Although the remains of Mastodonsaurus had been known and widely commented on for several years before Tschudi proposed this scheme, he does not include this genus in his classification of the Amphibia, for the reason that for nearly a quarter of a century after the discovery of the labyrinthodonts they were regarded as reptiles, even so eminent an authority as von Meyer ([423]) including them in his "System der fossilen Saurier." The view that the labyrinthodonts were reptiles was at times disputed, but no one seemed to pay any attention to the argument of Quenstedt in 1850 that "Die Mastodonsaurier im grünen Keupersandstein Würtemburgs sind Batrachier" ([527]), nor to the contention of Vogt ([581]) in 1854 that "Archegosaurus und alle Labyrinthodonten sind Amphibien, nicht Reptilien."
In 1842 von Meyer ([420]) proposed to include all the early forms allied to the Mastodonsaurus in the "Labyrinthodontes." His definition of the group follows:
Labyrinthodontes: Saurier deren Zahn-Struktur jener ähnlich ist, welche in den nach prismatischer Art gebauten Säugethier-Zähnen wahrgenommen wird, u.s.w.
| I. | Mastodonsaurus Jaeger. (Salamandroides Jaeger, Batrachosaurus Fitzinger, Labyrinthodon Owen.) M. Jaegeri Meyer. |
| II. | Capitosaurus Münster. |
| C. arenaceus Münst. C. robustus Meyer. | |
| III. | Metopias Meyer. |
| M. diagnosticus Meyer. |
Three years later von Meyer ([423]) proposed his "System der fossilen Saurier," where the extinct Amphibia are treated as follows:
| Labyrinthodontes. | |||
| 1. | Prosthopthalmi (Augen-höhlen in der vordern Hälfte der Schädel-Länge) | ||
| Metopias MeyerKeuper. | |||
| 2. | Mesopthalmi (Augen-höhlen in der mitte der Schädel) | ||
| Mastodonsaurus Jaeger Keuper, Muschelkalk. | |||
| 3. | Opisthopthalmi (Augen-höhlen in der hintern Hälfte der Schädel-Länge) | ||
| Capitosaurus MünsterKeuper. | |||
| 4. | Labyrinthodonten ungewisser Stellung | ||
| Labyrinthodon Owen | Keuper. | ||
| Xestorrhytias Meyer | Muschelkalk. | ||
| Odontosaurus Meyer | Bunter Sandstein. | ||
| Trematosaurus Braun | Bunter Sandstein. | ||
No other classification was proposed for the extinct Amphibia for 15 years, when Owen ([512]) in 1859 proposed the new order Ganocephala and retained von Meyer's Labyrinthodontes under Labyrinthodontia. Owen's classification is as follows:
Class Reptilia.
Order I. Ganocephala.
Genera: Archegosaurus, Dendrerpeton, Raniceps.
Order II. Labyrinthodontia.
Genera: Mastodonsaurus, Anisopus, Trematosaurus , Metopias, Capitosaurus,
Zygosaurus, Xestorrhytias.
In his Paleontology published in 1861, Owen gives the same classification, but adds new genera.
Huxley in 1863 ([332]) did not accept Owen's Ganocephala, but instead proposed the following: