2.4 meters long.
Known locations: Canada - Alberta - Dinosaur
Park Formation.
Time period: Campanian of the Cretaceous.
Fossil representation: Partial remains of several
individuals.
Classification and controversy of
validity.
Stenonychosaurus
is a genus of troodontid dinosaur that spent much of its time depicted
as a synonym to Troodon.
Stenonychosaurus itself was first named in
1932 and for much of the twentieth century it was occasionally
depicted as a small predatory dinosaur. Stenonychosaurus
would also
become the inspiration of Dale Russel’s ‘dinosauroid’ (see
below). However, in 1987, palaeontologist Philip Currie wrote
a paper detailing how differences in teeth and jaw structure observed
in Stenonychosaurus and Troodon
were simply down to
age and growth
stages. Because Troodon was named earlier in
1856,
Stenonychosaurus became a synonym to the type genus
of the
Troodontidae.
Declaring
Stenonychosaurus as a synonym was controversial,
mostly because the
Troodon genus had been established upon the
description of just teeth.
A further idea that all troodontid dinosaur material was referable to
the Troodon genus was also problematic as it meant
referring fossils
from many different locations and slightly varying ages to one type of
dinosaur. Still, despite the misgivings of many palaeontologists
(including Philip Currie himself), Troodon,
recreated with
Stenonychosaurus fossils was commonly seen in
dinosaur documentaries
and books for the following thirty years.
By
2017 however things could not continue as they were. Troodon
was
first described as a ‘tooth taxon (known only from teeth), and
continuing study of fossils attributable to Troodon
not only failed
to establish a clear irrefutable link between Stenonychosaurus
and
Troodon, differences in the fossils themselves
also proved that they
represented multiple genera, not one genus of troodontid.
Subsequent papers in 2017 (Evans et al, van der Reest &
Currie) confirmed this analysis, leaving Troodon
to go back to
being a tooth taxon, and Stenonychosaurus
resurrected as a valid
genus.
Not
all fossils that have been attributed to Stenonychosaurus
and Troodon
have been moved over to Stenonychosaurus however.
Once associated
with these genera, fossils of a particularly large type of troodontid
dinosaur have been used to establish a new genus named Latenivenatrix.
This assessment is backed upon by several identifiable differences
between the fossils of Latenivenatrix and Stenonychosaurus.
Stenonychosaurus
the Dinosaur.
Stenonychosaurus
was a typically built troodontid,
ranging between two and two and
half meters in length. A sickle shaped claw was present on each
foot, and like relative genera, probably the primary
hunting/killing tool of this dinosaur. Much of the later research
done in the name of Troodon is referable to the Stenonychosaurus
genus, and it’s worth remembering that these works are still about
the same animal, only our name for it has changed.
Stenonychosaurus
is noted for having a very large brain, one that in terms of
proportions is much larger than most other dinosaurs. It is also
known that Stenonychosaurus had large eyes, again
proportionately
larger than many other similarly sized dinosaurs. The combination of
large eyes and large brains leads to a very tempting analysis that
Stenonychosaurus was a strongly visually oriented
predator. The large
eyes could absorb more light, especially low levels, such as at
night time the moon and stars were the only sources of light. A
larger brain might not just have allowed for greater image processing,
but spacial reasoning, allowing Stenonychosaurus
to ‘figure out’
its environment, and be able to anticipate where to be before prey
got there instead of just mindlessly following behind it. Ultimately
however, we still do not know the full extent of Stenonychosaurus
brain function, but who can say what further research will reveal.
The
long legs and lightweight build of Stenonychosaurus
show without doubt
that Stenonychosaurus was built for speed and
agility. It is probable
that Stenonychosaurus hunted smaller creatures such
as lizards and
primitive mammals which would have all been plentiful and enough
sustenance to maintain a dinosaur the size of Stenonychosaurus.
There
were also other types of small dinosaur and juveniles of larger species
that would have also been within the predatory scope of
Stenonychosaurus.
Troodontids
however have sometimes been imagined to hunt if not in packs, but in
loosely knit groups. This does not necessarily mean a group of
Stenonychosaurus working together in an elaborate
plan to hunt other
dinosaurs, but if for example a sick hadrosaur caught the attention
of several Stenonychosaurus, then several
individuals might attack it
in behaviour known as mobbing. This is where several predators
realising an animal is weak attack it all at once, but with each one
making an individual choice to attack rather than hunting to help other
associates (like in lions). Mobbing behaviour has been observed
in some birds, and if Stenonychosaurus (and
other dinosaurs) did
this on occasion, they might have split up afterwards and gone their
separate ways, combining with different individuals if the
opportunity to take larger prey arose again.
The Dinosauroid proposal.
The
idea of dinosaurs with increasing intelligence and dexterous hands has
led many to wonder how dinosaurs like Stenonychosaurus
would have
evolved had the KT extinction which marks the end of the dinosaurs
not occurred. Well in 1982 a palaeontologist named Dale Russell
put form to the thought. Based upon Stenonychosaurus,
Russell
presented a humanoid dinosaur, which means that it was depicted as
walking in a similar stance and posture as a human being. The body
proportions were also close to that of a human. The eyes were still
large, and the Dinosauroid was envisioned as giving birth to live
young and feeding them upon regurgitated food.
Although
some have criticised the reconstruction on the grounds that it is
'too human', and descendants of intelligent dinosaurs would have
probably retained a more 'classic' theropod body, it is somewhat
missing the point as the Dinosauroid reconstruction is more of a
'what if' than an absolute. Choosing a more humanoid bipedal
posture at least makes it easier for people to relate too, which in
turns makes them think more about it. It is still worth thinking
about though that mankind is thought to have evolved from apes over the
course of hundreds of thousands of years. Imagine what a dinosaur
already smarter than a Chimpanzee could do over sixty-five million
Further reading
- Two new theropod dinosaurs from the Belly River Formation of
Alberta. Canadian Field-Naturalist 46(5):99-105. - Charles
M. Sternberg - 1932.
- 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. Séguin - 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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