Edmontosaurus
Name:
Edmontosaurus
(Edmonton lizard).
Phonetic: Ed-mon-toe-sore-us.
Named By: Lawrence Lambe - 1917.
Synonyms: Anatosaurus, Anatotitan,
Claosaurus annectens, Edmontosaurus saskatchewanensis, Hadrosaurus
longiceps, Thespesius saskatchewanensis, Trachodon longiceps.
Classification: Chordata, Reptilia, Dinosauria,
Ornithischia, Ornithopoda, Iguanodontia, Hadrosauroidea, Hadrosauridae,
Saurolophinae.
Species: E. regalis (type), E.
annectens.
Diet: Herbivore.
Size: Adults from 9 to as much as 12 meters
long. Largest individuals potentially up to 13 meters long. The
species E. annectens used to be widely considered
as being smaller
than E. regalis, but fossil analysis starting
from the early
twenty-first century has now hinted that E. annectens
was probably of
a similar size to E. regalis.
Known locations: Canada, Alberta and
Saskatchewan, and the USA, including the state of Montana, South
Dakota and Wyoming.
Time period: Late Campanian to Maastrichtian of the
Cretaceous.
Fossil representation: Multiple individuals,
including almost complete skulls and postcranial skeletons, but
mummified soft tissues as well as soft tissue impressions on rocks
surrounding skeletons. Bone beds including the remains of many
thousands of individual Edmontosaurus are known.
Edmontosaurus is without a doubt one of if not the most intensively studied hadrosaurid dinosaur. Not only are there many Edmontosaurus specimens known, but those that have been recovered include some of the best preserved hadrosaurid material so far found.
Classification history
Edmontosaurus
has one of the longest and most complicated taxonomic histories of any
dinosaur, and it is a subject that would need an entire article in
its own right to explain properly. The first Edmontosaurus
fossils
were being found at least as far back as the late nineteenth century
during a period in American paleontological history known as the
Bone Wars. During this period two rival palaeontologists, Edward
Drinker Cope and Othniel Charles Marsh, were desperately trying to
outdo one another by naming as many new prehistoric animals
(including but only dinosaurs) that they could. This led to a
great many genera and species being created quickly without adequate
study, and the task of identifying them properly fell to later
palaeontologists.
The
first Edmontosaurus fossils to be named were by
Edward Drinker Cope in
1871, but Cope named the remains as belonging to a species of
Trachodon (today regarded as a dubious genus of
hadrosaur), T.
atavus. Later in 1892, Cope’s rival Othniel Charles
Marsh named
another new species, Claosaurus annectens.
During this period most
hadrosaur fossils were being named as other earlier established generas
such as Trachodon, Diclonius,
Claosaurus and Hadrosaurus.
Not all
palaeontologists were in agreement as to what was and was not valid
however, and published opinions varied greatly between them.
The
first establishment of the name Edmontosaurus came
in 1917 when
Canadian palaeontologist Lawrence Lambe who at the time was naming two
partially preserved individuals recovered from the Edmonton Formation
(today known as the Horseshoe Canyon Formation). Lambe established
the type species as Edmontosaurus regalis, and
noted how the two
specimens appeared to be similar to another species named Diclonius
mirabilis.
In
the 1920s further hadrosaur species such as Thespesius
saskatchewanensis and Thespesius edmontoni
were named. However,
by the 1930s palaeontologists were starting to take note that many
of the older species assigned to early genera did not quite fit in well
where they were. Ultimately in 1942, Richard Lull and Nelda
Wright created an entirely new genus called Anatosaurus
which was based
upon Claosaurus annectens, and also included
other species such as
Thespesius edmontoni, T.
saskatchewanensis and Trachodon
longiceps. This led to the Anatosaurus
genus being represented by the
species A. annectens (type), A.
copei, A. edmontoni,
A. longiceps, and A.
saskatchewanensis.
Although
essentially a wastebasket taxon for holding various species that just
didn’t fit, Anatosaurus quickly became well known
in popular science
concerning dinosaurs. The name Anatosaurus
literally translates as
‘duck lizard’ in reference to the duck-like bill that Anatosaurus
would have had in life, and due to its popularity, the hadrosaurs
subsequently became more commonly known as the ‘duck billed’
dinosaurs. During this time, almost every depiction of a
duck-billed dinosaur was of an individual of Anatosaurus.
Towards
the end of the twentieth century our understanding of hadrosaurs and
particularly both Anatosaurus and Edmontosaurus
was again changing.
The trigger event of this was the studies of Michael K. Brett-Surman
who was examining the Anatosaurus fossils as part
of his graduate
studies. Brett-Surman came to the conclusion that all of the
Anatosaurus species with the exception of A.
copei and A.
longiceps, actually belonged to the older Edmontosaurus
genus,
though as a distinct species to the type species E. regalis.
Although Brett-Surman’s papers were not capable of being officially
recognised by the ICZN, they did get the attention of other
palaeontologists who agreed with his reasoning. The type species of
Anatosaurus, A. annectens
(originally Claosaurus annectens),
was used to create Edmontosaurus annectens, with
all others except
A. copei and A. longiceps
additionally being assigned to the
species.
Towards
the end of the twentieth century our understanding of hadrosaurs and
particularly both Anatosaurus and Edmontosaurus
was again changing.
The trigger event of this was the studies of Michael K. Brett-Surman
who was examining the Anatosaurus fossils as part
of his graduate
studies. Brett-Surman came to the conclusion that all of the
Anatosaurus species with the exception of A.
copei and A.
longiceps, actually belonged to the older Edmontosaurus
genus,
though as a distinct species to the type species E. regalis.
Although Brett-Surman’s papers were not capable of being officially
recognised by the ICZN, they did get the attention of other
palaeontologists who agreed with his reasoning. The type species of
Anatosaurus, A. annectens
(originally Claosaurus annectens),
was used to create Edmontosaurus annectens, with
all others except
A. copei and A. longiceps
additionally being assigned to the
species.
At
the time of writing there are two established species of
Edmontosaurus, the type species E.
regalis and
the later named
E.annectens. Analysis of known fossils and their
locations shows that
both of these species lived in the same locations as one another but at
different times, with E. regalis being
recognised as a Campanian
only era species, and E. annectens being a
later Maastrichtian era
species. This indicates that E.annectens replaced
E. regalis as the
dominant Edmontosaurus species.
Edmontosaurus as a living dinosaur
Hadrosaurid
dinosaurs can be divided into two main groups, lambeosaurines (with
Lambeosurus
as the type genus) which had hollow bony crests on their
skulls, and saurolophines (with Saurolophus
as the type genus)
that had solid to no bony crests on their skulls. Edmontosaurus
belongs to the latter group as the bone skull itself has no ornamental
protuberances, though soft tissue display structures could have still
been present, as indeed now seems the case.
As
previously mentioned above, Edmontosaurus is
represented by some of
the most numerous and best preserved fossil remains known, which
probably makes Edmontosaurus one of the best
understood hadrosaurs.
With that said however we must not let ourselves get over confident as
it was only in 2013, almost a century after the genus was first
named, that Edmontosaurus was discovered to have
had a small soft
tissue crest on the top of the skull. This crest was fairly small,
situated on top of the skull above the eyes to the back of the
skull, and has only been preserved as an impression on the rock
surrounding the bones. It’s possible though that this feature might
had been found sooner considering that in the very early days of
palaeontology, collectors would only concentrate upon extracting
fossil bones without looking for surrounding features. Indeed, many
potential soft tissue impressions of such areas as skin and muscle
tissue have been known to have been destroyed by collectors who only
cared about bones.
The
skull of Edmontosaurus in general was long and
triangular, with the
largest known complete skull being up to one hundred and eighteen
centimetres long. Like other hadrosaurs, the front of the mouth
would have had an additional covering of a keratinous beak. Usually
keratin does not get preserved, but at least one specimen of
Edmontosaurus has been so well preserved that we can
measure that the
keratin of the beak would have extended for at least eight centimetres
in front of the mouth.
The
overall form of the skull would change with age, with adults that had
proportionately flatter and longer skulls than juveniles. This change
in age is partially what contributed to some Edmontosaurus
specimens
being named as other species and genera, but when palaeontologists
realised the age changes, the names were re-classified as synonyms to
Edmontosaurus.
Many
Edmontosaurus skulls are so well preserved that it
has been possible
for some researchers to make casts of the brain cavity. Relative to
body size, the brain of Edmontosaurus was small
in proportion, and
elongate in form. Edmontosaurus are not expected
to have been
exceptionally intelligent since most of the brain was orientated
towards primal functions such as sight and smell, but they were
probably intelligent enough to survive on the landscape of late
Cretaceous North America.
The
teeth in the skull were arranged in the form of dental batteries in the
posterior region of the mouth. The method of feeding for
Edmontosaurus (and other hadrosaurs) is thought
to have been along
the lines of plants being cropped by the keratinous beak, and then
ground by the teeth at the back. As in all dinosaurs, when these
teeth became worn and lost, new teeth would erupt to replace them.
A 2009 study by Williams et al studied the micro wear patterns on
the teeth and concluded that Edmontosaurus were
probably grazers as
opposed to selective browsers.
As
far as the rest of the body is concerned, Edmontosaurus
were quite
generic in their appearance. The centre of balance in the body would
have been just in front of the hips, with the large rear legs serving
the focus of the weight bearing function. Because of the developed
rear legs, it certainly would have been possible for Edmontosaurus
to
adopt a bipedal posture, however they mostly seem to have been
bipedal. The main evidence for this comes from the simple observation
of the fore limbs which although are not as well developed as the rear
limbs, are still formed for a weight bearing function. Fossil
track ways of hadrosaurs also show that these kinds of dinosaurs walked
about on all fours, and not just their rear legs.
Much
analysis has been done upon how Edmontosaurus
moved, with the 2009
study by Sellers et al being one of the better known. Hadrosaurs
like Edmontosaurus were long thought to by earlier
palaeontologists to
have tried to escape from predators by running on their hind legs,
but computer modelling from that study revealed that Edmontosaurus
would have likely been faster if moving on all fours in the form of a
gallop rather than running on just the rear legs.
As
in other hadrosaurs, the tail vertebrae in the tail of Edmontosaurus
were reinforced by a lattice network of tendons that became ossified
with age. This means that the tail would have been quite rigid and
not open to much movement save for at the base. Such a tail is
speculated to have primarily been as a counterbalance, particularly
when changing between quadrupedal and bipedal postures. Another
function of the tail may have been as a display feature, perhaps
being differently coloured than the rest of the body, though we
cannot know this for certain at this time.
Preserved
skin impressions have revealed that Edmontosaurus
had non overlapping
scales, most of which were small at being between one and three
millimetres across. Larger polygonal scales ranging from below five
to up to ten millimetres across are known to have been on areas such as
the fore arms and shoulder. The smaller scales were more typical of
the flanks while scales got slightly larger further up and down the
body. There also seems to have been a frilly ridge of soft tissue
that ran down the centreline of the neck and back. Preserved segments
of this frill were about five centimetres long and about eight
centimetres high.
It
used to be that how big an Edmontosaurus was
depending upon which
species you were talking about. The type species E.
regalis has
been considered to have been the larger with individuals reaching nine
meters at adulthood with the oldest individuals reaching twelve and
potentially even thirteen meters in length. The second species E.
annectens has often been credited as being much smaller at
about eight
to nine meters long, however new studies of existing Edmontosaurus
material has now revealed that E. annectens may
have actually reached
sizes up to twelve meters long as well. This would mean that E.
anenctens was actually comparable to E.
regalis in terms of size
after all.
In
terms of behaviour Edmontosaurus have been
perceived to be herding
animals based largely upon the evidence of bone beds of Edmontosaurus
individuals collected together, ranging from a few, to many
thousands of individuals. Herding would make sense for a plant eating
animal to survive, especially an animal that lived on a landscape
which included predators as large as itself, particularly
tyrannosaurs
such as Albertosaurus,
Daspletosaurus
and of course
Tyrannosaurus
itself.
There
is also strong evidence to suggest that Edmontosaurus
were frequently
targeted and eaten by the predators of the North American late
Cretaceous. Tyrannosaur tooth marks from Albertosaurus
and
Daspletosaurus are known upon Edmontosaurus
fossils, though these can
be perceived as signs of scavenging. Teeth marks from smaller
theropod dinosaurs are also known upon the jaws of Edmontosaurus,
suggesting that the neck may have been the preferred vulnerable spot
targeted by such predators.
The
most exciting discovery showing predator prey interaction though can be
seen upon the damaged caudal vertebrae of a mounted Edmontosaurus
specimen that is on display at the Denver Museum of Nature and
Science. Some of the vertebrae on this specimen have been bitten into
by a large predatory theropod with a bite pattern similar to what you
would expect from a tyrannosaur. In addition to this the only large
theropod that is known to have existed in the same formation as this
individual Edmontosaurus and also to have been
big enough to reach
high enough to inflict such a bite is Tyrannosaurus.
What
is really astonishing about this individual Edmontosaurus
is that after
the bite was inflicted, the bone started to heal, indicating that
the attack was not immediately successful in killing it, and that the
individual survived for long enough for the bone to partially heal.
This proves that this Edmontosaurus was alive at
the time of the
attack and therefore it cannot be a case of scavenging. Further study
of the specimen by renowned palaeontologist Kenneth Carpenter has also
revealed that the left hip also has a partially healed fracture from an
injury that likely happened before the attack that resulted in the tail
injury. This may mean that the when this individual Edmontosaurus
was
attacked, it may have had a slight limp which resulted in it being
targeted by a tyrannosaur.
Edmontosaurus
is known to have had one of the broadest geographical distributions of
all the known hadrosaurs, something that a 2008 study by Bell and
Snively considered to have been the result of migratory behaviour.
Migratory behaviour may have also been possible considering that if
Edmontosaurus did live in groups, they may have
had to continually
move to avoid exhausting available food resources. In addition the
occurrence of vast bone beds may have been caused by many Edmontosaurus
drowning together as they tried to cross rivers swollen with flood
water, as has been proposed for other types of dinosaur such as
ceratopsians.
However
there are doubts as to whether Edmontosaurus were
truly migratory,
potentially moving many hundreds if not thousands of miles with the
seasonal growth of plants, or if they instead did not roam as far.
One study by Chisamy et al in 2012, revealed that hadrosaur
remains recovered from what were more polar regions, were from
populations that lived there all the time rather than from a migratory
population. Perhaps a more general scenario would be that as with
most animals, Edmontosaurus stayed where the food
was, only moving
on to the next horizon for food when they had to.
Further reading
- Supplement to the synopsis of the extinct Batrachia and Reptilia of
North America - American Philosophical Society, Proceedings 12 (86):
41–52. - Edward Drinker Cope - 1871.
- Report on the vertebrate paleontology of Colorado - U.S. Geological
and Geographical Survey of the Territories Annual Report 2: 429–454. -
Edward Drinker Cope - 1874.
- Report on the stratigraphy and Pliocene vertebrate paleontology of
northern Colorado - U.S. Geological and Geographical Survey of the
Territories Annual Report 1: 9–28. - Edward Drinker Cope - 1874.
- On the characters of the skull in the Hadrosauridae - Proceedings of
the Philadelphia Academy of Natural Sciences 35: 97–107. - Edward
Drinker Cope - 1883.
- The genus and species of the Trachodontidae (Hadrosauridae,
Claosauridae) Marsh - Annals of the Carnegie Museum 1 (14): 377–386.
John B. Hatcher - 1902.
- The dinosaur Trachodon annectens - Smithsonian
Miscellaneous
Collections 45: 317–320 - Frederic A. Lucas - 1904.
- The epidermis of an iguanodont dinosaur - Science 29 (750): 793–795.
- Henry Fairfield Osborn - 1909.
- Integument of the iguanodont dinosaur Trachodon -
Memoirs of the
American Museum of Natural History 1: 33–54 - Henry Fairfield Osborn -
1912.
- The manus in a specimen of Trachodon from the
Edmonton Formation of
Alberta - The Ottawa Naturalist 27: 21–25. - Lawrence M. Lambe - 1913.
- On the fore-limb of a carnivorous dinosaur from the Belly River
Formation of Alberta, and a new genus of Ceratopsia from the same
horizon, with remarks on the integument of some Cretaceous herbivorous
dinosaurs - The Ottawa Naturalist 27: 129–135. - Lawrence M. Lambe -
1914.
- On the genus Trachodon - Science 41 (1061):
658–660 - Charles W.
Gilmore - 1915.
- A new genus and species of crestless hadrosaur from the Edmonton
Formation of Alberta. - The Ottawa Naturalist 31 (7): 65–73. - Lawrence
M. Lambe - 1917.
- The hadrosaur Edmontosaurus from the Upper
Cretaceous of Alberta.
Memoir 120. - Department of Mines, Geological Survey of Canada. pp.
1–79. - Lawrence M. Lambe - 1920.
- A new species of hadrosaurian dinosaur from the Edmonton Formation
(Cretaceous) of Alberta. Bulletin 38. - Department of Mines, Geological
Survey of Canada. pp. 13–26. - Charles W. Gilmore - 1924.
- Hadrosaurian Dinosaurs of North America. Geological Society of
America Special Paper 40. - Geological Society of America. - Richard
Swann Lull & Nelda E. Wright - 1942.
- A reconsideration of the paleoecology of the hadrosaurian dinosaurs -
American Journal of Science 262 (8): 975–997. - John H. Ostrom - 1964.
- The posture of hadrosaurian dinosaurs - Journal of Paleontology 44
(3): 464–473. - Peter M. Galton - 1970.
- Hadrosaurian dinosaur bills — morphology and function - Contributions
in Science (Los Angeles County Museum of Natural History) 193: 1–14. -
William J. Morris - 1970.
- The evolution of cranial display structures in hadrosaurian dinosaurs
- Paleobiology 1 (1): 21–43. - James A. Hopson - 1975.
- A "segmented" epidermal frill in a species of hadrosaurian dinosaur -
Journal of Paleontology 58 (1): 270–271. - John R. Horner - 1984.
- Evidence of predatory behavior by theropod dinosaurs - Gaia 15:
135–144. - Kenneth Carpenter - 1998/2000.
- Taphonomic aspects of theropod tooth-marked bones from an
Edmontosaurus bone bed (Lower Maastrichtian),
Alberta, Canada - Journal
of Vertebrate Paleontology 19 - Aase Roland Jacobson, Michael J. Ryan -
2000.
- Dinosaur forebrains - Journal of Vertebrate Paleontology 21 (3,
Suppl.): 64A - Harry J. Jerison, John R.Horner& Celeste C.
Horner - 2001.
- New skin structures from a juvenile Edmontosaurus
from the Late
Cretaceous of North Dakota - Abstracts with Programs — Geological
Society of America 35 (2): 13. - Tyler R. Lyson, Douglas H. Hanks
& Emily S. Tremain - 2003.
- An allometric study comparing metatarsal IIs in Edmontosaurus
from a
low-diversity hadrosaur bone bed in Corson Co., SD - Journal of
Vertebrate Paleontology 23 (3, suppl.): 56A–57A. - Rebecca Gould, Robb
Larson & Ron Nellermoe - 2003.
- Microscale δ18O and δ13C isotopic analysis of an ontogenetic series
of the hadrosaurid dinosaur Edmontosaurus:
implications for physiology
and ecology - Palaeogeography, Palaeoclimatology, and Palaeoecology 206
(2004): 257–287 - Kathryn J. Stanton Thomas & Sandra J. Carlson
- 2004.
- Preliminary depositional model for an Upper Cretaceous Edmontosaurus
bonebed - Journal of Vertebrate Paleontology 26 (3, suppl.): 49A.,
Arthur Chadwick, Lee Spencer & Larry Turner 2006.
- How to make a fossil: part 2 – Dinosaur mummies and other soft
tissue. - The Journal of Paleontological Sciences. - Kenneth Carpenter
- 2007.
- A three-dimensional animation model of Edmontosaurus
(Hadrosauridae)
for testing chewing hypotheses - Palaeontologia Electronica 11 (2) -
Natalia Rybczynski, Alex Tirabasso, Paul Bloskie, Robin Cuthbertson,
Casey Holliday - 2008.
- Polar dinosaurs on parade: a review of dinosaur migration -
Alcheringa 32 (3): 271–284. - Phil R. Bell & E. Snively - 2008.
- Cranial kinesis in dinosaurs: intracranial joints, protractor
muscles, and their significance for cranial evolution and function in
diapsids - Journal of Vertebrate Paleontology 28 (4): 1073–1088. -
Casey M. Holliday & Lawrence M. Witmer - 2008.
- Mineralized soft-tissue structure and chemistry in a mummified
hadrosaur from the Hell Creek Formation, North Dakota (USA) -
Proceedings of the Royal Society B 276 (1672): 3429–3437 - Phillip L.
Manning, Peter M. Morris, Adam McMahon, Emrys Jones, Andy Gize, Joe H.
S.Macquaker, G. Wolff, Anu Thompson, Jim Marshall, Kevin G. Taylor,
Tyler Lyson, Simon Gaskell, Onrapak Reamtong, William I. Sellers, Bart
E. van Dongen, Mike Buckley, Roy A. Wogelius - 2009.
- Cranial variation in Edmontosaurus
(Hadrosauridae) from the Late
Cretaceous of North America - North American Paleontological Convention
(NAPC 2009): Abstracts, p. 95a. - N. E. Campione - 2009.
- Virtual palaeontology: gait reconstruction of extinct vertebrates
using high performance computing -Palaeontologia Electronica 12 (3). -
W. I. Sellers, P. L. Manning, T. Lyson, K. Stevens & L.
Margetts - 2009.
- Quantitative analysis of dental microwear in hadrosaurid dinosaurs,
and the implications for hypotheses of jaw mechanics and feeding -
Proceedings of the National Academy of Sciences 106 (27): 11194–11199.
- Vincent S. Williams, Paul M. Barrett & Mark A. Purnell - 2009.
- Cranial Growth and Variation in Edmontosaurs (Dinosauria:
Hadrosauridae): Implications for Latest Cretaceous Megaherbivore
Diversity in North America. - PLoS ONE, 6(9): e25186 - N. E. Campione
& D. C. Evans - 2011.
- Complex dental structure and wear biomechanics in hadrosaurid
dinosaurs - Science 338 (6103): 98–101 - Gregory M. Erickson, Brandon
A. Krick, Matthew Hamilton, Gerald R. Bourne, Mark A. Norell, Erica
Lilleodden & W. Gregory Sawyer - 2012.
- Kinetic limitations of intracranial joints in Brachylophosaurus
canadensis and Edmontosaurus regalis
(Dinosauria: Hadrosauridae), and
their implications for the chewing mechanics of hadrosaurids - The
Anatomical Record 295 (6): 968–979. - Robin S. Cuthbertson, Alex
Tirabasso, Natalia Rybczynski & Robert B. Holmes - 2012.
- Hadrosaurs were perennial polar residents - The Anatomical Record:
Advances in Integrative Anatomy and Evolutionary Biology. - A.
Chinsamy, D. B. Thomas, A. R. Tumarkin-Deratzian & A. R.
Fiorillo - 2012.
- A Mummified Duck-Billed Dinosaur with a Soft-Tissue Cock's Comb -
Current Biology. - Phil R. Bell, Federico Fanti, Philip J. Currie
& Victoria M. Arbour - 2013.
- Supplementary cranial description of the types of Edmontosaurus
regalis (Ornithischia: Hadrosauridae), with comments on the
phylogenetics and biogeography of Hadrosaurinae. - PLOS ONE. 12 (4). -
H. Xing, J. C. Mallion & M. L. Currie - 2017.
Skeletal Trauma with Implications for Intratail Mobility in
Edmontosaurus annectens from a Monodominant Bonebed, Lance Formation
(Maastrichtian), Wyoming USA. - PALAIOS. 35 (4): 201–214 - Bethania C.
T. Siviero, Elizabeth Rega, William K. Hayes, Allen M. Cooper, Leonard
R. Brand & Art V. Chadwick - 2020.
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