ANCIENT ORNITHOSAURS FROM THE LIAS
Cuvier's discourse on the revolutions of the Earth made the Pterodactyle
known to English readers early in the nineteenth century. Dr. Buckland,
the distinguished professor of Geology at Oxford, discovered in 1829 a
far larger specimen in the Lias of Lyme Regis, and it became known by a
figure published by the Geological Society, and by the description in
his famous Bridgewater Treatise, p. 164. This animal was tantalising in
imperfect preservation. The bones were scattered in the clay, so as to
give no idea of the animal's aspect. Knowledge of its limbs and body has
been gradually acquired; and now, for some years, the tail and most
parts of the skeleton have been well known in this oldest and most
interesting British Pterodactyle.
Sir Richard Owen after some time separated the fossil as a distinct
genus, named Dimorphodon; for it was in many ways unlike the
Pterodactyles described from Bavaria. The name Dimorphodon indicated the
two distinct kinds of teeth in the jaws, a character which is still
unparalleled among Pterodactyles of newer age. There are a few large
pointed, piercing and tearing teeth in the front of the jaws, with
smaller teeth further back, placed among the tearing teeth in the upper
jaw; while in the lower jaw the small teeth are continuous, close-set,
and form a fine cutting edge like a saw.
[Illustration: FIG. 49. LEFT SIDE OF DIMORPHODON (RESTORED) AT REST]
The Dimorphodon has a short beak, a deep head, and deep lower jaw, which
is overlapped by the cheek bones. The side of the head is occupied by
four vacuities, separated by narrow bars of bone. First, in front, is
the immense opening for the nostril, triangular in form, with the long
upper side following the rounded curve of the face. A large triangular
opening intervenes between the nose hole and the eye hole, scarcely
smaller than the former, but much larger than the orbit of the eye. The
eye hole is shaped like a kite or inverted pear. Further back still is a
narrower vertical opening known as the lateral or inferior temporal
vacuity. The back of the head is badly preserved. The two principal
skulls differ in depth, probably from the strains under which they were
pressed flat in the clay. A singular detail of structure is found in the
extremity of the lower jaw, which is turned slightly downward, and
terminates in a short toothless point. The head of Dimorphodon is
about eight inches long.
[Illustration: FIG. 50. DIMORPHODON MACRONYX
RESTORED FORM OF THE ANIMAL]
The neck bones are of suitable stoutness and width to support the head.
The bones are yoked together by strong processes. The neck was about 6
inches long, did not include more than seven bones, and appeared short
owing only to the depth and size of the head. The length of the backbone
which supported the ribs was also about 6 inches. Its joints are
remarkably short when compared with those of the neck. The tail is about
20 inches long.
The extreme length of the animal from the tip of the nose to the end of
the tail may have been 3 feet 4 inches, supposing it to have walked on
all fours in the manner of a Reptile or Mammal. This may have been a
common position, but Dimorphodon may probably also have been a biped.
Before 1875, when the first restoration appeared in the _Illustrated
London News_, the legs had been regarded as too short to have supported
the animal, standing upon its hind limbs. They are here seen to be well
adapted for such a purpose. The upper leg bone is 3-1/4 inches long, the
lower leg bone is 4-1/2 inches long, and the singularly strong instep
bones are firmly packed together side by side as in a leaping or jumping
Mammal, and measure 1-1/2 inches in length. Dimorphodon differs from
several other Pterodactyles in having the hind limb provided with a
fifth outermost short instep bone, to which two toe bones are attached.
These bones are elongated in a way that may be compared, on a small
scale, with the elongation of the wing finger in the fore limb. The
digit was manifestly used in the same way as the wing finger, in partial
support of a flying membrane, though its direction may have been upward
and outward, rather than inward. There is no evidence of a pulley joint
between the metatarsal and the adjacent phalange.
The height of the Dimorphodon, standing on its hind legs in the position
of a Bird, with the wings folded upon the body in the manner of a Bird,
was about 20 inches. An ungainly, ill-balanced animal in aspect, but not
more so than many big-headed birds, and probably capable of resting upon
the instep bones as many birds do. The chief point of variation from the
Pterodactyle wing is in the relative length of the metacarpus in
Dimorphodon. It is shorter than the other bones in the wing, never
exceeding 1-1/2 inches. The total length of all the arm bones down to
the point where the metacarpus might have touched the ground, or where
the wing finger is bent upon it, is about 9 inches, which gives a length
of less than 6 inches below the upper arm bone. The four bones of the
wing finger measure, from the point where the first bone bends upon the
metacarpus, less than 18 inches. So that the wings could only have been
carried in the manner of the wings of a Bat, folded at the side and
directed obliquely over the back when the animal moved on all fours. Its
body would appear to have been raised high above the ground, in a manner
almost unparalleled in Reptiles, and comparable to Birds and Mammals.
Dimorphodon is to be imagined in full flight, with the body extended
like that of a Bird, when the wings would have had a spread from side to
side of about 4 feet 4 inches. As in other animals of this group, the
three claws on the front feet are larger than the similar four claws on
the hind feet; as though the fingers might have functions in grasping
prey, which were not shared by the toes.
[Illustration: FIG. 51. DIMORPHODON MACRONYX WALKING AS A QUADRUPED
RESTORATION OF THE SKELETON]
The restorations give faithful pictures of the skeleton, and the form of
the body is built upon the indications of muscular structure seen in the
bones.
A second English Pterodactyle is found in the Upper Lias of Whitby. It
is only known from an imperfect skull, published in 1888. It has the
great advantage of preserving the bones in their natural relations to
each other, and with a length of head probably similar to Dimorphodon
shows that the depth at the back of the eye was much less; and the skull
wants the arched contour of face seen in Dimorphodon. The head has the
same four lateral vacuities, but the nostril is relatively small and
elongated, extending partly above the oval antorbital opening, which was
larger. There is thus a difference of proportion, but it is precisely
such as might result from the species having the skull flatter. The head
is easily distinguished by the small nostril, which is smaller than the
orbit of the eye. The animal is referred to another genus. The quadrate
bones which give attachment to the lower jaw send a process inward to
meet the bones of the palate, which differ somewhat from the usual
condition. Two bony rods extend from the quadrate bones backward and
upward to the sphenoid, and two more slender bones extend from the
quadrate bones forward, and converge in a #V#-shape, to define the
division between the openings of the nostrils on the palate. The
#V#-shaped bone in front is called the vomer, while the hinder part is
called pterygoid. The bones that extend backward to the sphenoid are not
easily identified. This animal is one of the most interesting of
Pterodactyles from the very reptilian character exhibited in the back of
the head, which appears to be different from other specimens, which are
more like a bird in that region. Yet underneath this reptilian aspect,
with the bony bar at the side of the temporal region of the head formed
by the squamosal and quadrate bones, defining the two temporal vacuities
as in Reptiles, a mould is preserved of the cavity once occupied by the
brain, showing the chief details of structure of that organ, and proving
that in so far as it departs from the brain of a Bird it appears to
resemble the brain of a Mammal, and is unlike the brain of a Reptile.
The Pterodactyles from the Lias of Germany are similar to the English
types, in so far as they can be compared. In 1878 I had the opportunity
of studying those which were preserved in the Castle at Banz, which
Professor Andreas Wagner, in 1860, referred to the new genus
Dorygnathus. The skull is unknown, but the lower jaw, 6-1/2 inches long,
is less than 2-1/2 inches wide at the articulation with the quadrate
bone in the skull. The depth of the lower jaw does not exceed 1/4 inch,
so that it is in marked contrast to Buckland's Dimorphodon. The
symphysis, which completely blends the rami of the jaw, is short. As far
as it extends it contains large tearing teeth, followed by smaller teeth
behind, like those of Dimorphodon. But this German fossil appears to
differ from the English type in having the front of the lower jaw, for
about 3/4 inch, compressed from side to side into a sharp blade or
spear, more marked than in any other Pterodactyle, and directed _upward_
instead of downward as in Dimorphodon. Nearly all the measurements in
the skeleton are practically identical with those of the English
Dimorphodon, and extend to the jaw, humerus, ulna and radius, wing
metacarpal, first phalange of the wing finger. The principal bones of
the hind limb appear to be a little shorter; but the scapula and
coracoid are slightly larger. All these bones are so similar in form to
Dimorphodon that they could not be separated from the Lyme Regis
species, if they were found in the same locality.
[Illustration: FIG. 52. DIMORPHODON MACRONYX WALKING AS A BIPED
_Based chiefly on remains in the British Museum_]
[Illustration: FIG. 53. LOWER JAW OF DORYGNATHUS SEEN FROM BELOW
From the Lower Lias of Germany, showing the spear in front of the
tooth sockets]
Just as the Upper Lias in England has yielded a second Pterodactyle, so
the Upper Lias in Germany has yielded a skeleton, to which Felix
Plieninger, in 1894, gave the name Campylognathus. It is an instructive
skeleton, with the head much smaller than in Dimorphodon, being less
than 6 inches long, but, unfortunately, broken and disturbed. A lower
jaw gives the length 4-1/2 inches. Like the other Pterodactyles from
the Lias, it has the extremity of the beak toothless, with larger teeth
in the region of the symphysis in front and smaller teeth behind. The
jaw is deeper than in the Banz specimen from the Lower Lias, but not so
deep as in Dimorphodon. The teeth of the upper jaw vary in size, and
there appears to be an exceptionally large tooth in the position of the
Mammalian canine at the junction of the bones named maxillary and
intermaxillary.
The nasal opening is small and elongated, as in the English specimen
from Whitby. As in that type there is little or no indication of the
convex contour of the face seen in Dimorphodon.
The neck does not appear to be preserved. In the back the vertebrae are
about 3/10 inch long, so that twelve, which is the usual number, would
only occupy a length of a little more than 3-1/2 inches. The tail is
elongated like that of Dimorphodon, and bordered in the same way by
ossified ligaments. There are thirty-five tail vertebrae. Those which
immediately follow the pelvis are short, like the vertebrae of the back.
But they soon elongate, and reach a maximum length of nearly 1-1/2
inches at the eighth, and then gradually diminish till the last scarcely
exceeds 1/8 inch in length. The length of the tail is about 22 inches;
this appears to be an inch or two longer than in Dimorphodon. The
longest rib measures 2-1/2 inches, and the shortest 2 inches. These ribs
probably were connected with the sternum, which is imperfectly
preserved.
[Illustration: FIG. 54. DIMORPHODON MACRONYX
SHOWING THE MAXIMUM SPREAD OF THE WING MEMBRANES]
The bones of the limbs have about the same length as those of
Dimorphodon, so far as they can be compared, except that the ulna and
radius are shorter. The wing metacarpal is of about the same length, but
the first phalange of the wing finger measures 6-1/4 inches, the second
is about 8-1/4 inches, the third 6-1/2 inches, and the fourth 4-3/4
inches; so that the total length of the wing finger was about half an
inch short of 2 feet. One character especially deserves attention in the
apparent successive elongation of the first three phalanges in the wing
finger in Dimorphodon. The third phalange is the longest in the only
specimen in which the finger bones are all preserved. Usually the first
phalange is much longer than the second, so that it is a further point
of interest to find that this German type shares with Dimorphodon a
character of the wing finger which distinguishes both from some members
of the group by its short first phalange.
[Illustration: FIG. 55. THE LEFT SIDE OF THE PELVIS OF DIMORPHODON
SHOWING THE TWO PREPUBIC BONES]
The pelvis is exceptionally strong in Campylognathus, and although it is
crushed the bones manifestly met at the base of the ischium, while the
pubic bones were separated from each other in front. The bones of the
hind limb are altogether shorter in the German fossil than in
Dimorphodon, especially in the tibia; but the structure of the
metatarsus is just the same, even to the short fifth metatarsal with its
two digits, only those bones are extremely short, instead of being
elongated as in Dimorphodon. It is therefore convenient, from the
different proportions of the body, that Campylognathus may be separated
from Dimorphodon; but so much as is preserved of the English specimen
from the Upper Lias of Whitby rather favours the belief that our species
should also be referred to Campylognathus, which had not been figured
when the Whitby skull was referred to Scaphognathus by Mr. Newton. It
may be doubtful whether there is sufficient evidence to establish the
distinctness of the other German genus Dorygnathus, though it may be
retained pending further knowledge.
In these characters are grounds for placing the Lias Pterodactyles in a
distinct family, the Dimorphodontidae, as was suggested in 1870. This
evidence is found in the five metatarsal bones, of which four are in
close contact, the middle two being slightly the longest, so as to
present the general aspect of the corresponding bones in a Mammal rather
than a Bird. Secondly, the very slender fibula, prolonged down the
length of the shin bone, which ends in a rounded pulley like the
corresponding bone of a Bird. Thirdly, the great elongation of the third
wing phalange. Fourthly, the prolongation of the coracoid bone beyond
the articulation for the humerus, as in a Bird. And the toothless,
spear-shaped beak, and jaw with large teeth in front and small teeth
behind, are also distinctive characters.