Erierpeton branchialis Moodie.
Moodie, Kans. Univ. Sci. Bull., VI, No. 2, pp. 329-330, pl. 1, fig. 3; pl. 2, fig. I, 1912.
Type: Specimen No. 801 ([222]) 5, Yale University, Museum.
Horizon and locality: Mazon Creek shales, near Morris, Illinois.
The amphibian remains designated by the above name consist of a distinct mandible and some rather indefinite body impressions ([plate 3, fig. 4]). Three elongate impressions occur between the rami of the mandibles ([fig. 15, A]), which, I suppose, must represent hyoid bones belonging to the hyobranchial arches. The lateral elements are paired and the median impression is straight and lies between the paired impressions of the hyoids. The paired portions probably represent the hypohyals or hypohyals plus the ceratohyals, and the unpaired portion of the first basibranchial, according to the nomenclature of Wiedersheim (Comparative Anatomy of Vertebrates, 1897, p. 86). If the impressions have been correctly interpreted the present specimen is of very great interest, since it is the first evidence we have of the hyobranchial arches in the Amphibia of Mazon Creek, and the second in the Carboniferous of North America. Dawson doubtfully identified ([216]) some elements of the Joggins Amphibia as hyoids, but was uncertain as to their position. Cope described fully the well-developed hyobranchial apparatus of Cocytinus gyrinoides ([123]) from the Coal Measures of Ohio. Among other Paleozoic Amphibia Williston ([614]) has described branchial arches in the peculiar form Lysorophus tricarinatus Cope, from the Permian of Texas.
The form of the impression of the mandible in the present specimen is unlike anything known to the writer among other Carboniferous or later Amphibia. The rami are long, slender, deep, slightly curved, and pointed anteriorly. The anterior symphysis was not a complete sutural union, but was occupied partly by cartilage or other connective tissue.
There are no definite traces of the appendicular skeleton. The traces of the body ([fig. 15, A]) indicate an elongated, rather slender animal, but further than this nothing can be said in regard to its structure.
The occurrence of a typically caudate form in the Carboniferous is unusual and complicates still further our understanding of the origin and relationships of the early Amphibia.
| Measurements of the Type. | |
| mm. | |
| Length of entire impression | 50 |
| Length of mandible along median line | 10 |
| Width of mandibular ramus | 9 |
| Length of basibranchial | 2.5 |
| Width of basibranchial | 0.75 |
| Length of hypohyal | 2.4 |
| Width of hypohyal | 1.5 |