Rhomaleosaurus
Name:
Rhomaleosaurus
(Strong lizard).
Phonetic: Roe-may-lay-oh-sore-us.
Named By: Harry Govier Seeley - 1874.
Synonyms: Plesiosaurus cramptoni,
Plesiosaurus propinquus, Rhomaleosaurus thorntoni, Thaumatosaurus
cramptoni, Thaumatosaurus propinquus.
Classification: Chordata, Reptilia,
Sauropterygia, Plesiosauria, Pliosauroidea, Rhomaleosauridae.
Species: R. cramptoni (type), R.
propinquus, R. thorntoni, R. zetlandicus.
Diet: Carnivore.
Size: Larger individuals about 7 meters long.
Known locations: England, Northamptonshire and
Yorkshire - Whitby Mudstone Formation.
Time period: Toarcian of the Jurassic.
Fossil representation: Many specimens, some almost
complete making Rhomaleosaurus one of the best
preserved marine
reptiles.
Classification and naming history
of Rhomaleosaurus
The
first remains of Rhomaleosaurus were originally
named by Alexander
Carte and W. H. Bailey as a species of Plesiosaurus,
P.
cramptoni, which was in honour of Sir Philip Crampton,
an
anatomist who brought the remains to wider public attention. In
1874 Harry Govier Seeley found the remains to be very different from
Plesiosaurus and so erected them as the new genus of
Rhomaleosaurus.
However this was the beginning of a naming confusion with another
marine reptile called Thaumatosaurus (‘wonder
lizard’) that had
been named by Christian Erich Hermann von Meyer in 1841, and
described in more detail in 1856. The source of the problem was not
von Meyer himself however but the naturalist Richard Lydekker who in
1889 insisted that the remains attributed to Rhomaleosaurus
were in
fact the same as those of Thaumatosaurus. Both
Govier and Lydekker
insisted that the other was in the wrong but no further clarification
happened until over a hundred years later.
1910
saw the attribution of a new set of remains by Fraas that were
recognised as belonging to either Thaumatosaurus or
Rhomaleosaurus,
although Fraas did go for the full name of Thaumatosaurus
victor.
This led to other palaeontologists recognising the name
Thaumatosaurus, but ultimately time and further
study would fall upon
the side of Govier. You see, while Thaumatosaurus
was named before
Rhomaleosaurus, it was named upon very partial
remains that today are
considered to be too poorly preserved to identify a specific genus.
For this reason Thaumatosaurus is today considered
to be a nomen
dubium, and is why later remains attributed to it were re-named as
new species of Rhomaleosaurus.
Rhomaleosaurus
has had a greater number of remains attributed to it than what it does
today, mainly because the new species created from remains that were
originally attributed to Thaumatosaurus are now
thought to represent
different pliosaur genera. Rhomaleosaurus victor
has now become
Meyerasaurus
victor, while Rhomaleosaurus
megacephalus has been
included with Eurycleidus, although the
possibility has been
recognised that it yet represent its own genus. As you can see in the
case of Meyerasaurus the original species name has
been retained in
created the type species of the genus. This is standard procedure
when elevating a species to its own genus level, and helps future
researchers track the origins of new and shuffled species and genera.
In
addition to the above re-shuffling two more of the existing
Rhomaleosaurus species have had their validity
questioned. In 2007
Adam S. Smith considered the possibility that R.
propinquus was synonymous with R. zetlandicus.
R. zetlandicus
itself along with R. thorntoni were questioned as
being synonyms to
the type species R. cramptoni in 1996 by
Cruickshank. Later
study in 2008 by Adam S. Smith and Gareth J. Dyke has since
come to the conclusion that the current four species are actually valid.
Rhomaleosaurus
as a marine reptile
Rhomaleosaurus
is the type genus of the Rhomaleosauridae, a group of long necked
pliosaurs
that includes others such as Macroplata,
Yuzhoupliosaurus,
Maresaurus
as well as Eurycleidus
and Meyerasaurus that were mentioned
above. At up to seven meters long Rhomaleosaurus
was a large pliosaur
for its time, although other marine reptiles such as the ichthyosaur
Temnodontosaurus
grew larger.
The
predatory nature of Rhomaleosaurus is an
interesting subject as even
though it was a large pliosaur (for the early Jurassic at least),
the teeth and long neck are more suited for capturing smaller prey
like fish. The teeth themselves are not especially large but seem to
intermesh so that they were better suited to gripping small prey rather
than tearing chunks out of larger animals. Aside from fish, prey
could include creatures like cephalopods, specifically squid, as
well as possibly small marine reptiles, especially small juveniles of
larger forms.
Aside
from the overall robust construction of the skull, special attention
has been paid to the nasal cavities. It’s thought that marine
reptiles like Rhomaleosaurus may have been able to
‘sniff’ the
water to detect traces of things like blood in the water around them.
This ability may have been so sensitive that predators like
Rhomaleosaurus could not just smell it, but
identify its direction so
that it would have been able to investigate the source. Overall such
an ability would allow marine reptiles to find prey before it was
within visual range, considerably increasing their effectiveness as
marine predators.
Rhomaleosaurus
seems to have been limited to the waters of early Jurassic Europe with
all currently known specimens coming from England. Most fossils of
Rhomaleosaurus are from the Whitby Mudstone
Formation in the county of
Yorkshire, with an exception being R. thorntoni
which is from the
county of Northamptonshire. Most of the pliosaurs related to
Rhomaleosaurus are known from Europe except for Yuzhoupliosaurus
which
is known from China, something which suggests that Rhomaleosaurus
and
others may have had a wider distribution.
Further reading
- Note on some generic modifications of the plesiosaurian pectoral
arch. - Quarterly Journal of the Geological Society of London
30:436-449. - Harry Govier Seeley - 1874.
- Functional Anatomy of the Head of the Large Aquatic Predator
Rhomaleosaurus zetlandicus (Plesiosauria, Reptilia)
from the Toarcian
(Lower Jurassic) of Yorkshire, England. - Philosophical Transactions B
vol 335. issue 1274 - Michael Alan Taylor - 1992.
- Anatomy and systematics of the Rhomaleosauridae (Sauropterygia,
Plesiosauria). - Ph.D. thesis. - University CollegeDublin. - Adam S.
Smith - 2007.
- The skull of the giant predatory pliosaur Rhomaleosaurus
cramptoni:
implications for plesiosaur phylogenetics. - Naturwissenschaften - vol
95, issue 10 pp975-980 - Adam S. Smith & Gareth J. Dyke - 2008.
- Osteology of Rhomaleosaurus Thorntoni
(Sauropterygia:
Rhomaleosauridae) from the Lower Jurassic (Toarcian) of
Northamptonshire, England, by Adam S. Smith and Roger B. J. Benson -
Monograph of the Palaeontographical Society, London, 168 (no. 642)
(Darren Naish). 2014.- Osteology of Rhomaleosaurus Thorntoni
(Sauropterygia: Rhomaleosauridae) from the Lower Jurassic (Toarcian) of
Northamptonshire, England, by Adam S. Smith and Roger B. J. Benson -
Monograph of the Palaeontographical Society, London, 168 (no. 642)
(Darren Naish). 2014.
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