Vallecillosaurus
Name:
Vallecillosaurus
Phonetic: Val-le-sil-lo-sore-us.
Named By: K. T. Smith & M. C.
Buchy - 2008.
Classification: Chordata, Reptilia, Squamata,
Mosasauroidea.
Species: V. donrobertoi (type).
Diet: Carnivore.
Size: Uncertain, but the rear portion of the post
cranial skeleton is 2 meters long, suggesting a small to medium
size for this mosasaur.
Known locations: Mexico - Agua Nueva Formation.
Time period: Early Turonian of the Cretaceous.
Fossil representation: Rear half of the post cranial
skeleton.
Although
not known from very complete fossil material, one thing that can be
established about this mosasaur is that the rear limbs are not as well
developed to aquatic life as they are in later forms. This reveals
that Vallecillosaurus was a basal (sometimes
referred to as
primitive) mosasaur form, although it was not the only one from
this part of the world. Across the border in the United States, a
basal mosasaur named Russellosaurus
is known from Texas. Also from
Texas is the even more primitive Dallasaurus
that is regarded as one of
the earliest mosasaur ancestors, and further south in Columbia is
Yaguarasaurus.
It would however be a mistake to assume that the early
Turonian mosasaurs were restricted to these areas however as they are
also known from the other side of the Atlantic with Tethysaurus
from
Morocco hinting that the early mosasaurs established themselves across
the growing Atlantic ocean at the very least. Additionally the form
thought to be most similar to Vallecillosaurus is Komensaurus
that is
currently known from Europe (specifically Slovenia).
Although
incomplete, the remains of Vallecillosaurus were
preserved with skin
impressions that reveal Vallecillosaurus had
rhomboid shaped scales
across the rear portion of the body. However more complete skin
impressions like those found with the later Platecarpus
show that
different parts of the body had different shaped scales on them, and
it’s possible that the same may also be true for Vallecillosaurus.
Also fifteen pebbles were found in what would have been the stomach
area. The presence of these pebbles has long been assumed to be for
the purpose of ballast so that the animal could swim through the water
instead of just bobbing around on the surface. However in depth study
of the marine reptiles like the elasmosaurid plesiosaur Styxosaurus
has
revealed the presence of ground fish bones amongst similar stones.
This suggests that the stones in Vallecillosaurus
may have primarily
been for use as gastroliths, with additional effects of extra ballast
being a secondary benefit.
Further reading
- A new aigialosaur (Squamata: Anguimorpha) with soft tissue remains
from the Upper Cretaceous of Nuevo León, Mexico. - Journal of
Vertebrate Paleontology. 28: 85–94. - Krister T. Smith &
Marie-Céline Buchy - 2008.
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