Ammosaurus
Name:
Ammosaurus
(Sand lizard).
Phonetic: Am-moe-sore-us.
Named By: Othniel Charles Marsh - 1889.
Synonyms: Ammosaurus solus, Anchisaurus
major, Anchisaurus solus.
Classification: Chordata, Reptilia, Dinosauria,
Saurischia, Sauropodomorpha, Anchisauria.
Species: A. major (type).
Diet: Herbivore/Omnivore?
Size: 4 meters long.
Known locations: Canada, Nova Scotia - McCoy
Brook Formation. USA, Connecticut - Upper Portland Formation,
Arizona - Navajo Sandstone.
Time period: Pliensbachian through to the Bajocian
of the Jurassic.
Fossil representation: Partial post cranial remains
of adult and juvenile specimens.
Ammosaurus
has a long taxonomic relationship with Anchisaurus.
The holotype
fossils of Ammosaurus were originally described as
a large species of
Anchisaurus by Othniel Charles Marsh before they
were erected as a
distinct genus. Marsh then named a new species of Anchisaurus,
A.
solus, but then attributed that to Ammosaurus.
Later
palaeontologists found that the A. solus remains
were just those of a
juvenile of Ammosaurus major, and so A.
solus became a synonym to
the type species.
Around
the end of the twentieth and beginning of the twenty-first centuries,
fresh debate surrounded Ammosaurus with many
prominent
palaeontologists considering Ammosaurus to actually
be synonymous with
Anchisaurus. Others however pointed out subtle
difference in the
pelvis between Anchisaurus and Ammosaurus
and
continue to treat the two
as separate genera, even though some have said that the differences
are at a species level not a genus one. As such the validity of
Ammosaurus as a distinct genus can vary greatly
depending upon who you
ask, but a safe statement is that the fossils from Ammosaurus
and
Anchisaurus, if not from the same genus of
dinosaur, represent two
that are very similar to one another in everything but size.
I
terms of being a dinosaur, Ammosaurus was a
prosauropod dinosaur,
the form that was the precursor to the huge quadrupedal sauropods that
would become commonplace towards the later stages of the Jurassic.
Ammosaurus may have been quadrupedal, but their
lighter frames mean
that they would have better been able to rear up on their hind legs to
reach high vegetation. Prosauropods like Ammosaurus
were also
recently descended from meat eating ancestors back in the Triassic,
and it is possible but currently unknown for sure if Ammosaurus
occasionally ate meat as well as plants. This is not to say that
Ammosaurus was an active predator, it may have
simply supplemented
its herbivorous diet by scavenging meat off the carcasses of other
animals. With some remains of Ammosaurus dating
to the Bajocian
stage, Ammosaurus is one of the few prosauropods
known to have
survived into the late Jurassic.
The
wide geographical and temporal range of Ammosaurus
means that it would
have come into contact with many other early/mid Jurassic dinosaurs
and other creatures. These included crocodyliforms like Protosuchus
to predatory theropod dinosaurs like Dilophosaurus
which may have been
predators of Ammosaurus early on in the Jurassic.
Further reading
- The prosauropod dinosaur Ammosaurus, the
crocodile Postosuchus,
and their bearing on the age of the Navajo Sandstone of Northeastern
Arizona, P. M. galton - 1971.
- Anchisaurus polyzelus (Hitchcock): the
smallest known
sauropod dinosaur and the evolution of gigantism among sauropodomorph
dinosaurs, Adam M. Yates - 2004.
- Description and evolutionary significance of the sauropodomorph
dinosaurs from the early Jurassic (Hettangian) McCoy Brook
Formation. Ph.D. dissertation. Halifax, Nova Scotia, T. J.
Fedak - 2007.
- A revision of the problematic sauropodomorph dinosaurs from
Manchester, Connecticut and the status of Anchisaurus Marsh,
Adam
M. Yates - 2010.
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