Styxosaurus
Name:
Styxosaurus
(Styx lizard).
Phonetic: Sticks-oh-sore-us.
Named By: Samuel Paul Welles - 1943.
Synonyms: Alzadasaurus kansasensis,
Alzadasaurus pembertonii, Cimoliasaurus snowii, Elasmosaurus
snowii, Thalassiosaurus ischiadicus, Thalassonomosaurus marshi.
Classification: Chordata, Reptilia,
Sauropterygia, Plesiosauria, Elasmosauridae.
Species: S. snowii (type), S.
browni.
Diet: Piscivore.
Size: 11 to 12 meters long.
Known locations: USA, Kansas, and South Dakota.
Time period: Santonian to Campanian of the
Cretaceous.
Fossil representation: At least two specimens.
The first specimen of Styxosaurus was of a skull and twenty cervical (neck) vertebrae, but was initially described as a species of Cimoliasaurus (C. snowii) by Samuel Wendell Williston in 1890. Williston then shifted it over as a species of Elasmosaurus in 1906 as E. snowii. Later study by Samuel Paul Welles led to the material being used to create the new genus of Styxosaurus, naming it after the river that in Greek Mythology separated the underworld from the land of the living. A second and more complete elasmosaurid skeleton was described by Welles and James Bump as a new species Alzadasaurus pembertoni in 1949. However later study by Ken carpenter in 1999 found that it was actually another specimen of Styxosaurus. The transferal of fossil material has not always been towards Styxosaurus however, as a second species named S. browni (named by Welles in 1952) was later found to be a specimen of Hydralmosaurus.
Like
other elamosaurid plesiosaurs
Styxosaurus had a
very long neck that
accounted for up to half its body length. This neck is thought to
have been the primary feeding adaptation which allowed Styxosaurus
to
reach into shoals of fish. An increasingly popular theory is that
elasmosaurids like Styxosaurus may have approached
fish from beneath so
that they could use the murk of deeper waters to hide their bodies
while they presented a small profile of the front of the head to the
prey. Such behaviour would greatly reduce the chance of being
spotted by the prey that Styxosaurus was
stalking, increasing
the chance of a successful hunt. Styxosaurus also
had the typical
sharp thin teeth that intermeshed together when the jaws closed so that
there was absolutely no escape for any fish caught between them.
Like
many other marine reptiles like it, Styxosaurus
has been found with a
large number of gastrolith stones within its body. The swallowing of
stones by plesiosaurs has long been interpreted as an attempt to
counter the lifting effect of the air in the lungs so that the
individual could swim more easily below the surface. Today though
things are not so clear cut as this Styxosaurus
specimen actually has
fish bones which look like they have been ground by the stones. This
fits in with the type of teeth in the mouth of Styxosaurus
which are
perfectly adapted for seizing fast and slippery prey, but next to
useless for cutting through flesh. This means that after prey was
swallowed whole, the stones would rub off things like scales so that
the flesh could be digested as well as the remaining bones being ground
and broken up. Additionally the weight of the gastroliths when
measured resulted in a combined weight that was but a tiny fraction of
the total weight of the living animal. With this in mind it seems
reasonable that the primary function of the gastroliths in Styxosaurus
and other plesiosaurs was to help with digestion, while any
additional effect of the stones providing increased ballast was more of
a secondary benefit.
Though
predatory, Styxosaurus, especially smaller
juveniles would have been
vulnerable to larger sharks
such as Cretoxyrhina
and Cardabiodon,
while
the emerging mosasaurs
would become the top predators of the seas, and
even threaten adult Styxosaurus.
Further reading
- Structure of the Plesiosaurian Skull. - Science 16 (405): 262. - S.
W. Williston - 1890a.
- North American plesiosaurs: Elasmosaurus, Cimoliasaurus,
and
Polycotylus. - American Journal of Science Series 4
21: 221–236. - S.
W. Williston - 1906.
- Elasmosaurid plesiosaurs with description of new material from
California and Colorado. - Memoirs of the University of California
13:125-254. - S. P. Welles - 1943.
- Revision of North American elasmosaurs from the Cretaceous of the
western interior. - Paludicola 2(2):148-173. - K. Carpenter - 1999.
- Gastroliths associated with plesiosaur remains in the Sharon Springs
Member of the Pierre Shale (Late Cretaceous), western Kansas. -
Transactions of the Kansas Academy of Science 103(1-2): 58-69. - M. J.
Everhart - 2000.
- Taxonomic reassessment of Hydralmosaurus as Styxosaurus:
new insights
on the elasmosaurid neck evolution throughout the Cretaceous. - PeerJ
4:e1777. - R. A. Otero - 2016.
Random favourites
 |
|
 |
|