Carcharodontosauridae
As a group the carcharodontosaurids don’t seem to receive a lot of attention in popular science, which is surprising since when they are studied upon an individual genus by genus basis, the carcharodontosaurids are actually among the most popular theropod dinosaurs in the world. For example, there is the North American Acrocanthosaurus with a ridge like hump on its back, the huge Giganotosaurus and Carcharodontosaurus, the possibly pack hunting Mapusaurus as well as the bizarre Concavenator. These predators are also all quite specialised despite initial appearances of being more ‘classic’ kinds of theropod dinosaurs.
The ‘biggest’ theropods?
Everybody
has heard of Tyrannosaurus,
the theropod that for a long time was
thought to be the biggest meat eating dinosaur. Today a lot of people
are aware that in terms of length, Spinosaurus
shattered the notion
of Tyrannosaurus being at least the longest
theropod dinosaur.
Spinosaurus is so far known from only partial
remains, which mean
the exact length of weight of this dinosaur continues to be a matter of
debate, and will likely stay so unless an almost complete specimen is
found. The largest mostly complete Tyrannosaurus
was a specimen
nicknamed ‘Sue’, and was about 12.8 meters long. Isolated
and partial fossils which seem to come from individuals of
Tyrannosaurus are known, and scaling complete
specimens to these
yields estimates of around the 13 metre mark for Tyrannosaurus.
Due to the incomplete nature of such remains however, these are not
‘official’ figures, but serve as a guide for an upper potential.
The
first indications that there were rivals to the mantle of largest
theropod dinosaur came with the study of Acrocanthosaurus,
another
North American genus that is quite comfortably estimated to have been
around the 11.5 meter mark for length. Although a touch on the
short side, this does not take away the significance of
Acrocanthosaurus being a theropod almost as large as
Tyrannosaurus,
yet roaming around and hunting dinosaurs on what would be the United
States roughly around fifty million years before Tyrannosaurus.
The
next contender was Carcharodontosaurus from North
Africa. Often
nicknamed the ‘African T-rex’ (a very misleading name since it is
not a tyrannosaur) Carcharodontosaurus is roughly
as big as
Tyrannosaurus since it is estimated as ranging
between 12 and 13
meters long. Even if Carcharodontosaurus could
not best
Tyrannosaurus in terms of size, it is at least a
respectable equal to
it. Hailing from South America, the third contender came to light
in the early 1990s, and today it hardly needs any introduction;
Giganotosaurus. Now Giganotosaurus
is known only from incomplete
remains but those that are known are usually seen to indicate a size of
somewhere in between 12 and 13 meters long. Other partial
remains of the genus have led to past speculation that Giganotosaurus
may have been up to fifteen meters long, though a 2001 study
(Blanco and Mazzetta) speculates that an upper size of 14 meters
is more realistic since physically running beyond this would be
problematic.
Mass
studies for dinosaurs can vary greatly depending upon the source, but
Giganotosaurus often comes out as being slightly
heavier than
Tyrannosaurus, and this is also significant
because usually the size
for a given animal is often established by its weight rather than
length. This is why Giganotosaurus and even Tyrannosaurus
are
sometimes considered to be bigger on the grounds of weight than
Spinosaurus, because the spinosaurids
seem to have
been very gracile
and lightweight for theropods.
How
big carcharodontosaurids are considered to be today and in the future
is more down to what perspective you are studying them from, be it
length, height, weight, etc. and the lack of fossils for other
kinds of large theropods such as Spinosaurus mean that a future fossil
discovery could greatly upset the notions of what some people perceive
to be the biggest. What can be said for carcharodontosaurids however
is that many of the genera currently assigned to the
Carcharodontosauridae are easily amongst the largest predatory
dinosaurs known, and by extension among the largest meat eating
animals to ever walk on land.
Common features
Although
some carcharodontosaurids genera are noted for their large size, not
all of the carcharodontosaurids were giants. They do however seem to
have had skulls that were proportionately large relative to their body
size. The skulls of the larger carcharodontosaurid genera are amongst
the largest dinosaur skulls known with the skull of Acrocanthosaurus
being about 1.3 meters long, the skull of Carcharodontosaurus
being about 1.6 meters long, and the larger estimate of the skull
of Giganotosaurus being 1.95 meters long.
These large sizes were
possible because carcharodontosaurid had very large fenestra
(openings), which meant that the skulls were not as solid, and
therefore quite lightweight given the size. The antorbital fenestra
(the opening between the eye socket and nasal opening) is often
particularly large when compared to the skulls of other theropods.
When viewed in profile the anterior (front) end of the lower jaws
of carcharodontosaurids also tend to appear squared off.
The
carcharodontosaurids are defined by the type genus
Carcharodontosaurus, and the name of this genus
means
‘sharp-toothed-lizard’ (alternatively ‘jagged-toothed-lizard’).
Carcharodon is also the name of a genus of sharks
which also have
jagged teeth and include Carcharodon carcharias,
better known as the
great white shark. Carcharodontosaurids have broad teeth that were
laterally compressed (flattened from the sides) so that when viewed
in profile the teeth seem thick, but when viewed from the front the
teeth look thin. These teeth also have large serrations that enabled
them to cut through skin and muscle. These slicing teeth that
operated in the same way as a serrated knife could easily cut through
the flesh of any other dinosaur that lacked armoured skin.
Like
most theropods the arms of carcharodontosaurids were much smaller than
the legs, but they were still larger and more robust than those of
later and more specialised theropods like tyrannosaurs and abelisaurs.
Carcharodontosaurids also retained three fingered hands like most
other theropods during the late Jurassic and early Cretaceous.
Acrocanthosaurus
&
Concavenator
These
two genera are ‘special cases’ because they both have vertebrae
where the neural spines are elongated to support growths on their
backs. The elongation of the neural spines in Acrocanthosaurus
runs
all the way down the back, and given the robust nature of the
spines, it seems more likely that they supported a fleshy hump rather
than a sail. Likewise the spines of Concavenator
also seem to have
supported a fleshy hump, but in Concavenator the
hump seems to have
been restricted to just the hip region.
Why
Acrocanthosaurus and Concavenator
had these growths is still unknown,
but theories range from thermoregulation, to display, to fat
storage for survival in lean times to even a combination of these.
These theories are discussed in more depth on the pages devoted to the
genera, just click on the name links or search through the species
link at the top of the page. Although it is bizarre that these two
should have had back growths whereas their relatives did not, it’s
quite possible that future discoveries may reveal new
carcharodontosaurid genera that also have back growths.
Geographic and temporal
distribution
As
a group carcharodontosaurids shared a similar distribution to another
group of theropods called the spinosaurids. Both these groups seem to
have been most numerous during the early Cretaceous, but they are
also known from deposits laid down during the early stages of the late
Cretaceous. The description of Veterupristisaurus
also indicates that
the carcharodontosaurids as a group had their origins at least as far
back as the late Jurassic. Again this is similar to the spinosaurids
which also seem to have had their origins in the Jurassic since the
naming of Ostafrikasaurus
in 2012. Partial remains from the
Presidente Prudente Formation of Brazil however may indicate that at
least in South America the carcharodontosaurids may have survived until
the very end of the Cretaceous (Maastrichtian) period rather than
going extinct during the Cenomanian/Turonian periods (Fernandes de
Azevedo et al, 2013). Again spinosaurids that were also once
thought to have gone extinct during this time are now considered to
have possibly survived at least until the Santonian age thanks to the
discovery of spinosaurid teeth in China from a deposit dating to this
time.
Most
fossils of carcharodontosaurids are known from South America and
Africa, but also as far as Europe and Asia. The
carcharodontosaurids are also known to have gone as far as North
America thanks to the discovery of fossils belonging to
Acrocanthosaurus. Further discoveries of
carcharodontosaurids are
likely to be made in other areas of the world, especially those that
link up current known fossil sites and have Cretaceous era rocks,
particularly those dating to the early Cretaceous.
One
continent where carcharodontosaurids are not yet known is Australia,
yet even here it is not inconceivable that carcharodontosaurid fossils
may one day be recovered. Many of the fossil bearing rock formations
of Australia are age appropriate for carcharodontosaurids, and other
Cretaceous era theropods such as spinosaurids and neovenatorids
(specifically those of the Megaraptora sub group) are known to be
present here.
What dinosaurs did
carcharodontosaurids eat, and how did they hunt?
The
large predators often eat large prey, and while there are many
documented exceptions to this rule in the natural world, the
carcharodontosaurids were not. Two types of dinosaurs that are both
fairly large and present with concentrations of carcharodontosaurid
fossils are sauropods and ornithopods. Acrocanthosaurus
had access to
Sauroposeidon
and Tenontosaurus,
Carcharodontosaurus
had access to
Nigersaurus
and Ouranosaurus
while Giganotosaurus
had access to
Andesaurus and iguanodonts, and these are just
some of the potential
dinosaur genera that may have ended up as being food for
carcharodontosaurids.
Carcharodontosaurid
genera are seen as being quite physical predators, with some such as
Acrocanthosaurus being noted as possessing primitive
yet powerful
forearms that could be used for grabbing and holding onto prey. Again
with Acrocanthosaurus, the neck seems to be
particularly strong and
developed for providing extra support when an individual gripped onto a
large animal with its mouth. Fossil track ways of a sauropod with
what could be footprints from an Acrocanthosaurus
alongside have also
been interpreted as the Acrocanthosaurus chasing a
sauropod and then
actually climbing onto it. This all suggests that
carcharodontosaurids like Acrocanthosaurus would
latch on and not let
go until their prey was down.
There
are alternative theories regarding how carcharodontosaurids killed prey
however, if indeed at all. The slicing teeth of
carcharodontosaurids were very efficient at cutting through flesh,
but some genera, particularly larger ones may have been too big or
heavy to grip large prey with just the mouth since the teeth may have
cut themselves loose as they struggled. Either they had to grab onto
their prey such as scenarios proposed for Acrocanthosaurus,
or they
may have employed a different feeding strategy such as the concept of
‘flesh grazing’.
The
idea of flesh grazing is commonly associated with the South American
carcharodontosaurids which lived alongside some of the largest sauropod
dinosaurs of all time. These dinosaurs were conceivably too big for a
predator to bring down which in turn brought forth the suggestion that
a predator like Giganotosaurus may have just taken
a few bites from the
sides of a sauropod, just enough to satisfy its hunger. The
predator then leaves the sauropod which is injured but still alive,
and stands a good chance to recover from the wound because of its
large size. Further merit to this idea is granted when you realise
that the bones of some of this sauropods would have been simply too big
to fit in the mouth of even a large carcharodontosaurid like
Giganotosaurus, and singly would have been too
much meat for a single
Giganotosaurus to eat even if it were capable of
killing one.
Another
idea associated with South American carcharodontosaurids is that they
were potentially pack hunters. This all stems from the discovery and
description of the first fossils of Mapusaurus, a
smaller
carcharodontosaurid than Giganotosaurus but still
easily classed as a
large theropod. Mapusaurus was described from the
collected remains
of five individuals of different ages and sizes. This find combined
with the lack of remains of any other types of dinosaurs in that
location ticks all of the right boxes to lead to the suggestion that
these individual Mapusaurus were living in a group
at the time of their
death. As stated above, one large carcharodontosaurid like
Giganotosaurus may have been able to bring down a
moderately sized
sauropod, but not a giant like Argentinosaurus.
A group of
carcharodontosaurids however, all attacking at once may have been
able to overwhelm such a large dinosaur, while the resulting feast
would have easily been able to support them for quite some time
afterwards.
It
should be said at this point that the idea of carcharodontosaurids like
Mapusaurus working together to kill other dinosaurs
is a possible but
not a definite scenario. The subject of pack hunting dinosaurs
remains a controversial one, and while most palaeontologists consider
the possibilities there are some who dismiss the idea completely,
saying that such same predator species collections are just freak
occurrences. However as time goes on, such ‘freak’ occurrences
are very slowly becoming more common, and group hunting in dinosaurs
does not necessarily mean the execution of carefully planned
strategies. A group of dinosaurs could simply be a case of several
individuals mobbing an already weak individual and then going their
separate ways after the kill, similar to how some birds are seen to
behave today. These ideas and principals are discussed in more detail
in the article Pack
Hunting Dinosaurs.
Carcharodontosaurids
are less well equipped for dealing with armoured dinosaurs since their
teeth are more likely to break when brought down with force against
bony armour. Stegosaurs
would have still been present in the early
Cretaceous, though they already seem to have been on the decline from
their Jurassic heyday. Armoured
dinosaurs that relied upon heavier
armour such as polacanthids, nodosaurids and later on ankylosaurids
would have been very tough targets, and breaking teeth upon attacking
one would mean that a carcharodontosaurid would at least in the short
term go hungry as it waited for replacement teeth to grow through.
How are carcharodontosaurids
related to other dinosaurs?
Carcharodontosaurids
are obviously members of the Carcharodontosauridae which is usually
filed under the Allosauroidea, which also includes the Allosauridae
(type genus Allosaurus),
Metriacanthosauridae (type genus
Metriacanthosaurus)
and the Neovenatoridae (type genus
Neovenator).
Carcharodontosaurids like the members of all of these
other family groups were medium to large theropods that had three
fingered hands. These would be the closer relatives of the
carcharodontosaurids, though other theropods would still be related
as well, just more distantly.
The
dinosaurs ancestral to the carcharodontosaurids would have likely been
ancestral to these other groups, just that the Carcharodontosauridae
represents a specific offshoot from that group of ancient progenitors.
The carcharodontosaurids however do not seem to have spawned any
specific theropod groups that carried specialised adaptations even
further. For example, the two main groups of large theropods that
appeared during and after the decline of the carcharodontosaurids,
the tyrannosaurids
and abelisaurids,
are both known to have
ancestors already adapted and living when the carcharodontosaurids were
the apex predators of the time.
Why did the carcharodontosaurids
decline during the Cretaceous?
Fossil
evidence from Brazil suggests that as a group the carcharodontosaurids
had living genera that were still alive around the time of the KT
extinction sixty-five million years ago. This is much later than the
early stages of the late Cretaceous which up until the early years of
the twenty-first century was thought to be the time when they
disappeared from the globe. However the lack of late Cretaceous
remains does suggest that carcharodontosaurids, where still active
would have been a minority group of theropods, only existing where
habitats were still suitable for them to exist.
Key
to this downturn in numbers would be the appearance of new types of
dinosaurs, especially, herbivores that were both armoured and could
potentially fight back. Specifically these were the horned
dinosaurs, often called ceratopsians that were like Styracosaurus
and
Triceratops
and more advanced ankylosaurs like Ankylosaurus
and
Euoplocephalus.
Both of these groups became very common around areas
such as North America and Asia, and as already stated,
carcharodontosaurids did not have the right kind of teeth for dealing
with the horns and armour of these kinds of dinosaurs. Tyrannosaurids
by contrast were supremely adapted for dealing with these kinds of
dinosaurs, with both teeth and bite forces capable of defeating their
defences.
Tyrannosaurids
could also of course hunt other dinosaurs such as hadrosaurs,
and
possibly even late surviving sauropods
in places like Asia. The rise
of new apex predators in these locales would have put pressure on
surviving carcharodontosaurids, which being restricted to hunting
only certain types of dinosaur, would have always been at a
disadvantage to more generalist large predators. In time,
especially over thousands of generations over millions of years,
this combined pressure could have likely pushed carcharodontosaurids
populations into very small numbers, possibly even extinction.
In
the southern continents another group of new theropods, the
abelisaurids, rose up to displace the carcharodontosaurids as top
predators. These theropods had a very different skull form than
carcharodontosaurids, but seem to have a different strategy of
relying upon the strength of the skull to actually turn their heads
into weapons. As far as prey is concerned, sauropods were still
present, though they were now mostly in the form of titanosaurs,
and some of these genera, Saltasaurus
being one example, had
actually developed dermal armour. Carcharodontosaurids in the south
would again have faced prey that they were not as well adapted to
kill, and faced competition from new theropods that were better able
to hunt and kill the new prey forms. Just like in the northern
continents, carcharodontosaurids would have been reduced to second
rate predators, still dangerous animals in their own right, just
not as broadly successful as the new predator forms.
With
the latest known carcharodontosaurids coming from South America, it
could be that the apparent geographic isolation of South America from
the rest of the world during the late Cretaceous meant that older
dinosaur forms, predator and prey, were able to survive for longer
due to the relative lack of new types of dinosaurs migrating to this
continent. Again however, the appearance of both abelisaurids and
advanced armoured titanosaurs may have impacted numbers of
carcharodontosaurids here too.
Future carcharodontosaurids
discoveries
As
always it is impossible to accurately predict the new discovery of
fossils, but as a diverse group of theropods, it is almost a
certainty that new carcharodontosaurid fossils will be found, and
probably many times in the future. At this point any continent,
probably even Australia, has the potential to yield further
discoveries, though the hot spots seem to be South America and
Africa. As for deposits, early Cretaceous and early late
Cretaceous (Cenomanian and Turonian) sedimentary rocks are the most
likely to yield results.
There
is probably going to be a greater focus upon trying to discover
carcharodontosaurids that lived later in the Cretaceous. The work by
Fernandes de Azevedo et al is a start, but more complete remains
desperately need to be found in order to piece together a more complete
picture. South America, thanks to its isolation from the changes
taking place in other parts of the world during the late Cretaceous,
and history of previous discoveries, would be the logical place to
focus the search for late Cretaceous carcharodontosaurids. Africa
should not be completely ignored however, since this continent does
not seem to have had such a diverse change in dinosaur fauna, and it
may have been possible for carcharodontosaurids to hang on as a niche
group of predators on this continent. The most unlikely areas to find
very Late Cretaceous (all the way to the Maastrichtian)
carcharodontosaurids would be Asia and North America. Here the
faunal changes were the most dramatic, with many early Cretaceous
dinosaur forms being almost completely replaced by new types of
dinosaurs, and such radical change would have probably put more
pressure on older dinosaur forms than anywhere else in the world.
A
possible exception to this however may be indicated by the presence of
the saurolophine hadrosaur Willinakaqe
in the very late Cretaceous of
Argentina. This is the first hadrosaur discovered in South America,
and its presence is taken as a possible indication that at some point
in the Late Cretaceous, North and South America were temporarily
joined. If true, then this may have triggered a wider faunal
interchange between these two continents. So by extension, if
carcharodontosaurids were still around in South America at this time,
they might have been able to cross into North America from this
point. However assuming if even this could happen, arguments
against this could still be made since carcharodontosaurids would have
still been up against the same ecological pressures that drove them to
decline.
|
Acrocanthosaurus |
Mapusaurus |
Further reading
- First Brazilian carcharodontosaurid and other new theropod dinosaur
fossils from the Campanian–Maastrichtian Presidente Prudente
Formation, S�o Paulo State, southeastern Brazil, Rodrigo P.
Fernandes de Azevedo, Felipe Medeiros Simbras, Miguel Rodrigues
Furtado, Carlos Roberto A. Candeiro and L�lian Paglarelli
Bergqvist - 2013.
- Theropod teeth from the Mar�lia Formation (late Maastrichtian)
at the Paleontological Site of Peir�polis in Minas Gerais State,
Brazil, Carlos Roberto Candeiro, Philip Currie & L�lian
Bergqvist - 2012.
- The first definitive carcharodontosaurid (Dinosauria:
Theropoda) from Asia and the delayed ascent of tyrannosaurids, S.
Brusatte, R. Benson, D. Chure, X. Xu, C. Sullivan,
& D. Hone - 2009.
- A new approach to evaluate the cursorial ability of the giant
theropod Giganotosaurus carolinii, Ernesto R.
Blanco &
Gerardo V. Mazzetta - 2001.
- A bizarre, humped Carcharodontosauria (Theropoda) from the
Lower Cretaceous of Spain, F. Ortega, F. Escaso & J.
L. Sanz - 2010.
- A new carcharodontosaurid (Dinosauria, Theropoda) from the
Upper Cretaceous of Argentina, R. A. Coria & P. J.
Currie - 2006.
- Theropod dinosaurs from the Late Jurassic of Tendaguru
(Tanzania), Oliver W. M. Rauhut - 2011.
- A large Cretaceous theropod from Patagonia, Argentina, and the
evolution of carcharodontosaurids, Novas, de Valais,
Vickers-Rich, & Rich - 2005.
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