Dragons of the Air: An Account of Extinct Flying Reptiles

by H. G. Seeley

Although the young Mammal passes through a stage of growth in which the brain may be said to be Reptilian, there is no good ground for inferring that Mammal or Bird type of skeleton was developed later in time than that of Reptiles. The various types of Fishes have the brains in general so similar to those of Reptiles that it is more intelligible for all the vertebrate forms of brain to have differentiated at the same time, under the law of elimination of characters, than that there should be any other bond of union between the classes of animals.

If we ask what started the Ornithosauria into existence, and created the plan of construction of that animal type, I think science is justified in boldly affirming that the initial cause can only be sought under the development of patagial membranes, such as have been seen in various animals ministering to flight. Such membranes, in an animal which was potentially a Bird in its vital organs, have owed development to the absence of quill feathers. Thus the wing membrane may be the cause for the chief differences of the skeleton by which Ornithosaurs are separated from Birds, for the stretch of wing in one case is made by the skin attached to the bones, and in the other case by feathers on the skin so attached as to necessitate that the wing bones have different proportions from Ornithosaurs.

It is a well-known observation that each great epoch of geological time has had its dominant forms of animal life, which, so far as the earth's history is known now, came into existence, lived their time, and were seen no more. In the same way the smaller groups of species and genera included in an ordinal group of animals or class have abounded, giving a tone to the life of each geological formation, until the vitality of the animal is exhausted, and the species becomes extinct or ceases to preponderate. This process is seen to be still modifying the life on the earth, when some kinds of animals and plants are introduced to new conditions. Plants appear to wage successful war more easily than animals. The introduction of the Cactus in some parts of Cape Colony has locally modified both the fauna and flora, just as the Anacharis introduced into England spread from Cambridge over the whole country, and became for many years the predominant form of plant life in the streams. The Rabbit in Australia is a historic pest. Something similar to this physical fertility and increase appears to take place under new circumstances in certain organs within the bodies of animals, by the development of structures previously unknown. A familiar example is seen in the internal anatomy of the Trout introduced into New Zealand, where the number of pyloric appendages about the stomach has become rapidly augmented, while the size and the form of the animal have changed. The rapidity with which some of these changes have been brought about would appear to show that Nature is capable of transforming animals more rapidly than might have been inferred from their uniform life under ordinary circumstances. Growth of the vital organs in this way may modify the distinctive form of any vital organ, brain or lungs, and thus as a consequence of modification of the internal structures due to changes of food and habit, bring a new group of animals into existence. And just as the group of animals ceases to predominate after a time, so there comes a limit to the continued internal development of vital structures as their energy fails, for each organ behaves to some extent like an independent organism.

Under such explanations of the mutual relations of the parts of animals, and groups of animals, time ceases to be a factor of primary importance in their construction or elaboration. The supposed necessity for practically unlimited time to produce changes in the vital organs which separate animals into great orders or classes is a nightmare, born of hypothesis, and may be profitably dismissed. The geological evidence is too imperfect for dogmatism on speculative questions; but the nature of the affinities of Ornithosaurs to other animals has been established on a basis of comparison which has no need of theory to justify the facts. It is not improbable that the primary epoch of time, even as known at present, may be sufficiently long to contain the parent races from which Ornithosaurs and all their allies have arisen.

In thus stating the relation of Ornithosaurs to other animals the Flying Reptile has been traced home to kindred, though not to its actual parents or birthplace. There is no geological history of the rapid or gradual development of the wing finger, and although the wing membrane may be accepted as its cause of existence, the wing finger is powerfully developed in the oldest known Pterodactyles as in their latest representatives.

Pterodactyles show singularly little variation in structure in their geological history. We chronicle the loss of the tail and loss of teeth. There is also the loss of the outermost wing digit from the hind foot as a supporter of the wing membrane. But the other variations are in the length of the metacarpus, or of the neck, or head. One of the fundamental laws of life necessitates that when an animal type ceases to adapt its organisation and modify its structures to suit the altered circumstances forced upon it by revolutions of the earth's surface its life's history becomes broken. It must bend or break.

The final disappearance of these animals from the earth's history in the Chalk may yet be modified by future discoveries, but the Flying Reptiles have vanished, in the same way as so many other groups of animals which were contemporary with them in the Secondary period of time. Such extinctions have been attributed to catastrophes, like the submergence of land, so that the habitations of animals became an area gradually decreasing in size, which at last disappeared. It appears also to be a law of life, illustrated by many extinct groups of animals, that they endure for geological ages, and having fought their battle in life's history, grow old and unable to continue the fight, and then disappear from the earth, giving place to more vigorous types adapted to live under new conditions.

The extinct Pterodactyles hold a relation to Birds in the scheme of life not unlike that which Monotremata hold to other Mammals. Both are remarkable for the variety of their affinities and resemblances to Reptiles. The Ornithosauria have long passed away; the Monotremes are nearing extinction. Both appear to be supplanted by parallel groups which were their contemporaries. Birds now fill the earth in a way that Flying Reptiles never surpassed; but their flight is made in a different manner, and the wing is extended to support the animal in the air, chiefly by appendages to the skin.

If these fossils have taught that Ornithosaurs have a community of soft vital organs with Dinosaurs and Birds, they have also gone some way towards proving that causes similar to those which determined the structural peculiarities of their bony framework, originated the special forms of respiratory organs and brain which lifted them out of association with existing Reptiles.

These old flying animals sleep through geological ages, not without honour, for the study of their story has illuminated the mode of origin of animals which survive them, and in cleaving the rocks to display their bones we have opened a new page of the book of life.