The Salientia, or frogs, may possibly have their ancestral type in Pelion lyelli, the first known species from the Linton, Ohio, Coal Measures. Oddly enough, among the hundreds of specimens collected later from this horizon, not a fragment can be identified with this species. The type specimen is unique, and although incomplete its characters are suggestive.
The Branchiosauria are represented in North America by four species: Micrerpeton caudatum, Eumicrerpeton parvum, Mazonerpeton longicaudatum, and M. costatum. Three other genera which occur in North America have been placed ([642]) in this group, but they do not belong there, for reasons given below. The branchiosaurs were salamander-like in appearance. They were naked, with the exception of small ovoid scales on the back and the chevron-shaped armature of the ventral surface, the latter being almost universally present among the Paleozoic Amphibia. They were adapted for life in the water for at least the early part of their existence, as is shown by the possession of gills on many of the late Carboniferous and early Permian forms of Europe. The group is, without doubt, ancestral to the modern Caudata. No branchiosaurians have been described elsewhere from so low in the geological series as those here given and they are the first and only evidence of the occurrence of the group in the western hemisphere.
The Microsauria are represented in the Coal Measures by numerous forms which are usually characterized as lizard-like animals with a well-developed ventral scutellation. Other characters, such as the possession of lateral-line grooves on the cranium, the arrangement of the cranial elements, and the condition of the ribs, will be discussed further on. The pectoral arch is well developed and is composed of five dermal bones plus the regular skeletal elements. The skeletal membrane bones are sculptured after the manner of those of the cranium. The bodies of the animals were, in a few cases, covered with scales; but most of them appear to have been completely naked, even the ventral armature being absent in some cases. The ventral scutellation was especially strong and highly developed in some of the forms; e.g., in the genera Saurerpeton and Sauropleura. The vertebræ are uniformly of the hour-glass or notochordal type. This is so generally the case that the characters of the vertebræ and ribs are taken as the chief diagnostic characters of the major groups. Various peculiarities are seen among the Microsauria, such as the development of horns in various genera which are, apparently, related. The order seems to have gone completely out of existence during the early Permian, and if their descendants continued on as reptiles, as has been suggested ([469]), we do not know the intermediate stages.
The Aistopoda are without doubt specialized microsaurs, and, in the opinion of the writer, are not entitled to separate rank. Some of these forms reached a high degree of specialization. One American species has the skeleton reduced to a long, slender head and a slender series of elongate vertebræ, all other parts of the skeleton, even the ventral armature, being absent. The proportions attained by this species, Phlegethontia linearis Cope, recall those of the coach-whip snake, Zamenis flagellum Shaw, of the western plains. Some of the so-called Aistopoda have been credited by Fritsch with the possession of peculiar clasping organs, "Kammplatten." Newberry has written of the discovery of similar structures in the Ohio Coal Measures ([498]), but the statement of the actual association of these "Kammplatten" needs confirmation. Dr. R. H. Traquair wrote to the author under date of April 28, 1909:
"I maintain that the association of a bundle of 'Kammplatten' with a specimen of Ophiderpeton in the Bohemian gas coal was entirely accidental. Of such pitfalls the paleontologist has to beware or serious mistakes may be the consequence, as has happened more than once. I must, however, publish a short paper on the Kammplatten, for I think I know what they are now."
Fritsch, however, has very clearly figured a nearly complete specimen of Ophiderpeton ([251, Bd. IV]) as possessing the Kammplatten in place near the cloaca, where he suggests they may have served the function of accessory copulatory organs or claspers.
The Temnospondylia are represented by scanty remains of species from Illinois, Pennsylvania, and Nova Scotia. The forms belonging to this group are all relatively large, and they had a wide geographical distribution during the Permian. This group contains two types of vertebræ, known as the embolomerous and the rachitomous, both of which are present in the Coal Measures. Such forms as Eosaurus, Baphetes, Eobaphetes kansensis, Macrerpeton, and Dendrerpeton are regarded tentatively as temnospondyles, but there is no definite assurance that they are such. It is possible that Eosaurus is a stereospondyle, but the species is too incompletely known for a definite statement to be made. The close resemblance between the vertebræ of Eosaurus and Anthracosaurus has been noted by Huxley ([332]).
The Stereospondylia are very scantily represented in the Coal Measures, if at all. Eosaurus may belong here as indicated above. The tooth and cranial fragments discovered and described by Williston from the Coal Measures of Kansas may represent a stereospondyle as he states ([608]), but the evidence is incomplete. A fragment of a large rib ([plate 22, fig. 4]) of a species from Linton, Ohio, otherwise unknown, may be a stereospondyle. We would expect an early development for this group, but it is' an interesting fact that no stereospondyles are known definitely before the Triassic, during which period they had an extensive distribution.