A Manual of Elementary Geology / or, The Ancient Changes of the Earth and its Inhabitants as Illustrated by Geological Monuments

by Sir Charles Lyell

Transverse section of tooth of Labyrinthodon Jaegeri, Owen (Mastodonsaurus Jaegeri, Meyer); nat. size, and a segment magnified.

a. Pulp cavity, from which the processes of pulp and dentine radiate.

When Mr. Owen had satisfied himself, from an inspection of the cranium, jaws, and teeth, that a gigantic Batrachian had existed at the period of the Trias or Upper New Red Sandstone, he soon found, from the examination of various bones derived from the same formation, that he could define three species of Labyrinthodon, and that in this genus the hind extremities were much larger than the anterior ones. This circumstance, coupled with the fact of the Labyrinthodon having existed at the period when the Chirotherian footsteps were made, was the first step towards the identification of those tracks with the newly discovered Batrachian. It was at the same time observed that the footmarks of Chirotherium were more like those of toads than of any other living animal; and, lastly, that the size of the three species of Labyrinthodon corresponded with the size of three different kinds of footprints which had already been supposed to belong to three distinct Chirotheria. It was moreover inferred, with confidence, that the Labyrinthodon was an air-breathing reptile from the structure of the nasal cavity, in which the posterior outlets were at the back part of the mouth, instead of being directly under the anterior or external nostrils. It must have respired air after the manner of saurians, and may therefore have imprinted on the shore those footsteps, which, as we have seen, could not have originated from an animal walking under water.

It is true that the structure of the foot is still wanting, and that a more connected and complete skeleton is required for demonstration; but the circumstantial evidence above stated is strong enough to produce the conviction that the Chirotherium and Labyrinthodon are one and the same.

In order to show the manner in which one of these formidable Batrachians may have impressed the mark of its feet upon the shore, Mr. Owen has attempted a restoration, of which a reduced copy is annexed.

Fig. 331.

Labyrinthodon pachygnathus, Owen.

The only bones of this species at present known are those of the head, the pelvis, and part of the scapula, which are shown by stronger lines in the above figure. There is reason for believing that the head was not smooth externally, but protected by bony scutella.