CHAPTER VI.

A HISTORY OF THE CLASSIFICATION OF THE AMPHIBIA, WITH ESPECIAL REFERENCE TO THE SPECIES FROM THE COAL MEASURES.

It has been necessary, in the course of the present study, to review thoroughly the classifications which have been proposed for the group. A classification of some sort is necessary for the proper grouping of the species which have been recovered from the Coal Measures deposits of this continent, and my reason for publishing this relatively dry material is that the classifications formerly proposed (469), as well as the one here given, may have a proper historical background.

The review of the proposed systems of classification has been much facilitated by the discovery, in the University of Chicago, of some notes by the late Dr. George Baur on the "Stegocephali." The notes were not discovered until after the literature had been pretty thoroughly covered, and it was a source of some gratification, on comparing notes with those of Dr. Baur, to find but few omissions. Whether Dr. Baur had ever contemplated a work on the Stegocephala or not I have been unable to learn, but it is certain that he carefully and laboriously went through the literature on the subject and copied by hand the classifications of each author from 1842 to 1895, together with other notes of interest on the structure, distribution, and phylogeny, including many tracings. The classifications given below are taken, in part, from his notes, although all references have been verified with the original sources.

The first attempt to combine in classification the knowledge of the extinct and recent amphibians was made by Johannes Jacob von Tschudi in 1839 (574). Previous to that time Goldfuss (295) and von Meyer (418) had described various species of salamanders and frogs from the Tertiary deposits of Switzerland, and these Tschudi considered in his following classification:

A. Ranæ. a. Hylæ. b. Cystignathi. c. Ranæ. d. Ceratophrydes. e. Bombinatores. f. Bufones. g. Pipæ. B. Cœciliæ. a. Cœciliæ. C. Salamandrinæ. a. Pleurodeles. b. Salamandræ. c. Tritones. d. Tritonides. D. Protoideæ.

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 Meyer Keuper. 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 Münster Keuper. 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:

Labyrinthodontia. A. Archegosauria. Archegosaurus, Pholidogaster. B. Mastodonsauria. Mastodonsaurus, Labyrinthodon, Capitosaurus, Trematosaurus.

In the same year Dawson proposed (208) the term Microsauria to include the genera Hylonomus, Dendrerpeton, and Hylerpeton, all known from the Carboniferous rocks of Nova Scotia. Two years later Cope proposed the new order Xenorhachia (105) for the reception of the form Amphibamus grandiceps from the Coal Measures of Illinois. He gave as the characters of this order cartilaginous vertebræ and the absence of ribs.

In 1866 Owen proposed (516) the most elaborate and comprehensive scheme of classification which had thus far been offered. His classification is as follows:

Subclass Dipnoa. Order Ganocephala (extinct). Genera: Archegosaurus, Dendrerpeton, etc. Order Labyrinthodontia. Genera: Labyrinthodon, Rhombopholis, etc. Order Batrachia. Suborder Ophiomorpha. Family: Cœcilidæ. Suborder Ichthyomorpha. Family: Proteidæ, Salamandridæ. Suborder Theriomorpha (Anura). Family 1. Aglossa. Family 2. Ranidæ. Family 3. Hylidæ. Family 4. Bufonidæ.

Haeckel the same year proposed (312) an entirely different scheme of classification nd in some respects more acceptable than Owen's. Haeckel's classification is as follows:

Class Amphibia. Subclass I. Phractamphibia. Ordnung i. Ganocephala. Genera: Archegosaurus, Dendrerpeton, Raniceps. Ordnung 2. Labyrinthodonta. Genera: Baphetes, Zygosaurus, Mastodonsaurus, Trematosaurus, Capitosaurus. Ordnung 3. Peromela. Subclass II. Lissamphibia. Ordnung i. Socobranchia. Genera: Siren, Proteus, Menobranchus, etc. Ordnung 2. Sozura (Caudata). Genera: Cryptobranchus, Triton, Salamandra. Ordnung 3. Anura (Ecaudata). Families: Aglossa, Bufonidæ, Ranidæ.

This classification is further elaborated in the edition of 1895.

Cope in 1868 proposed (110) the scheme of classification which was in use for some time, although it has since suffered some change. His classification follows:

Batrachia. Order 1. Trachystoma. Order 2. Proteida. Order 3. Urodela. Order 4. Gymnophiona. Order 5. Stegocephali. Suborder Xenorhachia. Amphibamus grandiceps Cope. Suborder Microsauria. Genera: Pelion Wyman, Hylonomus Dawson, Pariostegus Cope, Dendrerpeton Owen, Hylerpeton Owen, Brachydectes Cope, Sauropleura Cope, Œstocephalus Cope, Molgophis Cope. Suborder Labyrinthodontia. Genera: Dictyocephalus Leidy, Centemodon Lea, Baphetes Owen, Eupelor Cope.

Huxley in 1869 proposed (335) the following classification, which does not differ essentially from that proposed in 1863:

Amphibia. Order 1. Urodela. Order 2. Batrachia. Order 3. Gymnophiona. Order 4. Labyrinthodontia. Suborder Archegosauria. Suborder Mastodonsauria.

The next classification of the extinct Amphibia of any importance was that devised by the committee (450) for the British Association in 1874. This committee was formed of Huxley, Harkness, Henry Woodward, Thompson, and Brigg, with Miall as secretary. This classification is, however, too cumbersome and has never come into general use, and indeed none but English authors have paid it a great deal of attention, although the contribution was a valuable one. The group Aistopoda, which was the ninth group proposed by the committee, has generally been accepted as the group represented by the snake-like forms. The committee's classification follows:

Labyrinthodontia.