Limusaurus
Name:
Limusaurus
(Mud lizard).
Phonetic: Le-moo-sore-us.
Named By: X. Xu, J. M. Clark, J. Mo,
J. Choiniere, C. A. Forster, G. M. Erickson, D. W.
E. Hone, C. Sullivan, D. A. Eberth, S. Nesbitt, Q.
Zhao, R. Hernandez, C.-K Jia, F.-L. Han, & Y.
Guo - 2009.
Classification: Chordata, Reptilia, Dinosauria,
Saurischia, Theropoda, Ceratosauria.
Species: L. inextricabilis (type).
Diet: Herbivore?
Size: Around 1.7 meters long.
Known locations: China, Junggar Basin -
Shishugou Formation.
Time period: Oxfordian of the Jurassic.
Fossil representation: Almost complete articulated
remains from two sub adults.
Although
known from very well preserved remains, there is still quite a bit of
mystery surrounding Limusaurus. Study of the
bones has revealed that
it is a member of the Ceratosauria (the first one known from
Asia), a group of theropods defined by the type genus
Ceratosaurus.
However the one specimen where the skull has been
preserved indicates that Limusaurus did not have
teeth and instead made
do with a beak-like mouth. Additionally gastroliths have also been
found along with Limusaurus remains, the presence
of which is usually
a herbivorous trait.
These
characteristics are very similar to the later ornithomimosaurs
of the
Cretaceous, many of which have also been found with toothless
beak-like mouths and gastroliths. However there is no one rule as to
what ornithomimosaurs ate (though a few select genera are a little
easier to ascertain) because the ‘beak could have been used to crop
plants or catch small vertebrates like lizards. While gastroliths are
usually associated with the grinding of plants it is not entirely
unknown for predators to also have them, particularly piscivores.
Another well-known example of a theropod dinosaur having gastroliths
is Lourinhanosaurus,
a theropod thought to be similar to dinosaurs
like Sinraptor
and Allosaurus.
For this reason Limusaurus may have
been a herbivore, specialist carnivore or perhaps even an omnivore,
speculations that will carry on in the absence of definitive evidence
to prove one above the others.
Limusaurus
is also noted for having four digits on its hands, something which
reveals it to be a primitive form of theropod. Additionally these
digits are composed of numbers II, III, IV and V, with digit I
being reduced to give the appearance of a ‘four fingered’ hand.
This is in contrast to previous theories about theropods since digit
reduction was thought to take place on the ulna side of the hand rather
than the radius side (the fore arms of vertebrates are made up of two
bones called the ulna and radius) as seen in Limusaurus.
Because
Limusaurus is so far only known from sub adult
remains it is quite
possible that it may have grown slightly larger than the 1.7 meters
stated above.
Limusaurus
is far from being the only theropod dinosaur known from the Shishugou
Formation with other genera including Sinraptor,
Guanlong,
Monolophosaurus,
Zuolong
and Haplocheirus.
Other types of dinosaur
from this formation include the sauropod Mamenchisaurus
and the basal
ceratopsian Yinlong.
Further reading
- A Jurassic ceratosaur from China helps clarify avian digital
homologies. - Nature 459(7249):940-944. - X. Xu, J. M. Clark, J. Mo, J.
Choiniere, C. A. Forster, G. M. Erickson, D. W. E. Hone, C. Sullivan,
D. A. Eberth, S. J. Nesbitt, Q. Zhao, R. Hernández, C.-k. Jia, F.-l.
Han & Y. Gou - 2009.
- Reply to "Limusaurus and bird digit identity". - Nature Precedings -
X. Xu, J. Clark, J. Choiniere, D. Hone & C. Sullivan - 2011.
- New anatomical details of the basal ceratosaur Limusaurus
and
implications for the Jurassic radiation of Theropoda. - Abstract of
Papers. 74th Annual Meeting Society of Vertebrate Paleontology. -
Journal of Vertebrate Paleontology. p. 235. - J. Stiegler & S.
Wang & X. Xu - 2014.
- Limusaurus inextricabilis (Theropoda:
Ceratosauria) gives a hand to
evolutionary teratology: a complementary view on avian manual digits
identities. - Zoological Journal of the Linnean Society. 176 (3):
674–685. - G. Guinard - 2016.
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