What makes a pterosaur a
pterosaur?
Firstly
a pterosaur is not a dinosaur, the pterosaurs evolved from a
different line to the one that gave rise to the dinosaurs. Nor are
pterosaurs the ancestors of birds. Enough complete fossil evidence
now exists to prove that birds evolved from the feathered dinosaurs.
Also there is no such animal called a pterodactyl. This word is a
shortened from of the name Pterodactylus,
and as
such
'pterodactyl' does not represent any particular genus.
Pterosaurs
are the earliest known vertebrates to master the air by flying, and
until their evolution the only other animals in the air where flying
insects. Pterosaurs are also the largest known flying animals ever
known to exist, with even the largest of today’s bids not even
coming close to the largest pterosaurs.
Discovery history
The
first pterosaur known to science was Pterodactylus,
although at the
time not everybody was certain as to what it actually was. Back in
1784 when Pterodactylus was first described by
the Italian
naturalist Cosimo Alessandro, it was envisioned as an aquatic
creature that used its 'wings' to propel itself through the water.
Amazingly even though the man who eventually named Pterodactylus,
George Cuvier, put forward the correct theory that it was a flying
creature, there were still many who held firm to the aquatic animal
theory for several decades afterwards.
Despite
this the idea that pterosaurs were flying creatures did rapidly gain
acceptance, although the exact type of creature was still being
debated amongst the scientific community of the time. Along with
giving it the name, George Cuvier also noted that the specimen
represented a reptile that could fly. Although he was correct, no
such precedent for a flying reptile was known in the realms of natural
history, and the very idea that a reptile could fly was simply beyond
the imagination of many of the day’s naturalist. A more comfortable
idea for them was that the pterosaurs were more like bats and possibly
to an extent, the birds.
The
problem with this apart from being incorrect biologically is that it
also inferred similar behaviour and characteristics to pterosaurs. It
would not be until fresh minds and the discovery of other fantastic
reptiles such as the dinosaurs that people realised and accepted that
reptiles once existed in forms that are completely different to
anything we know today.
A
further problem from the time is that the discovery of Pterodactylus
was so radical to the world of science that it had the effect of many
specimens being attributed to this genus as slightly different species
of the same genus, when in actual fact they represented different
kinds of pterosaur altogether. This 'wastebasket taxon' effect is
by no means unique to Pterodactylus or even the
pterosaurs as a group,
but at the time it caused much misunderstanding and confusion about
pterosaurs. It would not be until the closing years of the twentieth
century that the mass study between different specimens combined with
the new knowledge of changing morphology between individuals of
different ages of the same species, that many of the 'classic'
pterosaur genera could be cleaned up with the exhaustive lists of
unnecessary species names got reduced to the actual representative
types.
Classifications
Pterosaurs
are usually broken down into the two groups called Rhamphorhynchoidea
and Pterodactyloidea. Rhamphorhynchoid pterosaurs are the earliest
group and represent basal pterosaurs like Rhamphorhynchus
and
Anurognathus.
As a group they usually had long
tails and shorter
metacarpal bones in the wing. The group first enters the fossil
record towards the end of the Triassic and lasts until the end of the
Jurassic.
The
pterodactyloid group are thought to have their origins from within the
rhamphorhynchoid group, and first appear during the middle Jurassic.
Named after Pterodactylus, they were more
typified by having shorter
tails and longer beaks more suited to piscivorous lifestyles,
although some probably were still insectivorous, especially as
juveniles. This group lasted until the end of the Cretaceous where
they disappear from the fossil record along with the dinosaurs and the
large marine reptiles. The
pterodactyloid group is further broken up into ornithocheiroidea,
Ctenochasmatoidea, Dsungaripteroidea and Azhdarchoidea, all if
which are termed 'superfamilies' that can be broken down further
into smaller groups of similarly related pterosaurs.
A
third group called the Wukongopteridae also now exists, and is now
the home for pterosaurs that display both primitive and advanced
features. Although named after Wukongopterus,
the most famous
member of this group is called Darwinopterus.
This pterosaur has been
heralded as a transitional form, hence it’s naming after Charles
Darwin who really brought the idea of evolution to the public
consciousness. Classification of transitional forms is always
difficult however which is not only why the Wukongopteridae was
created, but a new currently unranked group called the Monofenestrata
has now been created to appear before both the Wukongopteridae and much
larger Pterodactyloidea super family. This is mainly because skull
forms long associated with the Pterodactyloidea are now known to have
existed in some more primitive forms as well. This is explained by
fossil evidence that shows pterosaurs advanced through a process of
modular evolution where only some body parts changed while others
stayed the same.
Origins
With
lightweight hollow bones and gracile builds, pterosaurs were very
delicately built in life. Because their bones were hollow, they
usually end up getting crushed under the weight of sediment deposits,
and this not just produces flattened reliefs, but can cause some
distortion to the shape of the bones. This means that only certain
areas such as the Solnhofen beds in Germany and Araripe plateau of
Brazil reveal detailed specimens. It is also why a clear lineage
between pterosaurs and their immediate ancestors is for the most part
largely unknown.
The
pterosaurs most probably evolved from arboreal (tree dwelling)
reptiles that had evolved thin growths of skin between their legs so
that they could glide from tree to tree. Even though all this does is
slow the rate of descent so that the animal can land on a tree before
it hits the ground, the principal mechanism is there. Such a
mechanism would be made more capable with a larger 'wing' area and
so the individuals with the larger wings could glide further and be
more successful. Greater success would mean a greater number of
offspring, which in turn would mean more, larger winged versions
like the progenitor.
Larger
wings would need stronger muscle attachment to move them around, and
eventually the wings could not just be manipulated for steering, but
also flapped so that the animal could go even further. Weight
reduction from lighter bones, larger skull fenestra and reduction of
non-essential body parts would eventually lead into a morphology
resembling the earliest pterosaurs.
Biology
Pterosaurs
had specially adapted bones which were exceptionally light weight.
This was achieved by the bones being hollow and filled with air.
These bones were also capable of maintaining rigid strength ensuring
that the wings kept their shape. The drawback as stated above is that
these bones were not very resilient to crushing forces such as the
build-up of sediment. However this was not a problem for the living
animal, as it would not be exposed to such forces until after it had
died.
Many
pterosaur species have the presence of pycnofibres preserved with their
remains. Pycnofibres are the pterosaur equivalent of mammal hair,
although the actual structure of hair and pycnofibres is actually
quite different. The amount of pycnofibre coverage can vary greatly
between species, with some kinds of pterosaur hardly having any
coverage to others that had their entire bodies covered.
The
purpose of pycnofibres is thought to have been exactly the same as the
purpose for hair in mammals; insulation. By having insulation, a
pterosaur could maintain a higher internal body temperature, and has
even led the idea that pterosaurs may have actually been warm blooded.
By having a warm blooded metabolism, pterosaurs would have more
easily been able to maintain the active movements required for flight.
A
higher metabolism also means a higher rate of respiration, but
evidence for this exists in the presence of internal air sacs. These
air sacs would have helped to greatly increase the rate of respiration
when active, and if they worked in the same way as air sacs in modern
birds do, would have ensured that the lungs had available oxygen
supply whether the pterosaur was breathing in or out. The drawback to
a high metabolism is that it requires a high calorie intake to
maintain. With this in mind it’s possible that some pterosaurs may
have learned to use flight techniques such as 'dynamic soaring' to
reduce the required amount of calories, or lived lifestyles that
required very little energy expenditure to find food.
CAT
scanning of extinct animal skulls is now a common practice, and helps
to reveal the layout and position of the brain and associated soft
tissue of the creature when it was alive. This of course has been
done with numerous pterosaurs, and here it is usually seen that the
areas for determining balance are highly developed, indicating that
pterosaurs were very adept at making precise adjustments in posture and
wing movement.
Of
particular importance is the orientation of the inner ear which can
reveal if a pterosaur held its head straight and level with the body
during flight, or down towards the ground at an angle. Not only can
knowing this allow palaeontologists to infer to specific hunting
strategies, in can also reveal information about the flight dynamics
at work with the morphology of differing pterosaurs.
Wing structure
Pterosaur
wings are often overlooked as being simple stretches of skin supported
by a bony rod, when in all actuality nothing could be further from
the truth. Pterosaur wings start with the arms which form the central
support for the wing. Imagine looking down on the wing from the top
down, you would see that the first part of the wing stretches from
the wrist to the shoulder. This part of the wing is referred to as
the Propatagium which was further supported by a bone called the
pteroid, something that appears to be unique to pterosaurs. The
arrangement of the pteroid continues to be a matter of dispute, as is
its possible articulation. It could also be that how it worked may
have varied according to different species.
The
hands of pterosaurs had four fingers or 'digits' as they are
actually called. The first three digits were not connected to the
wing and would likely have been of use in gripping to surfaces,
especially in the smaller pterosaurs. The fourth digit was different
to the first three in that it was extremely elongated, and it was in
fact this 'finger' that formed the main trailing edge support for
the wing.
From
the tip of the fourth digit towards the body and sometimes hind
quarters was the main wing area. This is called the Brachiopatagium,
although it is often hard to ascertain where exactly it joined the
main pterosaur body. Fossil evidence of some pterosaurs where soft
tissue impressions have been preserved such as with the pterosaur
Sordes, show that the wings connected to the hind limbs, but it is
uncertain if this applies to all pterosaurs. Despite the evidence
that supports the joining of the wing to the hind limbs, it is very
likely that the exact area of attachment was more dependent upon the
individual species of pterosaur.
The
actual construction of the wing area is more than just a skin
membrane. The wings had a latticework of fibres known as
actinofibrils. This criss-crossing arrangement would have helped
strengthen the wing especially during in-flight manoeuvres. The
internal structure of the wings also included a small amount of muscle
and a network of circular blood vessels. Larger pterosaurs also seem
to have had air sacs present in their wings as well. Whether these
sacs were for weight reduction or even an aid for respiration for a
larger pterosaur is hard to establish with certainty.
Some
pterosaurs, particularly some members of the more basal
rhamphorhynchoid group, also have a membrane between their hind
legs. This is called the Uropatagium, but its precise function
remains unknown, and its extent most certainly varied between
species. It could have acted like an 'air brake' used when the
pterosaur descended to land, or for pulling a tight manoeuvre when
chasing agile prey. This feature could have been a throwback to a
feature present in pterosaur ancestors, as it seems to be largely
absent from the lore advanced pterosaurs.
Flight
In
the early days of pterosaur discovery most researchers considered them
to be only capable of gliding and as such reliant upon thermal currents
and up draughts to maintain flight. This in part was fuelled by the
notion that all reptiles, based on those we know today, are cold
blooded. A cold blooded creature they thought would be required to
glide to reduce the need for active muscle movement, something
associated with warm blooded animals. It was also thought that some
of the larger kinds such as Pteranodon
had wings
that were simply too
big to flap up and down.
Today
the idea that pterosaurs could only glide is laughably obsolete,
although it is recognised that some pterosaurs especially the larger
varieties may have glided for extended periods in order to reduce the
amount of calories required for flight. This would have been
especially useful for pterosaurs that required keeping their energy
expenditure to a minimum when searching for prey.
Smaller
pterosaurs certainly did not glide when chasing after insectivorous
prey. Anyone who has seen a dragonfly on the wing can appreciate how
sudden they can turn without even a hint of slowing down, and
capturing such manoeuvrable prey by just gliding after it would be near
impossible.
Larger
pterosaurs like Pteranodon are thought to have
hunted for fish across
the open ocean and as such spent extended periods away from land. In
order to reduce their expenditure they did not just simply glide but
may have used a method referred to as dynamic soaring, in this case a
method of exploiting the air patterns over the ocean waves.
By
flying low into a trough between two sets of waves, a Pteranodon
could turn into the oncoming wind as it rises over the crest of a
wave. Because the air has to rise over the wave, it gets packed
together increasing its pressure. This increased pressure would cause
the Pteranodon to rise up into the air without any
effort on its part.
Once up, the Pteranodon could then change
direction and dive again,
this time with the wind behind it, increasing its speed so that the
next time it pulls the manoeuvre the effect is even greater.
This
building of momentum by using the wind is the exact same method used by
a modern day Albatross, a bird of similar size and wing area to
Pteranodon. The principal of dynamic soaring is
also used by glider
pilots to remain airborne for longer.
The
exact flight technique used by pterosaurs is still not known with
certainty, although much study has been done, including flying
model reconstructions of pterosaurs. Now making a working model of a
living creature that has all the degrees of motion that the original
animal has is a very difficult task. The National Geographic 'Sky
Monsters' documentary featured a groups attempt to create a flying
pterosaur model. Due to technological limitations the model was
carried up by a remote aircraft which then released the model in
flight. Although technical failure of the parts inside meant that the
demonstration was unsuccessful, the group still managed to
demonstrate the aerodynamics of a pterosaur wing and basic manoeuvring
ability.
A
very exciting possibility is that pterosaurs were able to fly soon
after hatching from the egg. This is evidenced by looking at the
proportions of the wing bones throughout the growth stages. Juvenile
specimens often exhibit morphological differences from their adult
forms, but the proportions of the wing bones always remain the same
with the different wing bones growing at the same rate as one another.
This indicates that the wings of a pterosaur juvenile were just as
flight capable as when they grew larger in later life.
How
pterosaurs got airborne is another disputed area with early depictions
hailing from the time when they were thought to only glide, which had
pterosaurs leaping from cliff tops and catching the strong up draughts
in their wings. While this can be still used as a model for some
species, it cannot be applied to all pterosaurs. Fossilised track
ways prove that pterosaurs spent time on the ground, and some
researchers think that they could have run while flapping.
Another
theory, one that is gaining wider acceptance, is that pterosaurs
could 'vault' themselves into the air. This would work by
suddenly pushing their bodies off the ground with their wings. Once
off the ground, they would then lift their wings and begin flapping
towards the ground to give them lift. This makes good sense as the
muscles that moved the wings were probably the strongest in the body.
Couple this with the lightweight construction of the skeleton, and
it’s easy to imagine a pterosaur pushing itself into the air before
flying off.
Ground movement
When
pterosaurs were first realised to be flying animals, they were
thought to have perched in trees like birds. The summarisation for
this was simple; birds fly, pterosaurs flew, therefore pterosaurs
must have perched like birds. Although some pterosaurs did indeed
live in the tree canopy, and probably rested on branches, it is now
accepted that the vast majority of pterosaurs lived on the ground when
not flying. However, pterosaurs likely chose their resting places
carefully, perhaps preferring high up, hard to reach places like
rock outcroppings and plateaus away from predators like carnivorous
dinosaurs.
Because
of continuing comparisons to birds, pterosaurs were also thought to
have been bipedal when on the ground. This led to the now out-dated
reconstruction of pterosaurs holding their wings up to keep them off
the ground, something that is considered extremely unlikely for a
resting posture. For example, if you try holding your arms out to
your side, you'll find that while you can keep them there for a short
period of time, they'll eventually start to ache after a bit. In
pterosaurs, the bones were lighter, but in order to maintain the
posture they would still have to be tensing muscles to keep their wings
high.
Today
the fossilised track ways of pterosaurs are well documented, and
these clearly show not only the rear feet, but the hands of the wings
in contact with the ground, confirming that pterosaurs did indeed
walk in a quadrupedal fashion when on the ground. Study also
shows that some pterosaurs walked with the wings supporting the body
from underneath as opposed to the sides.
How
well a pterosaur moved on the land depended somewhat on the species in
question. Pterosaurs with larger feet were suited to walking on soft
ground like the muddy banks of a lake or river, while those with
smaller feet were more suited to dry and firm soil. Some pterosaurs
are even thought to have been able to run, perhaps to chase after
prey items that tried to escape by running into the undergrowth,
giving them a taller, erect walking gait.
Reproduction & growth
As
briefly mentioned above, much of the confusion over numerous
pterosaur species came from the fact that no one knew how much
pterosaurs changed during their lives. These changes can be seen in
some species where the juvenile specimens have radically different
skeletal structures to those of the adults. Often the most striking
difference is the length and proportion of the skull. A common trait
is juveniles having shorter jaws and dentition more suited to catching
insects, where in adults the jaws are proportionately longer, with
teeth suited more seizing fish.
These
changes are best known for pterosaurs where multiple remains exist for
the genera which clearly show the changing morphology across different
aged individuals. It also suggests that the younger individuals of a
pterosaur species filled a different ecological niche to that of their
parents, thereby avoiding direct competition with them.
The
size of the hips in pterosaur remains is usually taken as a reliable
indicator between male and female individuals, with females having
wider hips to help with the passage of eggs. This is taken as a more
reliable indicator than the study of crests which can change greatly
over the course of a pterosaurs life, especially in males.
The
ratio of female to male remains is considered by some to be an
indicator of the reproductive habits of some pterosaurs. In Pteranodon
the number of females greatly outnumbers the number of males,
especially the mature males with fully developed crests. This has
been interpreted as males taking up residence in a particular area and
living a polyganous lifestyle, mating with all the females that are
within their territory. Such behaviour would mean that males would
constantly have to defend their territory, and only the most
successful males would breed. This competition may also have driven
out the lesser males, possibly stunting their development by driving
them away from the main gathering and feeding areas, reducing their
chances of surviving long enough to reach full maturity.
Due
to the diverse nature of different pterosaur species, it is uncertain
how well this model can be applied to other species. It is just as
probable that some pterosaurs could have formed loose colonies of
mating pairs, or perhaps isolated themselves from a larger group
while nesting.
Display crests
Although
not all pterosaurs have crests, those that do can truly astound
palaeontologists. Crest shapes can vary from simple raised structures
only a few centimetres high to the preposterously ornate and huge
crests on others like Nyctosaurus,
whose ‘L
shaped’ head crest is
over half as high as one of its wings is long. Crests are also not
just restricted to the back of the head, but can also run forwards
and down the snout as well.
The
easy explanation for these crests is that they were primarily for
display. The display answer covers both inter species recognition so
that two pterosaurs of the same species can recognise each other, as
well as for the purpose of attracting a mate. The latter is a very
credible theory as the study of male pterosaur specimens of the same
species but different ages reveals that the crests only became fully
developed when the males reached reproductive maturity.
Female
pterosaurs of crested species also had crests of their own, although
usually they were not as developed as the males, and this has in the
past caused confusion between female and immature male specimens.
Aside from the shape of the crest, it is highly plausible that
crests may have been brightly coloured to accentuate their presence,
especially if pterosaurs had specific breeding seasons.
Some
pterosaur researchers also speculate upon other functions that can be
attributed to crests. The higher and broader crests are considered by
some to have acted like rudders, helping with steering during
flight. Some of the broader crests or 'head sails' like in the
tapejarids may have been able to catch the wind, reducing the
amount of work necessary for a pterosaur to keep itself airborne.
Many
studies have been conducted upon the aerodynamic effects of different
head crests, and for the most part, no overly negative or positive
effects have been noted. What is known is that not all pterosaurs had
crests, and those that do have such large variation between different
species, that the only universal explanation that can be applied to
all pterosaurs is display.
Daily activity
One
of the most common fossilised parts of pterosaur remains where the
skull has been preserved are the scleral rings. Study of how these
rings can reveal important insights into the life of the living
creature, such as if it was active by day or during the night. This
is sometimes referred to as niche partitioning, and means that a
pterosaur that is active throughout the night would avoid direct
competition with another species of pterosaur that was active in the
same area but during the day instead.
Being
active at different times can also be because a particular food supply
was more abundant at certain times of the day. Also, it can be a
survival strategy to avoid hunters. Some creatures are known to be
active only during the twilight of dusk and dawn to avoid the predators
of both the day and the night.
Diet
The
earliest pterosaurs were most likely to have been insectivores, and
many of the later examples such as Jeholopterus
show specialised
adaptations for this way of life. Later members of the pterosaurs
started to include fish into their diets, with some such as
Pterodactylus and Rhamphorhynchus
being considered to take either fish
or insects. It is also highly probable that what pterosaurs ate
depends on how old they were, with juvenile specimens having shorter
beaks with thin pointed teeth more suitable for insects, whereas
older members of the same species having proportionately longer beaks,
with stronger teeth more suited to a fish diet.
Pterosaurs
that did have a piscivorous diet are usually imagined as hunting by
skim fishing. This is where the pterosaur would fly so close to the
water that when it opened its jaws at least the lower jaw dipped
beneath the surface of the water. When the jaw hit a fish the jaws
were closed, and the pterosaur then carried the fish from the water.
Many
species of pterosaur have teeth that are actually smaller near the tip
of the beak, becoming larger towards the back, sometimes to the
extent that two groups of teeth can be clearly be identified. At a
glance it may seem unusual when you compare this dentition arrangement
to other predators which typically have the larger teeth at the front
for prey capture, but you have to bear in mind the resistance of the
water against the tip of the beak when travelling through the water at
speed. Larger teeth would create more resistance, making skim
feeding more cumbersome and possibly reducing reaction time in closing
the jaws around the prey. Smaller teeth are not so much of a
problem, and it would be a simple technique for a pterosaur to seize
its prey with the tip of its beak before quickly flicking its head back
and tossing its prey further back into its mouth where it could then be
held by the larger teeth. Not only would this allow more grip on a
struggling fish, it may have allowed the hunter to better protect its
meal from other marauding pterosaurs that may have tried to steal its
prey.
On
the over hand some pterosaurs like Zhenyuanopterus
had quite the
reverse with larger teeth towards the front and much smaller teeth
towards the back. The strength of the teeth need to be taken into
consideration, and many people think that they would have been too
fragile to cope with larger and more powerful prey. It may be that
pterosaurs with this kind of dentition focused their attentions on
smaller prey, and perhaps used a dipping motion to pluck fish out of
the water.
Some
pterosaurs actually had toothless beaks but still managed to have been
active hunters. Pteranodon, whose name
translates to English as
'Toothless wing' was almost certainly a dedicated piscivore, as
evidenced by the large amount of fish remains such as bones and scales
that are often found inside Pteranodon remains.
New thinking to
Pteranodon’s feeding strategy has brought the
proposition that it did
not just scoop up fish as it flew overhead, but may have actually
landed on the water, or even dived into it from a height like Gannets
do today.
Not
all pterosaurs were thought to have fed while on the wing and the
azhdarchoid line of pterosaurs that include members like Quetzalcoatlus
and Zhejiangopterus,
which are now thought to
have hunted for food
like storks do today. Not only could this include hunting like
plucking fish from the water’s edge, it could also include stalking
through long grass to find things like snakes and lizards to eat.
One
of the most specialist pterosaurs was Peterodaustro,
a filter feeding
pterosaur that perhaps lived like a modern day flamingo. Pterodaustro
had a beak that curved upwards that instead of being filled with strong
needle teeth like some other pterosaurs, it had up to a thousand
bristle teeth that protruded upwards from the lower jaw. These highly
specialised teeth would have allowed Pterodaustro
to scoop up a beak
full of water, and then strain it out so that only a beak full of
small invertebrates, plankton and algae would remain.
It's
also entirely probable that some pterosaurs were scavengers looking for
carrion while out in the wing like vultures do today. A gliding flyer
would have expended very little energy while still covering a massive
area in its pursuit for food.
Not
all pterosaurs may have been carnivorous however. Some
palaeontologists have put forward the idea that some pterosaurs also
included fruit in their diets, making them possibly omnivores, or
to the extreme end of the scale, frugivores.
Predators
Pterosaurs
would have been attacked and eaten by any predator able to get to
them. There is a reported case of a spinosaurid tooth embedded in the
vertebra of a pterosaur, and the tooth of a dromaeosaurid dinosaur
embedded in pterosaur remains from Canada. Pterosaurs would also need
to drink, a time when they were probably at their most vulnerable as
there were not just dinosaurs, but large crocodiles lurking in the
water. At sea, they would have had to avoid plesiosaurs and
mosasaurs, and if some did indeed take to the water during feeding,
then sharks may have been a problem too. It is also possible that
some larger pterosaur genera may have fed upon the smaller species.
The pterosaur one main survival advantage was that as flyers, they
would have been out of reach of any of the terrestrial and marine
predators when flying high.
Extinction
No
one can agree exactly on what finished the pterosaurs, but one
popular theory is competition with the newly evolved birds. The birds
are generally thought to have been more manoeuvrable, and more
resilient to harm than the pterosaurs, and simply outcompeted them.
This may actually be true for the rhamphorhynchoid group that largely
disappeared at the end of the Jurassic. The rhamphorhynchoid group
had more of a focus on being insectivores, and when the birds
appeared, the food supply could not support both kinds of creature
indefinitely, especially if the birds were more successful breeders,
raising more successful broods with a higher number of young.
However
the appearance of birds on its own cannot explain the disappearance of
the pterodactyloid group, although they did probably help drive the
smaller members of the group to extinction by being more successful,
as well as competing with the juvenile forms of some pterosaur
species. The larger members such as Pteranodon
and Quetzalcoatlus
however survived to the very end and had lifestyles that kept them out
of direct competition with birds.
It’s
highly probable that the asteroid impact that marked the end of the
Cretaceous caused a severe reduction in marine life. This would have
happened from large amounts of dust and debris being thrown up into the
atmosphere from the impact reducing the amount of light falling upon
the world’s oceans. This would cause a massive drop in the amount
of phytoplankton which would be food to fish and by extension
everything that preyed and relied upon the fish to survive. The long
term survival of all animals that relied upon fish would have been
bleak, and only a few weeks of starvation at most would have been
enough to finish most of the predators. By the time the phytoplankton
and the fish stocks began to recover it was already too late.
It
would not have been plain sailing for pterosaurs that lived on the land
and ate other prey items either. The ensuing darkness may have
affected their ability to see to hunt, and weather patterns may have
also been chaotic in the immediate aftermath of the impact, making
flying difficult if not impossible. Also many of the later pterosaurs
had grown gigantic, and as such would require a much larger calorie
intake to survive. If it were not maintained, they too would
eventually starve.
When
considering what one event finished a group, it is more likely that
it was not just one thing, but an amalgamation of several different
factors that brought the end for the pterosaurs.
Really extinct?
Even
though pterosaurs are
considered to be an extinct group, in cryptozoological circles,
occasional descriptions of animals that match those of ancient
pterosaurs are still sometimes made. These sightings usually come
from eye witnesses who claim to have been 'buzzed' by a creature
while they were out about their business, or explorers who have heard
reports of pterosaur like creatures from native peoples, who in turn
recognise and pick out images of pterosaurs as the creatures in their
stories when they are shown them. There have even been cave drawings
made several thousand years ago that feature drawings of winged
creatures that resemble pterosaurs.
Although
some researchers
continue to search for the existence of living pterosaurs, these
sightings are not accepted by the wider scientific community. They do
however serve as writing material for popular fiction in the same way
as the Loch Ness Monster gets described as being a plesiosaur.