Bicentenaria
Name:
Bicentenaria
(Named for the two hundredth anniversary of the Argentinian
revolution that started in 1810 that would ultimately lead to the
establishment of Argentina as an independent country).
Phonetic: By-sen-ten-ah-re-ah.
Named By: Fernando E. Novas, Martin D.
Ezcurra, Federico L. Agnolin, Diego Pol & Raul Ortiz
- 2012.
Classification: Chordata, Reptilia, Dinosauria,
Saurischia, Theropoda, Coelurosauria.
Species: B. argentina
(type).
Diet: Carnivore.
Size: Estimated around 2.5 to 3 meters long.
Known locations: Argentina.
Time period: Turonian of the Cretaceous.
Fossil representation: Disarticulated remains of
several individuals.
Bicentenaria
is an interesting theropod whose remains were recovered from the
Ezequiel Ramos Mexia Reservoir, Rio Negro Province, Argentina by
Raul Spedale in 1998. The remains were of a concentration of
disarticulated remains of many individuals, but their similarity to
one another strongly suggests that they were all from the same genus of
dinosaur. Of these remains there are three large left femora
(plural of femur, the thigh bone) which is an indication that the
remains are of at least three individuals of this genus. In addition
to this, there is some variation in the size of some of these bones
which suggests that the individuals were of different ages. However a
look at how the bones were deposited has led to the describing team
coming up with the hypothesis that the site of the bones discovery was
not the site where these dinosaurs died. Instead it seems that the
bones were deposited elsewhere and then later washed to their new
location.
Because
the remains of several individuals were located together, this does
raise the possibility that Bicentenaria may have
spent time living in
groups. The deposit of what appears to be the remains of several
individuals of only one genus and of different ages certainly does
help with this hypothesis. However detractors to this theory could
simply state that the collection of several remains of the same
dinosaur genus may merely be coincidental. However if the collection
was purely down to chance then one would expect to find the remains of
different genera. The fact that the remains seem to be of the same
genus does not the entirely discredit the ‘by chance’ theory, but
it does count for a lot against it.
As
a coelurosaur, Bicentenaria would have been a
relatively small
theropod predator in the ecosystems of Late Cretaceous South America.
This places it between the slightly earlier large carcharadontosaurid
theropods like Giganotosaurus
and Mapusaurus,
and the later
abelisaurids
such as Abelisaurus
and Aucasaurus.
However given the
inherent incompleteness of the South American fossil record, it is
not implausible that Bicentenaria itself may have
been targeted by
other large theropods, particularly basal abelisaurs such as
Ilokelesia.
One interesting thing of note is that most coelurosaurs
that Bicentenaria seems to have been most like to
are so far dated to
the Late Jurassic/Early Cretaceous, indicating that Bicentenaria
may
be a late surviving example of these kinds of earlier theropods.
At
the time of its description Bicentenaria was
incorrectly lauded by some
popular media sources as the ancestor to and even a species of
Tyrannosaurus.
To understand the true relationship of Bicentenaria
to
Tyrannosaurus, and tyrannosaurs
in general, you
have to understand
this. Bicentenaria seems to have been a type of
coelurosaur, and
fossil evidence along with the majority of palaeontologists think that
the tyrannosaurs evolved from this group of theropods. However this
evolution seems to have taken place much further back in the Mesozoic
with many forms of primitive tyrannosauroids being dated back to many
tens of millions years before Bicentenaria is
currently known to have
existed. One example for instance is Yutyrannus,
a basal
tyrannosauroid that is dated to the much earlier Aptian stage of Asia,
making it around one hundred and twenty-five million years old against
the estimated ninety million years old Bicentenaria.
It is the
appearance of these other forms as well as the geographic isolation of
North and South America during these periods that serve to discredit
the notion that Bicentenaria was the
‘granddaddy’ of
Tyrannosaurus. Instead Bicentenaria
represents a type of
coelurosaurian theropod that is at best a distant cousin to the
tyrannosaurs that dominated the Northern hemisphere.
Further reading
- New Patagonian Cretaceous theropod sheds light about the early
radiation of Coelurosauria. - Revista del Museo
Argentino de Ciencias Naturales, nueva serie, 14: 57–81. - F. E. Novas,
M. D. Ezcurra, F. L. Agnolin, D. Pol & R. Ortiz - 2012.
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