Torosaurus
Name:
Torosaurus
(Perforated lizard).
Phonetic: Toh-ro-sore-us.
Named By: Othniel Charles Marsh - 1891.
Synonyms: Arrhinoceratops utahensis?
Torosaurus gladius.
Classification: Chordata, Reptilia, Dinosauria,
Ornithischia, Ceratopsidae, Chasmosaurinae, Triceratopsini.
Species: T. latus (type),
T. utahensis?
Diet: Herbivore.
Size: Roughly about 7.5-7.6 meters long.
Known locations: Canada, Alberta - Scollard
Formation, Saskatchewan - Frenchman Formation. USA, Colorado
- Laramie Formation, North Dakota - Hell Creek Formation,
South Dakota - Hell Creek Formation, Texas - Javelina
Formation, Utah - North Horn Formation, Wyoming - Lance
Formation.
Time period: Maastrichtian of the Cretaceous.
Fossil representation: Multiple individuals,
together revealing most of the skull and post cranial skeleton.
Torosaurus the dinosaur
Torosaurus
was first named upon the description of two partial skulls by Othniel
Charles Marsh all the way back in 1891, two years after he had
named the much more famous Triceratops.
The most common mistake
regarding the name Torosaurus is the meaning,
with many people
misquoting it as meaning ‘bull lizard’ after the Spanish word
‘toro’ which means bull. However, Spanish is not a commonly used
language in establishing binomial names, and in the late nineteenth
century the two most commonly used languages were Latin and
particularly Ancient Greek. In this respect Torosaurus
is based upon
the Ancient Greek words ‘toreo’, which means ‘perforate’ or
‘to pierce’ and ‘sauros’ which means ‘lizard’.
Torosaurus
was a large ceratopsian
dinosaur that lived on the North American
continent towards the end of the Cretaceous. Like with others of its
kind, Torosaurus was an herbivore cropping low
growing vegetation and
may have lived in social groups. Torosaurus is
noted for having one
of the largest skulls of not just any dinosaur but any land animal.
Most of this is physical length formed by the neck frill which grows
out from the back of the skull, which covers the neck, but was
almost certainly for display as opposed for defence. The defence
theory is no longer thought to be a primary function given to save
weight the bone of the frill was relatively thin and perforated (clue
is in the name!) with large openings. However, new skulls
attributed to the genera Pentaceratops
and Titanoceratops
seem to be
even larger, suggesting that Torosaurus while
large may not have had
‘the’ biggest skull. In addition to this a Triceratops
skull
measuring 2.8 meters long and nicknamed Lung Wong (Dragon King)
is now known.
Currently
the only valid species of Torosaurus is the type
species T. latus,
though as we will see, this may in fact be synonymous with
Triceratops. A former species T.
gladius has
now been ascertained
to be synonymous with the type species. Fossils originally attributed
as a species of the genus Arrhinoceratops,
A. utahensis, have now
been credited by some researchers as representing a species of
Torosaurus. However again, the debate about
synonymy with
Triceratops has cast this in doubt.
The Triceratops/Torosaurus synonymy debate
Around
2009-2010 new study into the skulls of Torosaurus
and Triceratops by
John Scanella and John R. Horner (better known as Jack Horner)
led to the idea that the skulls of Torosaurus were
actually the fully
mature forms of Triceratops. This would mean that
Torosaurus
was not
only a synonym, but reconstructions of Triceratops
for over a hundred
years had been slightly wrong, with a neck frill far too short. At
the time this was big news with most online news outlets and many
printed newspapers covering the story, and many erroneously reporting
that ‘Triceratops never existed’, though if
the theory were true
then it would technically be the other way around given that
Triceratops was named first.
The
theory is quite detailed but the finer points are this. Ceratopsian
dinosaur bones are known to be composed of large amounts of metaplastic
bone, and as an animal matures this metaplastic bone can change in
both size and shape (its why little baby ceratopsian dinosaurs have
short stubby neck frills, they wouldn’t fit into the egg
otherwise!). Scanella and Horner noted that all the known specimens
of Torosaurus were of very old and mature adults,
while those of
Triceratops were of sub adults and young adults.
They also noted that
while known Triceratops skulls don’t have holes in
the neck frill,
they do have areas of thin bone. Their theory was that Torosaurus
skulls represented the true adult form of fully mature Triceratops,
with the thin areas of bone giving way to the holes that we see in
Torosaurus neck frills. This also led to the
phrase ‘toromorph’
to describe the Torosaurus skulls as fully mature Triceratops
skulls.
The
theory was however was not perfect, and there were still some areas
that were blank. First it’s that even after over a hundred years of
study and dozens of skulls, no actual transitional form showing the
change of a Triceratops skull to the toromorph form
had been found.
However in 2007 a ceratopsian dinosaur skull was used to
establish a new ceratopsian genus called Nedoceratops.
Scanella and
Horner considered this skull to possibly be a missing transitional form
given that it appeared to show the development of holes and reduction
in nasal horn on an otherwise Triceratops skull.
Scanella and Horner
also addressed the issues of epoccipitals, the osteoderms that grow
along the edges of the neck frill. Triceratops
skulls average around
five epoccipitals with one centred along the midline of the skull.
Torosaurus however are noted for having ten to
twelve epoccipitals
with none centred on the midline. Scanella and Horner noted however
that the number of epoccipitals in some Triceratops
skulls does vary
from the norm, and at least one has no midline epoccipital.
Scanella and Horner also proposed that the epoccipitals in Triceratops
may have each split in half allowing for a ten count as seen in some
Torosaurus.
Since
their theory was published, other palaeontologists have not
recognised the study as correct, and indeed some have even
published counter studies to test this theory with the conclusion that
Torosaurus skulls can’t be those of Triceratops.
To start
Nedoceratops was re-described in 2011 by
Andrew Farke who noted
that the holes in the Nedoceratops holotype were
surrounded by thicker
bone growths, leading him to conclude that the holes were a result of
injury and/or disease with possible infection. Therefore according to
this study, the holes in the Nedoceratops skull
were not formed by
the beginning of a new growth stage, and so it cannot be heralded as
a transitional form. Since this Scanella and Horner have conceded
that the Nedoceratops skull is not an ideal
candidate for a
transitional form but yet they considered it to represent a diseased
Triceratops and not a distinct genus.
In
2012 Nicholas Longrich and D. J. Field tested Scanella’s and
Horner’s theory upon the basis of three predictions that should all be
proven true if correct. First is that both Triceratops
and Torosaurus
should being found from the same locations, but in depth study of the
currently known locations of both genera show that while close,
very little overlap occurs. However the fossil record will never be
complete, and only a relatively rare few animals will be preserved.
Older individuals may have also shifted to different parts within the
ecosystem, and the difference in the length of the snout of
Torosaurus as opposed to Triceratops
may indicate a different feeding
and by extension ecological placement. In short however, this
information cannot conclusively prove or disprove Scanella’s and
Horner’s theory.
Second
is that all Torosaurus skulls should be of very old
and mature
individuals while those of Triceratops should be no
older than just
beyond sub adult. Horner did state that all Triceratops
skulls that
were tested had a sub adult bone structure, however, not all known
Triceratops skulls were tested. When Triceratops
skulls from other
locations were investigated many were concluded to be older than sub
adult, and some seemingly quite old, with at least ten being of the
same level of maturity as older Torosaurus.
Also, while all the
Torosaurus skulls were thought to be of very old
individuals, at
least two Torosaurus skulls are now known to have
come from much
younger individuals, with a lack of fusion in some parts of the skull
indicating that they themselves were not much past the sub adult level
when then died. These younger Torosaurus skulls
already show an
extended neck frill with established openings far beyond that of
similarly aged Triceratops. Furthermore, one of
these skulls is
also missing the epoccipitals, showing that this individual was so
young when it died that the epoccipitals had not even fused to the main
neck frill. In the second part, not only is there no evidence to
establish an age/maturity difference, but the available fossils seem
to support the opposite.
The
third prediction was that there should be at least some transitional
forms that show a Triceratops skull growing into
the toromorph. At
the time of writing there are no known skulls that show us this change
happening, and again, what fossils we do have seem to show that
Triceratops and Torosaurus
should be separate. Firstly, while
Triceratops skulls often show slight depressions,
these seem to be
surrounded by a slight thickening of bone, while the holes in
Torosaurus are surrounded only by thin bone.
Also, the depressions
in Triceratops while mostly on the parietal bone of
the skull also
extend to the squamosal bone. In Torosaurus the
holes are only on the
parietal bone. Out of these three predictions proposed by Longrich,
one is neutral, neither confirming of denying the theory, while
two conclude that Triceratops and Torosaurus
are separate species.
The
differences in the number of epoccipitals has also been discredited.
Firstly, the numbers of epoccipitals between members of the same
species has been known to vary, meaning that identification of a
ceratopsian species by counting epoccipitals can only be used as a very
rough guide at best. At the time of writing there are no known cases
of epoccipitals doubling themselves by splitting. If anything, the
epoccipitals should proportionately increase in size with age.
Although
ceratopsian dinosaur skulls are known to have metaplastic bone which
changes, it has been noted that due to the age of some Triceratops
skulls, this bone would have already matured and hardened to hold its
shape. If these individuals were to be capable of forming a toromorph
skull, this bone would have had to have been rejuvenated to be able
to morph again, before finally setting once more into the new form.
This is a sequence that currently has no known precedence, and is
seen as further support to keep Torosaurus and Triceratops
separate.
2013
saw the publication of another paper, this time by Andrew Farke and
Leonardo Maiorino, this time involving morphometric research upon the
two main Triceratops species, T.
horridus and T. prorsus,
Torosaurus and Nedoceratops.
The conclusions were that T. horridus
and T. prorsus overlapped one another in
development, as would be
expected within two species of the same genus. Torosaurus
data was
limited due to the much lower number of known Torosaurus
remains when
counted against Triceratops, but those that were
able to be tested
showed that the Torosaurus skulls did not overlap
with those of
Triceratops. When Nedoceratops
was included, it was shown that it
could not be a transitional form between Triceratops
and Torosaurus.
One interesting side theory from this study however is that
Triceratops and Torosaurus could
form a chronospecies. If correct
then this would mean a direct familial relation between Triceratops
and
Torosaurus with them both being on the same line.
It
should also be noted however that fully grown Torosaurus
seem to have
reached total lengths of just over seven and a half meters. Large
Triceratops by comparison are known to have ranged
between eight and
nine metres in length. It would be unprecedented for a large land
vertebrate to grow large and then actually reduce in body length as it
matured. The largest Triceratops skulls are also
known to have
reached up to two hundred and eighty centimetres in length (length of
the specimen nicknamed Lung Wong, a.k.a Dragon King), just a
little bit longer that large Torosaurus skulls.
The discovery of such
a large skull counts a lot against the theory that Triceratops
grew
into toromorphs to save on skull weight, as here is one individual
that obviously didn’t have to.
So
what is likely to happen in the future? At the time of writing there
are three distinct possibilities. One is that future research and
discoveries will prove that Torosaurus and Triceratops
are one and the
same, and if so then this will mean that the Torosaurus
genus is
attributed to one of the Triceratops species. Two
is that Torosaurus
is proven to not represent a mature form of Triceratops,
but may
still be moved to the Triceratops genus as a
separate species to those
we currently know. Third, Torosaurus and Triceratops
continue to be
regarded as distinct species and genera, and things go on like they
have done for over a hundred years now. Indeed, most
palaeontologists and researchers continue to regard Triceratops
and
Torosaurus as distinct genera.
Further reading
- A skull of Torosaurus from South Dakota and a
revision of the
genus - Proceedings of the Academy of Natural Sciences of
Philadelphia, 99: 93–106. - E. H. Colbert & J.
D. Bump - 1947.
- Tyrannosaurus and Torosaurus,
Maastrichtian dinosaurs from
Trans-Pecos, Texas. - Journal of Paleontology 50(1):
158-164. - D. A. Lawson - 1976.
- The Ceratopsian dinosaur Torosaurus from the
Upper Cretaceous McRae
Formation, Sierra County, New Mexico. - New Mexico Geological
Society Guidebook, 49th Field Conference, Las Cruces County II.
- S. G. Lucas, G. H. Mack & G. W. Estep -
1998.
- A review of Torosaurus (Dinosauria:
Ceratopsidae) specimens
from Texas and New Mexico. - Journal of Vertebrate Paleontology,
22: 52A. - A. Farke - 2002.
- Redescription of the ceratopsid dinosaur Torosaurus
utahensis
(Gilmore, 1946) and a revision of the genus. - Journal of
Paleontology 79:564-582. - R. M. Sullivan, A. C. Boere
& S. G. Lucas - 2005.
- Attributes of the ceratopsian dinosaur Torosaurus,
and new
material from the Javelina Formation (Maastrichtian) of Texas. -
Journal of Paleontology 82(6): 1127-1138. - Rebecca K.
Hunt & Thomas M. Lehman - 2008.
- And then there was one: synonymy consequences of Triceratops
cranial ontogeny. - Journal of Vertebrate Paleontology 29:
177A. - J. Scanella - 2009.
- Torosaurus Marsh, 1891, is Triceratops
Marsh, 1889
(Ceratopsidae: Chasmosaurinae): synonymy through ontogeny .
- Journal of Vertebrate Paleontology, 30(4): 1157 -
1168. - J. Scanella & J. R. Horner 2010.
- Nedoceratops: An Example of a Transitional
Morphology. -
PLoS ONE 6 (12). - John B. Scanella, John R. Horner
& Leon Claessens - 2011.
- Anatomy and Taxonomic Status of the Chasmosaurine Ceratopsid
Nedoceratops hatcheri from the Upper Cretaceous
Lance Formation of
Wyoming, U.S.A. PLoS ONE 6 (1). - A. A. Farke (Leon
Claessens, ed) - 2011.
- Torosaurus is not Triceratops:
Ontogeny in chasmosaurine
ceratopsids as a case study in dinosaur taxonomy. - PLoS ONE 7
(2): e32623. - N. R. Longrich & D. J. Field
- 2012.
- Is Torosaurus Triceratops?
Geometric Morphometric Evidence of
Late Maastrichtian Ceratopsid Dinosaurs. - PLoS ONE 8 (11):
e81608. - Leonardo Maiorino, Andrew A. Farke, Tassos
Kotsakis, Paolo Piras & Richard J. Butler - 2013.
----------------------------------------------------------------------------
Random favourites
 |
 |
 |
 |