Pterodactylus is a genus of pterosaurs, whose
members are popularly known as pterodactyls.
It is currently thought to contain only a
single species, Pterodactylus antiquus, the
first pterosaur species to be named and identified
as a flying reptile. The fossil remains of
this species have been found primarily in
the Solnhofen limestone of Bavaria, Germany,
dated to the late Jurassic Period, about 150.8–148.5
million years ago, though more fragmentary
remains have been tentatively identified from
elsewhere in Europe and in Africa. It was
a carnivore and probably preyed upon fish
and other small animals. Like all pterosaurs,
Pterodactylus had wings formed by a skin and
muscle membrane stretching from its elongated
fourth finger to its hind limbs. It was supported
internally by collagen fibres and externally
by keratinous ridges.
Description
Pterodactylus is known from over 30 fossil
specimens, and though most of those are juveniles,
many preserve complete skeletons. Pterodactylus
antiquus was a relatively small pterosaur,
with an estimated adult wingspan of about
1.04 meters. Other "species" were once thought
to be smaller. However, these smaller specimens
have been shown to represent juveniles of
Pterodactylus, as well as its contemporary
relatives including Ctenochasma, Germanodactylus,
Aerodactylus, Aurorazhdarcho, and Gnathosaurus.
The skulls of adult Pterodactylus were long
and thin with about 90 narrow, conical teeth.
The teeth extended back from the tips of both
jaws, and became smaller farther away from
the jaw tips. The teeth extended farther back
into the jaw than in close relatives, as some
were present below the front of the nasoantorbital
fenestra, the largest opening in the skull.
Unlike related species, the skull and jaws
were straight, not curved upwards.
Pterodactylus, like related pterosaurs, had
a crest on its skull composed mainly of soft
tissues. In adult Pterodactylus, this crest
extended between the back edge of the antorbital
fenestra and the back of the skull. In at
least one specimen, the crest had a short
bony base, also seen in related pterosaurs
like Germanodactylus. Solid crests have only
been found on large, fully adult specimens
of Pterodactylus, indicating that this was
a display structure that became larger and
more well developed as individuals reached
maturity. Bennett noted that other authors
claimed that the soft tissue crest of Pterodactylus
extended backward behind the skull; Bennett
himself, however, didn't find any evidence
for the crest extending past the back of the
skull. Two specimens of P. antiquus have a
low bony crest on their skulls; in BMMS 7
it is 47.5 mm long and has a maximum height
of 0.9 mm above the orbit.
Paleobiology
Year classes
Like other pterosaurs, Pterodactylus specimens
can vary considerably based on age or level
of maturity. Both the proportions of the limb
bones, size and shape of the skull, and size
and number of teeth changed as the animals
grew. Historically, this has led to various
growth stages being mistaken for new species
of Pterodactylus. Several detailed studies
using various methods to measure growth curves
among known specimens have suggested that
there is actually only one valid Pterodactylus
species, P. antiquus.
The youngest immature Pterodactylus antiquus
specimens have a small number of teeth, and
the teeth have a relatively broad base. The
teeth of other P. antiquus specimens are both
narrower and more numerous.
Pterodactylus specimens can be divided into
two distinct year classes. In the first year
class, the skulls are only 15-45mm in length.
The second year class is characterized by
skulls 55-95mm long, but still immature. These
first two size groups were once classified
as juveniles and adults of the species P.
kochi, until further study showed that even
the supposed "adults" were immature, and possibly
belong to a distinct genus. A third year class
is represented by specimens of the "traditional"
P. antiquus, as well as a few isolated, large
specimens once assigned to P. kochi that overlap
P. antiquus in size. However, all specimens
in this third year class also show sign of
immaturity. Fully mature Pterodactylus specimens
remain unknown, or may have been mistakenly
classified as a different genus.
Growth and breeding seasons
The distinct year classes of Pterodactylus
antiquus specimens show that this species,
like the contemporary Rhamphorhynchus muensteri,
likely bred seasonally and grew consistently
during its lifetime. A new generation of 1st
year class P. antiquus would have been produced
seasonally, and reached 2nd-year size by the
time the next generation hatched, creating
distinct 'clumps' of similarly-sized and aged
individuals in the fossil record. The smallest
size class probably consisted of individuals
that had just begun to fly and were less than
one year old. The second year class represents
individuals one to two years old, and the
rare third year class is composed of specimens
over two years old. This growth pattern is
similar to modern crocodilians, rather than
the rapid growth of modern birds.
Daily activity patterns
Comparisons between the scleral rings of Pterodactylus
antiquus and modern birds and reptiles suggest
that it may have been diurnal. This may also
indicate niche partitioning with contemporary
pterosaurs inferred to be nocturnal, such
as Ctenochasma and Rhamphorhynchus.
History
The type specimen of the animal now known
as Pterodactylus antiquus was one of the first
pterosaur fossils ever to be identified. The
first Pterodactylus specimen was described
by the Italian scientist Cosimo Alessandro
Collini in 1784, based on a fossil skeleton
that had been unearthed from the Solnhofen
limestone of Bavaria. Collini was the curator
of the "Naturalienkabinett", or nature cabinet,
in the palace of Charles Theodore, Elector
of Bavaria at Mannheim. The specimen had been
given to the collection by Count Friedrich
Ferdinand zu Pappenheim, probably around 1780,
having been recovered from a lithographic
limestone quarry in Eichstätt. The actual
date of the specimen's discovery and entry
into the collection is unknown. It was not
mentioned in a catalogue of the collection
taken in 1767 and so must have been acquired
at some point between that date and its 1784
description by Collini. This makes it potentially
the earliest documented pterosaur find; the
"Pester Exemplar" of Pterodactylus micronyx
was described in 1779 and possibly discovered
earlier than the Mannheim specimen, but it
was at first considered to be a fossil crustacean.
Collini, in his first description of the Mannheim
specimen, did not conclude that it was a flying
animal. In fact, Collini could not fathom
what kind of animal it might have been, rejecting
affinities with the birds or the bats. He
speculated that it may have been a sea creature,
not for any anatomical reason, but because
he thought the ocean depths were more likely
to have housed unknown types of animals. The
idea that pterosaurs were aquatic animals
persisted among a minority of scientists as
late as 1830, when the German zoologist Johann
Georg Wagler published a text on "amphibians"
which included an illustration of Pterodactylus
using its wings as flippers. Wagler went so
far as to classify Pterodactylus, along with
other aquatic vertebrates, in the class Gryphi,
between birds and mammals.
It was the German/French scientist Johann
Hermann who first stated that Pterodactylus
used its long fourth finger to support a wing
membrane. In March 1800, Hermann alerted the
French scientist George Cuvier to the existence
of Collini's fossil, believing that it had
been captured by the occupying armies of Napoleon
and sent to the French collections in Paris
as war booty; at the time special French political
commissars systematically seized art treasures
and objects of scientific interest. Hermann
sent Cuvier a letter containing his own interpretation
of the specimen, which he believed to be a
mammal, including the first known life restoration
of a pterosaur. Hermann restored the animal
with wing membranes extending from the long
fourth finger to the ankle and a covering
of fur. Hermann also added a membrane between
the neck and wrist, as is the condition in
bats. Cuvier agreed with this interpretation,
and at Hermann's suggestion, Cuvier became
the first to publish these ideas in December
1800 in a very short description. Cuvier remarked,
"[It is not possible to doubt that the long
finger served to support a membrane that,
by lengthening the anterior extremity of this
animal, formed a good wing.]" However, contrary
to Hermann, Cuvier was convinced the animal
was a reptile.
The specimen had not in fact been seized by
the French. Rather, in 1802, following the
death of Charles Theodore, it was brought
to Munich, where Baron Johann Paul Carl von
Moll had obtained a general exemption of confiscation
for the Bavarian collections. Cuvier asked
von Moll to study the fossil but was informed
it could not be found. In 1809 Cuvier published
a somewhat longer description, in which he
named the animal a "ptero-dactyle" and refuted
a hypothesis by Johann Friedrich Blumenbach
that it would have been a shore bird.
Contrary to von Moll's report, the fossil
was not missing; it was being studied by Samuel
Thomas von Sömmerring, who gave a public
lecture about it on 27 December 1810. In January
1811, von Sömmerring wrote a letter to Cuvier
deploring the fact that he had only recently
been informed of Cuvier's request for information.
His lecture was published in 1812, and in
it von Sömmerring named the species Ornithocephalus
antiquus. The animal was described as being
both a mammal, a bat, and a form in between
mammals and birds, i.e. not intermediate in
descent but in "affinity" or archetype. Cuvier
disagreed, and the same year in his Ossemens
fossiles provided a lengthy description in
which he restated that the animal was a reptile.
It was not until 1817 that a second specimen
of Pterodactylus came to light, again from
Solnhofen. This tiny specimen was that year
described by von Soemmerring as Ornithocephalus
brevirostris, named for its short snout, now
understood to be a juvenile character. He
provided a restoration of the skeleton, the
first one published for any pterosaur. This
restoration was very inaccurate, von Soemmerring
mistaking the long metacarpals for the bones
of the lower arm, the lower arm for the humerus,
this upper arm for the breast bone and this
sternum again for the shoulder blades. Soemmerring
did not change his opinion that these forms
were bats and this "bat model" for interpreting
pterosaurs would remain influential long after
a consensus had been reached around 1860 that
they were reptiles. The standard assumptions
were that pterosaurs were quadrupedal, clumsy
on the ground, furred, warmblooded and had
a wing membrane reaching the ankle. Some of
these elements have been confirmed, some refuted
by modern research, while others remain disputed.
Classification
The genus now known as Pterodactylus was originally
named Petro-Dactyle by Cuvier in 1809, though
this was a typographical error, later corrected
by him to Ptéro-Dactyle. In 1812, Samuel
Thomas von Sömmerring named the same specimen
Ornithocephalus antiquus. The genus name was
emended to the current Pterodactylus by Constantine
Samuel Rafinesque in 1815. Unaware of Rafinesque's
publication, Cuvier himself in 1819 again
emended the genus name, but the specific name
he then gave, longirostris, has to give precedence
to von Soemmerring's antiquus. In 1888 Richard
Lydekker designated Pterodactylus antiquus
the type species. The original specimen is
the holotype of the genus, BSP No. AS.I.739.
Hermann von Meyer, in 1830, used the name
Pterodactyli to contain Pterodactylus and
other pterosaurs known at the time. This was
emended to the family Pterodactylidae by Prince
Charles Lucien Bonaparte in 1838. This family
has more recently been used to refer to many
similar species from Germany and elsewhere,
though recent studies suggest it may be a
paraphyletic or polyphyletic unnatural grouping
with respect to more advanced members of the
Ctenochasmatoidea.
Below is a cladogram showing the results of
a phylogenetic analysis presented by Andres,
Clark & Xu, 2014.
Species
Numerous species have been assigned to Pterodactylus
in the years since its discovery. In the first
half of the nineteenth century any new pterosaur
species would be named Pterodactylus, which
thus became a typical "waste-basket taxon".
Even after clearly different forms had later
been given their own generic name, new species
would be created from the very productive
late Jurassic German sites, often based on
only slightly different material.
Around 1980, subsequent revisions by Peter
Wellnhofer had reduced the number of recognized
species to about half a dozen. Many species
assigned to Pterodactylus had been based on
juvenile specimens, and subsequently been
recognized as immature individuals of other
species or genera. By the 1990s it was understood
that this was even true for part of the remaining
species. P. elegans, for example, was found
by numerous studies to be an immature Ctenochasma.
Another species of Pterodactylus originally
based on small, immature specimens was P.
micronyx. However, it has been difficult to
determine exactly of what genus and species
P. micronyx might be the juvenile form. Stéphane
Jouve, Christopher Bennett and others had
once suggested that it probably belonged either
to Gnathosaurus subulatus or one of the Ctenochasma
species, though after additional research
Bennett assigned it to the genus Aurorazhdarcho.
Another species with a complex history is
P. longicollum, named by von Meyer in 1854,
based on a large specimen with a long neck
and fewer teeth. Many researchers, including
David Unwin, have found P. longicollum to
be distinct from P. kochi and P. antiquus.
Unwin found P. longicollum to be closer to
Germanodactylus and therefore requiring a
new genus name. It has sometimes been placed
in the genus Diopecephalus because Harry Govier
Seeley based this genus partly on the P. longicollum
material. However, it was shown by Bennett
that the type specimen later designated for
Diopecephalus was a fossil belonging to P.
kochi, and no longer thought to be separate
from Pterodactylus. Diopecephalus is therefore
a synonym of Pterodactylus, and as such is
unavailable for use as a new genus for "P."
longicollum. "P." longicollum was eventually
made the type species of a separate genus
Ardeadactylus. In 2014, P. scolopaciceps,
formerly regarded as a junior synonym, was
moved to its own genus, Aerodactylus.
The only well-known and well-supported species
left by the first decades of the 21st century
were P. antiquus and P. kochi. However, most
studies between 1995 and 2010 found little
reason to separate even these two species,
and treated them as synonymous. In 1996, Bennett
suggested that the differences between specimens
of P. kochi and P. antiquus could be explained
by differences in age. In a 2004 paper, Jouve
used a different method of analysis and recovered
the same result, showing that the "distinctive"
features of P. kochi were age-related, and
using mathematical comparison to show that
the two forms are different growth stages
of the same species. An additional review
of the specimens published in 2013 demonstrated
that some of the supposed differences between
P. kochi and P. antiquus were due to measurement
errors, further supporting their synonymy.
However, in 2014 Steven Vidovic and David
Martill concluded that the differences between
P. kochi and P. antiquus, including the shorter
neck vertebrae of P. kochi, were significant
enough to separate them. Vidovic and Martill
also performed a phylogenetic analysis which
treated all relevant specimens as distinct
units, and found the P. kochi type specimen
did not form a clade with that of P. antiquus.
They concluded that the genus Diopecephalus
could be returned to use to distinguish "P".
kochi from P. antiquus, and further suggested
that Germanodactylus rhamphastinus was probably
the adult form of "P." kochi, due in part
to its short neck vertebrae and much larger
size.
List of species and synonyms
During its over 200 year history, the various
species of Pterodactylus have gone through
a number of changes in classification, and
thus have acquired a large number of synonyms.
Additionally, a number of species assigned
to Pterodactylus are based on poor remains
that have proven difficult to assign to one
species or another, and are therefore considered
nomina dubia. The following list includes
names that are based on German material presently,
or until recently, thought to be pertaining
to Pterodactylus proper and names based on
other material that has as yet not been assigned
to other genera.
References
