Tawa
Name: Tawa
(Named after the Puebloan sun god).
Phonetic: Tah-wah.
Named By: Sterling J. Nesbitt et al - 2009.
Classification: Chordata, Reptilia, Dinosauria,
Saurischia, Eusaurischia, Theropoda.
Species: T. hallae (type).
Diet: Carnivore.
Size: Estimated about 2 meters long.
Known locations: USA, New Mexico - Chinle
Formation, Ghost Ranch.
Time period: Norian of the Triassic.
Fossil representation: At least eight individuals
represented by partial skeletons.
Tawa
is yet another dinosaur genus from the late Triassic of the Ghost Ranch
North America, and as you might expect, one quite primitive in
form. Tawa were bipedal dinosaurs of the theropod
line, noted for
having femurs that were proportionately quite long when compared to the
lower leg bones. Tawa also had a kink between the
maxilla and
premaxillae, the tooth bearing bones of the upper jaw. This means
that in life Tawa may have had a notch in the upper
jaw similar to
Dilophosaurus
of the early Jurassic, though perhaps not quite as
pronounced. Tawa are also noted as having a more
slender build
compared to other early dinosaurs, a trait that would continue to
some later descendants.
One
area of interest about Tawa which has wider
implications for other
dinosaurs, is that the neck vertebrae are known to have air sacs,
almost identical to the air sacs of birds. This reveals that Tawa
had an avian like (bird-like) respiratory system, something which
has been seen in other dinosaur genera such as the sauropodomorph
Plateosaurus
and the late Cretaceous theropod Aerosteon.
The presence
of an avian-like respiratory system in Tawa however
is an indication
that this system first evolved in the early dinosaurs of the Triassic.
This is also yet further support for the theory that birds are
directly evolved from dinosaurs, and is an indicator the avian
respiratory system is at least as old as the late Triassic. This kind
of respiratory system also suggests that Tawa had
an endothermic
metabolism, meaning that it lived more as a ‘warm-blooded’
creature than a ‘cold-blooded’ one.
In
terms of evolutionary placement, Tawa seems to
have been more
advanced than forms such as Eoraptor
and Herreasaurus,
but not as
advanced as other dinosaur genera like Coelophysis.
Also, because
Coelophysis is known to have lived in the same time
and locations as
Tawa, then it raises the notion that Tawa
may have been a late
surviving form.
The
point of origin of the Dinosaurs is still thought to have been South
America since this is where the oldest true dinosaur genera are known
from. However the discovery of Tawa has helped to
establish that by
the late Triassic there were at least several genera of early dinosaurs
living in North America. Dinosauromorph reptiles (similar to
dinosaurs but not quite dinosaurs) are also starting to be discovered
in higher numbers, and in the future Africa may also become a key
area of study in our wider understanding of early dinosaur evolution.
Further reading
- A complete skeleton of a Late Triassic saurischian and the early
evolution of dinosaurs, S. J. Nesbitt, N. D. Smith, R.
B. Irmis, A. H. Turner, A. Downs & M. A.
Norell - 2009.
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