Fig. 45.HYOID PLATE OF THURSO ASTEROLEPIS.[20](One fifth the nat. size, linear.)
Fig. 45.
HYOID PLATE OF THURSO ASTEROLEPIS.[20]
(One fifth the nat. size, linear.)
The size of theAsterolepismust, in the larger specimens, have been very great. In all those ganoidal fishes of the Old Red Sandstone that had the head covered with osseous plates, we find that the cranial buckler bore a certain definite proportion,—various in the several genera and species,—to the length of the body. The drawing-master still teaches his pupils to regulate the proportions of the human figure by the seven head-lengths which it contains; and perhaps shows them how an otherwise meritorious draftsman,[21]much employed half an age ago in drawing for the wood-engraver, used to render his figures squat and ungraceful by making them a head too short. Now, those ancient Ganoids which possessed a cranial buckler may, we find, be also measured by head-lengths. Thus, in theCoccosteus decipiens, the length of the cranial buckler from nape to snout equalledone fifth the entire length of the creature from snout to tail. The entire length of theGlyptolepiswas equal to about five one half times that of its cranial buckler. ThePterichthyswas formed in nearly the same proportions. TheDiplopteruswas fully seven times the length of its buckler: and theOsteolepisfrom six and a half to seven. In all the cranial bucklers of theAsterolepisyet found, the snout is wanting. The very fine specimen figured inpage 99(fig. 28) terminates abruptly at the little plate between the eyes, the specimen figured inpage 98(fig. 27) terminates at the upper line of the eye. The terminal portion which formed the snout is wanting in both, and we thus lack the measure, ormodule, as the architect might say, by which the proportions of the rest of the creature were regulated. We can, however, very nearly approximate to it. A hyoid plate in my collection (fig. 45) is, I find, so exactly proportioned in size to the cranial buckler, (fig. 28,) that it might have belongedto the same individual; and by fitting it in its proper place, and then making the necessary allowance for the breadth of the nether jaw, which swept two thirds around it, and was surmounted by the snout, we ascertain that the buckler, when entire, must have been, as nearly as may be, a foot in length. If theAsterolepiswas formed in the proportions of theCoccosteus, the buckler (fig. 28) must have belonged to an individual five feet in length; if in the proportions of thePterichthysorGlyptolepis, to an individual five and a half feet in length; and if in those of theDiplopterusorOsteolepis, to an individual of from six and a half to seven feet in length. Now I find that the hyoid plate can be inscribed—such is its form—in a semicircle, of which the nail-shaped ridge in the middle (if we strike off a minute portion of the sharp point, usually wanting in detached specimens) forms very nearly the radius, and of which the diameter equals the breadth of the cranial buckler, along a line drawn across at a distance from the nape, equal to two thirds of the distance between the nape and the eyes. Thus, the largest diameter of a hyoid plate which belonged to a cranial buckler a foot in length is, I find, equal to seven one quarter inches, while the length of its nape somewhat exceeds three five eighth inches. The nail of the Stromness specimen measures five and a half inches. It must have run along a hyoid plate eleven inches in transverse breadth, and have been associated with a cranial buckler eighteen one eighth inches in length; and theAsterolepisto which it belonged must have measured from snout to tail, if formed, as it probably was, in the proportions of its brother Cœlacanth theGlyptolepis, eight feet three inches; and if in those of theDiplopterus, from nine feet nine to ten feet six inches. This oldest of Scottish fish—thisearliest-born of the Ganoids yet known—was at least as bulky as a large porpoise.
It was small, however, compared with specimens of theAsterolepisfound elsewhere. The hyoid plate figured inpage 110, (fig. 36,)—a Thurso specimen which I owe to the kindness of Mr. Dick,—measures nearly fourteen inches, and the cranial buckler of the same individual, fifteen one fourth inches, in breadth. The latter, when entire, must have measured twenty-three one half inches in length; and the fish to which it belonged, if formed in the proportions of theGlyptolepis, ten feet six inches; and if in those of theDiplopterus, from twelve feet five to thirteen feet eight inches in length. Did the shield still exist in its original state as a buckler of tough, enamel-crusted bone, it might be converted into a Highland target, nearly broad enough to cover the ample chest of a Rob Roy or Allan M’Aulay, and strong enough to dash aside the keenest broadsword. Another hyoid plate found by Mr. Dick measures sixteen one half inches in breadth; and a cast in the British Museum, from one of the Russian specimens of Professor Asmus, (fig. 46,) twenty-four inches. The individual to which this last plate belonged must, if built in the shorter proportions, have measured eighteen, and if in the longer, twenty-three feet in length. The two hyoid plates of the specimen ofHoloptychiusin the British Museum measure but four and a half inches along that transverse line in which the RussianAsterolepismeasures two feet, and the largest Thurso specimen sixteen inches and a half. The maxillary bone of a cod-fish two and a half feet from snout to tail measures three inches in length. One of the Russian maxillary bones in the possession of Professor Asmus measures in length twenty-eight inches. And that space circumscribedby the sweep of the lower jaw which it took, in the Russian specimen, a hyoid plate twenty-four inches in breadth to fill, could be filled in the two-and-a-half-feet cod by a plate whose breadth equalled but an inch and a half. Thus, in the not unimportant circumstance of size, the most ancient Ganoids yet known, instead of taking their places, agreeably to the demands of the development hypothesis, among the sprats, sticklebacks, and minnows of their class, took their place among its huge basking sharks, gigantic sturgeons, and bulky sword-fishes. They were giants, not dwarfs.
Fig. 46.HYOID PLATE OF RUSSIAN ASTEROLEPIS.(One twelfth the natural size, linear.)
Fig. 46.
HYOID PLATE OF RUSSIAN ASTEROLEPIS.
(One twelfth the natural size, linear.)
But what of their organization? Were they fishes low or high in the scale? On this head we can, of course, determine merely by the analogies which their structure exhibits to that of fishes of the existing period; and these point in three several directions;—in two of the number, directly on genera of the high Ganoid order; and in the third, on the still higher Placoids and Enaliosaurs. No trace of vertebræ has yet been found; and so we infer—lodging, however, a precautionary protest, as the evidence is purely negative, and therefore itsome degree inconclusive—that the vertebral column of theAsterolepiswas, like that of the sturgeon, cartilaginous. Respecting its external covering, we positively know, as has been already shown, that, like theLepidosteusof America and thePolypterusof the Nile, it was composed of strong plates and scales of solid bone; and, regarding its dentition, that, as in these last genera, and even more decidedly than in these, it was of the mixed ichthyic-reptilian character,—an outer row of thickly-set fish-teeth being backed by an inner row of thinly-set reptile-teeth. And its form of coprolite indicates the spiral disposition of intestine common to the Rays and Sharks of the existing period, and of the Ichthyosauri of the Secondary ages. Instead of being, as the development hypothesis would require, a fish low in its organization, it seems to have ranged on the level of the highest ichthyic-reptilian families ever called into existence. Had an intelligent being, ignorant of what was going on upon earth during the week of creation, visited Eden on the morning of the sixth day, he would have found in it many of the inferior animals, but no trace of man. Had he returned again in the evening, he would have seen, installed in the office of keepers of the garden, and ruling with no tyrant sway as the humble monarchs of its brute inhabitants, two mature human creatures, perfect in their organization, and arrived at the full stature of their race. The entire evidence regarding them, in the absence of all such information as that imparted to Adam by Milton’s angel, would amount simply to this, that in the morning manwas not, and that in the evening hewas. There, of course, could not exist, in the circumstances, a single appearance to sanction the belief that the two human creatures whom he saw walking together among the trees at sunset had been “developed from infusorial points,” not created mature.The evidence would, on the contrary, lie all the other way. And in no degree does the geologic testimony respecting the earliest Ganoids differ from what, in the supposed case, would be the testimony of Eden regarding the earliest men. Up to a certain point in the geologic scale we find that the Ganoidsare not; and when they at length make their appearance upon the stage, they enter large in their stature and high in their organization.