Name:
Apatosaurus
(Deceptive lizard).
Phonetic: A-pat-oh-sore-us.
Named By: Othniel Charles Marsh - 1877.
Classification: Chordata, Reptilia, Dinosauria,
Saurischia, Sauropodomorpha, Sauropoda, Diplodocidae,
Apatosaurinae.
Species: A. ajax (type),
A. louisae.
Diet: Herbivore.
Size: Individuals roughly between 20-23 meters
long.
Known locations: USA, Colorado, Oklahoma, Utah
and Wyoming.
Time period: Kimmeridgian to early Tithonian of the
Jurassic.
Fossil representation: Many individuals, usually
of partial remains.
Apatosaurus or
Brontosaurus?
Even
though Apatosaurus is one of the sauropod
dinosaurs best
known to palaeontology
yet most people confused it with Brontosaurus.
The reason
for this goes all the way back to 1879, roughly two years after the
naming of Apatosaurus ajax when a new sauropod
specimen was given the
name Brontosaurus excelsus by Othniel Charles
Marsh, the same person
who named Apatosaurus earlier in 1877. This
specimen was in a
better state of preservation than the earlier Apatosaurus
and also
clearly had several notable differences which led Marsh to the
conclusion that it was a similar but altogether different genus.
No
one put much more thought into further classifying the two genera
until 1903 when Elmer S. Riggs studied the fossils. One of the
key areas that Riggs is remembered for is his study of sauropods and
after reviewing the fossils he found that while Brontosaurus
excelsus
was different to Apatosaurus ajax, the
differences were not great
enough to warrant the creation of a new genus. The majority of other
palaeontologists in the twentieth century agreed with this conclusion
and for that time
Brontosaurus has been a junior synonym to Apatosaurus.
This follows
standard naming procedure where for the exception of very rare and
special cases (see Tyrannosaurus)
the name of the first genus
created must be used to refer to all subsequent discoveries. In this
case Brontosaurus excelsus was renamed Apatosaurus
excelsus.
Now
normally the above would be a cut and dry procedure that has been done
countless times in the history of zoological nomenclature for other
genera, but not so in this case. The naming confusion for the
general public begins in 1905 with the mounting of an Apatosaurus
skeleton for public display. Here it was not because the people
reconstructing the skeleton had to use parts of other sauropods to
complete the skeleton, including the wrong skull that was the
problem, but the fact that they named it Brontosaurus
despite the new
classification by Riggs two years earlier.
The
new reconstruction nonetheless gave museum patrons an idea to the sheer
size that the dinosaurs could attain, and news of the display spread
around the world, albeit under the name of Brontosaurus.
As such
Brontosaurus began to appear in popular culture and
even became one to
the first dinosaur movie stars. This included the 1914 animated
short called Gertie the Dinosaur and the
1925 silent film
The Lost World where a stop motion Brontosaurus
features in a
climatic sequence as it goes on a rampage in London. From here the
name Brontosaurus became common usage, something
eased by the fact
that it translates as ‘Thunder lizard’. The true name of
Apatosaurus however, ‘deceptive lizard’ might
now be more correct
than ever before.
In
2015, a detailed study by Tschopp, Mateus and Benson concerning
fossils of Apatosaurus and Diplodocus
came to a clear conclusion;
that fossils of Apatosaurus excelsus were in fact
different enough
from the Apatosaurus type species to keep them as a
new genus. This
meant that Brontosaurus was a valid genus after
all, and so all
fossils described as Apatosaurus excelsus have now
been re-labelled
as Brontosaurus excelsus.
Reconstruction of Apatosaurus
Many
specimens of Apatosaurus are known but they usually
share a problem
common to many other sauropod genera in that usually they are of just
partial postcranial remains. Like many others Apatosaurus
went a long
time without a complete skull confirmed to be its own. When the
infamous 1905 reconstruction was made the skull mounted upon this
skeleton was actually a composite of different Camarasaurus
skull parts
and teeth, something that was not only incorrect but resulted in
every depiction of Apatosaurus for most of the
following century being
given a ‘box-like’ skull and head. When an Apatosaurus
skull was
eventually discovered in 1970, it was found to have a long sloping
snout, nothing like Camarasaurus but very similar
to Diplodocus.
In
fact the skull is not the only similarity between Apatosaurus
and
Diplodocus, the overall shape of the skeleton and
proportions are
also very similar. The key areas of difference though are
Apatosaurus’s more robust cervical vertebrae that
are shorter than
those of Diplodocus, as well as legs that are
both longer and
thicker. The latter indicates support for a sauropod that was
similar in proportion but much more heavily built than Diplodocus.
Still, because of the overall similarity, Apatosaurus
now sits
within a sub-group to the larger Diplodocidae along with other
similar sauropods such as
Barosaurus
and
Dinheirosaurus.
Apatosaurus as
a living dinosaur
Because
of its popularity Apatosaurus is one of the most
often recreated
dinosaurs in art and exhibits. However most of the early
reconstructions of Apatosaurus wallowing in lakes
and swamps, arcing
its neck to reach up into trees or limply dragging its massive tail
behind its body are now considered to be quite inaccurate.
Analysis
of the areas where Apatosaurus fossils are known
from has found them to
have been deposited in areas that were dry and not waterlogged like
swamps would have been. Further study incorporating other fossil
specimens of different animals and plants has revealed these areas to
have been areas of fairly open ground that supported low growing
vegetation intermixed with areas of sparse woodland.
Another
factor to consider that counts against Apatosaurus
spending most of its
time in the water is that of water pressure. As you go deeper down in
a fluid body, the weight of the fluid on top of whatever level you
are on pushes down on the fluid where you are resulting in a higher
pressure. If Apatosaurus submerged its body in
water then not only
would it have to deal with this pressure but it would be pressing upon
the large surface area that would be Apatosaurus’s
body. This would
make a number of bodily functions including respiration more difficult
because of the force of the water pressure compacting the lungs,
making inside a lake possibly one of the most uncomfortable places for
Apatosaurus to choose to be.
Dedicated
research to the flexibility of Apatosaurus’s neck
has revealed that it
was quite inflexible, especially to the extent of strongly curving
almost serpentine poses of early reconstructions. Instead the neck
seems to have been held out straight at a horizontal to slightly
upwards angle. This neck would have allowed Apatosaurus
to sweep
its head in an arc in front of the body as it cropped low to
medium height vegetation without much need to constantly expend energy
on moving its body. However Apatosaurus seems to
have been restricted
to this level of vegetation as the cervical (neck) vertebrae would
not have allowed Apatosaurus to reach high up into
the trees with its
neck. This may actually be a form of niche partitioning on the part
of Apatosaurus as other sauropods such as Brachiosaurus
had a body
posture that was better suited to allow them to feed from the tree
canopy. Niche partitioning behaviour like this would allow several
types of large herbivore to live in the same ecosystem without directly
competing with one another.
To
counterbalance the forward facing neck the tail would have been held
high off the ground, and not dragged along it like most antiquated
reconstructions. The tail may have served more of a purpose than just
counterbalancing the neck as the vertebrae narrow towards the end where
it thins to a whip like end. Why the tail did this is uncertain but
it does seem to be a signature feature of the diplodocid sauropods.
Apatosaurus’s
respiration has been another area of study as how such a large creature
can get enough oxygen from breathing through such a long neck raises
a lot of questions. Slowly however some possible answers have come to
light, the most plausible being that Apatosaurus
had a respiratory
system similar to that found in birds. This would involve a process
of air sacs that ran down the length of the neck to the lungs that
supplied a constant amount of new unbreathed air so that Apatosaurus
always had a supply of oxygen coming in. The exact system may not
however have been identical to that seen in birds but would have likely
been present in a more primitive form. Fossil evidence that supports
the theory for such a respiratory system has been found for other
sauropods as well as for other different kinds of dinosaur such as the
theropod Aerosteon.
The final bit of support for this theory comes
from the birds themselves. Since fossil evidence now proves that
birds evolved from dinosaurs, their respiratory system would have
likely been descended from them too. How far back this respiratory
blue print goes remains uncertain, but if it goes as far back as the
common ancestors to dinosaurs, then it makes it very likely that
Apatosaurus also had one.
A
more efficient form of respiration also imparts the possibility of a
warm blooded metabolism. Such a metabolism would have been much more
efficient for moving an animal the size of Apatosaurus,
although
the exact principal behind this warm metabolism may not be as simple as
being like that of mammals. Animals that have a large body mass but a
relatively small surface area are known to have to live with the
effects of what is termed gigantothermy. In the simplest terms this
means that the body surrounding the internal organs is so thick that
the outer layers of tissue end up insulating the internal layers
against heat loss so that the base temperature of the animal is higher
than you might expect it to be. This results in the body metabolism
operating at a level similar to that traditionally associated with warm
blooded creatures like mammals.
Another
hall mark of a warm blooded metabolism comes from studies of the bones
of juveniles and how fast they grew. While no one knows for certain
exactly how long Apatosaurus lived for, juveniles
are thought to have
reached almost full size in just ten years. Warm blooded creatures
are known to attain adult size in a very short space of time because
the metabolism operates at a faster rate than in cold blooded creatures
such as crocodiles which can continue growing for decades before
reaching maximum size.
The
fast growth of juveniles was probably an evolutional response to the
large predators that roamed North America at the end of the Jurassic
such as Allosaurus
and Saurophaganax.
Although the idea that sauropods relied upon
their immense size alone to protect them from attack does not have as
much support as it used to (titanosaurid sauropods like Saltasaurus
had bony armour on their backs) a fully grown Apatosaurus
would have
been a very difficult prey animal for an Allosaurus
when you consider
that there would have been other smaller and easier dinosaurs for it to
hunt.
Further reading
- Structure and Relationships of Opisthocoelian Dinosaurs. Part I,
Apatosaurus Marsh. - Publications of the Field
Columbian Museum.
Geological Series (2): 165–196. - Elmer Riggs - 1903.
- Description of the palate and lower jaw of the sauropod dinosaur
Diplodocus (Reptilia: Saurischia) with remarks on
the nature of the
skull of Apatosaurus. - Journal of Paleontology 49
(1): 187–199. - J.
S. McIntosh & D. S. Berman - 1975.
- Remarks on the North American sauropod Apatosaurus
Marsh. - Sixth
Symposium on Mesozoic Terrestrial Ecosystems and Biota, Short Papers,
A. Sun and Y. Wang (eds.), China Ocean Press, Beijing 119–123 - J. S.
McIntosh - 1995.
- Ontogenetic histology of Apatosaurus (Dinosauria:
Sauropoda): new
insights on growth rates and longevity. - Journal of Vertebrate
Paleontology 19 (4): 654–665. - Kristina A. Curry - 1999.
- Neck posture and feeding habits of two Jurassic sauropod dinosaurs. -
Science 284 (5415): 798–800. - K. A. Stevens & J. M. Parrish -
1999.
- A new method to calculate allometric length-mass relationships of
dinosaurs. - Journal of Vertebrate Paleontology 21: 51–52. - Frank
Seebacher - 2001.
- Dinosaurian growth patterns and rapid avian growth rates. - Nature
412 (6845): 429–33. - Gregory, M. Erickson, Kristina Curry Rogers
& Scott A. Yerby - 2001.
- A new specimen of Apatosaurus ajax (Sauropoda:
Diplodocidae) from the
Morrison Formation (Upper Jurassic) of Wyoming, USA. - National Science
Museum monographs 26: i-118 ISSN:13429574. - Paul Upchurch, Yukimitsu
Tomida, Paul M. Barrett - 2004.
- Bully for Apatosaurus. - Endeavour 30 (4):
126–130. - P. Brinkman -
2006.
- Burly Gaits: Centers of mass, stability, and the trackways of
sauropod dinosaurs. - Journal of Vertebrae Paleontology 26 (4):
907–921. - Donald M. Henderson - 2006.
- Inferences of diplodocoid (Sauropoda: Dinosauria) feeding behavior
from snout shape and microwear snalyses. - In Farke, A. A. PLoS ONE 6
(4): e18304. - J. A. Whitlock - 2011.
- Aging, Maturation and Growth of Sauropodomorph Dinosaurs as Deduced
from Growth Curves Using Long Bone Histological Data: An Assessment of
Methodological Constraints and Solutions. - PLoS ONE 8(6): e67012. - E.
M. Griebler, N. Klein & P. M. Sander - 2013.
- A specimen-level phylogenetic analysis and taxonomic revision of -
Diplodocidae (Dinosauria, Sauropoda). - PeerJ 3:e857. - E. Tschopp,
O. Mateus & R. B. J. Benson -2015.
- First report of Apatosaurus (Diplodocidae: Apatosaurinae) from the
Cleveland-Lloyd Quarry in the Upper Jurassic Morrison Formation of
Utah: Abundance, distribution, paleoecology, and taphonomy of an
endemic North American sauropod clade. - Palaeoworld. 25 (3): 431–443.
- John R.Foster & Joseph E.Peterson - 2016.