ORNITHOLITES; OR FOSSIL BIRDS.

Excepting in strata of comparatively modern origin, the remains of Birds are of extreme rarity in a fossil state. In the caverns that contain the skeletons of carnivorous animals, and which in many cases were once their dens, the bones of several species of existing genera of Birds have been discovered, in England, on the Continent, in America, and in Australia; and recently there have been obtained from alluvial deposits in New Zealand the skeletons of Birds, some of enormous magnitude, and under conditions which leave some doubt whether, like the Dodo, the species may not have been extirpated by man during the last few centuries; or even if some stray individuals of the race may not, according to the belief of the aborigines, be still, in existence in the interior of the country.

From the gypsum quarries at Montmartre, near Paris, Baron Cuvier obtained several species of Ornitholites; and Prof. Owen has described the relics of three or four species from the London Clay: these fossil birds of the eocene tertiary deposits are the most ancient relics of this class known to the geologist, with the exception of the foot-prints on the New Red sandstone of North America, that have been referred to animals of this class.

The rarity of the remains of Birds may probably in some measure be attributable, as Sir C. Lyell has suggested, to the peculiar organization of these animals; for their power of flight necessarily renders them less liable to be engulphed and imbedded in the deltas of rivers or in the bed of the ocean, than quadrupeds; and the lightness of their structure, occasioned by their tubular bones and feathery dermal integument, generally prevents the sinking of the bodies of such as die on, or fall into, the water; so that their carcases are devoured or decomposed.

In illustration of this subject, I purpose, in the first place, to explain such peculiarities in the osteology of the animals of this class, as may assist the collector in the identification of their fossil remains; secondly, to take a cursory survey of the geological distribution of fossil Birds, and examine a few of the most interesting examples; and lastly, consider the striking phenomena presented by the foot-prints of supposed Birds on the strata of those ancient deposits which are comprised in the Trias or New Red formation.

I. Osteological Characters.—The skull in adult birds presents this remarkable feature, that it is composed of but one bone without any trace of suture: the osseous tissue is very compact; the bone is white, and very smooth externally. The lower jaw is formed, as in reptiles, of several bones, namely, articular, angular, supra-angular, and dental; it is united to the skull by the intervention of a bone (os quadratum), as in certain reptiles. Both jaws are destitute of teeth, and are protected by dense horny sheaths, which form powerful dentary organs. The vertebral column of the neck is exceedingly flexible, and is composed of a greater number of bones than in any other living animals; for the cervical vertebÆ, which in the mammalia amount to seven, in birds vary from ten to twenty-four, as in the Swan. To admit of this extreme mobility of the neck without injury to the enclosed spinal cord, the annular part, or neural arch, of each cervical vertebra is enlarged at the extremities that form a junction with the corresponding bones; thus presenting a modification of vertebral development directly the reverse of that possessed by the extinct saurian of the Magnesian conglomerate (see p. 714). The dorsal and sacra vertebral, on the contrary, are firmly interlocked, and often anchylosed together, and constitute a strong, inflexible pillar to afford a fixed point of support to the powerful locomotive organs of flight. There are no lumbar, or rib-less vertebrÆ. The sacrum often consists of eighteen, twenty, or more vertebrÆ, anchylosed into a solid bone. In the young Ostrich the vertebrÆ may be found separate and distinct; and the neural arch is shifted to the union of two vertebrÆ, as in the Megalosaurus. The sacral spinal cord is almost as large as the brain; to supply the large muscles. The foramina for the passage of the nerves are double, one for the sensitive, and the other for the motive root, which pass out separately and unite in. a ganglion externally. The ribs are formed so as to combine strength with lightness in the construction of the walls of the chest, for each rib has a recurrent apophysis, or process, that extends backwards, and glides over the contiguous bone; this is a very peculiar and obvious character.[719] The ribs are united in front to the sternum by bony processes, analogous to the costal-arcs of the Plesiosaurus. The pectoral arch is distinguished by the prominent longitudinal keel or crest of the sternum; a structure designed to give attachment to the powerful pectoral muscles which move the wings, and which presents characteristic modifications in the different orders; and by the peculiar bone, termed the furcula, or merry-thought, which connects the clavicles. The clavicles are strongest and most open in birds of strongest flight. The coracoids (in birds) relate to respiration, and serve to admit of contraction and expansion of the sternum and abdomen. The bones of the anterior extremities are modified to adapt these instruments for the purposes of flight, and those of the fore-arm (radius and ulna) are very long, and firmly united together; the ulna has a row of slight eminences for the attachment of the quills of the secondary feathers. The wrist, or carpus, is composed of but two bones, articulated to the radius and ulna, and which admit only of a lateral movement, by which the wings are folded close to the body. The bones of the hinder extremities consist of the thigh or femur;[720] the leg-bones, tibia[721] and fibula, the latter very small and anchylosed to the former; and of a single shank-bone, which supplies the place of the tarsal and metatarsal bones of other animals. This bone is articulated at its upper extremity to the tibia, and terminates at the lower end in distinct processes, which correspond in number with the toes; each process having a groove for the pulley-like tendon that moves the corresponding toe. This construction is peculiar to birds; for although in some quadrupeds, as the horse for example, the metatarsus consists of but one piece, the tarsus is composed of several bones.

The toes of birds present deviations equally recognisable; for the number of the articulations (or phalangeal pieces of bone) in each toe is different. Thus the thumb, or short toe, has two bones; the first toe on the inner side three; the the middle toe four; and the outer toe five. In general, three toes are directed forwards, and one backwards. In some species, the thumb or opposable toe is altogether wanting; in others, as in the swallow, it is directed forwards; in climbing birds, both the outer and the back toe are situated behind. The position of the hind toe, therefore, affords an important indication of the habits of the bird (see Wond. p. 146, Lign. 23), and from a fragment of the lower extremity of the shank or tarso-metatarsal bone, with any trace of this articulation, we may determine whether the individual to which it belonged was a climber, wader, &c. In the toes of Crocodiles alone, the number of joints is the same as in birds; but in these reptiles, each toe is supported by a distinct metatarsal bone. The osteological peculiarities above enumerated may assist the collector in arriving at some general inferences as to the nature of any fossil remains of birds.

II. Ornitholites, or Fossil Birds.—The fossil remains of birds consist in general of their osseous skeletons, and of detached bones, and rarely of the feathers and eggs.

Pleistocene Epoch.—Bones of the Dodo[722] (see Wond. p. 131), a bird which appears to have become extinct by human agency within the last two centuries, have been found, associated with the remains of a recent species of Tortoise, beneath a bed of lava in the Isle of France. And in some caverns in the island of Rodriguez, the bones of one or more large birds allied to the Dodo have also been discovered.

Dinornis (fearfully great bird). Pict. Atlas, frontispiece, and p. 172—Numerous bones of large extinct birds have been obtained in New Zealand by Mr. Rule, the Rev. W. Williams, Col. Wakefield, Mr. Walter Mantell, and others. These have been referred by Professor Owen to tridactylous struthious birds (one of which was one-third larger than the African ostrich), resembling the living Apteryx of New Zealand (Wond. p. 128, Petrif. p. 106) in the proportions of the tibia to the metatarsus, and also in the rudimental state of the wings. The bones are found in the recent alluvium, but probably in some cases at least they have been washed by the streams from older alluvial deposits.

An account of the history of the discovery of the gigantic Moa’s bones in New Zealand (Wond. p. 129) is given in full in Petrif. p. 93, et seq.; and the scientific description of the various parts of the skeleton of the Dinornis and Palapteryx, chiefly collected from Professor Owen’s elaborate and finely illustrated memoirs in the Transactions of the Zoological Society, should be consulted, Petrif. p. 108, &c. Of Dinornis Professor Owen discriminates seven or eight species; of Palapteryx, three species; and indications of a species of a third associated genus, Aptornis.

Fragments of egg-shell accompany these interesting relics of birds from New Zealand. From Madagascar also bird-bones and eggs have been obtained in a fossil state, that indicate the original bird (Æpyornis) to have been even of a greater size than the Dinornis.

Ornitholites of the Caverns.—Many limestone districts abound in fissures and caves, which vary in extent from more superficial hollows to deep excavations and caverns of considerable magnitude (Wond. p. 175, &c.) Beneath the stalagmitic or sparry floors of some of these caverns, the bones of extinct species of Cats, Bears, and HyÆnas, occur in immense quantities; but the full consideration of these phenomena will be reserved for the next chapter. The skeletons and detached bones of several kinds of Birds are often found imbedded with these remains; and under circumstances which seem to indicate that they were brought into these caverns as prey by the carnivora, with whose relics they are now associated. Some examples show that the birds had fallen into the fissure; others, that their bones had been transported to their present situation by the action of water.

In the Cave of Kirkdale, in Yorkshire (Wond. p. 179), Dr. Buckland found bones of the Raven, Lark, Pigeon, Duck, and others; and as almost all the specimens were the remains of wing-bones, it is considered probable that they are the relics of dead birds, which had been brought into the cave by the hyÆnas, whose den it is supposed to have been for a considerable period (ReliquiÆ DiluvianÆ, p. 34).

Similar remains have been discovered in the Kent’s Hole cavern, and in that at Berry Head, Torbay; from the latter Professor Owen has obtained the wing-bones of a Falcon (Brit. Fos. Mam. and Birds, p. 558).

In France, the Lunel-Viel caverns have yielded a few bird-bones; and many such remains occur in the caves of Brazil, described by M. Lund.

The so-called "bone-breccia" of the coasts and islands of the Mediterranean (Wond. p. 185) contains frequent remains of birds: they have been especially noticed at Cette, Nice, Sardinia, and Gibraltar.

In the deposits especially referred to the northern drift or Boulder-clay period, fossil birds appear to be very rare, although the remains of vertebrate terrestrial animals are locally abundant. Dr. Buckland states that some bones, apparently of a species of goose, found at Lawford, with the remains of HyÆna, Elephant, Rhinoceros, &c., is the only instance he has met with of fossil birds in the drift of England (Reliq. Diluv. p. 27).

On the Continent, bird-bones have been found, at Quedlingbourg, Meissen, and in the Lahn Valley, in deposits said to be of this age.

Ornitholites of the older Tertiary Deposits. (Lign. 246.)—The very rich pliocene deposits at Œningen (p. 559) have afforded a few fragments of birds’ bones.

Three or four species of Ornitholites (Duck, Heron, Flamingo, &c.), and several examples of the eggs of birds, have been discovered in the lacustrine strata of Auvergne. Birds’ bones also occur in the fresh-water limestone near Issoire, in the Buy de DÔme, associated with the remains of eocene mammalia. In Germany, bird-bones have been found in tertiary deposits at Wiesbaden, Wiesnau, and Mornbach. In the Siwalik Hills the remains of birds are associated with the fossil reptilia and mammalia, to which reference has already been made (p. 731).

From the quarries of gypseous limestone of Montmartre, near Paris, Baron Cuvier obtained many bones, and some connected portions of the skeletons of several birds related to the Pelican, Sea-lark, Curlew, Woodcock, Owl, Buzzard, and Quail.[723] In several of these examples there are the imprints and remains of the quills and feathers; in some the skeleton has perished, and a pellicle of dark-brown substance, with the configuration of the original, alone remains (see Lign. 246). These Ornitholites are associated with the bones of the PalÆotheria, and other extinct mammalia of the eocene period. Two or three Ornitholites have been discovered at Montmartre, in which almost the entire skeleton is preserved. In one example, described by Cuvier, the remains of a bird are displayed in such a manner as to render it probable that the animal had fallen on its belly, and become partially impacted in the surface of the soft gypsum, which is now become solid stone; and that, previously to its being completely enveloped, the principal part of its head and the left leg were removed either by some voracious animal, or by the action of the water. In addition to the other parts of the skeleton, the under side of the bill is very distinctly impressed on the stone, and the left branch is entire; there are also the remains of the cellular basis of the skull; and both the wings are well preserved. Nine or ten species of fossil birds were identified by Cuvier from the Paris eocene strata.

Lithornis vulturinus. Geol. Trans. 2d series, vol. vi. p. 206, pl. xxi. figs. 5 and 6.—Under the name of Lithornis (petrified-bird), Professor Owen has described the fossil remains of a bird, consisting of two most characteristic bones,—the sternum and sacrum,—and fragments of other bones, obtained from the London Clay of the Isle of Sheppey. These relics present a close agreement with the corresponding bones of the Vulture tribe, but indicate a smaller species of Vulture than any now known to exist.

In his "History of British Fossil Mammalia and Birds," 1846, Professor Owen has also described another sacrum from the Sheppey Clay, a sternum from Primrose Hill, and the cranium of a bird, probably of the HalcyonidÆ family, from the same eocene deposit at Sheppey. This has also yielded a portion of shank-bone, which, according to Mr. Bowerbank, indicates a bird of the size of a full-grown albatross. Brit. Assoc. 1851.

Some few specimens of cylindrical bones from the Chalk and the Wealden[724] have been previously referred to Birds, and described as remains of species of that family. These fossils, however, have lately been reexamined in comparison with more perfect bones of similar character; and, with the exception of a few, the structure of which decidedly has the characters belonging to bird’s bone, the result of this investigation has assigned them to Pterodactyles.[725] The long thin cylindrical bones from the Stonesfield Oolite are probably all Pterodactylian also, as suggested by the late Mr. Miller.

III. Ornithoidichnites. (Bird-like foot-prints.) Ligns. 247, 248. Bd. pl. xxvi. a, xxvi.b.—The palÆontological history of the class of birds, as evidenced by the foregoing pages, is carried back but to a comparatively recent era in the earth’s history: and indeed, in the present state of our knowledge, it may be said that all positive evidence of the former existence of this highly organized class of vertebrated animals is confined to the Tertiary and Wealden deposits. A most interesting discovery, however, by Dr. James Deane,[726] of Greenfield, U. S. seems to prove that numerous bird-like bipeds, and some of gigantic size, existed at the period when the Triassic or New Red strata were in the progress of formation; that period, as the reader will remember, in which the Labyrinthodonts and other extraordinary reptiles flourished. Rep. Brit. Assoc. 1841, p. 230, note.

In certain localities of the New Red sandstone in the valley of the Connecticut, numerous tridactyle markings had been occasionally observed on the surfaces of the slabs of stone when split asunder, in like manner as the ripple-marks appear on the successive layers of sandstone in Corncockle Muir, Tilgate Forest, &c. Some remarkable distinct impressions of this kind at Turner’s Falls (Massachusetts) happening to attract the attention of Dr. Deane, that sagacious observer was struck with their resemblance to the foot-marks left on the mud-banks of the adjacent river by the aquatic birds which had recently frequented the spot. The conviction that the imprints on the stone were referable to a similar origin with those on the mud was so strongly impressed on his mind, that he immediately collected a series of specimens, and communicated his discovery and opinion to Professor E. Hitchcock, who followed up the inquiry with a zeal and success that have led to the most interesting results. No reasonable doubt now exists that the imprints in question have been produced by the tracks of bipeds, impressed on the stone when in a soft state. The announcement of this extraordinary phenomenon was first made by Professor Hitchcock, in the American Journal of Science (January, 1836); and that eminent geologist has subsequently published full descriptions of the different species of imprints which he has detected, with excellent lithographs, in his "Geology of Massachusetts." (See Petrif. pp. 64-73.)

Three highly interesting specimens of the Ornithoidichnites of North America, collected and developed by Dr. James Deane, have been lately added to the collection of organic remains in the British Museum. They exhibit several varieties of the foot-prints, and are in a very fine state of preservation. The surface of the largest slab is eight feet by six, and bears upwards of seventy distinct impressions, disposed in several tracks, as shown in the Lign. 247. The direction and disposition of the foot-tracks are rendered more distinct by the lines drawn from one imprint to another in the consecutive series.

The principal tracks on this slab, Lign. 247, are as follow;

I subjoin also a representation of one of the smaller foot-prints, of the natural size, the surface of the stone being sprinkled also with hemispherical markings produced by drops of rain. (Lign. 248.)

A Slab of New Red Sandstone (eight feet by six), from Turner’s Falls, Massachusetts, United States, covered with numerous Foot-marks of Bipeds; indicating the Tracks of ten or twelve individuals, of various sizes. Discovered by Dr. James Deane, of Greenfield, Massachusetts. This Specimen is now in the British Museum.—(From the American Journal of Science, vol. xlvi. p. 73.)

The above will suffice to give the reader a general idea of the nature of these extraordinary impressions. A few shapeless fragments of bones are the only vestiges of the skeletons of any animals, with the exception of fishes, that have been found in the strata which have furnished the slabs of Ornithoidichnites. Some Coprolites also have been discovered.

The enormous size of some of the foot-marks is calculated to excite great surprise. I have in my possession (through the kindness of Dr. Deane) imprints that prove the size of the foot to have been fifteen inches in length, and ten inches in width, exclusive of the hind claw, which is present in some species, and is here two inches long. The foot-prints of this biped when in a consecutive series of five or six, are from four to six feet apart; which, of course, must have been the length of the stride; the longest stride was probably made by the animal when running; the shortest, when walking at a moderate pace. These footsteps indicate proportions so far exceeding those of all known living bipeds,—for the foot of the African ostrich is but ten inches long,—that the geologist may be pardoned for having hesitated to adopt the opinions of the American savans, in the absence of any relics of the osseous structure of the supposed birds; although sanctioned by the high authority of Dr. Buckland, who, from the first, concurred in the views of Professor Hitchcock (Bd. ii. p. 39): but this objection has been in a great measure removed by the discovery of the remains of the gigantic Moa or Dinornis of New Zealand, with feet equal in magnitude to the largest of the Connecticut foot-prints. See p. 763, and Pict. Atlas, frontispiece. Professor Hitchcock is of opinion that upwards of forty species of these biped foot-prints may be distinguished. Foot-prints referable to chelonians, batrachians, and lizards are associated with the above.[727]

In the New Red Sandstone of Stourton Hill, near Liverpool, Mr. Cunningham has observed tridactylous, webbed foot-prints,[728] 2¹/₂ inches long, which he refers to a bird; Mr. Hawkshaw also noticed some bird-like tracks at Lymm; and Professor Harkness met with a trace of a biped at Weston Point, near Runcorn. These appear to be the only indications of ornithoidichnites in the Trias of England; and these are very obscure.

In the Wealden of Hastings and the Isle of Wight, the natural casts of large tridactylous foot-prints have been observed by Mr. Taggart and Mr. Beckles (see Quart. Journ. Geol. Soc. vol. ii. p. 267, vol. vii. p. 117, vol. viii. p. 396, and Geol. Isle of Wight, p. 328), but as yet no solution of the mystery at present enwrapping these gigantic, tridactylous, biped (?) ichnolites has presented itself: we only know that the creature that left them traversed the borders of the mighty river which floated down the bulky carcases of the HylÆosaur and Iguanodon.

On Collecting the Fossil Remains of Birds.—Notwithstanding the extreme rarity of fossils of this class, the student should not be discouraged in his search for the remains of Birds in the secondary rocks. That far more instructive specimens than any that have fallen under my observation may be discovered in the Wealden strata by diligent research, there can be no reasonable doubt. It is also very probable that the Stonesfield slate, which abounds in remains of terrestrial plants and animals, will be found to contain Ornitholites. It is important for the collector to bear in mind, that when only a fragment of the shaft of a bone remains imbedded in the stone, if the imprint of the other portions be preserved, he may obtain a knowledge of the form of the extremities; in the same manner as the external markings of the surface of a shell may be ascertained, when the shell itself is lost or destroyed, and a smooth stony cast of the internal cavity only is left. The same remark will apply to the bones of reptiles and other animals; for example, a perfect leg-bone may be imbedded in a block of limestone; but, when exposed by breaking the stone, a portion of the shaft may alone remain attached, and both extremities be shattered to pieces by the concussion of the blow; yet, if the impression remains, the entire form of the original may be determined.

The foot-prints, not only of birds, but of reptiles and other animals, should be diligently sought for on the surfaces of laminated strata of sand and clay, and especially where the presence of ripple-marks, and the impressions of rain-drops, indicate that the beds were deposited in shallow water. The forest-marble flags at Castle Comb, north of Bath, the Stonesfield slates, and the sandstones around Horsham (in Sussex), and particularly at Stammerham (see Geol. S. E. p. 213), are often rippled, and it is therefore probable that the foot-prints of some of the Oolitic and Wealden quadrupeds and bipeds, if such existed, will sooner or later be discovered.