Name: Dilophosaurus
(Two crested lizard).
Phonetic: Di-lo-fo-sore-us.
Named By: Samuel Paul Welles - 1970.
Classification: Chordata, Reptilia, Dinosauria,
Saurischia, Theropoda, Dilophosauridae.
Species: D. wetherilli
(type).
Diet: Carnivore.
Size: Typically about 6 meters long, some fossils
suggest larger individuals may have attained lengths of up to 7 meters..
Known locations: USA, Arizona - Kayenta Formation.
Time period: Sinemurian of the Jurassic.
Fossil representation: A few specimens, three of
which were found together.
Dilophosaurus
is a very distinctive dinosaur that is instantly recognisable by the
two crests that are on top of its neck. It must be remembered however
that Dilophosaurus never had a neck frill or spat
venom, as was depicted in the 1993 film Jurassic Park.
Those were
the creations of artistic licence, not paleontological fact.
The
crests themselves are most likely there for display, and could have
been brightly coloured, particularly in the males. The crests are
usually found disarticulated from the skull, but
careful reconstruction has shown that they most likely sat on top of
the skull. This arrangement is also considered more accurate than
some earlier artistic reconstructions that have the crests running from
the back of the skull and onto the neck. Such a reconstruction would
have restricted the movement of the neck vertebra, a flawed
configuration for a predator, hence the acceptance of the crests on
top of the skull.
The
skull also features a large notch in the upper jaw between the teeth of
the pre-maxilla and maxilla. This notch is actually an inherent
weakness in the skull and suggests that Dilophosaurus
probably did not
have a high bite force as other similarly sized dinosaurs that lacked
the notch. One theory is that the notch would have enabled
Dilophosaurus to dig out small prey items out of
things like rock
crevices, although bearing in mind that it was six meters long, it
would not really be an efficient method of feeding for such a large
dinosaur. Another theory is that Dilophosaurus
lived the life of a
scavenger. In this scenario Dilophosaurus would
only need a bite
force large enough to tear meat from a carcass, and could have used
its size to intimidate and drive off smaller carnivores from their
kill.
The
notch may yet prove to be a bit of a red herring in describing its
feeding behaviour. There were other dinosaurs present that were well
within the predatory scope of Dilophosaurus and it
may have also
employed the use of its claws in making kills. The notch may have
even been of use in picking flesh off the bones off kills as a weaker
bite force would mean that Dilophosaurus may have
had difficulty in
crunching bones. All that can be said is that carnivores in general
will kill an animal for food when able, but will also scavenge
carrion when the opportunity presents itself.
A
smaller version of this notch is also present in the earlier dinosaur
Coelophysis,
and it is part of the reason why some palaeontologists
think that Dilophosaurus and Coelophysis
have a common lineage, with
Dilophosaurus maybe being a direct descendent of Coelophysis.
Unfortunately there are so many possible ways that Coelophysis
fits in
with other dinosaurs that it’s hard to pick one out as being more
likely.
One
Dilophosaurus specimen shows an underdeveloped left
arm that has a
reduced humerus, while the right is quite robust. This discrepancy
may have been caused by harsh living conditions and could be an example
of fluctuating asymmetry. The majority of animal organisms have
completely symmetrical body morphology and when one differs from the
rest in this way, the answer is either genetic or the result of an
outside factor.
When
first discovered in 1942, the Dilophosaurus
specimen was lacking
the head crests and was named Megalosaurus
wetherilli.
It was not
until another and more complete specimen that featured the crests was
recovered over a decade later that the distinction could be made. The
fact that three Dilophosaurus individuals were
found together has lent
support to the theory that some dinosaurs hunted in packs. Dilophsaurus
is now the type genus of its own special group of theropod dinosaurs
called the Dilophosauridae.
In
1993 a second species of Dilophsaurus called D.
sinensis was named.
Later analysis of this species however has now determined that it is
not a species of Dilophosaurus but a separate
genus, and is now known
as Sinosaurus.
Further reading
- Dilophosaurus (Reptilia: Saurischia), a new name
for a dinosaur. -
Journal of Paleontology 44:989. - S. P. Welles - 1970.
- Dilophosaurus wetherilli (Dinosauria, Theropoda),
osteology and
comparison. - Palaeontogr. Abt. A 185: 85–180. - S. P. Welles - 1984.
- Multi-element osteohistological analysis of Dilphosaurus
wetherilli.
- Journal of Vertebrate Paleontology, v. 16, supplement to n. 3,
Abstracts of Papers, Fifty-sixth Annual Meeting, Society of Vertebrate
Paleontology, American Museum of Natural History, New York, New York. -
J. S. Tkach - 1996.
- New specimens of Dilophosaurus wetherilli
(Dinosauria: Theropoda)
from the early Jurassic Kayenta Formation of northern Arizona. -
Western Association of Vertebrate Paleontologists annual meeting volume
Mesa, Arizona 1: 1. - Robert Gay - 2001.
- Evidence for sexual dimorphism in the Early Jurassic theropod
dinosaur, Dilophosaurus and a comparison with other
related forms In:
Carpenter, Ken, ed. The Carnivorous Dinosaurs. - The Carnivorous
Dinosaurs. Indiana University Press. pp. 277–283. - Robert Gay - 2005.
- Forelimbs of the theropod dinosaur Dilophosaurus wetherilli:
Range of
motion, influence of paleopathology and soft tissues, and description
of a distal carpal bone. - Palaeontologia Electronica. - P. Senter
& C. Sullivan - 2019.
- A comprehensive anatomical and phylogenetic evaluation of
Dilophosaurus wetherilli (Dinosauria, Theropoda)
with descriptions of
new specimens from the Kayenta Formation of northern Arizona. - Journal
of Paleontology. 94 (S78): 1–103. - A. D. Marsh & T. B. Rowe -
2020.