Kritosaurus
Name:
Kritosaurus
(Seperated lizard).
Phonetic: Krit-o-sore-us.
Named By: Barnum Brown - 1910.
Synonyms: Possibly Anasazisaurus.
Classification: Chordata, Reptilia, Dinosauria,
Ornithischia, Ornithopoda, Hadrosauroidea, Hadrosauridae,
Saurolophinae.
Species: K. navajovius
(type).
Diet: Herbivore.
Size: Estimated around the 10 meter mark, but
this is now based upon comparison to other more complete genera.
Known locations: USA - New Mexico - Kirtland
Formation.
Time period: Campanian of the Cretaceous.
Fossil representation: Based upon a partial skull,
many other sets of remains once attributed to the genus have since
been removed.
Kritosaurus
was first described in 1910 upon a description of a partial skull
that was not only incomplete but partially eroded. To fill in the
gaps, Brown used a second skull that would later be referred to
Anatotitan to complete the reconstruction. Not all
the fragments were
used, and the final reconstruction was of a hadrosaurid
(duck
billed) dinosaur with a reasonable flat snout. Brown seems to have
had some suspicions about his restoration and in 1914 when a new
genus called Gryposaurus
was discovered with a high nasal arch, Brown
came to the idea that the Kritosaurus
reconstruction should have been
more along the lines of Gryposaurus, and this
time reconstructing the
skull with all the fragments, was able to produce a skull very much
like that of Gryposaurus.
It
was this reconstruction
that actually led to a lot of misinterpretation about the name
Kritosaurus. Many sources have credited the name Kritosaurus
with
meaning ‘noble lizard’ because the arch of the nasal bone bore a
superficial resemblance to the hooked nose associated with classical
Roman nobility. However as I am sure you can already appreciate,
this interpretation was impossible until many years after the name had
already been established. Instead the name Kritosaurus
actually
means ‘separated lizard’ in reference to the separated cheek bones
of the holotype skull. On a side note, Barnum Brown had initially
intended to call Kritosaurus, Nectosaurus,
but
was unable because
the name had already been granted to a Triassic era thallatosaur.
The
new reconstruction was
also the start of a lot of controversy about Kritosaurus.
Not only
did Brown recreate Kritosaurus to be similar to Gryposaurus,
but he
also declared the latter to be a synonym to Kritosaurus.
At the time
this was supported by many other palaeontologists and all Gryposaurus
fossils were renamed and classified as Kritosaurus.
With these
additional fossils, Kritosaurus went on to become
one of the most
popular hadrosaurids (though still usually called duck billed
dinosaurs) in popular media such as books.
Problems
first came to light
in the late 1970s to early 1980s when Kritosaurus
was considered to
be a possible synonym to another genus called Hadrosaurus.
By the
late 1980s Kritosaurus was once again widely
accepted as being
separate from Hadrosaurus, but in depth study of Kritosaurus
during
this time resulted in a new idea; Kritosaurus and Gryposaurus
were
actually not the same at all. The biggest doubt was centred on the
second restoration of the Kritosaurus holotype
skull. When first
reconstructed, Barnum Brown was working without a frame of
reference, but the second time he was working to an existing skull,
and doubts are now cast as to if he accidentally made the skull of
Kritosaurus to look like Gryposaurus,
thus causing the similarity.
In
1990 the
palaeontologists Jack Horner and David B. Weishampel separated
Gryposaurus from Kritosaurus,
resurrecting the genus. However all
of the subsequent additions to Kritosaurus after Gryposaurus
had been
declared a synonym could only be attributed to Gryposaurus
because
Kritosaurus was only founded upon the basis of a
single incomplete
skull. This saw two of the original three species of Kritosaurus
now
regarded as synonyms to Gryposaurus with no further
post cranial
remains for Kritosaurus.
Further
remains attributed to
Kritosaurus from have also been referred to new
genera. Before the
Kritosaurus/Gryposaurus split,
a skull from Patagonia, South
America was assigned to Kritosaurus in 1984,
but this has
subsequently been used to establish the genus. Secernosaurus.
In
1992, Jack Horner described two more skulls for Kritosaurus,
and
confidently described them as being quite different from Gryposaurus.
However in moves that have since proven controversial, both of these
skulls were re-described as new genera by Adrian Hunt and Spencer G.
Lucas. These new genera were Anasazisaurus and Naashoibitosaurus,
and although some palaeontologists have treated them as valid,
others still agree with Horners original interpretation.
At
the time of writing
Kritosaurus is still only recognised by the original
partial skull that
established the holotype back in 1910. There has been a lot of
speculation about how some new fossil discoveries that may belong to
Kritosaurus, but so far these have proven
inclusive due to the fact
that the fossils cannot be matched up to the skull, particularly the
forward portion of Kritosaurus. Additionally
although Anasazisaurus
has been treated as being distinct by some researchers, there are
still suggestions that it should be referred back to Kritosaurus.
As
a duck billed dinosaur,
Kritosaurus would have at least been similar to
other hadrosaurids,
primarily walking around on four legs, but being capable of rearing
up on two. This would have seen it capable of browsing upon a
variety of plants at different heights which could be snipped with the
forward beak before being processed by the grinding teeth. Coming
from the Kirtland Formation of New Mexico, Kritosaurus
might have
been preyed upon by tyrannosaurs
such as Bistahieversor.
Further reading
- The Cretaceous Ojo Alamo beds of New Mexico with description of the
new dinosaur genus Kritosaurus. - Bulletin of the
American Museum of
Natural History 28(24):267-274. - Barnum Brown - 1910.
- The osteology of the trachodont dinosaur Kritosaurus
incurvimanus. -
University of Toronto Studies, Geology Series 11: 1–76. - William A.
Parks - 1920.
- A new species of Kritosaurus from the Cretaceous
of Big Bend National
Park, Brewster County, Texas. - Journal of Vertebrate Paleontology 21
(3, Suppl.): 110A–111A. - Jonathan R. Wagner & Thomas M. Lehman
- 2001.
- A re–evaluation of Secernosaurus koerneri and Kritosaurus
australis
(Dinosauria, Hadrosauridae) from the Late Cretaceous of Argentina. -
Journal of Vertebrate Paleontology 30 (3): 813–837. - Alberto
Prieto–Marquez & Guillermo C. Salinas - 2010.
- Skeletal morphology of Kritosaurus navajovius
(Dinosauria:Hadrosauridae) from the Late Cretaceous of the North
American south-west, with an evaluation of the phylogenetic systematics
and biogeography of Kritosaurini. - Journal of Systematic
Palaeontology. - Alberto Prieto-M�rquez - 2013.
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