The Coal Measures Amphibia of North America

by Roy Lee Moodie

Dawson, Acadian Geology, 3d ed., p. 362.

Dawson, Phil. Trans. Roy. Soc. London, pt. II, p. 642, pl. 40, figs. 46 to 51; pl. 44, figs. 129 to 137. 1882.

Type: Specimens Nos. 434-438, British Museum of Natural History. Horizon and locality: Coal formation at South Joggins, Nova Scotia. ([Plate 6.]) This species has been fully described and figured by Dawson (Air-breathers of the Coal Period, pp. 17-30, pl. III, figs. 1 to 30, 1863), who gives a detailed account of the discovery of the material of this species by himself and Sir Charles Lyell. He says, in part:

"In form, Dendrerpeton acadianum was probably lizard-like; with a broad flat head, short, stout limbs and an elongated tail; and having its skin, and more particularly that of the belly, protected by small bony plates closely overlapping each other. It may have attained the length of 2 feet. The form of the head is not unlike that of Baphetes, but longer in proportion; and much resembles that of the labyrinthodont reptiles of the Trias. The bones of the skull are sculptured as in Baphetes, but in a smaller pattern. The nostrils are small, and near the muzzle; the orbits are circular, and separated by a space of more than their own diameter. In the upper jaw there is a series of conical teeth on the maxillary and intermaxillary bones. Those on the intermaxillaries are much larger than the others, and have the aspect of canines or tusks. Within this outer series of teeth, but implanted apparently in the same bones, there is as in Archegosaurus a second series of teeth, closely placed, or with intervals equal to the diameter of one tooth. These inner teeth are longer than the others, implanted in shallow sockets, to which they are anchylosed, and have the dentine plicated, except toward the point. A third group of teeth, blunt at the points, largely hollow in the interior, and with the dentine quite simple, appears in detached bones, which may represent the vomer. Only a part of this formidable armature of the teeth appears in the skull, as the bones of the roof of the mouth have been removed, adhering to the opposite side of the matrix; but the fact of the occurrence of two sets of teeth was ascertained by Professor Wyman, from the original specimens, and is manifest in the fragment * * * while the other teeth, supposed to be vomerine, appear in fragments which must, from their size and collocation, have belonged to Dendrerpeton. It will be observed that all of these teeth are anchylosed to the bone; and that those of the vomer are thinly walled and simple, the outer series on the maxillaries and intermaxillaries simple and flattened, while the inner series of teeth are conical and plicated. In the lower jaw there was a uniform series of conical teeth, not perceptibly enlarged toward the front; at least this is the case in the only specimen at present in my collection; which is, however, merely an imperfect cast in hard sandstone.

"The scapular and sternal bones seem to have been well developed and strong, but only portions of them are known. The fore limb of the adult animal, including the toes, must have been 4 or 5 inches in length, and is of massive proportions. The bones are hollow, and in the case of the phalanges the bony walls were thin, so that they are often found crushed flat. The humerus, however, was a strong bone, with thick walls and a cancellated structure toward its extremities; still, even these have sometimes yielded to the great pressure to which they have been subjected. The cavity of the interior of the limb-bones is usually filled with calc-spar stained with organic matter, but showing no structure; and the inner side of the bony wall is smooth, without any indications of cartilaginous matter lining it.

"The vertebræ, in the external aspect of their bodies, remind one of those of fishes, expanding toward the extremities, and being deeply hollowed by conical cavities, which appear even to meet in the center. There is, however, a large and flattened neural spine. The vertebræ are usually much crushed, and it is almost impossible to disengage them from the stone. * * * in its long neural and hæmal spines, reminds us of the caudal vertebræ of those batrachians and reptiles which have tails flattened for swimming, and probably indicates that this was the case with Dendrerpeton. The ribs are long and curved, with an expanded head, near to which they are solid, but become hollow toward the middle; and the distal extremities are flattened and thin-walled. The posterior seems to have been not larger than the anterior, perhaps smaller. The tibia is much flattened at the extremity, as in some labyrinthodonts, and the foot must have been broad, and probably suited for swimming or walking on soft mud, or both. That the hind limb was adapted for walking is shown not merely by the form of the bones, but also by that of the pelvis, the best preserved specimen of which I have represented ([208, pl. III, fig. 28]).

"The external scales are thin, oblique-rhomboidal or elongated-oval, marked with slight concentric lines, but otherwise smooth, and having a thickened ridge or margin; in which they resemble those of Archegosaurus, and also those of Pholidogaster. * * * The microscopic structure of the scales is quite similar to that of the other bones, and different from that of the scales of ganoid fishes * * * ."

Dendrerpeton oweni Dawson.

Dawson, Quart. Jour. Geol. Soc. London, XVIII, p. 460.